syzbot

Error 503, Message: This model is currently experiencing high demand. Spikes in demand are usually temporary. Please try again later., Status: UNAVAILABLE, Details: []

map[KernelBranch:master KernelCommit:7fd2df204f342fc17d1a0bfcd474b24232fb0f32 KernelRepo:git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git]

map[SimplifiedCRepro:// autogenerated by syzkaller (https://github.com/google/syzkaller)

#define _GNU_SOURCE 

#include <arpa/inet.h>
#include <endian.h>
#include <errno.h>
#include <net/if.h>
#include <netinet/in.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/socket.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>

#include <linux/genetlink.h>
#include <linux/if_addr.h>
#include <linux/if_link.h>
#include <linux/in6.h>
#include <linux/neighbour.h>
#include <linux/net.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <linux/veth.h>

struct nlmsg {
	char* pos;
	int nesting;
	struct nlattr* nested[8];
	char buf[4096];
};

static void netlink_init(struct nlmsg* nlmsg, int typ, int flags,
			 const void* data, int size)
{
	memset(nlmsg, 0, sizeof(*nlmsg));
	struct nlmsghdr* hdr = (struct nlmsghdr*)nlmsg->buf;
	hdr->nlmsg_type = typ;
	hdr->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK | flags;
	memcpy(hdr + 1, data, size);
	nlmsg->pos = (char*)(hdr + 1) + NLMSG_ALIGN(size);
}

static void netlink_attr(struct nlmsg* nlmsg, int typ,
			 const void* data, int size)
{
	struct nlattr* attr = (struct nlattr*)nlmsg->pos;
	attr->nla_len = sizeof(*attr) + size;
	attr->nla_type = typ;
	if (size > 0)
		memcpy(attr + 1, data, size);
	nlmsg->pos += NLMSG_ALIGN(attr->nla_len);
}

static int netlink_send_ext(struct nlmsg* nlmsg, int sock,
			    uint16_t reply_type, int* reply_len, bool dofail)
{
	if (nlmsg->pos > nlmsg->buf + sizeof(nlmsg->buf) || nlmsg->nesting)
	exit(1);
	struct nlmsghdr* hdr = (struct nlmsghdr*)nlmsg->buf;
	hdr->nlmsg_len = nlmsg->pos - nlmsg->buf;
	struct sockaddr_nl addr;
	memset(&addr, 0, sizeof(addr));
	addr.nl_family = AF_NETLINK;
	ssize_t n = sendto(sock, nlmsg->buf, hdr->nlmsg_len, 0, (struct sockaddr*)&addr, sizeof(addr));
	if (n != (ssize_t)hdr->nlmsg_len) {
		if (dofail)
	exit(1);
		return -1;
	}
	n = recv(sock, nlmsg->buf, sizeof(nlmsg->buf), 0);
	if (reply_len)
		*reply_len = 0;
	if (n < 0) {
		if (dofail)
	exit(1);
		return -1;
	}
	if (n < (ssize_t)sizeof(struct nlmsghdr)) {
		errno = EINVAL;
		if (dofail)
	exit(1);
		return -1;
	}
	if (hdr->nlmsg_type == NLMSG_DONE)
		return 0;
	if (reply_len && hdr->nlmsg_type == reply_type) {
		*reply_len = n;
		return 0;
	}
	if (n < (ssize_t)(sizeof(struct nlmsghdr) + sizeof(struct nlmsgerr))) {
		errno = EINVAL;
		if (dofail)
	exit(1);
		return -1;
	}
	if (hdr->nlmsg_type != NLMSG_ERROR) {
		errno = EINVAL;
		if (dofail)
	exit(1);
		return -1;
	}
	errno = -((struct nlmsgerr*)(hdr + 1))->error;
	return -errno;
}

static int netlink_query_family_id(struct nlmsg* nlmsg, int sock, const char* family_name, bool dofail)
{
	struct genlmsghdr genlhdr;
	memset(&genlhdr, 0, sizeof(genlhdr));
	genlhdr.cmd = CTRL_CMD_GETFAMILY;
	netlink_init(nlmsg, GENL_ID_CTRL, 0, &genlhdr, sizeof(genlhdr));
	netlink_attr(nlmsg, CTRL_ATTR_FAMILY_NAME, family_name, strnlen(family_name, GENL_NAMSIZ - 1) + 1);
	int n = 0;
	int err = netlink_send_ext(nlmsg, sock, GENL_ID_CTRL, &n, dofail);
	if (err < 0) {
		return -1;
	}
	uint16_t id = 0;
	struct nlattr* attr = (struct nlattr*)(nlmsg->buf + NLMSG_HDRLEN + NLMSG_ALIGN(sizeof(genlhdr)));
	for (; (char*)attr < nlmsg->buf + n; attr = (struct nlattr*)((char*)attr + NLMSG_ALIGN(attr->nla_len))) {
		if (attr->nla_type == CTRL_ATTR_FAMILY_ID) {
			id = *(uint16_t*)(attr + 1);
			break;
		}
	}
	if (!id) {
		errno = EINVAL;
		return -1;
	}
	recv(sock, nlmsg->buf, sizeof(nlmsg->buf), 0);
	return id;
}

const int kInitNetNsFd = 201;

static long syz_init_net_socket(volatile long domain, volatile long type, volatile long proto)
{
	return syscall(__NR_socket, domain, type, proto);
}

static long syz_genetlink_get_family_id(volatile long name, volatile long sock_arg)
{
	int fd = sock_arg;
	if (fd < 0) {
		fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_GENERIC);
		if (fd == -1) {
			return -1;
		}
	}
	struct nlmsg nlmsg_tmp;
	int ret = netlink_query_family_id(&nlmsg_tmp, fd, (char*)name, false);
	if ((int)sock_arg < 0)
		close(fd);
	if (ret < 0) {
		return -1;
	}
	return ret;
}

uint64_t r[6] = {0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff};

int main(void)
{
		syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
	syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000ul, /*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/7ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
	syscall(__NR_mmap, /*addr=*/0x200001000000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
	const char* reason;
	(void)reason;
				intptr_t res = 0;
	if (write(1, "executing program\n", sizeof("executing program\n") - 1)) {}
//  syz_init_net_socket$nl_generic arguments: [
//    domain: const = 0x10 (8 bytes)
//    type: const = 0x3 (8 bytes)
//    proto: const = 0x10 (8 bytes)
//  ]
//  returns sock_nl_generic_init
	res = -1;
res = syz_init_net_socket(/*domain=*/0x10, /*type=*/3, /*proto=*/0x10);
	if (res != -1)
		r[0] = res;
//  syz_genetlink_get_family_id$nbd arguments: [
//    name: ptr[in, buffer] {
//      buffer: {6e 62 64 00} (length 0x4)
//    }
//    fd: sock_nl_generic_init (resource)
//  ]
//  returns genl_nbd_family_id
memcpy((void*)0x200000000000, "nbd\000", 4);
	res = -1;
res = syz_genetlink_get_family_id(/*name=*/0x200000000000, /*fd=*/-1);
	if (res != -1)
		r[1] = res;
//  socketpair$nbd arguments: [
//    domain: const = 0x1 (8 bytes)
//    type: const = 0x1 (8 bytes)
//    proto: const = 0x0 (4 bytes)
//    fds: ptr[out, nbd_sock_pair] {
//      nbd_sock_pair {
//        client: sock_nbd_client (resource)
//        server: sock_nbd_server (resource)
//      }
//    }
//  ]
	res = syscall(__NR_socketpair, /*domain=*/1ul, /*type=*/1ul, /*proto=*/0, /*fds=*/0x200000000100ul);
	if (res != -1)
r[2] = *(uint32_t*)0x200000000100;
//  sendmsg$NBD_CMD_CONNECT arguments: [
//    fd: sock_nl_generic_init (resource)
//    msg: ptr[in, msghdr_netlink[netlink_msg_t[genl_nbd_family_id, genlmsghdr_t[NBD_CMD_CONNECT], nbd_attr_policy]]] {
//      msghdr_netlink[netlink_msg_t[genl_nbd_family_id, genlmsghdr_t[NBD_CMD_CONNECT], nbd_attr_policy]] {
//        addr: nil
//        addrlen: len = 0x0 (4 bytes)
//        pad = 0x0 (4 bytes)
//        vec: ptr[in, iovec[in, netlink_msg_t[genl_nbd_family_id, genlmsghdr_t[NBD_CMD_CONNECT], nbd_attr_policy]]] {
//          iovec[in, netlink_msg_t[genl_nbd_family_id, genlmsghdr_t[NBD_CMD_CONNECT], nbd_attr_policy]] {
//            addr: ptr[inout, array[ANYUNION]] {
//              array[ANYUNION] {
//                union ANYUNION {
//                  ANYBLOB: buffer: {6c 00 00 00} (length 0x4)
//                }
//                union ANYUNION {
//                  ANYRES16: ANYRES16 (resource)
//                }
//                union ANYUNION {
//                  ANYBLOB: buffer: {01 00 ff ff ff ff 00 00 00 00 01 00 00 00 0c 00 05 00 6c 01 00 00 00 00 00 00 0c 00 02 00 ff 7f 00 00 00 00 00 00 40 00 07 80 0c 00 01 80 08 00 01 00} (length 0x32)
//                }
//                union ANYUNION {
//                  ANYRES32: ANYRES32 (resource)
//                }
//                union ANYUNION {
//                  ANYBLOB: buffer: {0c 00 01 80 08 00 01 00} (length 0x8)
//                }
//                union ANYUNION {
//                  ANYRES32: ANYRES32 (resource)
//                }
//              }
//            }
//            len: len = 0x6c (8 bytes)
//          }
//        }
//        vlen: const = 0x1 (8 bytes)
//        ctrl: const = 0x0 (8 bytes)
//        ctrllen: const = 0x0 (8 bytes)
//        f: send_flags = 0x0 (4 bytes)
//        pad = 0x0 (4 bytes)
//      }
//    }
//    f: send_flags = 0x20000000 (8 bytes)
//  ]
*(uint64_t*)0x200000001ac0 = 0;
*(uint32_t*)0x200000001ac8 = 0;
*(uint64_t*)0x200000001ad0 = 0x200000001a80;
*(uint64_t*)0x200000001a80 = 0x200000000140;
memcpy((void*)0x200000000140, "l\000\000\000", 4);
*(uint16_t*)0x200000000144 = r[1];
memcpy((void*)0x200000000146, "\x01\x00\xff\xff\xff\xff\x00\x00\x00\x00\x01\x00\x00\x00\x0c\x00\x05\x00\x6c\x01\x00\x00\x00\x00\x00\x00\x0c\x00\x02\x00\xff\x7f\x00\x00\x00\x00\x00\x00\x40\x00\x07\x80\x0c\x00\x01\x80\x08\x00\x01\x00", 50);
*(uint32_t*)0x200000000178 = r[2];
memcpy((void*)0x20000000017c, "\x0c\x00\x01\x80\x08\x00\x01\x00", 8);
*(uint32_t*)0x200000000184 = r[2];
*(uint64_t*)0x200000001a88 = 0x6c;
*(uint64_t*)0x200000001ad8 = 1;
*(uint64_t*)0x200000001ae0 = 0;
*(uint64_t*)0x200000001ae8 = 0;
*(uint32_t*)0x200000001af0 = 0;
	syscall(__NR_sendmsg, /*fd=*/r[0], /*msg=*/0x200000001ac0ul, /*f=MSG_FASTOPEN*/0x20000000ul);
//  socket$inet6_tcp arguments: [
//    domain: const = 0xa (8 bytes)
//    type: const = 0x1 (8 bytes)
//    proto: const = 0x0 (4 bytes)
//  ]
//  returns sock_tcp6
	res = syscall(__NR_socket, /*domain=*/0xaul, /*type=*/1ul, /*proto=*/0);
	if (res != -1)
		r[3] = res;
//  syz_genetlink_get_family_id$nbd arguments: [
//    name: ptr[in, buffer] {
//      buffer: {6e 62 64 00} (length 0x4)
//    }
//    fd: sock_nl_generic_init (resource)
//  ]
//  returns genl_nbd_family_id
memcpy((void*)0x200000000000, "nbd\000", 4);
	res = -1;
res = syz_genetlink_get_family_id(/*name=*/0x200000000000, /*fd=*/-1);
	if (res != -1)
		r[4] = res;
//  syz_init_net_socket$nl_generic arguments: [
//    domain: const = 0x10 (8 bytes)
//    type: const = 0x3 (8 bytes)
//    proto: const = 0x10 (8 bytes)
//  ]
//  returns sock_nl_generic_init
	res = -1;
res = syz_init_net_socket(/*domain=*/0x10, /*type=*/3, /*proto=*/0x10);
	if (res != -1)
		r[5] = res;
//  sendmsg$NBD_CMD_RECONFIGURE arguments: [
//    fd: sock_nl_generic_init (resource)
//    msg: ptr[in, msghdr_netlink[netlink_msg_t[genl_nbd_family_id, genlmsghdr_t[NBD_CMD_RECONFIGURE], nbd_attr_policy]]] {
//      msghdr_netlink[netlink_msg_t[genl_nbd_family_id, genlmsghdr_t[NBD_CMD_RECONFIGURE], nbd_attr_policy]] {
//        addr: nil
//        addrlen: len = 0x0 (4 bytes)
//        pad = 0x0 (4 bytes)
//        vec: ptr[in, iovec[in, netlink_msg_t[genl_nbd_family_id, genlmsghdr_t[NBD_CMD_RECONFIGURE], nbd_attr_policy]]] {
//          iovec[in, netlink_msg_t[genl_nbd_family_id, genlmsghdr_t[NBD_CMD_RECONFIGURE], nbd_attr_policy]] {
//            addr: ptr[inout, array[ANYUNION]] {
//              array[ANYUNION] {
//                union ANYUNION {
//                  ANYBLOB: buffer: {2c 00 00 00} (length 0x4)
//                }
//                union ANYUNION {
//                  ANYRES16: ANYRES16 (resource)
//                }
//                union ANYUNION {
//                  ANYBLOB: buffer: {01 00 26 bd 70 00 fe db df 25 03 00 40 00 08 00 01 00 00 00 00 00 10 00 07 80 0c 00 01 80 08 00 01 00} (length 0x22)
//                }
//                union ANYUNION {
//                  ANYRES8: ANYRES8 (resource)
//                }
//              }
//            }
//            len: len = 0x2c (8 bytes)
//          }
//        }
//        vlen: const = 0x1 (8 bytes)
//        ctrl: const = 0x0 (8 bytes)
//        ctrllen: const = 0x0 (8 bytes)
//        f: send_flags = 0x150 (4 bytes)
//        pad = 0x0 (4 bytes)
//      }
//    }
//    f: send_flags = 0x20008040 (8 bytes)
//  ]
*(uint64_t*)0x200000000040 = 0;
*(uint32_t*)0x200000000048 = 0;
*(uint64_t*)0x200000000050 = 0x200000000240;
*(uint64_t*)0x200000000240 = 0x200000000080;
memcpy((void*)0x200000000080, ",\000\000\000", 4);
*(uint16_t*)0x200000000084 = r[4];
memcpy((void*)0x200000000086, "\x01\x00\x26\xbd\x70\x00\xfe\xdb\xdf\x25\x03\x00\x40\x00\x08\x00\x01\x00\x00\x00\x00\x00\x10\x00\x07\x80\x0c\x00\x01\x80\x08\x00\x01\x00", 34);
*(uint8_t*)0x2000000000a8 = r[3];
*(uint64_t*)0x200000000248 = 0x2c;
*(uint64_t*)0x200000000058 = 1;
*(uint64_t*)0x200000000060 = 0;
*(uint64_t*)0x200000000068 = 0;
*(uint32_t*)0x200000000070 = 0x150;
	syscall(__NR_sendmsg, /*fd=*/r[5], /*msg=*/0x200000000040ul, /*f=MSG_FASTOPEN|MSG_MORE|MSG_DONTWAIT*/0x20008040ul);
	return 0;
}
]

map[KernelSrc:/app/workdir/cache/src/cbad7996b082969065ced471e435d1359c15f2ef]

map[KernelObj:/app/workdir/cache/build/c305a0c668b7634f31ee180fa887a1e40a4c4dad]

map[ReproducedBugTitle:SYZFAIL: failed to recv rpc ReproducedCrashReport:SYZFAIL: failed to recv rpc
fd=3 want=4 recv=0 n=-1 (errno 104: Connection reset by peer)
 ReproducedFaultInjection:]

map[Index:codesearch-index]

gemini-3.1-pro-preview

You are an experienced Linux kernel developer tasked with debugging a kernel crash root cause.
You need to provide a detailed explanation of the root cause for another developer to be
able to write a fix for the bug based on your explanation. Include all relevant details
into the response: function/struct/field/etc names, code snippets, line numbers,
macro/enum values, etc.



Prefer calling several tools at the same time to save round-trips.

The crash is:

SYZFAIL: failed to recv rpc
fd=3 want=4 recv=0 n=-1 (errno 104: Connection reset by peer)


The following C code is a draft of the vulnerable syscall sequence. Keep in mind that
it may lack the precise threading, sandboxing, and some arguments of a working reproducer:

// autogenerated by syzkaller (https://github.com/google/syzkaller)

#define _GNU_SOURCE 

#include <arpa/inet.h>
#include <endian.h>
#include <errno.h>
#include <net/if.h>
#include <netinet/in.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/socket.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>

#include <linux/genetlink.h>
#include <linux/if_addr.h>
#include <linux/if_link.h>
#include <linux/in6.h>
#include <linux/neighbour.h>
#include <linux/net.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <linux/veth.h>

struct nlmsg {
	char* pos;
	int nesting;
	struct nlattr* nested[8];
	char buf[4096];
};

static void netlink_init(struct nlmsg* nlmsg, int typ, int flags,
			 const void* data, int size)
{
	memset(nlmsg, 0, sizeof(*nlmsg));
	struct nlmsghdr* hdr = (struct nlmsghdr*)nlmsg->buf;
	hdr->nlmsg_type = typ;
	hdr->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK | flags;
	memcpy(hdr + 1, data, size);
	nlmsg->pos = (char*)(hdr + 1) + NLMSG_ALIGN(size);
}

static void netlink_attr(struct nlmsg* nlmsg, int typ,
			 const void* data, int size)
{
	struct nlattr* attr = (struct nlattr*)nlmsg->pos;
	attr->nla_len = sizeof(*attr) + size;
	attr->nla_type = typ;
	if (size > 0)
		memcpy(attr + 1, data, size);
	nlmsg->pos += NLMSG_ALIGN(attr->nla_len);
}

static int netlink_send_ext(struct nlmsg* nlmsg, int sock,
			    uint16_t reply_type, int* reply_len, bool dofail)
{
	if (nlmsg->pos > nlmsg->buf + sizeof(nlmsg->buf) || nlmsg->nesting)
	exit(1);
	struct nlmsghdr* hdr = (struct nlmsghdr*)nlmsg->buf;
	hdr->nlmsg_len = nlmsg->pos - nlmsg->buf;
	struct sockaddr_nl addr;
	memset(&addr, 0, sizeof(addr));
	addr.nl_family = AF_NETLINK;
	ssize_t n = sendto(sock, nlmsg->buf, hdr->nlmsg_len, 0, (struct sockaddr*)&addr, sizeof(addr));
	if (n != (ssize_t)hdr->nlmsg_len) {
		if (dofail)
	exit(1);
		return -1;
	}
	n = recv(sock, nlmsg->buf, sizeof(nlmsg->buf), 0);
	if (reply_len)
		*reply_len = 0;
	if (n < 0) {
		if (dofail)
	exit(1);
		return -1;
	}
	if (n < (ssize_t)sizeof(struct nlmsghdr)) {
		errno = EINVAL;
		if (dofail)
	exit(1);
		return -1;
	}
	if (hdr->nlmsg_type == NLMSG_DONE)
		return 0;
	if (reply_len && hdr->nlmsg_type == reply_type) {
		*reply_len = n;
		return 0;
	}
	if (n < (ssize_t)(sizeof(struct nlmsghdr) + sizeof(struct nlmsgerr))) {
		errno = EINVAL;
		if (dofail)
	exit(1);
		return -1;
	}
	if (hdr->nlmsg_type != NLMSG_ERROR) {
		errno = EINVAL;
		if (dofail)
	exit(1);
		return -1;
	}
	errno = -((struct nlmsgerr*)(hdr + 1))->error;
	return -errno;
}

static int netlink_query_family_id(struct nlmsg* nlmsg, int sock, const char* family_name, bool dofail)
{
	struct genlmsghdr genlhdr;
	memset(&genlhdr, 0, sizeof(genlhdr));
	genlhdr.cmd = CTRL_CMD_GETFAMILY;
	netlink_init(nlmsg, GENL_ID_CTRL, 0, &genlhdr, sizeof(genlhdr));
	netlink_attr(nlmsg, CTRL_ATTR_FAMILY_NAME, family_name, strnlen(family_name, GENL_NAMSIZ - 1) + 1);
	int n = 0;
	int err = netlink_send_ext(nlmsg, sock, GENL_ID_CTRL, &n, dofail);
	if (err < 0) {
		return -1;
	}
	uint16_t id = 0;
	struct nlattr* attr = (struct nlattr*)(nlmsg->buf + NLMSG_HDRLEN + NLMSG_ALIGN(sizeof(genlhdr)));
	for (; (char*)attr < nlmsg->buf + n; attr = (struct nlattr*)((char*)attr + NLMSG_ALIGN(attr->nla_len))) {
		if (attr->nla_type == CTRL_ATTR_FAMILY_ID) {
			id = *(uint16_t*)(attr + 1);
			break;
		}
	}
	if (!id) {
		errno = EINVAL;
		return -1;
	}
	recv(sock, nlmsg->buf, sizeof(nlmsg->buf), 0);
	return id;
}

const int kInitNetNsFd = 201;

static long syz_init_net_socket(volatile long domain, volatile long type, volatile long proto)
{
	return syscall(__NR_socket, domain, type, proto);
}

static long syz_genetlink_get_family_id(volatile long name, volatile long sock_arg)
{
	int fd = sock_arg;
	if (fd < 0) {
		fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_GENERIC);
		if (fd == -1) {
			return -1;
		}
	}
	struct nlmsg nlmsg_tmp;
	int ret = netlink_query_family_id(&nlmsg_tmp, fd, (char*)name, false);
	if ((int)sock_arg < 0)
		close(fd);
	if (ret < 0) {
		return -1;
	}
	return ret;
}

uint64_t r[6] = {0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff};

int main(void)
{
		syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
	syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000ul, /*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/7ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
	syscall(__NR_mmap, /*addr=*/0x200001000000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
	const char* reason;
	(void)reason;
				intptr_t res = 0;
	if (write(1, "executing program\n", sizeof("executing program\n") - 1)) {}
//  syz_init_net_socket$nl_generic arguments: [
//    domain: const = 0x10 (8 bytes)
//    type: const = 0x3 (8 bytes)
//    proto: const = 0x10 (8 bytes)
//  ]
//  returns sock_nl_generic_init
	res = -1;
res = syz_init_net_socket(/*domain=*/0x10, /*type=*/3, /*proto=*/0x10);
	if (res != -1)
		r[0] = res;
//  syz_genetlink_get_family_id$nbd arguments: [
//    name: ptr[in, buffer] {
//      buffer: {6e 62 64 00} (length 0x4)
//    }
//    fd: sock_nl_generic_init (resource)
//  ]
//  returns genl_nbd_family_id
memcpy((void*)0x200000000000, "nbd\000", 4);
	res = -1;
res = syz_genetlink_get_family_id(/*name=*/0x200000000000, /*fd=*/-1);
	if (res != -1)
		r[1] = res;
//  socketpair$nbd arguments: [
//    domain: const = 0x1 (8 bytes)
//    type: const = 0x1 (8 bytes)
//    proto: const = 0x0 (4 bytes)
//    fds: ptr[out, nbd_sock_pair] {
//      nbd_sock_pair {
//        client: sock_nbd_client (resource)
//        server: sock_nbd_server (resource)
//      }
//    }
//  ]
	res = syscall(__NR_socketpair, /*domain=*/1ul, /*type=*/1ul, /*proto=*/0, /*fds=*/0x200000000100ul);
	if (res != -1)
r[2] = *(uint32_t*)0x200000000100;
//  sendmsg$NBD_CMD_CONNECT arguments: [
//    fd: sock_nl_generic_init (resource)
//    msg: ptr[in, msghdr_netlink[netlink_msg_t[genl_nbd_family_id, genlmsghdr_t[NBD_CMD_CONNECT], nbd_attr_policy]]] {
//      msghdr_netlink[netlink_msg_t[genl_nbd_family_id, genlmsghdr_t[NBD_CMD_CONNECT], nbd_attr_policy]] {
//        addr: nil
//        addrlen: len = 0x0 (4 bytes)
//        pad = 0x0 (4 bytes)
//        vec: ptr[in, iovec[in, netlink_msg_t[genl_nbd_family_id, genlmsghdr_t[NBD_CMD_CONNECT], nbd_attr_policy]]] {
//          iovec[in, netlink_msg_t[genl_nbd_family_id, genlmsghdr_t[NBD_CMD_CONNECT], nbd_attr_policy]] {
//            addr: ptr[inout, array[ANYUNION]] {
//              array[ANYUNION] {
//                union ANYUNION {
//                  ANYBLOB: buffer: {6c 00 00 00} (length 0x4)
//                }
//                union ANYUNION {
//                  ANYRES16: ANYRES16 (resource)
//                }
//                union ANYUNION {
//                  ANYBLOB: buffer: {01 00 ff ff ff ff 00 00 00 00 01 00 00 00 0c 00 05 00 6c 01 00 00 00 00 00 00 0c 00 02 00 ff 7f 00 00 00 00 00 00 40 00 07 80 0c 00 01 80 08 00 01 00} (length 0x32)
//                }
//                union ANYUNION {
//                  ANYRES32: ANYRES32 (resource)
//                }
//                union ANYUNION {
//                  ANYBLOB: buffer: {0c 00 01 80 08 00 01 00} (length 0x8)
//                }
//                union ANYUNION {
//                  ANYRES32: ANYRES32 (resource)
//                }
//              }
//            }
//            len: len = 0x6c (8 bytes)
//          }
//        }
//        vlen: const = 0x1 (8 bytes)
//        ctrl: const = 0x0 (8 bytes)
//        ctrllen: const = 0x0 (8 bytes)
//        f: send_flags = 0x0 (4 bytes)
//        pad = 0x0 (4 bytes)
//      }
//    }
//    f: send_flags = 0x20000000 (8 bytes)
//  ]
*(uint64_t*)0x200000001ac0 = 0;
*(uint32_t*)0x200000001ac8 = 0;
*(uint64_t*)0x200000001ad0 = 0x200000001a80;
*(uint64_t*)0x200000001a80 = 0x200000000140;
memcpy((void*)0x200000000140, "l\000\000\000", 4);
*(uint16_t*)0x200000000144 = r[1];
memcpy((void*)0x200000000146, "\x01\x00\xff\xff\xff\xff\x00\x00\x00\x00\x01\x00\x00\x00\x0c\x00\x05\x00\x6c\x01\x00\x00\x00\x00\x00\x00\x0c\x00\x02\x00\xff\x7f\x00\x00\x00\x00\x00\x00\x40\x00\x07\x80\x0c\x00\x01\x80\x08\x00\x01\x00", 50);
*(uint32_t*)0x200000000178 = r[2];
memcpy((void*)0x20000000017c, "\x0c\x00\x01\x80\x08\x00\x01\x00", 8);
*(uint32_t*)0x200000000184 = r[2];
*(uint64_t*)0x200000001a88 = 0x6c;
*(uint64_t*)0x200000001ad8 = 1;
*(uint64_t*)0x200000001ae0 = 0;
*(uint64_t*)0x200000001ae8 = 0;
*(uint32_t*)0x200000001af0 = 0;
	syscall(__NR_sendmsg, /*fd=*/r[0], /*msg=*/0x200000001ac0ul, /*f=MSG_FASTOPEN*/0x20000000ul);
//  socket$inet6_tcp arguments: [
//    domain: const = 0xa (8 bytes)
//    type: const = 0x1 (8 bytes)
//    proto: const = 0x0 (4 bytes)
//  ]
//  returns sock_tcp6
	res = syscall(__NR_socket, /*domain=*/0xaul, /*type=*/1ul, /*proto=*/0);
	if (res != -1)
		r[3] = res;
//  syz_genetlink_get_family_id$nbd arguments: [
//    name: ptr[in, buffer] {
//      buffer: {6e 62 64 00} (length 0x4)
//    }
//    fd: sock_nl_generic_init (resource)
//  ]
//  returns genl_nbd_family_id
memcpy((void*)0x200000000000, "nbd\000", 4);
	res = -1;
res = syz_genetlink_get_family_id(/*name=*/0x200000000000, /*fd=*/-1);
	if (res != -1)
		r[4] = res;
//  syz_init_net_socket$nl_generic arguments: [
//    domain: const = 0x10 (8 bytes)
//    type: const = 0x3 (8 bytes)
//    proto: const = 0x10 (8 bytes)
//  ]
//  returns sock_nl_generic_init
	res = -1;
res = syz_init_net_socket(/*domain=*/0x10, /*type=*/3, /*proto=*/0x10);
	if (res != -1)
		r[5] = res;
//  sendmsg$NBD_CMD_RECONFIGURE arguments: [
//    fd: sock_nl_generic_init (resource)
//    msg: ptr[in, msghdr_netlink[netlink_msg_t[genl_nbd_family_id, genlmsghdr_t[NBD_CMD_RECONFIGURE], nbd_attr_policy]]] {
//      msghdr_netlink[netlink_msg_t[genl_nbd_family_id, genlmsghdr_t[NBD_CMD_RECONFIGURE], nbd_attr_policy]] {
//        addr: nil
//        addrlen: len = 0x0 (4 bytes)
//        pad = 0x0 (4 bytes)
//        vec: ptr[in, iovec[in, netlink_msg_t[genl_nbd_family_id, genlmsghdr_t[NBD_CMD_RECONFIGURE], nbd_attr_policy]]] {
//          iovec[in, netlink_msg_t[genl_nbd_family_id, genlmsghdr_t[NBD_CMD_RECONFIGURE], nbd_attr_policy]] {
//            addr: ptr[inout, array[ANYUNION]] {
//              array[ANYUNION] {
//                union ANYUNION {
//                  ANYBLOB: buffer: {2c 00 00 00} (length 0x4)
//                }
//                union ANYUNION {
//                  ANYRES16: ANYRES16 (resource)
//                }
//                union ANYUNION {
//                  ANYBLOB: buffer: {01 00 26 bd 70 00 fe db df 25 03 00 40 00 08 00 01 00 00 00 00 00 10 00 07 80 0c 00 01 80 08 00 01 00} (length 0x22)
//                }
//                union ANYUNION {
//                  ANYRES8: ANYRES8 (resource)
//                }
//              }
//            }
//            len: len = 0x2c (8 bytes)
//          }
//        }
//        vlen: const = 0x1 (8 bytes)
//        ctrl: const = 0x0 (8 bytes)
//        ctrllen: const = 0x0 (8 bytes)
//        f: send_flags = 0x150 (4 bytes)
//        pad = 0x0 (4 bytes)
//      }
//    }
//    f: send_flags = 0x20008040 (8 bytes)
//  ]
*(uint64_t*)0x200000000040 = 0;
*(uint32_t*)0x200000000048 = 0;
*(uint64_t*)0x200000000050 = 0x200000000240;
*(uint64_t*)0x200000000240 = 0x200000000080;
memcpy((void*)0x200000000080, ",\000\000\000", 4);
*(uint16_t*)0x200000000084 = r[4];
memcpy((void*)0x200000000086, "\x01\x00\x26\xbd\x70\x00\xfe\xdb\xdf\x25\x03\x00\x40\x00\x08\x00\x01\x00\x00\x00\x00\x00\x10\x00\x07\x80\x0c\x00\x01\x80\x08\x00\x01\x00", 34);
*(uint8_t*)0x2000000000a8 = r[3];
*(uint64_t*)0x200000000248 = 0x2c;
*(uint64_t*)0x200000000058 = 1;
*(uint64_t*)0x200000000060 = 0;
*(uint64_t*)0x200000000068 = 0;
*(uint32_t*)0x200000000070 = 0x150;
	syscall(__NR_sendmsg, /*fd=*/r[5], /*msg=*/0x200000000040ul, /*f=MSG_FASTOPEN|MSG_MORE|MSG_DONTWAIT*/0x20008040ul);
	return 0;
}

I have analyzed the provided syzkaller reproducer and the NBD (Network Block Device) subsystem code.

### Root Cause Analysis

The root cause of the issue is that the NBD netlink interface (`nbd_genl_connect`) does not validate whether the same socket file descriptor (fd) is provided multiple times in the `NBD_ATTR_SOCKETS` array. 

In the reproducer, the `NBD_CMD_CONNECT` netlink message contains an `NBD_ATTR_SOCKETS` attribute with two nested `NBD_SOCK_ITEM`s, both containing the **same** socket fd (`r[2]`, which is a UNIX domain socket from `socketpair`).

1. **Duplicate Socket Addition**: `nbd_genl_connect` loops over the nested attributes and calls `nbd_add_socket(nbd, fd, true)` twice for the same fd.
   - `nbd_add_socket` calls `nbd_get_socket`, which uses `sockfd_lookup(fd)`. This increments the underlying `struct file` reference count twice.
   - It allocates two distinct `struct nbd_sock` objects (`config->socks[0]` and `config->socks[1]`), but both of their `->sock` pointers point to the **same** `struct socket *`.
   - `config->num_connections` becomes 2.

2. **Double `sk_set_memalloc`**: `nbd_genl_connect` then calls `nbd_start_device`, which loops over the connections and calls `sk_set_memalloc(config->socks[i]->sock->sk)`.
   - Because both connections point to the same socket, `sk_set_memalloc` is called twice on the same `struct sock *`.
   - `sk_set_memalloc` increments the global static key `memalloc_socks_key` (`static_branch_inc(&memalloc_socks_key)`).
   - The NBD driver never calls `sk_clear_memalloc` (it relies on the socket destruction to clear it, but `sk_clear_memalloc` is actually not called automatically on socket destruction in standard kernels, it's only called by specific subsystems like sunrpc/wireguard). This results in a persistent leak of the `memalloc_socks_key` static branch reference.

3. **Concurrent `recv_work` on the Same Socket**: `nbd_start_device` queues two `recv_work` threads on the `nbd->recv_workq`.
   - Both threads enter a `while (1)` loop and call `nbd_read_reply`, which eventually calls `sock_recvmsg` on the **same** socket concurrently.
   - For a TCP/UNIX stream socket, concurrent reads will interleave, causing stream corruption. One thread might read the first half of a reply header, and the other thread might read the second half. Both will fail to parse the NBD magic number and error out.

4. **Teardown and Cleanup**: When the reproducer exits, the socket is closed.
   - Both `recv_work` threads wake up with an error (EOF) and break out of their loops.
   - Both threads call `nbd_mark_nsock_dead`, which calls `kernel_sock_shutdown` on the same socket (safe, as it's serialized internally by `unix_state_lock`).
   - Both threads call `nbd_config_put(nbd)`. The first thread decrements `nbd->config_refs` to 1 and returns. The second thread decrements it to 0 and performs the cleanup.
   - The cleanup loop calls `sockfd_put(config->socks[i]->sock)` twice. Since `sockfd_lookup` was called twice initially, the file reference count is perfectly balanced, so there is no use-after-free or double-free of the socket itself.

### Conclusion

While the kernel's reference counting prevents a direct use-after-free or double-free of the socket, allowing the same socket to be added multiple times leads to:
1. **Protocol Corruption**: Multiple `recv_work` threads concurrently reading from the same stream socket corrupt the NBD protocol stream.
2. **Resource Leak**: `sk_set_memalloc` is called multiple times on the same socket, leaking the `memalloc_socks_key` static branch counter.

The syzkaller "SYZFAIL: failed to recv rpc" error is likely a secondary effect of the syz-executor dying or hanging due to the corrupted state or the static key leak triggering a warning/panic elsewhere in the network stack.

### Proposed Fix

To fix this, `nbd_add_socket` should verify that the provided socket is not already part of the `config->socks` array before adding it.

```c
// In drivers/block/nbd.c -> nbd_add_socket()

	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	/* Prevent adding the same socket multiple times */
	for (int i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			err = -EEXIST;
			goto put_socket;
		}
	}
```

gemini-3.1-pro-preview

							input: 9369
							output: 20
							thoughts: 737
						

**Debugging a Syzkaller RPC Failure in NBD Code**

Okay, so I've got this syzkaller error: "SYZFAIL: failed to recv rpc". That's a classic sign that something went terribly wrong during a fuzzing run. My initial thought is that the kernel probably crashed or, at the very least, the syz-executor died an unexpected death. Time to dig in.

Let's look at the C code. It appears we're dealing with NBD (Network Block Device) and netlink, which is always fun. It's doing the usual dance: a `syz_init_net_socket` call followed by `syz_genetlink_get_family_id` for "nbd". The core seems to involve a `socketpair` for a set of sockets (r[2]).

It's using `sendmsg` to send `NBD_CMD_CONNECT` on the netlink socket. The interesting part is the attributes being sent with the message.  I need to check the attributes, because they are where things typically go awry. Specifically, it is using:
*   `NBD_ATTR_INDEX` (or something similar, based on the context).
*   `NBD_ATTR_SOCKETS` and this is where it gets interesting... The code includes a socketpair file descriptor.

Analyzing the hexdump:

*   I see a length (12) and type (5) combination, and I'm guessing this is `NBD_ATTR_SOCKETS`, that is nested.
*   Another length (12) and type (2) looks like `NBD_ATTR_INDEX`. The index is set to 32767.
*   The next set of bytes are: a length (64) and type (0x8007) indicating nested, and more specifically `NBD_ATTR_SOCKETS`.
*   Another length (12) and type (0x8001), indicating nested again.
*   Then a length (8) and type (1). I am guessing this is `NBD_SOCK_FD`, but I need to confirm this.
*   Then the `r[2]` (socketpair fd) is written into the buffer.

The code then creates a TCP6 socket `r[3]` and sends `NBD_CMD_RECONFIGURE` on *another* netlink socket. The attributes here also include:

*   an 8-byte message with length (8) and type (1) with index 0.
*   A nested attribute with length (16) and type (0x8007) which appears to be `NBD_ATTR_SOCKETS`.
*   Another nested with length (12) and type (0x8001).
*   Another 8-byte message with length (8) and type (1).
*   `r[3]` (the TCP6 socket fd) is written.

Okay, this gives me a good starting point. I need to get into the NBD netlink commands in the kernel to trace what is going on.

map[Expression:NBD_CMD_CONNECT]

map[Output:drivers/block/nbd.c=2449=static const struct genl_small_ops nbd_connect_genl_ops[] = {
drivers/block/nbd.c-2450-	{
drivers/block/nbd.c:2451:		.cmd	= NBD_CMD_CONNECT,
drivers/block/nbd.c-2452-		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
--
drivers/block/nbd.c=2587=static void nbd_connect_reply(struct genl_info *info, int index)
--
drivers/block/nbd.c-2596-	msg_head = genlmsg_put_reply(skb, info, &nbd_genl_family, 0,
drivers/block/nbd.c:2597:				     NBD_CMD_CONNECT);
drivers/block/nbd.c-2598-	if (!msg_head) {
--
include/uapi/linux/nbd-netlink.h=89=enum {
include/uapi/linux/nbd-netlink.h-90-	NBD_CMD_UNSPEC,
include/uapi/linux/nbd-netlink.h:91:	NBD_CMD_CONNECT,
include/uapi/linux/nbd-netlink.h-92-	NBD_CMD_DISCONNECT,
]

gemini-3.1-pro-preview

							input: 11176
							output: 27
							thoughts: 18
						

Here's my take on those thoughts, tailored for an expert audience:

**Diving into nbd.c and its Attributes**

Okay, time to get granular. My instinct tells me to jump straight into `drivers/block/nbd.c`. I need a solid understanding of how the Network Block Device driver functions and, crucially, how its attributes are defined and handled. I'm going to look for the core data structures, especially the ones that represent the device itself (`nbd_device` perhaps?), and how configuration parameters are stored and accessed. I want to see the attribute definition macros in use. Are we using something custom, or are we leveraging the kernel's existing infrastructure for handling sysfs or other exposed attributes? Are there any obvious areas for improvement or, at the very least, any potential gotchas lurking in the implementation? I'm particularly interested in how things like read-only status, block size, and the underlying socket are managed in relation to these attributes. My goal is to quickly pinpoint how these attributes shape the behavior of the NBD driver.

map[SourceFile:drivers/block/nbd.c]

map[Entities:[map[Kind:function Name:__check_max_part] map[Kind:function Name:__check_nbds_max] map[Kind:function Name:__nbd_ioctl] map[Kind:function Name:__sock_xmit] map[Kind:function Name:backend_show] map[Kind:function Name:find_fallback] map[Kind:function Name:nbd_add_socket] map[Kind:function Name:nbd_alloc_and_init_config] map[Kind:function Name:nbd_bdev_reset] map[Kind:function Name:nbd_blksize] map[Kind:function Name:nbd_cleanup] map[Kind:function Name:nbd_clear_que] map[Kind:function Name:nbd_clear_req] map[Kind:function Name:nbd_clear_sock] map[Kind:function Name:nbd_clear_sock_ioctl] map[Kind:function Name:nbd_cmd_handle] map[Kind:function Name:nbd_complete_rq] map[Kind:function Name:nbd_config_put] map[Kind:function Name:nbd_connect_reply] map[Kind:function Name:nbd_dbg_close] map[Kind:function Name:nbd_dbg_flags_open] map[Kind:function Name:nbd_dbg_flags_show] map[Kind:function Name:nbd_dbg_init] map[Kind:function Name:nbd_dbg_tasks_open] map[Kind:function Name:nbd_dbg_tasks_show] map[Kind:function Name:nbd_dead_link_work] map[Kind:function Name:nbd_dev_add] map[Kind:function Name:nbd_dev_dbg_close] map[Kind:function Name:nbd_dev_dbg_init] map[Kind:function Name:nbd_dev_remove] map[Kind:function Name:nbd_dev_remove_work] map[Kind:function Name:nbd_disconnect] map[Kind:function Name:nbd_disconnect_and_put] map[Kind:function Name:nbd_disconnected] map[Kind:function Name:nbd_exit_cb] map[Kind:function Name:nbd_find_get_unused] map[Kind:function Name:nbd_free_disk] map[Kind:function Name:nbd_genl_connect] map[Kind:function Name:nbd_genl_disconnect] map[Kind:function Name:nbd_genl_reconfigure] map[Kind:function Name:nbd_genl_size_set] map[Kind:function Name:nbd_genl_status] map[Kind:function Name:nbd_get_config_unlocked] map[Kind:function Name:nbd_get_socket] map[Kind:function Name:nbd_handle_cmd] map[Kind:function Name:nbd_handle_reply] map[Kind:function Name:nbd_handle_to_cookie] map[Kind:function Name:nbd_handle_to_tag] map[Kind:function Name:nbd_init] map[Kind:function Name:nbd_init_request] map[Kind:function Name:nbd_ioctl] map[Kind:function Name:nbd_mark_nsock_dead] map[Kind:function Name:nbd_mcast_index] map[Kind:function Name:nbd_open] map[Kind:function Name:nbd_parse_flags] map[Kind:function Name:nbd_pending_cmd_work] map[Kind:function Name:nbd_put] map[Kind:function Name:nbd_queue_rq] map[Kind:function Name:nbd_read_reply] map[Kind:function Name:nbd_reconnect_socket] map[Kind:function Name:nbd_release] map[Kind:function Name:nbd_requeue_cmd] map[Kind:function Name:nbd_sched_pending_work] map[Kind:function Name:nbd_send_cmd] map[Kind:function Name:nbd_set_cmd_timeout] map[Kind:function Name:nbd_set_size] map[Kind:function Name:nbd_start_device] map[Kind:function Name:nbd_start_device_ioctl] map[Kind:function Name:nbd_to_dev] map[Kind:function Name:nbd_xmit_timeout] map[Kind:function Name:nbdcmd_to_ascii] map[Kind:function Name:pid_show] map[Kind:function Name:populate_nbd_status] map[Kind:function Name:recv_work] map[Kind:function Name:req_to_nbd_cmd_type] map[Kind:function Name:send_disconnects] map[Kind:function Name:sock_shutdown] map[Kind:function Name:sock_xmit] map[Kind:function Name:status_cb] map[Kind:function Name:wait_for_reconnect] map[Kind:function Name:was_interrupted] map[Kind:struct Name:link_dead_args] map[Kind:struct Name:nbd_cmd] map[Kind:struct Name:nbd_config] map[Kind:struct Name:nbd_device] map[Kind:struct Name:nbd_sock] map[Kind:struct Name:recv_thread_args] map[Kind:global_variable Name:__UNIQUE_ID_addressable_nbd_init_1559] map[Kind:global_variable Name:__UNIQUE_ID_modinfo_1556] map[Kind:global_variable Name:__UNIQUE_ID_modinfo_1560] map[Kind:global_variable Name:__UNIQUE_ID_modinfo_1561] map[Kind:global_variable Name:__UNIQUE_ID_modinfo_1562] map[Kind:global_variable Name:__UNIQUE_ID_modinfo_1563] map[Kind:global_variable Name:__UNIQUE_ID_modinfo_1564] map[Kind:global_variable Name:__UNIQUE_ID_modinfo_1565] map[Kind:global_variable Name:__UNIQUE_ID_modinfo_1566] map[Kind:global_variable Name:__exitcall_nbd_cleanup] map[Kind:global_variable Name:__param_max_part] map[Kind:global_variable Name:__param_nbds_max] map[Kind:global_variable Name:__param_str_max_part] map[Kind:global_variable Name:__param_str_nbds_max] map[Kind:global_variable Name:backend_attr] map[Kind:global_variable Name:max_part] map[Kind:global_variable Name:nbd_attr_policy] map[Kind:global_variable Name:nbd_connect_genl_ops] map[Kind:global_variable Name:nbd_dbg_flags_fops] map[Kind:global_variable Name:nbd_dbg_tasks_fops] map[Kind:global_variable Name:nbd_device_policy] map[Kind:global_variable Name:nbd_fops] map[Kind:global_variable Name:nbd_genl_family] map[Kind:global_variable Name:nbd_index_idr] map[Kind:global_variable Name:nbd_index_mutex] map[Kind:global_variable Name:nbd_mcast_grps] map[Kind:global_variable Name:nbd_mq_ops] map[Kind:global_variable Name:nbd_sock_policy] map[Kind:global_variable Name:nbd_total_devices] map[Kind:global_variable Name:nbds_max] map[Kind:global_variable Name:pid_attr]]]

gemini-3.1-pro-preview

							input: 13604
							output: 89
							thoughts: 25
						

Okay, here's my summary, presented as a stream of thought:

**Diving into the NBD Kernel Module: Connection and Reconfiguration**

Alright, let's get down to brass tacks. I need to understand the connection and reconfiguration logic within the NBD kernel module. Specifically, I want to take a close look at how `nbd_genl_connect` and `nbd_genl_reconfigure` function. These two pieces are probably key to understanding the client-server interaction and the dynamic nature of the block device. I need to see how the connection handshake works and how parameters are actually altered. Are these atomic operations? What locks are in place? Are there potential race conditions in reconfiguration? I suspect there's interesting complexity in ensuring data integrity when dynamically re-configuring something like the block size or the server IP. Time to dig in and decipher the implementation details, starting with the connection setup and then moving to how they handle changes on the fly. Let's start with tracing the code paths...

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_genl_connect]

map[SourceCode:2073:	static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
2074:	{
2075:		struct nbd_device *nbd;
2076:		struct nbd_config *config;
2077:		int index = -1;
2078:		int ret;
2079:		bool put_dev = false;
2080:	
2081:		if (!netlink_capable(skb, CAP_SYS_ADMIN))
2082:			return -EPERM;
2083:	
2084:		if (info->attrs[NBD_ATTR_INDEX]) {
2085:			index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
2086:	
2087:			/*
2088:			 * Too big first_minor can cause duplicate creation of
2089:			 * sysfs files/links, since index << part_shift might overflow, or
2090:			 * MKDEV() expect that the max bits of first_minor is 20.
2091:			 */
2092:			if (index < 0 || index > MINORMASK >> part_shift) {
2093:				pr_err("illegal input index %d\n", index);
2094:				return -EINVAL;
2095:			}
2096:		}
2097:		if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SOCKETS)) {
2098:			pr_err("must specify at least one socket\n");
2099:			return -EINVAL;
2100:		}
2101:		if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SIZE_BYTES)) {
2102:			pr_err("must specify a size in bytes for the device\n");
2103:			return -EINVAL;
2104:		}
2105:	again:
2106:		mutex_lock(&nbd_index_mutex);
2107:		if (index == -1) {
2108:			nbd = nbd_find_get_unused();
2109:		} else {
2110:			nbd = idr_find(&nbd_index_idr, index);
2111:			if (nbd) {
2112:				if ((test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags) &&
2113:				     test_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags)) ||
2114:				    !refcount_inc_not_zero(&nbd->refs)) {
2115:					mutex_unlock(&nbd_index_mutex);
2116:					pr_err("device at index %d is going down\n",
2117:						index);
2118:					return -EINVAL;
2119:				}
2120:			}
2121:		}
2122:		mutex_unlock(&nbd_index_mutex);
2123:	
2124:		if (!nbd) {
2125:			nbd = nbd_dev_add(index, 2);
2126:			if (IS_ERR(nbd)) {
2127:				pr_err("failed to add new device\n");
2128:				return PTR_ERR(nbd);
2129:			}
2130:		}
2131:	
2132:		mutex_lock(&nbd->config_lock);
2133:		if (refcount_read(&nbd->config_refs)) {
2134:			mutex_unlock(&nbd->config_lock);
2135:			nbd_put(nbd);
2136:			if (index == -1)
2137:				goto again;
2138:			pr_err("nbd%d already in use\n", index);
2139:			return -EBUSY;
2140:		}
2141:	
2142:		ret = nbd_alloc_and_init_config(nbd);
2143:		if (ret) {
2144:			mutex_unlock(&nbd->config_lock);
2145:			nbd_put(nbd);
2146:			pr_err("couldn't allocate config\n");
2147:			return ret;
2148:		}
2149:	
2150:		config = nbd->config;
2151:		set_bit(NBD_RT_BOUND, &config->runtime_flags);
2152:		ret = nbd_genl_size_set(info, nbd);
2153:		if (ret)
2154:			goto out;
2155:	
2156:		if (info->attrs[NBD_ATTR_TIMEOUT])
2157:			nbd_set_cmd_timeout(nbd,
2158:					    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
2159:		if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
2160:			config->dead_conn_timeout =
2161:				nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
2162:			config->dead_conn_timeout *= HZ;
2163:		}
2164:		if (info->attrs[NBD_ATTR_SERVER_FLAGS])
2165:			config->flags =
2166:				nla_get_u64(info->attrs[NBD_ATTR_SERVER_FLAGS]);
2167:		if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
2168:			u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
2169:			if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
2170:				/*
2171:				 * We have 1 ref to keep the device around, and then 1
2172:				 * ref for our current operation here, which will be
2173:				 * inherited by the config.  If we already have
2174:				 * DESTROY_ON_DISCONNECT set then we know we don't have
2175:				 * that extra ref already held so we don't need the
2176:				 * put_dev.
2177:				 */
2178:				if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
2179:						      &nbd->flags))
2180:					put_dev = true;
2181:			} else {
2182:				if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
2183:						       &nbd->flags))
2184:					refcount_inc(&nbd->refs);
2185:			}
2186:			if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
2187:				set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
2188:					&config->runtime_flags);
2189:			}
2190:		}
2191:	
2192:		if (info->attrs[NBD_ATTR_SOCKETS]) {
2193:			struct nlattr *attr;
2194:			int rem, fd;
2195:	
2196:			nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
2197:					    rem) {
2198:				struct nlattr *socks[NBD_SOCK_MAX+1];
2199:	
2200:				if (nla_type(attr) != NBD_SOCK_ITEM) {
2201:					pr_err("socks must be embedded in a SOCK_ITEM attr\n");
2202:					ret = -EINVAL;
2203:					goto out;
2204:				}
2205:				ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
2206:								  attr,
2207:								  nbd_sock_policy,
2208:								  info->extack);
2209:				if (ret != 0) {
2210:					pr_err("error processing sock list\n");
2211:					ret = -EINVAL;
2212:					goto out;
2213:				}
2214:				if (!socks[NBD_SOCK_FD])
2215:					continue;
2216:				fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
2217:				ret = nbd_add_socket(nbd, fd, true);
2218:				if (ret)
2219:					goto out;
2220:			}
2221:		}
2222:	
2223:		if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
2224:			nbd->backend = nla_strdup(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
2225:						  GFP_KERNEL);
2226:			if (!nbd->backend) {
2227:				ret = -ENOMEM;
2228:				goto out;
2229:			}
2230:		}
2231:		ret = device_create_file(disk_to_dev(nbd->disk), &backend_attr);
2232:		if (ret) {
2233:			dev_err(disk_to_dev(nbd->disk),
2234:				"device_create_file failed for backend!\n");
2235:			goto out;
2236:		}
2237:		set_bit(NBD_RT_HAS_BACKEND_FILE, &config->runtime_flags);
2238:	
2239:		ret = nbd_start_device(nbd);
2240:	out:
2241:		if (!ret) {
2242:			set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);
2243:			refcount_inc(&nbd->config_refs);
2244:			nbd_connect_reply(info, nbd->index);
2245:		}
2246:		mutex_unlock(&nbd->config_lock);
2247:	
2248:		nbd_config_put(nbd);
2249:		if (put_dev)
2250:			nbd_put(nbd);
2251:		return ret;
2252:	}
 SourceFile:drivers/block/nbd.c]

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_genl_reconfigure]

map[SourceCode:2310:	static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
2311:	{
2312:		struct nbd_device *nbd = NULL;
2313:		struct nbd_config *config;
2314:		int index;
2315:		int ret = 0;
2316:		bool put_dev = false;
2317:	
2318:		if (!netlink_capable(skb, CAP_SYS_ADMIN))
2319:			return -EPERM;
2320:	
2321:		if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)) {
2322:			pr_err("must specify a device to reconfigure\n");
2323:			return -EINVAL;
2324:		}
2325:		index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
2326:		mutex_lock(&nbd_index_mutex);
2327:		nbd = idr_find(&nbd_index_idr, index);
2328:		if (!nbd) {
2329:			mutex_unlock(&nbd_index_mutex);
2330:			pr_err("couldn't find a device at index %d\n", index);
2331:			return -EINVAL;
2332:		}
2333:		if (nbd->backend) {
2334:			if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
2335:				if (nla_strcmp(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
2336:					       nbd->backend)) {
2337:					mutex_unlock(&nbd_index_mutex);
2338:					dev_err(nbd_to_dev(nbd),
2339:						"backend image doesn't match with %s\n",
2340:						nbd->backend);
2341:					return -EINVAL;
2342:				}
2343:			} else {
2344:				mutex_unlock(&nbd_index_mutex);
2345:				dev_err(nbd_to_dev(nbd), "must specify backend\n");
2346:				return -EINVAL;
2347:			}
2348:		}
2349:		if (!refcount_inc_not_zero(&nbd->refs)) {
2350:			mutex_unlock(&nbd_index_mutex);
2351:			pr_err("device at index %d is going down\n", index);
2352:			return -EINVAL;
2353:		}
2354:		mutex_unlock(&nbd_index_mutex);
2355:	
2356:		config = nbd_get_config_unlocked(nbd);
2357:		if (!config) {
2358:			dev_err(nbd_to_dev(nbd),
2359:				"not configured, cannot reconfigure\n");
2360:			nbd_put(nbd);
2361:			return -EINVAL;
2362:		}
2363:	
2364:		mutex_lock(&nbd->config_lock);
2365:		if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
2366:		    !nbd->pid) {
2367:			dev_err(nbd_to_dev(nbd),
2368:				"not configured, cannot reconfigure\n");
2369:			ret = -EINVAL;
2370:			goto out;
2371:		}
2372:	
2373:		ret = nbd_genl_size_set(info, nbd);
2374:		if (ret)
2375:			goto out;
2376:	
2377:		if (info->attrs[NBD_ATTR_TIMEOUT])
2378:			nbd_set_cmd_timeout(nbd,
2379:					    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
2380:		if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
2381:			config->dead_conn_timeout =
2382:				nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
2383:			config->dead_conn_timeout *= HZ;
2384:		}
2385:		if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
2386:			u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
2387:			if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
2388:				if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
2389:						      &nbd->flags))
2390:					put_dev = true;
2391:			} else {
2392:				if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
2393:						       &nbd->flags))
2394:					refcount_inc(&nbd->refs);
2395:			}
2396:	
2397:			if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
2398:				set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
2399:						&config->runtime_flags);
2400:			} else {
2401:				clear_bit(NBD_RT_DISCONNECT_ON_CLOSE,
2402:						&config->runtime_flags);
2403:			}
2404:		}
2405:	
2406:		if (info->attrs[NBD_ATTR_SOCKETS]) {
2407:			struct nlattr *attr;
2408:			int rem, fd;
2409:	
2410:			nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
2411:					    rem) {
2412:				struct nlattr *socks[NBD_SOCK_MAX+1];
2413:	
2414:				if (nla_type(attr) != NBD_SOCK_ITEM) {
2415:					pr_err("socks must be embedded in a SOCK_ITEM attr\n");
2416:					ret = -EINVAL;
2417:					goto out;
2418:				}
2419:				ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
2420:								  attr,
2421:								  nbd_sock_policy,
2422:								  info->extack);
2423:				if (ret != 0) {
2424:					pr_err("error processing sock list\n");
2425:					ret = -EINVAL;
2426:					goto out;
2427:				}
2428:				if (!socks[NBD_SOCK_FD])
2429:					continue;
2430:				fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
2431:				ret = nbd_reconnect_socket(nbd, fd);
2432:				if (ret) {
2433:					if (ret == -ENOSPC)
2434:						ret = 0;
2435:					goto out;
2436:				}
2437:				dev_info(nbd_to_dev(nbd), "reconnected socket\n");
2438:			}
2439:		}
2440:	out:
2441:		mutex_unlock(&nbd->config_lock);
2442:		nbd_config_put(nbd);
2443:		nbd_put(nbd);
2444:		if (put_dev)
2445:			nbd_put(nbd);
2446:		return ret;
2447:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 19035
							output: 87
							thoughts: 22
						

Here's my attempt at summarizing the thought process, tailored for an expert audience:

**Analyzing Socket Reconnection and Addition in NBD**

Alright, let's dive into this. The current line of thinking revolves around `nbd_reconnect_socket` and `nbd_add_socket`. I need to assess how these interact within the NBD framework. Specifically, I'm going to be scrutinizing the mechanics of the reconnection process. It's crucial to understand how a socket is re-established after a transient network failure or client disconnect. Is it a clean teardown and recreation, or something more nuanced? What's the state preservation like, if any? I'm anticipating that `nbd_reconnect_socket` will handle the low-level socket operations, potentially including re-binding, while `nbd_add_socket` likely focuses on integrating this renewed connection back into the broader NBD infrastructure – updating data structures, re-establishing session state, and resuming data transfer. I'll need to confirm if there are any race conditions between the initial socket and reconnection attempts. Perhaps there is some state that gets orphaned, or duplicate socket creation that I can identify, if I'm diligent. Gotta make sure there aren't any potential resource leaks or security vulnerabilities during the reconnection process. Let's see how they handle errors.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_reconnect_socket]

map[SourceCode:1313:	static int nbd_reconnect_socket(struct nbd_device *nbd, unsigned long arg)
1314:	{
1315:		struct nbd_config *config = nbd->config;
1316:		struct socket *sock, *old;
1317:		struct recv_thread_args *args;
1318:		int i;
1319:		int err;
1320:	
1321:		sock = nbd_get_socket(nbd, arg, &err);
1322:		if (!sock)
1323:			return err;
1324:	
1325:		args = kzalloc_obj(*args);
1326:		if (!args) {
1327:			sockfd_put(sock);
1328:			return -ENOMEM;
1329:		}
1330:	
1331:		for (i = 0; i < config->num_connections; i++) {
1332:			struct nbd_sock *nsock = config->socks[i];
1333:	
1334:			if (!nsock->dead)
1335:				continue;
1336:	
1337:			mutex_lock(&nsock->tx_lock);
1338:			if (!nsock->dead) {
1339:				mutex_unlock(&nsock->tx_lock);
1340:				continue;
1341:			}
1342:			sk_set_memalloc(sock->sk);
1343:			if (nbd->tag_set.timeout)
1344:				sock->sk->sk_sndtimeo = nbd->tag_set.timeout;
1345:			atomic_inc(&config->recv_threads);
1346:			refcount_inc(&nbd->config_refs);
1347:			old = nsock->sock;
1348:			nsock->fallback_index = -1;
1349:			nsock->sock = sock;
1350:			nsock->dead = false;
1351:			INIT_WORK(&args->work, recv_work);
1352:			args->index = i;
1353:			args->nbd = nbd;
1354:			args->nsock = nsock;
1355:			nsock->cookie++;
1356:			mutex_unlock(&nsock->tx_lock);
1357:			sockfd_put(old);
1358:	
1359:			clear_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);
1360:	
1361:			/* We take the tx_mutex in an error path in the recv_work, so we
1362:			 * need to queue_work outside of the tx_mutex.
1363:			 */
1364:			queue_work(nbd->recv_workq, &args->work);
1365:	
1366:			atomic_inc(&config->live_connections);
1367:			wake_up(&config->conn_wait);
1368:			return 0;
1369:		}
1370:		sockfd_put(sock);
1371:		kfree(args);
1372:		return -ENOSPC;
1373:	}
 SourceFile:drivers/block/nbd.c]

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_add_socket]

map[SourceCode:1241:	static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
1242:				  bool netlink)
1243:	{
1244:		struct nbd_config *config = nbd->config;
1245:		struct socket *sock;
1246:		struct nbd_sock **socks;
1247:		struct nbd_sock *nsock;
1248:		unsigned int memflags;
1249:		int err;
1250:	
1251:		/* Arg will be cast to int, check it to avoid overflow */
1252:		if (arg > INT_MAX)
1253:			return -EINVAL;
1254:		sock = nbd_get_socket(nbd, arg, &err);
1255:		if (!sock)
1256:			return err;
1257:	
1258:		/*
1259:		 * We need to make sure we don't get any errant requests while we're
1260:		 * reallocating the ->socks array.
1261:		 */
1262:		memflags = blk_mq_freeze_queue(nbd->disk->queue);
1263:	
1264:		if (!netlink && !nbd->task_setup &&
1265:		    !test_bit(NBD_RT_BOUND, &config->runtime_flags))
1266:			nbd->task_setup = current;
1267:	
1268:		if (!netlink &&
1269:		    (nbd->task_setup != current ||
1270:		     test_bit(NBD_RT_BOUND, &config->runtime_flags))) {
1271:			dev_err(disk_to_dev(nbd->disk),
1272:				"Device being setup by another task");
1273:			err = -EBUSY;
1274:			goto put_socket;
1275:		}
1276:	
1277:		nsock = kzalloc_obj(*nsock);
1278:		if (!nsock) {
1279:			err = -ENOMEM;
1280:			goto put_socket;
1281:		}
1282:	
1283:		socks = krealloc(config->socks, (config->num_connections + 1) *
1284:				 sizeof(struct nbd_sock *), GFP_KERNEL);
1285:		if (!socks) {
1286:			kfree(nsock);
1287:			err = -ENOMEM;
1288:			goto put_socket;
1289:		}
1290:	
1291:		config->socks = socks;
1292:	
1293:		nsock->fallback_index = -1;
1294:		nsock->dead = false;
1295:		mutex_init(&nsock->tx_lock);
1296:		nsock->sock = sock;
1297:		nsock->pending = NULL;
1298:		nsock->sent = 0;
1299:		nsock->cookie = 0;
1300:		INIT_WORK(&nsock->work, nbd_pending_cmd_work);
1301:		socks[config->num_connections++] = nsock;
1302:		atomic_inc(&config->live_connections);
1303:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1304:	
1305:		return 0;
1306:	
1307:	put_socket:
1308:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1309:		sockfd_put(sock);
1310:		return err;
1311:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 21390
							output: 40
							thoughts: 1007
						

**Analyzing the nbd_reconnect_socket flow**

Okay, let's break this down. I see that `nbd_reconnect_socket` is called during a reconfigure operation, specifically from `nbd_genl_reconfigure`. It seems to be iterating through a list of sockets, `config->socks[i]`, attempting to reconnect them.

The crucial part is the `nsock->dead` flag. If a socket is marked as dead, the code attempts to re-establish the connection. The loop checks `if (!nsock->dead)` and `if (!nsock->dead)` after taking a mutex, skipping if the socket isn't dead. If a dead socket is found, it attempts the reconnect by setting up the socket and queuing a work item.

The reproducer calls `NBD_CMD_CONNECT` and `NBD_CMD_RECONFIGURE` in sequence. The connect sets `config->num_connections` to 1. `NBD_CMD_RECONFIGURE` calls `nbd_reconnect_socket`. I see the logic attempts to reconnect sockets by setting up a socket and calling `recv_work`. The interesting part is that `nbd_reconnect_socket` returns `-ENOSPC` if no dead socket is found, and `nbd_genl_reconfigure` specifically handles this error by setting it to 0, effectively ignoring the error.

My concern is what sets `nsock->dead` to true. The code doesn't explicitly close the socketpair fd `r[2]` in the reproducer, so it seems like there is an implicit deadening of the socket, which is the crux of the issue.

The reproducer reads from the first fd of the socketpair `*(uint32_t*)0x200000000100`, which is the first fd, but not closing the second one. This is interesting. Is it possible that closing the second fd, `r[2] + 1`, is implicitly marking the first fd as dead, and the logic is not correctly handling that? If the second fd of the socketpair is closed, the first fd might get an error, and the error in `recv_work` will mark it dead.

I need to investigate `recv_work` to confirm how socket errors are handled.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:recv_work]

map[SourceCode: 970:	static void recv_work(struct work_struct *work)
 971:	{
 972:		struct recv_thread_args *args = container_of(work,
 973:							     struct recv_thread_args,
 974:							     work);
 975:		struct nbd_device *nbd = args->nbd;
 976:		struct nbd_config *config = nbd->config;
 977:		struct request_queue *q = nbd->disk->queue;
 978:		struct nbd_sock *nsock = args->nsock;
 979:		struct nbd_cmd *cmd;
 980:		struct request *rq;
 981:	
 982:		while (1) {
 983:			struct nbd_reply reply;
 984:	
 985:			if (nbd_read_reply(nbd, nsock->sock, &reply))
 986:				break;
 987:	
 988:			/*
 989:			 * Grab .q_usage_counter so request pool won't go away, then no
 990:			 * request use-after-free is possible during nbd_handle_reply().
 991:			 * If queue is frozen, there won't be any inflight requests, we
 992:			 * needn't to handle the incoming garbage message.
 993:			 */
 994:			if (!percpu_ref_tryget(&q->q_usage_counter)) {
 995:				dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n",
 996:					__func__);
 997:				break;
 998:			}
 999:	
1000:			cmd = nbd_handle_reply(nbd, args->index, &reply);
1001:			if (IS_ERR(cmd)) {
1002:				percpu_ref_put(&q->q_usage_counter);
1003:				break;
1004:			}
1005:	
1006:			rq = blk_mq_rq_from_pdu(cmd);
1007:			if (likely(!blk_should_fake_timeout(rq->q))) {
1008:				bool complete;
1009:	
1010:				mutex_lock(&cmd->lock);
1011:				complete = __test_and_clear_bit(NBD_CMD_INFLIGHT,
1012:								&cmd->flags);
1013:				mutex_unlock(&cmd->lock);
1014:				if (complete)
1015:					blk_mq_complete_request(rq);
1016:			}
1017:			percpu_ref_put(&q->q_usage_counter);
1018:		}
1019:	
1020:		mutex_lock(&nsock->tx_lock);
1021:		nbd_mark_nsock_dead(nbd, nsock, 1);
1022:		mutex_unlock(&nsock->tx_lock);
1023:	
1024:		atomic_dec(&config->recv_threads);
1025:		wake_up(&config->recv_wq);
1026:		nbd_config_put(nbd);
1027:		kfree(args);
1028:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 23868
							output: 44
							thoughts: 273
						

**Debugging a Potential Kernel Panic**

Okay, so `recv_work` is calling `nbd_read_reply`, and if that fails, it's supposed to break the loop and call `nbd_mark_nsock_dead`. That all seems normal at first glance. But the crash log says `SYZFAIL: failed to recv rpc`, and `fd=3 want=4 recv=0 n=-1 (errno 104: Connection reset by peer)`. Hmm, that's a syzkaller error message, isn't it? So, the syz-executor died because the syz-fuzzer closed the RPC connection. But why? The executor shouldn't just die like that unless there's an underlying problem – most likely, a kernel panic!

Let's look at `nbd_reconnect_socket` and `nbd_genl_reconfigure`. Maybe there's a known bug in either? Hang on... in `nbd_reconnect_socket`, it's allocating `args` with `kzalloc_obj(*args)`. That looks... odd. `kzalloc_obj` isn't a standard kernel function. So, what's really happening? Should it be `kzalloc(sizeof(*args), GFP_KERNEL)`? Let me check the source code again... it *says* `args = kzalloc_obj(*args);`? Wait, no! The code clearly shows `args = kzalloc(sizeof(*args), GFP_KERNEL);`. Let's verify that `nbd_reconnect_socket` code again.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_reconnect_socket]

map[SourceCode:1313:	static int nbd_reconnect_socket(struct nbd_device *nbd, unsigned long arg)
1314:	{
1315:		struct nbd_config *config = nbd->config;
1316:		struct socket *sock, *old;
1317:		struct recv_thread_args *args;
1318:		int i;
1319:		int err;
1320:	
1321:		sock = nbd_get_socket(nbd, arg, &err);
1322:		if (!sock)
1323:			return err;
1324:	
1325:		args = kzalloc_obj(*args);
1326:		if (!args) {
1327:			sockfd_put(sock);
1328:			return -ENOMEM;
1329:		}
1330:	
1331:		for (i = 0; i < config->num_connections; i++) {
1332:			struct nbd_sock *nsock = config->socks[i];
1333:	
1334:			if (!nsock->dead)
1335:				continue;
1336:	
1337:			mutex_lock(&nsock->tx_lock);
1338:			if (!nsock->dead) {
1339:				mutex_unlock(&nsock->tx_lock);
1340:				continue;
1341:			}
1342:			sk_set_memalloc(sock->sk);
1343:			if (nbd->tag_set.timeout)
1344:				sock->sk->sk_sndtimeo = nbd->tag_set.timeout;
1345:			atomic_inc(&config->recv_threads);
1346:			refcount_inc(&nbd->config_refs);
1347:			old = nsock->sock;
1348:			nsock->fallback_index = -1;
1349:			nsock->sock = sock;
1350:			nsock->dead = false;
1351:			INIT_WORK(&args->work, recv_work);
1352:			args->index = i;
1353:			args->nbd = nbd;
1354:			args->nsock = nsock;
1355:			nsock->cookie++;
1356:			mutex_unlock(&nsock->tx_lock);
1357:			sockfd_put(old);
1358:	
1359:			clear_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);
1360:	
1361:			/* We take the tx_mutex in an error path in the recv_work, so we
1362:			 * need to queue_work outside of the tx_mutex.
1363:			 */
1364:			queue_work(nbd->recv_workq, &args->work);
1365:	
1366:			atomic_inc(&config->live_connections);
1367:			wake_up(&config->conn_wait);
1368:			return 0;
1369:		}
1370:		sockfd_put(sock);
1371:		kfree(args);
1372:		return -ENOSPC;
1373:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 25433
							output: 18
							thoughts: 17
						

Here's my thought process, summarized as you requested:

**Investigating `kzalloc_obj`**

Okay, hold on a minute. `kzalloc_obj`... is that a macro? I need to quickly verify that. Before I go any further assuming it's a standard function, I should confirm what it actually *is*. Let's dig into that and make sure I understand its definition before I make any assumptions or proceed with analysis. It's crucial to know the real mechanics behind it.

map[Expression:kzalloc_obj]

map[Output:
Full output is too long, showing 500 out of 79123 lines.
Use more precise expression if possible.

[Documentation/process/deprecated.rst=393=become, respectively::
 --
 Documentation/process/deprecated.rst-395-	ptr = kmalloc_obj(*ptr, gfp);
 Documentation/process/deprecated.rst:396:	ptr = kzalloc_obj(*ptr, gfp);
 Documentation/process/deprecated.rst-397-	ptr = kmalloc_objs(*ptr, count, gfp);
 Documentation/process/deprecated.rst:398:	ptr = kzalloc_objs(*ptr, count, gfp);
 Documentation/process/deprecated.rst-399-	ptr = kmalloc_flex(*ptr, flex_member, count, gfp);
 --
 arch/alpha/kernel/module.c=64=module_frob_arch_sections(Elf64_Ehdr *hdr, Elf64_Shdr *sechdrs,
 --
 arch/alpha/kernel/module.c-95-	nsyms = symtab->sh_size / sizeof(Elf64_Sym);
 arch/alpha/kernel/module.c:96:	chains = kzalloc_objs(struct got_entry, nsyms);
 arch/alpha/kernel/module.c-97-	if (!chains) {
 --
 arch/alpha/kernel/setup.c=390=register_cpus(void)
 --
 arch/alpha/kernel/setup.c-394-	for_each_possible_cpu(i) {
 arch/alpha/kernel/setup.c:395:		struct cpu *p = kzalloc_obj(*p);
 arch/alpha/kernel/setup.c-396-		if (!p)
 --
 arch/arc/net/bpf_jit_core.c=1120=static int jit_prepare_final_mem_alloc(struct jit_context *ctx)
 --
 arch/arc/net/bpf_jit_core.c-1131-	if (ctx->need_extra_pass) {
 arch/arc/net/bpf_jit_core.c:1132:		ctx->jit_data = kzalloc_obj(*ctx->jit_data);
 arch/arc/net/bpf_jit_core.c-1133-		if (!ctx->jit_data)
 --
 arch/arm/common/locomo.c=220=locomo_init_one_child(struct locomo *lchip, struct locomo_dev_info *info)
 --
 arch/arm/common/locomo.c-224-
 arch/arm/common/locomo.c:225:	dev = kzalloc_obj(struct locomo_dev);
 arch/arm/common/locomo.c-226-	if (!dev) {
 --
 arch/arm/common/locomo.c=356=__locomo_probe(struct device *me, struct resource *mem, int irq)
 --
 arch/arm/common/locomo.c-362-
 arch/arm/common/locomo.c:363:	lchip = kzalloc_obj(struct locomo);
 arch/arm/common/locomo.c-364-	if (!lchip)
 --
 arch/arm/common/sa1111.c=733=sa1111_init_one_child(struct sa1111 *sachip, struct resource *parent,
 --
 arch/arm/common/sa1111.c-739-
 arch/arm/common/sa1111.c:740:	dev = kzalloc_obj(struct sa1111_dev);
 arch/arm/common/sa1111.c-741-	if (!dev) {
 --
 arch/arm/common/scoop.c=178=static int scoop_probe(struct platform_device *pdev)
 --
 arch/arm/common/scoop.c-187-
 arch/arm/common/scoop.c:188:	devptr = kzalloc_obj(struct scoop_dev);
 arch/arm/common/scoop.c-189-	if (!devptr)
 --
 arch/arm/kernel/smp.c=108=static int secondary_biglittle_prepare(unsigned int cpu)
 --
 arch/arm/kernel/smp.c-110-	if (!cpu_vtable[cpu])
 arch/arm/kernel/smp.c:111:		cpu_vtable[cpu] = kzalloc_obj(*cpu_vtable[cpu]);
 arch/arm/kernel/smp.c-112-
 --
 arch/arm/kernel/vdso.c=169=static int __init vdso_init(void)
 --
 arch/arm/kernel/vdso.c-181-	/* Allocate the VDSO text pagelist */
 arch/arm/kernel/vdso.c:182:	vdso_text_pagelist = kzalloc_objs(struct page *, text_pages);
 arch/arm/kernel/vdso.c-183-	if (vdso_text_pagelist == NULL)
 --
 arch/arm/mach-footbridge/dc21285.c=261=int __init dc21285_setup(int nr, struct pci_sys_data *sys)
 --
 arch/arm/mach-footbridge/dc21285.c-264-
 arch/arm/mach-footbridge/dc21285.c:265:	res = kzalloc_objs(struct resource, 2);
 arch/arm/mach-footbridge/dc21285.c-266-	if (!res) {
 --
 arch/arm/mach-footbridge/ebsa285.c=69=static int __init ebsa285_leds_init(void)
 --
 arch/arm/mach-footbridge/ebsa285.c-86-
 arch/arm/mach-footbridge/ebsa285.c:87:		led = kzalloc_obj(*led);
 arch/arm/mach-footbridge/ebsa285.c-88-		if (!led)
 --
 arch/arm/mach-footbridge/netwinder-hw.c=720=static int __init netwinder_leds_init(void)
 --
 arch/arm/mach-footbridge/netwinder-hw.c-729-
 arch/arm/mach-footbridge/netwinder-hw.c:730:		led = kzalloc_obj(*led);
 arch/arm/mach-footbridge/netwinder-hw.c-731-		if (!led)
 --
 arch/arm/mach-imx/mmdc.c=473=static int imx_mmdc_perf_init(struct platform_device *pdev, void __iomem *mmdc_base,
 --
 arch/arm/mach-imx/mmdc.c-479-
 arch/arm/mach-imx/mmdc.c:480:	pmu_mmdc = kzalloc_obj(*pmu_mmdc);
 arch/arm/mach-imx/mmdc.c-481-	if (!pmu_mmdc) {
 --
 arch/arm/mach-mvebu/board-v7.c=114=static void __init i2c_quirk(void)
 --
 arch/arm/mach-mvebu/board-v7.c-129-
 arch/arm/mach-mvebu/board-v7.c:130:		new_compat = kzalloc_obj(*new_compat);
 arch/arm/mach-mvebu/board-v7.c-131-
 --
 arch/arm/mach-mvebu/coherency.c=168=static void __init armada_375_380_coherency_init(struct device_node *np)
 --
 arch/arm/mach-mvebu/coherency.c-192-
 arch/arm/mach-mvebu/coherency.c:193:		p = kzalloc_obj(*p);
 arch/arm/mach-mvebu/coherency.c-194-		p->name = kstrdup("arm,io-coherent", GFP_KERNEL);
 --
 arch/arm/mach-mvebu/mvebu-soc-id.c=148=static int __init mvebu_soc_device(void)
 --
 arch/arm/mach-mvebu/mvebu-soc-id.c-156-
 arch/arm/mach-mvebu/mvebu-soc-id.c:157:	soc_dev_attr = kzalloc_obj(*soc_dev_attr);
 arch/arm/mach-mvebu/mvebu-soc-id.c-158-	if (!soc_dev_attr)
 --
 arch/arm/mach-mxs/mach-mxs.c=380=static void __init mxs_machine_init(void)
 --
 arch/arm/mach-mxs/mach-mxs.c-389-
 arch/arm/mach-mxs/mach-mxs.c:390:	soc_dev_attr = kzalloc_obj(*soc_dev_attr);
 arch/arm/mach-mxs/mach-mxs.c-391-	if (!soc_dev_attr)
 --
 arch/arm/mach-omap1/dma.c=294=static int __init omap1_system_dma_init(void)
 --
 arch/arm/mach-omap1/dma.c-321-
 arch/arm/mach-omap1/dma.c:322:	d = kzalloc_obj(*d);
 arch/arm/mach-omap1/dma.c-323-	if (!d) {
 --
 arch/arm/mach-omap1/mcbsp.c=292=static void omap_mcbsp_register_board_cfg(struct resource *res, int res_count,
 --
 arch/arm/mach-omap1/mcbsp.c-296-
 arch/arm/mach-omap1/mcbsp.c:297:	omap_mcbsp_devices = kzalloc_objs(struct platform_device *, size);
 arch/arm/mach-omap1/mcbsp.c-298-	if (!omap_mcbsp_devices) {
 --
 arch/arm/mach-omap1/timer.c=51=static int __init omap1_dm_timer_init(void)
 --
 arch/arm/mach-omap1/timer.c-127-
 arch/arm/mach-omap1/timer.c:128:		pdata = kzalloc_obj(*pdata);
 arch/arm/mach-omap1/timer.c-129-		if (!pdata) {
 --
 arch/arm/mach-omap2/clkt2xxx_virt_prcm_set.c=230=void omap2xxx_clkt_vps_init(void)
 --
 arch/arm/mach-omap2/clkt2xxx_virt_prcm_set.c-239-
 arch/arm/mach-omap2/clkt2xxx_virt_prcm_set.c:240:	hw = kzalloc_obj(*hw);
 arch/arm/mach-omap2/clkt2xxx_virt_prcm_set.c-241-	if (!hw)
 --
 arch/arm/mach-omap2/id.c=786=void __init omap_soc_device_init(void)
 --
 arch/arm/mach-omap2/id.c-790-
 arch/arm/mach-omap2/id.c:791:	soc_dev_attr = kzalloc_obj(*soc_dev_attr);
 arch/arm/mach-omap2/id.c-792-	if (!soc_dev_attr)
 --
 arch/arm/mach-omap2/omap_device.c=131=static int omap_device_build_from_dt(struct platform_device *pdev)
 --
 arch/arm/mach-omap2/omap_device.c-158-
 arch/arm/mach-omap2/omap_device.c:159:	hwmods = kzalloc_objs(struct omap_hwmod *, oh_cnt);
 arch/arm/mach-omap2/omap_device.c-160-	if (!hwmods) {
 --
 arch/arm/mach-omap2/omap_device.c=304=static struct omap_device *omap_device_alloc(struct platform_device *pdev,
 --
 arch/arm/mach-omap2/omap_device.c-311-
 arch/arm/mach-omap2/omap_device.c:312:	od = kzalloc_obj(struct omap_device);
 arch/arm/mach-omap2/omap_device.c-313-	if (!od)
 --
 arch/arm/mach-omap2/omap_hwmod.c=3381=static int omap_hwmod_allocate_module(struct device *dev, struct omap_hwmod *oh,
 --
 arch/arm/mach-omap2/omap_hwmod.c-3394-
 arch/arm/mach-omap2/omap_hwmod.c:3395:	sysc = kzalloc_obj(*sysc);
 arch/arm/mach-omap2/omap_hwmod.c-3396-	if (!sysc)
 --
 arch/arm/mach-omap2/omap_hwmod.c-3424-	if (list_empty(&oh->slave_ports)) {
 arch/arm/mach-omap2/omap_hwmod.c:3425:		oi = kzalloc_obj(*oi);
 arch/arm/mach-omap2/omap_hwmod.c-3426-		if (!oi)
 --
 arch/arm/mach-omap2/omap_hwmod.c=3513=int omap_hwmod_init_module(struct device *dev,
 --
 arch/arm/mach-omap2/omap_hwmod.c-3527-	if (!oh) {
 arch/arm/mach-omap2/omap_hwmod.c:3528:		oh = kzalloc_obj(*oh);
 arch/arm/mach-omap2/omap_hwmod.c-3529-		if (!oh)
 --
 arch/arm/mach-omap2/omap_hwmod.c-3538-
 arch/arm/mach-omap2/omap_hwmod.c:3539:		oh->class = kzalloc_obj(*oh->class);
 arch/arm/mach-omap2/omap_hwmod.c-3540-		if (!oh->class) {
 --
 arch/arm/mach-omap2/pm33xx-core.c=379=static int __init amx3_idle_init(struct device_node *cpu_node, int cpu)
 --
 arch/arm/mach-omap2/pm33xx-core.c-412-
 arch/arm/mach-omap2/pm33xx-core.c:413:	idle_states = kzalloc_objs(*idle_states, state_count);
 arch/arm/mach-omap2/pm33xx-core.c-414-	if (!idle_states)
 --
 arch/arm/mach-omap2/sr_device.c=30=static void __init sr_set_nvalues(struct omap_volt_data *volt_data,
 --
 arch/arm/mach-omap2/sr_device.c-41-
 arch/arm/mach-omap2/sr_device.c:42:	nvalue_table = kzalloc_objs(*nvalue_table, count);
 arch/arm/mach-omap2/sr_device.c-43-	if (!nvalue_table)
 --
 arch/arm/mach-orion5x/pci.c=139=static int __init pcie_setup(struct pci_sys_data *sys)
 --
 arch/arm/mach-orion5x/pci.c-171-	 */
 arch/arm/mach-orion5x/pci.c:172:	res = kzalloc_obj(struct resource);
 arch/arm/mach-orion5x/pci.c-173-	if (!res)
 --
 arch/arm/mach-orion5x/pci.c=466=static int __init pci_setup(struct pci_sys_data *sys)
 --
 arch/arm/mach-orion5x/pci.c-492-	 */
 arch/arm/mach-orion5x/pci.c:493:	res = kzalloc_obj(struct resource);
 arch/arm/mach-orion5x/pci.c-494-	if (!res)
 --
 arch/arm/mach-rpc/ecard.c=689=static struct expansion_card *__init ecard_alloc_card(int type, int slot)
 --
 arch/arm/mach-rpc/ecard.c-694-
 arch/arm/mach-rpc/ecard.c:695:	ec = kzalloc_obj(ecard_t);
 arch/arm/mach-rpc/ecard.c-696-	if (!ec) {
 --
 arch/arm/mach-sa1100/clock.c=93=int __init sa11xx_clk_init(void)
 --
 arch/arm/mach-sa1100/clock.c-109-
 arch/arm/mach-sa1100/clock.c:110:	hw = kzalloc_obj(*hw);
 arch/arm/mach-sa1100/clock.c-111-	if (!hw)
 --
 arch/arm/mach-sa1100/clock.c-131-
 arch/arm/mach-sa1100/clock.c:132:	hw = kzalloc_obj(*hw);
 arch/arm/mach-sa1100/clock.c-133-	if (!hw)
 --
 arch/arm/mach-sa1100/generic.c=317=int __init sa11x0_register_fixed_regulator(int n,
 --
 arch/arm/mach-sa1100/generic.c-323-
 arch/arm/mach-sa1100/generic.c:324:	cfg->init_data = id = kzalloc_obj(*cfg->init_data);
 arch/arm/mach-sa1100/generic.c-325-	if (!cfg->init_data)
 --
 arch/arm/mach-sa1100/neponset.c=225=static int neponset_probe(struct platform_device *dev)
 --
 arch/arm/mach-sa1100/neponset.c-278-
 arch/arm/mach-sa1100/neponset.c:279:	d = kzalloc_obj(*d);
 arch/arm/mach-sa1100/neponset.c-280-	if (!d) {
 --
 arch/arm/mach-shmobile/regulator-quirk-rcar-gen2.c=141=static int __init rcar_gen2_regulator_quirk(void)
 --
 arch/arm/mach-shmobile/regulator-quirk-rcar-gen2.c-166-
 arch/arm/mach-shmobile/regulator-quirk-rcar-gen2.c:167:		quirk = kzalloc_obj(*quirk);
 arch/arm/mach-shmobile/regulator-quirk-rcar-gen2.c-168-		if (!quirk) {
 --
 arch/arm/mach-versatile/spc.c=393=static int ve_spc_populate_opps(uint32_t cluster)
 --
 arch/arm/mach-versatile/spc.c-397-
 arch/arm/mach-versatile/spc.c:398:	opps = kzalloc_objs(*opps, MAX_OPPS);
 arch/arm/mach-versatile/spc.c-399-	if (!opps)
 --
 arch/arm/mach-versatile/spc.c=442=int __init ve_spc_init(void __iomem *baseaddr, u32 a15_clusid, int irq)
 --
 arch/arm/mach-versatile/spc.c-444-	int ret;
 arch/arm/mach-versatile/spc.c:445:	info = kzalloc_obj(*info);
 arch/arm/mach-versatile/spc.c-446-	if (!info)
 --
 arch/arm/mach-versatile/spc.c=523=static struct clk *ve_spc_clk_register(struct device *cpu_dev)
 --
 arch/arm/mach-versatile/spc.c-527-
 arch/arm/mach-versatile/spc.c:528:	spc = kzalloc_obj(*spc);
 arch/arm/mach-versatile/spc.c-529-	if (!spc)
 --
 arch/arm/mach-versatile/versatile.c=123=static void __init versatile_dt_pci_init(void)
 --
 arch/arm/mach-versatile/versatile.c-144-
 arch/arm/mach-versatile/versatile.c:145:	newprop = kzalloc_obj(*newprop);
 arch/arm/mach-versatile/versatile.c-146-	if (!newprop)
 --
 arch/arm/mach-zynq/common.c=105=static void __init zynq_init_machine(void)
 --
 arch/arm/mach-zynq/common.c-110-
 arch/arm/mach-zynq/common.c:111:	soc_dev_attr = kzalloc_obj(*soc_dev_attr);
 arch/arm/mach-zynq/common.c-112-	if (!soc_dev_attr)
 --
 arch/arm/mm/cache-l2x0-pmu.c=503=static __init int l2x0_pmu_init(void)
 --
 arch/arm/mm/cache-l2x0-pmu.c-509-
 arch/arm/mm/cache-l2x0-pmu.c:510:	l2x0_pmu = kzalloc_obj(*l2x0_pmu);
 arch/arm/mm/cache-l2x0-pmu.c-511-	if (!l2x0_pmu) {
 --
 arch/arm/mm/cache-uniphier.c=315=static int __init __uniphier_cache_init(struct device_node *np,
 --
 arch/arm/mm/cache-uniphier.c-344-
 arch/arm/mm/cache-uniphier.c:345:	data = kzalloc_obj(*data);
 arch/arm/mm/cache-uniphier.c-346-	if (!data)
 --
 arch/arm/mm/dma-mapping.c=533=static void *__dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
 --
 arch/arm/mm/dma-mapping.c-560-
 arch/arm/mm/dma-mapping.c:561:	buf = kzalloc_obj(*buf,
 arch/arm/mm/dma-mapping.c-562-			  gfp & ~(__GFP_DMA | __GFP_DMA32 | __GFP_HIGHMEM));
 --
 arch/arm/mm/dma-mapping.c=1487=arm_iommu_create_mapping(struct device *dev, dma_addr_t base, u64 size)
 --
 arch/arm/mm/dma-mapping.c-1506-
 arch/arm/mm/dma-mapping.c:1507:	mapping = kzalloc_obj(struct dma_iommu_mapping);
 arch/arm/mm/dma-mapping.c-1508-	if (!mapping)
 --
 arch/arm/xen/enlighten.c=316=int __init arch_xen_unpopulated_init(struct resource **res)
 --
 arch/arm/xen/enlighten.c-343-
 arch/arm/xen/enlighten.c:344:	regs = kzalloc_objs(*regs, nr_reg);
 arch/arm/xen/enlighten.c-345-	if (!regs) {
 --
 arch/arm/xen/enlighten.c-387-
 arch/arm/xen/enlighten.c:388:		tmp_res = kzalloc_obj(*tmp_res);
 arch/arm/xen/enlighten.c-389-		if (!tmp_res) {
 --
 arch/arm/xen/p2m.c=150=bool __set_phys_to_machine_multi(unsigned long pfn,
 --
 arch/arm/xen/p2m.c-178-
 arch/arm/xen/p2m.c:179:	p2m_entry = kzalloc_obj(*p2m_entry, GFP_NOWAIT);
 arch/arm/xen/p2m.c-180-	if (!p2m_entry)
 --
 arch/arm64/kernel/vdso.c=68=static int __init __vdso_init(enum vdso_abi abi)
 --
 arch/arm64/kernel/vdso.c-83-
 arch/arm64/kernel/vdso.c:84:	vdso_pagelist = kzalloc_objs(struct page *, vdso_info[abi].vdso_pages);
 arch/arm64/kernel/vdso.c-85-	if (vdso_pagelist == NULL)
 --
 arch/arm64/kvm/mmu.c=480=static int share_pfn_hyp(u64 pfn)
 --
 arch/arm64/kvm/mmu.c-492-
 arch/arm64/kvm/mmu.c:493:	this = kzalloc_obj(*this);
 arch/arm64/kvm/mmu.c-494-	if (!this) {
 --
 arch/arm64/kvm/mmu.c=954=int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu, unsigned long type)
 --
 arch/arm64/kvm/mmu.c-980-
 arch/arm64/kvm/mmu.c:981:	pgt = kzalloc_obj(*pgt, GFP_KERNEL_ACCOUNT);
 arch/arm64/kvm/mmu.c-982-	if (!pgt)
 --
 arch/arm64/kvm/mmu.c=1153=int topup_hyp_memcache(struct kvm_hyp_memcache *mc, unsigned long min_pages)
 --
 arch/arm64/kvm/mmu.c-1158-	if (!mc->mapping) {
 arch/arm64/kvm/mmu.c:1159:		mc->mapping = kzalloc_obj(struct pkvm_mapping,
 arch/arm64/kvm/mmu.c-1160-					  GFP_KERNEL_ACCOUNT);
 --
 arch/arm64/kvm/mmu.c=2465=int __init kvm_mmu_init(u32 hyp_va_bits)
 --
 arch/arm64/kvm/mmu.c-2498-
 arch/arm64/kvm/mmu.c:2499:	hyp_pgtable = kzalloc_obj(*hyp_pgtable);
 arch/arm64/kvm/mmu.c-2500-	if (!hyp_pgtable) {
 --
 arch/arm64/kvm/nested.c=1246=int kvm_vcpu_allocate_vncr_tlb(struct kvm_vcpu *vcpu)
 --
 arch/arm64/kvm/nested.c-1250-
 arch/arm64/kvm/nested.c:1251:	vcpu->arch.vncr_tlb = kzalloc_obj(*vcpu->arch.vncr_tlb,
 arch/arm64/kvm/nested.c-1252-					  GFP_KERNEL_ACCOUNT);
 --
 arch/arm64/kvm/nested.c=1710=int kvm_init_nv_sysregs(struct kvm_vcpu *vcpu)
 --
 arch/arm64/kvm/nested.c-1719-
 arch/arm64/kvm/nested.c:1720:	kvm->arch.sysreg_masks = kzalloc_obj(*(kvm->arch.sysreg_masks),
 arch/arm64/kvm/nested.c-1721-					     GFP_KERNEL_ACCOUNT);
 --
 arch/arm64/kvm/ptdump.c=116=static struct kvm_ptdump_guest_state *kvm_ptdump_parser_create(struct kvm_s2_mmu *mmu)
 --
 arch/arm64/kvm/ptdump.c-121-
 arch/arm64/kvm/ptdump.c:122:	st = kzalloc_obj(struct kvm_ptdump_guest_state, GFP_KERNEL_ACCOUNT);
 arch/arm64/kvm/ptdump.c-123-	if (!st)
 --
 arch/arm64/kvm/vgic/vgic-init.c=207=static int kvm_vgic_dist_init(struct kvm *kvm, unsigned int nr_spis)
 --
 arch/arm64/kvm/vgic/vgic-init.c-213-	dist->active_spis = (atomic_t)ATOMIC_INIT(0);
 arch/arm64/kvm/vgic/vgic-init.c:214:	dist->spis = kzalloc_objs(struct vgic_irq, nr_spis, GFP_KERNEL_ACCOUNT);
 arch/arm64/kvm/vgic/vgic-init.c-215-	if (!dist->spis)
 --
 arch/arm64/kvm/vgic/vgic-init.c=329=static int vgic_allocate_private_irqs_locked(struct kvm_vcpu *vcpu, u32 type)
 --
 arch/arm64/kvm/vgic/vgic-init.c-344-
 arch/arm64/kvm/vgic/vgic-init.c:345:	vgic_cpu->private_irqs = kzalloc_objs(struct vgic_irq,
 arch/arm64/kvm/vgic/vgic-init.c-346-					      num_private_irqs,
 --
 arch/arm64/kvm/vgic/vgic-irqfd.c=136=int kvm_vgic_setup_default_irq_routing(struct kvm *kvm)
 --
 arch/arm64/kvm/vgic/vgic-irqfd.c-142-
 arch/arm64/kvm/vgic/vgic-irqfd.c:143:	entries = kzalloc_objs(*entries, nr, GFP_KERNEL_ACCOUNT);
 arch/arm64/kvm/vgic/vgic-irqfd.c-144-	if (!entries)
 --
 arch/arm64/kvm/vgic/vgic-its.c=76=static struct vgic_irq *vgic_add_lpi(struct kvm *kvm, u32 intid,
 --
 arch/arm64/kvm/vgic/vgic-its.c-87-
 arch/arm64/kvm/vgic/vgic-its.c:88:	irq = kzalloc_obj(struct vgic_irq, GFP_KERNEL_ACCOUNT);
 arch/arm64/kvm/vgic/vgic-its.c-89-	if (!irq)
 --
 arch/arm64/kvm/vgic/vgic-its.c=957=static int vgic_its_alloc_collection(struct vgic_its *its,
 --
 arch/arm64/kvm/vgic/vgic-its.c-962-
 arch/arm64/kvm/vgic/vgic-its.c:963:	collection = kzalloc_obj(*collection, GFP_KERNEL_ACCOUNT);
 arch/arm64/kvm/vgic/vgic-its.c-964-	if (!collection)
 --
 arch/arm64/kvm/vgic/vgic-its.c=1001=static struct its_ite *vgic_its_alloc_ite(struct its_device *device,
 --
 arch/arm64/kvm/vgic/vgic-its.c-1006-
 arch/arm64/kvm/vgic/vgic-its.c:1007:	ite = kzalloc_obj(*ite, GFP_KERNEL_ACCOUNT);
 arch/arm64/kvm/vgic/vgic-its.c-1008-	if (!ite)
 --
 arch/arm64/kvm/vgic/vgic-its.c=1128=static struct its_device *vgic_its_alloc_device(struct vgic_its *its,
 --
 arch/arm64/kvm/vgic/vgic-its.c-1133-
 arch/arm64/kvm/vgic/vgic-its.c:1134:	device = kzalloc_obj(*device, GFP_KERNEL_ACCOUNT);
 arch/arm64/kvm/vgic/vgic-its.c-1135-	if (!device)
 --
 arch/arm64/kvm/vgic/vgic-its.c=1841=static int vgic_its_create(struct kvm_device *dev, u32 type)
 --
 arch/arm64/kvm/vgic/vgic-its.c-1848-
 arch/arm64/kvm/vgic/vgic-its.c:1849:	its = kzalloc_obj(struct vgic_its, GFP_KERNEL_ACCOUNT);
 arch/arm64/kvm/vgic/vgic-its.c-1850-	if (!its)
 --
 arch/arm64/kvm/vgic/vgic-mmio-v3.c=886=static int vgic_v3_alloc_redist_region(struct kvm *kvm, uint32_t index,
 --
 arch/arm64/kvm/vgic/vgic-mmio-v3.c-931-
 arch/arm64/kvm/vgic/vgic-mmio-v3.c:932:	rdreg = kzalloc_obj(*rdreg, GFP_KERNEL_ACCOUNT);
 arch/arm64/kvm/vgic/vgic-mmio-v3.c-933-	if (!rdreg)
 --
 arch/arm64/kvm/vgic/vgic-v4.c=242=int vgic_v4_init(struct kvm *kvm)
 --
 arch/arm64/kvm/vgic/vgic-v4.c-258-
 arch/arm64/kvm/vgic/vgic-v4.c:259:	dist->its_vm.vpes = kzalloc_objs(*dist->its_vm.vpes, nr_vcpus,
 arch/arm64/kvm/vgic/vgic-v4.c-260-					 GFP_KERNEL_ACCOUNT);
 --
 arch/arm64/net/bpf_jit_comp.c=2006=struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_prog *prog)
 --
 arch/arm64/net/bpf_jit_comp.c-2026-	if (!jit_data) {
 arch/arm64/net/bpf_jit_comp.c:2027:		jit_data = kzalloc_obj(*jit_data);
 arch/arm64/net/bpf_jit_comp.c-2028-		if (!jit_data)
 --
 arch/csky/kernel/vdso.c=17=static int __init vdso_init(void)
 --
 arch/csky/kernel/vdso.c-22-	vdso_pagelist =
 arch/csky/kernel/vdso.c:23:		kzalloc_objs(struct page *, vdso_pages);
 arch/csky/kernel/vdso.c-24-	if (unlikely(vdso_pagelist == NULL)) {
 --
 arch/loongarch/kernel/setup.c=466=static int __init add_legacy_isa_io(struct fwnode_handle *fwnode,
 --
 arch/loongarch/kernel/setup.c-472-
 arch/loongarch/kernel/setup.c:473:	range = kzalloc_obj(*range, GFP_ATOMIC);
 arch/loongarch/kernel/setup.c-474-	if (!range)
 --
 arch/loongarch/kernel/vdso.c=45=static int __init init_vdso(void)
 --
 arch/loongarch/kernel/vdso.c-55-	vdso_info.code_mapping.pages =
 arch/loongarch/kernel/vdso.c:56:		kzalloc_objs(struct page *, vdso_info.size / PAGE_SIZE);
 arch/loongarch/kernel/vdso.c-57-
 --
 arch/loongarch/kvm/intc/eiointc.c=614=static int kvm_eiointc_create(struct kvm_device *dev, u32 type)
 --
 arch/loongarch/kvm/intc/eiointc.c-624-
 arch/loongarch/kvm/intc/eiointc.c:625:	s = kzalloc_obj(struct loongarch_eiointc);
 arch/loongarch/kvm/intc/eiointc.c-626-	if (!s)
 --
 arch/loongarch/kvm/intc/ipi.c=394=static int kvm_ipi_create(struct kvm_device *dev, u32 type)
 --
 arch/loongarch/kvm/intc/ipi.c-411-
 arch/loongarch/kvm/intc/ipi.c:412:	s = kzalloc_obj(struct loongarch_ipi);
 arch/loongarch/kvm/intc/ipi.c-413-	if (!s)
 --
 arch/loongarch/kvm/intc/pch_pic.c=410=static int kvm_setup_default_irq_routing(struct kvm *kvm)
 --
 arch/loongarch/kvm/intc/pch_pic.c-415-
 arch/loongarch/kvm/intc/pch_pic.c:416:	entries = kzalloc_objs(*entries, nr);
 arch/loongarch/kvm/intc/pch_pic.c-417-	if (!entries)
 --
 arch/loongarch/kvm/intc/pch_pic.c=432=static int kvm_pch_pic_create(struct kvm_device *dev, u32 type)
 --
 arch/loongarch/kvm/intc/pch_pic.c-445-
 arch/loongarch/kvm/intc/pch_pic.c:446:	s = kzalloc_obj(struct loongarch_pch_pic);
 arch/loongarch/kvm/intc/pch_pic.c-447-	if (!s)
 --
 arch/loongarch/kvm/main.c=349=static int kvm_loongarch_env_init(void)
 --
 arch/loongarch/kvm/main.c-360-
 arch/loongarch/kvm/main.c:361:	kvm_loongarch_ops = kzalloc_obj(*kvm_loongarch_ops);
 arch/loongarch/kvm/main.c-362-	if (!kvm_loongarch_ops) {
 --
 arch/loongarch/kvm/vcpu.c=1530=int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
 --
 arch/loongarch/kvm/vcpu.c-1551-	vcpu->arch.guest_eentry = (unsigned long)kvm_loongarch_ops->exc_entry;
 arch/loongarch/kvm/vcpu.c:1552:	vcpu->arch.csr = kzalloc_obj(struct loongarch_csrs);
 arch/loongarch/kvm/vcpu.c-1553-	if (!vcpu->arch.csr)
 --
 arch/loongarch/net/bpf_jit.c=2169=struct bpf_prog *bpf_int_jit_compile(struct bpf_verifier_env *env, struct bpf_prog *prog)
 --
 arch/loongarch/net/bpf_jit.c-2187-	if (!jit_data) {
 arch/loongarch/net/bpf_jit.c:2188:		jit_data = kzalloc_obj(*jit_data);
 arch/loongarch/net/bpf_jit.c-2189-		if (!jit_data)
 --
 arch/loongarch/pci/acpi.c=94=static struct pci_config_window *arch_pci_ecam_create(struct device *dev,
 --
 arch/loongarch/pci/acpi.c-103-
 arch/loongarch/pci/acpi.c:104:	cfg = kzalloc_obj(*cfg);
 arch/loongarch/pci/acpi.c-105-	if (!cfg)
 --
 arch/loongarch/pci/acpi.c=193=struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
 --
 arch/loongarch/pci/acpi.c-201-
 arch/loongarch/pci/acpi.c:202:	info = kzalloc_obj(*info);
 arch/loongarch/pci/acpi.c-203-	if (!info) {
 --
 arch/loongarch/pci/acpi.c-207-
 arch/loongarch/pci/acpi.c:208:	root_ops = kzalloc_obj(*root_ops);
 arch/loongarch/pci/acpi.c-209-	if (!root_ops) {
 --
 arch/m68k/amiga/chipram.c=45=void *amiga_chip_alloc(unsigned long size, const char *name)
 --
 arch/m68k/amiga/chipram.c-49-
 arch/m68k/amiga/chipram.c:50:	res = kzalloc_obj(struct resource);
 arch/m68k/amiga/chipram.c-51-	if (!res)
 --
 arch/m68k/atari/stram.c=154=void *atari_stram_alloc(unsigned long size, const char *owner)
 --
 arch/m68k/atari/stram.c-163-
 arch/m68k/atari/stram.c:164:	res = kzalloc_obj(struct resource);
]
]

gemini-3.1-pro-preview

							input: 36666
							output: 46
							thoughts: 906
						

**Analyzing a Potential Socket Leak in the NBD Kernel Module**

Okay, let's break this down. First, `kzalloc_obj`... right, that's just a shorthand for `kzalloc` with the size determined from the `*args` pointer, which is `struct recv_thread_args *`.  Essentially, when `nbd_reconnect_socket` is called, it allocates `args`.  It then iterates through `config->socks`. If a dead socket is found, it queues a work item and returns. If no dead sockets are found, it *frees* `args` and returns `-ENOSPC`.

The tricky bit is if `config->num_connections` is 1 and the socket is *not* dead. In this scenario, `nbd_reconnect_socket` returns `-ENOSPC`. Now, `nbd_genl_reconfigure` handles that specific error:

```c
				ret = nbd_reconnect_socket(nbd, fd);
				if (ret) {
					if (ret == -ENOSPC)
						ret = 0;
					goto out;
				}
```

If it gets `-ENOSPC`, it sets `ret` to 0, which looks like a deliberate "no-op" and goes to `out`.  At `out`, the config lock is unlocked, resources are put, and the function returns `ret`. But hold on... if there are no dead sockets, the new socket isn't added. So the new file descriptor (`r[3]`) from the reproducer is essentially ignored.  The old socket (`r[2]`) is still in use.

The reproducer doesn't close `r[2]`.  Ah, right, it's a `socketpair`. `socketpair` creates two file descriptors.  The reproducer only captures `r[2]` from the `socketpair` call. The kernel is likely using the socket that `r[2]` points to, and the reproducer is missing the other end.

```c
res = syscall(__NR_socketpair, /*domain=*/1ul, /*type=*/1ul, /*proto=*/0, /*fds=*/0x200000000100ul);
r[2] = *(uint32_t*)0x200000000100;
```
Okay, `r[2]` is the first fd, the second fd is at `0x200000000104`.  The reproducer is only using the first fd.  Since the reproducer process exits, the second fd *should* be closed, which means it calls `close` on the second fd. The first fd (`r[2]`) has been passed to the kernel through netlink, meaning the kernel now has a reference to the first fd. When the second fd of the socketpair is closed, the underlying socketpair is disconnected.

So the process now: The `recv_work` thread reads from the first fd (`r[2]`). When the other side of the `socketpair` is closed, the kernel gets an EOF or an error.  It then calls `nbd_mark_nsock_dead(nbd, nsock, 1);` which marks the socket as dead. And then:

```c
	atomic_dec(&config->recv_threads);
	wake_up(&config->recv_wq);
	nbd_config_put(nbd);
	kfree(args);
```

Wait, is there a potential use-after-free here? I need to dig into `nbd_mark_nsock_dead` to verify. I need to be sure that the socket cleanup is done correctly and safely. It seems like the core issue could be a race condition during the reconnection process combined with the socketpair usage and how the reproducer closes the other end of the socketpair.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_mark_nsock_dead]

map[SourceCode: 305:	static void nbd_mark_nsock_dead(struct nbd_device *nbd, struct nbd_sock *nsock,
 306:					int notify)
 307:	{
 308:		if (!nsock->dead && notify && !nbd_disconnected(nbd->config)) {
 309:			struct link_dead_args *args;
 310:			args = kmalloc_obj(struct link_dead_args, GFP_NOIO);
 311:			if (args) {
 312:				INIT_WORK(&args->work, nbd_dead_link_work);
 313:				args->index = nbd->index;
 314:				queue_work(system_percpu_wq, &args->work);
 315:			}
 316:		}
 317:		if (!nsock->dead) {
 318:			kernel_sock_shutdown(nsock->sock, SHUT_RDWR);
 319:			if (atomic_dec_return(&nbd->config->live_connections) == 0) {
 320:				if (test_and_clear_bit(NBD_RT_DISCONNECT_REQUESTED,
 321:						       &nbd->config->runtime_flags)) {
 322:					set_bit(NBD_RT_DISCONNECTED,
 323:						&nbd->config->runtime_flags);
 324:					dev_info(nbd_to_dev(nbd),
 325:						"Disconnected due to user request.\n");
 326:				}
 327:			}
 328:		}
 329:		nsock->dead = true;
 330:		nsock->pending = NULL;
 331:		nsock->sent = 0;
 332:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 38988
							output: 45
							thoughts: 18
						

Okay, here's my interpretation of that thought process, assuming I'm an expert in this area:

**Digging into the Netlink Implications of `nbd_dead_link_work`**

Wait a second... `nbd_dead_link_work`? I was under the impression that the handling of a dead NBD link was largely localized. I'd need to remind myself of the full context, but my initial thought is that it doesn't involve external communication outside the kernel space. Sending a Netlink message in that context? That raises a few questions. Is this for reporting the dead link to userspace, perhaps to trigger some re-configuration or error handling? Or, is it intended for some internal coordination between different kernel modules or processes that are impacted by an NBD link failing? I need to look into this function's source code, and its calling context, immediately. There is no simple action, or response, that requires Netlink. I need to understand why a low-level routine like this would have such overhead. What are the specific Netlink messages being sent? What is the payload? How is the message handled on the other end? It's time to dig into the details and figure out why this is being done.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_dead_link_work]

map[SourceCode:2635:	static void nbd_dead_link_work(struct work_struct *work)
2636:	{
2637:		struct link_dead_args *args = container_of(work, struct link_dead_args,
2638:							   work);
2639:		nbd_mcast_index(args->index);
2640:		kfree(args);
2641:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 39456
							output: 44
							thoughts: 17
						

Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:

**Initial Realization and Connection to Netlink**

Wait a second... *nbd_mcast_index* is sending a netlink message. That's a significant detail I initially glossed over. I was focused on the potential multicast implications, but the core of the interaction, the mechanism used to signal the network changes, is Netlink. That triggers a cascade of considerations. How's it formatted? What attributes are involved? Are we talking about a raw socket, or a more structured Netlink family implementation? This immediately changes the scope of my investigation. It also makes me re-evaluate my mental model of the expected performance and potential bottlenecks, now that I know there's a kernel-space interaction and potential overhead involved in Netlink message creation, transmission, and processing.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_mcast_index]

map[SourceCode:2611:	static void nbd_mcast_index(int index)
2612:	{
2613:		struct sk_buff *skb;
2614:		void *msg_head;
2615:		int ret;
2616:	
2617:		skb = genlmsg_new(nla_total_size(sizeof(u32)), GFP_KERNEL);
2618:		if (!skb)
2619:			return;
2620:		msg_head = genlmsg_put(skb, 0, 0, &nbd_genl_family, 0,
2621:					     NBD_CMD_LINK_DEAD);
2622:		if (!msg_head) {
2623:			nlmsg_free(skb);
2624:			return;
2625:		}
2626:		ret = nla_put_u32(skb, NBD_ATTR_INDEX, index);
2627:		if (ret) {
2628:			nlmsg_free(skb);
2629:			return;
2630:		}
2631:		genlmsg_end(skb, msg_head);
2632:		genlmsg_multicast(&nbd_genl_family, skb, 0, 0, GFP_KERNEL);
2633:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 40101
							output: 43
							thoughts: 943
						

**Debugging a syz-executor Crash: A Concurrency Conundrum in nbd_reconnect_socket**

Okay, the crash report indicates a failure to receive an RPC, specifically `SYZFAIL: failed to recv rpc`, with a `Connection reset by peer` error. This strongly suggests the syz-executor died. My initial hunch is a kernel panic, so I need to dig deeper. Let's revisit the `nbd_reconnect_socket` function; I have a nagging feeling.

Looking at the code again:

```c
	args = kzalloc_obj(*args);
	if (!args) {
		sockfd_put(sock);
		return -ENOMEM;
	}

	for (i = 0; i < config->num_connections; i++) {
		struct nbd_sock *nsock = config->socks[i];

		if (!nsock->dead)
			continue;

		mutex_lock(&nsock->tx_lock);
		if (!nsock->dead) {
			mutex_unlock(&nsock->tx_lock);
			continue;
		}
		sk_set_memalloc(sock->sk);
		if (nbd->tag_set.timeout)
			sock->sk->sk_sndtimeo = nbd->tag_set.timeout;
		atomic_inc(&config->recv_threads);
		refcount_inc(&nbd->config_refs);
		old = nsock->sock;
		nsock->fallback_index = -1;
		nsock->sock = sock;
		nsock->dead = false;
		INIT_WORK(&args->work, recv_work);
		args->index = i;
		args->nbd = nbd;
		args->nsock = nsock;
		nsock->cookie++;
		mutex_unlock(&nsock->tx_lock);
		sockfd_put(old);

		clear_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);

		/* We take the tx_mutex in an error path in the recv_work, so we
		 * need to queue_work outside of the tx_mutex.
		 */
		queue_work(nbd->recv_workq, &args->work);

		atomic_inc(&config->live_connections);
		wake_up(&config->conn_wait);
		return 0;
	}
	sockfd_put(sock);
	kfree(args);
	return -ENOSPC;
```

I'm starting to think about concurrency. What if `nbd_reconnect_socket` is called multiple times concurrently? Fortunately, `nbd_genl_reconfigure` takes `nbd->config_lock`, which serializes calls to `nbd_reconnect_socket`. So `nbd_reconnect_socket` is safe... or is it? Wait a second.

Let's trace: `recv_work` *doesn't* hold `nbd->config_lock`, but it *does* take `nsock->tx_lock`. Specifically:

```c
	mutex_lock(&nsock->tx_lock);
	nbd_mark_nsock_dead(nbd, nsock, 1);
	mutex_unlock(&nsock->tx_lock);
```

And `nbd_mark_nsock_dead` sets `nsock->dead = true;`. So, `nsock->dead` can become true concurrently with `nbd_reconnect_socket` potentially. But `nbd_reconnect_socket` checks `nsock->dead` *without* `tx_lock`, then it takes `tx_lock` and checks *again*. This pattern seems correct, preventing races on the `nsock->dead` flag.

Alright, so what happens when `nbd_reconnect_socket` queues `args->work` on `nbd->recv_workq`? `recv_work` is executed, it loops, eventually calling `nbd_mark_nsock_dead`, then it `kfree(args)`.

Here's the problem: what happens if `nbd_reconnect_socket` is called, replaces `nsock->sock` with a *new* socket, and then queues `args->work`? What if the *OLD* `recv_work` is still running? That would be a use-after-free situation on `args`! However, let me double check the code... wait... `nbd_add_socket` does NOT queue `recv_work`! *That* function is responsible for creating a socket,

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_add_socket]

map[SourceCode:1241:	static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
1242:				  bool netlink)
1243:	{
1244:		struct nbd_config *config = nbd->config;
1245:		struct socket *sock;
1246:		struct nbd_sock **socks;
1247:		struct nbd_sock *nsock;
1248:		unsigned int memflags;
1249:		int err;
1250:	
1251:		/* Arg will be cast to int, check it to avoid overflow */
1252:		if (arg > INT_MAX)
1253:			return -EINVAL;
1254:		sock = nbd_get_socket(nbd, arg, &err);
1255:		if (!sock)
1256:			return err;
1257:	
1258:		/*
1259:		 * We need to make sure we don't get any errant requests while we're
1260:		 * reallocating the ->socks array.
1261:		 */
1262:		memflags = blk_mq_freeze_queue(nbd->disk->queue);
1263:	
1264:		if (!netlink && !nbd->task_setup &&
1265:		    !test_bit(NBD_RT_BOUND, &config->runtime_flags))
1266:			nbd->task_setup = current;
1267:	
1268:		if (!netlink &&
1269:		    (nbd->task_setup != current ||
1270:		     test_bit(NBD_RT_BOUND, &config->runtime_flags))) {
1271:			dev_err(disk_to_dev(nbd->disk),
1272:				"Device being setup by another task");
1273:			err = -EBUSY;
1274:			goto put_socket;
1275:		}
1276:	
1277:		nsock = kzalloc_obj(*nsock);
1278:		if (!nsock) {
1279:			err = -ENOMEM;
1280:			goto put_socket;
1281:		}
1282:	
1283:		socks = krealloc(config->socks, (config->num_connections + 1) *
1284:				 sizeof(struct nbd_sock *), GFP_KERNEL);
1285:		if (!socks) {
1286:			kfree(nsock);
1287:			err = -ENOMEM;
1288:			goto put_socket;
1289:		}
1290:	
1291:		config->socks = socks;
1292:	
1293:		nsock->fallback_index = -1;
1294:		nsock->dead = false;
1295:		mutex_init(&nsock->tx_lock);
1296:		nsock->sock = sock;
1297:		nsock->pending = NULL;
1298:		nsock->sent = 0;
1299:		nsock->cookie = 0;
1300:		INIT_WORK(&nsock->work, nbd_pending_cmd_work);
1301:		socks[config->num_connections++] = nsock;
1302:		atomic_inc(&config->live_connections);
1303:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1304:	
1305:		return 0;
1306:	
1307:	put_socket:
1308:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1309:		sockfd_put(sock);
1310:		return err;
1311:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 43172
							output: 21
							thoughts: 40
						

Okay, here's my take on those thoughts, framed as an expert's internal monologue:

**Investigating the `recv_work` Queue**

Right, so `nbd_add_socket` *doesn't* seem to be responsible for queuing up those `recv_work` items. That's a key observation. Okay, so if it's not adding the socket and queuing the receive work simultaneously, I need to trace this back. The question becomes, where *does* that `recv_work` get initiated? I need to find the place where it's first scheduled. Let's do a quick search for instances of `recv_work` throughout the codebase. I need to understand the entry point for handling incoming data on these NBD sockets. Knowing where the initial queuing happens will be crucial to debugging this issue. This will highlight how the data handling is actually structured.

map[Name:recv_work]

map[References:[map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:nbd_reconnect_socket SourceFile:drivers/block/nbd.c SourceLine:1351] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:nbd_start_device SourceFile:drivers/block/nbd.c SourceLine:1534]] TruncatedOutput:false]

gemini-3.1-pro-preview

							input: 43554
							output: 43
							thoughts: 12
						

Okay, here's my take on those thoughts, tailored for an expert audience, presented in the first person:

**Diving into `nbd_start_device`**

Alright, so the task at hand involves examining `nbd_start_device`. That function name alone tells me we're likely dealing with the initialization or activation of an NBD (Network Block Device) within the kernel. My immediate mental checklist starts:

*   **Device Structure:** I need to quickly refresh my understanding of the `nbd_device` struct. What fields are critical for the startup process? Things like the backing file descriptor, the connection state, any associated security parameters, and, of course, the access capabilities (read-only, write-enabled, etc.).
*   **Resource Allocation/Check:** What resources does this function likely need to manage? Memory allocation for buffers, interrupt handling setup (if applicable), potential registration with the block layer. I'll be looking for things like mutexes or semaphores protecting critical sections. Are any limits, such as concurrent NBD devices, checked?
*   **Error Handling:** It is very important to get a handle on the error handling within this function, especially within a kernel context. What are the potential failure scenarios? Is there proper cleanup of allocated resources? Are appropriate error codes being returned to the calling function? And also, can the kernel be brought down by this function?
*   **Security Context:** Given that this involves network access and potentially remote data, the security aspects are always top of mind. Authentication, authorization, and perhaps even encryption if this is supported. Is there any obvious attack surface in the logic?
*   **Concurrency:** Does `nbd_start_device` need to be thread-safe? Or is there any assumption of single-threaded operation? I'll be looking for synchronization primitives like mutexes or spinlocks protecting access to shared data structures. This is extremely important, as concurrency issues can lead to some tricky bugs.

Ultimately, I want to understand how this function transitions an NBD from an inactive to an active state, and where the potential bottlenecks or vulnerabilities might reside. Time to dig in and start tracing the code.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_start_device]

map[SourceCode:1471:	static int nbd_start_device(struct nbd_device *nbd)
1472:	{
1473:		struct nbd_config *config = nbd->config;
1474:		int num_connections = config->num_connections;
1475:		int error = 0, i;
1476:	
1477:		if (nbd->pid)
1478:			return -EBUSY;
1479:		if (!config->socks)
1480:			return -EINVAL;
1481:		if (num_connections > 1 &&
1482:		    !(config->flags & NBD_FLAG_CAN_MULTI_CONN)) {
1483:			dev_err(disk_to_dev(nbd->disk), "server does not support multiple connections per device.\n");
1484:			return -EINVAL;
1485:		}
1486:	
1487:	retry:
1488:		mutex_unlock(&nbd->config_lock);
1489:		blk_mq_update_nr_hw_queues(&nbd->tag_set, num_connections);
1490:		mutex_lock(&nbd->config_lock);
1491:	
1492:		/* if another code path updated nr_hw_queues, retry until succeed */
1493:		if (num_connections != config->num_connections) {
1494:			num_connections = config->num_connections;
1495:			goto retry;
1496:		}
1497:	
1498:		nbd->pid = task_pid_nr(current);
1499:	
1500:		nbd_parse_flags(nbd);
1501:	
1502:		error = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
1503:		if (error) {
1504:			dev_err(disk_to_dev(nbd->disk), "device_create_file failed for pid!\n");
1505:			return error;
1506:		}
1507:		set_bit(NBD_RT_HAS_PID_FILE, &config->runtime_flags);
1508:	
1509:		nbd_dev_dbg_init(nbd);
1510:		for (i = 0; i < num_connections; i++) {
1511:			struct recv_thread_args *args;
1512:	
1513:			args = kzalloc_obj(*args);
1514:			if (!args) {
1515:				sock_shutdown(nbd);
1516:				/*
1517:				 * If num_connections is m (2 < m),
1518:				 * and NO.1 ~ NO.n(1 < n < m) kzallocs are successful.
1519:				 * But NO.(n + 1) failed. We still have n recv threads.
1520:				 * So, add flush_workqueue here to prevent recv threads
1521:				 * dropping the last config_refs and trying to destroy
1522:				 * the workqueue from inside the workqueue.
1523:				 */
1524:				if (i)
1525:					flush_workqueue(nbd->recv_workq);
1526:				return -ENOMEM;
1527:			}
1528:			sk_set_memalloc(config->socks[i]->sock->sk);
1529:			if (nbd->tag_set.timeout)
1530:				config->socks[i]->sock->sk->sk_sndtimeo =
1531:					nbd->tag_set.timeout;
1532:			atomic_inc(&config->recv_threads);
1533:			refcount_inc(&nbd->config_refs);
1534:			INIT_WORK(&args->work, recv_work);
1535:			args->nbd = nbd;
1536:			args->nsock = config->socks[i];
1537:			args->index = i;
1538:			queue_work(nbd->recv_workq, &args->work);
1539:		}
1540:		return nbd_set_size(nbd, config->bytesize, nbd_blksize(config));
1541:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 45251
							output: 43
							thoughts: 3254
						

**Diving into the Netlink and NBD Conundrum**

Alright, let's break this down. The program's flow starts with `nbd_start_device`, queuing `recv_work` for the sockets. Then, `nbd_genl_connect` is called at the end of the initial flow, which triggers `recv_work` to run for `r[2]`. Next up, `nbd_genl_reconfigure` uses `nbd_reconnect_socket` for `r[3]`. My initial focus was on the conditional logic within `nbd_reconnect_socket` and why `r[3]` wasn't being added. It seemed like the `-ENOSPC` return was being ignored, leading to `r[3]` being skipped, and leading to the syzkaller program exiting. However, a "SYZFAIL: failed to recv rpc" on fd=3 with Connection reset by peer suggested something more. It looked like the syz-executor died, which pointed to a potential kernel panic or use-after-free issue. Though, after carefully stepping through the code, I confirmed that the memory allocations within `nbd_reconnect_socket` were sound.

Now, I shifted to understanding how `nsock->dead` could be true, suspecting that `r[2]` was being closed prematurely, before the reconfigure command. This turned out to not be the case. I then considered how the program handles socket pairs and quickly realized the second file descriptor from the socket pair was unused but still open. With this, `recv_work` will block in `nbd_read_reply` and thus `nsock->dead` will stay false. This results in the `-ENOSPC` and the associated return 0 on `nbd_genl_reconfigure`

Next, I wondered about the role of `nbd_release` if the device was closed, but the reproducer does not use the NBD device itself. So, no.

Diving into `nbd_genl_connect`, I examined `NBD_CFLAG_DESTROY_ON_DISCONNECT`. This led me to a thorough analysis of the netlink attributes in the `NBD_CMD_CONNECT` message, specifically focusing on the `NBD_ATTR_SOCKETS` attribute. This led me down a parse of ANYBLOB and the iovec structures. I carefully decoded the netlink message, identifying the `nlmsg_len`, `nlmsg_type`, attributes.

After parsing the attributes, I was now focused on the fact that the `NBD_CMD_CONNECT` message contains TWO sockets in `NBD_ATTR_SOCKETS`, BOTH the SAME.

This led me back to `nbd_genl_connect`, where I realized that `nbd_add_socket` is called TWICE with the SAME file descriptor, which could be the root of the problem. Time to understand the implications of this double addition...

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_add_socket]

map[SourceCode:1241:	static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
1242:				  bool netlink)
1243:	{
1244:		struct nbd_config *config = nbd->config;
1245:		struct socket *sock;
1246:		struct nbd_sock **socks;
1247:		struct nbd_sock *nsock;
1248:		unsigned int memflags;
1249:		int err;
1250:	
1251:		/* Arg will be cast to int, check it to avoid overflow */
1252:		if (arg > INT_MAX)
1253:			return -EINVAL;
1254:		sock = nbd_get_socket(nbd, arg, &err);
1255:		if (!sock)
1256:			return err;
1257:	
1258:		/*
1259:		 * We need to make sure we don't get any errant requests while we're
1260:		 * reallocating the ->socks array.
1261:		 */
1262:		memflags = blk_mq_freeze_queue(nbd->disk->queue);
1263:	
1264:		if (!netlink && !nbd->task_setup &&
1265:		    !test_bit(NBD_RT_BOUND, &config->runtime_flags))
1266:			nbd->task_setup = current;
1267:	
1268:		if (!netlink &&
1269:		    (nbd->task_setup != current ||
1270:		     test_bit(NBD_RT_BOUND, &config->runtime_flags))) {
1271:			dev_err(disk_to_dev(nbd->disk),
1272:				"Device being setup by another task");
1273:			err = -EBUSY;
1274:			goto put_socket;
1275:		}
1276:	
1277:		nsock = kzalloc_obj(*nsock);
1278:		if (!nsock) {
1279:			err = -ENOMEM;
1280:			goto put_socket;
1281:		}
1282:	
1283:		socks = krealloc(config->socks, (config->num_connections + 1) *
1284:				 sizeof(struct nbd_sock *), GFP_KERNEL);
1285:		if (!socks) {
1286:			kfree(nsock);
1287:			err = -ENOMEM;
1288:			goto put_socket;
1289:		}
1290:	
1291:		config->socks = socks;
1292:	
1293:		nsock->fallback_index = -1;
1294:		nsock->dead = false;
1295:		mutex_init(&nsock->tx_lock);
1296:		nsock->sock = sock;
1297:		nsock->pending = NULL;
1298:		nsock->sent = 0;
1299:		nsock->cookie = 0;
1300:		INIT_WORK(&nsock->work, nbd_pending_cmd_work);
1301:		socks[config->num_connections++] = nsock;
1302:		atomic_inc(&config->live_connections);
1303:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1304:	
1305:		return 0;
1306:	
1307:	put_socket:
1308:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1309:		sockfd_put(sock);
1310:		return err;
1311:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 50242
							output: 43
							thoughts: 105
						

**Analyzing the Socket Retrieval in `nbd_get_socket`**

Okay, so I'm digging into this `nbd_get_socket` function and something's clicked. It's returning a `struct socket *` based on the file descriptor (fd). That's standard practice, but the implications here are important. If I call it multiple times with the *same* fd, it should return the *same* `struct socket *` each time, right? That's how socket lookup should work to be efficient.

So, when I see `config->socks[0]->sock` and `config->socks[1]->sock`, I'm realizing they'll be pointing to the *exact* same memory location – the same `struct socket *`. This could potentially lead to problems down the road if we're not careful about how we handle that shared pointer. It's common to share sockets for connection reuse in this kind of setup, but we have to ensure it's handled safely.

Now, I need to confirm this assumption. Let's trace it down. The function `nbd_get_socket` calls `sockfd_lookup`. I'm going to quickly check that function and make sure it behaves as I expect, because if `sockfd_lookup` is doing something non-standard, then my assumptions here are wrong. Let me just open `nbd_get_socket` up and confirm.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_get_socket]

map[SourceCode:1213:	static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd,
1214:					     int *err)
1215:	{
1216:		struct socket *sock;
1217:	
1218:		*err = 0;
1219:		sock = sockfd_lookup(fd, err);
1220:		if (!sock)
1221:			return NULL;
1222:	
1223:		if (!sk_is_tcp(sock->sk) &&
1224:		    !sk_is_stream_unix(sock->sk)) {
1225:			dev_err(disk_to_dev(nbd->disk), "Unsupported socket: should be TCP or UNIX.\n");
1226:			*err = -EINVAL;
1227:			sockfd_put(sock);
1228:			return NULL;
1229:		}
1230:	
1231:		if (sock->ops->shutdown == sock_no_shutdown) {
1232:			dev_err(disk_to_dev(nbd->disk), "Unsupported socket: shutdown callout must be supported.\n");
1233:			*err = -EINVAL;
1234:			sockfd_put(sock);
1235:			return NULL;
1236:		}
1237:	
1238:		return sock;
1239:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 51106
							output: 43
							thoughts: 577
						

**Analyzing the Concurrency Issue**

Okay, so I'm digging into this code and I see that `sockfd_lookup` is incrementing the file's reference count. Then it's incremented again. Interesting. Then `nbd_start_device` is called. That function queues `recv_work` for both sockets in the socket pair. Hmm, that means *two* `recv_work` threads are going to be running concurrently, both reading from the *same* socket!

The `recv_work` thread calls `nbd_read_reply`, which does the actual socket read. If two threads are trying to read from the same socket concurrently, we're going to get interleaved bytes, which is a big no-no. But hold on, the reproducer doesn't actually send any replies, so both `recv_work` threads are going to end up blocking in `nbd_read_reply`, waiting for data that's never coming.

Then, `nbd_genl_reconfigure` is called, and it uses `nbd_reconnect_socket` with `r[3]`. `nbd_reconnect_socket` iterates through `config->socks`. Since neither socket is dead, it just returns `-ENOSPC`.

The reproducer then exits, which closes `r[2]`. This disconnects the socket pair. This should be interesting. Then both `recv_work` threads should wake up from `nbd_read_reply` and see an error or EOF.

Next, both threads call `nbd_mark_nsock_dead(nbd, nsock, 1)`. Wait, `nbd_mark_nsock_dead` takes `nsock->tx_lock`. Since they are different `nsock`s, they take different locks. That's good. They both call `kernel_sock_shutdown(nsock->sock, SHUT_RDWR)`. Since `nsock->sock` is the *same* socket, `kernel_sock_shutdown` is called twice on the same socket! Is that a problem? No, `kernel_sock_shutdown` is safe to call multiple times.

Then we get to the atomic dec:
```c
if (atomic_dec_return(&nbd->config->live_connections) == 0)
```
One thread decrements it to 1, the other to 0. The one that hits 0 will set `NBD_RT_DISCONNECTED`.

Finally, both threads execute this:
```c
atomic_dec(&config->recv_threads);
wake_up(&config->recv_wq);
nbd_config_put(nbd);
kfree(args);
```

Wait, `nbd_config_put` is called twice! That's a potential issue. I should really check how `nbd_config_put` is implemented to make sure it's safe to call more than once.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_config_put]

map[SourceCode:1432:	static void nbd_config_put(struct nbd_device *nbd)
1433:	{
1434:		if (refcount_dec_and_mutex_lock(&nbd->config_refs,
1435:						&nbd->config_lock)) {
1436:			struct nbd_config *config = nbd->config;
1437:			nbd_dev_dbg_close(nbd);
1438:			invalidate_disk(nbd->disk);
1439:			if (nbd->config->bytesize)
1440:				kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
1441:			if (test_and_clear_bit(NBD_RT_HAS_PID_FILE,
1442:					       &config->runtime_flags))
1443:				device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
1444:			nbd->pid = 0;
1445:			if (test_and_clear_bit(NBD_RT_HAS_BACKEND_FILE,
1446:					       &config->runtime_flags)) {
1447:				device_remove_file(disk_to_dev(nbd->disk), &backend_attr);
1448:				kfree(nbd->backend);
1449:				nbd->backend = NULL;
1450:			}
1451:			nbd_clear_sock(nbd);
1452:			if (config->num_connections) {
1453:				int i;
1454:				for (i = 0; i < config->num_connections; i++) {
1455:					sockfd_put(config->socks[i]->sock);
1456:					kfree(config->socks[i]);
1457:				}
1458:				kfree(config->socks);
1459:			}
1460:			kfree(nbd->config);
1461:			nbd->config = NULL;
1462:	
1463:			nbd->tag_set.timeout = 0;
1464:	
1465:			mutex_unlock(&nbd->config_lock);
1466:			nbd_put(nbd);
1467:			module_put(THIS_MODULE);
1468:		}
1469:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 53030
							output: 45
							thoughts: 1832
						

**Analyzing a Potential Race Condition in NBD Reconfiguration**

Okay, here's what's running through my head. I'm looking at this `nbd_config_put` function and the way it interacts with `nbd_reconnect_socket`. The initial thought is, "Wait, `nbd_config_put` frees `config->socks[i]`." But then I'm thinking about `nbd_reconnect_socket` and how it replaces the socket, which complicates things. I'm working through the code, particularly where `nbd_reconnect_socket` is called.

The key observation is how the reproducer triggers this. `nbd_reconnect_socket` returned an `-ENOSPC` initially, so it didn't do much. But, there seems to be a case where `nsock->dead` could be *true*, and this is my primary line of inquiry. The reproducer's use of `NBD_CMD_RECONFIGURE` with a TCP socket, and the socketpair used in `r[2]` are relevant. The fact that only one end of the socketpair is saved in `r[2]` and the other end is still open is critical. `recv_work` might block on the socketpair, so it's a valid way to look for a race.

The crash message suggests something's gone wrong ("SYZFAIL: failed to recv rpc", "fd=3 want=4 recv=0 n=-1 (errno 104: Connection reset by peer)"). This is where it gets interesting. I'm focusing on the interaction between `nbd_reconnect_socket` and a running `recv_work` thread. The main issue is that `nbd_reconnect_socket` may be called while the old `recv_work` thread is still running and potentially about to free memory. If the old `recv_work` marks the socket as dead, and the new `nbd_reconnect_socket` is running concurrently, there are a lot of timing issues.

The concurrency is where this is coming into focus. `recv_work` can mark the socket dead and unlock the `tx_lock`. Then, `nbd_reconnect_socket` can take the lock and queue a NEW `recv_work`. The OLD `recv_work` thread could then proceed to `nbd_config_put(nbd)`. The question is if `config->socks[i]` could be freed before the newly queued `recv_work` has a chance to execute. That would lead to a memory corruption.

The `refcount_inc(&nbd->config_refs)` call in `nbd_reconnect_socket` looks like a protection mechanism. It appears that it prevents the old `recv_work` from dropping the last reference. This is important. But, what if there's a problem with the lock ordering? `nbd_genl_reconfigure` uses `nbd->config_lock`, but `recv_work` does not, so `nbd_reconnect_socket` can execute concurrently with the potentially problematic `recv_work`.

The key question is the lifecycle of `config_refs`. If the initial `nbd_genl_reconfigure` drops it, there may be a window where it becomes zero. This part is still uncertain, but `nbd_genl_reconfigure` doesn't seem to hold a strong reference on it. The more I look at this, the more I believe there is indeed a concurrency issue where `recv_work` and `nbd_genl_reconfigure` could be racing.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_genl_reconfigure]

map[SourceCode:2310:	static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
2311:	{
2312:		struct nbd_device *nbd = NULL;
2313:		struct nbd_config *config;
2314:		int index;
2315:		int ret = 0;
2316:		bool put_dev = false;
2317:	
2318:		if (!netlink_capable(skb, CAP_SYS_ADMIN))
2319:			return -EPERM;
2320:	
2321:		if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)) {
2322:			pr_err("must specify a device to reconfigure\n");
2323:			return -EINVAL;
2324:		}
2325:		index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
2326:		mutex_lock(&nbd_index_mutex);
2327:		nbd = idr_find(&nbd_index_idr, index);
2328:		if (!nbd) {
2329:			mutex_unlock(&nbd_index_mutex);
2330:			pr_err("couldn't find a device at index %d\n", index);
2331:			return -EINVAL;
2332:		}
2333:		if (nbd->backend) {
2334:			if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
2335:				if (nla_strcmp(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
2336:					       nbd->backend)) {
2337:					mutex_unlock(&nbd_index_mutex);
2338:					dev_err(nbd_to_dev(nbd),
2339:						"backend image doesn't match with %s\n",
2340:						nbd->backend);
2341:					return -EINVAL;
2342:				}
2343:			} else {
2344:				mutex_unlock(&nbd_index_mutex);
2345:				dev_err(nbd_to_dev(nbd), "must specify backend\n");
2346:				return -EINVAL;
2347:			}
2348:		}
2349:		if (!refcount_inc_not_zero(&nbd->refs)) {
2350:			mutex_unlock(&nbd_index_mutex);
2351:			pr_err("device at index %d is going down\n", index);
2352:			return -EINVAL;
2353:		}
2354:		mutex_unlock(&nbd_index_mutex);
2355:	
2356:		config = nbd_get_config_unlocked(nbd);
2357:		if (!config) {
2358:			dev_err(nbd_to_dev(nbd),
2359:				"not configured, cannot reconfigure\n");
2360:			nbd_put(nbd);
2361:			return -EINVAL;
2362:		}
2363:	
2364:		mutex_lock(&nbd->config_lock);
2365:		if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
2366:		    !nbd->pid) {
2367:			dev_err(nbd_to_dev(nbd),
2368:				"not configured, cannot reconfigure\n");
2369:			ret = -EINVAL;
2370:			goto out;
2371:		}
2372:	
2373:		ret = nbd_genl_size_set(info, nbd);
2374:		if (ret)
2375:			goto out;
2376:	
2377:		if (info->attrs[NBD_ATTR_TIMEOUT])
2378:			nbd_set_cmd_timeout(nbd,
2379:					    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
2380:		if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
2381:			config->dead_conn_timeout =
2382:				nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
2383:			config->dead_conn_timeout *= HZ;
2384:		}
2385:		if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
2386:			u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
2387:			if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
2388:				if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
2389:						      &nbd->flags))
2390:					put_dev = true;
2391:			} else {
2392:				if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
2393:						       &nbd->flags))
2394:					refcount_inc(&nbd->refs);
2395:			}
2396:	
2397:			if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
2398:				set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
2399:						&config->runtime_flags);
2400:			} else {
2401:				clear_bit(NBD_RT_DISCONNECT_ON_CLOSE,
2402:						&config->runtime_flags);
2403:			}
2404:		}
2405:	
2406:		if (info->attrs[NBD_ATTR_SOCKETS]) {
2407:			struct nlattr *attr;
2408:			int rem, fd;
2409:	
2410:			nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
2411:					    rem) {
2412:				struct nlattr *socks[NBD_SOCK_MAX+1];
2413:	
2414:				if (nla_type(attr) != NBD_SOCK_ITEM) {
2415:					pr_err("socks must be embedded in a SOCK_ITEM attr\n");
2416:					ret = -EINVAL;
2417:					goto out;
2418:				}
2419:				ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
2420:								  attr,
2421:								  nbd_sock_policy,
2422:								  info->extack);
2423:				if (ret != 0) {
2424:					pr_err("error processing sock list\n");
2425:					ret = -EINVAL;
2426:					goto out;
2427:				}
2428:				if (!socks[NBD_SOCK_FD])
2429:					continue;
2430:				fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
2431:				ret = nbd_reconnect_socket(nbd, fd);
2432:				if (ret) {
2433:					if (ret == -ENOSPC)
2434:						ret = 0;
2435:					goto out;
2436:				}
2437:				dev_info(nbd_to_dev(nbd), "reconnected socket\n");
2438:			}
2439:		}
2440:	out:
2441:		mutex_unlock(&nbd->config_lock);
2442:		nbd_config_put(nbd);
2443:		nbd_put(nbd);
2444:		if (put_dev)
2445:			nbd_put(nbd);
2446:		return ret;
2447:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 57903
							output: 46
							thoughts: 67
						

**A Potential Resource Leak?**

Okay, so I'm looking at this `nbd_genl_reconfigure` function, and it's calling `nbd_get_config_unlocked(nbd)`. That's a little unusual, I need to check something important. Hang on... `nbd_get_config_unlocked`... and, wait a minute, it doesn't seem to be *incrementing* `config_refs`. That's a red flag! I need to dig into `nbd_get_config_unlocked` right now. This could be a significant resource leak if the reference count isn't being managed correctly. I need to understand exactly what's happening there.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_get_config_unlocked]

map[SourceCode: 435:	static struct nbd_config *nbd_get_config_unlocked(struct nbd_device *nbd)
 436:	{
 437:		if (refcount_inc_not_zero(&nbd->config_refs)) {
 438:			/*
 439:			 * Add smp_mb__after_atomic to ensure that reading nbd->config_refs
 440:			 * and reading nbd->config is ordered. The pair is the barrier in
 441:			 * nbd_alloc_and_init_config(), avoid nbd->config_refs is set
 442:			 * before nbd->config.
 443:			 */
 444:			smp_mb__after_atomic();
 445:			return nbd->config;
 446:		}
 447:	
 448:		return NULL;
 449:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 58440
							output: 40
							thoughts: 967
						

**Analyzing the NBD Reconfiguration Process**

Okay, so I'm diving into this `nbd_genl_reconfigure` function. Good, I see that `nbd_get_config_unlocked` does indeed increment `config_refs`, that makes sense. And because `nbd_genl_reconfigure` holds `config_refs` and then calls `nbd_config_put(nbd)` at the end, the `config_refs` are properly managed. That's what I expect.

But then I started thinking about the error handling. What happens if `nbd_reconnect_socket` returns `-ENOSPC`? Oh, right, it sets `ret = 0` and then goes to `out`, which calls `nbd_config_put(nbd)`. That seems safe, nothing to worry about there.

Now, what about the more interesting case... what if `nbd_reconnect_socket` *does* find a dead socket? How does `nsock->dead` get set to true? That's what I really need to understand. Let me trace how this could be achieved. If the reproducer sends an `NBD_CMD_RECONFIGURE` with `r[3]`, the socket `r[3]` is a TCP socket, this is the trigger.

Wait, does the `NBD_CMD_RECONFIGURE` have `NBD_ATTR_CLIENT_FLAGS`? Let's check.

Okay, let's look at the attributes in `NBD_CMD_RECONFIGURE`: `2c 00 00 00` (length 44), followed by something. I'll parse it.

`01` is the command: `NBD_CMD_RECONFIGURE`
`00` is the version: 0.
`26 bd` is reserved.
`70 00 fe db df 25 03 00` ... this looks interesting. This must be the part that matters.

Wait... this `70 00` is the `nla_len = 112`, and `fe db` is `nla_type = 0xdbfe`...  But the `ANYBLOB` following it is only 34 bytes! What's going on here?

If `nla_len` is 112, `nla_ok` will definitely fail! `nla_ok` checks that `nla_len >= sizeof(struct nlattr)` and also that `nla_len <= remaining`. The total length of the message is 44 bytes (`0x2c`), so `nla_len = 112` is INVALID!

Wait, the `vec[0].len = 0x2c` (44), so the buffer looks like this:

`2c 00 00 00` (nlmsg_len = 44)
`xx xx` (nlmsg_type = r[4])
`01 00 26 bd` (genlmsghdr)
`70 00 fe db df 25 03 00`

So, `70 00 fe db` implies that `nla_len = 112`.

If `nla_len` is 112, will `nlmsg_parse` ignore it, or return an error? Let me think... `genl_family_rcv_msg` calls `nlmsg_parse`. If `nlmsg_parse` fails, it returns an error. `nlmsg_parse` uses `nla_ok`.

Aha! If `nla_ok` fails, then `nlmsg_parse` returns `-EINVAL`. This means `NBD_CMD_RECONFIGURE` will *fail* with `-EINVAL`! I need to double-check `nlmsg_parse` to confirm, but this is a very strong lead.

map[ContextFile:lib/nlattr.c IncludeLines:true Name:__nla_parse]

map[SourceCode: 711:	/**
 712:	 * __nla_parse - Parse a stream of attributes into a tb buffer
 713:	 * @tb: destination array with maxtype+1 elements
 714:	 * @maxtype: maximum attribute type to be expected
 715:	 * @head: head of attribute stream
 716:	 * @len: length of attribute stream
 717:	 * @policy: validation policy
 718:	 * @validate: validation strictness
 719:	 * @extack: extended ACK pointer
 720:	 *
 721:	 * Parses a stream of attributes and stores a pointer to each attribute in
 722:	 * the tb array accessible via the attribute type.
 723:	 * Validation is controlled by the @validate parameter.
 724:	 *
 725:	 * Returns 0 on success or a negative error code.
 726:	 */
 727:	int __nla_parse(struct nlattr **tb, int maxtype,
 728:			const struct nlattr *head, int len,
 729:			const struct nla_policy *policy, unsigned int validate,
 730:			struct netlink_ext_ack *extack)
 731:	{
 732:		return __nla_validate_parse(head, len, maxtype, policy, validate,
 733:					    extack, tb, 0);
 734:	}
 SourceFile:lib/nlattr.c]

gemini-3.1-pro-preview

							input: 60726
							output: 42
							thoughts: 13
						

Okay, let's dive into this. Here's my thought process summarized, assuming I'm already pretty familiar with the subject matter:

**Checking `__nla_validate_parse`**

Alright, time to get to it. My initial thought is to take a look at `__nla_validate_parse`. This function is usually where the magic happens; where we're going to see how the code handles the parsing and validation of Netlink attributes. I need to refresh my memory on exactly how it's implemented. I'm probably going to be thinking about data structures like `nla_policy` and the different validation rules they support, like enforcing length constraints, type checks, and potentially even more complex constraints. I need to understand how the code handles error conditions, too. What happens if the input data is malformed or violates the defined policies? Are we gracefully failing, logging errors, or potentially even leading to a security issue? That's what I want to see. I expect it's a critical component in safeguarding against malicious input. So, let's see what `__nla_validate_parse` has to offer.

map[ContextFile:lib/nlattr.c IncludeLines:true Name:__nla_validate_parse]

map[SourceCode: 604:	static int __nla_validate_parse(const struct nlattr *head, int len, int maxtype,
 605:					const struct nla_policy *policy,
 606:					unsigned int validate,
 607:					struct netlink_ext_ack *extack,
 608:					struct nlattr **tb, unsigned int depth)
 609:	{
 610:		const struct nlattr *nla;
 611:		int rem;
 612:	
 613:		if (depth >= MAX_POLICY_RECURSION_DEPTH) {
 614:			NL_SET_ERR_MSG(extack,
 615:				       "allowed policy recursion depth exceeded");
 616:			return -EINVAL;
 617:		}
 618:	
 619:		if (tb)
 620:			memset(tb, 0, sizeof(struct nlattr *) * (maxtype + 1));
 621:	
 622:		nla_for_each_attr(nla, head, len, rem) {
 623:			u16 type = nla_type(nla);
 624:	
 625:			if (type == 0 || type > maxtype) {
 626:				if (validate & NL_VALIDATE_MAXTYPE) {
 627:					NL_SET_ERR_MSG_ATTR(extack, nla,
 628:							    "Unknown attribute type");
 629:					return -EINVAL;
 630:				}
 631:				continue;
 632:			}
 633:			type = array_index_nospec(type, maxtype + 1);
 634:			if (policy) {
 635:				int err = validate_nla(nla, maxtype, policy,
 636:						       validate, extack, depth);
 637:	
 638:				if (err < 0)
 639:					return err;
 640:			}
 641:	
 642:			if (tb)
 643:				tb[type] = (struct nlattr *)nla;
 644:		}
 645:	
 646:		if (unlikely(rem > 0)) {
 647:			pr_warn_ratelimited("netlink: %d bytes leftover after parsing attributes in process `%s'.\n",
 648:					    rem, current->comm);
 649:			NL_SET_ERR_MSG(extack, "bytes leftover after parsing attributes");
 650:			if (validate & NL_VALIDATE_TRAILING)
 651:				return -EINVAL;
 652:		}
 653:	
 654:		return 0;
 655:	}
 SourceFile:lib/nlattr.c]

gemini-3.1-pro-preview

							input: 61805
							output: 21
							thoughts: 149
						

**Analyzing the Netlink Attribute Validation**

Okay, so I'm digging into this Netlink attribute parsing, specifically how `nla_for_each_attr` interacts with validation. I need to understand this better. It seems like `nla_for_each_attr` relies heavily on `nla_ok`. The critical thing is that if `nla_ok` fails, the loop simply *terminates*. That means any remaining data, the `rem` value, will be greater than zero.

Now, if `validate & NL_VALIDATE_TRAILING` is true, a failure during this loop results in an `-EINVAL`. I have to figure out if `NL_VALIDATE_TRAILING` is even set when processing an `NBD_CMD_RECONFIGURE` command. That's the real question.

I know that for `nbd_connect_genl_ops`, when dealing with `NBD_CMD_CONNECT`, the `.validate` parameter is set to `GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP`. That makes sense for a connect command. But what about `NBD_CMD_RECONFIGURE`? Is it also skipping strict validation? That's the key difference I need to track down.

map[Expression:NBD_CMD_RECONFIGURE]

map[Output:drivers/block/nbd.c=2449=static const struct genl_small_ops nbd_connect_genl_ops[] = {
--
drivers/block/nbd.c-2460-	{
drivers/block/nbd.c:2461:		.cmd	= NBD_CMD_RECONFIGURE,
drivers/block/nbd.c-2462-		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
--
include/uapi/linux/nbd-netlink.h=89=enum {
--
include/uapi/linux/nbd-netlink.h-92-	NBD_CMD_DISCONNECT,
include/uapi/linux/nbd-netlink.h:93:	NBD_CMD_RECONFIGURE,
include/uapi/linux/nbd-netlink.h-94-	NBD_CMD_LINK_DEAD,
]

gemini-3.1-pro-preview

							input: 62494
							output: 46
							thoughts: 232
						

**Analyzing the Trailing Bytes Validation Logic**

Okay, so I've been digging into this code, and it's all starting to click. That `GENL_DONT_VALIDATE_STRICT` flag, it's the key. It means that trailing bytes are *not* validated. Consequently, when we use `nla_for_each_attr`, it's just going to stop parsing at the end of the specified attributes. And as a result, `__nla_validate_parse` is going to return 0.

So, in the case of `NBD_CMD_RECONFIGURE`, that means the command will be executed without *any* attributes being present. Now, if there aren’t any attributes, `info->attrs[NBD_ATTR_INDEX]` is going to be NULL. I know that for sure.

But hang on… I remember looking at `nbd_genl_reconfigure`, and it has this check:

```c
	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)) {
		pr_err("must specify a device to reconfigure\n");
		return -EINVAL;
	}
```

Okay, so `GENL_REQ_ATTR_CHECK` is there, and it specifically checks if the attribute is actually present. If it’s *not* present, it’s going to return `-EINVAL`. So, what that really means is, that with no attributes being present, the whole `NBD_CMD_RECONFIGURE` process is going to fail with a `-EINVAL` error! It's a bit of a contradiction if you are trying to configure the device.
I need to be sure though, so I'm going to check out `GENL_REQ_ATTR_CHECK`. I'll see what it actually does.

requested entity does not exist

map[ContextFile:include/net/genetlink.h IncludeLines:true Name:GENL_REQ_ATTR_CHECK]

map[SourceCode: SourceFile:]

gemini-3.1-pro-preview

							input: 63191
							output: 22
							thoughts: 15
						

Here's my attempt at summarizing the thought process, tailored for an expert audience:

**Analyzing the Codebase for Attribute Validation**

Okay, so I need to understand how the system validates attributes within the `GENL` framework. My first instinct is to zero in on the core validation logic. Let's start with a quick search using `grep`. I'm specifically targeting the macro `GENL_REQ_ATTR_CHECK`. This macro, if it's used the way I suspect, should be a central point for enforcing the required and permitted attributes in Netlink GENL requests. It's a key starting point because, based on my understanding of similar implementations, this macro likely encapsulates the checks for attribute presence, type, length, and potentially even value restrictions. By examining the instances of `GENL_REQ_ATTR_CHECK` I should be able to quickly gain an overview of the most crucial validation logic. I'm hoping to quickly identify the points within the request handling where the attributes and their associated restrictions are being checked.

map[Expression:GENL_REQ_ATTR_CHECK]

map[Output:drivers/block/nbd.c=2073=static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
--
drivers/block/nbd.c-2096-	}
drivers/block/nbd.c:2097:	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SOCKETS)) {
drivers/block/nbd.c-2098-		pr_err("must specify at least one socket\n");
--
drivers/block/nbd.c-2100-	}
drivers/block/nbd.c:2101:	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SIZE_BYTES)) {
drivers/block/nbd.c-2102-		pr_err("must specify a size in bytes for the device\n");
--
drivers/block/nbd.c=2275=static int nbd_genl_disconnect(struct sk_buff *skb, struct genl_info *info)
--
drivers/block/nbd.c-2282-
drivers/block/nbd.c:2283:	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)) {
drivers/block/nbd.c-2284-		pr_err("must specify an index to disconnect\n");
--
drivers/block/nbd.c=2310=static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
--
drivers/block/nbd.c-2320-
drivers/block/nbd.c:2321:	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)) {
drivers/block/nbd.c-2322-		pr_err("must specify a device to reconfigure\n");
--
drivers/dpll/dpll_netlink.c=2028=int dpll_pre_doit(const struct genl_split_ops *ops, struct sk_buff *skb,
--
drivers/dpll/dpll_netlink.c-2032-
drivers/dpll/dpll_netlink.c:2033:	if (GENL_REQ_ATTR_CHECK(info, DPLL_A_ID))
drivers/dpll/dpll_netlink.c-2034-		return -EINVAL;
--
drivers/dpll/dpll_netlink.c=2071=int dpll_pin_pre_doit(const struct genl_split_ops *ops, struct sk_buff *skb,
--
drivers/dpll/dpll_netlink.c-2076-	mutex_lock(&dpll_lock);
drivers/dpll/dpll_netlink.c:2077:	if (GENL_REQ_ATTR_CHECK(info, DPLL_A_PIN_ID)) {
drivers/dpll/dpll_netlink.c-2078-		ret = -EINVAL;
--
drivers/gpu/drm/drm_ras.c=234=int drm_ras_nl_get_error_counter_dumpit(struct sk_buff *skb,
--
drivers/gpu/drm/drm_ras.c-244-
drivers/gpu/drm/drm_ras.c:245:	if (!info->attrs || GENL_REQ_ATTR_CHECK(info, DRM_RAS_A_ERROR_COUNTER_ATTRS_NODE_ID))
drivers/gpu/drm/drm_ras.c-246-		return -EINVAL;
--
drivers/gpu/drm/drm_ras.c=301=int drm_ras_nl_get_error_counter_doit(struct sk_buff *skb,
--
drivers/gpu/drm/drm_ras.c-306-	if (!info->attrs ||
drivers/gpu/drm/drm_ras.c:307:	    GENL_REQ_ATTR_CHECK(info, DRM_RAS_A_ERROR_COUNTER_ATTRS_NODE_ID) ||
drivers/gpu/drm/drm_ras.c:308:	    GENL_REQ_ATTR_CHECK(info, DRM_RAS_A_ERROR_COUNTER_ATTRS_ERROR_ID))
drivers/gpu/drm/drm_ras.c-309-		return -EINVAL;
--
drivers/net/ovpn/netlink.c=36=ovpn_get_dev_from_attrs(struct net *net, const struct genl_info *info,
--
drivers/net/ovpn/netlink.c-42-
drivers/net/ovpn/netlink.c:43:	if (GENL_REQ_ATTR_CHECK(info, OVPN_A_IFINDEX))
drivers/net/ovpn/netlink.c-44-		return ERR_PTR(-EINVAL);
--
drivers/net/ovpn/netlink.c=347=int ovpn_nl_peer_new_doit(struct sk_buff *skb, struct genl_info *info)
--
drivers/net/ovpn/netlink.c-356-
drivers/net/ovpn/netlink.c:357:	if (GENL_REQ_ATTR_CHECK(info, OVPN_A_PEER))
drivers/net/ovpn/netlink.c-358-		return -EINVAL;
--
drivers/net/ovpn/netlink.c=473=int ovpn_nl_peer_set_doit(struct sk_buff *skb, struct genl_info *info)
--
drivers/net/ovpn/netlink.c-481-
drivers/net/ovpn/netlink.c:482:	if (GENL_REQ_ATTR_CHECK(info, OVPN_A_PEER))
drivers/net/ovpn/netlink.c-483-		return -EINVAL;
--
drivers/net/ovpn/netlink.c=660=int ovpn_nl_peer_get_doit(struct sk_buff *skb, struct genl_info *info)
--
drivers/net/ovpn/netlink.c-668-
drivers/net/ovpn/netlink.c:669:	if (GENL_REQ_ATTR_CHECK(info, OVPN_A_PEER))
drivers/net/ovpn/netlink.c-670-		return -EINVAL;
--
drivers/net/ovpn/netlink.c=786=int ovpn_nl_peer_del_doit(struct sk_buff *skb, struct genl_info *info)
--
drivers/net/ovpn/netlink.c-793-
drivers/net/ovpn/netlink.c:794:	if (GENL_REQ_ATTR_CHECK(info, OVPN_A_PEER))
drivers/net/ovpn/netlink.c-795-		return -EINVAL;
--
drivers/net/ovpn/netlink.c=885=int ovpn_nl_key_new_doit(struct sk_buff *skb, struct genl_info *info)
--
drivers/net/ovpn/netlink.c-893-
drivers/net/ovpn/netlink.c:894:	if (GENL_REQ_ATTR_CHECK(info, OVPN_A_KEYCONF))
drivers/net/ovpn/netlink.c-895-		return -EINVAL;
--
drivers/net/ovpn/netlink.c=990=int ovpn_nl_key_get_doit(struct sk_buff *skb, struct genl_info *info)
--
drivers/net/ovpn/netlink.c-1000-
drivers/net/ovpn/netlink.c:1001:	if (GENL_REQ_ATTR_CHECK(info, OVPN_A_KEYCONF))
drivers/net/ovpn/netlink.c-1002-		return -EINVAL;
--
drivers/net/ovpn/netlink.c=1072=int ovpn_nl_key_swap_doit(struct sk_buff *skb, struct genl_info *info)
--
drivers/net/ovpn/netlink.c-1079-
drivers/net/ovpn/netlink.c:1080:	if (GENL_REQ_ATTR_CHECK(info, OVPN_A_KEYCONF))
drivers/net/ovpn/netlink.c-1081-		return -EINVAL;
--
drivers/net/ovpn/netlink.c=1108=int ovpn_nl_key_del_doit(struct sk_buff *skb, struct genl_info *info)
--
drivers/net/ovpn/netlink.c-1116-
drivers/net/ovpn/netlink.c:1117:	if (GENL_REQ_ATTR_CHECK(info, OVPN_A_KEYCONF))
drivers/net/ovpn/netlink.c-1118-		return -EINVAL;
--
fs/lockd/svc.c=712=int lockd_nl_server_set_doit(struct sk_buff *skb, struct genl_info *info)
--
fs/lockd/svc.c-717-
fs/lockd/svc.c:718:	if (GENL_REQ_ATTR_CHECK(info, LOCKD_A_SERVER_GRACETIME))
fs/lockd/svc.c-719-		return -EINVAL;
--
fs/nfsd/nfsctl.c=1617=int nfsd_nl_threads_set_doit(struct sk_buff *skb, struct genl_info *info)
--
fs/nfsd/nfsctl.c-1624-
fs/nfsd/nfsctl.c:1625:	if (GENL_REQ_ATTR_CHECK(info, NFSD_A_SERVER_THREADS))
fs/nfsd/nfsctl.c-1626-		return -EINVAL;
--
fs/nfsd/nfsctl.c=1779=int nfsd_nl_version_set_doit(struct sk_buff *skb, struct genl_info *info)
--
fs/nfsd/nfsctl.c-1784-
fs/nfsd/nfsctl.c:1785:	if (GENL_REQ_ATTR_CHECK(info, NFSD_A_SERVER_PROTO_VERSION))
fs/nfsd/nfsctl.c-1786-		return -EINVAL;
--
fs/nfsd/nfsctl.c=2140=int nfsd_nl_pool_mode_set_doit(struct sk_buff *skb, struct genl_info *info)
--
fs/nfsd/nfsctl.c-2143-
fs/nfsd/nfsctl.c:2144:	if (GENL_REQ_ATTR_CHECK(info, NFSD_A_POOL_MODE_MODE))
fs/nfsd/nfsctl.c-2145-		return -EINVAL;
--
include/net/genetlink.h=156=static inline void *genl_info_userhdr(const struct genl_info *info)
--
include/net/genetlink.h-166-/* Report that a root attribute is missing */
include/net/genetlink.h:167:#define GENL_REQ_ATTR_CHECK(info, attr) ({				\
include/net/genetlink.h-168-	const struct genl_info *__info = (info);			\
--
net/core/netdev-genl.c=111=int netdev_nl_dev_get_doit(struct sk_buff *skb, struct genl_info *info)
--
net/core/netdev-genl.c-117-
net/core/netdev-genl.c:118:	if (GENL_REQ_ATTR_CHECK(info, NETDEV_A_DEV_IFINDEX))
net/core/netdev-genl.c-119-		return -EINVAL;
--
net/core/netdev-genl.c=221=int netdev_nl_napi_get_doit(struct sk_buff *skb, struct genl_info *info)
--
net/core/netdev-genl.c-227-
net/core/netdev-genl.c:228:	if (GENL_REQ_ATTR_CHECK(info, NETDEV_A_NAPI_ID))
net/core/netdev-genl.c-229-		return -EINVAL;
--
net/core/netdev-genl.c=359=int netdev_nl_napi_set_doit(struct sk_buff *skb, struct genl_info *info)
--
net/core/netdev-genl.c-364-
net/core/netdev-genl.c:365:	if (GENL_REQ_ATTR_CHECK(info, NETDEV_A_NAPI_ID))
net/core/netdev-genl.c-366-		return -EINVAL;
--
net/core/netdev-genl.c=551=int netdev_nl_queue_get_doit(struct sk_buff *skb, struct genl_info *info)
--
net/core/netdev-genl.c-557-
net/core/netdev-genl.c:558:	if (GENL_REQ_ATTR_CHECK(info, NETDEV_A_QUEUE_ID) ||
net/core/netdev-genl.c:559:	    GENL_REQ_ATTR_CHECK(info, NETDEV_A_QUEUE_TYPE) ||
net/core/netdev-genl.c:560:	    GENL_REQ_ATTR_CHECK(info, NETDEV_A_QUEUE_IFINDEX))
net/core/netdev-genl.c-561-		return -EINVAL;
--
net/core/netdev-genl.c=1011=int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
--
net/core/netdev-genl.c-1022-
net/core/netdev-genl.c:1023:	if (GENL_REQ_ATTR_CHECK(info, NETDEV_A_DEV_IFINDEX) ||
net/core/netdev-genl.c:1024:	    GENL_REQ_ATTR_CHECK(info, NETDEV_A_DMABUF_FD) ||
net/core/netdev-genl.c:1025:	    GENL_REQ_ATTR_CHECK(info, NETDEV_A_DMABUF_QUEUES))
net/core/netdev-genl.c-1026-		return -EINVAL;
--
net/core/netdev-genl.c=1122=int netdev_nl_bind_tx_doit(struct sk_buff *skb, struct genl_info *info)
--
net/core/netdev-genl.c-1132-
net/core/netdev-genl.c:1133:	if (GENL_REQ_ATTR_CHECK(info, NETDEV_A_DEV_IFINDEX) ||
net/core/netdev-genl.c:1134:	    GENL_REQ_ATTR_CHECK(info, NETDEV_A_DMABUF_FD))
net/core/netdev-genl.c-1135-		return -EINVAL;
--
net/core/netdev-genl.c=1199=int netdev_nl_queue_create_doit(struct sk_buff *skb, struct genl_info *info)
--
net/core/netdev-genl.c-1214-
net/core/netdev-genl.c:1215:	if (GENL_REQ_ATTR_CHECK(info, NETDEV_A_QUEUE_IFINDEX) ||
net/core/netdev-genl.c:1216:	    GENL_REQ_ATTR_CHECK(info, NETDEV_A_QUEUE_TYPE) ||
net/core/netdev-genl.c:1217:	    GENL_REQ_ATTR_CHECK(info, NETDEV_A_QUEUE_LEASE))
net/core/netdev-genl.c-1218-		return -EINVAL;
--
net/core/page_pool_user.c=177=int netdev_nl_page_pool_stats_get_doit(struct sk_buff *skb,
--
net/core/page_pool_user.c-184-
net/core/page_pool_user.c:185:	if (GENL_REQ_ATTR_CHECK(info, NETDEV_A_PAGE_POOL_STATS_INFO))
net/core/page_pool_user.c-186-		return -EINVAL;
--
net/core/page_pool_user.c=293=int netdev_nl_page_pool_get_doit(struct sk_buff *skb, struct genl_info *info)
--
net/core/page_pool_user.c-296-
net/core/page_pool_user.c:297:	if (GENL_REQ_ATTR_CHECK(info, NETDEV_A_PAGE_POOL_ID))
net/core/page_pool_user.c-298-		return -EINVAL;
--
net/devlink/dev.c=1133=int devlink_nl_flash_update_doit(struct sk_buff *skb, struct genl_info *info)
--
net/devlink/dev.c-1144-
net/devlink/dev.c:1145:	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_FLASH_UPDATE_FILE_NAME))
net/devlink/dev.c-1146-		return -EINVAL;
--
net/devlink/dev.c=1372=int devlink_nl_selftests_run_doit(struct sk_buff *skb, struct genl_info *info)
--
net/devlink/dev.c-1384-
net/devlink/dev.c:1385:	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_SELFTESTS))
net/devlink/dev.c-1386-		return -EINVAL;
--
net/devlink/dpipe.c=563=int devlink_nl_dpipe_entries_get_doit(struct sk_buff *skb,
--
net/devlink/dpipe.c-569-
net/devlink/dpipe.c:570:	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_DPIPE_TABLE_NAME))
net/devlink/dpipe.c-571-		return -EINVAL;
--
net/devlink/dpipe.c=747=int devlink_nl_dpipe_table_counters_set_doit(struct sk_buff *skb,
--
net/devlink/dpipe.c-753-
net/devlink/dpipe.c:754:	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_DPIPE_TABLE_NAME) ||
net/devlink/dpipe.c:755:	    GENL_REQ_ATTR_CHECK(info,
net/devlink/dpipe.c-756-				DEVLINK_ATTR_DPIPE_TABLE_COUNTERS_ENABLED))
--
net/devlink/param.c=493=devlink_param_type_get_from_info(struct genl_info *info,
--
net/devlink/param.c-495-{
net/devlink/param.c:496:	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_PARAM_TYPE))
net/devlink/param.c-497-		return -EINVAL;
--
net/devlink/param.c=555=devlink_param_get_from_info(struct xarray *params, struct genl_info *info)
--
net/devlink/param.c-558-
net/devlink/param.c:559:	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_PARAM_NAME))
net/devlink/param.c-560-		return NULL;
--
net/devlink/param.c=593=static int __devlink_nl_cmd_param_set_doit(struct devlink *devlink,
--
net/devlink/param.c-630-
net/devlink/param.c:631:	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_PARAM_VALUE_CMODE))
net/devlink/param.c-632-		return -EINVAL;
--
net/devlink/port.c=857=int devlink_nl_port_split_doit(struct sk_buff *skb, struct genl_info *info)
--
net/devlink/port.c-862-
net/devlink/port.c:863:	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_PORT_SPLIT_COUNT))
net/devlink/port.c-864-		return -EINVAL;
--
net/devlink/region.c=470=int devlink_nl_region_get_doit(struct sk_buff *skb, struct genl_info *info)
--
net/devlink/region.c-479-
net/devlink/region.c:480:	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_REGION_NAME))
net/devlink/region.c-481-		return -EINVAL;
--
net/devlink/region.c=589=int devlink_nl_region_del_doit(struct sk_buff *skb, struct genl_info *info)
--
net/devlink/region.c-598-
net/devlink/region.c:599:	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_REGION_NAME) ||
net/devlink/region.c:600:	    GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_REGION_SNAPSHOT_ID))
net/devlink/region.c-601-		return -EINVAL;
--
net/devlink/region.c=634=int devlink_nl_region_new_doit(struct sk_buff *skb, struct genl_info *info)
--
net/devlink/region.c-646-
net/devlink/region.c:647:	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_REGION_NAME)) {
net/devlink/region.c-648-		NL_SET_ERR_MSG(info->extack, "No region name provided");
--
net/devlink/resource.c=118=int devlink_nl_resource_set_doit(struct sk_buff *skb, struct genl_info *info)
--
net/devlink/resource.c-125-
net/devlink/resource.c:126:	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_RESOURCE_ID) ||
net/devlink/resource.c:127:	    GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_RESOURCE_SIZE))
net/devlink/resource.c-128-		return -EINVAL;
--
net/devlink/sb.c=416=int devlink_nl_sb_pool_set_doit(struct sk_buff *skb, struct genl_info *info)
--
net/devlink/sb.c-437-
net/devlink/sb.c:438:	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_SB_POOL_SIZE))
net/devlink/sb.c-439-		return -EINVAL;
--
net/devlink/sb.c=624=int devlink_nl_sb_port_pool_set_doit(struct sk_buff *skb,
--
net/devlink/sb.c-642-
net/devlink/sb.c:643:	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_SB_THRESHOLD))
net/devlink/sb.c-644-		return -EINVAL;
--
net/devlink/sb.c=864=int devlink_nl_sb_tc_pool_bind_set_doit(struct sk_buff *skb,
--
net/devlink/sb.c-893-
net/devlink/sb.c:894:	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_SB_THRESHOLD))
net/devlink/sb.c-895-		return -EINVAL;
--
net/ethtool/eeprom.c=153=static int eeprom_parse_request(struct ethnl_req_info *req_info,
--
net/ethtool/eeprom.c-159-
net/ethtool/eeprom.c:160:	if (GENL_REQ_ATTR_CHECK(info, ETHTOOL_A_MODULE_EEPROM_OFFSET) ||
net/ethtool/eeprom.c:161:	    GENL_REQ_ATTR_CHECK(info, ETHTOOL_A_MODULE_EEPROM_LENGTH) ||
net/ethtool/eeprom.c:162:	    GENL_REQ_ATTR_CHECK(info, ETHTOOL_A_MODULE_EEPROM_PAGE) ||
net/ethtool/eeprom.c:163:	    GENL_REQ_ATTR_CHECK(info, ETHTOOL_A_MODULE_EEPROM_I2C_ADDRESS))
net/ethtool/eeprom.c-164-		return -EINVAL;
--
net/ethtool/module.c=349=static int module_flash_fw(struct net_device *dev, struct nlattr **tb,
--
net/ethtool/module.c-355-
net/ethtool/module.c:356:	if (GENL_REQ_ATTR_CHECK(info, ETHTOOL_A_MODULE_FW_FLASH_FILE_NAME))
net/ethtool/module.c-357-		return -EINVAL;
--
net/ethtool/netlink.c=498=static int ethnl_default_doit(struct sk_buff *skb, struct genl_info *info)
--
net/ethtool/netlink.c-511-		return -EOPNOTSUPP;
net/ethtool/netlink.c:512:	if (GENL_REQ_ATTR_CHECK(info, ops->hdr_attr))
net/ethtool/netlink.c-513-		return -EINVAL;
--
net/ethtool/netlink.c=879=static int ethnl_default_set_doit(struct sk_buff *skb, struct genl_info *info)
--
net/ethtool/netlink.c-889-		return -EOPNOTSUPP;
net/ethtool/netlink.c:890:	if (GENL_REQ_ATTR_CHECK(info, ops->hdr_attr))
net/ethtool/netlink.c-891-		return -EINVAL;
--
net/ethtool/rss.c=1148=int ethnl_rss_delete_doit(struct sk_buff *skb, struct genl_info *info)
--
net/ethtool/rss.c-1157-
net/ethtool/rss.c:1158:	if (GENL_REQ_ATTR_CHECK(info, ETHTOOL_A_RSS_CONTEXT))
net/ethtool/rss.c-1159-		return -EINVAL;
--
net/handshake/netlink.c=90=int handshake_nl_accept_doit(struct sk_buff *skb, struct genl_info *info)
--
net/handshake/netlink.c-102-	err = -EINVAL;
net/handshake/netlink.c:103:	if (GENL_REQ_ATTR_CHECK(info, HANDSHAKE_A_ACCEPT_HANDLER_CLASS))
net/handshake/netlink.c-104-		goto out_status;
--
net/handshake/netlink.c=136=int handshake_nl_done_doit(struct sk_buff *skb, struct genl_info *info)
--
net/handshake/netlink.c-142-
net/handshake/netlink.c:143:	if (GENL_REQ_ATTR_CHECK(info, HANDSHAKE_A_DONE_SOCKFD))
net/handshake/netlink.c-144-		return -EINVAL;
--
net/mptcp/pm_kernel.c=981=int mptcp_pm_nl_add_addr_doit(struct sk_buff *skb, struct genl_info *info)
--
net/mptcp/pm_kernel.c-987-
net/mptcp/pm_kernel.c:988:	if (GENL_REQ_ATTR_CHECK(info, MPTCP_PM_ENDPOINT_ADDR))
net/mptcp/pm_kernel.c-989-		return -EINVAL;
--
net/mptcp/pm_kernel.c=1151=int mptcp_pm_nl_del_addr_doit(struct sk_buff *skb, struct genl_info *info)
--
net/mptcp/pm_kernel.c-1158-
net/mptcp/pm_kernel.c:1159:	if (GENL_REQ_ATTR_CHECK(info, MPTCP_PM_ENDPOINT_ADDR))
net/mptcp/pm_kernel.c-1160-		return -EINVAL;
--
net/mptcp/pm_netlink.c=178=int mptcp_pm_nl_get_addr_doit(struct sk_buff *skb, struct genl_info *info)
--
net/mptcp/pm_netlink.c-185-
net/mptcp/pm_netlink.c:186:	if (GENL_REQ_ATTR_CHECK(info, MPTCP_PM_ENDPOINT_ADDR))
net/mptcp/pm_netlink.c-187-		return -EINVAL;
--
net/mptcp/pm_netlink.c=261=static int mptcp_pm_set_flags(struct genl_info *info)
--
net/mptcp/pm_netlink.c-266-
net/mptcp/pm_netlink.c:267:	if (GENL_REQ_ATTR_CHECK(info, MPTCP_PM_ATTR_ADDR))
net/mptcp/pm_netlink.c-268-		return ret;
--
net/mptcp/pm_userspace.c=162=static struct mptcp_sock *mptcp_userspace_pm_get_sock(const struct genl_info *info)
--
net/mptcp/pm_userspace.c-166-
net/mptcp/pm_userspace.c:167:	if (GENL_REQ_ATTR_CHECK(info, MPTCP_PM_ATTR_TOKEN))
net/mptcp/pm_userspace.c-168-		return NULL;
--
net/mptcp/pm_userspace.c=187=int mptcp_pm_nl_announce_doit(struct sk_buff *skb, struct genl_info *info)
--
net/mptcp/pm_userspace.c-194-
net/mptcp/pm_userspace.c:195:	if (GENL_REQ_ATTR_CHECK(info, MPTCP_PM_ATTR_ADDR))
net/mptcp/pm_userspace.c-196-		return err;
--
net/mptcp/pm_userspace.c=297=int mptcp_pm_nl_remove_doit(struct sk_buff *skb, struct genl_info *info)
--
net/mptcp/pm_userspace.c-305-
net/mptcp/pm_userspace.c:306:	if (GENL_REQ_ATTR_CHECK(info, MPTCP_PM_ATTR_LOC_ID))
net/mptcp/pm_userspace.c-307-		return err;
--
net/mptcp/pm_userspace.c=357=int mptcp_pm_nl_subflow_create_doit(struct sk_buff *skb, struct genl_info *info)
--
net/mptcp/pm_userspace.c-366-
net/mptcp/pm_userspace.c:367:	if (GENL_REQ_ATTR_CHECK(info, MPTCP_PM_ATTR_ADDR) ||
net/mptcp/pm_userspace.c:368:	    GENL_REQ_ATTR_CHECK(info, MPTCP_PM_ATTR_ADDR_REMOTE))
net/mptcp/pm_userspace.c-369-		return err;
--
net/mptcp/pm_userspace.c=476=int mptcp_pm_nl_subflow_destroy_doit(struct sk_buff *skb, struct genl_info *info)
--
net/mptcp/pm_userspace.c-484-
net/mptcp/pm_userspace.c:485:	if (GENL_REQ_ATTR_CHECK(info, MPTCP_PM_ATTR_ADDR) ||
net/mptcp/pm_userspace.c:486:	    GENL_REQ_ATTR_CHECK(info, MPTCP_PM_ATTR_ADDR_REMOTE))
net/mptcp/pm_userspace.c-487-		return err;
--
net/mptcp/pm_userspace.c=555=int mptcp_userspace_pm_set_flags(struct mptcp_pm_addr_entry *local,
--
net/mptcp/pm_userspace.c-565-
net/mptcp/pm_userspace.c:566:	if (GENL_REQ_ATTR_CHECK(info, MPTCP_PM_ATTR_ADDR_REMOTE))
net/mptcp/pm_userspace.c-567-		return ret;
--
net/psp/psp_nl.c=68=int psp_device_get_locked(const struct genl_split_ops *ops,
--
net/psp/psp_nl.c-70-{
net/psp/psp_nl.c:71:	if (GENL_REQ_ATTR_CHECK(info, PSP_A_DEV_ID))
net/psp/psp_nl.c-72-		return -EINVAL;
--
net/psp/psp_nl.c=282=int psp_assoc_device_get_locked(const struct genl_split_ops *ops,
--
net/psp/psp_nl.c-289-
net/psp/psp_nl.c:290:	if (GENL_REQ_ATTR_CHECK(info, PSP_A_ASSOC_SOCK_FD))
net/psp/psp_nl.c-291-		return -EINVAL;
--
net/psp/psp_nl.c-319-
net/psp/psp_nl.c:320:	if (!psd && GENL_REQ_ATTR_CHECK(info, PSP_A_ASSOC_DEV_ID)) {
net/psp/psp_nl.c-321-		err = -EINVAL;
--
net/psp/psp_nl.c=413=int psp_nl_rx_assoc_doit(struct sk_buff *skb, struct genl_info *info)
--
net/psp/psp_nl.c-422-
net/psp/psp_nl.c:423:	if (GENL_REQ_ATTR_CHECK(info, PSP_A_ASSOC_VERSION))
net/psp/psp_nl.c-424-		return -EINVAL;
--
net/psp/psp_nl.c=469=int psp_nl_tx_assoc_doit(struct sk_buff *skb, struct genl_info *info)
--
net/psp/psp_nl.c-478-
net/psp/psp_nl.c:479:	if (GENL_REQ_ATTR_CHECK(info, PSP_A_ASSOC_VERSION) ||
net/psp/psp_nl.c:480:	    GENL_REQ_ATTR_CHECK(info, PSP_A_ASSOC_TX_KEY))
net/psp/psp_nl.c-481-		return -EINVAL;
--
net/shaper/shaper.c=176=static int net_shaper_ctx_setup(const struct genl_info *info, int type,
--
net/shaper/shaper.c-182-
net/shaper/shaper.c:183:	if (GENL_REQ_ATTR_CHECK(info, type))
net/shaper/shaper.c-184-		return -EINVAL;
--
net/shaper/shaper.c=207=static int net_shaper_ctx_setup_lock(const struct genl_info *info, int type,
--
net/shaper/shaper.c-213-
net/shaper/shaper.c:214:	if (GENL_REQ_ATTR_CHECK(info, type))
net/shaper/shaper.c-215-		return -EINVAL;
--
net/shaper/shaper.c=777=int net_shaper_nl_get_doit(struct sk_buff *skb, struct genl_info *info)
--
net/shaper/shaper.c-784-
net/shaper/shaper.c:785:	if (GENL_REQ_ATTR_CHECK(info, NET_SHAPER_A_HANDLE))
net/shaper/shaper.c-786-		return -EINVAL;
--
net/shaper/shaper.c=1108=int net_shaper_nl_delete_doit(struct sk_buff *skb, struct genl_info *info)
--
net/shaper/shaper.c-1115-
net/shaper/shaper.c:1116:	if (GENL_REQ_ATTR_CHECK(info, NET_SHAPER_A_HANDLE))
net/shaper/shaper.c-1117-		return -EINVAL;
--
net/shaper/shaper.c=1170=int net_shaper_nl_group_doit(struct sk_buff *skb, struct genl_info *info)
--
net/shaper/shaper.c-1179-
net/shaper/shaper.c:1180:	if (GENL_REQ_ATTR_CHECK(info, NET_SHAPER_A_LEAVES))
net/shaper/shaper.c-1181-		return -EINVAL;
--
net/shaper/shaper.c=1315=int net_shaper_nl_cap_get_doit(struct sk_buff *skb, struct genl_info *info)
--
net/shaper/shaper.c-1323-
net/shaper/shaper.c:1324:	if (GENL_REQ_ATTR_CHECK(info, NET_SHAPER_A_CAPS_SCOPE))
net/shaper/shaper.c-1325-		return -EINVAL;
]

gemini-3.1-pro-preview

							input: 73534
							output: 41
							thoughts: 893
						

**Analyzing the NBD Connection Bug**

Okay, let's break this down. First, I noticed that `GENL_REQ_ATTR_CHECK` in `include/net/genetlink.h` is defined such that it checks if the provided attribute in the generic netlink message is present. Specifically, if `info->attrs` is NULL or if a specific attribute, `info->attrs[attr]`, is NULL, it returns true, indicating an error.

I saw that with `NBD_CMD_RECONFIGURE`, while `nla_len` is 112, the actual message is only 44 bytes. This means `nla_for_each_attr` will terminate immediately. As a result, `info->attrs` will be empty. This in turn causes `GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)` to return true, leading `nbd_genl_reconfigure` to simply return `-EINVAL`. This means the `reconfigure` command is a red herring. It never does anything meaningful. And the `r[3]` values are never used. 

This means that `r[3]` is completely irrelevant, and the bug *must* be in `NBD_CMD_CONNECT`! Let's examine that again. The reproducer's sending `NBD_CMD_CONNECT` with `NBD_ATTR_SOCKETS`, which contains *two* nested `NBD_SOCK_ITEM`s. Both of these items include the *same* file descriptor, `r[2]`.

So, `nbd_add_socket` is called twice with the same file descriptor. Let's trace it.
First call:
`sock = nbd_get_socket(nbd, arg, &err);` -> gets `struct socket *sock1`.
`nsock1 = kzalloc_obj(*nsock1);`
`nsock1->sock = sock1;`
`config->socks[0] = nsock1;`
`config->num_connections = 1;`

Second call:
`sock = nbd_get_socket(nbd, arg, &err);` -> gets the SAME `struct socket *sock1`.
`nsock2 = kzalloc_obj(*nsock2);`
`nsock2->sock = sock1;`
`config->socks[1] = nsock2;`
`config->num_connections = 2;`

Then, `nbd_genl_connect` calls `nbd_start_device`. `nbd_start_device` iterates based on `num_connections` (which is 2).
For `i = 0`:
`args1 = kzalloc_obj(*args1);`
`args1->nsock = config->socks[0];` (which is `nsock1`)
`queue_work(nbd->recv_workq, &args1->work);`

For `i = 1`:
`args2 = kzalloc_obj(*args2);`
`args2->nsock = config->socks[1];` (which is `nsock2`)
`queue_work(nbd->recv_workq, &args2->work);`

This means *two* `recv_work` threads are queued. Both execute `recv_work`, and call `nbd_read_reply(nbd, nsock->sock, &reply)`. Since `nsock1->sock` and `nsock2->sock` are the SAME `struct socket *`, both threads will call `sock_xmit` on the same socket *concurrently*. The question then is, is `sock_xmit` safe for concurrent calls on the same socket? I need to check `sock_xmit`.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:sock_xmit]

map[SourceCode: 595:	/*
 596:	 *  Send or receive packet. Return a positive value on success and
 597:	 *  negtive value on failure, and never return 0.
 598:	 */
 599:	static int sock_xmit(struct nbd_device *nbd, int index, int send,
 600:			     struct iov_iter *iter, int msg_flags, int *sent)
 601:	{
 602:		struct nbd_config *config = nbd->config;
 603:		struct socket *sock = config->socks[index]->sock;
 604:	
 605:		return __sock_xmit(nbd, sock, send, iter, msg_flags, sent);
 606:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 75536
							output: 42
							thoughts: 11
						

Okay, here's my attempt at summarizing that thought process, keeping in mind I'm speaking to a fellow expert:

**Diving into `__sock_xmit`**

Alright, time to dig in. I'm going to start by getting a handle on `__sock_xmit`. That's where the rubber meets the road, so to speak, in the kernel's network stack. I need to refresh my memory on the ins and outs of this function – what it does, how it's called, and most importantly, where the potential bottlenecks or areas of interest for whatever problem I'm currently tracking might lie. I'm thinking about the various code paths it takes, the locks it acquires, and the interaction with hardware. Let's see what we can find.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:__sock_xmit]

map[SourceCode: 551:	static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
 552:			       struct iov_iter *iter, int msg_flags, int *sent)
 553:	{
 554:		int result;
 555:		struct msghdr msg = {} ;
 556:		unsigned int noreclaim_flag;
 557:	
 558:		if (unlikely(!sock)) {
 559:			dev_err_ratelimited(disk_to_dev(nbd->disk),
 560:				"Attempted %s on closed socket in sock_xmit\n",
 561:				(send ? "send" : "recv"));
 562:			return -EINVAL;
 563:		}
 564:	
 565:		msg.msg_iter = *iter;
 566:	
 567:		noreclaim_flag = memalloc_noreclaim_save();
 568:	
 569:		scoped_with_kernel_creds() {
 570:			do {
 571:				sock->sk->sk_allocation = GFP_NOIO | __GFP_MEMALLOC;
 572:				sock->sk->sk_use_task_frag = false;
 573:				msg.msg_flags = msg_flags | MSG_NOSIGNAL;
 574:	
 575:				if (send)
 576:					result = sock_sendmsg(sock, &msg);
 577:				else
 578:					result = sock_recvmsg(sock, &msg, msg.msg_flags);
 579:	
 580:				if (result <= 0) {
 581:					if (result == 0)
 582:						result = -EPIPE; /* short read */
 583:					break;
 584:				}
 585:				if (sent)
 586:					*sent += result;
 587:			} while (msg_data_left(&msg));
 588:		}
 589:	
 590:		memalloc_noreclaim_restore(noreclaim_flag);
 591:	
 592:		return result;
 593:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 76393
							output: 43
							thoughts: 470
						

**Analyzing the Race Condition in Concurrent Socket Reads**

Okay, so I'm looking at this code and I see that `sock_recvmsg` is being called concurrently on the *same* socket by two different threads. My initial thought is: is `sock_recvmsg` thread-safe? I know for TCP sockets, the `tcp_recvmsg` implementation uses `lock_sock(sk)`, which should serialize access. Similarly, for UNIX domain sockets, `unix_stream_recvmsg` utilizes `unix_state_lock(sk)` or something equivalent to manage concurrency.

The reproducer here is using `socketpair(AF_UNIX, SOCK_STREAM, 0)`. That means it's a UNIX domain socket. So, if two threads are calling `unix_stream_recvmsg` concurrently, they should be serializing on the socket lock, which would make it thread safe.

But then I had a realization. What if the socket is closed before `unix_stream_recvmsg` can do its job? The syzkaller program exits, and at that point the socket is closed. Both threads then wake up from `unix_stream_recvmsg` receiving 0 (EOF) and return.

Then `__sock_xmit` will return `-EPIPE` to both threads. This causes `nbd_read_reply` to also return `-EPIPE`. This breaks the `recv_work` loop. Then both threads call `nbd_mark_nsock_dead(nbd, nsock, 1)`. Because they are different `nsock`s (`nsock1` and `nsock2`), they're going to take different `tx_lock`s.

But then, the threads *both* call `kernel_sock_shutdown(nsock->sock, SHUT_RDWR)`. And here is where it gets interesting: because they both have the *same* socket, `kernel_sock_shutdown` gets called twice. That's not ideal.

Both threads then decrement `nbd->config->live_connections` with `atomic_dec_return()`. One thread brings it to 1, the other brings it to 0. Both threads then continue. They *both* decrement `config->recv_threads`, wake up `config->recv_wq`, call `nbd_config_put(nbd)`, and `kfree(args)`.

Here's the problem: `nbd_config_put` is getting called TWICE! I need to re-examine that `nbd_config_put` function to understand what's happening. This looks like a classic double-free or reference counting issue. This is likely the root of the bug.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_config_put]

map[SourceCode:1432:	static void nbd_config_put(struct nbd_device *nbd)
1433:	{
1434:		if (refcount_dec_and_mutex_lock(&nbd->config_refs,
1435:						&nbd->config_lock)) {
1436:			struct nbd_config *config = nbd->config;
1437:			nbd_dev_dbg_close(nbd);
1438:			invalidate_disk(nbd->disk);
1439:			if (nbd->config->bytesize)
1440:				kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
1441:			if (test_and_clear_bit(NBD_RT_HAS_PID_FILE,
1442:					       &config->runtime_flags))
1443:				device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
1444:			nbd->pid = 0;
1445:			if (test_and_clear_bit(NBD_RT_HAS_BACKEND_FILE,
1446:					       &config->runtime_flags)) {
1447:				device_remove_file(disk_to_dev(nbd->disk), &backend_attr);
1448:				kfree(nbd->backend);
1449:				nbd->backend = NULL;
1450:			}
1451:			nbd_clear_sock(nbd);
1452:			if (config->num_connections) {
1453:				int i;
1454:				for (i = 0; i < config->num_connections; i++) {
1455:					sockfd_put(config->socks[i]->sock);
1456:					kfree(config->socks[i]);
1457:				}
1458:				kfree(config->socks);
1459:			}
1460:			kfree(nbd->config);
1461:			nbd->config = NULL;
1462:	
1463:			nbd->tag_set.timeout = 0;
1464:	
1465:			mutex_unlock(&nbd->config_lock);
1466:			nbd_put(nbd);
1467:			module_put(THIS_MODULE);
1468:		}
1469:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 78151
							output: 21
							thoughts: 444
						

**Analyzing Socket Lifecycle in NBD Configuration**

Okay, let me think this through. `nbd_config_put` calls `sockfd_put(config->socks[i]->sock)`. But, hold on... `config->socks[0]->sock` and `config->socks[1]->sock` are actually the *same* socket! So `sockfd_put` is called twice for the *identical* socket. Is that going to cause a problem?

Let's trace back. `nbd_add_socket` was called twice, which in turn calls `nbd_get_socket` twice. `nbd_get_socket`, of course, calls `sockfd_lookup` twice. Crucially, `sockfd_lookup` increments the file reference count. So, the count went up by two! Then `nbd_config_put` calls `sockfd_put` twice. Which decrements the reference count twice. Ah, it perfectly cancels out! Two increments, two decrements. No apparent use-after-free issue here, that seems safe.

But, wait...what if the `NBD_CMD_RECONFIGURE` command *does* something unexpected? Let's re-examine that part. The reproducer's sending `NBD_CMD_RECONFIGURE` with `NBD_ATTR_SOCKETS` and `r[3]`. Okay, and the `ANYBLOB` data in `NBD_CMD_RECONFIGURE` looks like this: `01 00 26 bd 70 00 fe db df 25 03 00 40 00 08 00 01 00 00 00 00 00 10 00 07 80 0c 00 01 80 08 00 01 00`. Let's re-parse that.

`01 00 26 bd`... is that...?  Oh, *no!* `01` is actually `NBD_CMD_CONNECT`! That's not `NBD_CMD_RECONFIGURE` at all! This is a completely different command! I'd better double check the value for `NBD_CMD_RECONFIGURE`. This could be important.

map[Expression:NBD_CMD_RECONFIGURE]

map[Output:drivers/block/nbd.c=2449=static const struct genl_small_ops nbd_connect_genl_ops[] = {
--
drivers/block/nbd.c-2460-	{
drivers/block/nbd.c:2461:		.cmd	= NBD_CMD_RECONFIGURE,
drivers/block/nbd.c-2462-		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
--
include/uapi/linux/nbd-netlink.h=89=enum {
--
include/uapi/linux/nbd-netlink.h-92-	NBD_CMD_DISCONNECT,
include/uapi/linux/nbd-netlink.h:93:	NBD_CMD_RECONFIGURE,
include/uapi/linux/nbd-netlink.h-94-	NBD_CMD_LINK_DEAD,
]

gemini-3.1-pro-preview

							input: 79364
							output: 41
							thoughts: 1286
						

**Analyzing the NBD Connection Vulnerability**

Okay, let's break this down. First, `NBD_CMD_UNSPEC` is zero, got it. `NBD_CMD_CONNECT` is one, `NBD_CMD_DISCONNECT` two, and `NBD_CMD_RECONFIGURE` is three. But that ANYBLOB in the second `sendmsg` starts with `01 00 26 bd`, which indicates `NBD_CMD_CONNECT` again, even though syzkaller annotated it as a reconfigure. Why? Maybe it's serializing `genlmsghdr_t[NBD_CMD_RECONFIGURE]` as `01 00`? No, because `NBD_CMD_RECONFIGURE` is 3. Hmmm... If it's `01 00`, it *is* `NBD_CMD_CONNECT`.

Let's revisit `nbd_genl_connect`. If it's called twice for the same index, the first `NBD_CMD_CONNECT` has index 32767. Let's parse the second ANYBLOB to confirm. `01 00 26 bd` confirms `cmd=1` (CONNECT). `70 00 fe db` indicates `len=112, type=0xdbfe`. Now, that's weird. If `nla_len` is 112, but the message is only 44 bytes, `nla_ok` should fail because there isn't enough data. The second `NBD_CMD_CONNECT` *should* fail with `-EINVAL`, effectively doing nothing. It would be ignored.

However, maybe the *first* `NBD_CMD_CONNECT` is the culprit? Let's analyze it, and its ANYBLOB data: `01 00 ff ff ff ff 00 00 00 00 01 00 00 00 0c 00 05 00 6c 01 00 00 00 00 00 00 0c 00 02 00 ff 7f 00 00 00 00 00 00 40 00 07 80 0c 00 01 80 08 00 01 00`. Parsing it: `01 00 ff ff` means `cmd=1, version=0, reserved=0xffff`. And `ff ff 00 00` makes `len=65535, type=0`.

Here's the problem: `nla_len` is 65535! Is `nla_ok` really failing? The remaining bytes are (108 total message length - 20 header) = 88. 65535 is *not* less than or equal to 88, so `nla_ok` *should* fail. Which means `nla_for_each_attr` would break immediately. Thus `info->attrs` would be empty. Then `nbd_genl_connect` is called...

```c
	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SOCKETS)) {
		pr_err("must specify at least one socket\n");
		return -EINVAL;
	}
```

If `info->attrs` is empty, `GENL_REQ_ATTR_CHECK` returns true. Therefore, `nbd_genl_connect` returns `-EINVAL`. Both calls to `sendmsg` would fail. Then nothing changes in the kernel, so why the crash? I am missing something.

Re-reading the ANYBLOB... The ANYBLOB is:
`01 00 ff ff` (genlmsghdr)
`ff ff 00 00` (nlattr: len=65535, type=0)

Syzkaller generated this! Maybe `nla_ok` is *not* failing? I need to double-check `nla_ok` and how it handles these lengths. This is a very interesting case.

map[ContextFile:include/net/netlink.h IncludeLines:true Name:nla_ok]

map[SourceCode:1299:	/**
1300:	 * nla_ok - check if the netlink attribute fits into the remaining bytes
1301:	 * @nla: netlink attribute
1302:	 * @remaining: number of bytes remaining in attribute stream
1303:	 */
1304:	static inline int nla_ok(const struct nlattr *nla, int remaining)
1305:	{
1306:		return remaining >= (int) sizeof(*nla) &&
1307:		       nla->nla_len >= sizeof(*nla) &&
1308:		       nla->nla_len <= remaining;
1309:	}
 SourceFile:include/net/netlink.h]

gemini-3.1-pro-preview

							input: 81841
							output: 44
							thoughts: 2570
						

**Deep Dive into the NBD Kernel Module Vulnerability**

Okay, let's break this down step by step. I'm starting by confirming a crucial point. Yes, the code checks `nla->nla_len <= remaining`, and it *should* break out of the `nla_for_each_attr` loop if `nla_len` is greater than `remaining`. But then, there's a thought: what if the large length *isn't* an attribute directly? Could it be part of some larger data structure?

Aha! The `ANYBLOB` is actually part of `vec[0].addr`, which is the beginning of the `iovec` buffer. Time to examine that `iovec` closely. The code here is crucial!

Looking at the C code provided, it seems like the `ANYBLOB` contains more than I initially thought. Examining the byte stream, I find that the first bytes aren't a standalone attribute. Instead, they contain the `nlmsg_len`, `nlmsg_flags`, `nlmsg_seq`, `nlmsg_pid`, and `genlmsghdr`. This means a single, large "blob" that appears to be nested within a larger Netlink message. Parsing it, I'm able to identify all of the Netlink attributes in a valid way, including the `NBD_ATTR_SIZE_BYTES`, `NBD_ATTR_INDEX`, and nested `NBD_ATTR_SOCKETS` with `NBD_SOCK_ITEM` and `NBD_SOCK_FD`.

Yes! This is all valid Netlink. So, `nbd_genl_connect` *is* called, and it *does* correctly parse these attributes, which is confirmed by its ability to identify the nested attributes. I also see that it calls `nbd_add_socket` twice with the same file descriptor `r[2]`, which is the UNIX domain socket. This seems odd, but it is legal based on the parsing.

Let's shift focus to the second `sendmsg`, which is the `NBD_CMD_RECONFIGURE`. I'll analyze the `ANYBLOB` again. Parsing this second `ANYBLOB` confirms it is valid and that it reconfigures index 0.

Here's the key: the first `sendmsg` connects index 32767. The second `sendmsg` reconfigures index 0. If it reconfigures index 0, it has to look up index 0 in `nbd_index_idr`. The reproducer only creates index 32767. So, the `nbd` associated with index 0 won't exist! This causes the `nbd_genl_reconfigure` to fail with `-EINVAL`, as the device isn't found. This means the second `sendmsg` doesn't *do* anything.

The bug is in the first `sendmsg`! It calls `nbd_add_socket` twice with the same socket file descriptor. This results in the same socket being added twice to `config->socks`. This results in two queued `recv_work` threads, both trying to read from the same socket. This is a UNIX domain socket. This means that concurrent access to the same socket can occur because `unix_stream_recvmsg` is called concurrently by two different threads. Fortunately, my understanding is that the `unix_stream_recvmsg` uses `mutex_lock(&u->iolock)` so it is thread safe.

map[ContextFile:net/unix/af_unix.c IncludeLines:true Name:unix_stream_recvmsg]

map[SourceCode:3151:	static int unix_stream_recvmsg(struct socket *sock, struct msghdr *msg,
3152:				       size_t size, int flags)
3153:	{
3154:		struct unix_stream_read_state state = {
3155:			.recv_actor = unix_stream_read_actor,
3156:			.socket = sock,
3157:			.msg = msg,
3158:			.size = size,
3159:			.flags = flags
3160:		};
3161:	
3162:	#ifdef CONFIG_BPF_SYSCALL
3163:		struct sock *sk = sock->sk;
3164:		const struct proto *prot = READ_ONCE(sk->sk_prot);
3165:	
3166:		if (prot != &unix_stream_proto)
3167:			return prot->recvmsg(sk, msg, size, flags);
3168:	#endif
3169:		return unix_stream_read_generic(&state, true);
3170:	}
 SourceFile:net/unix/af_unix.c]

gemini-3.1-pro-preview

							input: 85537
							output: 45
							thoughts: 13
						

Okay, here's my take on those thoughts, tailored for an expert audience, and delivered as a first-person summary:

**Diving into `unix_stream_read_generic`**

Alright, time to dig in. Let's see what we've got here. My immediate focus is on that `unix_stream_read_generic` function. Gotta understand exactly how it's handling the read operation on Unix domain sockets. I'm already anticipating some of the nuances – potential blocking behavior, interrupt handling, error conditions… the usual suspects when dealing with low-level I/O. I'm especially interested in how it's dealing with partial reads and any buffering strategies implemented. Is there any use of `recv` or `read` system calls directly? Any clever tricks to improve throughput or minimize latency? Gotta get my head around the core logic first.

map[ContextFile:net/unix/af_unix.c IncludeLines:true Name:unix_stream_read_generic]

map[SourceCode:2913:	static int unix_stream_read_generic(struct unix_stream_read_state *state,
2914:					    bool freezable)
2915:	{
2916:		int noblock = state->flags & MSG_DONTWAIT;
2917:		struct socket *sock = state->socket;
2918:		struct msghdr *msg = state->msg;
2919:		struct sock *sk = sock->sk;
2920:		size_t size = state->size;
2921:		int flags = state->flags;
2922:		bool check_creds = false;
2923:		struct scm_cookie scm;
2924:		unsigned int last_len;
2925:		struct unix_sock *u;
2926:		int copied = 0;
2927:		int err = 0;
2928:		long timeo;
2929:		int target;
2930:		int skip;
2931:	
2932:		if (unlikely(READ_ONCE(sk->sk_state) != TCP_ESTABLISHED)) {
2933:			err = -EINVAL;
2934:			goto out;
2935:		}
2936:	
2937:		if (unlikely(flags & MSG_OOB)) {
2938:			err = -EOPNOTSUPP;
2939:	#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
2940:			err = unix_stream_recv_urg(state);
2941:	#endif
2942:			goto out;
2943:		}
2944:	
2945:		target = sock_rcvlowat(sk, flags & MSG_WAITALL, size);
2946:		timeo = sock_rcvtimeo(sk, noblock);
2947:	
2948:		memset(&scm, 0, sizeof(scm));
2949:	
2950:		u = unix_sk(sk);
2951:	
2952:	redo:
2953:		/* Lock the socket to prevent queue disordering
2954:		 * while sleeps in memcpy_tomsg
2955:		 */
2956:		mutex_lock(&u->iolock);
2957:	
2958:		skip = max(sk_peek_offset(sk, flags), 0);
2959:	
2960:		do {
2961:			struct sk_buff *skb, *last;
2962:			int chunk;
2963:	
2964:			unix_state_lock(sk);
2965:			if (sock_flag(sk, SOCK_DEAD)) {
2966:				err = -ECONNRESET;
2967:				goto unlock;
2968:			}
2969:			last = skb = skb_peek(&sk->sk_receive_queue);
2970:			last_len = last ? last->len : 0;
2971:	
2972:	again:
2973:	#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
2974:			if (skb) {
2975:				skb = manage_oob(skb, sk, flags, copied);
2976:				if (!skb && copied) {
2977:					unix_state_unlock(sk);
2978:					break;
2979:				}
2980:			}
2981:	#endif
2982:			if (skb == NULL) {
2983:				if (copied >= target)
2984:					goto unlock;
2985:	
2986:				/*
2987:				 *	POSIX 1003.1g mandates this order.
2988:				 */
2989:	
2990:				err = sock_error(sk);
2991:				if (err)
2992:					goto unlock;
2993:				if (sk->sk_shutdown & RCV_SHUTDOWN)
2994:					goto unlock;
2995:	
2996:				unix_state_unlock(sk);
2997:				if (!timeo) {
2998:					err = -EAGAIN;
2999:					break;
3000:				}
3001:	
3002:				mutex_unlock(&u->iolock);
3003:	
3004:				timeo = unix_stream_data_wait(sk, timeo, last,
3005:							      last_len, freezable);
3006:	
3007:				if (signal_pending(current)) {
3008:					err = sock_intr_errno(timeo);
3009:					scm_destroy(&scm);
3010:					goto out;
3011:				}
3012:	
3013:				goto redo;
3014:	unlock:
3015:				unix_state_unlock(sk);
3016:				break;
3017:			}
3018:	
3019:			while (skip >= unix_skb_len(skb)) {
3020:				skip -= unix_skb_len(skb);
3021:				last = skb;
3022:				last_len = skb->len;
3023:				skb = skb_peek_next(skb, &sk->sk_receive_queue);
3024:				if (!skb)
3025:					goto again;
3026:			}
3027:	
3028:			unix_state_unlock(sk);
3029:	
3030:			if (check_creds) {
3031:				/* Never glue messages from different writers */
3032:				if (!unix_skb_scm_eq(skb, &scm))
3033:					break;
3034:			} else if (unix_may_passcred(sk)) {
3035:				/* Copy credentials */
3036:				unix_skb_to_scm(skb, &scm);
3037:				check_creds = true;
3038:			}
3039:	
3040:			/* Copy address just once */
3041:			if (msg && msg->msg_name) {
3042:				DECLARE_SOCKADDR(struct sockaddr_un *, sunaddr, msg->msg_name);
3043:	
3044:				unix_copy_addr(msg, skb->sk);
3045:				BPF_CGROUP_RUN_PROG_UNIX_RECVMSG_LOCK(sk, msg->msg_name,
3046:								      &msg->msg_namelen);
3047:	
3048:				sunaddr = NULL;
3049:			}
3050:	
3051:			chunk = min_t(unsigned int, unix_skb_len(skb) - skip, size);
3052:			chunk = state->recv_actor(skb, skip, chunk, state);
3053:			if (chunk < 0) {
3054:				if (copied == 0)
3055:					copied = -EFAULT;
3056:				break;
3057:			}
3058:			copied += chunk;
3059:			size -= chunk;
3060:	
3061:			/* Mark read part of skb as used */
3062:			if (!(flags & MSG_PEEK)) {
3063:				UNIXCB(skb).consumed += chunk;
3064:	
3065:				sk_peek_offset_bwd(sk, chunk);
3066:	
3067:				if (UNIXCB(skb).fp) {
3068:					scm_stat_del(sk, skb);
3069:					unix_detach_fds(&scm, skb);
3070:				}
3071:	
3072:				if (unix_skb_len(skb))
3073:					break;
3074:	
3075:				spin_lock(&sk->sk_receive_queue.lock);
3076:				WRITE_ONCE(u->inq_len, u->inq_len - skb->len);
3077:				__skb_unlink(skb, &sk->sk_receive_queue);
3078:				spin_unlock(&sk->sk_receive_queue.lock);
3079:	
3080:				consume_skb(skb);
3081:	
3082:				if (scm.fp)
3083:					break;
3084:			} else {
3085:				/* It is questionable, see note in unix_dgram_recvmsg.
3086:				 */
3087:				if (UNIXCB(skb).fp)
3088:					unix_peek_fds(&scm, skb);
3089:	
3090:				sk_peek_offset_fwd(sk, chunk);
3091:	
3092:				if (UNIXCB(skb).fp)
3093:					break;
3094:	
3095:				skip = 0;
3096:				last = skb;
3097:				last_len = skb->len;
3098:				unix_state_lock(sk);
3099:				skb = skb_peek_next(skb, &sk->sk_receive_queue);
3100:				if (skb)
3101:					goto again;
3102:				unix_state_unlock(sk);
3103:				break;
3104:			}
3105:		} while (size);
3106:	
3107:		mutex_unlock(&u->iolock);
3108:		if (msg) {
3109:			bool do_cmsg = READ_ONCE(u->recvmsg_inq);
3110:	
3111:			scm_recv_unix(sock, msg, &scm, flags);
3112:	
3113:			if ((do_cmsg | msg->msg_get_inq) && (copied ?: err) >= 0) {
3114:				msg->msg_inq = READ_ONCE(u->inq_len);
3115:				if (do_cmsg)
3116:					put_cmsg(msg, SOL_SOCKET, SCM_INQ,
3117:						 sizeof(msg->msg_inq), &msg->msg_inq);
3118:			}
3119:		} else {
3120:			scm_destroy(&scm);
3121:		}
3122:	out:
3123:		return copied ? : err;
3124:	}
 SourceFile:net/unix/af_unix.c]

gemini-3.1-pro-preview

							input: 88733
							output: 43
							thoughts: 1834
						

**Analyzing a Potential Race Condition in the NBD Kernel Module**

Okay, let's break this down. I'm seeing a possible race condition related to socket handling and config management in the NBD kernel module.  The key problem I'm concerned about is a use-after-free scenario, potentially triggered by the interaction between the `recv_work` threads, `nbd_config_put`, and the socket array `config->socks`.

First, I observe that `unix_stream_read_generic` serializes access to the socket with `mutex_lock(&u->iolock)`. This suggests the `recv_work` threads will contend on `u->iolock`, but this seems expected.  When the socket closes, both threads will wake up, see `RCV_SHUTDOWN`, and return 0. After that, `nbd_mark_nsock_dead` is called.

The concern comes because `nbd_mark_nsock_dead` acquires `nsock->tx_lock`. So, this seems safe so far.  Then it calls `kernel_sock_shutdown`, decrements `live_connections` and `recv_threads`.  After that, `nbd_config_put` is called in both threads.  `nbd_config_put` frees `config->socks[i]`. But there is an important detail:

`nbd_config_put` uses `refcount_dec_and_mutex_lock(&nbd->config_refs, &nbd->config_lock)`.  Only ONE thread will enter the `if` block here because it performs an atomic decrement. The other thread will just return. The thread that enters the `if` block will free `config->socks`. Here's where it gets interesting: the other thread is still running `recv_work`, calling `nbd_config_put` *after* the first thread frees `config->socks`.

The crucial question is about the reference count (`config_refs`). `nbd_start_device` increments it twice and `nbd_genl_connect` once, making it 3. When `nbd_genl_connect` finishes, it calls `nbd_config_put`, decreasing the refcount to 2. The two `recv_work` threads then call `nbd_config_put`, decrementing the refcount to 1 and then to 0. The second thread will decrement to 0 and thus enter the `if` block, so it will free `nbd->config`.  *This seems perfectly safe.*

Now, I analyze `nsock`.  `recv_work` uses `nsock = args->nsock;`, which points to `config->socks[i]`. So `nsock` is safe because it is only freed when the LAST reference is dropped, that is, when the thread enters the `if` block in `nbd_config_put`.  It is not freed earlier.

I check that calls to `nbd_mark_nsock_dead` and `nbd_clear_sock` should be safe.

Finally, I remember the "SYZFAIL: failed to recv rpc" error and panic. I then go back to the code and look at `nbd_add_socket`. I note that `krealloc` does not initialize the new memory. But, this is *safe*.

I then observe that `blk_mq_update_nr_hw_queues` is called with a `num_connections` of 2.  However, I realize `nbd_add_socket` is called TWICE.  Therefore, the SAME socket is added twice! This means that `cmd->index` can be 0 or 1, and since both refer to the SAME socket, `nbd_send_cmd` will be called concurrently on the SAME socket!  This is a serious problem.  This explains the crash. I need to verify that `nbd_send_cmd` is safe to call concurrently or I need to redesign this code.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_send_cmd]

map[SourceCode: 641:	/*
 642:	 * Returns BLK_STS_RESOURCE if the caller should retry after a delay.
 643:	 * Returns BLK_STS_IOERR if sending failed.
 644:	 */
 645:	static blk_status_t nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd,
 646:					 int index)
 647:	{
 648:		struct request *req = blk_mq_rq_from_pdu(cmd);
 649:		struct nbd_config *config = nbd->config;
 650:		struct nbd_sock *nsock = config->socks[index];
 651:		int result;
 652:		struct nbd_request request = {.magic = htonl(NBD_REQUEST_MAGIC)};
 653:		struct kvec iov = {.iov_base = &request, .iov_len = sizeof(request)};
 654:		struct iov_iter from;
 655:		struct bio *bio;
 656:		u64 handle;
 657:		u32 type;
 658:		u32 nbd_cmd_flags = 0;
 659:		int sent = nsock->sent, skip = 0;
 660:	
 661:		lockdep_assert_held(&cmd->lock);
 662:		lockdep_assert_held(&nsock->tx_lock);
 663:	
 664:		iov_iter_kvec(&from, ITER_SOURCE, &iov, 1, sizeof(request));
 665:	
 666:		type = req_to_nbd_cmd_type(req);
 667:		if (type == U32_MAX)
 668:			return BLK_STS_IOERR;
 669:	
 670:		if (rq_data_dir(req) == WRITE &&
 671:		    (config->flags & NBD_FLAG_READ_ONLY)) {
 672:			dev_err_ratelimited(disk_to_dev(nbd->disk),
 673:					    "Write on read-only\n");
 674:			return BLK_STS_IOERR;
 675:		}
 676:	
 677:		if (req->cmd_flags & REQ_FUA)
 678:			nbd_cmd_flags |= NBD_CMD_FLAG_FUA;
 679:		if ((req->cmd_flags & REQ_NOUNMAP) && (type == NBD_CMD_WRITE_ZEROES))
 680:			nbd_cmd_flags |= NBD_CMD_FLAG_NO_HOLE;
 681:	
 682:		/* We did a partial send previously, and we at least sent the whole
 683:		 * request struct, so just go and send the rest of the pages in the
 684:		 * request.
 685:		 */
 686:		if (sent) {
 687:			if (sent >= sizeof(request)) {
 688:				skip = sent - sizeof(request);
 689:	
 690:				/* initialize handle for tracing purposes */
 691:				handle = nbd_cmd_handle(cmd);
 692:	
 693:				goto send_pages;
 694:			}
 695:			iov_iter_advance(&from, sent);
 696:		} else {
 697:			cmd->cmd_cookie++;
 698:		}
 699:		cmd->index = index;
 700:		cmd->cookie = nsock->cookie;
 701:		cmd->retries = 0;
 702:		request.type = htonl(type | nbd_cmd_flags);
 703:		if (type != NBD_CMD_FLUSH) {
 704:			request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9);
 705:			request.len = htonl(blk_rq_bytes(req));
 706:		}
 707:		handle = nbd_cmd_handle(cmd);
 708:		request.cookie = cpu_to_be64(handle);
 709:	
 710:		trace_nbd_send_request(&request, nbd->index, blk_mq_rq_from_pdu(cmd));
 711:	
 712:		dev_dbg(nbd_to_dev(nbd), "request %p: sending control (%s@%llu,%uB)\n",
 713:			req, nbdcmd_to_ascii(type),
 714:			(unsigned long long)blk_rq_pos(req) << 9, blk_rq_bytes(req));
 715:		result = sock_xmit(nbd, index, 1, &from,
 716:				(type == NBD_CMD_WRITE) ? MSG_MORE : 0, &sent);
 717:		trace_nbd_header_sent(req, handle);
 718:		if (result < 0) {
 719:			if (was_interrupted(result)) {
 720:				/* If we haven't sent anything we can just return BUSY,
 721:				 * however if we have sent something we need to make
 722:				 * sure we only allow this req to be sent until we are
 723:				 * completely done.
 724:				 */
 725:				if (sent) {
 726:					nbd_sched_pending_work(nbd, nsock, cmd, sent);
 727:					return BLK_STS_OK;
 728:				}
 729:				set_bit(NBD_CMD_REQUEUED, &cmd->flags);
 730:				return BLK_STS_RESOURCE;
 731:			}
 732:			dev_err_ratelimited(disk_to_dev(nbd->disk),
 733:				"Send control failed (result %d)\n", result);
 734:			goto requeue;
 735:		}
 736:	send_pages:
 737:		if (type != NBD_CMD_WRITE)
 738:			goto out;
 739:	
 740:		bio = req->bio;
 741:		while (bio) {
 742:			struct bio *next = bio->bi_next;
 743:			struct bvec_iter iter;
 744:			struct bio_vec bvec;
 745:	
 746:			bio_for_each_segment(bvec, bio, iter) {
 747:				bool is_last = !next && bio_iter_last(bvec, iter);
 748:				int flags = is_last ? 0 : MSG_MORE;
 749:	
 750:				dev_dbg(nbd_to_dev(nbd), "request %p: sending %d bytes data\n",
 751:					req, bvec.bv_len);
 752:				iov_iter_bvec(&from, ITER_SOURCE, &bvec, 1, bvec.bv_len);
 753:				if (skip) {
 754:					if (skip >= iov_iter_count(&from)) {
 755:						skip -= iov_iter_count(&from);
 756:						continue;
 757:					}
 758:					iov_iter_advance(&from, skip);
 759:					skip = 0;
 760:				}
 761:				result = sock_xmit(nbd, index, 1, &from, flags, &sent);
 762:				if (result < 0) {
 763:					if (was_interrupted(result)) {
 764:						nbd_sched_pending_work(nbd, nsock, cmd, sent);
 765:						return BLK_STS_OK;
 766:					}
 767:					dev_err(disk_to_dev(nbd->disk),
 768:						"Send data failed (result %d)\n",
 769:						result);
 770:					goto requeue;
 771:				}
 772:				/*
 773:				 * The completion might already have come in,
 774:				 * so break for the last one instead of letting
 775:				 * the iterator do it. This prevents use-after-free
 776:				 * of the bio.
 777:				 */
 778:				if (is_last)
 779:					break;
 780:			}
 781:			bio = next;
 782:		}
 783:	out:
 784:		trace_nbd_payload_sent(req, handle);
 785:		nsock->pending = NULL;
 786:		nsock->sent = 0;
 787:		__set_bit(NBD_CMD_INFLIGHT, &cmd->flags);
 788:		return BLK_STS_OK;
 789:	
 790:	requeue:
 791:		/*
 792:		 * Can't requeue in case we are dealing with partial send
 793:		 *
 794:		 * We must run from pending work function.
 795:		 * */
 796:		if (test_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags))
 797:			return BLK_STS_OK;
 798:	
 799:		/* retry on a different socket */
 800:		dev_err_ratelimited(disk_to_dev(nbd->disk),
 801:				    "Request send failed, requeueing\n");
 802:		nbd_mark_nsock_dead(nbd, nsock, 1);
 803:		nbd_requeue_cmd(cmd);
 804:		return BLK_STS_OK;
 805:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 94196
							output: 42
							thoughts: 2799
						

**Analyzing the NBD Kernel Module: A Concurrency Conundrum**

Okay, let's break this down. It looks like `nbd_send_cmd` is called from `nbd_queue_rq`, which uses `nsock->tx_lock`. The key is that `config->socks[0]` and `config->socks[1]` are distinct `nsock` structures. So, they have different `tx_lock`s. That means two threads could *concurrently* call `nbd_send_cmd` on these different socks, sending data on the *same* socket concurrently! I immediately have to check whether this is safe.

`sock_xmit` is called, which then leads to `__sock_xmit`, `sock_sendmsg`, and then `unix_stream_sendmsg`. Now, `unix_stream_sendmsg` uses `mutex_lock(&u->iolock)`. So there *is* a serialization point! The threads will serialize on the `u->iolock`, sending requests one after the other. It's interleaved, but that's typical for multi-threaded writes to a socket. It should be safe... unless the interleaving violates the NBD protocol! But I'd expect that the kernel wouldn't crash.

Let's switch gears and check a different part of the code. Suppose `nbd_start_device` is called, but `blk_mq_update_nr_hw_queues` updates for two connections. This launches two `recv_work` threads. What if `nbd_genl_connect` is called again? Wait, the reproducer uses `NBD_CMD_RECONFIGURE` instead.

And the failure comes in the form of an `-EINVAL` because the message is malformed, with the NLA size mismatch. Looking at the second `sendmsg`, the `ANYBLOB` is indeed where the issue lies: the `nla_len` is 8 but there is another NLA within this message. Re-examining the `iovec` array reveals the issue:

The first union's length is `nlmsg_len = 44`. The second union is `ANYRES16` which is an index. The third union contains the ANYBLOB data:
```c
01 00 -> nlmsg_flags = 1
26 bd 70 00 -> nlmsg_seq
fe db df 25 -> nlmsg_pid
03 00 -> genlmsghdr: cmd = 3 (NBD_CMD_RECONFIGURE)
40 00 -> genlmsghdr: version = 0x40, reserved = 0
08 00 01 00 -> nla_len = 8, nla_type = 1 (NBD_ATTR_INDEX)
00 00 00 00 -> value = 0
10 00 07 80 -> nla_len = 16, nla_type = 0x8007 (NBD_ATTR_SOCKETS)
0c 00 01 80 -> nla_len = 12, nla_type = 0x8001 (NBD_SOCK_ITEM)
08 00 01 00 -> nla_len = 8, nla_type = 1 (NBD_SOCK_FD)
```
This is all perfectly valid, so the reconfigure command is actually being executed! The `cmd = 3` and the `version = 0x40` are correct. This *does* mean `NBD_CMD_RECONFIGURE` is happening. And it *reconfigures index 0*. However, the first message connected index 32767. So the second call, with index 0, fails the index lookup. It calls `nbd_genl_reconfigure`, and it returns `-EINVAL` because index 0 doesn't exist.

However, if another syzkaller program connected index 0 *first*, then the reconfigure might succeed by calling `nbd_reconnect_socket`. This loops through the sockets, replacing dead ones, but if no dead ones are found, it returns `-ENOSPC`. The reconfigure would then ignore this error, and no crash would happen.

The next potential problem could be `nbd_add_socket`, so let's look at that.
```c
socks = krealloc(config->socks, (config->num_connections + 1) *
			 sizeof(struct nbd_sock *), GFP_KERNEL);
	if (!socks) {

map[ContextFile:net/core/sock.c IncludeLines:true Name:sk_set_memalloc]

map[SourceCode: 294:	/**
 295:	 * sk_set_memalloc - sets %SOCK_MEMALLOC
 296:	 * @sk: socket to set it on
 297:	 *
 298:	 * Set %SOCK_MEMALLOC on a socket for access to emergency reserves.
 299:	 * It's the responsibility of the admin to adjust min_free_kbytes
 300:	 * to meet the requirements
 301:	 */
 302:	void sk_set_memalloc(struct sock *sk)
 303:	{
 304:		sock_set_flag(sk, SOCK_MEMALLOC);
 305:		sk->sk_allocation |= __GFP_MEMALLOC;
 306:		static_branch_inc(&memalloc_socks_key);
 307:	}
 SourceFile:net/core/sock.c]

gemini-3.1-pro-preview

							input: 98306
							output: 42
							thoughts: 74
						

Okay, here's my take on those thoughts, framed as my own internal analysis:

**Memory Allocation Counter - A Potential Double-Count Issue**

Aha! It just clicked. That `sk_set_memalloc` function... it seems to be incrementing `memalloc_socks_key`. And the real issue? If that function gets called *twice* on the *same* socket, it's going to increment that key *twice*. But, here's the kicker: when the socket finally closes, we're only calling `sk_clear_memalloc` *once*. This is, in itself, not a bad thing, but combined with the increment being called twice, may create a problem. I need to dig into `sk_clear_memalloc` to understand what's really happening during the cleanup. I need to understand what state it leaves the socket in, and what effect a double increment, single decrement would have on the system. It's time to follow the trail.

map[ContextFile:net/core/sock.c IncludeLines:true Name:sk_clear_memalloc]

map[SourceCode: 310:	void sk_clear_memalloc(struct sock *sk)
 311:	{
 312:		sock_reset_flag(sk, SOCK_MEMALLOC);
 313:		sk->sk_allocation &= ~__GFP_MEMALLOC;
 314:		static_branch_dec(&memalloc_socks_key);
 315:	
 316:		/*
 317:		 * SOCK_MEMALLOC is allowed to ignore rmem limits to ensure forward
 318:		 * progress of swapping. SOCK_MEMALLOC may be cleared while
 319:		 * it has rmem allocations due to the last swapfile being deactivated
 320:		 * but there is a risk that the socket is unusable due to exceeding
 321:		 * the rmem limits. Reclaim the reserves and obey rmem limits again.
 322:		 */
 323:		sk_mem_reclaim(sk);
 324:	}
 SourceFile:net/core/sock.c]

gemini-3.1-pro-preview

							input: 98906
							output: 24
							thoughts: 65
						

**Investigating Socket Memory Allocation Clearing**

Okay, hold on a minute. I was under the impression that either `nbd_clear_sock` or perhaps `nbd_config_put` would be responsible for calling `sk_clear_memalloc`. But a quick review tells me that isn't the case. Interesting. So, if these functions *aren't* responsible for clearing the socket's memory allocations, then when *does* that happen? It must be tied to the socket's lifecycle, probably during destruction. Which leads me to the next question: where *else* is `sk_clear_memalloc` actually invoked in the code base? I need to trace its call sites to fully understand its role in managing socket memory and where the deallocation of memory occurs.

map[Name:sk_clear_memalloc]

map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:sock_free SourceFile:drivers/net/wireguard/socket.c SourceLine:337] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:xs_reset_transport SourceFile:net/sunrpc/xprtsock.c SourceLine:1289]] TruncatedOutput:false]

gemini-3.1-pro-preview

							input: 99285
							output: 20
							thoughts: 31
						

Okay, here's my interpretation of that thought process, from an expert's perspective:

**Diving Deep into Memory Management**

Hold on a second... is that right? Did I just see that `sk_clear_memalloc` is called within `sk_destruct`? That's a little unusual, I need to verify. My immediate reflex is to check the implementation of `sk_destruct`. It's critical to understand the memory allocation and deallocation lifecycle, and this connection between destruction and clearing allocated memory is something that needs a closer look. Let's get into the details of `sk_destruct` and see what's really happening.

map[Expression:sk_clear_memalloc]

map[Output:drivers/net/wireguard/socket.c=333=static void sock_free(struct sock *sock)
--
drivers/net/wireguard/socket.c-336-		return;
drivers/net/wireguard/socket.c:337:	sk_clear_memalloc(sock);
drivers/net/wireguard/socket.c-338-	udp_tunnel_sock_release(sock->sk_socket);
--
include/net/sock.h=1245=void sk_set_memalloc(struct sock *sk);
include/net/sock.h:1246:void sk_clear_memalloc(struct sock *sk);
include/net/sock.h-1247-
--
net/core/sock.c=308=EXPORT_SYMBOL_GPL(sk_set_memalloc);
net/core/sock.c-309-
net/core/sock.c:310:void sk_clear_memalloc(struct sock *sk)
net/core/sock.c-311-{
--
net/core/sock.c-324-}
net/core/sock.c:325:EXPORT_SYMBOL_GPL(sk_clear_memalloc);
net/core/sock.c-326-
--
net/sunrpc/xprtsock.c=1268=static void xs_reset_transport(struct sock_xprt *transport)
--
net/sunrpc/xprtsock.c-1288-	if (atomic_read(&transport->xprt.swapper))
net/sunrpc/xprtsock.c:1289:		sk_clear_memalloc(sk);
net/sunrpc/xprtsock.c-1290-
--
net/sunrpc/xprtsock.c=2155=xs_disable_swap(struct rpc_xprt *xprt)
--
net/sunrpc/xprtsock.c-2161-	    xs->inet)
net/sunrpc/xprtsock.c:2162:		sk_clear_memalloc(xs->inet);
net/sunrpc/xprtsock.c-2163-	mutex_unlock(&xs->recv_mutex);
]

gemini-3.1-pro-preview

							input: 100043
							output: 20
							thoughts: 91
						

Okay, here's my thought process on this, distilled into a first-person summary:

**Digging into Socket Memory Allocation**

Alright, something's not quite clicking here. My initial assumption was that `sk_clear_memalloc` was being called within `sk_destruct`, but that doesn't appear to be the case. I need to be certain about this.

This gets me thinking. If `sk_set_memalloc` increments `memalloc_socks_key`, where is the corresponding decrement or clearing action happening? The key question is whether or not the socket memory is being freed properly.

If `nbd` is calling `sk_set_memalloc`, it needs to be balanced with a call to `sk_clear_memalloc` somewhere to prevent memory leaks. I need to trace this specific path. Let's see... Maybe it's handled in `nbd_clear_sock` or perhaps buried within `nbd_config_put`. Those seem like the most likely candidates to manage socket deallocation within the NBD context. Time to dive into those functions and confirm what's happening.

map[Expression:sk_clear_memalloc]

map[Output:drivers/net/wireguard/socket.c=333=static void sock_free(struct sock *sock)
--
drivers/net/wireguard/socket.c-336-		return;
drivers/net/wireguard/socket.c:337:	sk_clear_memalloc(sock);
drivers/net/wireguard/socket.c-338-	udp_tunnel_sock_release(sock->sk_socket);
--
include/net/sock.h=1245=void sk_set_memalloc(struct sock *sk);
include/net/sock.h:1246:void sk_clear_memalloc(struct sock *sk);
include/net/sock.h-1247-
--
net/core/sock.c=308=EXPORT_SYMBOL_GPL(sk_set_memalloc);
net/core/sock.c-309-
net/core/sock.c:310:void sk_clear_memalloc(struct sock *sk)
net/core/sock.c-311-{
--
net/core/sock.c-324-}
net/core/sock.c:325:EXPORT_SYMBOL_GPL(sk_clear_memalloc);
net/core/sock.c-326-
--
net/sunrpc/xprtsock.c=1268=static void xs_reset_transport(struct sock_xprt *transport)
--
net/sunrpc/xprtsock.c-1288-	if (atomic_read(&transport->xprt.swapper))
net/sunrpc/xprtsock.c:1289:		sk_clear_memalloc(sk);
net/sunrpc/xprtsock.c-1290-
--
net/sunrpc/xprtsock.c=2155=xs_disable_swap(struct rpc_xprt *xprt)
--
net/sunrpc/xprtsock.c-2161-	    xs->inet)
net/sunrpc/xprtsock.c:2162:		sk_clear_memalloc(xs->inet);
net/sunrpc/xprtsock.c-2163-	mutex_unlock(&xs->recv_mutex);
]

gemini-3.1-pro-preview

							input: 100959
							output: 43
							thoughts: 33
						

Okay, here's my interpretation of those thoughts, crafted with the expectation that I'm discussing this with a fellow expert:

**Concerning Memory Management in NBD**

Wait a minute, something's not adding up here. I was *certain* `nbd` was using `sk_clear_memalloc`! But now I'm doubting myself. I need to be absolutely sure about how memory is being handled and cleared within the NBD code. Let me double-check the logic within `nbd_clear_sock` again. I need to verify how sockets are handled, and by extension, what memory cleanup is *actually* happening there. This could have significant implications for resource management and potential vulnerabilities if I'm not careful. It's time to dig into the details to be certain.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_clear_sock]

map[SourceCode:1425:	static void nbd_clear_sock(struct nbd_device *nbd)
1426:	{
1427:		sock_shutdown(nbd);
1428:		nbd_clear_que(nbd);
1429:		nbd->task_setup = NULL;
1430:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 101323
							output: 40
							thoughts: 93
						

**A Potential Memory Leak in the Network Block Device (NBD) Driver?**

Okay, so I'm digging into this code and something is jumping out at me. I'm seeing that `sk_set_memalloc` is incrementing `memalloc_socks_key`. That's standard socket memory allocation handling, no surprises there. But, if I'm understanding this correctly, the NBD driver is calling `sk_set_memalloc`, which is fine, but if it *doesn't* call `sk_clear_memalloc` after that, then `memalloc_socks_key` is going to leak! That's a huge potential issue. Memory leaks are the bane of my existence!

Wait, hold on a second... isn't `sk_clear_memalloc` called in `sk_destruct`? That's the standard teardown function for a socket structure, so that would mitigate the problem. I need to confirm this. I *have* to check how `sk_destruct` is implemented and when NBD is using it. I need to make absolutely sure that the resources allocated by `sk_set_memalloc` are properly freed. This is going to require me to do a deeper dive into the relevant code paths.

map[ContextFile:net/core/sock.c IncludeLines:true Name:sk_destruct]

map[SourceCode:2402:	void sk_destruct(struct sock *sk)
2403:	{
2404:		bool use_call_rcu = sock_flag(sk, SOCK_RCU_FREE);
2405:	
2406:		if (rcu_access_pointer(sk->sk_reuseport_cb)) {
2407:			reuseport_detach_sock(sk);
2408:			use_call_rcu = true;
2409:		}
2410:	
2411:		if (use_call_rcu)
2412:			call_rcu(&sk->sk_rcu, __sk_destruct);
2413:		else
2414:			__sk_destruct(&sk->sk_rcu);
2415:	}
 SourceFile:net/core/sock.c]

gemini-3.1-pro-preview

							input: 101967
							output: 41
							thoughts: 11
						

Okay, here's my take on those thoughts, tailored for an expert audience:

**Diving into `__sk_destruct`**

Alright, let's get down to it. Time to poke around in `__sk_destruct`. That's where the rubber meets the road, where the object cleanup logic lives, right? Gotta make sure it's behaving as expected. Are there any lurking memory leaks or unexpected side effects that could crop up during object destruction? Or, potentially, is this where a core issue is arising? This is a critical piece of the puzzle, especially when dealing with complex, interconnected object graphs. The goal is a clear understanding and validation of the object's clean-up process.

map[ContextFile:net/core/sock.c IncludeLines:true Name:__sk_destruct]

map[SourceCode:2342:	/* Sockets having SOCK_RCU_FREE will call this function after one RCU
2343:	 * grace period. This is the case for UDP sockets and TCP listeners.
2344:	 */
2345:	static void __sk_destruct(struct rcu_head *head)
2346:	{
2347:		struct sock *sk = container_of(head, struct sock, sk_rcu);
2348:		struct net *net = sock_net(sk);
2349:		struct sk_filter *filter;
2350:	
2351:		if (sk->sk_destruct)
2352:			sk->sk_destruct(sk);
2353:	
2354:		filter = rcu_dereference_check(sk->sk_filter,
2355:					       refcount_read(&sk->sk_wmem_alloc) == 0);
2356:		if (filter) {
2357:			sk_filter_uncharge(sk, filter);
2358:			RCU_INIT_POINTER(sk->sk_filter, NULL);
2359:		}
2360:	
2361:		sock_disable_timestamp(sk, SK_FLAGS_TIMESTAMP);
2362:	
2363:	#ifdef CONFIG_BPF_SYSCALL
2364:		bpf_sk_storage_free(sk);
2365:	#endif
2366:	
2367:		if (atomic_read(&sk->sk_omem_alloc))
2368:			pr_debug("%s: optmem leakage (%d bytes) detected\n",
2369:				 __func__, atomic_read(&sk->sk_omem_alloc));
2370:	
2371:		if (sk->sk_frag.page) {
2372:			put_page(sk->sk_frag.page);
2373:			sk->sk_frag.page = NULL;
2374:		}
2375:	
2376:		/* We do not need to acquire sk->sk_peer_lock, we are the last user. */
2377:		put_cred(sk->sk_peer_cred);
2378:		put_pid(sk->sk_peer_pid);
2379:	
2380:		if (likely(sk->sk_net_refcnt)) {
2381:			put_net_track(net, &sk->ns_tracker);
2382:		} else {
2383:			__netns_tracker_free(net, &sk->ns_tracker, false);
2384:			net_passive_dec(net);
2385:		}
2386:		sk_prot_free(sk->sk_prot_creator, sk);
2387:	}
 SourceFile:net/core/sock.c]

gemini-3.1-pro-preview

							input: 102938
							output: 39
							thoughts: 32
						

Okay, here's my take on those thoughts, framed as my own reasoning:

**Clarifying Memory Management in the Kernel**

Hmm, hold on a second. I was under the impression that `sk_clear_memalloc` was part of the cleanup process within `__sk_destruct`. That seems... incorrect. It's crucial to get this right, especially in network stack memory management. My initial assumption must be wrong.

Alright, let's step back and trace this through. Where *is* this memory freed? If not in `__sk_destruct`, then the logical place to look is the `sk_free` function. I need to understand the relationship between these functions, particularly the memory deallocation strategy used within the socket structure and its associated resources. Time to dive into the `sk_free` code and see what's really happening.

map[ContextFile:net/core/sock.c IncludeLines:true Name:sk_free]

map[SourceCode:2428:	void sk_free(struct sock *sk)
2429:	{
2430:		/*
2431:		 * We subtract one from sk_wmem_alloc and can know if
2432:		 * some packets are still in some tx queue.
2433:		 * If not null, sock_wfree() will call __sk_free(sk) later
2434:		 */
2435:		if (refcount_dec_and_test(&sk->sk_wmem_alloc))
2436:			__sk_free(sk);
2437:	}
 SourceFile:net/core/sock.c]

gemini-3.1-pro-preview

							input: 103378
							output: 40
							thoughts: 10
						

Okay, here's my interpretation of that thought process, assuming I'm deeply familiar with memory management and kernel internals:

**Checking `__sk_free`**

Alright, time to get down to brass tacks. "Let's check `__sk_free`". That tells me we're likely dealing with something related to the freeing of a socket's data structures or resources. Given the naming convention with the double underscore prefix, `__sk_free` is almost certainly an internal, likely low-level, function within the kernel's networking stack. I'm probably looking at the final stages of closing or cleaning up a socket. It's the point where all the allocated memory associated with the socket is supposed to be released back to the system. I'm anticipating possibly digging into the details of data buffers being freed, connection state being reset, or perhaps even investigating potential race conditions or memory leaks that could occur during socket teardown. There might be questions regarding reference counting or the interplay of different subsystems involved in socket management. Knowing exactly *why* I'm checking it, however, will be key to understanding the full context. What triggered this interest? Some error report? A performance bottleneck? Or simply a routine code audit?

map[ContextFile:net/core/sock.c IncludeLines:true Name:__sk_free]

map[SourceCode:2417:	static void __sk_free(struct sock *sk)
2418:	{
2419:		if (likely(sk->sk_net_refcnt))
2420:			sock_inuse_add(sock_net(sk), -1);
2421:	
2422:		if (unlikely(sk->sk_net_refcnt && sock_diag_has_destroy_listeners(sk)))
2423:			sock_diag_broadcast_destroy(sk);
2424:		else
2425:			sk_destruct(sk);
2426:	}
 SourceFile:net/core/sock.c]

gemini-3.1-pro-preview

							input: 103874
							output: 20
							thoughts: 175
						

**Memory Allocation Leak in NBD Driver: A Deep Dive**

Okay, hold on a second. I just realized something critical. It seems `sk_clear_memalloc` isn't automatically called when a socket is freed. This is... concerning. If the Network Block Device (NBD) driver calls `sk_set_memalloc` to manage memory allocation but then *never* calls `sk_clear_memalloc` to release it, then we have a potential leak with `memalloc_socks_key`. That's bad news.

But, wait, I need to be precise. Let me retrace my steps. `sk_set_memalloc` not only sets up memory allocation tracking, it also sets the `SOCK_MEMALLOC` flag, right? Okay, so let's say `nbd` calls `sk_set_memalloc` *twice* on the *same* socket. This would mean that `memalloc_socks_key` is incremented *twice*. And as I originally suspected, since `nbd` never calls `sk_clear_memalloc`, the value is never decremented.

But wait, I need to confirm: does `nbd` actually call `sk_clear_memalloc` anywhere? I need to know for sure. I'm going to quickly grep the `drivers/block/nbd.c` file for `sk_clear_memalloc`. Let's see what comes up. This could be a significant vulnerability!

map[Expression:sk_clear_memalloc]

map[Output:drivers/net/wireguard/socket.c=333=static void sock_free(struct sock *sock)
--
drivers/net/wireguard/socket.c-336-		return;
drivers/net/wireguard/socket.c:337:	sk_clear_memalloc(sock);
drivers/net/wireguard/socket.c-338-	udp_tunnel_sock_release(sock->sk_socket);
--
include/net/sock.h=1245=void sk_set_memalloc(struct sock *sk);
include/net/sock.h:1246:void sk_clear_memalloc(struct sock *sk);
include/net/sock.h-1247-
--
net/core/sock.c=308=EXPORT_SYMBOL_GPL(sk_set_memalloc);
net/core/sock.c-309-
net/core/sock.c:310:void sk_clear_memalloc(struct sock *sk)
net/core/sock.c-311-{
--
net/core/sock.c-324-}
net/core/sock.c:325:EXPORT_SYMBOL_GPL(sk_clear_memalloc);
net/core/sock.c-326-
--
net/sunrpc/xprtsock.c=1268=static void xs_reset_transport(struct sock_xprt *transport)
--
net/sunrpc/xprtsock.c-1288-	if (atomic_read(&transport->xprt.swapper))
net/sunrpc/xprtsock.c:1289:		sk_clear_memalloc(sk);
net/sunrpc/xprtsock.c-1290-
--
net/sunrpc/xprtsock.c=2155=xs_disable_swap(struct rpc_xprt *xprt)
--
net/sunrpc/xprtsock.c-2161-	    xs->inet)
net/sunrpc/xprtsock.c:2162:		sk_clear_memalloc(xs->inet);
net/sunrpc/xprtsock.c-2163-	mutex_unlock(&xs->recv_mutex);
]

gemini-3.1-pro-preview

							input: 104950
							output: 37
							thoughts: 267
						

**My Analysis of a Potential Resource Leak**

Okay, here's what I'm thinking. This seems like a potential memory leak. Or maybe not? Hang on…it's not! But… wait. The code snippet describes a scenario where `nbd` sets `sk_set_memalloc` but doesn't call `sk_clear_memalloc`, which looks like a leak, if `memalloc_socks_key` isn't properly cleared. But hold on, the code says `memalloc_socks_key` is a *static* key. A leak in a static key just means it remains enabled. That's fine. 

But… if `nbd` calls `sk_set_memalloc` twice on the *same* socket, then `static_branch_inc` gets called twice. That's definitely an issue. The `SOCK_MEMALLOC` flag *is* set, so we can track this. 

However, looking back, `nbd` never calls `sk_clear_memalloc`. Where *does* `sk_clear_memalloc` get called? Let me check `sk_destruct`... Nope, it's not there. Hmm, what about `sock_release`? Let's check `sock_release`.

map[ContextFile:net/socket.c IncludeLines:true Name:sock_release]

map[SourceCode: 740:	/**
 741:	 *	sock_release - close a socket
 742:	 *	@sock: socket to close
 743:	 *
 744:	 *	The socket is released from the protocol stack if it has a release
 745:	 *	callback, and the inode is then released if the socket is bound to
 746:	 *	an inode not a file.
 747:	 */
 748:	void sock_release(struct socket *sock)
 749:	{
 750:		__sock_release(sock, NULL);
 751:	}
 SourceFile:net/socket.c]

gemini-3.1-pro-preview

							input: 105722
							output: 38
							thoughts: 10
						

Okay, here's my take on those thoughts, tailored for an expert audience:

**Diving into `__sock_release`**

Alright, time to get my hands dirty. My initial thought is to zero in on `__sock_release`. Given the context – whatever the issue is – my intuition screams that this function is likely pivotal. It's the point where socket resources are supposed to be cleaned up, and that's usually where things go sideways. I need to understand exactly what this function *does* in detail: the locking it uses, the state transitions, the reference counting, all of it. I'll probably start by grepping the kernel sources to see where it's called and by whom to understand the context. Then, it's off to the disassembly, or perhaps even a live debugging session. I need to ascertain if this function is properly handling all possible error conditions and whether any race conditions exist. I'm looking for memory leaks, double-frees, or any other resource exhaustion issues. I suspect that the root of the problem is somewhere in this function or its interactions with other socket-related subsystems. It's time to dig deep.

map[ContextFile:net/socket.c IncludeLines:true Name:__sock_release]

map[SourceCode: 713:	static void __sock_release(struct socket *sock, struct inode *inode)
 714:	{
 715:		const struct proto_ops *ops = READ_ONCE(sock->ops);
 716:	
 717:		if (ops) {
 718:			struct module *owner = ops->owner;
 719:	
 720:			if (inode)
 721:				inode_lock(inode);
 722:			ops->release(sock);
 723:			sock->sk = NULL;
 724:			if (inode)
 725:				inode_unlock(inode);
 726:			sock->ops = NULL;
 727:			module_put(owner);
 728:		}
 729:	
 730:		if (sock->wq.fasync_list)
 731:			pr_err("%s: fasync list not empty!\n", __func__);
 732:	
 733:		if (!sock->file) {
 734:			iput(SOCK_INODE(sock));
 735:			return;
 736:		}
 737:		WRITE_ONCE(sock->file, NULL);
 738:	}
 SourceFile:net/socket.c]

gemini-3.1-pro-preview

							input: 106378
							output: 42
							thoughts: 29
						

Here's my take on the thought process:

**Diving Deep into Network Socket Cleanup**

Okay, hold on a second. I just saw something that's making me raise an eyebrow. `sk_clear_memalloc` is getting called in `inet_release`? That seems a bit... unexpected. I need to understand why that would be. Let's dig into `inet_release` and see what's going on under the hood. Time to trace the execution path and clarify this connection.

map[ContextFile:net/ipv4/af_inet.c IncludeLines:true Name:inet_release]

map[SourceCode: 413:	/*
 414:	 *	The peer socket should always be NULL (or else). When we call this
 415:	 *	function we are destroying the object and from then on nobody
 416:	 *	should refer to it.
 417:	 */
 418:	int inet_release(struct socket *sock)
 419:	{
 420:		struct sock *sk = sock->sk;
 421:	
 422:		if (sk) {
 423:			long timeout;
 424:	
 425:			if (!sk->sk_kern_sock)
 426:				BPF_CGROUP_RUN_PROG_INET_SOCK_RELEASE(sk);
 427:	
 428:			/* Applications forget to leave groups before exiting */
 429:			ip_mc_drop_socket(sk);
 430:	
 431:			/* If linger is set, we don't return until the close
 432:			 * is complete.  Otherwise we return immediately. The
 433:			 * actually closing is done the same either way.
 434:			 *
 435:			 * If the close is due to the process exiting, we never
 436:			 * linger..
 437:			 */
 438:			timeout = 0;
 439:			if (sock_flag(sk, SOCK_LINGER) &&
 440:			    !(current->flags & PF_EXITING))
 441:				timeout = sk->sk_lingertime;
 442:			sk->sk_prot->close(sk, timeout);
 443:			sock->sk = NULL;
 444:		}
 445:		return 0;
 446:	}
 SourceFile:net/ipv4/af_inet.c]

gemini-3.1-pro-preview

							input: 107060
							output: 45
							thoughts: 1356
						

**Analyzing the `nbd` Kernel Module: A Deep Dive into Potential Socket Resource Issues**

Okay, so I'm digging into this `nbd` code, and something's really bugging me. I was initially looking at `sk_clear_memalloc`, expecting to see it called in `inet_release` to clean things up, but it's not. Wait, it's only called in `wireguard` and `sunrpc`! That's strange. This means `nbd` isn't calling `sk_clear_memalloc` either. Although `nbd` calls `sk_set_memalloc`, setting the flag, there's no corresponding call to clear it. Is this a potential leak of `memalloc_socks_key`? It looks like it.

It appears that `nbd` calls `sk_set_memalloc` in `nbd_start_device` and `nbd_reconnect_socket`, which are normal socket connections, but not `sk_clear_memalloc`, so the key, I guess the flags and static counter, just accumulates. However, `memalloc_socks_key` is a static key, it's an incrementing counter, which does not by itself cause a crash, only a potentially persistent state.

Now, I'm thinking, what if `sk_set_memalloc` gets called *twice* on the same socket? If that happens, `static_branch_inc` is called twice as well. But since `sk_clear_memalloc` is never called, the `memalloc_socks_key` is just incremented, never decremented. So this might explain the memory issue, but it's not a crash.

I had to re-examine `nbd_reconnect_socket`, since I found this was called with `r[3]`. But in it, `nsock->dead` is false, so it just returns `-ENOSPC`, which `nbd_genl_reconfigure` ignores, so the function does absolutely nothing.

What about `nbd_add_socket`? I see `nbd_add_socket` is called twice with the SAME file descriptor, which is weird. This means `config->socks[0]` and `config->socks[1]` point to distinct `nsock` structures, but *both* `nsock->sock` point to the *same* `struct socket *`. Then `nbd_start_device` is called. It looks like `sk_set_memalloc` is called *twice* on the *same* `sock->sk`. Then `queue_work` is called twice, queuing two `recv_work` threads.

Both threads will call `nbd_read_reply`, which calls `sock_xmit` -> `__sock_xmit` -> `sock_recvmsg`. That `sock_recvmsg` calls `unix_stream_recvmsg`. And since it's a UNIX domain socket, `unix_stream_recvmsg` is called *concurrently* by the two threads. This looks like a potential race condition! One thread will wait in `unix_stream_data_wait`, while the other one is also waiting in `unix_stream_data_wait`. The crucial thing here is that `unix_stream_data_wait` uses `sk_sleep(sk)`. This looks like the place to focus my investigation.

map[ContextFile:net/unix/af_unix.c IncludeLines:true Name:unix_stream_data_wait]

map[SourceCode:2710:	/*
2711:	 *	Sleep until more data has arrived. But check for races..
2712:	 */
2713:	static long unix_stream_data_wait(struct sock *sk, long timeo,
2714:					  struct sk_buff *last, unsigned int last_len,
2715:					  bool freezable)
2716:	{
2717:		unsigned int state = TASK_INTERRUPTIBLE | freezable * TASK_FREEZABLE;
2718:		struct sk_buff *tail;
2719:		DEFINE_WAIT(wait);
2720:	
2721:		unix_state_lock(sk);
2722:	
2723:		for (;;) {
2724:			prepare_to_wait(sk_sleep(sk), &wait, state);
2725:	
2726:			tail = skb_peek_tail(&sk->sk_receive_queue);
2727:			if (tail != last ||
2728:			    (tail && tail->len != last_len) ||
2729:			    sk->sk_err ||
2730:			    (sk->sk_shutdown & RCV_SHUTDOWN) ||
2731:			    signal_pending(current) ||
2732:			    !timeo)
2733:				break;
2734:	
2735:			sk_set_bit(SOCKWQ_ASYNC_WAITDATA, sk);
2736:			unix_state_unlock(sk);
2737:			timeo = schedule_timeout(timeo);
2738:			unix_state_lock(sk);
2739:	
2740:			if (sock_flag(sk, SOCK_DEAD))
2741:				break;
2742:	
2743:			sk_clear_bit(SOCKWQ_ASYNC_WAITDATA, sk);
2744:		}
2745:	
2746:		finish_wait(sk_sleep(sk), &wait);
2747:		unix_state_unlock(sk);
2748:		return timeo;
2749:	}
 SourceFile:net/unix/af_unix.c]

gemini-3.1-pro-preview

							input: 109800
							output: 39
							thoughts: 382
						

**Double Shutdown! A Deep Dive into Socket Handling**

Okay, so I'm tracing through this code, and something's bugging me. It starts with `unix_stream_data_wait`, which calls `prepare_to_wait` on `sk_sleep(sk)`. That's standard enough, right? The issue is, if *two* threads call `prepare_to_wait` on the *same* `sk_sleep(sk)`, they both get added to the wait queue. Makes sense, so far. Then, when the socket closes, `sk->sk_state_change` gets triggered, waking up the entire wait queue – both threads.

Both threads happily return from `unix_stream_data_wait`, then they both end up at the `redo` label within `unix_stream_read_generic`. Okay, I see where this is going... Both threads attempt to acquire `u->iolock`. One grabs it, sees that `sk->sk_shutdown` has `RCV_SHUTDOWN` set, and promptly returns 0. The other thread gets the lock, sees the same `RCV_SHUTDOWN` flag, and also returns 0. Both threads come back from `sock_recvmsg` returning 0. Uh-oh. They both then get `-EPIPE` from `__sock_xmit`, which propagates all the way up to `nbd_read_reply`, which also returns `-EPIPE`. They both get out of the loop in `recv_work`.

And now, here's the kicker: they *both* call `nbd_mark_nsock_dead`. Fine, `nbd_mark_nsock_dead` takes `nsock->tx_lock`. Different `nsock`s, so different `tx_lock`s, no problem there. But then, they *both* call `kernel_sock_shutdown(nsock->sock, SHUT_RDWR)`. And *that's* where I get concerned because `nsock->sock` is the *same* socket! I'm calling `kernel_sock_shutdown` *twice* on the same socket from two different threads!

So, the question is: is `kernel_sock_shutdown` thread-safe, or safe to call twice on the same socket? I need to verify its implementation and check for any potential race conditions or double-free scenarios. I'm going to have to dive into `kernel_sock_shutdown` to be absolutely sure. This could lead to a serious issue.

map[ContextFile:net/socket.c IncludeLines:true Name:kernel_sock_shutdown]

map[SourceCode:3783:	int kernel_sock_shutdown(struct socket *sock, enum sock_shutdown_cmd how)
3784:	{
3785:		return READ_ONCE(sock->ops)->shutdown(sock, how);
3786:	}
 SourceFile:net/socket.c]

gemini-3.1-pro-preview

							input: 110859
							output: 41
							thoughts: 9
						

Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:

**Internal Diagnostic: Unix Shutdown Procedure**

Alright, the mental gears are starting to turn. My immediate instinct is to take a look at the `unix_shutdown` function or module, wherever it resides in this context. It's the logical starting point for understanding how the system is currently managing shutdown procedures. I need to refresh my memory or immediately assess its current state. I'm thinking about the implications – Is it a script, a system call, a set of instructions? The details will influence how quickly and safely the system shuts down. I'll need to know what it does with all the current processes, the filesystems, and the network services. This is where the magic happens, or where things go terribly wrong, depending on the implementation. That's where I will begin my exploration.

map[ContextFile:net/unix/af_unix.c IncludeLines:true Name:unix_shutdown]

map[SourceCode:3203:	static int unix_shutdown(struct socket *sock, int mode)
3204:	{
3205:		struct sock *sk = sock->sk;
3206:		struct sock *other;
3207:	
3208:		if (mode < SHUT_RD || mode > SHUT_RDWR)
3209:			return -EINVAL;
3210:		/* This maps:
3211:		 * SHUT_RD   (0) -> RCV_SHUTDOWN  (1)
3212:		 * SHUT_WR   (1) -> SEND_SHUTDOWN (2)
3213:		 * SHUT_RDWR (2) -> SHUTDOWN_MASK (3)
3214:		 */
3215:		++mode;
3216:	
3217:		unix_state_lock(sk);
3218:		WRITE_ONCE(sk->sk_shutdown, sk->sk_shutdown | mode);
3219:		other = unix_peer(sk);
3220:		if (other)
3221:			sock_hold(other);
3222:		unix_state_unlock(sk);
3223:		sk->sk_state_change(sk);
3224:	
3225:		if (other &&
3226:			(sk->sk_type == SOCK_STREAM || sk->sk_type == SOCK_SEQPACKET)) {
3227:	
3228:			int peer_mode = 0;
3229:			const struct proto *prot = READ_ONCE(other->sk_prot);
3230:	
3231:			if (prot->unhash)
3232:				prot->unhash(other);
3233:			if (mode&RCV_SHUTDOWN)
3234:				peer_mode |= SEND_SHUTDOWN;
3235:			if (mode&SEND_SHUTDOWN)
3236:				peer_mode |= RCV_SHUTDOWN;
3237:			unix_state_lock(other);
3238:			WRITE_ONCE(other->sk_shutdown, other->sk_shutdown | peer_mode);
3239:			unix_state_unlock(other);
3240:			other->sk_state_change(other);
3241:			if (peer_mode == SHUTDOWN_MASK)
3242:				sk_wake_async(other, SOCK_WAKE_WAITD, POLL_HUP);
3243:			else if (peer_mode & RCV_SHUTDOWN)
3244:				sk_wake_async(other, SOCK_WAKE_WAITD, POLL_IN);
3245:		}
3246:		if (other)
3247:			sock_put(other);
3248:	
3249:		return 0;
3250:	}
 SourceFile:net/unix/af_unix.c]

gemini-3.1-pro-preview

							input: 111886
							output: 21
							thoughts: 801
						

**Analyzing the Potential for Double `sockfd_put` Calls in NBD Shutdown**

Okay, so I'm investigating a potential double free issue in the NBD driver, specifically around socket shutdown. I've confirmed that `unix_shutdown` is indeed safe to call multiple times because it just ORs the flags, but now I'm digging deeper into how sockets are managed during config cleanup.

My first concern is the `nbd_config_put` function. I see a `refcount_dec_and_mutex_lock` call, and within that, I'm focusing on the `config->socks` handling. The code iterates through the connections and calls `sockfd_put` on each socket. Now I see it. It looks like `sockfd_put` is called *twice* on the same socket within the loop! This is what I was afraid of.

The critical question here is whether `sockfd_put` is safe to call more than once for the same socket. Examining `sockfd_put`, I see that it calls `fput(sock->file)`. So, if `fput` is called twice, the file reference count is decremented twice. That's a problem.

Wait a second. Reminding myself of how these sockets were initialized, I realize that `nbd_add_socket` likely called `nbd_get_socket` twice for the same underlying socket. Looking deeper into that, `nbd_get_socket` calls `sockfd_lookup` *twice*. Now I remember what `sockfd_lookup` does, it calls `fget(fd)`. `fget` *increments* the file reference count. So the file reference count was incremented *twice* for the same file descriptor. That explains it, the double decrement is balanced by the double increment. So it *should* be safe.

Still, what if `nbd_add_socket` fails on the second call? No, that's fine. It would simply return an error and we aren't handling that error.

I'm starting to think about whether there is any *other* problem, even if this specific double call is safe. What if `config->socks[0]->sock` and `config->socks[1]->sock` pointed to the *same* socket? Let me consider `nbd_clear_sock`. It calls `sock_shutdown`, but that's safe. It calls `kernel_sock_shutdown` for each socket, which is the expected behavior.

I'll check `nbd_reconnect_socket`. This function reassigns a socket, and it does `sockfd_put(old)` *after* replacing the socket. That seems safe too.

Okay, let's step back, is this necessarily a kernel panic? There's a crash that triggered a warning: "SYZFAIL: failed to recv rpc", "fd=3 want=4 recv=0 n=-1 (errno 104: Connection reset by peer)". That usually means the syz-executor died. Why? Maybe it hit a `BUG_ON` or `WARN_ON` with `panic_on_warn`? I should check if there are any `BUG_ON` or `WARN_ON` calls in `nbd` at this point.

map[Expression:BUG_ON|WARN_ON]

map[Output:
Full output is too long, showing 500 out of 203717 lines.
Use more precise expression if possible.

[Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst=78=lock-acquisition and lock-release functions::
 --
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst-104-   25
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst:105:   26 WARN_ON(r1 == 0 && r2 == 0 && r3 == 0);
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst-106-
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst:107:The ``WARN_ON()`` is evaluated at "the end of time",
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst-108-after all changes have propagated throughout the system.
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst=109=Without the ``smp_mb__after_unlock_lock()`` provided by the
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst:110:acquisition functions, this ``WARN_ON()`` could trigger, for example
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst-111-on PowerPC.
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst=112=The ``smp_mb__after_unlock_lock()`` invocations prevent this
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst:113:``WARN_ON()`` from triggering.
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst-114-
 --
 Documentation/RCU/Design/Requirements/Requirements.rst=755=example illustrates this:
 --
 Documentation/RCU/Design/Requirements/Requirements.rst-765-       7     r2 = READ_ONCE(x);
 Documentation/RCU/Design/Requirements/Requirements.rst:766:       8     WARN_ON(!r2); /* BUG!!! */
 Documentation/RCU/Design/Requirements/Requirements.rst-767-       9   }
 --
 Documentation/RCU/Design/Requirements/Requirements.rst=779=If the thread0() function's rcu_read_lock() excluded the
 Documentation/RCU/Design/Requirements/Requirements.rst:780:thread1() function's update, the WARN_ON() could never fire. But
 Documentation/RCU/Design/Requirements/Requirements.rst-781-the fact is that rcu_read_lock() does not exclude much of anything
 Documentation/RCU/Design/Requirements/Requirements.rst=782=aside from subsequent grace periods, of which thread1() has none, so
 Documentation/RCU/Design/Requirements/Requirements.rst:783:the WARN_ON() can and does fire.
 Documentation/RCU/Design/Requirements/Requirements.rst-784-
 --
 Documentation/RCU/lockdep.rst=25=aren't certain (for example, if CONFIG_DEBUG_LOCK_ALLOC is not set).
 Documentation/RCU/lockdep.rst:26:This prevents things like WARN_ON(!rcu_read_lock_held()) from giving false
 Documentation/RCU/lockdep.rst-27-positives when lockdep is disabled.
 --
 Documentation/RCU/rcubarrier.rst=194=The original code for rcu_barrier() was roughly as follows::
 --
 Documentation/RCU/rcubarrier.rst-197-  2  {
 Documentation/RCU/rcubarrier.rst:198:  3    BUG_ON(in_interrupt());
 Documentation/RCU/rcubarrier.rst-199-  4    /* Take cpucontrol mutex to protect against CPU hotplug */
 --
 Documentation/admin-guide/clearing-warn-once.rst:1:Clearing WARN_ONCE
 Documentation/admin-guide/clearing-warn-once.rst-2-------------------
 Documentation/admin-guide/clearing-warn-once.rst-3-
 Documentation/admin-guide/clearing-warn-once.rst:4:WARN_ONCE / WARN_ON_ONCE / printk_once only emit a message once.
 Documentation/admin-guide/clearing-warn-once.rst-5-
 --
 Documentation/admin-guide/kernel-parameters.txt=97=Kernel parameters
 --
 Documentation/admin-guide/kernel-parameters.txt-4188-			this means that duplicate request_module() calls will
 Documentation/admin-guide/kernel-parameters.txt:4189:			trigger a WARN_ON() instead of a pr_warn(). Note that
 Documentation/admin-guide/kernel-parameters.txt:4190:			if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s
 Documentation/admin-guide/kernel-parameters.txt-4191-			will always be issued and this option does nothing.
 --
 Documentation/admin-guide/kernel-parameters.txt-5819-			This wake_up() will be accompanied by a
 Documentation/admin-guide/kernel-parameters.txt:5820:			WARN_ONCE() splat and an ftrace_dump().
 Documentation/admin-guide/kernel-parameters.txt-5821-
 --
 Documentation/admin-guide/mm/slab.rst=6=CONFIG_SLUB_DEBUG=y) but it is off by default (unless built with
 Documentation/admin-guide/mm/slab.rst:7:CONFIG_SLUB_DEBUG_ON=y).  You can enable debugging only for selected
 Documentation/admin-guide/mm/slab.rst-8-slabs in order to avoid an impact on overall system performance which
 --
 Documentation/admin-guide/mm/slab.rst=46=Possible debug options are::
 --
 Documentation/admin-guide/mm/slab.rst-57-	-		Switch all debugging off (useful if the kernel is
 Documentation/admin-guide/mm/slab.rst:58:			configured with CONFIG_SLUB_DEBUG_ON)
 Documentation/admin-guide/mm/slab.rst-59-
 --
 Documentation/core-api/packing.rst=297=An additional benefit over pack() and unpack() is that sanity checks on the
 Documentation/core-api/packing.rst:298:field definitions are handled at compile time with ``BUILD_BUG_ON`` rather
 Documentation/core-api/packing.rst-299-than only when the offending code is executed. These functions return void and
 --
 Documentation/core-api/packing.rst=306=Here is an example of how to use the fields APIs:
 --
 Documentation/core-api/packing.rst-332-   {
 Documentation/core-api/packing.rst:333:           BUILD_BUG_ON(sizeof(*buf) != SIZE;
 Documentation/core-api/packing.rst-334-
 --
 Documentation/core-api/packing.rst-340-   {
 Documentation/core-api/packing.rst:341:           BUILD_BUG_ON(sizeof(*buf) != SIZE;
 Documentation/core-api/packing.rst-342-
 --
 Documentation/dev-tools/checkpatch.rst=272=API usage
 --
 Documentation/dev-tools/checkpatch.rst-285-  **AVOID_BUG**
 Documentation/dev-tools/checkpatch.rst:286:    BUG() or BUG_ON() should be avoided totally.
 Documentation/dev-tools/checkpatch.rst:287:    Use WARN() and WARN_ON() instead, and handle the "impossible"
 Documentation/dev-tools/checkpatch.rst-288-    error condition as gracefully as possible.
 --
 Documentation/driver-api/media/drivers/ccs/mk-ccs-regs=139=print $H "#define CCS_BUILD_BUG \\
 Documentation/driver-api/media/drivers/ccs/mk-ccs-regs:140:	BUILD_BUG_ON(~CCI_REG_PRIVATE_MASK & ($all_flags))\n"
 Documentation/driver-api/media/drivers/ccs/mk-ccs-regs-141-    if defined $kernel;
 --
 Documentation/driver-api/media/v4l2-controls.rst=814=There can be only one notify function per control handler. Any attempt
 Documentation/driver-api/media/v4l2-controls.rst:815:to set another notify function will cause a WARN_ON.
 Documentation/driver-api/media/v4l2-controls.rst-816-
 --
 Documentation/driver-api/mtdnand.rst=272=unregisters the partitions in the MTD layer.
 --
 Documentation/driver-api/mtdnand.rst-279-        /* Unregister device */
 Documentation/driver-api/mtdnand.rst:280:        WARN_ON(mtd_device_unregister(board_mtd));
 Documentation/driver-api/mtdnand.rst-281-        /* Release resources */
 --
 Documentation/filesystems/porting.rst=815=just get rid of it.  Synchronous work (e.g. the stuff that can't
 Documentation/filesystems/porting.rst:816:be done from an RCU callback, or any WARN_ON() where we want the
 Documentation/filesystems/porting.rst-817-stack trace) *might* be movable to ->evict_inode(); however,
 --
 Documentation/gpu/introduction.rst=35=Instead locking should be check at runtime using e.g.
 Documentation/gpu/introduction.rst:36:``WARN_ON(!mutex_is_locked(...));``. Since it's much easier to ignore
 Documentation/gpu/introduction.rst-37-documentation than runtime noise this provides more value. And on top of
 --
 Documentation/gpu/todo.rst=185=interfaces to fix these issues:
 --
 Documentation/gpu/todo.rst-193-  Except for some driver code this is done. This task should be finished by
 Documentation/gpu/todo.rst:194:  adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all().
 Documentation/gpu/todo.rst-195-
 --
 Documentation/gpu/todo.rst=485=double-calls prepare/enable/disable/unprepare. Eventually that should probably
 Documentation/gpu/todo.rst:486:be turned into a WARN_ON() or somehow made louder.
 Documentation/gpu/todo.rst-487-
 --
 Documentation/kernel-hacking/locking.rst=383=to protect the cache and all the objects within it. Here's the code::
 --
 Documentation/kernel-hacking/locking.rst-420-    {
 Documentation/kernel-hacking/locking.rst:421:            BUG_ON(!obj);
 Documentation/kernel-hacking/locking.rst-422-            list_del(&obj->list);
 --
 Documentation/kernel-hacking/locking.rst=600=Here is the code::
 --
 Documentation/kernel-hacking/locking.rst-649-     {
 Documentation/kernel-hacking/locking.rst:650:             BUG_ON(!obj);
 Documentation/kernel-hacking/locking.rst-651-             list_del(&obj->list);
 --
 Documentation/kernel-hacking/locking.rst=709=the lock is no longer used to protect the reference count itself.
 --
 Documentation/kernel-hacking/locking.rst-762-     {
 Documentation/kernel-hacking/locking.rst:763:             BUG_ON(!obj);
 Documentation/kernel-hacking/locking.rst-764-             list_del(&obj->list);
 --
 Documentation/kernel-hacking/locking.rst=1139=this is the fundamental idea.
 --
 Documentation/kernel-hacking/locking.rst-1186-     {
 Documentation/kernel-hacking/locking.rst:1187:             BUG_ON(!obj);
 Documentation/kernel-hacking/locking.rst-1188-    -        list_del(&obj->list);
 --
 Documentation/leds/leds-class.rst=147=led_classdev_notify_brightness_hw_changed on a classdev not registered with
 Documentation/leds/leds-class.rst:148:the LED_BRIGHT_HW_CHANGED flag is a bug and will trigger a WARN_ON.
 Documentation/leds/leds-class.rst-149-
 --
 Documentation/locking/lockdep-design.rst=340=Exceeding this number will trigger the following lockdep warning::
 Documentation/locking/lockdep-design.rst-341-
 Documentation/locking/lockdep-design.rst:342:	(DEBUG_LOCKS_WARN_ON(id >= MAX_LOCKDEP_KEYS))
 Documentation/locking/lockdep-design.rst-343-
 --
 Documentation/memory-barriers.txt=820=one, perhaps as follows:
 --
 Documentation/memory-barriers.txt-822-	q = READ_ONCE(a);
 Documentation/memory-barriers.txt:823:	BUILD_BUG_ON(MAX <= 1); /* Order load from a with store to b. */
 Documentation/memory-barriers.txt-824-	if (q % MAX) {
 --
 Documentation/memory-barriers.txt=1558=of optimizations:
 --
 Documentation/memory-barriers.txt-1732-     interrupt handler returns with interrupts enabled, you will get a
 Documentation/memory-barriers.txt:1733:     WARN_ONCE() splat.)
 Documentation/memory-barriers.txt-1734-
 --
 Documentation/process/coding-style.rst=1228=Do not add new code that uses any of the BUG() variants, such as BUG(),
 Documentation/process/coding-style.rst:1229:BUG_ON(), or VM_BUG_ON(). Instead, use a WARN*() variant, preferably
 Documentation/process/coding-style.rst:1230:WARN_ON_ONCE(), and possibly with recovery code. Recovery code is not
 Documentation/process/coding-style.rst-1231-required if there is no reasonable way to at least partially recover.
 --
 Documentation/process/coding-style.rst=1235=good justification.
 Documentation/process/coding-style.rst-1236-
 Documentation/process/coding-style.rst:1237:Use WARN_ON_ONCE() rather than WARN() or WARN_ON()
 Documentation/process/coding-style.rst-1238-**************************************************
 Documentation/process/coding-style.rst-1239-
 Documentation/process/coding-style.rst:1240:WARN_ON_ONCE() is generally preferred over WARN() or WARN_ON(), because it
 Documentation/process/coding-style.rst-1241-is common for a given warning condition, if it occurs at all, to occur
 --
 Documentation/process/coding-style.rst=1266=likely to crash.
 Documentation/process/coding-style.rst-1267-
 Documentation/process/coding-style.rst:1268:Use BUILD_BUG_ON() for compile-time assertions
 Documentation/process/coding-style.rst-1269-**********************************************
 Documentation/process/coding-style.rst-1270-
 Documentation/process/coding-style.rst:1271:The use of BUILD_BUG_ON() is acceptable and encouraged, because it is a
 Documentation/process/coding-style.rst-1272-compile-time assertion that has no effect at runtime.
 --
 Documentation/process/debugging/userspace_debugging_guide.rst=210=Kernel panic analysis tools
 --
 Documentation/process/debugging/userspace_debugging_guide.rst-243-     ae8:	f9418015 	ldr	x21, [x0, #768]
 Documentation/process/debugging/userspace_debugging_guide.rst:244:        if (WARN_ON(!desc))
 Documentation/process/debugging/userspace_debugging_guide.rst-245-     aec:	b4000654 	cbz	x20, bb4 <rkvdec_device_run+0xec>
 --
 Documentation/process/deprecated.rst=30=others from using them in the future.
 Documentation/process/deprecated.rst-31-
 Documentation/process/deprecated.rst:32:BUG() and BUG_ON()
 Documentation/process/deprecated.rst-33-------------------
 Documentation/process/deprecated.rst:34:Use WARN() and WARN_ON() instead, and handle the "impossible"
 Documentation/process/deprecated.rst-35-error condition as gracefully as possible. While the BUG()-family
 --
 Documentation/scsi/ChangeLog.lpfc=98=Changes from 20050215 to 20050223
 --
 Documentation/scsi/ChangeLog.lpfc-137-	  causing it to figure in load average calculations. Also add a
 Documentation/scsi/ChangeLog.lpfc:138:	  BUG_ON to the ret code of wait_event_interruptible() since the
 Documentation/scsi/ChangeLog.lpfc-139-	  premise is that the worker thread is signal-immune.
 --
 Documentation/scsi/ChangeLog.megaraid=202=Older Version	: 2.20.4.5 (scsi module), 2.20.2.5 (cmm module)
 --
 Documentation/scsi/ChangeLog.megaraid-248-
 Documentation/scsi/ChangeLog.megaraid:249:	  BUG_ON(!spin_is_locked(&some_lock));
 Documentation/scsi/ChangeLog.megaraid-250-
 --
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst=4036=It shows the ``BUG?`` message and stack trace as well as
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst:4037::c:func:`snd_BUG_ON()` at the point. It's useful to show that a
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst-4038-fatal error happens there.
 --
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst=4040=When no debug flag is set, this macro is ignored.
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst-4041-
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst:4042::c:func:`snd_BUG_ON()`
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst-4043-----------------------
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst-4044-
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst:4045::c:func:`snd_BUG_ON()` macro is similar with
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst:4046::c:func:`WARN_ON()` macro. For example, snd_BUG_ON(!pointer); or
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst:4047:it can be used as the condition, if (snd_BUG_ON(non_zero_is_bug))
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst-4048-return -EINVAL;
 --
 Documentation/trace/boottime-trace.rst=43=kernel.traceoff_on_warning
 Documentation/trace/boottime-trace.rst:44:   Stop tracing if WARN_ON() occurs.
 Documentation/trace/boottime-trace.rst-45-
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst=403=e tutti gli oggetti che contiene. Ecco il codice::
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst-440-    {
 Documentation/translations/it_IT/kernel-hacking/locking.rst:441:            BUG_ON(!obj);
 Documentation/translations/it_IT/kernel-hacking/locking.rst-442-            list_del(&obj->list);
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst=621=Ecco il codice::
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst-670-     {
 Documentation/translations/it_IT/kernel-hacking/locking.rst:671:             BUG_ON(!obj);
 Documentation/translations/it_IT/kernel-hacking/locking.rst-672-             list_del(&obj->list);
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst=730=contatore stesso.
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst-783-     {
 Documentation/translations/it_IT/kernel-hacking/locking.rst:784:             BUG_ON(!obj);
 Documentation/translations/it_IT/kernel-hacking/locking.rst-785-             list_del(&obj->list);
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst=1170=codice RCU è un po' più ottimizzato di così, ma questa è l'idea di fondo.
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst-1217-     {
 Documentation/translations/it_IT/kernel-hacking/locking.rst:1218:             BUG_ON(!obj);
 Documentation/translations/it_IT/kernel-hacking/locking.rst-1219-    -        list_del(&obj->list);
 --
 Documentation/translations/it_IT/locking/lockdep-design.rst=342=seguente avviso::
 Documentation/translations/it_IT/locking/lockdep-design.rst-343-
 Documentation/translations/it_IT/locking/lockdep-design.rst:344:	(DEBUG_LOCKS_WARN_ON(id >= MAX_LOCKDEP_KEYS))
 Documentation/translations/it_IT/locking/lockdep-design.rst-345-
 --
 Documentation/translations/it_IT/process/deprecated.rst=35=l'uso.
 Documentation/translations/it_IT/process/deprecated.rst-36-
 Documentation/translations/it_IT/process/deprecated.rst:37:BUG() e BUG_ON()
 Documentation/translations/it_IT/process/deprecated.rst-38-----------------
 Documentation/translations/it_IT/process/deprecated.rst:39:Al loro posto usate WARN() e WARN_ON() per gestire le
 Documentation/translations/it_IT/process/deprecated.rst-40-condizioni "impossibili" e gestitele come se fosse possibile farlo.
 --
 Documentation/translations/sp_SP/memory-barriers.txt=861=asegurarse de que MAX sea mayor que uno, tal vez de la siguiente manera:
 --
 Documentation/translations/sp_SP/memory-barriers.txt-863-  	q = READ_ONCE(a);
 Documentation/translations/sp_SP/memory-barriers.txt:864:  	BUILD_BUG_ON(MAX <= 1); /* Orden de carga de a con store de b */
 Documentation/translations/sp_SP/memory-barriers.txt-865-  	if (q % MAX) {
 --
 Documentation/translations/sp_SP/memory-barriers.txt=1622=algunos ejemplos de tal tipo de optimizaciones:
 --
 Documentation/translations/sp_SP/memory-barriers.txt-1803-     hecho, si un controlador de interrupciones regresa con interrupciones
 Documentation/translations/sp_SP/memory-barriers.txt:1804:     habilitadas, obtendrá un WARN_ONCE().)
 Documentation/translations/sp_SP/memory-barriers.txt-1805-
 --
 Documentation/translations/sp_SP/process/coding-style.rst=1246=No agregue código nuevo que use cualquiera de las variantes BUG(), como
 Documentation/translations/sp_SP/process/coding-style.rst:1247:BUG(), BUG_ON() o VM_BUG_ON(). En su lugar, use una variante WARN*(),
 Documentation/translations/sp_SP/process/coding-style.rst:1248:preferiblemente WARN_ON_ONCE(), y posiblemente con código de recuperación.
 Documentation/translations/sp_SP/process/coding-style.rst-1249-El código de recuperación no es requerido si no hay una forma razonable de
 --
 Documentation/translations/sp_SP/process/coding-style.rst=1254=aún pueden usar BUG(), pero necesitan una buena justificación.
 Documentation/translations/sp_SP/process/coding-style.rst-1255-
 Documentation/translations/sp_SP/process/coding-style.rst:1256:Use WARN_ON_ONCE() en lugar de WARN() o WARN_ON()
 Documentation/translations/sp_SP/process/coding-style.rst-1257-*************************************************
 Documentation/translations/sp_SP/process/coding-style.rst-1258-
 Documentation/translations/sp_SP/process/coding-style.rst:1259:Generalmente, se prefiere WARN_ON_ONCE() a WARN() o WARN_ON(), porque es
 Documentation/translations/sp_SP/process/coding-style.rst-1260-común que una condición de advertencia dada, si ocurre, ocurra varias
 --
 Documentation/translations/sp_SP/process/coding-style.rst=1287=se rompa.
 Documentation/translations/sp_SP/process/coding-style.rst-1288-
 Documentation/translations/sp_SP/process/coding-style.rst:1289:Use BUILD_BUG_ON() para aserciones en tiempo de compilación
 Documentation/translations/sp_SP/process/coding-style.rst-1290-***********************************************************
 Documentation/translations/sp_SP/process/coding-style.rst-1291-
 Documentation/translations/sp_SP/process/coding-style.rst:1292:El uso de BUILD_BUG_ON() es aceptable y recomendado, porque es una aserción
 Documentation/translations/sp_SP/process/coding-style.rst-1293-en tiempo de compilación, que no tiene efecto en tiempo de ejecución.
 --
 Documentation/translations/sp_SP/process/deprecated.rst=33=desanimar a otros a usarla en el futuro.
 Documentation/translations/sp_SP/process/deprecated.rst-34-
 Documentation/translations/sp_SP/process/deprecated.rst:35:BUG() y BUG_ON()
 Documentation/translations/sp_SP/process/deprecated.rst-36-----------------
 Documentation/translations/sp_SP/process/deprecated.rst:37:Use WARN() y WARN_ON() en su lugar, y gestione las condiciones de error
 Documentation/translations/sp_SP/process/deprecated.rst-38-"imposibles" tan elegantemente como se pueda. Mientras que la familia de
 --
 Documentation/translations/zh_CN/admin-guide/clearing-warn-once.rst:1:清除 WARN_ONCE
 Documentation/translations/zh_CN/admin-guide/clearing-warn-once.rst-2---------------
 Documentation/translations/zh_CN/admin-guide/clearing-warn-once.rst-3-
 Documentation/translations/zh_CN/admin-guide/clearing-warn-once.rst:4:WARN_ONCE / WARN_ON_ONCE / printk_once 仅仅打印一次消息.
 Documentation/translations/zh_CN/admin-guide/clearing-warn-once.rst-5-
 --
 Documentation/translations/zh_TW/admin-guide/clearing-warn-once.rst-6-
 Documentation/translations/zh_TW/admin-guide/clearing-warn-once.rst:7:清除 WARN_ONCE
 Documentation/translations/zh_TW/admin-guide/clearing-warn-once.rst-8---------------
 Documentation/translations/zh_TW/admin-guide/clearing-warn-once.rst-9-
 Documentation/translations/zh_TW/admin-guide/clearing-warn-once.rst:10:WARN_ONCE / WARN_ON_ONCE / printk_once 僅僅打印一次消息.
 Documentation/translations/zh_TW/admin-guide/clearing-warn-once.rst-11-
 --
 Makefile=850=ifeq ("$(origin UT)", "command line")
 Makefile:851:  WARN_ON_UNUSED_TRACEPOINTS := $(UT)
 Makefile-852-endif
 Makefile=853=endif # CONFIG_TRACEPOINTS
 Makefile-854-
 Makefile:855:export WARN_ON_UNUSED_TRACEPOINTS
 Makefile-856-
 --
 arch/alpha/include/asm/cmpxchg.h=217=____cmpxchg(volatile void *ptr, unsigned long old, unsigned long new,
 --
 arch/alpha/include/asm/cmpxchg.h-245-({									\
 arch/alpha/include/asm/cmpxchg.h:246:	BUILD_BUG_ON(sizeof(*(ptr)) != 8);				\
 arch/alpha/include/asm/cmpxchg.h-247-	cmpxchg_local((ptr), (o), (n));					\
 --
 arch/alpha/include/asm/cmpxchg.h-278-({									\
 arch/alpha/include/asm/cmpxchg.h:279:	BUILD_BUG_ON(sizeof(*(ptr)) != 8);				\
 arch/alpha/include/asm/cmpxchg.h-280-	arch_cmpxchg((ptr), (o), (n));					\
 --
 arch/alpha/include/asm/err_ev7.h=164=static inline int ev7_lf_env_index(int type)
 arch/alpha/include/asm/err_ev7.h-165-{
 arch/alpha/include/asm/err_ev7.h:166:	BUG_ON((type < EL_TYPE__PAL__ENV__AMBIENT_TEMPERATURE) 
 arch/alpha/include/asm/err_ev7.h-167-	       || (type > EL_TYPE__PAL__ENV__HOT_PLUG));
 --
 arch/alpha/kernel/io.c=320=void ioread16_rep(const void __iomem *port, void *dst, unsigned long count)
 --
 arch/alpha/kernel/io.c-324-			return;
 arch/alpha/kernel/io.c:325:		BUG_ON((unsigned long)dst & 0x1);
 arch/alpha/kernel/io.c-326-		count--;
 --
 arch/alpha/kernel/io.c=414=void iowrite16_rep(void __iomem *port, const void *src, unsigned long count)
 --
 arch/alpha/kernel/io.c-418-			return;
 arch/alpha/kernel/io.c:419:		BUG_ON((unsigned long)src & 0x1);
 arch/alpha/kernel/io.c-420-		iowrite16(*(unsigned short *)src, port);
 --
 arch/alpha/kernel/pci_iommu.c=300=static struct pci_dev *alpha_gendev_to_pci(struct device *dev)
 --
 arch/alpha/kernel/pci_iommu.c-306-	   BUG() otherwise. */
 arch/alpha/kernel/pci_iommu.c:307:	BUG_ON(!isa_bridge);
 arch/alpha/kernel/pci_iommu.c-308-
 --
 arch/alpha/kernel/pci_iommu.c=623=static int alpha_pci_map_sg(struct device *dev, struct scatterlist *sg,
 --
 arch/alpha/kernel/pci_iommu.c-633-
 arch/alpha/kernel/pci_iommu.c:634:	BUG_ON(dir == DMA_NONE);
 arch/alpha/kernel/pci_iommu.c-635-
 --
 arch/alpha/kernel/pci_iommu.c=704=static void alpha_pci_unmap_sg(struct device *dev, struct scatterlist *sg,
 --
 arch/alpha/kernel/pci_iommu.c-715-
 arch/alpha/kernel/pci_iommu.c:716:	BUG_ON(dir == DMA_NONE);
 arch/alpha/kernel/pci_iommu.c-717-
 --
 arch/alpha/kernel/perf_event.c=152=static int ev67_check_constraints(struct perf_event **event,
 --
 arch/alpha/kernel/perf_event.c-162-
 arch/alpha/kernel/perf_event.c:163:	BUG_ON(n_ev != 2);
 arch/alpha/kernel/perf_event.c-164-
 --
 arch/alpha/kernel/perf_event.c=552=static void alpha_pmu_start(struct perf_event *event, int flags)
 --
 arch/alpha/kernel/perf_event.c-556-
 arch/alpha/kernel/perf_event.c:557:	if (WARN_ON_ONCE(!(hwc->state & PERF_HES_STOPPED)))
 arch/alpha/kernel/perf_event.c-558-		return;
 --
 arch/alpha/kernel/perf_event.c-560-	if (flags & PERF_EF_RELOAD) {
 arch/alpha/kernel/perf_event.c:561:		WARN_ON_ONCE(!(hwc->state & PERF_HES_UPTODATE));
 arch/alpha/kernel/perf_event.c-562-		alpha_perf_event_set_period(event, hwc, hwc->idx);
 --
 arch/arc/kernel/mcip.c=376=idu_of_init(struct device_node *intc, struct device_node *parent)
 --
 arch/arc/kernel/mcip.c-409-		virq = irq_create_mapping(NULL, i + FIRST_EXT_IRQ);
 arch/arc/kernel/mcip.c:410:		BUG_ON(!virq);
 arch/arc/kernel/mcip.c-411-		irq_set_chained_handler_and_data(virq, idu_cascade_isr, domain);
 --
 arch/arc/kernel/perf_event.c=451=static void arc_pmu_start(struct perf_event *event, int flags)
 --
 arch/arc/kernel/perf_event.c-455-
 arch/arc/kernel/perf_event.c:456:	if (WARN_ON_ONCE(idx == -1))
 arch/arc/kernel/perf_event.c-457-		return;
 --
 arch/arc/kernel/perf_event.c-459-	if (flags & PERF_EF_RELOAD)
 arch/arc/kernel/perf_event.c:460:		WARN_ON_ONCE(!(hwc->state & PERF_HES_UPTODATE));
 arch/arc/kernel/perf_event.c-461-
 --
 arch/arc/kernel/perf_event.c=562=static irqreturn_t arc_pmu_intr(int irq, void *dev)
 --
 arch/arc/kernel/perf_event.c-597-
 arch/arc/kernel/perf_event.c:598:		WARN_ON_ONCE(hwc->idx != idx);
 arch/arc/kernel/perf_event.c-599-
 --
 arch/arc/kernel/perf_event.c=721=static int arc_pmu_device_probe(struct platform_device *pdev)
 --
 arch/arc/kernel/perf_event.c-741-	}
 arch/arc/kernel/perf_event.c:742:	BUILD_BUG_ON(ARC_PERF_MAX_COUNTERS > 32);
 arch/arc/kernel/perf_event.c:743:	if (WARN_ON(pct_bcr.c > ARC_PERF_MAX_COUNTERS))
 arch/arc/kernel/perf_event.c-744-		return -EINVAL;
 --
 arch/arc/kernel/process.c=46=SYSCALL_DEFINE3(arc_usr_cmpxchg, int __user *, uaddr, int, expected, int, new)
 --
 arch/arc/kernel/process.c-57-	 */
 arch/arc/kernel/process.c:58:	WARN_ON_ONCE(IS_ENABLED(CONFIG_SMP));
 arch/arc/kernel/process.c-59-
 --
 arch/arc/kernel/smp.c=131=static void arc_default_smp_cpu_kick(int cpu, unsigned long pc)
 arch/arc/kernel/smp.c-132-{
 arch/arc/kernel/smp.c:133:	BUG_ON(cpu == 0);
 arch/arc/kernel/smp.c-134-
 --
 arch/arc/kernel/unwind.c=33=do {						\
 --
 arch/arc/kernel/unwind.c-43-#define EXTRA_INFO(f) { \
 arch/arc/kernel/unwind.c:44:		BUILD_BUG_ON_ZERO(offsetof(struct unwind_frame_info, f) \
 arch/arc/kernel/unwind.c-45-				% sizeof_field(struct unwind_frame_info, f)) \
 --
 arch/arc/kernel/unwind.c=244=static void init_unwind_hdr(struct unwind_table *table,
 --
 arch/arc/kernel/unwind.c-312-	put_unaligned((unsigned long)table->address, &header->eh_frame_ptr);
 arch/arc/kernel/unwind.c:313:	BUILD_BUG_ON(offsetof(typeof(*header), fde_count)
 arch/arc/kernel/unwind.c-314-		     % __alignof(typeof(header->fde_count)));
 --
 arch/arc/kernel/unwind.c-316-
 arch/arc/kernel/unwind.c:317:	BUILD_BUG_ON(offsetof(typeof(*header), table)
 arch/arc/kernel/unwind.c-318-		     % __alignof(typeof(*header->table)));
 --
 arch/arc/kernel/unwind.c-333-	}
 arch/arc/kernel/unwind.c:334:	WARN_ON(n != header->fde_count);
 arch/arc/kernel/unwind.c-335-
 --
 arch/arc/kernel/unwind.c=525=static unsigned long read_pointer(const u8 **pLoc, const void *end,
 --
 arch/arc/kernel/unwind.c-559-	case DW_EH_PE_data8:
 arch/arc/kernel/unwind.c:560:		BUILD_BUG_ON(sizeof(u64) != sizeof(value));
 arch/arc/kernel/unwind.c-561-#else
 arch/arc/kernel/unwind.c:562:		BUILD_BUG_ON(sizeof(u32) != sizeof(value));
 arch/arc/kernel/unwind.c-563-#endif
 --
 arch/arc/kernel/unwind.c-570-	case DW_EH_PE_leb128:
 arch/arc/kernel/unwind.c:571:		BUILD_BUG_ON(sizeof(uleb128_t) > sizeof(value));
 arch/arc/kernel/unwind.c-572-		value = ptrType & DW_EH_PE_signed ? get_sleb128(&ptr.p8, end)
 --
 arch/arc/mm/cache.c=100=int arc_cache_mumbojumbo(int c, char *buf, int len)
 --
 arch/arc/mm/cache.c-111-	if (is_isa_arcompact() && (ibcr.ver <= 3)) {
 arch/arc/mm/cache.c:112:		BUG_ON(ibcr.config != 3);
 arch/arc/mm/cache.c-113-		assoc = 2;		/* Fixed to 2w set assoc */
 --
 arch/arc/mm/cache.c-133-	if (is_isa_arcompact() && (dbcr.ver <= 3)) {
 arch/arc/mm/cache.c:134:		BUG_ON(dbcr.config != 2);
 arch/arc/mm/cache.c-135-		vipt = 1;
 --
 arch/arc/mm/cache.c=995=static noinline void __init arc_cache_init_master(void)
 --
 arch/arc/mm/cache.c-1036-	 */
 arch/arc/mm/cache.c:1037:	BUILD_BUG_ON_MSG(L1_CACHE_BYTES > SMP_CACHE_BYTES,
 arch/arc/mm/cache.c-1038-			 "SMP_CACHE_BYTES must be >= any cache line length");
 --
 arch/arc/mm/highmem.c=64=void __init kmap_init(void)
 --
 arch/arc/mm/highmem.c-66-	/* Due to recursive include hell, we can't do this in processor.h */
 arch/arc/mm/highmem.c:67:	BUILD_BUG_ON(PAGE_OFFSET < (VMALLOC_END + FIXMAP_SIZE + PKMAP_SIZE));
 arch/arc/mm/highmem.c:68:	BUILD_BUG_ON(LAST_PKMAP > PTRS_PER_PTE);
 arch/arc/mm/highmem.c:69:	BUILD_BUG_ON(FIX_KMAP_SLOTS > PTRS_PER_PTE);
 arch/arc/mm/highmem.c-70-
 --
 arch/arc/mm/init.c=159=void __init arch_mm_preinit(void)
 --
 arch/arc/mm/init.c-164-
 arch/arc/mm/init.c:165:	BUILD_BUG_ON((PTRS_PER_PGD * sizeof(pgd_t)) > PAGE_SIZE);
 arch/arc/mm/init.c:166:	BUILD_BUG_ON((PTRS_PER_PUD * sizeof(pud_t)) > PAGE_SIZE);
 arch/arc/mm/init.c:167:	BUILD_BUG_ON((PTRS_PER_PMD * sizeof(pmd_t)) > PAGE_SIZE);
 arch/arc/mm/init.c:168:	BUILD_BUG_ON((PTRS_PER_PTE * sizeof(pte_t)) > PAGE_SIZE);
 arch/arc/mm/init.c-169-}
 --
 arch/arc/mm/tlb.c=616=void arc_mmu_init(void)
 --
 arch/arc/mm/tlb.c-623-	 */
 arch/arc/mm/tlb.c:624:	BUILD_BUG_ON(!IS_ALIGNED((CONFIG_ARC_KVADDR_SIZE << 20), PMD_SIZE));
 arch/arc/mm/tlb.c-625-
 --
 arch/arc/mm/tlb.c-629-	 */
 arch/arc/mm/tlb.c:630:	BUILD_BUG_ON(!IS_ALIGNED(STACK_TOP, PMD_SIZE));
 arch/arc/mm/tlb.c-631-
 --
 arch/arc/mm/tlb.c=694=void do_tlb_overlap_fault(unsigned long cause, unsigned long address,
]
]

gemini-3.1-pro-preview

							input: 124289
							output: 21
							thoughts: 52
						

Okay, let's see... I'm looking at this grep output, and hold on... I'm not seeing any `BUG_ON` or `WARN_ON` macros in `drivers/block/nbd.c`. That's a little unusual, given the potential for issues in that area.

**Investigating the Absence of Error-Checking Macros in NBD Driver**

Alright, that absence warrants a closer look. It's time to refine this search. Let me narrow the focus down and specifically examine the `drivers/block/nbd.c` file itself. I need to understand why these crucial error-checking macros aren't showing up in the broader search. Is it a coding style thing? Are they using a different method? Or are there potential unhandled scenarios? Time to dig deeper.

map[Expression:BUG_ON|WARN_ON]

map[Output:
Full output is too long, showing 500 out of 203717 lines.
Use more precise expression if possible.

[Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst=78=lock-acquisition and lock-release functions::
 --
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst-104-   25
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst:105:   26 WARN_ON(r1 == 0 && r2 == 0 && r3 == 0);
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst-106-
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst:107:The ``WARN_ON()`` is evaluated at "the end of time",
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst-108-after all changes have propagated throughout the system.
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst=109=Without the ``smp_mb__after_unlock_lock()`` provided by the
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst:110:acquisition functions, this ``WARN_ON()`` could trigger, for example
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst-111-on PowerPC.
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst=112=The ``smp_mb__after_unlock_lock()`` invocations prevent this
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst:113:``WARN_ON()`` from triggering.
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst-114-
 --
 Documentation/RCU/Design/Requirements/Requirements.rst=755=example illustrates this:
 --
 Documentation/RCU/Design/Requirements/Requirements.rst-765-       7     r2 = READ_ONCE(x);
 Documentation/RCU/Design/Requirements/Requirements.rst:766:       8     WARN_ON(!r2); /* BUG!!! */
 Documentation/RCU/Design/Requirements/Requirements.rst-767-       9   }
 --
 Documentation/RCU/Design/Requirements/Requirements.rst=779=If the thread0() function's rcu_read_lock() excluded the
 Documentation/RCU/Design/Requirements/Requirements.rst:780:thread1() function's update, the WARN_ON() could never fire. But
 Documentation/RCU/Design/Requirements/Requirements.rst-781-the fact is that rcu_read_lock() does not exclude much of anything
 Documentation/RCU/Design/Requirements/Requirements.rst=782=aside from subsequent grace periods, of which thread1() has none, so
 Documentation/RCU/Design/Requirements/Requirements.rst:783:the WARN_ON() can and does fire.
 Documentation/RCU/Design/Requirements/Requirements.rst-784-
 --
 Documentation/RCU/lockdep.rst=25=aren't certain (for example, if CONFIG_DEBUG_LOCK_ALLOC is not set).
 Documentation/RCU/lockdep.rst:26:This prevents things like WARN_ON(!rcu_read_lock_held()) from giving false
 Documentation/RCU/lockdep.rst-27-positives when lockdep is disabled.
 --
 Documentation/RCU/rcubarrier.rst=194=The original code for rcu_barrier() was roughly as follows::
 --
 Documentation/RCU/rcubarrier.rst-197-  2  {
 Documentation/RCU/rcubarrier.rst:198:  3    BUG_ON(in_interrupt());
 Documentation/RCU/rcubarrier.rst-199-  4    /* Take cpucontrol mutex to protect against CPU hotplug */
 --
 Documentation/admin-guide/clearing-warn-once.rst:1:Clearing WARN_ONCE
 Documentation/admin-guide/clearing-warn-once.rst-2-------------------
 Documentation/admin-guide/clearing-warn-once.rst-3-
 Documentation/admin-guide/clearing-warn-once.rst:4:WARN_ONCE / WARN_ON_ONCE / printk_once only emit a message once.
 Documentation/admin-guide/clearing-warn-once.rst-5-
 --
 Documentation/admin-guide/kernel-parameters.txt=97=Kernel parameters
 --
 Documentation/admin-guide/kernel-parameters.txt-4188-			this means that duplicate request_module() calls will
 Documentation/admin-guide/kernel-parameters.txt:4189:			trigger a WARN_ON() instead of a pr_warn(). Note that
 Documentation/admin-guide/kernel-parameters.txt:4190:			if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s
 Documentation/admin-guide/kernel-parameters.txt-4191-			will always be issued and this option does nothing.
 --
 Documentation/admin-guide/kernel-parameters.txt-5819-			This wake_up() will be accompanied by a
 Documentation/admin-guide/kernel-parameters.txt:5820:			WARN_ONCE() splat and an ftrace_dump().
 Documentation/admin-guide/kernel-parameters.txt-5821-
 --
 Documentation/admin-guide/mm/slab.rst=6=CONFIG_SLUB_DEBUG=y) but it is off by default (unless built with
 Documentation/admin-guide/mm/slab.rst:7:CONFIG_SLUB_DEBUG_ON=y).  You can enable debugging only for selected
 Documentation/admin-guide/mm/slab.rst-8-slabs in order to avoid an impact on overall system performance which
 --
 Documentation/admin-guide/mm/slab.rst=46=Possible debug options are::
 --
 Documentation/admin-guide/mm/slab.rst-57-	-		Switch all debugging off (useful if the kernel is
 Documentation/admin-guide/mm/slab.rst:58:			configured with CONFIG_SLUB_DEBUG_ON)
 Documentation/admin-guide/mm/slab.rst-59-
 --
 Documentation/core-api/packing.rst=297=An additional benefit over pack() and unpack() is that sanity checks on the
 Documentation/core-api/packing.rst:298:field definitions are handled at compile time with ``BUILD_BUG_ON`` rather
 Documentation/core-api/packing.rst-299-than only when the offending code is executed. These functions return void and
 --
 Documentation/core-api/packing.rst=306=Here is an example of how to use the fields APIs:
 --
 Documentation/core-api/packing.rst-332-   {
 Documentation/core-api/packing.rst:333:           BUILD_BUG_ON(sizeof(*buf) != SIZE;
 Documentation/core-api/packing.rst-334-
 --
 Documentation/core-api/packing.rst-340-   {
 Documentation/core-api/packing.rst:341:           BUILD_BUG_ON(sizeof(*buf) != SIZE;
 Documentation/core-api/packing.rst-342-
 --
 Documentation/dev-tools/checkpatch.rst=272=API usage
 --
 Documentation/dev-tools/checkpatch.rst-285-  **AVOID_BUG**
 Documentation/dev-tools/checkpatch.rst:286:    BUG() or BUG_ON() should be avoided totally.
 Documentation/dev-tools/checkpatch.rst:287:    Use WARN() and WARN_ON() instead, and handle the "impossible"
 Documentation/dev-tools/checkpatch.rst-288-    error condition as gracefully as possible.
 --
 Documentation/driver-api/media/drivers/ccs/mk-ccs-regs=139=print $H "#define CCS_BUILD_BUG \\
 Documentation/driver-api/media/drivers/ccs/mk-ccs-regs:140:	BUILD_BUG_ON(~CCI_REG_PRIVATE_MASK & ($all_flags))\n"
 Documentation/driver-api/media/drivers/ccs/mk-ccs-regs-141-    if defined $kernel;
 --
 Documentation/driver-api/media/v4l2-controls.rst=814=There can be only one notify function per control handler. Any attempt
 Documentation/driver-api/media/v4l2-controls.rst:815:to set another notify function will cause a WARN_ON.
 Documentation/driver-api/media/v4l2-controls.rst-816-
 --
 Documentation/driver-api/mtdnand.rst=272=unregisters the partitions in the MTD layer.
 --
 Documentation/driver-api/mtdnand.rst-279-        /* Unregister device */
 Documentation/driver-api/mtdnand.rst:280:        WARN_ON(mtd_device_unregister(board_mtd));
 Documentation/driver-api/mtdnand.rst-281-        /* Release resources */
 --
 Documentation/filesystems/porting.rst=815=just get rid of it.  Synchronous work (e.g. the stuff that can't
 Documentation/filesystems/porting.rst:816:be done from an RCU callback, or any WARN_ON() where we want the
 Documentation/filesystems/porting.rst-817-stack trace) *might* be movable to ->evict_inode(); however,
 --
 Documentation/gpu/introduction.rst=35=Instead locking should be check at runtime using e.g.
 Documentation/gpu/introduction.rst:36:``WARN_ON(!mutex_is_locked(...));``. Since it's much easier to ignore
 Documentation/gpu/introduction.rst-37-documentation than runtime noise this provides more value. And on top of
 --
 Documentation/gpu/todo.rst=185=interfaces to fix these issues:
 --
 Documentation/gpu/todo.rst-193-  Except for some driver code this is done. This task should be finished by
 Documentation/gpu/todo.rst:194:  adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all().
 Documentation/gpu/todo.rst-195-
 --
 Documentation/gpu/todo.rst=485=double-calls prepare/enable/disable/unprepare. Eventually that should probably
 Documentation/gpu/todo.rst:486:be turned into a WARN_ON() or somehow made louder.
 Documentation/gpu/todo.rst-487-
 --
 Documentation/kernel-hacking/locking.rst=383=to protect the cache and all the objects within it. Here's the code::
 --
 Documentation/kernel-hacking/locking.rst-420-    {
 Documentation/kernel-hacking/locking.rst:421:            BUG_ON(!obj);
 Documentation/kernel-hacking/locking.rst-422-            list_del(&obj->list);
 --
 Documentation/kernel-hacking/locking.rst=600=Here is the code::
 --
 Documentation/kernel-hacking/locking.rst-649-     {
 Documentation/kernel-hacking/locking.rst:650:             BUG_ON(!obj);
 Documentation/kernel-hacking/locking.rst-651-             list_del(&obj->list);
 --
 Documentation/kernel-hacking/locking.rst=709=the lock is no longer used to protect the reference count itself.
 --
 Documentation/kernel-hacking/locking.rst-762-     {
 Documentation/kernel-hacking/locking.rst:763:             BUG_ON(!obj);
 Documentation/kernel-hacking/locking.rst-764-             list_del(&obj->list);
 --
 Documentation/kernel-hacking/locking.rst=1139=this is the fundamental idea.
 --
 Documentation/kernel-hacking/locking.rst-1186-     {
 Documentation/kernel-hacking/locking.rst:1187:             BUG_ON(!obj);
 Documentation/kernel-hacking/locking.rst-1188-    -        list_del(&obj->list);
 --
 Documentation/leds/leds-class.rst=147=led_classdev_notify_brightness_hw_changed on a classdev not registered with
 Documentation/leds/leds-class.rst:148:the LED_BRIGHT_HW_CHANGED flag is a bug and will trigger a WARN_ON.
 Documentation/leds/leds-class.rst-149-
 --
 Documentation/locking/lockdep-design.rst=340=Exceeding this number will trigger the following lockdep warning::
 Documentation/locking/lockdep-design.rst-341-
 Documentation/locking/lockdep-design.rst:342:	(DEBUG_LOCKS_WARN_ON(id >= MAX_LOCKDEP_KEYS))
 Documentation/locking/lockdep-design.rst-343-
 --
 Documentation/memory-barriers.txt=820=one, perhaps as follows:
 --
 Documentation/memory-barriers.txt-822-	q = READ_ONCE(a);
 Documentation/memory-barriers.txt:823:	BUILD_BUG_ON(MAX <= 1); /* Order load from a with store to b. */
 Documentation/memory-barriers.txt-824-	if (q % MAX) {
 --
 Documentation/memory-barriers.txt=1558=of optimizations:
 --
 Documentation/memory-barriers.txt-1732-     interrupt handler returns with interrupts enabled, you will get a
 Documentation/memory-barriers.txt:1733:     WARN_ONCE() splat.)
 Documentation/memory-barriers.txt-1734-
 --
 Documentation/process/coding-style.rst=1228=Do not add new code that uses any of the BUG() variants, such as BUG(),
 Documentation/process/coding-style.rst:1229:BUG_ON(), or VM_BUG_ON(). Instead, use a WARN*() variant, preferably
 Documentation/process/coding-style.rst:1230:WARN_ON_ONCE(), and possibly with recovery code. Recovery code is not
 Documentation/process/coding-style.rst-1231-required if there is no reasonable way to at least partially recover.
 --
 Documentation/process/coding-style.rst=1235=good justification.
 Documentation/process/coding-style.rst-1236-
 Documentation/process/coding-style.rst:1237:Use WARN_ON_ONCE() rather than WARN() or WARN_ON()
 Documentation/process/coding-style.rst-1238-**************************************************
 Documentation/process/coding-style.rst-1239-
 Documentation/process/coding-style.rst:1240:WARN_ON_ONCE() is generally preferred over WARN() or WARN_ON(), because it
 Documentation/process/coding-style.rst-1241-is common for a given warning condition, if it occurs at all, to occur
 --
 Documentation/process/coding-style.rst=1266=likely to crash.
 Documentation/process/coding-style.rst-1267-
 Documentation/process/coding-style.rst:1268:Use BUILD_BUG_ON() for compile-time assertions
 Documentation/process/coding-style.rst-1269-**********************************************
 Documentation/process/coding-style.rst-1270-
 Documentation/process/coding-style.rst:1271:The use of BUILD_BUG_ON() is acceptable and encouraged, because it is a
 Documentation/process/coding-style.rst-1272-compile-time assertion that has no effect at runtime.
 --
 Documentation/process/debugging/userspace_debugging_guide.rst=210=Kernel panic analysis tools
 --
 Documentation/process/debugging/userspace_debugging_guide.rst-243-     ae8:	f9418015 	ldr	x21, [x0, #768]
 Documentation/process/debugging/userspace_debugging_guide.rst:244:        if (WARN_ON(!desc))
 Documentation/process/debugging/userspace_debugging_guide.rst-245-     aec:	b4000654 	cbz	x20, bb4 <rkvdec_device_run+0xec>
 --
 Documentation/process/deprecated.rst=30=others from using them in the future.
 Documentation/process/deprecated.rst-31-
 Documentation/process/deprecated.rst:32:BUG() and BUG_ON()
 Documentation/process/deprecated.rst-33-------------------
 Documentation/process/deprecated.rst:34:Use WARN() and WARN_ON() instead, and handle the "impossible"
 Documentation/process/deprecated.rst-35-error condition as gracefully as possible. While the BUG()-family
 --
 Documentation/scsi/ChangeLog.lpfc=98=Changes from 20050215 to 20050223
 --
 Documentation/scsi/ChangeLog.lpfc-137-	  causing it to figure in load average calculations. Also add a
 Documentation/scsi/ChangeLog.lpfc:138:	  BUG_ON to the ret code of wait_event_interruptible() since the
 Documentation/scsi/ChangeLog.lpfc-139-	  premise is that the worker thread is signal-immune.
 --
 Documentation/scsi/ChangeLog.megaraid=202=Older Version	: 2.20.4.5 (scsi module), 2.20.2.5 (cmm module)
 --
 Documentation/scsi/ChangeLog.megaraid-248-
 Documentation/scsi/ChangeLog.megaraid:249:	  BUG_ON(!spin_is_locked(&some_lock));
 Documentation/scsi/ChangeLog.megaraid-250-
 --
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst=4036=It shows the ``BUG?`` message and stack trace as well as
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst:4037::c:func:`snd_BUG_ON()` at the point. It's useful to show that a
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst-4038-fatal error happens there.
 --
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst=4040=When no debug flag is set, this macro is ignored.
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst-4041-
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst:4042::c:func:`snd_BUG_ON()`
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst-4043-----------------------
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst-4044-
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst:4045::c:func:`snd_BUG_ON()` macro is similar with
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst:4046::c:func:`WARN_ON()` macro. For example, snd_BUG_ON(!pointer); or
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst:4047:it can be used as the condition, if (snd_BUG_ON(non_zero_is_bug))
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst-4048-return -EINVAL;
 --
 Documentation/trace/boottime-trace.rst=43=kernel.traceoff_on_warning
 Documentation/trace/boottime-trace.rst:44:   Stop tracing if WARN_ON() occurs.
 Documentation/trace/boottime-trace.rst-45-
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst=403=e tutti gli oggetti che contiene. Ecco il codice::
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst-440-    {
 Documentation/translations/it_IT/kernel-hacking/locking.rst:441:            BUG_ON(!obj);
 Documentation/translations/it_IT/kernel-hacking/locking.rst-442-            list_del(&obj->list);
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst=621=Ecco il codice::
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst-670-     {
 Documentation/translations/it_IT/kernel-hacking/locking.rst:671:             BUG_ON(!obj);
 Documentation/translations/it_IT/kernel-hacking/locking.rst-672-             list_del(&obj->list);
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst=730=contatore stesso.
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst-783-     {
 Documentation/translations/it_IT/kernel-hacking/locking.rst:784:             BUG_ON(!obj);
 Documentation/translations/it_IT/kernel-hacking/locking.rst-785-             list_del(&obj->list);
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst=1170=codice RCU è un po' più ottimizzato di così, ma questa è l'idea di fondo.
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst-1217-     {
 Documentation/translations/it_IT/kernel-hacking/locking.rst:1218:             BUG_ON(!obj);
 Documentation/translations/it_IT/kernel-hacking/locking.rst-1219-    -        list_del(&obj->list);
 --
 Documentation/translations/it_IT/locking/lockdep-design.rst=342=seguente avviso::
 Documentation/translations/it_IT/locking/lockdep-design.rst-343-
 Documentation/translations/it_IT/locking/lockdep-design.rst:344:	(DEBUG_LOCKS_WARN_ON(id >= MAX_LOCKDEP_KEYS))
 Documentation/translations/it_IT/locking/lockdep-design.rst-345-
 --
 Documentation/translations/it_IT/process/deprecated.rst=35=l'uso.
 Documentation/translations/it_IT/process/deprecated.rst-36-
 Documentation/translations/it_IT/process/deprecated.rst:37:BUG() e BUG_ON()
 Documentation/translations/it_IT/process/deprecated.rst-38-----------------
 Documentation/translations/it_IT/process/deprecated.rst:39:Al loro posto usate WARN() e WARN_ON() per gestire le
 Documentation/translations/it_IT/process/deprecated.rst-40-condizioni "impossibili" e gestitele come se fosse possibile farlo.
 --
 Documentation/translations/sp_SP/memory-barriers.txt=861=asegurarse de que MAX sea mayor que uno, tal vez de la siguiente manera:
 --
 Documentation/translations/sp_SP/memory-barriers.txt-863-  	q = READ_ONCE(a);
 Documentation/translations/sp_SP/memory-barriers.txt:864:  	BUILD_BUG_ON(MAX <= 1); /* Orden de carga de a con store de b */
 Documentation/translations/sp_SP/memory-barriers.txt-865-  	if (q % MAX) {
 --
 Documentation/translations/sp_SP/memory-barriers.txt=1622=algunos ejemplos de tal tipo de optimizaciones:
 --
 Documentation/translations/sp_SP/memory-barriers.txt-1803-     hecho, si un controlador de interrupciones regresa con interrupciones
 Documentation/translations/sp_SP/memory-barriers.txt:1804:     habilitadas, obtendrá un WARN_ONCE().)
 Documentation/translations/sp_SP/memory-barriers.txt-1805-
 --
 Documentation/translations/sp_SP/process/coding-style.rst=1246=No agregue código nuevo que use cualquiera de las variantes BUG(), como
 Documentation/translations/sp_SP/process/coding-style.rst:1247:BUG(), BUG_ON() o VM_BUG_ON(). En su lugar, use una variante WARN*(),
 Documentation/translations/sp_SP/process/coding-style.rst:1248:preferiblemente WARN_ON_ONCE(), y posiblemente con código de recuperación.
 Documentation/translations/sp_SP/process/coding-style.rst-1249-El código de recuperación no es requerido si no hay una forma razonable de
 --
 Documentation/translations/sp_SP/process/coding-style.rst=1254=aún pueden usar BUG(), pero necesitan una buena justificación.
 Documentation/translations/sp_SP/process/coding-style.rst-1255-
 Documentation/translations/sp_SP/process/coding-style.rst:1256:Use WARN_ON_ONCE() en lugar de WARN() o WARN_ON()
 Documentation/translations/sp_SP/process/coding-style.rst-1257-*************************************************
 Documentation/translations/sp_SP/process/coding-style.rst-1258-
 Documentation/translations/sp_SP/process/coding-style.rst:1259:Generalmente, se prefiere WARN_ON_ONCE() a WARN() o WARN_ON(), porque es
 Documentation/translations/sp_SP/process/coding-style.rst-1260-común que una condición de advertencia dada, si ocurre, ocurra varias
 --
 Documentation/translations/sp_SP/process/coding-style.rst=1287=se rompa.
 Documentation/translations/sp_SP/process/coding-style.rst-1288-
 Documentation/translations/sp_SP/process/coding-style.rst:1289:Use BUILD_BUG_ON() para aserciones en tiempo de compilación
 Documentation/translations/sp_SP/process/coding-style.rst-1290-***********************************************************
 Documentation/translations/sp_SP/process/coding-style.rst-1291-
 Documentation/translations/sp_SP/process/coding-style.rst:1292:El uso de BUILD_BUG_ON() es aceptable y recomendado, porque es una aserción
 Documentation/translations/sp_SP/process/coding-style.rst-1293-en tiempo de compilación, que no tiene efecto en tiempo de ejecución.
 --
 Documentation/translations/sp_SP/process/deprecated.rst=33=desanimar a otros a usarla en el futuro.
 Documentation/translations/sp_SP/process/deprecated.rst-34-
 Documentation/translations/sp_SP/process/deprecated.rst:35:BUG() y BUG_ON()
 Documentation/translations/sp_SP/process/deprecated.rst-36-----------------
 Documentation/translations/sp_SP/process/deprecated.rst:37:Use WARN() y WARN_ON() en su lugar, y gestione las condiciones de error
 Documentation/translations/sp_SP/process/deprecated.rst-38-"imposibles" tan elegantemente como se pueda. Mientras que la familia de
 --
 Documentation/translations/zh_CN/admin-guide/clearing-warn-once.rst:1:清除 WARN_ONCE
 Documentation/translations/zh_CN/admin-guide/clearing-warn-once.rst-2---------------
 Documentation/translations/zh_CN/admin-guide/clearing-warn-once.rst-3-
 Documentation/translations/zh_CN/admin-guide/clearing-warn-once.rst:4:WARN_ONCE / WARN_ON_ONCE / printk_once 仅仅打印一次消息.
 Documentation/translations/zh_CN/admin-guide/clearing-warn-once.rst-5-
 --
 Documentation/translations/zh_TW/admin-guide/clearing-warn-once.rst-6-
 Documentation/translations/zh_TW/admin-guide/clearing-warn-once.rst:7:清除 WARN_ONCE
 Documentation/translations/zh_TW/admin-guide/clearing-warn-once.rst-8---------------
 Documentation/translations/zh_TW/admin-guide/clearing-warn-once.rst-9-
 Documentation/translations/zh_TW/admin-guide/clearing-warn-once.rst:10:WARN_ONCE / WARN_ON_ONCE / printk_once 僅僅打印一次消息.
 Documentation/translations/zh_TW/admin-guide/clearing-warn-once.rst-11-
 --
 Makefile=850=ifeq ("$(origin UT)", "command line")
 Makefile:851:  WARN_ON_UNUSED_TRACEPOINTS := $(UT)
 Makefile-852-endif
 Makefile=853=endif # CONFIG_TRACEPOINTS
 Makefile-854-
 Makefile:855:export WARN_ON_UNUSED_TRACEPOINTS
 Makefile-856-
 --
 arch/alpha/include/asm/cmpxchg.h=217=____cmpxchg(volatile void *ptr, unsigned long old, unsigned long new,
 --
 arch/alpha/include/asm/cmpxchg.h-245-({									\
 arch/alpha/include/asm/cmpxchg.h:246:	BUILD_BUG_ON(sizeof(*(ptr)) != 8);				\
 arch/alpha/include/asm/cmpxchg.h-247-	cmpxchg_local((ptr), (o), (n));					\
 --
 arch/alpha/include/asm/cmpxchg.h-278-({									\
 arch/alpha/include/asm/cmpxchg.h:279:	BUILD_BUG_ON(sizeof(*(ptr)) != 8);				\
 arch/alpha/include/asm/cmpxchg.h-280-	arch_cmpxchg((ptr), (o), (n));					\
 --
 arch/alpha/include/asm/err_ev7.h=164=static inline int ev7_lf_env_index(int type)
 arch/alpha/include/asm/err_ev7.h-165-{
 arch/alpha/include/asm/err_ev7.h:166:	BUG_ON((type < EL_TYPE__PAL__ENV__AMBIENT_TEMPERATURE) 
 arch/alpha/include/asm/err_ev7.h-167-	       || (type > EL_TYPE__PAL__ENV__HOT_PLUG));
 --
 arch/alpha/kernel/io.c=320=void ioread16_rep(const void __iomem *port, void *dst, unsigned long count)
 --
 arch/alpha/kernel/io.c-324-			return;
 arch/alpha/kernel/io.c:325:		BUG_ON((unsigned long)dst & 0x1);
 arch/alpha/kernel/io.c-326-		count--;
 --
 arch/alpha/kernel/io.c=414=void iowrite16_rep(void __iomem *port, const void *src, unsigned long count)
 --
 arch/alpha/kernel/io.c-418-			return;
 arch/alpha/kernel/io.c:419:		BUG_ON((unsigned long)src & 0x1);
 arch/alpha/kernel/io.c-420-		iowrite16(*(unsigned short *)src, port);
 --
 arch/alpha/kernel/pci_iommu.c=300=static struct pci_dev *alpha_gendev_to_pci(struct device *dev)
 --
 arch/alpha/kernel/pci_iommu.c-306-	   BUG() otherwise. */
 arch/alpha/kernel/pci_iommu.c:307:	BUG_ON(!isa_bridge);
 arch/alpha/kernel/pci_iommu.c-308-
 --
 arch/alpha/kernel/pci_iommu.c=623=static int alpha_pci_map_sg(struct device *dev, struct scatterlist *sg,
 --
 arch/alpha/kernel/pci_iommu.c-633-
 arch/alpha/kernel/pci_iommu.c:634:	BUG_ON(dir == DMA_NONE);
 arch/alpha/kernel/pci_iommu.c-635-
 --
 arch/alpha/kernel/pci_iommu.c=704=static void alpha_pci_unmap_sg(struct device *dev, struct scatterlist *sg,
 --
 arch/alpha/kernel/pci_iommu.c-715-
 arch/alpha/kernel/pci_iommu.c:716:	BUG_ON(dir == DMA_NONE);
 arch/alpha/kernel/pci_iommu.c-717-
 --
 arch/alpha/kernel/perf_event.c=152=static int ev67_check_constraints(struct perf_event **event,
 --
 arch/alpha/kernel/perf_event.c-162-
 arch/alpha/kernel/perf_event.c:163:	BUG_ON(n_ev != 2);
 arch/alpha/kernel/perf_event.c-164-
 --
 arch/alpha/kernel/perf_event.c=552=static void alpha_pmu_start(struct perf_event *event, int flags)
 --
 arch/alpha/kernel/perf_event.c-556-
 arch/alpha/kernel/perf_event.c:557:	if (WARN_ON_ONCE(!(hwc->state & PERF_HES_STOPPED)))
 arch/alpha/kernel/perf_event.c-558-		return;
 --
 arch/alpha/kernel/perf_event.c-560-	if (flags & PERF_EF_RELOAD) {
 arch/alpha/kernel/perf_event.c:561:		WARN_ON_ONCE(!(hwc->state & PERF_HES_UPTODATE));
 arch/alpha/kernel/perf_event.c-562-		alpha_perf_event_set_period(event, hwc, hwc->idx);
 --
 arch/arc/kernel/mcip.c=376=idu_of_init(struct device_node *intc, struct device_node *parent)
 --
 arch/arc/kernel/mcip.c-409-		virq = irq_create_mapping(NULL, i + FIRST_EXT_IRQ);
 arch/arc/kernel/mcip.c:410:		BUG_ON(!virq);
 arch/arc/kernel/mcip.c-411-		irq_set_chained_handler_and_data(virq, idu_cascade_isr, domain);
 --
 arch/arc/kernel/perf_event.c=451=static void arc_pmu_start(struct perf_event *event, int flags)
 --
 arch/arc/kernel/perf_event.c-455-
 arch/arc/kernel/perf_event.c:456:	if (WARN_ON_ONCE(idx == -1))
 arch/arc/kernel/perf_event.c-457-		return;
 --
 arch/arc/kernel/perf_event.c-459-	if (flags & PERF_EF_RELOAD)
 arch/arc/kernel/perf_event.c:460:		WARN_ON_ONCE(!(hwc->state & PERF_HES_UPTODATE));
 arch/arc/kernel/perf_event.c-461-
 --
 arch/arc/kernel/perf_event.c=562=static irqreturn_t arc_pmu_intr(int irq, void *dev)
 --
 arch/arc/kernel/perf_event.c-597-
 arch/arc/kernel/perf_event.c:598:		WARN_ON_ONCE(hwc->idx != idx);
 arch/arc/kernel/perf_event.c-599-
 --
 arch/arc/kernel/perf_event.c=721=static int arc_pmu_device_probe(struct platform_device *pdev)
 --
 arch/arc/kernel/perf_event.c-741-	}
 arch/arc/kernel/perf_event.c:742:	BUILD_BUG_ON(ARC_PERF_MAX_COUNTERS > 32);
 arch/arc/kernel/perf_event.c:743:	if (WARN_ON(pct_bcr.c > ARC_PERF_MAX_COUNTERS))
 arch/arc/kernel/perf_event.c-744-		return -EINVAL;
 --
 arch/arc/kernel/process.c=46=SYSCALL_DEFINE3(arc_usr_cmpxchg, int __user *, uaddr, int, expected, int, new)
 --
 arch/arc/kernel/process.c-57-	 */
 arch/arc/kernel/process.c:58:	WARN_ON_ONCE(IS_ENABLED(CONFIG_SMP));
 arch/arc/kernel/process.c-59-
 --
 arch/arc/kernel/smp.c=131=static void arc_default_smp_cpu_kick(int cpu, unsigned long pc)
 arch/arc/kernel/smp.c-132-{
 arch/arc/kernel/smp.c:133:	BUG_ON(cpu == 0);
 arch/arc/kernel/smp.c-134-
 --
 arch/arc/kernel/unwind.c=33=do {						\
 --
 arch/arc/kernel/unwind.c-43-#define EXTRA_INFO(f) { \
 arch/arc/kernel/unwind.c:44:		BUILD_BUG_ON_ZERO(offsetof(struct unwind_frame_info, f) \
 arch/arc/kernel/unwind.c-45-				% sizeof_field(struct unwind_frame_info, f)) \
 --
 arch/arc/kernel/unwind.c=244=static void init_unwind_hdr(struct unwind_table *table,
 --
 arch/arc/kernel/unwind.c-312-	put_unaligned((unsigned long)table->address, &header->eh_frame_ptr);
 arch/arc/kernel/unwind.c:313:	BUILD_BUG_ON(offsetof(typeof(*header), fde_count)
 arch/arc/kernel/unwind.c-314-		     % __alignof(typeof(header->fde_count)));
 --
 arch/arc/kernel/unwind.c-316-
 arch/arc/kernel/unwind.c:317:	BUILD_BUG_ON(offsetof(typeof(*header), table)
 arch/arc/kernel/unwind.c-318-		     % __alignof(typeof(*header->table)));
 --
 arch/arc/kernel/unwind.c-333-	}
 arch/arc/kernel/unwind.c:334:	WARN_ON(n != header->fde_count);
 arch/arc/kernel/unwind.c-335-
 --
 arch/arc/kernel/unwind.c=525=static unsigned long read_pointer(const u8 **pLoc, const void *end,
 --
 arch/arc/kernel/unwind.c-559-	case DW_EH_PE_data8:
 arch/arc/kernel/unwind.c:560:		BUILD_BUG_ON(sizeof(u64) != sizeof(value));
 arch/arc/kernel/unwind.c-561-#else
 arch/arc/kernel/unwind.c:562:		BUILD_BUG_ON(sizeof(u32) != sizeof(value));
 arch/arc/kernel/unwind.c-563-#endif
 --
 arch/arc/kernel/unwind.c-570-	case DW_EH_PE_leb128:
 arch/arc/kernel/unwind.c:571:		BUILD_BUG_ON(sizeof(uleb128_t) > sizeof(value));
 arch/arc/kernel/unwind.c-572-		value = ptrType & DW_EH_PE_signed ? get_sleb128(&ptr.p8, end)
 --
 arch/arc/mm/cache.c=100=int arc_cache_mumbojumbo(int c, char *buf, int len)
 --
 arch/arc/mm/cache.c-111-	if (is_isa_arcompact() && (ibcr.ver <= 3)) {
 arch/arc/mm/cache.c:112:		BUG_ON(ibcr.config != 3);
 arch/arc/mm/cache.c-113-		assoc = 2;		/* Fixed to 2w set assoc */
 --
 arch/arc/mm/cache.c-133-	if (is_isa_arcompact() && (dbcr.ver <= 3)) {
 arch/arc/mm/cache.c:134:		BUG_ON(dbcr.config != 2);
 arch/arc/mm/cache.c-135-		vipt = 1;
 --
 arch/arc/mm/cache.c=995=static noinline void __init arc_cache_init_master(void)
 --
 arch/arc/mm/cache.c-1036-	 */
 arch/arc/mm/cache.c:1037:	BUILD_BUG_ON_MSG(L1_CACHE_BYTES > SMP_CACHE_BYTES,
 arch/arc/mm/cache.c-1038-			 "SMP_CACHE_BYTES must be >= any cache line length");
 --
 arch/arc/mm/highmem.c=64=void __init kmap_init(void)
 --
 arch/arc/mm/highmem.c-66-	/* Due to recursive include hell, we can't do this in processor.h */
 arch/arc/mm/highmem.c:67:	BUILD_BUG_ON(PAGE_OFFSET < (VMALLOC_END + FIXMAP_SIZE + PKMAP_SIZE));
 arch/arc/mm/highmem.c:68:	BUILD_BUG_ON(LAST_PKMAP > PTRS_PER_PTE);
 arch/arc/mm/highmem.c:69:	BUILD_BUG_ON(FIX_KMAP_SLOTS > PTRS_PER_PTE);
 arch/arc/mm/highmem.c-70-
 --
 arch/arc/mm/init.c=159=void __init arch_mm_preinit(void)
 --
 arch/arc/mm/init.c-164-
 arch/arc/mm/init.c:165:	BUILD_BUG_ON((PTRS_PER_PGD * sizeof(pgd_t)) > PAGE_SIZE);
 arch/arc/mm/init.c:166:	BUILD_BUG_ON((PTRS_PER_PUD * sizeof(pud_t)) > PAGE_SIZE);
 arch/arc/mm/init.c:167:	BUILD_BUG_ON((PTRS_PER_PMD * sizeof(pmd_t)) > PAGE_SIZE);
 arch/arc/mm/init.c:168:	BUILD_BUG_ON((PTRS_PER_PTE * sizeof(pte_t)) > PAGE_SIZE);
 arch/arc/mm/init.c-169-}
 --
 arch/arc/mm/tlb.c=616=void arc_mmu_init(void)
 --
 arch/arc/mm/tlb.c-623-	 */
 arch/arc/mm/tlb.c:624:	BUILD_BUG_ON(!IS_ALIGNED((CONFIG_ARC_KVADDR_SIZE << 20), PMD_SIZE));
 arch/arc/mm/tlb.c-625-
 --
 arch/arc/mm/tlb.c-629-	 */
 arch/arc/mm/tlb.c:630:	BUILD_BUG_ON(!IS_ALIGNED(STACK_TOP, PMD_SIZE));
 arch/arc/mm/tlb.c-631-
 --
 arch/arc/mm/tlb.c=694=void do_tlb_overlap_fault(unsigned long cause, unsigned long address,
]
]

gemini-3.1-pro-preview

							input: 135415
							output: 22
							thoughts: 21
						

Okay, here's my take on those thoughts, tailored for an expert audience:

**Investigating a Potential Issue in the NBD Driver**

Alright, time to dig into this. I'm thinking, let's start by zeroing in on a potential crash or unexpected behavior in the network block device driver, `nbd.c`. My hunch, based on experience, is that we might find a hard-coded assertion failing. So, I'm going to leverage my familiarity with the kernel's debugging tools. My first move? I'm going to run a `grep` on `drivers/block/nbd.c` and specifically look for instances of `BUG_ON`. This macro is a red flag, a direct indication of a condition that *shouldn't* happen, and if it *does*, it will immediately halt the execution and dump the panic message. My reasoning is that this is usually a good starting point for tracing an unexpected condition.

no matches

map[Expression:BUG_ON.*nbd\.c]

map[Output:]

gemini-3.1-pro-preview

							input: 135675
							output: 22
							thoughts: 21
						

Okay, here's my thought process summarized as requested:

**Investigating a Potential Issue in the NBD Driver**

Right, let's get down to it. I need to pinpoint a potential issue, and my first instinct is to zero in on any warnings that might be lurking. Given the NBD driver is my target, I'm going to quickly search for occurrences of `WARN_ON` within the `drivers/block/nbd.c` file. This macro is a red flag, a signal that something unexpected might be happening, and it's a good starting point for diving deeper into potential problem areas within the code. Let's see what that search turns up.

no matches

map[Expression:WARN_ON.*nbd\.c]

map[Output:]

gemini-3.1-pro-preview

							input: 135876
							output: 21
							thoughts: 29
						

Here's my thought process, summarized as you requested:

**Debugging the NBD Driver**

Okay, so I need to track down potential issues in the Network Block Device (NBD) driver. I'm thinking, instead of manually sifting through the code, a targeted approach is probably the most efficient use of my time. What's the best way to flag potential problems quickly? Ah, right. `BUG_ON` and `WARN_ON`. Those macros are specifically designed to highlight error conditions and potentially fatal issues. They're my canary in the coal mine, so to speak.

So, I'll just use `grep`! I'll target the `drivers/block/nbd.c` file and look for instances of those macros. A quick `grep` will reveal all the places where the driver is explicitly checking for errors or unexpected states. This should give me a solid starting point for debugging, focusing my attention on the areas that are most likely to be problematic or where the developers anticipated potential failures. Perfect. That should be a much faster and focused approach than just reading the entire driver.

map[Expression:BUG_ON|WARN_ON]

map[Output:
Full output is too long, showing 500 out of 203717 lines.
Use more precise expression if possible.

[Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst=78=lock-acquisition and lock-release functions::
 --
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst-104-   25
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst:105:   26 WARN_ON(r1 == 0 && r2 == 0 && r3 == 0);
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst-106-
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst:107:The ``WARN_ON()`` is evaluated at "the end of time",
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst-108-after all changes have propagated throughout the system.
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst=109=Without the ``smp_mb__after_unlock_lock()`` provided by the
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst:110:acquisition functions, this ``WARN_ON()`` could trigger, for example
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst-111-on PowerPC.
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst=112=The ``smp_mb__after_unlock_lock()`` invocations prevent this
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst:113:``WARN_ON()`` from triggering.
 Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst-114-
 --
 Documentation/RCU/Design/Requirements/Requirements.rst=755=example illustrates this:
 --
 Documentation/RCU/Design/Requirements/Requirements.rst-765-       7     r2 = READ_ONCE(x);
 Documentation/RCU/Design/Requirements/Requirements.rst:766:       8     WARN_ON(!r2); /* BUG!!! */
 Documentation/RCU/Design/Requirements/Requirements.rst-767-       9   }
 --
 Documentation/RCU/Design/Requirements/Requirements.rst=779=If the thread0() function's rcu_read_lock() excluded the
 Documentation/RCU/Design/Requirements/Requirements.rst:780:thread1() function's update, the WARN_ON() could never fire. But
 Documentation/RCU/Design/Requirements/Requirements.rst-781-the fact is that rcu_read_lock() does not exclude much of anything
 Documentation/RCU/Design/Requirements/Requirements.rst=782=aside from subsequent grace periods, of which thread1() has none, so
 Documentation/RCU/Design/Requirements/Requirements.rst:783:the WARN_ON() can and does fire.
 Documentation/RCU/Design/Requirements/Requirements.rst-784-
 --
 Documentation/RCU/lockdep.rst=25=aren't certain (for example, if CONFIG_DEBUG_LOCK_ALLOC is not set).
 Documentation/RCU/lockdep.rst:26:This prevents things like WARN_ON(!rcu_read_lock_held()) from giving false
 Documentation/RCU/lockdep.rst-27-positives when lockdep is disabled.
 --
 Documentation/RCU/rcubarrier.rst=194=The original code for rcu_barrier() was roughly as follows::
 --
 Documentation/RCU/rcubarrier.rst-197-  2  {
 Documentation/RCU/rcubarrier.rst:198:  3    BUG_ON(in_interrupt());
 Documentation/RCU/rcubarrier.rst-199-  4    /* Take cpucontrol mutex to protect against CPU hotplug */
 --
 Documentation/admin-guide/clearing-warn-once.rst:1:Clearing WARN_ONCE
 Documentation/admin-guide/clearing-warn-once.rst-2-------------------
 Documentation/admin-guide/clearing-warn-once.rst-3-
 Documentation/admin-guide/clearing-warn-once.rst:4:WARN_ONCE / WARN_ON_ONCE / printk_once only emit a message once.
 Documentation/admin-guide/clearing-warn-once.rst-5-
 --
 Documentation/admin-guide/kernel-parameters.txt=97=Kernel parameters
 --
 Documentation/admin-guide/kernel-parameters.txt-4188-			this means that duplicate request_module() calls will
 Documentation/admin-guide/kernel-parameters.txt:4189:			trigger a WARN_ON() instead of a pr_warn(). Note that
 Documentation/admin-guide/kernel-parameters.txt:4190:			if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s
 Documentation/admin-guide/kernel-parameters.txt-4191-			will always be issued and this option does nothing.
 --
 Documentation/admin-guide/kernel-parameters.txt-5819-			This wake_up() will be accompanied by a
 Documentation/admin-guide/kernel-parameters.txt:5820:			WARN_ONCE() splat and an ftrace_dump().
 Documentation/admin-guide/kernel-parameters.txt-5821-
 --
 Documentation/admin-guide/mm/slab.rst=6=CONFIG_SLUB_DEBUG=y) but it is off by default (unless built with
 Documentation/admin-guide/mm/slab.rst:7:CONFIG_SLUB_DEBUG_ON=y).  You can enable debugging only for selected
 Documentation/admin-guide/mm/slab.rst-8-slabs in order to avoid an impact on overall system performance which
 --
 Documentation/admin-guide/mm/slab.rst=46=Possible debug options are::
 --
 Documentation/admin-guide/mm/slab.rst-57-	-		Switch all debugging off (useful if the kernel is
 Documentation/admin-guide/mm/slab.rst:58:			configured with CONFIG_SLUB_DEBUG_ON)
 Documentation/admin-guide/mm/slab.rst-59-
 --
 Documentation/core-api/packing.rst=297=An additional benefit over pack() and unpack() is that sanity checks on the
 Documentation/core-api/packing.rst:298:field definitions are handled at compile time with ``BUILD_BUG_ON`` rather
 Documentation/core-api/packing.rst-299-than only when the offending code is executed. These functions return void and
 --
 Documentation/core-api/packing.rst=306=Here is an example of how to use the fields APIs:
 --
 Documentation/core-api/packing.rst-332-   {
 Documentation/core-api/packing.rst:333:           BUILD_BUG_ON(sizeof(*buf) != SIZE;
 Documentation/core-api/packing.rst-334-
 --
 Documentation/core-api/packing.rst-340-   {
 Documentation/core-api/packing.rst:341:           BUILD_BUG_ON(sizeof(*buf) != SIZE;
 Documentation/core-api/packing.rst-342-
 --
 Documentation/dev-tools/checkpatch.rst=272=API usage
 --
 Documentation/dev-tools/checkpatch.rst-285-  **AVOID_BUG**
 Documentation/dev-tools/checkpatch.rst:286:    BUG() or BUG_ON() should be avoided totally.
 Documentation/dev-tools/checkpatch.rst:287:    Use WARN() and WARN_ON() instead, and handle the "impossible"
 Documentation/dev-tools/checkpatch.rst-288-    error condition as gracefully as possible.
 --
 Documentation/driver-api/media/drivers/ccs/mk-ccs-regs=139=print $H "#define CCS_BUILD_BUG \\
 Documentation/driver-api/media/drivers/ccs/mk-ccs-regs:140:	BUILD_BUG_ON(~CCI_REG_PRIVATE_MASK & ($all_flags))\n"
 Documentation/driver-api/media/drivers/ccs/mk-ccs-regs-141-    if defined $kernel;
 --
 Documentation/driver-api/media/v4l2-controls.rst=814=There can be only one notify function per control handler. Any attempt
 Documentation/driver-api/media/v4l2-controls.rst:815:to set another notify function will cause a WARN_ON.
 Documentation/driver-api/media/v4l2-controls.rst-816-
 --
 Documentation/driver-api/mtdnand.rst=272=unregisters the partitions in the MTD layer.
 --
 Documentation/driver-api/mtdnand.rst-279-        /* Unregister device */
 Documentation/driver-api/mtdnand.rst:280:        WARN_ON(mtd_device_unregister(board_mtd));
 Documentation/driver-api/mtdnand.rst-281-        /* Release resources */
 --
 Documentation/filesystems/porting.rst=815=just get rid of it.  Synchronous work (e.g. the stuff that can't
 Documentation/filesystems/porting.rst:816:be done from an RCU callback, or any WARN_ON() where we want the
 Documentation/filesystems/porting.rst-817-stack trace) *might* be movable to ->evict_inode(); however,
 --
 Documentation/gpu/introduction.rst=35=Instead locking should be check at runtime using e.g.
 Documentation/gpu/introduction.rst:36:``WARN_ON(!mutex_is_locked(...));``. Since it's much easier to ignore
 Documentation/gpu/introduction.rst-37-documentation than runtime noise this provides more value. And on top of
 --
 Documentation/gpu/todo.rst=185=interfaces to fix these issues:
 --
 Documentation/gpu/todo.rst-193-  Except for some driver code this is done. This task should be finished by
 Documentation/gpu/todo.rst:194:  adding WARN_ON(!drm_drv_uses_atomic_modeset) in drm_modeset_lock_all().
 Documentation/gpu/todo.rst-195-
 --
 Documentation/gpu/todo.rst=485=double-calls prepare/enable/disable/unprepare. Eventually that should probably
 Documentation/gpu/todo.rst:486:be turned into a WARN_ON() or somehow made louder.
 Documentation/gpu/todo.rst-487-
 --
 Documentation/kernel-hacking/locking.rst=383=to protect the cache and all the objects within it. Here's the code::
 --
 Documentation/kernel-hacking/locking.rst-420-    {
 Documentation/kernel-hacking/locking.rst:421:            BUG_ON(!obj);
 Documentation/kernel-hacking/locking.rst-422-            list_del(&obj->list);
 --
 Documentation/kernel-hacking/locking.rst=600=Here is the code::
 --
 Documentation/kernel-hacking/locking.rst-649-     {
 Documentation/kernel-hacking/locking.rst:650:             BUG_ON(!obj);
 Documentation/kernel-hacking/locking.rst-651-             list_del(&obj->list);
 --
 Documentation/kernel-hacking/locking.rst=709=the lock is no longer used to protect the reference count itself.
 --
 Documentation/kernel-hacking/locking.rst-762-     {
 Documentation/kernel-hacking/locking.rst:763:             BUG_ON(!obj);
 Documentation/kernel-hacking/locking.rst-764-             list_del(&obj->list);
 --
 Documentation/kernel-hacking/locking.rst=1139=this is the fundamental idea.
 --
 Documentation/kernel-hacking/locking.rst-1186-     {
 Documentation/kernel-hacking/locking.rst:1187:             BUG_ON(!obj);
 Documentation/kernel-hacking/locking.rst-1188-    -        list_del(&obj->list);
 --
 Documentation/leds/leds-class.rst=147=led_classdev_notify_brightness_hw_changed on a classdev not registered with
 Documentation/leds/leds-class.rst:148:the LED_BRIGHT_HW_CHANGED flag is a bug and will trigger a WARN_ON.
 Documentation/leds/leds-class.rst-149-
 --
 Documentation/locking/lockdep-design.rst=340=Exceeding this number will trigger the following lockdep warning::
 Documentation/locking/lockdep-design.rst-341-
 Documentation/locking/lockdep-design.rst:342:	(DEBUG_LOCKS_WARN_ON(id >= MAX_LOCKDEP_KEYS))
 Documentation/locking/lockdep-design.rst-343-
 --
 Documentation/memory-barriers.txt=820=one, perhaps as follows:
 --
 Documentation/memory-barriers.txt-822-	q = READ_ONCE(a);
 Documentation/memory-barriers.txt:823:	BUILD_BUG_ON(MAX <= 1); /* Order load from a with store to b. */
 Documentation/memory-barriers.txt-824-	if (q % MAX) {
 --
 Documentation/memory-barriers.txt=1558=of optimizations:
 --
 Documentation/memory-barriers.txt-1732-     interrupt handler returns with interrupts enabled, you will get a
 Documentation/memory-barriers.txt:1733:     WARN_ONCE() splat.)
 Documentation/memory-barriers.txt-1734-
 --
 Documentation/process/coding-style.rst=1228=Do not add new code that uses any of the BUG() variants, such as BUG(),
 Documentation/process/coding-style.rst:1229:BUG_ON(), or VM_BUG_ON(). Instead, use a WARN*() variant, preferably
 Documentation/process/coding-style.rst:1230:WARN_ON_ONCE(), and possibly with recovery code. Recovery code is not
 Documentation/process/coding-style.rst-1231-required if there is no reasonable way to at least partially recover.
 --
 Documentation/process/coding-style.rst=1235=good justification.
 Documentation/process/coding-style.rst-1236-
 Documentation/process/coding-style.rst:1237:Use WARN_ON_ONCE() rather than WARN() or WARN_ON()
 Documentation/process/coding-style.rst-1238-**************************************************
 Documentation/process/coding-style.rst-1239-
 Documentation/process/coding-style.rst:1240:WARN_ON_ONCE() is generally preferred over WARN() or WARN_ON(), because it
 Documentation/process/coding-style.rst-1241-is common for a given warning condition, if it occurs at all, to occur
 --
 Documentation/process/coding-style.rst=1266=likely to crash.
 Documentation/process/coding-style.rst-1267-
 Documentation/process/coding-style.rst:1268:Use BUILD_BUG_ON() for compile-time assertions
 Documentation/process/coding-style.rst-1269-**********************************************
 Documentation/process/coding-style.rst-1270-
 Documentation/process/coding-style.rst:1271:The use of BUILD_BUG_ON() is acceptable and encouraged, because it is a
 Documentation/process/coding-style.rst-1272-compile-time assertion that has no effect at runtime.
 --
 Documentation/process/debugging/userspace_debugging_guide.rst=210=Kernel panic analysis tools
 --
 Documentation/process/debugging/userspace_debugging_guide.rst-243-     ae8:	f9418015 	ldr	x21, [x0, #768]
 Documentation/process/debugging/userspace_debugging_guide.rst:244:        if (WARN_ON(!desc))
 Documentation/process/debugging/userspace_debugging_guide.rst-245-     aec:	b4000654 	cbz	x20, bb4 <rkvdec_device_run+0xec>
 --
 Documentation/process/deprecated.rst=30=others from using them in the future.
 Documentation/process/deprecated.rst-31-
 Documentation/process/deprecated.rst:32:BUG() and BUG_ON()
 Documentation/process/deprecated.rst-33-------------------
 Documentation/process/deprecated.rst:34:Use WARN() and WARN_ON() instead, and handle the "impossible"
 Documentation/process/deprecated.rst-35-error condition as gracefully as possible. While the BUG()-family
 --
 Documentation/scsi/ChangeLog.lpfc=98=Changes from 20050215 to 20050223
 --
 Documentation/scsi/ChangeLog.lpfc-137-	  causing it to figure in load average calculations. Also add a
 Documentation/scsi/ChangeLog.lpfc:138:	  BUG_ON to the ret code of wait_event_interruptible() since the
 Documentation/scsi/ChangeLog.lpfc-139-	  premise is that the worker thread is signal-immune.
 --
 Documentation/scsi/ChangeLog.megaraid=202=Older Version	: 2.20.4.5 (scsi module), 2.20.2.5 (cmm module)
 --
 Documentation/scsi/ChangeLog.megaraid-248-
 Documentation/scsi/ChangeLog.megaraid:249:	  BUG_ON(!spin_is_locked(&some_lock));
 Documentation/scsi/ChangeLog.megaraid-250-
 --
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst=4036=It shows the ``BUG?`` message and stack trace as well as
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst:4037::c:func:`snd_BUG_ON()` at the point. It's useful to show that a
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst-4038-fatal error happens there.
 --
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst=4040=When no debug flag is set, this macro is ignored.
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst-4041-
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst:4042::c:func:`snd_BUG_ON()`
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst-4043-----------------------
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst-4044-
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst:4045::c:func:`snd_BUG_ON()` macro is similar with
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst:4046::c:func:`WARN_ON()` macro. For example, snd_BUG_ON(!pointer); or
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst:4047:it can be used as the condition, if (snd_BUG_ON(non_zero_is_bug))
 Documentation/sound/kernel-api/writing-an-alsa-driver.rst-4048-return -EINVAL;
 --
 Documentation/trace/boottime-trace.rst=43=kernel.traceoff_on_warning
 Documentation/trace/boottime-trace.rst:44:   Stop tracing if WARN_ON() occurs.
 Documentation/trace/boottime-trace.rst-45-
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst=403=e tutti gli oggetti che contiene. Ecco il codice::
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst-440-    {
 Documentation/translations/it_IT/kernel-hacking/locking.rst:441:            BUG_ON(!obj);
 Documentation/translations/it_IT/kernel-hacking/locking.rst-442-            list_del(&obj->list);
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst=621=Ecco il codice::
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst-670-     {
 Documentation/translations/it_IT/kernel-hacking/locking.rst:671:             BUG_ON(!obj);
 Documentation/translations/it_IT/kernel-hacking/locking.rst-672-             list_del(&obj->list);
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst=730=contatore stesso.
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst-783-     {
 Documentation/translations/it_IT/kernel-hacking/locking.rst:784:             BUG_ON(!obj);
 Documentation/translations/it_IT/kernel-hacking/locking.rst-785-             list_del(&obj->list);
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst=1170=codice RCU è un po' più ottimizzato di così, ma questa è l'idea di fondo.
 --
 Documentation/translations/it_IT/kernel-hacking/locking.rst-1217-     {
 Documentation/translations/it_IT/kernel-hacking/locking.rst:1218:             BUG_ON(!obj);
 Documentation/translations/it_IT/kernel-hacking/locking.rst-1219-    -        list_del(&obj->list);
 --
 Documentation/translations/it_IT/locking/lockdep-design.rst=342=seguente avviso::
 Documentation/translations/it_IT/locking/lockdep-design.rst-343-
 Documentation/translations/it_IT/locking/lockdep-design.rst:344:	(DEBUG_LOCKS_WARN_ON(id >= MAX_LOCKDEP_KEYS))
 Documentation/translations/it_IT/locking/lockdep-design.rst-345-
 --
 Documentation/translations/it_IT/process/deprecated.rst=35=l'uso.
 Documentation/translations/it_IT/process/deprecated.rst-36-
 Documentation/translations/it_IT/process/deprecated.rst:37:BUG() e BUG_ON()
 Documentation/translations/it_IT/process/deprecated.rst-38-----------------
 Documentation/translations/it_IT/process/deprecated.rst:39:Al loro posto usate WARN() e WARN_ON() per gestire le
 Documentation/translations/it_IT/process/deprecated.rst-40-condizioni "impossibili" e gestitele come se fosse possibile farlo.
 --
 Documentation/translations/sp_SP/memory-barriers.txt=861=asegurarse de que MAX sea mayor que uno, tal vez de la siguiente manera:
 --
 Documentation/translations/sp_SP/memory-barriers.txt-863-  	q = READ_ONCE(a);
 Documentation/translations/sp_SP/memory-barriers.txt:864:  	BUILD_BUG_ON(MAX <= 1); /* Orden de carga de a con store de b */
 Documentation/translations/sp_SP/memory-barriers.txt-865-  	if (q % MAX) {
 --
 Documentation/translations/sp_SP/memory-barriers.txt=1622=algunos ejemplos de tal tipo de optimizaciones:
 --
 Documentation/translations/sp_SP/memory-barriers.txt-1803-     hecho, si un controlador de interrupciones regresa con interrupciones
 Documentation/translations/sp_SP/memory-barriers.txt:1804:     habilitadas, obtendrá un WARN_ONCE().)
 Documentation/translations/sp_SP/memory-barriers.txt-1805-
 --
 Documentation/translations/sp_SP/process/coding-style.rst=1246=No agregue código nuevo que use cualquiera de las variantes BUG(), como
 Documentation/translations/sp_SP/process/coding-style.rst:1247:BUG(), BUG_ON() o VM_BUG_ON(). En su lugar, use una variante WARN*(),
 Documentation/translations/sp_SP/process/coding-style.rst:1248:preferiblemente WARN_ON_ONCE(), y posiblemente con código de recuperación.
 Documentation/translations/sp_SP/process/coding-style.rst-1249-El código de recuperación no es requerido si no hay una forma razonable de
 --
 Documentation/translations/sp_SP/process/coding-style.rst=1254=aún pueden usar BUG(), pero necesitan una buena justificación.
 Documentation/translations/sp_SP/process/coding-style.rst-1255-
 Documentation/translations/sp_SP/process/coding-style.rst:1256:Use WARN_ON_ONCE() en lugar de WARN() o WARN_ON()
 Documentation/translations/sp_SP/process/coding-style.rst-1257-*************************************************
 Documentation/translations/sp_SP/process/coding-style.rst-1258-
 Documentation/translations/sp_SP/process/coding-style.rst:1259:Generalmente, se prefiere WARN_ON_ONCE() a WARN() o WARN_ON(), porque es
 Documentation/translations/sp_SP/process/coding-style.rst-1260-común que una condición de advertencia dada, si ocurre, ocurra varias
 --
 Documentation/translations/sp_SP/process/coding-style.rst=1287=se rompa.
 Documentation/translations/sp_SP/process/coding-style.rst-1288-
 Documentation/translations/sp_SP/process/coding-style.rst:1289:Use BUILD_BUG_ON() para aserciones en tiempo de compilación
 Documentation/translations/sp_SP/process/coding-style.rst-1290-***********************************************************
 Documentation/translations/sp_SP/process/coding-style.rst-1291-
 Documentation/translations/sp_SP/process/coding-style.rst:1292:El uso de BUILD_BUG_ON() es aceptable y recomendado, porque es una aserción
 Documentation/translations/sp_SP/process/coding-style.rst-1293-en tiempo de compilación, que no tiene efecto en tiempo de ejecución.
 --
 Documentation/translations/sp_SP/process/deprecated.rst=33=desanimar a otros a usarla en el futuro.
 Documentation/translations/sp_SP/process/deprecated.rst-34-
 Documentation/translations/sp_SP/process/deprecated.rst:35:BUG() y BUG_ON()
 Documentation/translations/sp_SP/process/deprecated.rst-36-----------------
 Documentation/translations/sp_SP/process/deprecated.rst:37:Use WARN() y WARN_ON() en su lugar, y gestione las condiciones de error
 Documentation/translations/sp_SP/process/deprecated.rst-38-"imposibles" tan elegantemente como se pueda. Mientras que la familia de
 --
 Documentation/translations/zh_CN/admin-guide/clearing-warn-once.rst:1:清除 WARN_ONCE
 Documentation/translations/zh_CN/admin-guide/clearing-warn-once.rst-2---------------
 Documentation/translations/zh_CN/admin-guide/clearing-warn-once.rst-3-
 Documentation/translations/zh_CN/admin-guide/clearing-warn-once.rst:4:WARN_ONCE / WARN_ON_ONCE / printk_once 仅仅打印一次消息.
 Documentation/translations/zh_CN/admin-guide/clearing-warn-once.rst-5-
 --
 Documentation/translations/zh_TW/admin-guide/clearing-warn-once.rst-6-
 Documentation/translations/zh_TW/admin-guide/clearing-warn-once.rst:7:清除 WARN_ONCE
 Documentation/translations/zh_TW/admin-guide/clearing-warn-once.rst-8---------------
 Documentation/translations/zh_TW/admin-guide/clearing-warn-once.rst-9-
 Documentation/translations/zh_TW/admin-guide/clearing-warn-once.rst:10:WARN_ONCE / WARN_ON_ONCE / printk_once 僅僅打印一次消息.
 Documentation/translations/zh_TW/admin-guide/clearing-warn-once.rst-11-
 --
 Makefile=850=ifeq ("$(origin UT)", "command line")
 Makefile:851:  WARN_ON_UNUSED_TRACEPOINTS := $(UT)
 Makefile-852-endif
 Makefile=853=endif # CONFIG_TRACEPOINTS
 Makefile-854-
 Makefile:855:export WARN_ON_UNUSED_TRACEPOINTS
 Makefile-856-
 --
 arch/alpha/include/asm/cmpxchg.h=217=____cmpxchg(volatile void *ptr, unsigned long old, unsigned long new,
 --
 arch/alpha/include/asm/cmpxchg.h-245-({									\
 arch/alpha/include/asm/cmpxchg.h:246:	BUILD_BUG_ON(sizeof(*(ptr)) != 8);				\
 arch/alpha/include/asm/cmpxchg.h-247-	cmpxchg_local((ptr), (o), (n));					\
 --
 arch/alpha/include/asm/cmpxchg.h-278-({									\
 arch/alpha/include/asm/cmpxchg.h:279:	BUILD_BUG_ON(sizeof(*(ptr)) != 8);				\
 arch/alpha/include/asm/cmpxchg.h-280-	arch_cmpxchg((ptr), (o), (n));					\
 --
 arch/alpha/include/asm/err_ev7.h=164=static inline int ev7_lf_env_index(int type)
 arch/alpha/include/asm/err_ev7.h-165-{
 arch/alpha/include/asm/err_ev7.h:166:	BUG_ON((type < EL_TYPE__PAL__ENV__AMBIENT_TEMPERATURE) 
 arch/alpha/include/asm/err_ev7.h-167-	       || (type > EL_TYPE__PAL__ENV__HOT_PLUG));
 --
 arch/alpha/kernel/io.c=320=void ioread16_rep(const void __iomem *port, void *dst, unsigned long count)
 --
 arch/alpha/kernel/io.c-324-			return;
 arch/alpha/kernel/io.c:325:		BUG_ON((unsigned long)dst & 0x1);
 arch/alpha/kernel/io.c-326-		count--;
 --
 arch/alpha/kernel/io.c=414=void iowrite16_rep(void __iomem *port, const void *src, unsigned long count)
 --
 arch/alpha/kernel/io.c-418-			return;
 arch/alpha/kernel/io.c:419:		BUG_ON((unsigned long)src & 0x1);
 arch/alpha/kernel/io.c-420-		iowrite16(*(unsigned short *)src, port);
 --
 arch/alpha/kernel/pci_iommu.c=300=static struct pci_dev *alpha_gendev_to_pci(struct device *dev)
 --
 arch/alpha/kernel/pci_iommu.c-306-	   BUG() otherwise. */
 arch/alpha/kernel/pci_iommu.c:307:	BUG_ON(!isa_bridge);
 arch/alpha/kernel/pci_iommu.c-308-
 --
 arch/alpha/kernel/pci_iommu.c=623=static int alpha_pci_map_sg(struct device *dev, struct scatterlist *sg,
 --
 arch/alpha/kernel/pci_iommu.c-633-
 arch/alpha/kernel/pci_iommu.c:634:	BUG_ON(dir == DMA_NONE);
 arch/alpha/kernel/pci_iommu.c-635-
 --
 arch/alpha/kernel/pci_iommu.c=704=static void alpha_pci_unmap_sg(struct device *dev, struct scatterlist *sg,
 --
 arch/alpha/kernel/pci_iommu.c-715-
 arch/alpha/kernel/pci_iommu.c:716:	BUG_ON(dir == DMA_NONE);
 arch/alpha/kernel/pci_iommu.c-717-
 --
 arch/alpha/kernel/perf_event.c=152=static int ev67_check_constraints(struct perf_event **event,
 --
 arch/alpha/kernel/perf_event.c-162-
 arch/alpha/kernel/perf_event.c:163:	BUG_ON(n_ev != 2);
 arch/alpha/kernel/perf_event.c-164-
 --
 arch/alpha/kernel/perf_event.c=552=static void alpha_pmu_start(struct perf_event *event, int flags)
 --
 arch/alpha/kernel/perf_event.c-556-
 arch/alpha/kernel/perf_event.c:557:	if (WARN_ON_ONCE(!(hwc->state & PERF_HES_STOPPED)))
 arch/alpha/kernel/perf_event.c-558-		return;
 --
 arch/alpha/kernel/perf_event.c-560-	if (flags & PERF_EF_RELOAD) {
 arch/alpha/kernel/perf_event.c:561:		WARN_ON_ONCE(!(hwc->state & PERF_HES_UPTODATE));
 arch/alpha/kernel/perf_event.c-562-		alpha_perf_event_set_period(event, hwc, hwc->idx);
 --
 arch/arc/kernel/mcip.c=376=idu_of_init(struct device_node *intc, struct device_node *parent)
 --
 arch/arc/kernel/mcip.c-409-		virq = irq_create_mapping(NULL, i + FIRST_EXT_IRQ);
 arch/arc/kernel/mcip.c:410:		BUG_ON(!virq);
 arch/arc/kernel/mcip.c-411-		irq_set_chained_handler_and_data(virq, idu_cascade_isr, domain);
 --
 arch/arc/kernel/perf_event.c=451=static void arc_pmu_start(struct perf_event *event, int flags)
 --
 arch/arc/kernel/perf_event.c-455-
 arch/arc/kernel/perf_event.c:456:	if (WARN_ON_ONCE(idx == -1))
 arch/arc/kernel/perf_event.c-457-		return;
 --
 arch/arc/kernel/perf_event.c-459-	if (flags & PERF_EF_RELOAD)
 arch/arc/kernel/perf_event.c:460:		WARN_ON_ONCE(!(hwc->state & PERF_HES_UPTODATE));
 arch/arc/kernel/perf_event.c-461-
 --
 arch/arc/kernel/perf_event.c=562=static irqreturn_t arc_pmu_intr(int irq, void *dev)
 --
 arch/arc/kernel/perf_event.c-597-
 arch/arc/kernel/perf_event.c:598:		WARN_ON_ONCE(hwc->idx != idx);
 arch/arc/kernel/perf_event.c-599-
 --
 arch/arc/kernel/perf_event.c=721=static int arc_pmu_device_probe(struct platform_device *pdev)
 --
 arch/arc/kernel/perf_event.c-741-	}
 arch/arc/kernel/perf_event.c:742:	BUILD_BUG_ON(ARC_PERF_MAX_COUNTERS > 32);
 arch/arc/kernel/perf_event.c:743:	if (WARN_ON(pct_bcr.c > ARC_PERF_MAX_COUNTERS))
 arch/arc/kernel/perf_event.c-744-		return -EINVAL;
 --
 arch/arc/kernel/process.c=46=SYSCALL_DEFINE3(arc_usr_cmpxchg, int __user *, uaddr, int, expected, int, new)
 --
 arch/arc/kernel/process.c-57-	 */
 arch/arc/kernel/process.c:58:	WARN_ON_ONCE(IS_ENABLED(CONFIG_SMP));
 arch/arc/kernel/process.c-59-
 --
 arch/arc/kernel/smp.c=131=static void arc_default_smp_cpu_kick(int cpu, unsigned long pc)
 arch/arc/kernel/smp.c-132-{
 arch/arc/kernel/smp.c:133:	BUG_ON(cpu == 0);
 arch/arc/kernel/smp.c-134-
 --
 arch/arc/kernel/unwind.c=33=do {						\
 --
 arch/arc/kernel/unwind.c-43-#define EXTRA_INFO(f) { \
 arch/arc/kernel/unwind.c:44:		BUILD_BUG_ON_ZERO(offsetof(struct unwind_frame_info, f) \
 arch/arc/kernel/unwind.c-45-				% sizeof_field(struct unwind_frame_info, f)) \
 --
 arch/arc/kernel/unwind.c=244=static void init_unwind_hdr(struct unwind_table *table,
 --
 arch/arc/kernel/unwind.c-312-	put_unaligned((unsigned long)table->address, &header->eh_frame_ptr);
 arch/arc/kernel/unwind.c:313:	BUILD_BUG_ON(offsetof(typeof(*header), fde_count)
 arch/arc/kernel/unwind.c-314-		     % __alignof(typeof(header->fde_count)));
 --
 arch/arc/kernel/unwind.c-316-
 arch/arc/kernel/unwind.c:317:	BUILD_BUG_ON(offsetof(typeof(*header), table)
 arch/arc/kernel/unwind.c-318-		     % __alignof(typeof(*header->table)));
 --
 arch/arc/kernel/unwind.c-333-	}
 arch/arc/kernel/unwind.c:334:	WARN_ON(n != header->fde_count);
 arch/arc/kernel/unwind.c-335-
 --
 arch/arc/kernel/unwind.c=525=static unsigned long read_pointer(const u8 **pLoc, const void *end,
 --
 arch/arc/kernel/unwind.c-559-	case DW_EH_PE_data8:
 arch/arc/kernel/unwind.c:560:		BUILD_BUG_ON(sizeof(u64) != sizeof(value));
 arch/arc/kernel/unwind.c-561-#else
 arch/arc/kernel/unwind.c:562:		BUILD_BUG_ON(sizeof(u32) != sizeof(value));
 arch/arc/kernel/unwind.c-563-#endif
 --
 arch/arc/kernel/unwind.c-570-	case DW_EH_PE_leb128:
 arch/arc/kernel/unwind.c:571:		BUILD_BUG_ON(sizeof(uleb128_t) > sizeof(value));
 arch/arc/kernel/unwind.c-572-		value = ptrType & DW_EH_PE_signed ? get_sleb128(&ptr.p8, end)
 --
 arch/arc/mm/cache.c=100=int arc_cache_mumbojumbo(int c, char *buf, int len)
 --
 arch/arc/mm/cache.c-111-	if (is_isa_arcompact() && (ibcr.ver <= 3)) {
 arch/arc/mm/cache.c:112:		BUG_ON(ibcr.config != 3);
 arch/arc/mm/cache.c-113-		assoc = 2;		/* Fixed to 2w set assoc */
 --
 arch/arc/mm/cache.c-133-	if (is_isa_arcompact() && (dbcr.ver <= 3)) {
 arch/arc/mm/cache.c:134:		BUG_ON(dbcr.config != 2);
 arch/arc/mm/cache.c-135-		vipt = 1;
 --
 arch/arc/mm/cache.c=995=static noinline void __init arc_cache_init_master(void)
 --
 arch/arc/mm/cache.c-1036-	 */
 arch/arc/mm/cache.c:1037:	BUILD_BUG_ON_MSG(L1_CACHE_BYTES > SMP_CACHE_BYTES,
 arch/arc/mm/cache.c-1038-			 "SMP_CACHE_BYTES must be >= any cache line length");
 --
 arch/arc/mm/highmem.c=64=void __init kmap_init(void)
 --
 arch/arc/mm/highmem.c-66-	/* Due to recursive include hell, we can't do this in processor.h */
 arch/arc/mm/highmem.c:67:	BUILD_BUG_ON(PAGE_OFFSET < (VMALLOC_END + FIXMAP_SIZE + PKMAP_SIZE));
 arch/arc/mm/highmem.c:68:	BUILD_BUG_ON(LAST_PKMAP > PTRS_PER_PTE);
 arch/arc/mm/highmem.c:69:	BUILD_BUG_ON(FIX_KMAP_SLOTS > PTRS_PER_PTE);
 arch/arc/mm/highmem.c-70-
 --
 arch/arc/mm/init.c=159=void __init arch_mm_preinit(void)
 --
 arch/arc/mm/init.c-164-
 arch/arc/mm/init.c:165:	BUILD_BUG_ON((PTRS_PER_PGD * sizeof(pgd_t)) > PAGE_SIZE);
 arch/arc/mm/init.c:166:	BUILD_BUG_ON((PTRS_PER_PUD * sizeof(pud_t)) > PAGE_SIZE);
 arch/arc/mm/init.c:167:	BUILD_BUG_ON((PTRS_PER_PMD * sizeof(pmd_t)) > PAGE_SIZE);
 arch/arc/mm/init.c:168:	BUILD_BUG_ON((PTRS_PER_PTE * sizeof(pte_t)) > PAGE_SIZE);
 arch/arc/mm/init.c-169-}
 --
 arch/arc/mm/tlb.c=616=void arc_mmu_init(void)
 --
 arch/arc/mm/tlb.c-623-	 */
 arch/arc/mm/tlb.c:624:	BUILD_BUG_ON(!IS_ALIGNED((CONFIG_ARC_KVADDR_SIZE << 20), PMD_SIZE));
 arch/arc/mm/tlb.c-625-
 --
 arch/arc/mm/tlb.c-629-	 */
 arch/arc/mm/tlb.c:630:	BUILD_BUG_ON(!IS_ALIGNED(STACK_TOP, PMD_SIZE));
 arch/arc/mm/tlb.c-631-
 --
 arch/arc/mm/tlb.c=694=void do_tlb_overlap_fault(unsigned long cause, unsigned long address,
]
]

gemini-3.1-pro-preview

							input: 147040
							output: 31
							thoughts: 27
						

Here's my thought process, summarized as you requested:

**Debugging the NBD Driver**

Okay, I need to investigate potential issues within the Network Block Device (NBD) driver. Hmm, instead of just randomly sifting through the code, I should be targeted in my approach. Let's see...I want to quickly identify places where the code explicitly checks for and handles error conditions, or at least where it asserts that something is true.  The best way to do that is to look for `BUG_ON` and `WARN_ON` macros. Those are the kernels' way of dealing with potentially serious bugs and warnings, respectively. I'll use `grep`, and I want to use extended regular expressions so I don't have to keep escaping special characters. That will make the search cleaner and easier to read. The file I need to look in is `drivers/block/nbd.c`. So, I'll execute the command: `grep -E 'BUG_ON|WARN_ON' drivers/block/nbd.c`. This should give me a focused list of the critical error-handling points within the NBD driver. This should be a good starting point for understanding how the driver handles potentially problematic scenarios.

no matches

map[Expression:(BUG_ON|WARN_ON).*drivers/block/nbd\.c]

map[Output:]

gemini-3.1-pro-preview

							input: 147371
							output: 47
							thoughts: 1965
						

**Analyzing Potential Socket Leak Issues in NBD Driver**

Okay, so I'm trying to figure out if there's a file descriptor leak in the NBD driver, specifically related to socket management. First, I thought about using `grepper` but realized that's overkill; I can just read the relevant files, specifically looking for `BUG_ON` or `WARN_ON`, or maybe use `codesearch-find-references` for them. But, let's assume those aren't present in `nbd.c` for now.

My first thought is around `nbd_reconnect_socket`. Let's look at the logic there. If `nbd_reconnect_socket` returns `-ENOSPC`, it calls `sockfd_put(sock)`. Now, `sock` comes from `nbd_get_socket`, which calls `sockfd_lookup` and *increments* the reference count on the file descriptor. So, when `-ENOSPC` happens and `sockfd_put` is called, the reference count is decremented. Perfect, that's balanced. No leak there.

What if `nbd_reconnect_socket` finds a dead socket? It replaces `nsock->sock` with `sock` and calls `sockfd_put(old)`. This decrements the reference count of the *old* socket, but keeps the reference of the *new* socket, which is also balanced! Okay, good.

Next, I looked at `nbd_add_socket`. Again, we're using `nbd_get_socket` and then calling `sockfd_put` in the error path. Balanced again, there's no leak.

Okay, let's check `nbd_genl_reconfigure`. It parses `NBD_ATTR_SOCKETS` and calls `nbd_reconnect_socket`. If `nbd_reconnect_socket` returns `-ENOSPC`, the return value is set to 0 and the loop breaks. It's okay because the return value is 0, so the function itself won't return an error. So that's also fine.

Now, `nbd_genl_connect` is called. It parses `NBD_ATTR_SOCKETS` and calls `nbd_add_socket`. If there's an error from `nbd_add_socket`, it jumps to `out`. In the `out` block, if there's an error (`ret` is not 0), we *skip* `refcount_inc(&nbd->config_refs)`. Then we call `nbd_config_put(nbd)`. Now, hold on, `nbd_config_put` will *decrement* `config_refs`, right? So let's look at how `config_refs` are initialized and checked in `nbd_alloc_and_init_config`.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_alloc_and_init_config]

map[SourceCode:1670:	static int nbd_alloc_and_init_config(struct nbd_device *nbd)
1671:	{
1672:		struct nbd_config *config;
1673:	
1674:		if (WARN_ON(nbd->config))
1675:			return -EINVAL;
1676:	
1677:		if (!try_module_get(THIS_MODULE))
1678:			return -ENODEV;
1679:	
1680:		config = kzalloc_obj(struct nbd_config, GFP_NOFS);
1681:		if (!config) {
1682:			module_put(THIS_MODULE);
1683:			return -ENOMEM;
1684:		}
1685:	
1686:		atomic_set(&config->recv_threads, 0);
1687:		init_waitqueue_head(&config->recv_wq);
1688:		init_waitqueue_head(&config->conn_wait);
1689:		config->blksize_bits = NBD_DEF_BLKSIZE_BITS;
1690:		atomic_set(&config->live_connections, 0);
1691:	
1692:		nbd->config = config;
1693:		/*
1694:		 * Order refcount_set(&nbd->config_refs, 1) and nbd->config assignment,
1695:		 * its pair is the barrier in nbd_get_config_unlocked().
1696:		 * So nbd_get_config_unlocked() won't see nbd->config as null after
1697:		 * refcount_inc_not_zero() succeed.
1698:		 */
1699:		smp_mb__before_atomic();
1700:		refcount_set(&nbd->config_refs, 1);
1701:	
1702:		return 0;
1703:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 150560
							output: 43
							thoughts: 789
						

**Analyzing Potential Reference Count Issues**

Okay, so I'm looking at this code and trying to ensure that reference counts are properly managed, especially when things go wrong. Right now, `config_refs` is definitely starting at 1. The initial scenario makes sense: if `nbd_add_socket` fails, `nbd_genl_connect` jumps to `out`, skipping the increment of `config_refs`. Then, `nbd_config_put` is called, which decrements `config_refs` to 0 and frees `nbd->config`. That's clean, balanced.

But, here's where it gets interesting. What if `nbd_add_socket` succeeds, but then `nbd_start_device` fails? I see that if `nbd_start_device` returns an error (`ret` is non-zero), we skip the `refcount_inc` and then call `nbd_config_put`. Again, this looks correct – decrementing `config_refs` to zero and cleaning up. But, wait... `nbd_start_device` *might* have queued some `recv_work` threads *before* failing! I need to investigate that.

Okay, let me check the code of `nbd_start_device` itself. I see it allocates and queues several `recv_work` threads. Importantly, inside this loop, *each* successful `kzalloc_obj` call for a new thread increment `nbd->config_refs`. Even more importantly, there is a `flush_workqueue` call in case there are queued jobs when allocation of a thread fails.

So, this means if `nbd_start_device` *does* fail after queuing some of those threads, and the thread allocation fails, it will call `flush_workqueue`, which will cause `recv_work` threads to be destroyed. This could potentially cause a race condition, where we try to destroy the workqueue from inside a workqueue, but the reference should still be fine.

But `nbd_start_device` is not just threads! It also calls `nbd_set_size`. So, I'll need to double check that part of the code too. What if *that* call fails, possibly after starting some threads?

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_set_size]

map[SourceCode: 334:	static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize, loff_t blksize)
 335:	{
 336:		struct queue_limits lim;
 337:		int error;
 338:	
 339:		if (!blksize)
 340:			blksize = 1u << NBD_DEF_BLKSIZE_BITS;
 341:	
 342:		if (blk_validate_block_size(blksize))
 343:			return -EINVAL;
 344:	
 345:		if (bytesize < 0)
 346:			return -EINVAL;
 347:	
 348:		nbd->config->bytesize = bytesize;
 349:		nbd->config->blksize_bits = __ffs(blksize);
 350:	
 351:		if (!nbd->pid)
 352:			return 0;
 353:	
 354:		lim = queue_limits_start_update(nbd->disk->queue);
 355:		if (nbd->config->flags & NBD_FLAG_SEND_TRIM)
 356:			lim.max_hw_discard_sectors = UINT_MAX >> SECTOR_SHIFT;
 357:		else
 358:			lim.max_hw_discard_sectors = 0;
 359:		if (!(nbd->config->flags & NBD_FLAG_SEND_FLUSH)) {
 360:			lim.features &= ~(BLK_FEAT_WRITE_CACHE | BLK_FEAT_FUA);
 361:		} else if (nbd->config->flags & NBD_FLAG_SEND_FUA) {
 362:			lim.features |= BLK_FEAT_WRITE_CACHE | BLK_FEAT_FUA;
 363:		} else {
 364:			lim.features |= BLK_FEAT_WRITE_CACHE;
 365:			lim.features &= ~BLK_FEAT_FUA;
 366:		}
 367:		if (nbd->config->flags & NBD_FLAG_ROTATIONAL)
 368:			lim.features |= BLK_FEAT_ROTATIONAL;
 369:		if (nbd->config->flags & NBD_FLAG_SEND_WRITE_ZEROES)
 370:			lim.max_write_zeroes_sectors = UINT_MAX >> SECTOR_SHIFT;
 371:	
 372:		lim.logical_block_size = blksize;
 373:		lim.physical_block_size = blksize;
 374:		error = queue_limits_commit_update_frozen(nbd->disk->queue, &lim);
 375:		if (error)
 376:			return error;
 377:	
 378:		if (max_part)
 379:			set_bit(GD_NEED_PART_SCAN, &nbd->disk->state);
 380:		if (!set_capacity_and_notify(nbd->disk, bytesize >> 9))
 381:			kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
 382:		return 0;
 383:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 152787
							output: 41
							thoughts: 2668
						

**Deep Dive into Potential NBD Driver Vulnerabilities**

Okay, so I'm digging into this NBD driver code, and first glance, it looks like `queue_limits_commit_update_frozen` and `nbd_set_size` returning errors can cascade into some interesting scenarios. My initial thought is that if `nbd_set_size` errors out, and `nbd_start_device` returns an error, there's a reference count issue.  Specifically, `nbd_genl_connect` might skip incrementing `nbd->config_refs`, then calls `nbd_config_put(nbd)`. Now, if `nbd_start_device` queued work threads, each of those threads *did* increment `config_refs`, so `config_refs` effectively became `1 + num_connections`, right? And when `nbd_config_put` gets called (at the error path), it decrements it back down to `num_connections`, *not* zero. So the config isn't freed.  Then `nbd_genl_connect` returns, and the `recv_work` threads exit, and each calls `nbd_config_put`, which is safe and decrement it to zero.  

But what if there's an error in `nbd_start_device` *before* the workqueue flush? Say in `kzalloc_obj`? It shuts down the socket and calls `flush_workqueue`.  My concern is that `flush_workqueue` *waits* for those threads to finish. But, they call `nbd_config_put`, which tries to lock `nbd->config_lock`. However,  `nbd_start_device` is called *with* `nbd->config_lock` held!  A deadlock?  Let's look more closely. `nbd_genl_connect` and `nbd_ioctl` *both* hold that lock when they call `nbd_start_device`, so no, `flush_workqueue` won't cause that deadlock in either function.  So, no deadlock.

Now, what if there's a use-after-free of the `nbd` struct itself? `nbd_genl_connect` calls `nbd_find_get_unused` and might add a new device with `refs = 1`. Then, if the flag `NBD_CFLAG_DESTROY_ON_DISCONNECT` is set, `put_dev` becomes true, and `nbd_put(nbd)` is called, which could free `nbd` when its reference count hits zero. But the `recv_work` threads are still running, and they have pointers to `nbd`. So this is a huge problem! Let's check `nbd_start_device` again. Okay, it increments `nbd->config_refs`, but *not* `nbd->refs`. `nbd_config_put` calls `nbd_put` if `config_refs` drops to zero. `config_refs` acts as a sub-reference to hold a reference for nbd. It looks like `nbd_alloc_and_init_config` sets `config_refs=1`, but *doesn't* increment `nbd->refs`! Okay, so `nbd_alloc_and_init_config` assumes that the calling code *already* has a reference to `nbd`. Let's trace it through.  `nbd_genl_connect` gets a ref on `nbd`. Then it calls `nbd_alloc_and_init_config` (which sets `config_refs=1`).  Then, if `NBD_CFLAG_DESTROY_ON_DISCONNECT` is set, `nbd_put(nbd)` might be called *before* the work threads finish. Now, in `nbd_genl_connect`, if `nbd_start_device` succeeds, `config_refs` gets incremented. So `config_refs` is now 2 (plus the `recv_work` threads).  The `nbd_config_put` decrements it back to 1.  So it *doesn't* free the config or call `nbd_put`. Then, if `put_dev` is true, the `nbd_put(nbd)` is called.  This decrements `nbd->refs`. If it was 1, it drops to 0, *and the `nbd` struct is freed*! But the `recv_work` threads are still running with a dangling pointer!  A use-after-free!

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_put]

map[SourceCode: 287:	static void nbd_put(struct nbd_device *nbd)
 288:	{
 289:		if (!refcount_dec_and_test(&nbd->refs))
 290:			return;
 291:	
 292:		/* Call del_gendisk() asynchrounously to prevent deadlock */
 293:		if (test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags))
 294:			queue_work(nbd_del_wq, &nbd->remove_work);
 295:		else
 296:			nbd_dev_remove(nbd);
 297:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 156719
							output: 43
							thoughts: 43
						

Okay, let's see. My first thought is: **`nbd_put` and the Removal Conundrum**. I need to be sure about this – because I'm looking at this nbd driver code, and my understanding is that `nbd_put` either directly calls `nbd_dev_remove(nbd)` or, crucially, queues up `nbd->remove_work`. The latter hints at potential issues with race conditions, or more likely that the system needs to clean up the device and associated resources.

So, since I need the full picture, I’m going to focus my analysis on `nbd_dev_remove`. I need to ensure that the cleanup and device unregistration are handled correctly. I’ll make a note of this.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_dev_remove]

map[SourceCode: 264:	static void nbd_dev_remove(struct nbd_device *nbd)
 265:	{
 266:		struct gendisk *disk = nbd->disk;
 267:	
 268:		del_gendisk(disk);
 269:		blk_mq_free_tag_set(&nbd->tag_set);
 270:	
 271:		/*
 272:		 * Remove from idr after del_gendisk() completes, so if the same ID is
 273:		 * reused, the following add_disk() will succeed.
 274:		 */
 275:		mutex_lock(&nbd_index_mutex);
 276:		idr_remove(&nbd_index_idr, nbd->index);
 277:		mutex_unlock(&nbd_index_mutex);
 278:		destroy_workqueue(nbd->recv_workq);
 279:		put_disk(disk);
 280:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 157265
							output: 43
							thoughts: 318
						

**Race Condition Analysis in NBD Device Removal**

Okay, hold on a second! This `nbd_dev_remove` function, it's calling `destroy_workqueue` on `nbd->recv_workq`. And `destroy_workqueue`, crucially, it *waits* for all the pending work in that queue to complete. That means it will definitely wait for `recv_work` to finish. But here's the kicker: `recv_work` itself calls `nbd_config_put(nbd)`. And `nbd_config_put`... well, it's possible it'll drop `config_refs` down to zero, which then *calls* `nbd_put(nbd)`! But isn't `nbd_put` already in the process of being executed? It is.

Wait, so `nbd_config_put` also calls `nbd_put(nbd)`. This means `nbd_put` might be called twice. If `nbd_put` is called again, it's going to decrement `nbd->refs`. But hang on... `nbd->refs` is *already* zero!

So, the `refcount_dec_and_test(&nbd->refs)` function could very well trigger a warning or, even worse, a use-after-free scenario!

However, the refcount is already zero, so it won't be able to call `nbd_dev_remove` again.

Wait! The important thing is that `nbd_dev_remove` frees the `nbd` structure by calling `put_disk(disk)`. `put_disk` is going to free the disk, and isn't the `nbd` structure allocated *as part of* the disk structure?

We need to check this on the device add stage to be sure.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_dev_add]

map[SourceCode:1907:	static struct nbd_device *nbd_dev_add(int index, unsigned int refs)
1908:	{
1909:		struct queue_limits lim = {
1910:			.max_hw_sectors		= 65536,
1911:			.io_opt			= 256 << SECTOR_SHIFT,
1912:			.max_segments		= USHRT_MAX,
1913:			.max_segment_size	= UINT_MAX,
1914:		};
1915:		struct nbd_device *nbd;
1916:		struct gendisk *disk;
1917:		int err = -ENOMEM;
1918:	
1919:		nbd = kzalloc_obj(struct nbd_device);
1920:		if (!nbd)
1921:			goto out;
1922:	
1923:		nbd->tag_set.ops = &nbd_mq_ops;
1924:		nbd->tag_set.nr_hw_queues = 1;
1925:		nbd->tag_set.queue_depth = 128;
1926:		nbd->tag_set.numa_node = NUMA_NO_NODE;
1927:		nbd->tag_set.cmd_size = sizeof(struct nbd_cmd);
1928:		nbd->tag_set.flags = BLK_MQ_F_BLOCKING;
1929:		nbd->tag_set.driver_data = nbd;
1930:		INIT_WORK(&nbd->remove_work, nbd_dev_remove_work);
1931:		nbd->backend = NULL;
1932:	
1933:		err = blk_mq_alloc_tag_set(&nbd->tag_set);
1934:		if (err)
1935:			goto out_free_nbd;
1936:	
1937:		mutex_lock(&nbd_index_mutex);
1938:		if (index >= 0) {
1939:			err = idr_alloc(&nbd_index_idr, nbd, index, index + 1,
1940:					GFP_KERNEL);
1941:			if (err == -ENOSPC)
1942:				err = -EEXIST;
1943:		} else {
1944:			err = idr_alloc(&nbd_index_idr, nbd, 0,
1945:					(MINORMASK >> part_shift) + 1, GFP_KERNEL);
1946:			if (err >= 0)
1947:				index = err;
1948:		}
1949:		nbd->index = index;
1950:		mutex_unlock(&nbd_index_mutex);
1951:		if (err < 0)
1952:			goto out_free_tags;
1953:	
1954:		disk = blk_mq_alloc_disk(&nbd->tag_set, &lim, NULL);
1955:		if (IS_ERR(disk)) {
1956:			err = PTR_ERR(disk);
1957:			goto out_free_idr;
1958:		}
1959:		nbd->disk = disk;
1960:	
1961:		nbd->recv_workq = alloc_workqueue("nbd%d-recv",
1962:						  WQ_MEM_RECLAIM | WQ_HIGHPRI |
1963:						  WQ_UNBOUND, 0, nbd->index);
1964:		if (!nbd->recv_workq) {
1965:			dev_err(disk_to_dev(nbd->disk), "Could not allocate knbd recv work queue.\n");
1966:			err = -ENOMEM;
1967:			goto out_err_disk;
1968:		}
1969:	
1970:		mutex_init(&nbd->config_lock);
1971:		refcount_set(&nbd->config_refs, 0);
1972:		/*
1973:		 * Start out with a zero references to keep other threads from using
1974:		 * this device until it is fully initialized.
1975:		 */
1976:		refcount_set(&nbd->refs, 0);
1977:		INIT_LIST_HEAD(&nbd->list);
1978:		disk->major = NBD_MAJOR;
1979:		disk->first_minor = index << part_shift;
1980:		disk->minors = 1 << part_shift;
1981:		disk->fops = &nbd_fops;
1982:		disk->private_data = nbd;
1983:		sprintf(disk->disk_name, "nbd%d", index);
1984:		err = add_disk(disk);
1985:		if (err)
1986:			goto out_free_work;
1987:	
1988:		/*
1989:		 * Now publish the device.
1990:		 */
1991:		refcount_set(&nbd->refs, refs);
1992:		nbd_total_devices++;
1993:		return nbd;
1994:	
1995:	out_free_work:
1996:		destroy_workqueue(nbd->recv_workq);
1997:	out_err_disk:
1998:		put_disk(disk);
1999:	out_free_idr:
2000:		mutex_lock(&nbd_index_mutex);
2001:		idr_remove(&nbd_index_idr, index);
2002:		mutex_unlock(&nbd_index_mutex);
2003:	out_free_tags:
2004:		blk_mq_free_tag_set(&nbd->tag_set);
2005:	out_free_nbd:
2006:		kfree(nbd);
2007:	out:
2008:		return ERR_PTR(err);
2009:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 159714
							output: 43
							thoughts: 245
						

**Investigating the NBD Device Removal Process**

Okay, so I'm looking at this `nbd_dev_remove` function, and something immediately jumps out. We allocate the `nbd` structure using `kzalloc_obj`, which means it's memory that needs to be freed. But, looking at the code, I don't *see* a `kfree` for `nbd` in this function. That's a red flag.

The code calls `del_gendisk` and `blk_mq_free_tag_set`. Then, it removes the `nbd` from the IDR and destroys a workqueue. Finally, it calls `put_disk(disk)`. Now, I know `put_disk` can call `__put_disk` which, ultimately, frees the `gendisk` structure. I'm reasonably sure that takes care of the block device itself. But, who is responsible for freeing the `nbd` structure itself? It's not in this function. I need to track this down; I have to know where the memory for `nbd` gets released. Let's dig into the `nbd_free_disk` function.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_free_disk]

map[SourceCode:1760:	static void nbd_free_disk(struct gendisk *disk)
1761:	{
1762:		struct nbd_device *nbd = disk->private_data;
1763:	
1764:		kfree(nbd);
1765:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 160369
							output: 42
							thoughts: 36
						

Okay, here's my interpretation of those thoughts, speaking as an expert:

**Investigating the `nbd_free_disk` Function**

Hmm, so `nbd_free_disk` is *supposed* to be bound to the `disk->fops->free_disk` function pointer? Interesting. My immediate instinct is to confirm that's how it's actually set up. I need to quickly verify that binding. Let's dig into `nbd_fops` and confirm if the registration is correct. I want to see how `nbd_free_disk` is actually plugged into the larger file operations structure for the NBD driver. This is a critical point; if the function binding is incorrect it'll lead to all sorts of issues down the line. I'll focus on how `nbd_fops` defines that free function.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_fops]

map[SourceCode:1767:	static const struct block_device_operations nbd_fops =
1768:	{
1769:		.owner =	THIS_MODULE,
1770:		.open =		nbd_open,
1771:		.release =	nbd_release,
1772:		.ioctl =	nbd_ioctl,
1773:		.compat_ioctl =	nbd_ioctl,
1774:		.free_disk =	nbd_free_disk,
1775:	};
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 160801
							output: 44
							thoughts: 2021
						

**Deadlock Analysis in NBD Driver: A Deep Dive**

Okay, so here's the breakdown of what I'm thinking. I'm looking at how the NBD driver handles resource management, specifically around workqueues and reference counting, and I think I see a deadlock. At first, I thought that `nbd_dev_remove` freed the `nbd` structure directly, but that's not quite right. It calls `destroy_workqueue` first, which should wait for any pending `recv_work` to complete. This initially made me think there was a use-after-free issue, but that seems to be averted due to the workqueue synchronization.

Then, I started to worry about a scenario where `recv_work` might call `nbd_config_put`, which could, under certain circumstances, trigger `nbd_put` and ultimately `nbd_dev_remove`. If `nbd_dev_remove` *were* called from `recv_work`, that would mean the workqueue is being destroyed by work *within* the workqueue itself! A clear deadlock. I quickly dug into `destroy_workqueue`, confirming that this would be a deadlock as it tries to wait for itself.

I then considered `nbd_put` and noted that, based on the flags, it can call `nbd_dev_remove` directly or queue a work item to `nbd_del_wq`. Since I see that the reproducer sets `NBD_CFLAG_DESTROY_ON_DISCONNECT`, my initial conclusion was incorrect. I went back to the reproducer to look at the ANYBLOB value. This is when I tried to verify that the flag was set, but it was not. I was able to see that the `test_bit` was FALSE and it will call `nbd_dev_remove` directly.

So, I re-confirmed my hypothesis:  `recv_work` could call `nbd_config_put`, which, if a reference count hits 0, calls `nbd_dev_remove` on the same workqueue as `recv_work`.  This means the program calls `destroy_workqueue` from within the `recv_work`, causing a deadlock! I was able to verify this sequence step by step.

I noted that the deadlock manifests as a hung task panic, which is critical. The "SYZFAIL" message and the connection reset confirm this.

However, I needed to double-check a crucial assumption:  Does the reference count actually drop to zero? I re-traced the reference count flow through `nbd_genl_connect`.  I saw that `nbd_dev_add` gives the `nbd` a `refs` count of 2. One reference is for the device, and the other is returned to the caller (`nbd_genl_connect`). But if `NBD_CFLAG_DESTROY_ON_DISCONNECT` is not set, then the reference count is NOT incremented, and remains at 2. This is crucial: the decrement in `recv_work` won't bring it to zero, which means `nbd_dev_remove` isn't called, and no deadlock!

This reference count behavior leads to the device being connected. When the `NBD_CMD_DISCONNECT` command is sent the device reference should be dropped.

So, the issue isn't quite the deadlock I initially suspected. It seems the problem has been avoided. I'll need to re-evaluate the code to see why the syzbot is seeing the hang. It also appears the connection reference leak may be of interest for future debugging.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_genl_disconnect]

map[SourceCode:2275:	static int nbd_genl_disconnect(struct sk_buff *skb, struct genl_info *info)
2276:	{
2277:		struct nbd_device *nbd;
2278:		int index;
2279:	
2280:		if (!netlink_capable(skb, CAP_SYS_ADMIN))
2281:			return -EPERM;
2282:	
2283:		if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)) {
2284:			pr_err("must specify an index to disconnect\n");
2285:			return -EINVAL;
2286:		}
2287:		index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
2288:		mutex_lock(&nbd_index_mutex);
2289:		nbd = idr_find(&nbd_index_idr, index);
2290:		if (!nbd) {
2291:			mutex_unlock(&nbd_index_mutex);
2292:			pr_err("couldn't find device at index %d\n", index);
2293:			return -EINVAL;
2294:		}
2295:		if (!refcount_inc_not_zero(&nbd->refs)) {
2296:			mutex_unlock(&nbd_index_mutex);
2297:			pr_err("device at index %d is going down\n", index);
2298:			return -EINVAL;
2299:		}
2300:		mutex_unlock(&nbd_index_mutex);
2301:		if (!refcount_inc_not_zero(&nbd->config_refs))
2302:			goto put_nbd;
2303:		nbd_disconnect_and_put(nbd);
2304:		nbd_config_put(nbd);
2305:	put_nbd:
2306:		nbd_put(nbd);
2307:		return 0;
2308:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 164233
							output: 41
							thoughts: 636
						

**Analyzing the NBD Device Disconnect and Removal Process**

Okay, let's break down this `nbd_disconnect_and_put` function. My initial thought is, "Wait, what does this actually *do*?" It looks like it's handling the teardown after a disconnect. It calls `nbd_disconnect`, shuts down the socket, and wakes up the connection wait. Then it flushes the receive work queue, clears the I/O queue, and nulls out the task setup. Makes sense so far. It also calls `nbd_config_put(nbd)`. Ah, *that's* important.

It clicked that this `nbd_config_put` call means it's dropping the `config_refs` that were incremented in `nbd_genl_connect`. So, `nbd_genl_connect` is responsible for setting up the config reference and setting the `NBD_RT_HAS_CONFIG_REF` flag. Then `nbd_disconnect_and_put` clears that flag and decrements the reference. But I need to follow the references here.

I need to understand what happens to `nbd->refs`. After `nbd_genl_connect`, that value is 2. The code in the function doesn't drop `nbd->refs` below 1 if `NBD_CMD_DISCONNECT` is called. It only releases the reference that was obtained with `refcount_inc_not_zero`. So `nbd->refs` is still 1. I need to know when that drops to zero!

I remember `nbd_dev_remove` being called when `nbd->refs` drops to 0. But it appears it's not the caller. So who is dropping the last reference?

I've got it, look at `nbd_genl_connect` again. There's this check:

```c
	if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
		if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
				      &nbd->flags))
			put_dev = true;
	}
```
If `NBD_CFLAG_DESTROY_ON_DISCONNECT` is *not* set, the device is *never* destroyed until module unload! That's the key. So, the device persists. But wait... on module unload, `nbd_cleanup` gets called. I better check that. Time to go deeper.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_cleanup]

map[SourceCode:2708:	static void __exit nbd_cleanup(void)
2709:	{
2710:		struct nbd_device *nbd;
2711:		LIST_HEAD(del_list);
2712:	
2713:		/*
2714:		 * Unregister netlink interface prior to waiting
2715:		 * for the completion of netlink commands.
2716:		 */
2717:		genl_unregister_family(&nbd_genl_family);
2718:	
2719:		nbd_dbg_close();
2720:	
2721:		mutex_lock(&nbd_index_mutex);
2722:		idr_for_each(&nbd_index_idr, &nbd_exit_cb, &del_list);
2723:		mutex_unlock(&nbd_index_mutex);
2724:	
2725:		while (!list_empty(&del_list)) {
2726:			nbd = list_first_entry(&del_list, struct nbd_device, list);
2727:			list_del_init(&nbd->list);
2728:			if (refcount_read(&nbd->config_refs))
2729:				pr_err("possibly leaking nbd_config (ref %d)\n",
2730:						refcount_read(&nbd->config_refs));
2731:			if (refcount_read(&nbd->refs) != 1)
2732:				pr_err("possibly leaking a device\n");
2733:			nbd_put(nbd);
2734:		}
2735:	
2736:		/* Also wait for nbd_dev_remove_work() completes */
2737:		destroy_workqueue(nbd_del_wq);
2738:	
2739:		idr_destroy(&nbd_index_idr);
2740:		unregister_blkdev(NBD_MAJOR, "nbd");
2741:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 166027
							output: 45
							thoughts: 1516
						

**Deep Dive into NBD Device Lifecycle and Potential Deadlocks**

Okay, let's break this down. First, `nbd_cleanup` indeed correctly calls `nbd_put(nbd)` on all devices in `nbd_index_idr`, which should free them after dropping the last reference. That's expected.

Now, I need to consider scenarios involving `NBD_CFLAG_DESTROY_ON_DISCONNECT`. If it's set, `nbd_genl_connect` does a `nbd_put(nbd)` after the initial add. So, the device's reference count immediately drops. When a disconnect then happens, `nbd_disconnect_and_put` calls `nbd_config_put`, which itself calls `nbd_put`. This is all good, resulting in a clean destruction of the device.

However, if `NBD_CFLAG_DESTROY_ON_DISCONNECT` is *not* set, then `nbd_genl_connect` doesn't do that initial `nbd_put`, leaving `nbd->refs` at 2. Then, `nbd_config_put` drops `config_refs` to 0 and calls `nbd_put`, leaving `nbd->refs` at 1. The device remains, which is the correct behavior.

Now, what if the reproducer *doesn't* call `NBD_CMD_DISCONNECT`? If the program exits abruptly, the sockets close, `recv_work` detects EOF and calls `nbd_config_put`. But `nbd_genl_connect` will have incremented `nbd->config_refs` and set the `NBD_RT_HAS_CONFIG_REF` flag. This means `config_refs` is going to be > 1.  When the `recv_work` threads exit, they drop their references, leaving `config_refs` at 1, so `nbd->config` isn't freed. The device remains connected, but with dead sockets. This is definitely a broken block device, but thankfully, no crash.

Okay, let's dig into failure scenarios during connection. If `nbd_start_device` fails, and we look at the code block, and suppose `nbd_start_device` fails.  If `nbd_start_device` fails it skips the increment of `nbd->config_refs`, calls `nbd_config_put`. Because `config_refs` starts at 1, `nbd_config_put` drops to 0, which frees the config and calls `nbd_put`.  However, if `recv_work` threads have *already* been queued, each will increment `config_refs`. So, if `num_threads` are active, and `nbd_start_device` fails, `config_refs` will start at `1 + num_threads`. `nbd_config_put` then reduces this to `num_threads`, and the config is *not* freed.  Then when the `recv_work` threads exit, they each call `nbd_config_put`, and the *last* one will bring it to zero, which is safe.

Now, the critical part. What if `nbd_start_device` *fails*, and `put_dev` *is* true? If `put_dev` is true, then the very first step `nbd_genl_connect` calls `nbd_put(nbd)`. So the reference count is set at one! Then when the last `recv_work` thread calls `nbd_config_put`, it then calls `nbd_put(nbd)`. The device reference goes to zero, which means `nbd_dev_remove` is called. That calls `destroy_workqueue(nbd->recv_workq)`.  But `nbd_dev_remove` is *also* called from `recv_work`! This means we are destroying a workqueue from within a workqueue that is being destroyed.  This is a deadlock!

Okay, let's verify. `put_dev` is true only if `NBD_CFLAG_DESTROY_ON_DISCONNECT` is set, but the reproducer *doesn't* set this. So `put_dev` is false. So `nbd_genl_connect` does *not* do the initial `nbd_put`. So `nbd->refs` stays at 2.  Thus the last `recv_work` thread causes `nbd->refs` to drop to 1.  `nbd_dev_remove` is *not* called. No deadlock. Phew.

Wait, is it

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_find_get_unused]

map[SourceCode:2011:	static struct nbd_device *nbd_find_get_unused(void)
2012:	{
2013:		struct nbd_device *nbd;
2014:		int id;
2015:	
2016:		lockdep_assert_held(&nbd_index_mutex);
2017:	
2018:		idr_for_each_entry(&nbd_index_idr, nbd, id) {
2019:			if (refcount_read(&nbd->config_refs) ||
2020:			    test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags))
2021:				continue;
2022:			if (refcount_inc_not_zero(&nbd->refs))
2023:				return nbd;
2024:		}
2025:	
2026:		return NULL;
2027:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 168894
							output: 146
							thoughts: 62915
						

map[Question:In drivers/block/nbd.c, if nbd_add_socket is called twice with the SAME fd, config->socks[0]->sock and config->socks[1]->sock will point to the SAME struct socket *. Then nbd_start_device is called, which queues TWO recv_work threads. Both threads will call nbd_read_reply on the SAME socket. When the socket is closed, both threads wake up, call nbd_mark_nsock_dead, and then call nbd_config_put. Is there any use-after-free, double-free, or deadlock in this scenario?]

map[Answer:In `drivers/block/nbd.c`, the scenario where `nbd_add_socket` is called twice with the same file descriptor (`fd`) does not lead to a use-after-free, double-free, or deadlock. Here is a detailed analysis of why this is the case:

### 1. Reference Counting of the Socket
When `nbd_add_socket` is called, it invokes `nbd_get_socket`, which calls `sockfd_lookup(fd, ...)`. `sockfd_lookup` increments the reference count of the underlying `struct file` (and thus the socket). If called twice with the same `fd`, the socket's reference count is incremented twice. 
In `nbd_config_put` (the cleanup function), the code iterates through all connections and calls `sockfd_put` for each `nsock->sock`. Since there are two `nsock` structures both pointing to the same socket, `sockfd_put` is called twice. This correctly balances the two references acquired during setup, avoiding both use-after-free and double-free of the socket.

### 2. Memory Management of `nsock` Structures
Each call to `nbd_add_socket` allocates a new `struct nbd_sock` (`nsock`). Even if they point to the same socket, they are distinct memory objects. They are added to the `config->socks` array and are individually freed in `nbd_config_put`. There is no double-free of these structures.

### 3. Synchronization and `nbd_mark_nsock_dead`
When the socket is closed, both `recv_work` threads (one for each `nsock`) will wake up from `nbd_read_reply` with an error. They both proceed to call `nbd_mark_nsock_dead`.
- **Locks:** `nbd_mark_nsock_dead` is called with `nsock->tx_lock` held. Since the threads have different `nsock` objects, they hold different locks and do not deadlock each other.
- **Socket Shutdown:** Both threads call `kernel_sock_shutdown` on the same socket. Calling shutdown multiple times on the same socket is a safe operation in the Linux kernel.
- **Live Connections:** `config->live_connections` is an atomic counter. It is incremented twice during setup and decremented twice (once by each thread) during teardown. It correctly reaches zero.

### 4. `nbd_config_put` and Cleanup
Both threads call `nbd_config_put` at the end of their execution. This function uses `refcount_dec_and_mutex_lock` on `nbd->config_refs`.
- The first thread to call it will decrement the reference count and return.
- The last thread to call it (or the last closer of the device) will decrement the count to zero, acquire the `config_lock`, and perform the actual cleanup (freeing `config->socks`, the `config` structure itself, etc.).
This ensures that cleanup happens exactly once and only when no threads are using the configuration anymore.

### 5. Deadlock Avoidance in Workqueue Destruction
A potential deadlock in NBD involves a `recv_work` thread calling `nbd_config_put`, which might trigger `nbd_dev_remove` and `destroy_workqueue(nbd->recv_workq)`. Since `recv_work` is running on that same workqueue, `destroy_workqueue` would wait for it to finish, while the thread waits for `destroy_workqueue` to return.
NBD avoids this in two ways:
- For static devices, the device reference count never reaches zero during normal operation (it's held until module unload).
- For dynamic devices (netlink), the removal is queued to a separate workqueue (`nbd_del_wq`), allowing the `recv_work` thread to complete before the workqueue is destroyed.

### Conclusion
While calling `nbd_add_socket` twice with the same `fd` will cause **protocol corruption** (as two threads will interleave reads from the same TCP stream), it is **safe from a kernel memory and locking perspective**. There are no use-after-free, double-free, or deadlock conditions created by this specific scenario.]

gemini-3-flash-preview

You are a capable Linux kernel developer tasked with researching complex questions
about kernel source code. You will be given a concrete question, and need to provide
a concrete answer.
Use tools extensively while researching the question. Don't make assumptions,
or rely on your previous knowledge about the kernel source code, use available tools
to access the actual source code.
Use all available sources of information:
 - kernel source code
 - documentation in the Documentation dir in the source tree
 - git commits descriptions, git blame

Prefer calling several tools at the same time to save round-trips.

In drivers/block/nbd.c, if nbd_add_socket is called twice with the SAME fd, config->socks[0]->sock and config->socks[1]->sock will point to the SAME struct socket *. Then nbd_start_device is called, which queues TWO recv_work threads. Both threads will call nbd_read_reply on the SAME socket. When the socket is closed, both threads wake up, call nbd_mark_nsock_dead, and then call nbd_config_put. Is there any use-after-free, double-free, or deadlock in this scenario?

In `drivers/block/nbd.c`, the scenario where `nbd_add_socket` is called twice with the same file descriptor (`fd`) does not lead to a use-after-free, double-free, or deadlock. Here is a detailed analysis of why this is the case:

### 1. Reference Counting of the Socket
When `nbd_add_socket` is called, it invokes `nbd_get_socket`, which calls `sockfd_lookup(fd, ...)`. `sockfd_lookup` increments the reference count of the underlying `struct file` (and thus the socket). If called twice with the same `fd`, the socket's reference count is incremented twice. 
In `nbd_config_put` (the cleanup function), the code iterates through all connections and calls `sockfd_put` for each `nsock->sock`. Since there are two `nsock` structures both pointing to the same socket, `sockfd_put` is called twice. This correctly balances the two references acquired during setup, avoiding both use-after-free and double-free of the socket.

### 2. Memory Management of `nsock` Structures
Each call to `nbd_add_socket` allocates a new `struct nbd_sock` (`nsock`). Even if they point to the same socket, they are distinct memory objects. They are added to the `config->socks` array and are individually freed in `nbd_config_put`. There is no double-free of these structures.

### 3. Synchronization and `nbd_mark_nsock_dead`
When the socket is closed, both `recv_work` threads (one for each `nsock`) will wake up from `nbd_read_reply` with an error. They both proceed to call `nbd_mark_nsock_dead`.
- **Locks:** `nbd_mark_nsock_dead` is called with `nsock->tx_lock` held. Since the threads have different `nsock` objects, they hold different locks and do not deadlock each other.
- **Socket Shutdown:** Both threads call `kernel_sock_shutdown` on the same socket. Calling shutdown multiple times on the same socket is a safe operation in the Linux kernel.
- **Live Connections:** `config->live_connections` is an atomic counter. It is incremented twice during setup and decremented twice (once by each thread) during teardown. It correctly reaches zero.

### 4. `nbd_config_put` and Cleanup
Both threads call `nbd_config_put` at the end of their execution. This function uses `refcount_dec_and_mutex_lock` on `nbd->config_refs`.
- The first thread to call it will decrement the reference count and return.
- The last thread to call it (or the last closer of the device) will decrement the count to zero, acquire the `config_lock`, and perform the actual cleanup (freeing `config->socks`, the `config` structure itself, etc.).
This ensures that cleanup happens exactly once and only when no threads are using the configuration anymore.

### 5. Deadlock Avoidance in Workqueue Destruction
A potential deadlock in NBD involves a `recv_work` thread calling `nbd_config_put`, which might trigger `nbd_dev_remove` and `destroy_workqueue(nbd->recv_workq)`. Since `recv_work` is running on that same workqueue, `destroy_workqueue` would wait for it to finish, while the thread waits for `destroy_workqueue` to return.
NBD avoids this in two ways:
- For static devices, the device reference count never reaches zero during normal operation (it's held until module unload).
- For dynamic devices (netlink), the removal is queued to a separate workqueue (`nbd_del_wq`), allowing the `recv_work` thread to complete before the workqueue is destroyed.

### Conclusion
While calling `nbd_add_socket` twice with the same `fd` will cause **protocol corruption** (as two threads will interleave reads from the same TCP stream), it is **safe from a kernel memory and locking perspective**. There are no use-after-free, double-free, or deadlock conditions created by this specific scenario.

gemini-3-flash-preview

							input: 2384
							output: 43
							thoughts: 306
						

**Investigating a Potential Race Condition in nbd.c**

Okay, so the user's raising a red flag about a possible race condition or bug lurking within `drivers/block/nbd.c`, specifically related to the `nbd_add_socket` function. It seems they're concerned about a scenario where the same file descriptor (`fd`) gets added to the NBD device twice. This sounds like it could lead to some nasty concurrency issues.

My immediate concern is: if `nbd_add_socket` is called with the same `fd` twice, will it properly handle the duplication? Their scenario highlights that both `config->socks[0]->sock` and `config->socks[1]->sock` would end up pointing to the *same* `struct socket *`, which is the very thing I would be suspicious of. Then, `nbd_start_device` spins up two `recv_work` threads, which will both try to interact with this shared socket.

The real meat of the problem is likely in `nbd_read_reply`, which is then called by both threads on the *same* socket. This could lead to a race. The user flags the socket closure, which would be the trigger for this issue. After the close, both `recv_work` threads wake up, execute `nbd_mark_nsock_dead`, and then execute `nbd_config_put`.

My thoughts now are centered around confirming how these functions interact. I need to dig into:

*   **`nbd_add_socket`**:  First, I need to know *precisely* how it handles duplicate file descriptors. Does it even attempt to prevent them? If not, what happens if it's fed the same socket twice? Does it just create a new socket entry? Or does it attempt to reuse something?
*   **`nbd_start_device`**: What is the mechanism for spawning these `recv_work` threads? Does it do any synchronization? How are the threads given access to the socket?
*   **`nbd_read_reply`**:  This is the likely point of contention. What's the socket interaction in detail? Does it use locking? Does it assume the socket is valid, but multiple threads are calling it?
*   **`nbd_mark_nsock_dead`**: What specifically does this function do? What are its side effects? Does it clean up any resources? How is it coordinated with the other threads?
*   **`nbd_config_put`**:  This function, coupled with the previous functions, is a key piece. It likely handles reference counting or resource cleanup. It's crucial to understand how it interacts with the socket and thread state, in the scenario where one thread is closing the socket, but another is still trying to access it. What is the locking strategy here?

My gut tells me this has the potential for a Use-After-Free (UAF) situation, or even a double-free, or a deadlock, all from conflicting access on the same socket from multiple threads. I better start by examining `nbd_add_socket` to understand how it handles this very specific edge case.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_add_socket]

map[SourceCode:1241:	static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
1242:				  bool netlink)
1243:	{
1244:		struct nbd_config *config = nbd->config;
1245:		struct socket *sock;
1246:		struct nbd_sock **socks;
1247:		struct nbd_sock *nsock;
1248:		unsigned int memflags;
1249:		int err;
1250:	
1251:		/* Arg will be cast to int, check it to avoid overflow */
1252:		if (arg > INT_MAX)
1253:			return -EINVAL;
1254:		sock = nbd_get_socket(nbd, arg, &err);
1255:		if (!sock)
1256:			return err;
1257:	
1258:		/*
1259:		 * We need to make sure we don't get any errant requests while we're
1260:		 * reallocating the ->socks array.
1261:		 */
1262:		memflags = blk_mq_freeze_queue(nbd->disk->queue);
1263:	
1264:		if (!netlink && !nbd->task_setup &&
1265:		    !test_bit(NBD_RT_BOUND, &config->runtime_flags))
1266:			nbd->task_setup = current;
1267:	
1268:		if (!netlink &&
1269:		    (nbd->task_setup != current ||
1270:		     test_bit(NBD_RT_BOUND, &config->runtime_flags))) {
1271:			dev_err(disk_to_dev(nbd->disk),
1272:				"Device being setup by another task");
1273:			err = -EBUSY;
1274:			goto put_socket;
1275:		}
1276:	
1277:		nsock = kzalloc_obj(*nsock);
1278:		if (!nsock) {
1279:			err = -ENOMEM;
1280:			goto put_socket;
1281:		}
1282:	
1283:		socks = krealloc(config->socks, (config->num_connections + 1) *
1284:				 sizeof(struct nbd_sock *), GFP_KERNEL);
1285:		if (!socks) {
1286:			kfree(nsock);
1287:			err = -ENOMEM;
1288:			goto put_socket;
1289:		}
1290:	
1291:		config->socks = socks;
1292:	
1293:		nsock->fallback_index = -1;
1294:		nsock->dead = false;
1295:		mutex_init(&nsock->tx_lock);
1296:		nsock->sock = sock;
1297:		nsock->pending = NULL;
1298:		nsock->sent = 0;
1299:		nsock->cookie = 0;
1300:		INIT_WORK(&nsock->work, nbd_pending_cmd_work);
1301:		socks[config->num_connections++] = nsock;
1302:		atomic_inc(&config->live_connections);
1303:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1304:	
1305:		return 0;
1306:	
1307:	put_socket:
1308:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1309:		sockfd_put(sock);
1310:		return err;
1311:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 4472
							output: 43
							thoughts: 41
						

Here's a summary of my thought process:

**Diving into the Socket Acquisition**

Okay, so `nbd_add_socket` is the function that's being called, and I see it's using `nbd_get_socket`.  My initial thought is to trace the execution and understand what this `nbd_get_socket` function does. I need to figure out what parameters are being passed and what the expected return value is. I need to understand how the socket is acquired and why. Let's dig into `nbd_get_socket` and figure out what's going on with this `nbd` and `arg` parameters and the potential `err` variable that's also being passed in. It looks like it might return an error code or status, which is important to understand. Let's see how the socket is actually obtained.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_get_socket]

map[SourceCode:1213:	static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd,
1214:					     int *err)
1215:	{
1216:		struct socket *sock;
1217:	
1218:		*err = 0;
1219:		sock = sockfd_lookup(fd, err);
1220:		if (!sock)
1221:			return NULL;
1222:	
1223:		if (!sk_is_tcp(sock->sk) &&
1224:		    !sk_is_stream_unix(sock->sk)) {
1225:			dev_err(disk_to_dev(nbd->disk), "Unsupported socket: should be TCP or UNIX.\n");
1226:			*err = -EINVAL;
1227:			sockfd_put(sock);
1228:			return NULL;
1229:		}
1230:	
1231:		if (sock->ops->shutdown == sock_no_shutdown) {
1232:			dev_err(disk_to_dev(nbd->disk), "Unsupported socket: shutdown callout must be supported.\n");
1233:			*err = -EINVAL;
1234:			sockfd_put(sock);
1235:			return NULL;
1236:		}
1237:	
1238:		return sock;
1239:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 5156
							output: 43
							thoughts: 142
						

Okay, let me break this down.

**Analyzing the NBD Socket Handling**

Right, so `nbd_get_socket` is using `sockfd_lookup`, which is key here. I'm seeing that if I pass the same file descriptor, `fd`, to `sockfd_lookup` multiple times, it's going to return the *exact same* `struct socket *` each time. Crucially, the reference count on that socket is incremented. No surprises there, that's expected behavior.

Now, back to `nbd_add_socket`. I can see that this function is allocating a new `struct nbd_sock *nsock` each time it's called, and then it adds it to the `config->socks` list. That makes it clear - if I feed `nbd_add_socket` the *same* `fd` twice, then the list `config->socks` is going to contain multiple `nbd_sock` entries, but `config->socks[0]->sock` and `config->socks[1]->sock` (or any other subsequent entries) will be pointing to the *same* underlying `struct socket *`. It's sharing a reference to the same socket, albeit with the different `nbd_sock` data structures, each managing its own lifecycle, I imagine.

Now, the important question is how does this play out further down the line with how `nbd_start_device` and other routines use this setup. That's the part I need to analyze in order to figure out if there is some memory management issue, or some other threading issue, in the code.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_start_device]

map[SourceCode:1471:	static int nbd_start_device(struct nbd_device *nbd)
1472:	{
1473:		struct nbd_config *config = nbd->config;
1474:		int num_connections = config->num_connections;
1475:		int error = 0, i;
1476:	
1477:		if (nbd->pid)
1478:			return -EBUSY;
1479:		if (!config->socks)
1480:			return -EINVAL;
1481:		if (num_connections > 1 &&
1482:		    !(config->flags & NBD_FLAG_CAN_MULTI_CONN)) {
1483:			dev_err(disk_to_dev(nbd->disk), "server does not support multiple connections per device.\n");
1484:			return -EINVAL;
1485:		}
1486:	
1487:	retry:
1488:		mutex_unlock(&nbd->config_lock);
1489:		blk_mq_update_nr_hw_queues(&nbd->tag_set, num_connections);
1490:		mutex_lock(&nbd->config_lock);
1491:	
1492:		/* if another code path updated nr_hw_queues, retry until succeed */
1493:		if (num_connections != config->num_connections) {
1494:			num_connections = config->num_connections;
1495:			goto retry;
1496:		}
1497:	
1498:		nbd->pid = task_pid_nr(current);
1499:	
1500:		nbd_parse_flags(nbd);
1501:	
1502:		error = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
1503:		if (error) {
1504:			dev_err(disk_to_dev(nbd->disk), "device_create_file failed for pid!\n");
1505:			return error;
1506:		}
1507:		set_bit(NBD_RT_HAS_PID_FILE, &config->runtime_flags);
1508:	
1509:		nbd_dev_dbg_init(nbd);
1510:		for (i = 0; i < num_connections; i++) {
1511:			struct recv_thread_args *args;
1512:	
1513:			args = kzalloc_obj(*args);
1514:			if (!args) {
1515:				sock_shutdown(nbd);
1516:				/*
1517:				 * If num_connections is m (2 < m),
1518:				 * and NO.1 ~ NO.n(1 < n < m) kzallocs are successful.
1519:				 * But NO.(n + 1) failed. We still have n recv threads.
1520:				 * So, add flush_workqueue here to prevent recv threads
1521:				 * dropping the last config_refs and trying to destroy
1522:				 * the workqueue from inside the workqueue.
1523:				 */
1524:				if (i)
1525:					flush_workqueue(nbd->recv_workq);
1526:				return -ENOMEM;
1527:			}
1528:			sk_set_memalloc(config->socks[i]->sock->sk);
1529:			if (nbd->tag_set.timeout)
1530:				config->socks[i]->sock->sk->sk_sndtimeo =
1531:					nbd->tag_set.timeout;
1532:			atomic_inc(&config->recv_threads);
1533:			refcount_inc(&nbd->config_refs);
1534:			INIT_WORK(&args->work, recv_work);
1535:			args->nbd = nbd;
1536:			args->nsock = config->socks[i];
1537:			args->index = i;
1538:			queue_work(nbd->recv_workq, &args->work);
1539:		}
1540:		return nbd_set_size(nbd, config->bytesize, nbd_blksize(config));
1541:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 6874
							output: 40
							thoughts: 209
						

**Analyzing the Socket Connection Setup**

Okay, so I'm looking at how `nbd_start_device` initializes the network connections. It seems straightforward enough: it iterates through `num_connections` and queues a `recv_work` instance for each one. But then I noticed something potentially problematic. Specifically, if the configuration, `config->socks[0]` and `config->socks[1]` share the *same* `sock`, the routine will still queue *two* `recv_work` instances. Each gets a different `nsock`, but they share the same underlying socket (`nsock->sock`).

Hang on... Let me double-check how `nsock` is actually created. Ah, right! `nbd_add_socket` allocates a NEW `nsock` every time it's called. So, like I suspected, `config->socks[0]` and `config->socks[1]` are distinct `struct nbd_sock` objects. They *point* to the same `struct socket` though.

Alright, with that confirmed, let's turn our attention to the `recv_work` function itself.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:recv_work]

map[SourceCode: 970:	static void recv_work(struct work_struct *work)
 971:	{
 972:		struct recv_thread_args *args = container_of(work,
 973:							     struct recv_thread_args,
 974:							     work);
 975:		struct nbd_device *nbd = args->nbd;
 976:		struct nbd_config *config = nbd->config;
 977:		struct request_queue *q = nbd->disk->queue;
 978:		struct nbd_sock *nsock = args->nsock;
 979:		struct nbd_cmd *cmd;
 980:		struct request *rq;
 981:	
 982:		while (1) {
 983:			struct nbd_reply reply;
 984:	
 985:			if (nbd_read_reply(nbd, nsock->sock, &reply))
 986:				break;
 987:	
 988:			/*
 989:			 * Grab .q_usage_counter so request pool won't go away, then no
 990:			 * request use-after-free is possible during nbd_handle_reply().
 991:			 * If queue is frozen, there won't be any inflight requests, we
 992:			 * needn't to handle the incoming garbage message.
 993:			 */
 994:			if (!percpu_ref_tryget(&q->q_usage_counter)) {
 995:				dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n",
 996:					__func__);
 997:				break;
 998:			}
 999:	
1000:			cmd = nbd_handle_reply(nbd, args->index, &reply);
1001:			if (IS_ERR(cmd)) {
1002:				percpu_ref_put(&q->q_usage_counter);
1003:				break;
1004:			}
1005:	
1006:			rq = blk_mq_rq_from_pdu(cmd);
1007:			if (likely(!blk_should_fake_timeout(rq->q))) {
1008:				bool complete;
1009:	
1010:				mutex_lock(&cmd->lock);
1011:				complete = __test_and_clear_bit(NBD_CMD_INFLIGHT,
1012:								&cmd->flags);
1013:				mutex_unlock(&cmd->lock);
1014:				if (complete)
1015:					blk_mq_complete_request(rq);
1016:			}
1017:			percpu_ref_put(&q->q_usage_counter);
1018:		}
1019:	
1020:		mutex_lock(&nsock->tx_lock);
1021:		nbd_mark_nsock_dead(nbd, nsock, 1);
1022:		mutex_unlock(&nsock->tx_lock);
1023:	
1024:		atomic_dec(&config->recv_threads);
1025:		wake_up(&config->recv_wq);
1026:		nbd_config_put(nbd);
1027:		kfree(args);
1028:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 8298
							output: 46
							thoughts: 223
						

**Analyzing the Network Socket Handling in `recv_work`**

Okay, so I'm looking closely at how `recv_work` handles network socket interactions, particularly in the event of a socket closure. The key sequence is: first, a call to `nbd_read_reply`, which is how we get data back from the network. If that fails – let's say the socket is closed – we break out of the loop. Then, and this is important, we're calling `nbd_mark_nsock_dead`. And after that, we put the configuration down by calling `nbd_config_put`.

The potential issue I see immediately is this: if we have two threads both calling `nbd_read_reply` on the same socket, both threads could attempt to read from it. If the socket closes while this is happening, both of those `nbd_read_reply` calls are going to return an error. Consequently, both threads will then proceed to execute `nbd_mark_nsock_dead` on their respective `nsock` objects. Since each `nsock` is likely a distinct object (e.g., `config->socks[0]` and `config->socks[1]`), they will each independently try to mark their specific `nsock` as "dead". This appears to be correct, but let's make sure by checking the internals of `nbd_mark_nsock_dead` to ensure there are no unintended consequences.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_mark_nsock_dead]

map[SourceCode: 305:	static void nbd_mark_nsock_dead(struct nbd_device *nbd, struct nbd_sock *nsock,
 306:					int notify)
 307:	{
 308:		if (!nsock->dead && notify && !nbd_disconnected(nbd->config)) {
 309:			struct link_dead_args *args;
 310:			args = kmalloc_obj(struct link_dead_args, GFP_NOIO);
 311:			if (args) {
 312:				INIT_WORK(&args->work, nbd_dead_link_work);
 313:				args->index = nbd->index;
 314:				queue_work(system_percpu_wq, &args->work);
 315:			}
 316:		}
 317:		if (!nsock->dead) {
 318:			kernel_sock_shutdown(nsock->sock, SHUT_RDWR);
 319:			if (atomic_dec_return(&nbd->config->live_connections) == 0) {
 320:				if (test_and_clear_bit(NBD_RT_DISCONNECT_REQUESTED,
 321:						       &nbd->config->runtime_flags)) {
 322:					set_bit(NBD_RT_DISCONNECTED,
 323:						&nbd->config->runtime_flags);
 324:					dev_info(nbd_to_dev(nbd),
 325:						"Disconnected due to user request.\n");
 326:				}
 327:			}
 328:		}
 329:		nsock->dead = true;
 330:		nsock->pending = NULL;
 331:		nsock->sent = 0;
 332:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 9392
							output: 43
							thoughts: 130
						

**Analyzing the Socket Shutdown and Connection Count**

Okay, so I'm looking at `nbd_mark_nsock_dead` and how it handles a dead network socket. The function calls `kernel_sock_shutdown(nsock->sock, SHUT_RDWR)`.  Essentially, I'm shutting down the socket for both reading and writing, which is standard practice in these scenarios.  I've considered the possibility of a race condition: what if two threads simultaneously call this function with the same socket? The code handles this gracefully, as `kernel_sock_shutdown` can be called multiple times on the same socket without causing significant problems. This is important for robustness.

Then, there's the `atomic_dec_return(&nbd->config->live_connections)`. This is where I'm tracking the number of live connections associated with the device.  It decrements the `live_connections` counter atomically.  If, let's say, `live_connections` was initially at 2, the first thread decrements it to 1, and the second thread decrements it again to 0. This is the expected behavior, allowing me to carefully track usage. I need to be sure the counter properly reflects the number of active connections to the device.

Now, I need to look at the implications of this, and how it relates to `nbd_config_put`. I want to consider the overall impact to the resource usage, and how the connection shutdown cascades.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_config_put]

map[SourceCode:1432:	static void nbd_config_put(struct nbd_device *nbd)
1433:	{
1434:		if (refcount_dec_and_mutex_lock(&nbd->config_refs,
1435:						&nbd->config_lock)) {
1436:			struct nbd_config *config = nbd->config;
1437:			nbd_dev_dbg_close(nbd);
1438:			invalidate_disk(nbd->disk);
1439:			if (nbd->config->bytesize)
1440:				kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
1441:			if (test_and_clear_bit(NBD_RT_HAS_PID_FILE,
1442:					       &config->runtime_flags))
1443:				device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
1444:			nbd->pid = 0;
1445:			if (test_and_clear_bit(NBD_RT_HAS_BACKEND_FILE,
1446:					       &config->runtime_flags)) {
1447:				device_remove_file(disk_to_dev(nbd->disk), &backend_attr);
1448:				kfree(nbd->backend);
1449:				nbd->backend = NULL;
1450:			}
1451:			nbd_clear_sock(nbd);
1452:			if (config->num_connections) {
1453:				int i;
1454:				for (i = 0; i < config->num_connections; i++) {
1455:					sockfd_put(config->socks[i]->sock);
1456:					kfree(config->socks[i]);
1457:				}
1458:				kfree(config->socks);
1459:			}
1460:			kfree(nbd->config);
1461:			nbd->config = NULL;
1462:	
1463:			nbd->tag_set.timeout = 0;
1464:	
1465:			mutex_unlock(&nbd->config_lock);
1466:			nbd_put(nbd);
1467:			module_put(THIS_MODULE);
1468:		}
1469:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 10547
							output: 21
							thoughts: 134
						

**Analyzing the Reference Counting in NBD Configuration**

Okay, so I'm looking at how the NBD configuration is managed, specifically the reference counting. The function `nbd_config_put` is using `refcount_dec_and_mutex_lock` on `nbd->config_refs` and the corresponding lock. Right, that makes sense – decrement the reference count and grab the lock before doing anything with the configuration. Now, I'm recalling that `nbd_start_device` increments this `config_refs` count for *each* connection. So, with two active connections, the reference count would have been incremented twice. I need to make sure I understand the full lifecycle here.

Wait a second, where is this `config_refs` initialized in the first place? I need to track down the root cause. This is important to ensure everything is thread-safe and properly managed. Typically, a structure like `nbd->config` would be created and the reference counter initialized within the same process. I'll need to go back and check where that happens, likely in `nbd_open`. Right, let's go check there.

requested entity does not exist

map[Name:config_refs]

map[References:<nil> TruncatedOutput:false]

gemini-3-flash-preview

							input: 10969
							output: 22
							thoughts: 16
						

Okay, here's my summary, in the first person, as an expert in my field, starting with the bolded header:

**Diving into `nbd_device::config_refs`**

Right, I need to get started on this. The task at hand likely requires me to look into the configuration references within the `nbd_device` context. I need to track down exactly where those are being stored, how they are accessed, and ideally, what interactions are performed with them. A direct search for `nbd_device::config_refs` seems like the most logical first step. That keyword, along with the device name gives a precise point to start with. From there, I'll be able to trace the usage and determine the implications. Hopefully, this should lead me to the relevant code quickly.

map[Name:nbd_device]

map[Fields:[map[Name:tag_set OffsetBits:0 SizeBits:3904] map[Name:index OffsetBits:3904 SizeBits:32] map[Name:config_refs OffsetBits:3936 SizeBits:32] map[Name:refs OffsetBits:3968 SizeBits:32] map[Name:config OffsetBits:4032 SizeBits:64] map[Name:config_lock OffsetBits:4096 SizeBits:1088] map[Name:disk OffsetBits:5184 SizeBits:64] map[Name:recv_workq OffsetBits:5248 SizeBits:64] map[Name:remove_work OffsetBits:5312 SizeBits:576] map[Name:list OffsetBits:5888 SizeBits:128] map[Name:task_setup OffsetBits:6016 SizeBits:64] map[Name:flags OffsetBits:6080 SizeBits:64] map[Name:pid OffsetBits:6144 SizeBits:32] map[Name:backend OffsetBits:6208 SizeBits:64]]]

gemini-3-flash-preview

							input: 11489
							output: 26
							thoughts: 28
						

Here's my thought process, summarized as you requested:

**Navigating the Configuration Reference Landscape**

Alright, the debugger is pointing to `config_refs` sitting at an offset of 3936 bits. That's the starting point. Now, the critical question is where this thing is *initialized*. I need to trace back through the code, ideally using the debugger's ability to show me cross-references or call sites, to understand how `config_refs` gets its initial value. Is it a compile-time constant? Is it read from flash? Is it computed at runtime based on some other values? Knowing its initialization is absolutely key to understanding its purpose and potential for modification down the line. I'll start with a search for its use.

map[Name:nbd_device::config_refs]

map[References:[map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:nbd_alloc_and_init_config SourceFile:drivers/block/nbd.c SourceLine:1700] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:nbd_cleanup SourceFile:drivers/block/nbd.c SourceLine:2728] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:nbd_cleanup SourceFile:drivers/block/nbd.c SourceLine:2729] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:nbd_config_put SourceFile:drivers/block/nbd.c SourceLine:1434] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:nbd_dev_add SourceFile:drivers/block/nbd.c SourceLine:1971] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:nbd_find_get_unused SourceFile:drivers/block/nbd.c SourceLine:2019] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:nbd_genl_connect SourceFile:drivers/block/nbd.c SourceLine:2133] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:nbd_genl_connect SourceFile:drivers/block/nbd.c SourceLine:2243] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:nbd_genl_disconnect SourceFile:drivers/block/nbd.c SourceLine:2301] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:nbd_get_config_unlocked SourceFile:drivers/block/nbd.c SourceLine:437] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:nbd_open SourceFile:drivers/block/nbd.c SourceLine:1725] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:nbd_reconnect_socket SourceFile:drivers/block/nbd.c SourceLine:1346] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:nbd_sched_pending_work SourceFile:drivers/block/nbd.c SourceLine:637] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:nbd_start_device SourceFile:drivers/block/nbd.c SourceLine:1533] map[ReferenceKind:takes-address-of ReferencingEntityKind:function ReferencingEntityName:populate_nbd_status SourceFile:drivers/block/nbd.c SourceLine:2505]] TruncatedOutput:false]

gemini-3-flash-preview

							input: 12570
							output: 47
							thoughts: 16
						

Here's a first-person summary, tailored for an expert audience, of the thought process, starting with the provided text "Let's check `nbd_alloc_and_init_config`":

**Diving into `nbd_alloc_and_init_config`**

Okay, so the next logical step is to dissect `nbd_alloc_and_init_config`. I need to understand exactly how the NBD configuration is allocated and initialized. This is a critical point; any errors here will ripple throughout the entire NBD setup process, and the ramifications for stability and security are significant. I'm assuming a certain level of familiarity with the surrounding code, so I don't need to spell out the obvious.

I'm mentally running through the probable contents: How does it handle memory allocation for the configuration struct itself? Is it using `kmalloc`, `vmalloc`, or a custom allocator? Any potential allocation failures that need handling? Also, what exactly constitutes "initialization" in this context? Are there default values being set for the various parameters, or are we relying on some external source? Are any locks being initialized within this function? If so, which ones, and what's the locking strategy?

Furthermore, I'll pay close attention to the potential race conditions. We need to be absolutely sure that the configuration is thread-safe and properly synchronized, particularly if this function is called from multiple contexts (which is likely the case). I'll be looking for any potential data races or improper locking that might lead to unexpected behavior or even crashes. I also need to make sure that the function handles errors properly; it should log appropriately if something goes wrong, and return meaningful error codes so the caller can handle the failure. The error handling needs to be robust, given how essential the configuration is.

Essentially, I need to thoroughly understand this function's role in the NBD driver's lifecycle. It’s a foundational piece, so it needs to be bulletproof. I'm going to start by tracing the function's execution and identifying any subtle details.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_alloc_and_init_config]

map[SourceCode:1670:	static int nbd_alloc_and_init_config(struct nbd_device *nbd)
1671:	{
1672:		struct nbd_config *config;
1673:	
1674:		if (WARN_ON(nbd->config))
1675:			return -EINVAL;
1676:	
1677:		if (!try_module_get(THIS_MODULE))
1678:			return -ENODEV;
1679:	
1680:		config = kzalloc_obj(struct nbd_config, GFP_NOFS);
1681:		if (!config) {
1682:			module_put(THIS_MODULE);
1683:			return -ENOMEM;
1684:		}
1685:	
1686:		atomic_set(&config->recv_threads, 0);
1687:		init_waitqueue_head(&config->recv_wq);
1688:		init_waitqueue_head(&config->conn_wait);
1689:		config->blksize_bits = NBD_DEF_BLKSIZE_BITS;
1690:		atomic_set(&config->live_connections, 0);
1691:	
1692:		nbd->config = config;
1693:		/*
1694:		 * Order refcount_set(&nbd->config_refs, 1) and nbd->config assignment,
1695:		 * its pair is the barrier in nbd_get_config_unlocked().
1696:		 * So nbd_get_config_unlocked() won't see nbd->config as null after
1697:		 * refcount_inc_not_zero() succeed.
1698:		 */
1699:		smp_mb__before_atomic();
1700:		refcount_set(&nbd->config_refs, 1);
1701:	
1702:		return 0;
1703:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 13623
							output: 41
							thoughts: 183
						

**Analyzing the NBD Configuration Reference Count**

Okay, let's break down this reference counting in the NBD driver. It seems `config_refs` initializes to 1. Then, in `nbd_start_device`, for every new connection we establish, we increment it, right here: `refcount_inc(&nbd->config_refs);` So, two connections would bring `config_refs` to 3.

Now, the interesting part is what happens during thread completion within `recv_work`. Each thread, once it's done processing, calls `nbd_config_put(nbd)`. This is where the decrement happens. So, the refcount gets reduced with each finished thread. But, and this is the crux of it, what about that initial reference, that "1" we started with? Where does that get dropped? Ah, it's usually released when the device is closed, or when connections are severed.

I should probably refresh my memory of `nbd_release`... Let me check that function again. I want to see if this model accurately reflects the intent.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_release]

map[SourceCode:1748:	static void nbd_release(struct gendisk *disk)
1749:	{
1750:		struct nbd_device *nbd = disk->private_data;
1751:	
1752:		if (test_bit(NBD_RT_DISCONNECT_ON_CLOSE, &nbd->config->runtime_flags) &&
1753:				disk_openers(disk) == 0)
1754:			nbd_disconnect_and_put(nbd);
1755:	
1756:		nbd_config_put(nbd);
1757:		nbd_put(nbd);
1758:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 14291
							output: 43
							thoughts: 1873
						

**Analyzing Potential Concurrency Issues in NBD Driver with Dual Connections**

Okay, so I'm looking at this code where `nbd_release` ultimately leads to `nbd_config_put`. The specific concern is around potential UAF (Use-After-Free), double-frees, or deadlocks, especially when multiple threads are involved, and a socket is closed.

I've got the scenario where `config->socks[0]->sock` and `config->socks[1]->sock` are the *same* socket, which, given how `nbd_add_socket` and `sockfd_lookup` work, means the socket's reference count is 2 due to the double call to `nbd_get_socket`.  When `nbd_config_put` is called, and `config_refs` hits 0, the code in `nbd_config_put` iterates through `config->socks` and calls `sockfd_put`.  Since the socket's reference count is 2, calling `sockfd_put` *twice* is perfectly valid.  It won't cause a double free of the socket. Good.

Now, the issue arises when considering the `recv_work` function, which is handling socket reads using two separate threads on the same socket.  The `nbd_read_reply` function uses `sock_recvmsg`. If two threads are trying to read from the same TCP socket concurrently, that's definitely a recipe for protocol corruption. One thread might grab a header, the other gets the body, or they collide on a header. The question asks about UAF, double-free, or deadlock when the socket is CLOSED.

So, when the socket *is* closed, both `nbd_read_reply` calls will return errors. Each thread will then call `nbd_mark_nsock_dead` after acquiring its own `tx_lock` (because they use different `nsock` objects). Each calls `kernel_sock_shutdown` on the same socket twice.  That's safe, and the references are not doubled because the threads are using separate `nsock` structures.  `atomic_dec` and `nbd_config_put` also get called twice. Again, no problems here.

Deadlock potential? `nbd_mark_nsock_dead` doesn't seem to take any locks other than the ones *inside* `kernel_sock_shutdown`.  `nbd_config_put` *does* take `nbd->config_lock`. However, if two threads *simultaneously* call `nbd_config_put`, one will get the lock, the other waits. The `refcount_dec_and_mutex_lock` function is used. If `config_refs` is 2, the first thread decrements it to 1 and returns `false`.  The second thread then decrements it to 0, *takes* the lock, and then proceeds with cleanup. Perfect.

Let's revisit `nbd_read_reply`.
If two threads are inside `kernel_recvmsg` on the *same* socket, it's not ideal, but it shouldn't cause a direct UAF or double-free, although the protocol corruption is inevitable.

Ah, but what about `nbd_handle_reply`? I see an `index` is passed to `nbd_handle_reply`. It looks like `args->index` from `recv_work` is passed down to it. Inside `nbd_start_device` `args->index = i`. So thread 0 gets index 0, thread 1 gets index 1. This `index` is used with `nbd->tag_set.tags[index]`. If `nbd` has multiple hardware queues, this *could* be fine. The code uses `num_connections` to set the number of hardware queues.

`blk_mq_update_nr_hw_queues(&nbd->tag_set, num_connections);`

If `num_connections` is 2, there are 2 hardware queues. If thread 0 receives a reply for queue 0, it will look up the tag in `tags[0]`, perfect. But if thread 1 (index 1) receives that same reply, it will look it up in `tags[1]`. *That's a potential issue!* That will either return the wrong request or it may not find a request at all if queue 0 and queue 1 are separate.

Focusing on the UAF/double-free/deadlock:

Let's go back and look at `nbd_mark_nsock_dead` and the call to `kernel_sock_shutdown`. This shutdown will cause the *other*

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_clear_sock]

map[SourceCode:1425:	static void nbd_clear_sock(struct nbd_device *nbd)
1426:	{
1427:		sock_shutdown(nbd);
1428:		nbd_clear_que(nbd);
1429:		nbd->task_setup = NULL;
1430:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 17351
							output: 40
							thoughts: 6
						

Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:

**Delving into `sock_shutdown`**

Alright, so we're talking about `sock_shutdown`. My immediate thought is, "Ah, yes, the finer points of graceful socket closure." I'm mentally parsing the implications. This isn't just a simple `close()` call, we're talking about a more controlled, deliberate shutdown. I'm already anticipating the nuances of TCP's connection termination handshake, the states involved, and the implications for data transmission.

Specifically, I'm considering the potential scenarios. Will I be shutting down for read, write, or both? `SHUT_RD`, `SHUT_WR`, or `SHUT_RDWR` – each has its own behavioral fingerprint and consequences, and I'm instantly weighing them. The choice dictates whether I'm signaling that I'm done *receiving*, done *sending*, or done with the whole communication stream. I'm practically diagramming the TCP state machine in my head, visualizing the FIN and ACK segments.

My brain is now mapping this onto the practicalities of my application. What's the protocol? Is it a request-response pattern, a streaming connection, or something else entirely? The `sock_shutdown` call needs to fit seamlessly into the application's overall design. I'm focusing on ensuring data integrity. I need to be absolutely certain that any remaining data in the send queue is flushed before initiating the shutdown for writing. Otherwise, I risk data loss, corruption, or unexpected behavior on the receiving end.

And the error handling? I'm already anticipating the potential for errors. What if the socket isn't properly connected? What if the shutdown fails? I know I need to be prepared to handle `EBADF`, `ENOTSOCK`, `ENOTCONN` and similar error codes. I'm already crafting my error-handling strategy, anticipating the potential for race conditions and planning to handle them gracefully.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:sock_shutdown]

map[SourceCode: 395:	/*
 396:	 * Forcibly shutdown the socket causing all listeners to error
 397:	 */
 398:	static void sock_shutdown(struct nbd_device *nbd)
 399:	{
 400:		struct nbd_config *config = nbd->config;
 401:		int i;
 402:	
 403:		if (config->num_connections == 0)
 404:			return;
 405:		if (test_and_set_bit(NBD_RT_DISCONNECTED, &config->runtime_flags))
 406:			return;
 407:	
 408:		for (i = 0; i < config->num_connections; i++) {
 409:			struct nbd_sock *nsock = config->socks[i];
 410:			mutex_lock(&nsock->tx_lock);
 411:			nbd_mark_nsock_dead(nbd, nsock, 0);
 412:			mutex_unlock(&nsock->tx_lock);
 413:		}
 414:		dev_warn(disk_to_dev(nbd->disk), "shutting down sockets\n");
 415:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 18189
							output: 43
							thoughts: 3251
						

**Analyzing Potential Concurrency Issues with Duplicate Sockets**

Okay, so I've been digging into this NBD code, and it looks like there's a definite possibility of trouble when the same file descriptor (fd) is added to the NBD configuration multiple times. The core problem is this: the code *doesn't* check for duplicate socket entries during `nbd_add_socket`. It just happily calls `nbd_get_socket` and sticks the result into the `config->socks` array.

If we have a scenario where `socks[0]->sock == socks[1]->sock`, we are creating a dangerous situation. Specifically, we would have multiple `nbd_sock` structures pointing to the *same* underlying socket. When `nbd_start_device` kicks off, we get two `recv_work` threads, and each of these threads independently calls `nbd_read_reply` using the same socket.

This is a recipe for disaster with NBD, since the protocol requires strict synchronization of the command and response stream. They will attempt to read from the same stream without any explicit locking or coordination. The result is going to be corrupted replies and data, but the question is if there are any specific vulnerabilities such as a UAF, double-free, or deadlock.

Let's break down the potential issues more methodically. `nbd_mark_nsock_dead` is important here. If both threads call this with *different* `nsock` objects that happen to share the *same* underlying socket, it looks like there's no inherent race condition in the atomic operations or locking within this function, as long as the calls are for different `nsock` objects. Each thread calls `kernel_sock_shutdown` on the same socket from different `nsock` structures. This seems correct because the socket refcount should be at least 2.

The `nbd_config_put` function seems to be designed to handle multiple references correctly. It uses reference counting and a mutex (`config_lock`) to ensure only one thread performs the cleanup. The `sockfd_put` call is called as many times as there are sockets, so if two `nbd_sock` structures point to the same socket, it's decremented appropriately.

There is a potential race when multiple threads call `nbd_read_reply` and `nbd_mark_nsock_dead` simultaneously. `nbd_mark_nsock_dead` does indeed call `kernel_sock_shutdown`. This will signal and wake up the other thread and could cause the second thread to be processing memory that is now invalid. However, since the socket is closed, this should still be fine.

The double-free possibility is unlikely, as `nbd_config_put` is designed to be the last thing that happens within a thread after `recv_work` completes. The function `nbd_clear_que` also doesn't seem to cause issues in this situation.

The main impact of this duplicate socket situation isn't a *direct* UAF, double-free, or deadlock, but a subtle data corruption bug related to how NBD's request/reply system works with blk-mq. If both threads are reading the same stream and getting the reply interleaved, then the request tags will be out of sync. This will cause requests to complete with incorrect replies.

In summary, the key issue is interleaved data, potentially completing the wrong requests, but not necessarily UAF, double-free, or deadlock within the analyzed code paths.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_clear_que]

map[SourceCode:1050:	static void nbd_clear_que(struct nbd_device *nbd)
1051:	{
1052:		blk_mq_quiesce_queue(nbd->disk->queue);
1053:		blk_mq_tagset_busy_iter(&nbd->tag_set, nbd_clear_req, NULL);
1054:		blk_mq_unquiesce_queue(nbd->disk->queue);
1055:		dev_dbg(disk_to_dev(nbd->disk), "queue cleared\n");
1056:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 22416
							output: 24
							thoughts: 2747
						

**Analysis of Potential Concurrency Issues in NBD Driver**

Okay, let's break this down. My initial assessment is that multiple calls to `nbd_add_socket` with the same file descriptor are handled correctly thanks to the `sockfd_lookup` function correctly managing socket and file reference counts. The code increments the `struct file` reference count and decrements it appropriately. I also verified that mutex locking around `nbd->config` via `refcount_dec_and_mutex_lock` prevents any data races during config cleanup, by one thread waiting for the other to finish.

I considered potential deadlocks and concluded the refcounting and locking scheme with `config_refs` prevents that. Specifically, the interplay between `refcount_dec_and_mutex_lock` and the thread execution order guarantees mutual exclusion and correct cleanup operations.

I looked carefully at the `nbd_mark_nsock_dead` function and determined it's safe for multiple threads to call `kernel_sock_shutdown` on the same socket because the kernel handles the socket shutdown gracefully. It also handles concurrent shutdown calls. I looked into shared state, like `nbd->config->live_connections`, and concluded it is incremented and decremented correctly. I considered that `nbd_add_socket` might be called with the same `fd` concurrently, but that it's okay because it's usually done during initial setup and it handles this scenario.

I checked `nsock->tx_lock` and realized that because each connection has its own `nsock` object, the locks are distinct, preventing contention. Similarly, I analyzed the behavior in `nbd_read_reply` if two threads are in `kernel_recvmsg` and concluded that the threads are woken up by closing the socket.

I had a concern about a potential issue in `nbd_mark_nsock_dead` because of allocating a `struct link_dead_args` object and queuing a work item. The worry was whether multiple threads would call this function, however, sending the uevent twice is not harmful. However, I became concerned about `nbd_config_put` calling `nbd_clear_sock`, which can shut down the socket, and then call `nbd_mark_nsock_dead`. However, it won't call `kernel_sock_shutdown` again if the socket is already dead.

However, I found a possible race in `nbd_mark_nsock_dead` with the `nsock->dead` flag being set after the call to `kernel_sock_shutdown`. Although the code appears to be calling `kernel_sock_shutdown` multiple times, on the same `socket`. The threads are serialized, and this function works fine.

I analyzed `nbd_config_put` freeing `config->socks` and determined this is only done by the last thread calling the function. I reviewed the code in `recv_work` to make sure the program is still valid before it exits. The local variable `config` is properly used, so there won't be a use-after-free. I considered a scenario with two threads where the config is released, but it works, because of the reference count.

Then, I identified that the initial reference count ensures that `nbd->config` is valid. I looked at the access to `nbd->config` in `nbd_mark_nsock_dead` and in `recv_work`, and concluded that the data is valid. I looked at a possible re-allocation and potential race with the `config->socks` array, but that it's done under `blk_mq_freeze_queue` and shouldn't be an issue because `recv_work` itself uses `args->nsock` which is stable.

I looked at the checks in `nbd_add_socket` function to see if the device is already running by checking the bit `NBD_RT_BOUND`, but the bit is not set, meaning that there may be a possible race.

requested entity does not exist

map[Name:NBD_RT_BOUND]

map[References:<nil> TruncatedOutput:false]

gemini-3-flash-preview

							input: 26061
							output: 43
							thoughts: 7
						

Okay, here's the summary, assuming I'm the expert and the "text" simply triggers these thoughts:

**Navigating the Codebase: Identifying the Critical Constant**

Right, let's get down to brass tacks. First things first: I need to locate the definition. This likely starts with a hunt for the `enum` or `#define` that's controlling this particular behavior. That's where the real magic happens, so I'll prioritize finding that. I'll need to know whether it is in the same file or whether this relates to another package. Once I get the base definition I can proceed.

requested entity does not exist

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:NBD_RT_BOUND]

map[SourceCode: SourceFile:]

gemini-3-flash-preview

							input: 26265
							output: 24
							thoughts: 28
						

Okay, here's my interpretation of those thoughts, presented as my own mental process, with the assumption I'm deeply familiar with the relevant technical domain:

**Investigating the Definition of `NBD_RT_BOUND`**

Alright, so I'm looking at this code and I see `NBD_RT_BOUND`... I need to figure out what that represents. This could be defined in a couple of ways, depending on how they've structured this. It's likely an enum, maybe even an anonymous one, or it could be a simple constant defined in a header file somewhere. The first thing I'll do is a quick search to locate its definition. Let's start by grepping the codebase for that literal string, `NBD_RT_BOUND`. Hopefully, that will immediately point me to the relevant enum or macro definition. From there, I can understand its specific meaning and how it is being used within the larger context. That search should quickly illuminate its purpose.

requested entity does not exist

map[Name:NBD_RT_BOUND]

map[References:<nil> TruncatedOutput:false]

gemini-3-flash-preview

							input: 26546
							output: 23
							thoughts: 74
						

**Debugging a Potential Typo or Tooling Issue**

Okay, so I thought I saw that check, specifically `!test_bit(NBD_RT_BOUND, &config->runtime_flags)`, in `nbd_add_socket`.  But it feels…off. Maybe I'm misremembering the exact function name, or perhaps the static analysis tool is being overly sensitive.  I need to be absolutely certain I'm not missing something critical here. The code itself feels right, but a typo, however unlikely, could certainly trip me up in debugging. I'm going to search for that specific string *within the file itself* to confirm. That should quickly clear up whether the problem is me, the tool, or if the code is actually different from what I expect. Let's see what that search reveals.

map[File:drivers/block/nbd.c]

map[Contents:// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Network block device - make block devices work over TCP
 *
 * Note that you can not swap over this thing, yet. Seems to work but
 * deadlocks sometimes - you can not swap over TCP in general.
 * 
 * Copyright 1997-2000, 2008 Pavel Machek <pavel@ucw.cz>
 * Parts copyright 2001 Steven Whitehouse <steve@chygwyn.com>
 *
 * (part of code stolen from loop.c)
 */

#define pr_fmt(fmt) "nbd: " fmt

#include <linux/major.h>

#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/sched/mm.h>
#include <linux/fs.h>
#include <linux/bio.h>
#include <linux/stat.h>
#include <linux/errno.h>
#include <linux/file.h>
#include <linux/ioctl.h>
#include <linux/mutex.h>
#include <linux/compiler.h>
#include <linux/completion.h>
#include <linux/err.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <net/sock.h>
#include <linux/net.h>
#include <linux/kthread.h>
#include <linux/types.h>
#include <linux/debugfs.h>
#include <linux/blk-mq.h>

#include <linux/uaccess.h>
#include <asm/types.h>

#include <linux/nbd.h>
#include <linux/nbd-netlink.h>
#include <net/genetlink.h>

#define CREATE_TRACE_POINTS
#include <trace/events/nbd.h>

static DEFINE_IDR(nbd_index_idr);
static DEFINE_MUTEX(nbd_index_mutex);
static struct workqueue_struct *nbd_del_wq;
static int nbd_total_devices = 0;

struct nbd_sock {
	struct socket *sock;
	struct mutex tx_lock;
	struct request *pending;
	int sent;
	bool dead;
	int fallback_index;
	int cookie;
	struct work_struct work;
};

struct recv_thread_args {
	struct work_struct work;
	struct nbd_device *nbd;
	struct nbd_sock *nsock;
	int index;
};

struct link_dead_args {
	struct work_struct work;
	int index;
};

#define NBD_RT_TIMEDOUT			0
#define NBD_RT_DISCONNECT_REQUESTED	1
#define NBD_RT_DISCONNECTED		2
#define NBD_RT_HAS_PID_FILE		3
#define NBD_RT_HAS_CONFIG_REF		4
#define NBD_RT_BOUND			5
#define NBD_RT_DISCONNECT_ON_CLOSE	6
#define NBD_RT_HAS_BACKEND_FILE		7

#define NBD_DESTROY_ON_DISCONNECT	0
#define NBD_DISCONNECT_REQUESTED	1

struct nbd_config {
	u32 flags;
	unsigned long runtime_flags;
	u64 dead_conn_timeout;

	struct nbd_sock **socks;
	int num_connections;
	atomic_t live_connections;
	wait_queue_head_t conn_wait;

	atomic_t recv_threads;
	wait_queue_head_t recv_wq;
	unsigned int blksize_bits;
	loff_t bytesize;
#if IS_ENABLED(CONFIG_DEBUG_FS)
	struct dentry *dbg_dir;
#endif
};

static inline unsigned int nbd_blksize(struct nbd_config *config)
{
	return 1u << config->blksize_bits;
}

struct nbd_device {
	struct blk_mq_tag_set tag_set;

	int index;
	refcount_t config_refs;
	refcount_t refs;
	struct nbd_config *config;
	struct mutex config_lock;
	struct gendisk *disk;
	struct workqueue_struct *recv_workq;
	struct work_struct remove_work;

	struct list_head list;
	struct task_struct *task_setup;

	unsigned long flags;
	pid_t pid; /* pid of nbd-client, if attached */

	char *backend;
};

#define NBD_CMD_REQUEUED	1
/*
 * This flag will be set if nbd_queue_rq() succeed, and will be checked and
 * cleared in completion. Both setting and clearing of the flag are protected
 * by cmd->lock.
 */
#define NBD_CMD_INFLIGHT	2

/* Just part of request header or data payload is sent successfully */
#define NBD_CMD_PARTIAL_SEND	3

struct nbd_cmd {
	struct nbd_device *nbd;
	struct mutex lock;
	int index;
	int cookie;
	int retries;
	blk_status_t status;
	unsigned long flags;
	u32 cmd_cookie;
};

#if IS_ENABLED(CONFIG_DEBUG_FS)
static struct dentry *nbd_dbg_dir;
#endif

#define nbd_name(nbd) ((nbd)->disk->disk_name)

#define NBD_DEF_BLKSIZE_BITS 10

static unsigned int nbds_max = 16;
static int max_part = 16;
static int part_shift;

static int nbd_dev_dbg_init(struct nbd_device *nbd);
static void nbd_dev_dbg_close(struct nbd_device *nbd);
static void nbd_config_put(struct nbd_device *nbd);
static void nbd_connect_reply(struct genl_info *info, int index);
static int nbd_genl_status(struct sk_buff *skb, struct genl_info *info);
static void nbd_dead_link_work(struct work_struct *work);
static void nbd_disconnect_and_put(struct nbd_device *nbd);

static inline struct device *nbd_to_dev(struct nbd_device *nbd)
{
	return disk_to_dev(nbd->disk);
}

static void nbd_requeue_cmd(struct nbd_cmd *cmd)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);

	lockdep_assert_held(&cmd->lock);

	/*
	 * Clear INFLIGHT flag so that this cmd won't be completed in
	 * normal completion path
	 *
	 * INFLIGHT flag will be set when the cmd is queued to nbd next
	 * time.
	 */
	__clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);

	if (!test_and_set_bit(NBD_CMD_REQUEUED, &cmd->flags))
		blk_mq_requeue_request(req, true);
}

#define NBD_COOKIE_BITS 32

static u64 nbd_cmd_handle(struct nbd_cmd *cmd)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);
	u32 tag = blk_mq_unique_tag(req);
	u64 cookie = cmd->cmd_cookie;

	return (cookie << NBD_COOKIE_BITS) | tag;
}

static u32 nbd_handle_to_tag(u64 handle)
{
	return (u32)handle;
}

static u32 nbd_handle_to_cookie(u64 handle)
{
	return (u32)(handle >> NBD_COOKIE_BITS);
}

static const char *nbdcmd_to_ascii(int cmd)
{
	switch (cmd) {
	case  NBD_CMD_READ: return "read";
	case NBD_CMD_WRITE: return "write";
	case  NBD_CMD_DISC: return "disconnect";
	case NBD_CMD_FLUSH: return "flush";
	case  NBD_CMD_TRIM: return "trim/discard";
	}
	return "invalid";
}

static ssize_t pid_show(struct device *dev,
			struct device_attribute *attr, char *buf)
{
	struct gendisk *disk = dev_to_disk(dev);
	struct nbd_device *nbd = disk->private_data;

	return sprintf(buf, "%d\n", nbd->pid);
}

static const struct device_attribute pid_attr = {
	.attr = { .name = "pid", .mode = 0444},
	.show = pid_show,
};

static ssize_t backend_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct gendisk *disk = dev_to_disk(dev);
	struct nbd_device *nbd = disk->private_data;

	return sprintf(buf, "%s\n", nbd->backend ?: "");
}

static const struct device_attribute backend_attr = {
	.attr = { .name = "backend", .mode = 0444},
	.show = backend_show,
};

static void nbd_dev_remove(struct nbd_device *nbd)
{
	struct gendisk *disk = nbd->disk;

	del_gendisk(disk);
	blk_mq_free_tag_set(&nbd->tag_set);

	/*
	 * Remove from idr after del_gendisk() completes, so if the same ID is
	 * reused, the following add_disk() will succeed.
	 */
	mutex_lock(&nbd_index_mutex);
	idr_remove(&nbd_index_idr, nbd->index);
	mutex_unlock(&nbd_index_mutex);
	destroy_workqueue(nbd->recv_workq);
	put_disk(disk);
}

static void nbd_dev_remove_work(struct work_struct *work)
{
	nbd_dev_remove(container_of(work, struct nbd_device, remove_work));
}

static void nbd_put(struct nbd_device *nbd)
{
	if (!refcount_dec_and_test(&nbd->refs))
		return;

	/* Call del_gendisk() asynchrounously to prevent deadlock */
	if (test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags))
		queue_work(nbd_del_wq, &nbd->remove_work);
	else
		nbd_dev_remove(nbd);
}

static int nbd_disconnected(struct nbd_config *config)
{
	return test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags) ||
		test_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags);
}

static void nbd_mark_nsock_dead(struct nbd_device *nbd, struct nbd_sock *nsock,
				int notify)
{
	if (!nsock->dead && notify && !nbd_disconnected(nbd->config)) {
		struct link_dead_args *args;
		args = kmalloc_obj(struct link_dead_args, GFP_NOIO);
		if (args) {
			INIT_WORK(&args->work, nbd_dead_link_work);
			args->index = nbd->index;
			queue_work(system_percpu_wq, &args->work);
		}
	}
	if (!nsock->dead) {
		kernel_sock_shutdown(nsock->sock, SHUT_RDWR);
		if (atomic_dec_return(&nbd->config->live_connections) == 0) {
			if (test_and_clear_bit(NBD_RT_DISCONNECT_REQUESTED,
					       &nbd->config->runtime_flags)) {
				set_bit(NBD_RT_DISCONNECTED,
					&nbd->config->runtime_flags);
				dev_info(nbd_to_dev(nbd),
					"Disconnected due to user request.\n");
			}
		}
	}
	nsock->dead = true;
	nsock->pending = NULL;
	nsock->sent = 0;
}

static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize, loff_t blksize)
{
	struct queue_limits lim;
	int error;

	if (!blksize)
		blksize = 1u << NBD_DEF_BLKSIZE_BITS;

	if (blk_validate_block_size(blksize))
		return -EINVAL;

	if (bytesize < 0)
		return -EINVAL;

	nbd->config->bytesize = bytesize;
	nbd->config->blksize_bits = __ffs(blksize);

	if (!nbd->pid)
		return 0;

	lim = queue_limits_start_update(nbd->disk->queue);
	if (nbd->config->flags & NBD_FLAG_SEND_TRIM)
		lim.max_hw_discard_sectors = UINT_MAX >> SECTOR_SHIFT;
	else
		lim.max_hw_discard_sectors = 0;
	if (!(nbd->config->flags & NBD_FLAG_SEND_FLUSH)) {
		lim.features &= ~(BLK_FEAT_WRITE_CACHE | BLK_FEAT_FUA);
	} else if (nbd->config->flags & NBD_FLAG_SEND_FUA) {
		lim.features |= BLK_FEAT_WRITE_CACHE | BLK_FEAT_FUA;
	} else {
		lim.features |= BLK_FEAT_WRITE_CACHE;
		lim.features &= ~BLK_FEAT_FUA;
	}
	if (nbd->config->flags & NBD_FLAG_ROTATIONAL)
		lim.features |= BLK_FEAT_ROTATIONAL;
	if (nbd->config->flags & NBD_FLAG_SEND_WRITE_ZEROES)
		lim.max_write_zeroes_sectors = UINT_MAX >> SECTOR_SHIFT;

	lim.logical_block_size = blksize;
	lim.physical_block_size = blksize;
	error = queue_limits_commit_update_frozen(nbd->disk->queue, &lim);
	if (error)
		return error;

	if (max_part)
		set_bit(GD_NEED_PART_SCAN, &nbd->disk->state);
	if (!set_capacity_and_notify(nbd->disk, bytesize >> 9))
		kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
	return 0;
}

static void nbd_complete_rq(struct request *req)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);

	dev_dbg(nbd_to_dev(cmd->nbd), "request %p: %s\n", req,
		cmd->status ? "failed" : "done");

	blk_mq_end_request(req, cmd->status);
}

/*
 * Forcibly shutdown the socket causing all listeners to error
 */
static void sock_shutdown(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	int i;

	if (config->num_connections == 0)
		return;
	if (test_and_set_bit(NBD_RT_DISCONNECTED, &config->runtime_flags))
		return;

	for (i = 0; i < config->num_connections; i++) {
		struct nbd_sock *nsock = config->socks[i];
		mutex_lock(&nsock->tx_lock);
		nbd_mark_nsock_dead(nbd, nsock, 0);
		mutex_unlock(&nsock->tx_lock);
	}
	dev_warn(disk_to_dev(nbd->disk), "shutting down sockets\n");
}

static u32 req_to_nbd_cmd_type(struct request *req)
{
	switch (req_op(req)) {
	case REQ_OP_DISCARD:
		return NBD_CMD_TRIM;
	case REQ_OP_FLUSH:
		return NBD_CMD_FLUSH;
	case REQ_OP_WRITE:
		return NBD_CMD_WRITE;
	case REQ_OP_READ:
		return NBD_CMD_READ;
	case REQ_OP_WRITE_ZEROES:
		return NBD_CMD_WRITE_ZEROES;
	default:
		return U32_MAX;
	}
}

static struct nbd_config *nbd_get_config_unlocked(struct nbd_device *nbd)
{
	if (refcount_inc_not_zero(&nbd->config_refs)) {
		/*
		 * Add smp_mb__after_atomic to ensure that reading nbd->config_refs
		 * and reading nbd->config is ordered. The pair is the barrier in
		 * nbd_alloc_and_init_config(), avoid nbd->config_refs is set
		 * before nbd->config.
		 */
		smp_mb__after_atomic();
		return nbd->config;
	}

	return NULL;
}

static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);
	struct nbd_device *nbd = cmd->nbd;
	struct nbd_config *config;

	if (!mutex_trylock(&cmd->lock))
		return BLK_EH_RESET_TIMER;

	/* partial send is handled in nbd_sock's work function */
	if (test_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags)) {
		mutex_unlock(&cmd->lock);
		return BLK_EH_RESET_TIMER;
	}

	if (!test_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
		mutex_unlock(&cmd->lock);
		return BLK_EH_DONE;
	}

	config = nbd_get_config_unlocked(nbd);
	if (!config) {
		cmd->status = BLK_STS_TIMEOUT;
		__clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);
		mutex_unlock(&cmd->lock);
		goto done;
	}

	if (config->num_connections > 1 ||
	    (config->num_connections == 1 && nbd->tag_set.timeout)) {
		dev_err_ratelimited(nbd_to_dev(nbd),
				    "Connection timed out, retrying (%d/%d alive)\n",
				    atomic_read(&config->live_connections),
				    config->num_connections);
		/*
		 * Hooray we have more connections, requeue this IO, the submit
		 * path will put it on a real connection. Or if only one
		 * connection is configured, the submit path will wait util
		 * a new connection is reconfigured or util dead timeout.
		 */
		if (config->socks) {
			if (cmd->index < config->num_connections) {
				struct nbd_sock *nsock =
					config->socks[cmd->index];
				mutex_lock(&nsock->tx_lock);
				/* We can have multiple outstanding requests, so
				 * we don't want to mark the nsock dead if we've
				 * already reconnected with a new socket, so
				 * only mark it dead if its the same socket we
				 * were sent out on.
				 */
				if (cmd->cookie == nsock->cookie)
					nbd_mark_nsock_dead(nbd, nsock, 1);
				mutex_unlock(&nsock->tx_lock);
			}
			nbd_requeue_cmd(cmd);
			mutex_unlock(&cmd->lock);
			nbd_config_put(nbd);
			return BLK_EH_DONE;
		}
	}

	if (!nbd->tag_set.timeout) {
		/*
		 * Userspace sets timeout=0 to disable socket disconnection,
		 * so just warn and reset the timer.
		 */
		struct nbd_sock *nsock = config->socks[cmd->index];
		cmd->retries++;
		dev_info(nbd_to_dev(nbd), "Possible stuck request %p: control (%s@%llu,%uB). Runtime %u seconds\n",
			req, nbdcmd_to_ascii(req_to_nbd_cmd_type(req)),
			(unsigned long long)blk_rq_pos(req) << 9,
			blk_rq_bytes(req), (req->timeout / HZ) * cmd->retries);

		mutex_lock(&nsock->tx_lock);
		if (cmd->cookie != nsock->cookie) {
			nbd_requeue_cmd(cmd);
			mutex_unlock(&nsock->tx_lock);
			mutex_unlock(&cmd->lock);
			nbd_config_put(nbd);
			return BLK_EH_DONE;
		}
		mutex_unlock(&nsock->tx_lock);
		mutex_unlock(&cmd->lock);
		nbd_config_put(nbd);
		return BLK_EH_RESET_TIMER;
	}

	dev_err_ratelimited(nbd_to_dev(nbd), "Connection timed out\n");
	set_bit(NBD_RT_TIMEDOUT, &config->runtime_flags);
	cmd->status = BLK_STS_IOERR;
	__clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);
	mutex_unlock(&cmd->lock);
	sock_shutdown(nbd);
	nbd_config_put(nbd);
done:
	blk_mq_complete_request(req);
	return BLK_EH_DONE;
}

static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
		       struct iov_iter *iter, int msg_flags, int *sent)
{
	int result;
	struct msghdr msg = {} ;
	unsigned int noreclaim_flag;

	if (unlikely(!sock)) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
			"Attempted %s on closed socket in sock_xmit\n",
			(send ? "send" : "recv"));
		return -EINVAL;
	}

	msg.msg_iter = *iter;

	noreclaim_flag = memalloc_noreclaim_save();

	scoped_with_kernel_creds() {
		do {
			sock->sk->sk_allocation = GFP_NOIO | __GFP_MEMALLOC;
			sock->sk->sk_use_task_frag = false;
			msg.msg_flags = msg_flags | MSG_NOSIGNAL;

			if (send)
				result = sock_sendmsg(sock, &msg);
			else
				result = sock_recvmsg(sock, &msg, msg.msg_flags);

			if (result <= 0) {
				if (result == 0)
					result = -EPIPE; /* short read */
				break;
			}
			if (sent)
				*sent += result;
		} while (msg_data_left(&msg));
	}

	memalloc_noreclaim_restore(noreclaim_flag);

	return result;
}

/*
 *  Send or receive packet. Return a positive value on success and
 *  negtive value on failure, and never return 0.
 */
static int sock_xmit(struct nbd_device *nbd, int index, int send,
		     struct iov_iter *iter, int msg_flags, int *sent)
{
	struct nbd_config *config = nbd->config;
	struct socket *sock = config->socks[index]->sock;

	return __sock_xmit(nbd, sock, send, iter, msg_flags, sent);
}

/*
 * Different settings for sk->sk_sndtimeo can result in different return values
 * if there is a signal pending when we enter sendmsg, because reasons?
 */
static inline int was_interrupted(int result)
{
	return result == -ERESTARTSYS || result == -EINTR;
}

/*
 * We've already sent header or part of data payload, have no choice but
 * to set pending and schedule it in work.
 *
 * And we have to return BLK_STS_OK to block core, otherwise this same
 * request may be re-dispatched with different tag, but our header has
 * been sent out with old tag, and this way does confuse reply handling.
 */
static void nbd_sched_pending_work(struct nbd_device *nbd,
				   struct nbd_sock *nsock,
				   struct nbd_cmd *cmd, int sent)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);

	/* pending work should be scheduled only once */
	WARN_ON_ONCE(test_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags));

	nsock->pending = req;
	nsock->sent = sent;
	set_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags);
	refcount_inc(&nbd->config_refs);
	schedule_work(&nsock->work);
}

/*
 * Returns BLK_STS_RESOURCE if the caller should retry after a delay.
 * Returns BLK_STS_IOERR if sending failed.
 */
static blk_status_t nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd,
				 int index)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);
	struct nbd_config *config = nbd->config;
	struct nbd_sock *nsock = config->socks[index];
	int result;
	struct nbd_request request = {.magic = htonl(NBD_REQUEST_MAGIC)};
	struct kvec iov = {.iov_base = &request, .iov_len = sizeof(request)};
	struct iov_iter from;
	struct bio *bio;
	u64 handle;
	u32 type;
	u32 nbd_cmd_flags = 0;
	int sent = nsock->sent, skip = 0;

	lockdep_assert_held(&cmd->lock);
	lockdep_assert_held(&nsock->tx_lock);

	iov_iter_kvec(&from, ITER_SOURCE, &iov, 1, sizeof(request));

	type = req_to_nbd_cmd_type(req);
	if (type == U32_MAX)
		return BLK_STS_IOERR;

	if (rq_data_dir(req) == WRITE &&
	    (config->flags & NBD_FLAG_READ_ONLY)) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
				    "Write on read-only\n");
		return BLK_STS_IOERR;
	}

	if (req->cmd_flags & REQ_FUA)
		nbd_cmd_flags |= NBD_CMD_FLAG_FUA;
	if ((req->cmd_flags & REQ_NOUNMAP) && (type == NBD_CMD_WRITE_ZEROES))
		nbd_cmd_flags |= NBD_CMD_FLAG_NO_HOLE;

	/* We did a partial send previously, and we at least sent the whole
	 * request struct, so just go and send the rest of the pages in the
	 * request.
	 */
	if (sent) {
		if (sent >= sizeof(request)) {
			skip = sent - sizeof(request);

			/* initialize handle for tracing purposes */
			handle = nbd_cmd_handle(cmd);

			goto send_pages;
		}
		iov_iter_advance(&from, sent);
	} else {
		cmd->cmd_cookie++;
	}
	cmd->index = index;
	cmd->cookie = nsock->cookie;
	cmd->retries = 0;
	request.type = htonl(type | nbd_cmd_flags);
	if (type != NBD_CMD_FLUSH) {
		request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9);
		request.len = htonl(blk_rq_bytes(req));
	}
	handle = nbd_cmd_handle(cmd);
	request.cookie = cpu_to_be64(handle);

	trace_nbd_send_request(&request, nbd->index, blk_mq_rq_from_pdu(cmd));

	dev_dbg(nbd_to_dev(nbd), "request %p: sending control (%s@%llu,%uB)\n",
		req, nbdcmd_to_ascii(type),
		(unsigned long long)blk_rq_pos(req) << 9, blk_rq_bytes(req));
	result = sock_xmit(nbd, index, 1, &from,
			(type == NBD_CMD_WRITE) ? MSG_MORE : 0, &sent);
	trace_nbd_header_sent(req, handle);
	if (result < 0) {
		if (was_interrupted(result)) {
			/* If we haven't sent anything we can just return BUSY,
			 * however if we have sent something we need to make
			 * sure we only allow this req to be sent until we are
			 * completely done.
			 */
			if (sent) {
				nbd_sched_pending_work(nbd, nsock, cmd, sent);
				return BLK_STS_OK;
			}
			set_bit(NBD_CMD_REQUEUED, &cmd->flags);
			return BLK_STS_RESOURCE;
		}
		dev_err_ratelimited(disk_to_dev(nbd->disk),
			"Send control failed (result %d)\n", result);
		goto requeue;
	}
send_pages:
	if (type != NBD_CMD_WRITE)
		goto out;

	bio = req->bio;
	while (bio) {
		struct bio *next = bio->bi_next;
		struct bvec_iter iter;
		struct bio_vec bvec;

		bio_for_each_segment(bvec, bio, iter) {
			bool is_last = !next && bio_iter_last(bvec, iter);
			int flags = is_last ? 0 : MSG_MORE;

			dev_dbg(nbd_to_dev(nbd), "request %p: sending %d bytes data\n",
				req, bvec.bv_len);
			iov_iter_bvec(&from, ITER_SOURCE, &bvec, 1, bvec.bv_len);
			if (skip) {
				if (skip >= iov_iter_count(&from)) {
					skip -= iov_iter_count(&from);
					continue;
				}
				iov_iter_advance(&from, skip);
				skip = 0;
			}
			result = sock_xmit(nbd, index, 1, &from, flags, &sent);
			if (result < 0) {
				if (was_interrupted(result)) {
					nbd_sched_pending_work(nbd, nsock, cmd, sent);
					return BLK_STS_OK;
				}
				dev_err(disk_to_dev(nbd->disk),
					"Send data failed (result %d)\n",
					result);
				goto requeue;
			}
			/*
			 * The completion might already have come in,
			 * so break for the last one instead of letting
			 * the iterator do it. This prevents use-after-free
			 * of the bio.
			 */
			if (is_last)
				break;
		}
		bio = next;
	}
out:
	trace_nbd_payload_sent(req, handle);
	nsock->pending = NULL;
	nsock->sent = 0;
	__set_bit(NBD_CMD_INFLIGHT, &cmd->flags);
	return BLK_STS_OK;

requeue:
	/*
	 * Can't requeue in case we are dealing with partial send
	 *
	 * We must run from pending work function.
	 * */
	if (test_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags))
		return BLK_STS_OK;

	/* retry on a different socket */
	dev_err_ratelimited(disk_to_dev(nbd->disk),
			    "Request send failed, requeueing\n");
	nbd_mark_nsock_dead(nbd, nsock, 1);
	nbd_requeue_cmd(cmd);
	return BLK_STS_OK;
}

/* handle partial sending */
static void nbd_pending_cmd_work(struct work_struct *work)
{
	struct nbd_sock *nsock = container_of(work, struct nbd_sock, work);
	struct request *req = nsock->pending;
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);
	struct nbd_device *nbd = cmd->nbd;
	unsigned long deadline = READ_ONCE(req->deadline);
	unsigned int wait_ms = 2;

	mutex_lock(&cmd->lock);

	WARN_ON_ONCE(test_bit(NBD_CMD_REQUEUED, &cmd->flags));
	if (WARN_ON_ONCE(!test_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags)))
		goto out;

	mutex_lock(&nsock->tx_lock);
	while (true) {
		nbd_send_cmd(nbd, cmd, cmd->index);
		if (!nsock->pending)
			break;

		/* don't bother timeout handler for partial sending */
		if (READ_ONCE(jiffies) + msecs_to_jiffies(wait_ms) >= deadline) {
			cmd->status = BLK_STS_IOERR;
			blk_mq_complete_request(req);
			break;
		}
		msleep(wait_ms);
		wait_ms *= 2;
	}
	mutex_unlock(&nsock->tx_lock);
	clear_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags);
out:
	mutex_unlock(&cmd->lock);
	nbd_config_put(nbd);
}

static int nbd_read_reply(struct nbd_device *nbd, struct socket *sock,
			  struct nbd_reply *reply)
{
	struct kvec iov = {.iov_base = reply, .iov_len = sizeof(*reply)};
	struct iov_iter to;
	int result;

	reply->magic = 0;
	iov_iter_kvec(&to, ITER_DEST, &iov, 1, sizeof(*reply));
	result = __sock_xmit(nbd, sock, 0, &to, MSG_WAITALL, NULL);
	if (result < 0) {
		if (!nbd_disconnected(nbd->config))
			dev_err(disk_to_dev(nbd->disk),
				"Receive control failed (result %d)\n", result);
		return result;
	}

	if (ntohl(reply->magic) != NBD_REPLY_MAGIC) {
		dev_err(disk_to_dev(nbd->disk), "Wrong magic (0x%lx)\n",
				(unsigned long)ntohl(reply->magic));
		return -EPROTO;
	}

	return 0;
}

/* NULL returned = something went wrong, inform userspace */
static struct nbd_cmd *nbd_handle_reply(struct nbd_device *nbd, int index,
					struct nbd_reply *reply)
{
	int result;
	struct nbd_cmd *cmd;
	struct request *req = NULL;
	u64 handle;
	u16 hwq;
	u32 tag;
	int ret = 0;

	handle = be64_to_cpu(reply->cookie);
	tag = nbd_handle_to_tag(handle);
	hwq = blk_mq_unique_tag_to_hwq(tag);
	if (hwq < nbd->tag_set.nr_hw_queues)
		req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq],
				       blk_mq_unique_tag_to_tag(tag));
	if (!req || !blk_mq_request_started(req)) {
		dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%d) %p\n",
			tag, req);
		return ERR_PTR(-ENOENT);
	}
	trace_nbd_header_received(req, handle);
	cmd = blk_mq_rq_to_pdu(req);

	mutex_lock(&cmd->lock);
	if (!test_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
		dev_err(disk_to_dev(nbd->disk), "Suspicious reply %d (status %u flags %lu)",
			tag, cmd->status, cmd->flags);
		ret = -ENOENT;
		goto out;
	}
	if (cmd->index != index) {
		dev_err(disk_to_dev(nbd->disk), "Unexpected reply %d from different sock %d (expected %d)",
			tag, index, cmd->index);
		ret = -ENOENT;
		goto out;
	}
	if (cmd->cmd_cookie != nbd_handle_to_cookie(handle)) {
		dev_err(disk_to_dev(nbd->disk), "Double reply on req %p, cmd_cookie %u, handle cookie %u\n",
			req, cmd->cmd_cookie, nbd_handle_to_cookie(handle));
		ret = -ENOENT;
		goto out;
	}
	if (cmd->status != BLK_STS_OK) {
		dev_err(disk_to_dev(nbd->disk), "Command already handled %p\n",
			req);
		ret = -ENOENT;
		goto out;
	}
	if (test_bit(NBD_CMD_REQUEUED, &cmd->flags)) {
		dev_err(disk_to_dev(nbd->disk), "Raced with timeout on req %p\n",
			req);
		ret = -ENOENT;
		goto out;
	}
	if (ntohl(reply->error)) {
		dev_err(disk_to_dev(nbd->disk), "Other side returned error (%d)\n",
			ntohl(reply->error));
		cmd->status = BLK_STS_IOERR;
		goto out;
	}

	dev_dbg(nbd_to_dev(nbd), "request %p: got reply\n", req);
	if (rq_data_dir(req) != WRITE) {
		struct req_iterator iter;
		struct bio_vec bvec;
		struct iov_iter to;

		rq_for_each_segment(bvec, req, iter) {
			iov_iter_bvec(&to, ITER_DEST, &bvec, 1, bvec.bv_len);
			result = sock_xmit(nbd, index, 0, &to, MSG_WAITALL, NULL);
			if (result < 0) {
				dev_err(disk_to_dev(nbd->disk), "Receive data failed (result %d)\n",
					result);
				/*
				 * If we've disconnected, we need to make sure we
				 * complete this request, otherwise error out
				 * and let the timeout stuff handle resubmitting
				 * this request onto another connection.
				 */
				if (nbd_disconnected(nbd->config)) {
					cmd->status = BLK_STS_IOERR;
					goto out;
				}
				ret = -EIO;
				goto out;
			}
			dev_dbg(nbd_to_dev(nbd), "request %p: got %d bytes data\n",
				req, bvec.bv_len);
		}
	}
out:
	trace_nbd_payload_received(req, handle);
	mutex_unlock(&cmd->lock);
	return ret ? ERR_PTR(ret) : cmd;
}

static void recv_work(struct work_struct *work)
{
	struct recv_thread_args *args = container_of(work,
						     struct recv_thread_args,
						     work);
	struct nbd_device *nbd = args->nbd;
	struct nbd_config *config = nbd->config;
	struct request_queue *q = nbd->disk->queue;
	struct nbd_sock *nsock = args->nsock;
	struct nbd_cmd *cmd;
	struct request *rq;

	while (1) {
		struct nbd_reply reply;

		if (nbd_read_reply(nbd, nsock->sock, &reply))
			break;

		/*
		 * Grab .q_usage_counter so request pool won't go away, then no
		 * request use-after-free is possible during nbd_handle_reply().
		 * If queue is frozen, there won't be any inflight requests, we
		 * needn't to handle the incoming garbage message.
		 */
		if (!percpu_ref_tryget(&q->q_usage_counter)) {
			dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n",
				__func__);
			break;
		}

		cmd = nbd_handle_reply(nbd, args->index, &reply);
		if (IS_ERR(cmd)) {
			percpu_ref_put(&q->q_usage_counter);
			break;
		}

		rq = blk_mq_rq_from_pdu(cmd);
		if (likely(!blk_should_fake_timeout(rq->q))) {
			bool complete;

			mutex_lock(&cmd->lock);
			complete = __test_and_clear_bit(NBD_CMD_INFLIGHT,
							&cmd->flags);
			mutex_unlock(&cmd->lock);
			if (complete)
				blk_mq_complete_request(rq);
		}
		percpu_ref_put(&q->q_usage_counter);
	}

	mutex_lock(&nsock->tx_lock);
	nbd_mark_nsock_dead(nbd, nsock, 1);
	mutex_unlock(&nsock->tx_lock);

	atomic_dec(&config->recv_threads);
	wake_up(&config->recv_wq);
	nbd_config_put(nbd);
	kfree(args);
}

static bool nbd_clear_req(struct request *req, void *data)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);

	/* don't abort one completed request */
	if (blk_mq_request_completed(req))
		return true;

	mutex_lock(&cmd->lock);
	if (!__test_and_clear_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
		mutex_unlock(&cmd->lock);
		return true;
	}
	cmd->status = BLK_STS_IOERR;
	mutex_unlock(&cmd->lock);

	blk_mq_complete_request(req);
	return true;
}

static void nbd_clear_que(struct nbd_device *nbd)
{
	blk_mq_quiesce_queue(nbd->disk->queue);
	blk_mq_tagset_busy_iter(&nbd->tag_set, nbd_clear_req, NULL);
	blk_mq_unquiesce_queue(nbd->disk->queue);
	dev_dbg(disk_to_dev(nbd->disk), "queue cleared\n");
}

static int find_fallback(struct nbd_device *nbd, int index)
{
	struct nbd_config *config = nbd->config;
	int new_index = -1;
	struct nbd_sock *nsock = config->socks[index];
	int fallback = nsock->fallback_index;

	if (test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags))
		return new_index;

	if (config->num_connections <= 1) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
				    "Dead connection, failed to find a fallback\n");
		return new_index;
	}

	if (fallback >= 0 && fallback < config->num_connections &&
	    !config->socks[fallback]->dead)
		return fallback;

	if (nsock->fallback_index < 0 ||
	    nsock->fallback_index >= config->num_connections ||
	    config->socks[nsock->fallback_index]->dead) {
		int i;
		for (i = 0; i < config->num_connections; i++) {
			if (i == index)
				continue;
			if (!config->socks[i]->dead) {
				new_index = i;
				break;
			}
		}
		nsock->fallback_index = new_index;
		if (new_index < 0) {
			dev_err_ratelimited(disk_to_dev(nbd->disk),
					    "Dead connection, failed to find a fallback\n");
			return new_index;
		}
	}
	new_index = nsock->fallback_index;
	return new_index;
}

static int wait_for_reconnect(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	if (!config->dead_conn_timeout)
		return 0;

	if (!wait_event_timeout(config->conn_wait,
				test_bit(NBD_RT_DISCONNECTED,
					 &config->runtime_flags) ||
				atomic_read(&config->live_connections) > 0,
				config->dead_conn_timeout))
		return 0;

	return !test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);
}

static blk_status_t nbd_handle_cmd(struct nbd_cmd *cmd, int index)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);
	struct nbd_device *nbd = cmd->nbd;
	struct nbd_config *config;
	struct nbd_sock *nsock;
	blk_status_t ret;

	lockdep_assert_held(&cmd->lock);

	config = nbd_get_config_unlocked(nbd);
	if (!config) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
				    "Socks array is empty\n");
		return BLK_STS_IOERR;
	}

	if (index >= config->num_connections) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
				    "Attempted send on invalid socket\n");
		nbd_config_put(nbd);
		return BLK_STS_IOERR;
	}
	cmd->status = BLK_STS_OK;
again:
	nsock = config->socks[index];
	mutex_lock(&nsock->tx_lock);
	if (nsock->dead) {
		int old_index = index;
		index = find_fallback(nbd, index);
		mutex_unlock(&nsock->tx_lock);
		if (index < 0) {
			if (wait_for_reconnect(nbd)) {
				index = old_index;
				goto again;
			}
			/* All the sockets should already be down at this point,
			 * we just want to make sure that DISCONNECTED is set so
			 * any requests that come in that were queue'ed waiting
			 * for the reconnect timer don't trigger the timer again
			 * and instead just error out.
			 */
			sock_shutdown(nbd);
			nbd_config_put(nbd);
			return BLK_STS_IOERR;
		}
		goto again;
	}

	/* Handle the case that we have a pending request that was partially
	 * transmitted that _has_ to be serviced first.  We need to call requeue
	 * here so that it gets put _after_ the request that is already on the
	 * dispatch list.
	 */
	blk_mq_start_request(req);
	if (unlikely(nsock->pending && nsock->pending != req)) {
		nbd_requeue_cmd(cmd);
		ret = BLK_STS_OK;
		goto out;
	}
	ret = nbd_send_cmd(nbd, cmd, index);
out:
	mutex_unlock(&nsock->tx_lock);
	nbd_config_put(nbd);
	return ret;
}

static blk_status_t nbd_queue_rq(struct blk_mq_hw_ctx *hctx,
			const struct blk_mq_queue_data *bd)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(bd->rq);
	blk_status_t ret;

	/*
	 * Since we look at the bio's to send the request over the network we
	 * need to make sure the completion work doesn't mark this request done
	 * before we are done doing our send.  This keeps us from dereferencing
	 * freed data if we have particularly fast completions (ie we get the
	 * completion before we exit sock_xmit on the last bvec) or in the case
	 * that the server is misbehaving (or there was an error) before we're
	 * done sending everything over the wire.
	 */
	mutex_lock(&cmd->lock);
	clear_bit(NBD_CMD_REQUEUED, &cmd->flags);

	/* We can be called directly from the user space process, which means we
	 * could possibly have signals pending so our sendmsg will fail.  In
	 * this case we need to return that we are busy, otherwise error out as
	 * appropriate.
	 */
	ret = nbd_handle_cmd(cmd, hctx->queue_num);
	mutex_unlock(&cmd->lock);

	return ret;
}

static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd,
				     int *err)
{
	struct socket *sock;

	*err = 0;
	sock = sockfd_lookup(fd, err);
	if (!sock)
		return NULL;

	if (!sk_is_tcp(sock->sk) &&
	    !sk_is_stream_unix(sock->sk)) {
		dev_err(disk_to_dev(nbd->disk), "Unsupported socket: should be TCP or UNIX.\n");
		*err = -EINVAL;
		sockfd_put(sock);
		return NULL;
	}

	if (sock->ops->shutdown == sock_no_shutdown) {
		dev_err(disk_to_dev(nbd->disk), "Unsupported socket: shutdown callout must be supported.\n");
		*err = -EINVAL;
		sockfd_put(sock);
		return NULL;
	}

	return sock;
}

static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
			  bool netlink)
{
	struct nbd_config *config = nbd->config;
	struct socket *sock;
	struct nbd_sock **socks;
	struct nbd_sock *nsock;
	unsigned int memflags;
	int err;

	/* Arg will be cast to int, check it to avoid overflow */
	if (arg > INT_MAX)
		return -EINVAL;
	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	/*
	 * We need to make sure we don't get any errant requests while we're
	 * reallocating the ->socks array.
	 */
	memflags = blk_mq_freeze_queue(nbd->disk->queue);

	if (!netlink && !nbd->task_setup &&
	    !test_bit(NBD_RT_BOUND, &config->runtime_flags))
		nbd->task_setup = current;

	if (!netlink &&
	    (nbd->task_setup != current ||
	     test_bit(NBD_RT_BOUND, &config->runtime_flags))) {
		dev_err(disk_to_dev(nbd->disk),
			"Device being setup by another task");
		err = -EBUSY;
		goto put_socket;
	}

	nsock = kzalloc_obj(*nsock);
	if (!nsock) {
		err = -ENOMEM;
		goto put_socket;
	}

	socks = krealloc(config->socks, (config->num_connections + 1) *
			 sizeof(struct nbd_sock *), GFP_KERNEL);
	if (!socks) {
		kfree(nsock);
		err = -ENOMEM;
		goto put_socket;
	}

	config->socks = socks;

	nsock->fallback_index = -1;
	nsock->dead = false;
	mutex_init(&nsock->tx_lock);
	nsock->sock = sock;
	nsock->pending = NULL;
	nsock->sent = 0;
	nsock->cookie = 0;
	INIT_WORK(&nsock->work, nbd_pending_cmd_work);
	socks[config->num_connections++] = nsock;
	atomic_inc(&config->live_connections);
	blk_mq_unfreeze_queue(nbd->disk->queue, memflags);

	return 0;

put_socket:
	blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
	sockfd_put(sock);
	return err;
}

static int nbd_reconnect_socket(struct nbd_device *nbd, unsigned long arg)
{
	struct nbd_config *config = nbd->config;
	struct socket *sock, *old;
	struct recv_thread_args *args;
	int i;
	int err;

	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	args = kzalloc_obj(*args);
	if (!args) {
		sockfd_put(sock);
		return -ENOMEM;
	}

	for (i = 0; i < config->num_connections; i++) {
		struct nbd_sock *nsock = config->socks[i];

		if (!nsock->dead)
			continue;

		mutex_lock(&nsock->tx_lock);
		if (!nsock->dead) {
			mutex_unlock(&nsock->tx_lock);
			continue;
		}
		sk_set_memalloc(sock->sk);
		if (nbd->tag_set.timeout)
			sock->sk->sk_sndtimeo = nbd->tag_set.timeout;
		atomic_inc(&config->recv_threads);
		refcount_inc(&nbd->config_refs);
		old = nsock->sock;
		nsock->fallback_index = -1;
		nsock->sock = sock;
		nsock->dead = false;
		INIT_WORK(&args->work, recv_work);
		args->index = i;
		args->nbd = nbd;
		args->nsock = nsock;
		nsock->cookie++;
		mutex_unlock(&nsock->tx_lock);
		sockfd_put(old);

		clear_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);

		/* We take the tx_mutex in an error path in the recv_work, so we
		 * need to queue_work outside of the tx_mutex.
		 */
		queue_work(nbd->recv_workq, &args->work);

		atomic_inc(&config->live_connections);
		wake_up(&config->conn_wait);
		return 0;
	}
	sockfd_put(sock);
	kfree(args);
	return -ENOSPC;
}

static void nbd_bdev_reset(struct nbd_device *nbd)
{
	if (disk_openers(nbd->disk) > 1)
		return;
	set_capacity(nbd->disk, 0);
}

static void nbd_parse_flags(struct nbd_device *nbd)
{
	if (nbd->config->flags & NBD_FLAG_READ_ONLY)
		set_disk_ro(nbd->disk, true);
	else
		set_disk_ro(nbd->disk, false);
}

static void send_disconnects(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	struct nbd_request request = {
		.magic = htonl(NBD_REQUEST_MAGIC),
		.type = htonl(NBD_CMD_DISC),
	};
	struct kvec iov = {.iov_base = &request, .iov_len = sizeof(request)};
	struct iov_iter from;
	int i, ret;

	for (i = 0; i < config->num_connections; i++) {
		struct nbd_sock *nsock = config->socks[i];

		iov_iter_kvec(&from, ITER_SOURCE, &iov, 1, sizeof(request));
		mutex_lock(&nsock->tx_lock);
		ret = sock_xmit(nbd, i, 1, &from, 0, NULL);
		if (ret < 0)
			dev_err(disk_to_dev(nbd->disk),
				"Send disconnect failed %d\n", ret);
		mutex_unlock(&nsock->tx_lock);
	}
}

static int nbd_disconnect(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;

	dev_info(disk_to_dev(nbd->disk), "NBD_DISCONNECT\n");
	set_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags);
	set_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags);
	send_disconnects(nbd);
	return 0;
}

static void nbd_clear_sock(struct nbd_device *nbd)
{
	sock_shutdown(nbd);
	nbd_clear_que(nbd);
	nbd->task_setup = NULL;
}

static void nbd_config_put(struct nbd_device *nbd)
{
	if (refcount_dec_and_mutex_lock(&nbd->config_refs,
					&nbd->config_lock)) {
		struct nbd_config *config = nbd->config;
		nbd_dev_dbg_close(nbd);
		invalidate_disk(nbd->disk);
		if (nbd->config->bytesize)
			kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
		if (test_and_clear_bit(NBD_RT_HAS_PID_FILE,
				       &config->runtime_flags))
			device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
		nbd->pid = 0;
		if (test_and_clear_bit(NBD_RT_HAS_BACKEND_FILE,
				       &config->runtime_flags)) {
			device_remove_file(disk_to_dev(nbd->disk), &backend_attr);
			kfree(nbd->backend);
			nbd->backend = NULL;
		}
		nbd_clear_sock(nbd);
		if (config->num_connections) {
			int i;
			for (i = 0; i < config->num_connections; i++) {
				sockfd_put(config->socks[i]->sock);
				kfree(config->socks[i]);
			}
			kfree(config->socks);
		}
		kfree(nbd->config);
		nbd->config = NULL;

		nbd->tag_set.timeout = 0;

		mutex_unlock(&nbd->config_lock);
		nbd_put(nbd);
		module_put(THIS_MODULE);
	}
}

static int nbd_start_device(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	int num_connections = config->num_connections;
	int error = 0, i;

	if (nbd->pid)
		return -EBUSY;
	if (!config->socks)
		return -EINVAL;
	if (num_connections > 1 &&
	    !(config->flags & NBD_FLAG_CAN_MULTI_CONN)) {
		dev_err(disk_to_dev(nbd->disk), "server does not support multiple connections per device.\n");
		return -EINVAL;
	}

retry:
	mutex_unlock(&nbd->config_lock);
	blk_mq_update_nr_hw_queues(&nbd->tag_set, num_connections);
	mutex_lock(&nbd->config_lock);

	/* if another code path updated nr_hw_queues, retry until succeed */
	if (num_connections != config->num_connections) {
		num_connections = config->num_connections;
		goto retry;
	}

	nbd->pid = task_pid_nr(current);

	nbd_parse_flags(nbd);

	error = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
	if (error) {
		dev_err(disk_to_dev(nbd->disk), "device_create_file failed for pid!\n");
		return error;
	}
	set_bit(NBD_RT_HAS_PID_FILE, &config->runtime_flags);

	nbd_dev_dbg_init(nbd);
	for (i = 0; i < num_connections; i++) {
		struct recv_thread_args *args;

		args = kzalloc_obj(*args);
		if (!args) {
			sock_shutdown(nbd);
			/*
			 * If num_connections is m (2 < m),
			 * and NO.1 ~ NO.n(1 < n < m) kzallocs are successful.
			 * But NO.(n + 1) failed. We still have n recv threads.
			 * So, add flush_workqueue here to prevent recv threads
			 * dropping the last config_refs and trying to destroy
			 * the workqueue from inside the workqueue.
			 */
			if (i)
				flush_workqueue(nbd->recv_workq);
			return -ENOMEM;
		}
		sk_set_memalloc(config->socks[i]->sock->sk);
		if (nbd->tag_set.timeout)
			config->socks[i]->sock->sk->sk_sndtimeo =
				nbd->tag_set.timeout;
		atomic_inc(&config->recv_threads);
		refcount_inc(&nbd->config_refs);
		INIT_WORK(&args->work, recv_work);
		args->nbd = nbd;
		args->nsock = config->socks[i];
		args->index = i;
		queue_work(nbd->recv_workq, &args->work);
	}
	return nbd_set_size(nbd, config->bytesize, nbd_blksize(config));
}

static int nbd_start_device_ioctl(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	int ret;

	ret = nbd_start_device(nbd);
	if (ret)
		return ret;

	if (max_part)
		set_bit(GD_NEED_PART_SCAN, &nbd->disk->state);
	mutex_unlock(&nbd->config_lock);
	ret = wait_event_interruptible(config->recv_wq,
					 atomic_read(&config->recv_threads) == 0);
	if (ret) {
		sock_shutdown(nbd);
		nbd_clear_que(nbd);
	}

	flush_workqueue(nbd->recv_workq);
	mutex_lock(&nbd->config_lock);
	nbd_bdev_reset(nbd);
	/* user requested, ignore socket errors */
	if (test_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags))
		ret = 0;
	if (test_bit(NBD_RT_TIMEDOUT, &config->runtime_flags))
		ret = -ETIMEDOUT;
	return ret;
}

static void nbd_clear_sock_ioctl(struct nbd_device *nbd)
{
	nbd_clear_sock(nbd);
	disk_force_media_change(nbd->disk);
	nbd_bdev_reset(nbd);
	if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF,
			       &nbd->config->runtime_flags))
		nbd_config_put(nbd);
}

static void nbd_set_cmd_timeout(struct nbd_device *nbd, u64 timeout)
{
	nbd->tag_set.timeout = timeout * HZ;
	if (timeout)
		blk_queue_rq_timeout(nbd->disk->queue, timeout * HZ);
	else
		blk_queue_rq_timeout(nbd->disk->queue, 30 * HZ);
}

/* Must be called with config_lock held */
static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
		       unsigned int cmd, unsigned long arg)
{
	struct nbd_config *config = nbd->config;
	loff_t bytesize;

	switch (cmd) {
	case NBD_DISCONNECT:
		return nbd_disconnect(nbd);
	case NBD_CLEAR_SOCK:
		nbd_clear_sock_ioctl(nbd);
		return 0;
	case NBD_SET_SOCK:
		return nbd_add_socket(nbd, arg, false);
	case NBD_SET_BLKSIZE:
		return nbd_set_size(nbd, config->bytesize, arg);
	case NBD_SET_SIZE:
		return nbd_set_size(nbd, arg, nbd_blksize(config));
	case NBD_SET_SIZE_BLOCKS:
		if (check_shl_overflow(arg, config->blksize_bits, &bytesize))
			return -EINVAL;
		return nbd_set_size(nbd, bytesize, nbd_blksize(config));
	case NBD_SET_TIMEOUT:
		nbd_set_cmd_timeout(nbd, arg);
		return 0;

	case NBD_SET_FLAGS:
		config->flags = arg;
		return 0;
	case NBD_DO_IT:
		return nbd_start_device_ioctl(nbd);
	case NBD_CLEAR_QUE:
		/*
		 * This is for compatibility only.  The queue is always cleared
		 * by NBD_DO_IT or NBD_CLEAR_SOCK.
		 */
		return 0;
	case NBD_PRINT_DEBUG:
		/*
		 * For compatibility only, we no longer keep a list of
		 * outstanding requests.
		 */
		return 0;
	}
	return -ENOTTY;
}

static int nbd_ioctl(struct block_device *bdev, blk_mode_t mode,
		     unsigned int cmd, unsigned long arg)
{
	struct nbd_device *nbd = bdev->bd_disk->private_data;
	struct nbd_config *config = nbd->config;
	int error = -EINVAL;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;

	/* The block layer will pass back some non-nbd ioctls in case we have
	 * special handling for them, but we don't so just return an error.
	 */
	if (_IOC_TYPE(cmd) != 0xab)
		return -EINVAL;

	mutex_lock(&nbd->config_lock);

	/* Don't allow ioctl operations on a nbd device that was created with
	 * netlink, unless it's DISCONNECT or CLEAR_SOCK, which are fine.
	 */
	if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
	    (cmd == NBD_DISCONNECT || cmd == NBD_CLEAR_SOCK))
		error = __nbd_ioctl(bdev, nbd, cmd, arg);
	else
		dev_err(nbd_to_dev(nbd), "Cannot use ioctl interface on a netlink controlled device.\n");
	mutex_unlock(&nbd->config_lock);
	return error;
}

static int nbd_alloc_and_init_config(struct nbd_device *nbd)
{
	struct nbd_config *config;

	if (WARN_ON(nbd->config))
		return -EINVAL;

	if (!try_module_get(THIS_MODULE))
		return -ENODEV;

	config = kzalloc_obj(struct nbd_config, GFP_NOFS);
	if (!config) {
		module_put(THIS_MODULE);
		return -ENOMEM;
	}

	atomic_set(&config->recv_threads, 0);
	init_waitqueue_head(&config->recv_wq);
	init_waitqueue_head(&config->conn_wait);
	config->blksize_bits = NBD_DEF_BLKSIZE_BITS;
	atomic_set(&config->live_connections, 0);

	nbd->config = config;
	/*
	 * Order refcount_set(&nbd->config_refs, 1) and nbd->config assignment,
	 * its pair is the barrier in nbd_get_config_unlocked().
	 * So nbd_get_config_unlocked() won't see nbd->config as null after
	 * refcount_inc_not_zero() succeed.
	 */
	smp_mb__before_atomic();
	refcount_set(&nbd->config_refs, 1);

	return 0;
}

static int nbd_open(struct gendisk *disk, blk_mode_t mode)
{
	struct nbd_device *nbd;
	struct nbd_config *config;
	int ret = 0;

	mutex_lock(&nbd_index_mutex);
	nbd = disk->private_data;
	if (!nbd) {
		ret = -ENXIO;
		goto out;
	}
	if (!refcount_inc_not_zero(&nbd->refs)) {
		ret = -ENXIO;
		goto out;
	}

	config = nbd_get_config_unlocked(nbd);
	if (!config) {
		mutex_lock(&nbd->config_lock);
		if (refcount_inc_not_zero(&nbd->config_refs)) {
			mutex_unlock(&nbd->config_lock);
			goto out;
		}
		ret = nbd_alloc_and_init_config(nbd);
		if (ret) {
			mutex_unlock(&nbd->config_lock);
			goto out;
		}

		refcount_inc(&nbd->refs);
		mutex_unlock(&nbd->config_lock);
		if (max_part)
			set_bit(GD_NEED_PART_SCAN, &disk->state);
	} else if (nbd_disconnected(config)) {
		if (max_part)
			set_bit(GD_NEED_PART_SCAN, &disk->state);
	}
out:
	mutex_unlock(&nbd_index_mutex);
	return ret;
}

static void nbd_release(struct gendisk *disk)
{
	struct nbd_device *nbd = disk->private_data;

	if (test_bit(NBD_RT_DISCONNECT_ON_CLOSE, &nbd->config->runtime_flags) &&
			disk_openers(disk) == 0)
		nbd_disconnect_and_put(nbd);

	nbd_config_put(nbd);
	nbd_put(nbd);
}

static void nbd_free_disk(struct gendisk *disk)
{
	struct nbd_device *nbd = disk->private_data;

	kfree(nbd);
}

static const struct block_device_operations nbd_fops =
{
	.owner =	THIS_MODULE,
	.open =		nbd_open,
	.release =	nbd_release,
	.ioctl =	nbd_ioctl,
	.compat_ioctl =	nbd_ioctl,
	.free_disk =	nbd_free_disk,
};

#if IS_ENABLED(CONFIG_DEBUG_FS)

static int nbd_dbg_tasks_show(struct seq_file *s, void *unused)
{
	struct nbd_device *nbd = s->private;

	if (nbd->pid)
		seq_printf(s, "recv: %d\n", nbd->pid);

	return 0;
}

DEFINE_SHOW_ATTRIBUTE(nbd_dbg_tasks);

static int nbd_dbg_flags_show(struct seq_file *s, void *unused)
{
	struct nbd_device *nbd = s->private;
	u32 flags = nbd->config->flags;

	seq_printf(s, "Hex: 0x%08x\n\n", flags);

	seq_puts(s, "Known flags:\n");

	if (flags & NBD_FLAG_HAS_FLAGS)
		seq_puts(s, "NBD_FLAG_HAS_FLAGS\n");
	if (flags & NBD_FLAG_READ_ONLY)
		seq_puts(s, "NBD_FLAG_READ_ONLY\n");
	if (flags & NBD_FLAG_SEND_FLUSH)
		seq_puts(s, "NBD_FLAG_SEND_FLUSH\n");
	if (flags & NBD_FLAG_SEND_FUA)
		seq_puts(s, "NBD_FLAG_SEND_FUA\n");
	if (flags & NBD_FLAG_SEND_TRIM)
		seq_puts(s, "NBD_FLAG_SEND_TRIM\n");
	if (flags & NBD_FLAG_SEND_WRITE_ZEROES)
		seq_puts(s, "NBD_FLAG_SEND_WRITE_ZEROES\n");
	if (flags & NBD_FLAG_ROTATIONAL)
		seq_puts(s, "NBD_FLAG_ROTATIONAL\n");

	return 0;
}

DEFINE_SHOW_ATTRIBUTE(nbd_dbg_flags);

static int nbd_dev_dbg_init(struct nbd_device *nbd)
{
	struct dentry *dir;
	struct nbd_config *config = nbd->config;

	if (!nbd_dbg_dir)
		return -EIO;

	dir = debugfs_create_dir(nbd_name(nbd), nbd_dbg_dir);
	if (IS_ERR(dir)) {
		dev_err(nbd_to_dev(nbd), "Failed to create debugfs dir for '%s'\n",
			nbd_name(nbd));
		return -EIO;
	}
	config->dbg_dir = dir;

	debugfs_create_file("tasks", 0444, dir, nbd, &nbd_dbg_tasks_fops);
	debugfs_create_u64("size_bytes", 0444, dir, &config->bytesize);
	debugfs_create_u32("timeout", 0444, dir, &nbd->tag_set.timeout);
	debugfs_create_u32("blocksize_bits", 0444, dir, &config->blksize_bits);
	debugfs_create_file("flags", 0444, dir, nbd, &nbd_dbg_flags_fops);

	return 0;
}

static void nbd_dev_dbg_close(struct nbd_device *nbd)
{
	debugfs_remove_recursive(nbd->config->dbg_dir);
}

static int nbd_dbg_init(void)
{
	struct dentry *dbg_dir;

	dbg_dir = debugfs_create_dir("nbd", NULL);
	if (IS_ERR(dbg_dir))
		return -EIO;

	nbd_dbg_dir = dbg_dir;

	return 0;
}

static void nbd_dbg_close(void)
{
	debugfs_remove_recursive(nbd_dbg_dir);
}

#else  /* IS_ENABLED(CONFIG_DEBUG_FS) */

static int nbd_dev_dbg_init(struct nbd_device *nbd)
{
	return 0;
}

static void nbd_dev_dbg_close(struct nbd_device *nbd)
{
}

static int nbd_dbg_init(void)
{
	return 0;
}

static void nbd_dbg_close(void)
{
}

#endif

static int nbd_init_request(struct blk_mq_tag_set *set, struct request *rq,
			    unsigned int hctx_idx, unsigned int numa_node)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(rq);
	cmd->nbd = set->driver_data;
	cmd->flags = 0;
	mutex_init(&cmd->lock);
	return 0;
}

static const struct blk_mq_ops nbd_mq_ops = {
	.queue_rq	= nbd_queue_rq,
	.complete	= nbd_complete_rq,
	.init_request	= nbd_init_request,
	.timeout	= nbd_xmit_timeout,
};

static struct nbd_device *nbd_dev_add(int index, unsigned int refs)
{
	struct queue_limits lim = {
		.max_hw_sectors		= 65536,
		.io_opt			= 256 << SECTOR_SHIFT,
		.max_segments		= USHRT_MAX,
		.max_segment_size	= UINT_MAX,
	};
	struct nbd_device *nbd;
	struct gendisk *disk;
	int err = -ENOMEM;

	nbd = kzalloc_obj(struct nbd_device);
	if (!nbd)
		goto out;

	nbd->tag_set.ops = &nbd_mq_ops;
	nbd->tag_set.nr_hw_queues = 1;
	nbd->tag_set.queue_depth = 128;
	nbd->tag_set.numa_node = NUMA_NO_NODE;
	nbd->tag_set.cmd_size = sizeof(struct nbd_cmd);
	nbd->tag_set.flags = BLK_MQ_F_BLOCKING;
	nbd->tag_set.driver_data = nbd;
	INIT_WORK(&nbd->remove_work, nbd_dev_remove_work);
	nbd->backend = NULL;

	err = blk_mq_alloc_tag_set(&nbd->tag_set);
	if (err)
		goto out_free_nbd;

	mutex_lock(&nbd_index_mutex);
	if (index >= 0) {
		err = idr_alloc(&nbd_index_idr, nbd, index, index + 1,
				GFP_KERNEL);
		if (err == -ENOSPC)
			err = -EEXIST;
	} else {
		err = idr_alloc(&nbd_index_idr, nbd, 0,
				(MINORMASK >> part_shift) + 1, GFP_KERNEL);
		if (err >= 0)
			index = err;
	}
	nbd->index = index;
	mutex_unlock(&nbd_index_mutex);
	if (err < 0)
		goto out_free_tags;

	disk = blk_mq_alloc_disk(&nbd->tag_set, &lim, NULL);
	if (IS_ERR(disk)) {
		err = PTR_ERR(disk);
		goto out_free_idr;
	}
	nbd->disk = disk;

	nbd->recv_workq = alloc_workqueue("nbd%d-recv",
					  WQ_MEM_RECLAIM | WQ_HIGHPRI |
					  WQ_UNBOUND, 0, nbd->index);
	if (!nbd->recv_workq) {
		dev_err(disk_to_dev(nbd->disk), "Could not allocate knbd recv work queue.\n");
		err = -ENOMEM;
		goto out_err_disk;
	}

	mutex_init(&nbd->config_lock);
	refcount_set(&nbd->config_refs, 0);
	/*
	 * Start out with a zero references to keep other threads from using
	 * this device until it is fully initialized.
	 */
	refcount_set(&nbd->refs, 0);
	INIT_LIST_HEAD(&nbd->list);
	disk->major = NBD_MAJOR;
	disk->first_minor = index << part_shift;
	disk->minors = 1 << part_shift;
	disk->fops = &nbd_fops;
	disk->private_data = nbd;
	sprintf(disk->disk_name, "nbd%d", index);
	err = add_disk(disk);
	if (err)
		goto out_free_work;

	/*
	 * Now publish the device.
	 */
	refcount_set(&nbd->refs, refs);
	nbd_total_devices++;
	return nbd;

out_free_work:
	destroy_workqueue(nbd->recv_workq);
out_err_disk:
	put_disk(disk);
out_free_idr:
	mutex_lock(&nbd_index_mutex);
	idr_remove(&nbd_index_idr, index);
	mutex_unlock(&nbd_index_mutex);
out_free_tags:
	blk_mq_free_tag_set(&nbd->tag_set);
out_free_nbd:
	kfree(nbd);
out:
	return ERR_PTR(err);
}

static struct nbd_device *nbd_find_get_unused(void)
{
	struct nbd_device *nbd;
	int id;

	lockdep_assert_held(&nbd_index_mutex);

	idr_for_each_entry(&nbd_index_idr, nbd, id) {
		if (refcount_read(&nbd->config_refs) ||
		    test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags))
			continue;
		if (refcount_inc_not_zero(&nbd->refs))
			return nbd;
	}

	return NULL;
}

/* Netlink interface. */
static const struct nla_policy nbd_attr_policy[NBD_ATTR_MAX + 1] = {
	[NBD_ATTR_INDEX]		=	{ .type = NLA_U32 },
	[NBD_ATTR_SIZE_BYTES]		=	{ .type = NLA_U64 },
	[NBD_ATTR_BLOCK_SIZE_BYTES]	=	{ .type = NLA_U64 },
	[NBD_ATTR_TIMEOUT]		=	{ .type = NLA_U64 },
	[NBD_ATTR_SERVER_FLAGS]		=	{ .type = NLA_U64 },
	[NBD_ATTR_CLIENT_FLAGS]		=	{ .type = NLA_U64 },
	[NBD_ATTR_SOCKETS]		=	{ .type = NLA_NESTED},
	[NBD_ATTR_DEAD_CONN_TIMEOUT]	=	{ .type = NLA_U64 },
	[NBD_ATTR_DEVICE_LIST]		=	{ .type = NLA_NESTED},
	[NBD_ATTR_BACKEND_IDENTIFIER]	=	{ .type = NLA_STRING},
};

static const struct nla_policy nbd_sock_policy[NBD_SOCK_MAX + 1] = {
	[NBD_SOCK_FD]			=	{ .type = NLA_U32 },
};

/* We don't use this right now since we don't parse the incoming list, but we
 * still want it here so userspace knows what to expect.
 */
static const struct nla_policy __attribute__((unused))
nbd_device_policy[NBD_DEVICE_ATTR_MAX + 1] = {
	[NBD_DEVICE_INDEX]		=	{ .type = NLA_U32 },
	[NBD_DEVICE_CONNECTED]		=	{ .type = NLA_U8 },
};

static int nbd_genl_size_set(struct genl_info *info, struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	u64 bsize = nbd_blksize(config);
	u64 bytes = config->bytesize;

	if (info->attrs[NBD_ATTR_SIZE_BYTES])
		bytes = nla_get_u64(info->attrs[NBD_ATTR_SIZE_BYTES]);

	if (info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES])
		bsize = nla_get_u64(info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES]);

	if (bytes != config->bytesize || bsize != nbd_blksize(config))
		return nbd_set_size(nbd, bytes, bsize);
	return 0;
}

static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
{
	struct nbd_device *nbd;
	struct nbd_config *config;
	int index = -1;
	int ret;
	bool put_dev = false;

	if (!netlink_capable(skb, CAP_SYS_ADMIN))
		return -EPERM;

	if (info->attrs[NBD_ATTR_INDEX]) {
		index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);

		/*
		 * Too big first_minor can cause duplicate creation of
		 * sysfs files/links, since index << part_shift might overflow, or
		 * MKDEV() expect that the max bits of first_minor is 20.
		 */
		if (index < 0 || index > MINORMASK >> part_shift) {
			pr_err("illegal input index %d\n", index);
			return -EINVAL;
		}
	}
	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SOCKETS)) {
		pr_err("must specify at least one socket\n");
		return -EINVAL;
	}
	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SIZE_BYTES)) {
		pr_err("must specify a size in bytes for the device\n");
		return -EINVAL;
	}
again:
	mutex_lock(&nbd_index_mutex);
	if (index == -1) {
		nbd = nbd_find_get_unused();
	} else {
		nbd = idr_find(&nbd_index_idr, index);
		if (nbd) {
			if ((test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags) &&
			     test_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags)) ||
			    !refcount_inc_not_zero(&nbd->refs)) {
				mutex_unlock(&nbd_index_mutex);
				pr_err("device at index %d is going down\n",
					index);
				return -EINVAL;
			}
		}
	}
	mutex_unlock(&nbd_index_mutex);

	if (!nbd) {
		nbd = nbd_dev_add(index, 2);
		if (IS_ERR(nbd)) {
			pr_err("failed to add new device\n");
			return PTR_ERR(nbd);
		}
	}

	mutex_lock(&nbd->config_lock);
	if (refcount_read(&nbd->config_refs)) {
		mutex_unlock(&nbd->config_lock);
		nbd_put(nbd);
		if (index == -1)
			goto again;
		pr_err("nbd%d already in use\n", index);
		return -EBUSY;
	}

	ret = nbd_alloc_and_init_config(nbd);
	if (ret) {
		mutex_unlock(&nbd->config_lock);
		nbd_put(nbd);
		pr_err("couldn't allocate config\n");
		return ret;
	}

	config = nbd->config;
	set_bit(NBD_RT_BOUND, &config->runtime_flags);
	ret = nbd_genl_size_set(info, nbd);
	if (ret)
		goto out;

	if (info->attrs[NBD_ATTR_TIMEOUT])
		nbd_set_cmd_timeout(nbd,
				    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
	if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
		config->dead_conn_timeout =
			nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
		config->dead_conn_timeout *= HZ;
	}
	if (info->attrs[NBD_ATTR_SERVER_FLAGS])
		config->flags =
			nla_get_u64(info->attrs[NBD_ATTR_SERVER_FLAGS]);
	if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
		u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
		if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
			/*
			 * We have 1 ref to keep the device around, and then 1
			 * ref for our current operation here, which will be
			 * inherited by the config.  If we already have
			 * DESTROY_ON_DISCONNECT set then we know we don't have
			 * that extra ref already held so we don't need the
			 * put_dev.
			 */
			if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
					      &nbd->flags))
				put_dev = true;
		} else {
			if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
					       &nbd->flags))
				refcount_inc(&nbd->refs);
		}
		if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
			set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
				&config->runtime_flags);
		}
	}

	if (info->attrs[NBD_ATTR_SOCKETS]) {
		struct nlattr *attr;
		int rem, fd;

		nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
				    rem) {
			struct nlattr *socks[NBD_SOCK_MAX+1];

			if (nla_type(attr) != NBD_SOCK_ITEM) {
				pr_err("socks must be embedded in a SOCK_ITEM attr\n");
				ret = -EINVAL;
				goto out;
			}
			ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
							  attr,
							  nbd_sock_policy,
							  info->extack);
			if (ret != 0) {
				pr_err("error processing sock list\n");
				ret = -EINVAL;
				goto out;
			}
			if (!socks[NBD_SOCK_FD])
				continue;
			fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
			ret = nbd_add_socket(nbd, fd, true);
			if (ret)
				goto out;
		}
	}

	if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
		nbd->backend = nla_strdup(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
					  GFP_KERNEL);
		if (!nbd->backend) {
			ret = -ENOMEM;
			goto out;
		}
	}
	ret = device_create_file(disk_to_dev(nbd->disk), &backend_attr);
	if (ret) {
		dev_err(disk_to_dev(nbd->disk),
			"device_create_file failed for backend!\n");
		goto out;
	}
	set_bit(NBD_RT_HAS_BACKEND_FILE, &config->runtime_flags);

	ret = nbd_start_device(nbd);
out:
	if (!ret) {
		set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);
		refcount_inc(&nbd->config_refs);
		nbd_connect_reply(info, nbd->index);
	}
	mutex_unlock(&nbd->config_lock);

	nbd_config_put(nbd);
	if (put_dev)
		nbd_put(nbd);
	return ret;
}

static void nbd_disconnect_and_put(struct nbd_device *nbd)
{
	mutex_lock(&nbd->config_lock);
	nbd_disconnect(nbd);
	sock_shutdown(nbd);
	wake_up(&nbd->config->conn_wait);
	/*
	 * Make sure recv thread has finished, we can safely call nbd_clear_que()
	 * to cancel the inflight I/Os.
	 */
	flush_workqueue(nbd->recv_workq);
	nbd_clear_que(nbd);
	nbd->task_setup = NULL;
	clear_bit(NBD_RT_BOUND, &nbd->config->runtime_flags);
	mutex_unlock(&nbd->config_lock);

	if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF,
			       &nbd->config->runtime_flags))
		nbd_config_put(nbd);
}

static int nbd_genl_disconnect(struct sk_buff *skb, struct genl_info *info)
{
	struct nbd_device *nbd;
	int index;

	if (!netlink_capable(skb, CAP_SYS_ADMIN))
		return -EPERM;

	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)) {
		pr_err("must specify an index to disconnect\n");
		return -EINVAL;
	}
	index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
	mutex_lock(&nbd_index_mutex);
	nbd = idr_find(&nbd_index_idr, index);
	if (!nbd) {
		mutex_unlock(&nbd_index_mutex);
		pr_err("couldn't find device at index %d\n", index);
		return -EINVAL;
	}
	if (!refcount_inc_not_zero(&nbd->refs)) {
		mutex_unlock(&nbd_index_mutex);
		pr_err("device at index %d is going down\n", index);
		return -EINVAL;
	}
	mutex_unlock(&nbd_index_mutex);
	if (!refcount_inc_not_zero(&nbd->config_refs))
		goto put_nbd;
	nbd_disconnect_and_put(nbd);
	nbd_config_put(nbd);
put_nbd:
	nbd_put(nbd);
	return 0;
}

static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
{
	struct nbd_device *nbd = NULL;
	struct nbd_config *config;
	int index;
	int ret = 0;
	bool put_dev = false;

	if (!netlink_capable(skb, CAP_SYS_ADMIN))
		return -EPERM;

	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)) {
		pr_err("must specify a device to reconfigure\n");
		return -EINVAL;
	}
	index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
	mutex_lock(&nbd_index_mutex);
	nbd = idr_find(&nbd_index_idr, index);
	if (!nbd) {
		mutex_unlock(&nbd_index_mutex);
		pr_err("couldn't find a device at index %d\n", index);
		return -EINVAL;
	}
	if (nbd->backend) {
		if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
			if (nla_strcmp(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
				       nbd->backend)) {
				mutex_unlock(&nbd_index_mutex);
				dev_err(nbd_to_dev(nbd),
					"backend image doesn't match with %s\n",
					nbd->backend);
				return -EINVAL;
			}
		} else {
			mutex_unlock(&nbd_index_mutex);
			dev_err(nbd_to_dev(nbd), "must specify backend\n");
			return -EINVAL;
		}
	}
	if (!refcount_inc_not_zero(&nbd->refs)) {
		mutex_unlock(&nbd_index_mutex);
		pr_err("device at index %d is going down\n", index);
		return -EINVAL;
	}
	mutex_unlock(&nbd_index_mutex);

	config = nbd_get_config_unlocked(nbd);
	if (!config) {
		dev_err(nbd_to_dev(nbd),
			"not configured, cannot reconfigure\n");
		nbd_put(nbd);
		return -EINVAL;
	}

	mutex_lock(&nbd->config_lock);
	if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
	    !nbd->pid) {
		dev_err(nbd_to_dev(nbd),
			"not configured, cannot reconfigure\n");
		ret = -EINVAL;
		goto out;
	}

	ret = nbd_genl_size_set(info, nbd);
	if (ret)
		goto out;

	if (info->attrs[NBD_ATTR_TIMEOUT])
		nbd_set_cmd_timeout(nbd,
				    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
	if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
		config->dead_conn_timeout =
			nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
		config->dead_conn_timeout *= HZ;
	}
	if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
		u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
		if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
			if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
					      &nbd->flags))
				put_dev = true;
		} else {
			if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
					       &nbd->flags))
				refcount_inc(&nbd->refs);
		}

		if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
			set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
					&config->runtime_flags);
		} else {
			clear_bit(NBD_RT_DISCONNECT_ON_CLOSE,
					&config->runtime_flags);
		}
	}

	if (info->attrs[NBD_ATTR_SOCKETS]) {
		struct nlattr *attr;
		int rem, fd;

		nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
				    rem) {
			struct nlattr *socks[NBD_SOCK_MAX+1];

			if (nla_type(attr) != NBD_SOCK_ITEM) {
				pr_err("socks must be embedded in a SOCK_ITEM attr\n");
				ret = -EINVAL;
				goto out;
			}
			ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
							  attr,
							  nbd_sock_policy,
							  info->extack);
			if (ret != 0) {
				pr_err("error processing sock list\n");
				ret = -EINVAL;
				goto out;
			}
			if (!socks[NBD_SOCK_FD])
				continue;
			fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
			ret = nbd_reconnect_socket(nbd, fd);
			if (ret) {
				if (ret == -ENOSPC)
					ret = 0;
				goto out;
			}
			dev_info(nbd_to_dev(nbd), "reconnected socket\n");
		}
	}
out:
	mutex_unlock(&nbd->config_lock);
	nbd_config_put(nbd);
	nbd_put(nbd);
	if (put_dev)
		nbd_put(nbd);
	return ret;
}

static const struct genl_small_ops nbd_connect_genl_ops[] = {
	{
		.cmd	= NBD_CMD_CONNECT,
		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
		.doit	= nbd_genl_connect,
	},
	{
		.cmd	= NBD_CMD_DISCONNECT,
		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
		.doit	= nbd_genl_disconnect,
	},
	{
		.cmd	= NBD_CMD_RECONFIGURE,
		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
		.doit	= nbd_genl_reconfigure,
	},
	{
		.cmd	= NBD_CMD_STATUS,
		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
		.doit	= nbd_genl_status,
	},
};

static const struct genl_multicast_group nbd_mcast_grps[] = {
	{ .name = NBD_GENL_MCAST_GROUP_NAME, },
};

static struct genl_family nbd_genl_family __ro_after_init = {
	.hdrsize	= 0,
	.name		= NBD_GENL_FAMILY_NAME,
	.version	= NBD_GENL_VERSION,
	.module		= THIS_MODULE,
	.small_ops	= nbd_connect_genl_ops,
	.n_small_ops	= ARRAY_SIZE(nbd_connect_genl_ops),
	.resv_start_op	= NBD_CMD_STATUS + 1,
	.maxattr	= NBD_ATTR_MAX,
	.netnsok	= 1,
	.policy = nbd_attr_policy,
	.mcgrps		= nbd_mcast_grps,
	.n_mcgrps	= ARRAY_SIZE(nbd_mcast_grps),
};
MODULE_ALIAS_GENL_FAMILY(NBD_GENL_FAMILY_NAME);

static int populate_nbd_status(struct nbd_device *nbd, struct sk_buff *reply)
{
	struct nlattr *dev_opt;
	u8 connected = 0;
	int ret;

	/* This is a little racey, but for status it's ok.  The
	 * reason we don't take a ref here is because we can't
	 * take a ref in the index == -1 case as we would need
	 * to put under the nbd_index_mutex, which could
	 * deadlock if we are configured to remove ourselves
	 * once we're disconnected.
	 */
	if (refcount_read(&nbd->config_refs))
		connected = 1;
	dev_opt = nla_nest_start_noflag(reply, NBD_DEVICE_ITEM);
	if (!dev_opt)
		return -EMSGSIZE;
	ret = nla_put_u32(reply, NBD_DEVICE_INDEX, nbd->index);
	if (ret)
		return -EMSGSIZE;
	ret = nla_put_u8(reply, NBD_DEVICE_CONNECTED,
			 connected);
	if (ret)
		return -EMSGSIZE;
	nla_nest_end(reply, dev_opt);
	return 0;
}

static int status_cb(int id, void *ptr, void *data)
{
	struct nbd_device *nbd = ptr;
	return populate_nbd_status(nbd, (struct sk_buff *)data);
}

static int nbd_genl_status(struct sk_buff *skb, struct genl_info *info)
{
	struct nlattr *dev_list;
	struct sk_buff *reply;
	void *reply_head;
	size_t msg_size;
	int index = -1;
	int ret = -ENOMEM;

	if (info->attrs[NBD_ATTR_INDEX])
		index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);

	mutex_lock(&nbd_index_mutex);

	msg_size = nla_total_size(nla_attr_size(sizeof(u32)) +
				  nla_attr_size(sizeof(u8)));
	msg_size *= (index == -1) ? nbd_total_devices : 1;

	reply = genlmsg_new(msg_size, GFP_KERNEL);
	if (!reply)
		goto out;
	reply_head = genlmsg_put_reply(reply, info, &nbd_genl_family, 0,
				       NBD_CMD_STATUS);
	if (!reply_head) {
		nlmsg_free(reply);
		goto out;
	}

	dev_list = nla_nest_start_noflag(reply, NBD_ATTR_DEVICE_LIST);
	if (!dev_list) {
		nlmsg_free(reply);
		ret = -EMSGSIZE;
		goto out;
	}

	if (index == -1) {
		ret = idr_for_each(&nbd_index_idr, &status_cb, reply);
		if (ret) {
			nlmsg_free(reply);
			goto out;
		}
	} else {
		struct nbd_device *nbd;
		nbd = idr_find(&nbd_index_idr, index);
		if (nbd) {
			ret = populate_nbd_status(nbd, reply);
			if (ret) {
				nlmsg_free(reply);
				goto out;
			}
		}
	}
	nla_nest_end(reply, dev_list);
	genlmsg_end(reply, reply_head);
	ret = genlmsg_reply(reply, info);
out:
	mutex_unlock(&nbd_index_mutex);
	return ret;
}

static void nbd_connect_reply(struct genl_info *info, int index)
{
	struct sk_buff *skb;
	void *msg_head;
	int ret;

	skb = genlmsg_new(nla_total_size(sizeof(u32)), GFP_KERNEL);
	if (!skb)
		return;
	msg_head = genlmsg_put_reply(skb, info, &nbd_genl_family, 0,
				     NBD_CMD_CONNECT);
	if (!msg_head) {
		nlmsg_free(skb);
		return;
	}
	ret = nla_put_u32(skb, NBD_ATTR_INDEX, index);
	if (ret) {
		nlmsg_free(skb);
		return;
	}
	genlmsg_end(skb, msg_head);
	genlmsg_reply(skb, info);
}

static void nbd_mcast_index(int index)
{
	struct sk_buff *skb;
	void *msg_head;
	int ret;

	skb = genlmsg_new(nla_total_size(sizeof(u32)), GFP_KERNEL);
	if (!skb)
		return;
	msg_head = genlmsg_put(skb, 0, 0, &nbd_genl_family, 0,
				     NBD_CMD_LINK_DEAD);
	if (!msg_head) {
		nlmsg_free(skb);
		return;
	}
	ret = nla_put_u32(skb, NBD_ATTR_INDEX, index);
	if (ret) {
		nlmsg_free(skb);
		return;
	}
	genlmsg_end(skb, msg_head);
	genlmsg_multicast(&nbd_genl_family, skb, 0, 0, GFP_KERNEL);
}

static void nbd_dead_link_work(struct work_struct *work)
{
	struct link_dead_args *args = container_of(work, struct link_dead_args,
						   work);
	nbd_mcast_index(args->index);
	kfree(args);
}

static int __init nbd_init(void)
{
	int i;

	BUILD_BUG_ON(sizeof(struct nbd_request) != 28);

	if (max_part < 0) {
		pr_err("max_part must be >= 0\n");
		return -EINVAL;
	}

	part_shift = 0;
	if (max_part > 0) {
		part_shift = fls(max_part);

		/*
		 * Adjust max_part according to part_shift as it is exported
		 * to user space so that user can know the max number of
		 * partition kernel should be able to manage.
		 *
		 * Note that -1 is required because partition 0 is reserved
		 * for the whole disk.
		 */
		max_part = (1UL << part_shift) - 1;
	}

	if ((1UL << part_shift) > DISK_MAX_PARTS)
		return -EINVAL;

	if (nbds_max > 1UL << (MINORBITS - part_shift))
		return -EINVAL;

	if (register_blkdev(NBD_MAJOR, "nbd"))
		return -EIO;

	nbd_del_wq = alloc_workqueue("nbd-del", WQ_UNBOUND, 0);
	if (!nbd_del_wq) {
		unregister_blkdev(NBD_MAJOR, "nbd");
		return -ENOMEM;
	}

	if (genl_register_family(&nbd_genl_family)) {
		destroy_workqueue(nbd_del_wq);
		unregister_blkdev(NBD_MAJOR, "nbd");
		return -EINVAL;
	}
	nbd_dbg_init();

	for (i = 0; i < nbds_max; i++)
		nbd_dev_add(i, 1);
	return 0;
}

static int nbd_exit_cb(int id, void *ptr, void *data)
{
	struct list_head *list = (struct list_head *)data;
	struct nbd_device *nbd = ptr;

	/* Skip nbd that is being removed asynchronously */
	if (refcount_read(&nbd->refs))
		list_add_tail(&nbd->list, list);

	return 0;
}

static void __exit nbd_cleanup(void)
{
	struct nbd_device *nbd;
	LIST_HEAD(del_list);

	/*
	 * Unregister netlink interface prior to waiting
	 * for the completion of netlink commands.
	 */
	genl_unregister_family(&nbd_genl_family);

	nbd_dbg_close();

	mutex_lock(&nbd_index_mutex);
	idr_for_each(&nbd_index_idr, &nbd_exit_cb, &del_list);
	mutex_unlock(&nbd_index_mutex);

	while (!list_empty(&del_list)) {
		nbd = list_first_entry(&del_list, struct nbd_device, list);
		list_del_init(&nbd->list);
		if (refcount_read(&nbd->config_refs))
			pr_err("possibly leaking nbd_config (ref %d)\n",
					refcount_read(&nbd->config_refs));
		if (refcount_read(&nbd->refs) != 1)
			pr_err("possibly leaking a device\n");
		nbd_put(nbd);
	}

	/* Also wait for nbd_dev_remove_work() completes */
	destroy_workqueue(nbd_del_wq);

	idr_destroy(&nbd_index_idr);
	unregister_blkdev(NBD_MAJOR, "nbd");
}

module_init(nbd_init);
module_exit(nbd_cleanup);

MODULE_DESCRIPTION("Network Block Device");
MODULE_LICENSE("GPL");

module_param(nbds_max, int, 0444);
MODULE_PARM_DESC(nbds_max, "number of network block devices to initialize (default: 16)");
module_param(max_part, int, 0444);
MODULE_PARM_DESC(max_part, "number of partitions per device (default: 16)");
]

gemini-3-flash-preview

							input: 55071
							output: 43
							thoughts: 10742
						

**Analysis of the NBD Code Under a Multiple Socket Scenario**

Alright, I've dug into this code and, based on the scenario presented, here’s my assessment. We're talking about a situation where `nbd_add_socket` is called twice with the same file descriptor, creating a somewhat unusual, but not inherently broken, setup. My primary goal here is to determine whether this specific scenario introduces any use-after-free, double-free, or deadlock conditions.

First, let's break down what happens when `nbd_add_socket` is called multiple times with the same `fd`. Essentially, we end up with two `nbd_sock` objects pointing to the same underlying socket. The code seems to correctly handle the socket refcounting, as `nbd_get_socket` is called twice, incrementing the file descriptor refcount, and the subsequent `sockfd_put` calls in cleanup properly decrement it. We now have 2 `struct nbd_sock` objects pointing to the same `socket`.

When `nbd_start_device` is invoked, the `config->num_connections` and `config->live_connections` variables get incremented to 2, respectively. Two `recv_work` threads are spawned to handle each of the sockets. The code appears to handle the incrementing of `config_refs` correctly to maintain control.

Here's where the real fun begins: the two `recv_work` threads are now racing to read from the *same* socket. Naturally, protocol corruption will happen because data is not meant to be read from a single socket across multiple threads. This isn't a bug in the memory management or locking; it's a consequence of the design flaw of using a single socket with multiple reads.

The socket is eventually closed. Both `recv_work` threads, having failed to read, call `nbd_mark_nsock_dead`. Since these threads have separate `nsock` structures, `kernel_sock_shutdown` is called on each `nsock` object's socket. This part is critical. We're shutting down the *same* socket twice via two threads, and this seems to be allowed. Each thread decrements `live_connections` atomically.

Then, both threads will call `nbd_config_put`. This is where the cleanup occurs. `config_refs` are decremented and memory is freed. The `config->socks` array is checked, then `sockfd_put` is called on the `socket` and freed. This is done to both socket objects, as they now point to the same socket, meaning it is safe.

Now, for potential issues, I've considered:

*   **Use-after-free (UAF):** Nope. The refcounting on the `socket` and the handling of the `config_refs` seem solid. The threads don't attempt to access the socket after its resources have been released and the array has been deleted (thanks to synchronization via `config_refs` and the `config_lock`).

*   **Double-free:** No. While we have duplicate entries in the `config->socks` array, `sockfd_put` is called twice, but the socket is a single object with a refcount of 2.

*   **Deadlock:** This is the one that requires a more careful look. There are no deadlocks that exist in the scenario due to the thread separation using individual `nsock` objects and their associated locks. The global `config_lock` also appears to be used correctly.

The primary potential issues occur when the socket is closed while a connection is still "alive" and working. In this case, `nbd_mark_nsock_dead` is called. It uses `nsock->tx_lock` to avoid races during cleanup. The code uses per-connection and per-request locks, and the global lock is used correctly with the refcount. The `destroy_workqueue` issue is avoided through careful design considerations, avoiding a deadlock.

In summary, I see no UAF, double-free, or deadlock in this specific scenario. The issue is purely protocol corruption resulting from multiple threads reading the same socket.

requested entity does not exist

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_get_device]

map[SourceCode: SourceFile:]

gemini-3-flash-preview

							input: 66767
							output: 932
							thoughts: 2677
						

**Analysis of nbd_add_socket and Potential Concurrency Issues**

Okay, let's break this down. First, I had to ensure I understood what `nbd_dead_link_work` was *actually* doing. Turns out it's just sending a netlink message, so no immediate concerns there. My initial worry about misinterpreting the code's behavior was unfounded. I was right about that.

Next, I needed to solidify my understanding of the `nbd_config_put` to work flow. My primary concern was a potential deadlock between a `recv_work` thread and `destroy_workqueue` called via `nbd_dev_remove` triggered by `nbd_put`, which is in turn called by `nbd_config_put`. Specifically, the concern was whether a thread could be blocked on `nbd_config_put` *and* be part of the workqueue being destroyed.

After thoroughly tracing the `config_refs`, I determined that, for a static device, the reference count management avoids this deadlock because the module is locked. For a dynamic device, the code uses `NBD_DESTROY_ON_DISCONNECT`, which queues the device removal to a separate workqueue to avoid the issue. If `NBD_DESTROY_ON_DISCONNECT` is *not* set, the device reference stays at 2, so the device isn't immediately removed, and the initial `recv_work` can complete. So, the initial concern about a deadlock was unfounded.

I then considered the user's specific scenario: calling `nbd_add_socket` twice with the same file descriptor. This would create two `recv_work` threads, working on the same socket. This doesn't change the deadlock analysis, though, and as such, it can safely be presumed that there is no deadlock.

I further analyzed potential paths to `nbd_config_put`, including the `nbd_release` path, where `config_refs` can decrement to 0 as a result of closing the device. The same logic applies, with the current `recv_work` thread finishing before cleanup. Still safe.

I also checked `nbd_start_device` which calls `sock_shutdown` in the case that `kzalloc` fails. This is safe, and I could confirm no issues here.

Finally, I examined `nbd_mark_nsock_dead` to see if there could be a race condition when calling `nbd_add_socket` twice with the same `fd`. I confirmed that the behavior is correct in that the `live_connections` count ensures that the behavior is correct for a multi-connection device.

Therefore, the main conclusions are:

*   The code allows `nbd_add_socket` to be called with the same `fd` twice.
*   The `socket` refcount is incremented correctly.
*   Two `recv_work` threads are created, which could cause protocol corruption but no memory safety issues.
*   The closing of the socket results in both threads calling `nbd_mark_nsock_dead` and `nbd_config_put`.
*   Concurrent calls to `nbd_mark_nsock_dead` are handled safely.
*   `nbd_config_put` properly handles the decrement with `refcount_dec_and_mutex_lock` to allow correct cleanup behavior.
*   `sockfd_put` is called twice, correctly, since two references exist.
*   Deadlock due to `destroy_workqueue` is avoided via correct reference management or asynchronous device removal.
*   No UAF or double-free scenarios.

So, in conclusion: the described scenario causes no memory safety issues, just potentially protocol-level corruption. The code is safe.

gemini-3.1-pro-preview

							input: 232898
							output: 189
							thoughts: 62914
						

map[Question:In drivers/block/nbd.c, nbd_genl_connect parses NBD_ATTR_SOCKETS. If the user provides the SAME fd twice in the nested attributes, nbd_add_socket is called twice with the same fd. This results in config->socks[0]->sock and config->socks[1]->sock pointing to the SAME socket. Then nbd_start_device is called, which queues TWO recv_work threads. Both threads call nbd_read_reply on the SAME socket. When the socket is closed, both threads wake up, call nbd_mark_nsock_dead, and then call nbd_config_put. In nbd_config_put, sockfd_put is called twice on the same socket. Is there any bug here? Could this cause a kernel panic or deadlock?]

map[Answer:The scenario you described is indeed possible because `nbd_genl_connect` (and the legacy `NBD_SET_SOCK` ioctl) does not check if the same file descriptor (fd) is provided multiple times. This leads to several issues, although a kernel panic or deadlock is unlikely.

### Analysis of the Issues

1.  **Duplicate Reference Counting**: When `nbd_add_socket` is called, it invokes `nbd_get_socket`, which calls `sockfd_lookup(fd, &err)`. This function increments the reference count of the underlying `struct file` (and thus the socket). If the same fd is provided twice, `sockfd_lookup` is called twice, incrementing the reference count twice. Consequently, when `nbd_config_put` calls `sockfd_put` twice on the same socket pointer, it is correctly decrementing the two references obtained earlier. **This part of the logic is actually correct and will not cause a double-free or a kernel panic.**

2.  **Stream Corruption (The Real Bug)**: Each call to `nbd_add_socket` allocates a new `struct nbd_sock` structure. Each `nbd_sock` has its own `tx_lock` mutex. If two `nsock` structures point to the same socket, the intended synchronization is bypassed. Two threads can simultaneously call `sock_sendmsg` on the same socket, leading to interleaved headers and data, which corrupts the NBD protocol stream.

3.  **Protocol Errors**: As you noted, two `recv_work` threads will be spawned, both calling `nbd_read_reply` on the same socket. Since TCP is a stream, the two threads will compete for data. One thread might read part of a reply header, and the other might read the rest. Both will encounter "Wrong magic" errors or invalid cookies and call `nbd_mark_nsock_dead`.

4.  **Resource Leak**: In `nbd_start_device`, `sk_set_memalloc` is called for each connection. This function increments a global `memalloc_socks_key` (a static branch counter). However, the NBD driver never calls `sk_clear_memalloc`. This results in a leak of the static branch reference. Providing the same FD twice doubles this leak. While not a panic, it's a persistent resource leak in the networking stack.

### Potential for Panic or Deadlock

*   **Panic**: Unlikely. The kernel's socket and file reference counting handles the duplicate `sockfd_put` correctly. The protocol corruption will lead to EPROTO errors and connection teardown, but the driver's state management (using `config_refs` and `config_lock`) is robust enough to handle this without crashing.
*   **Deadlock**: Unlikely. The locks (`cmd->lock`, `nsock->tx_lock`, `config_lock`) are used consistently. Since each `nsock` has its own `tx_lock`, there is no circular dependency introduced by having duplicate sockets; they simply fail to provide the necessary mutual exclusion for the shared socket.

### Summary
There is a **bug** in the sense that the driver allows a misconfigured state that leads to data corruption on the wire and a minor resource leak (`memalloc_socks_key`). However, it is **not** a bug that would typically cause a kernel panic or a deadlock. The reference counting for the socket itself is handled correctly by the underlying VFS and socket layers.

To fix this, the NBD driver should ideally check if a socket is already assigned to the device before adding it in `nbd_add_socket`.]

gemini-3-flash-preview

You are a capable Linux kernel developer tasked with researching complex questions
about kernel source code. You will be given a concrete question, and need to provide
a concrete answer.
Use tools extensively while researching the question. Don't make assumptions,
or rely on your previous knowledge about the kernel source code, use available tools
to access the actual source code.
Use all available sources of information:
 - kernel source code
 - documentation in the Documentation dir in the source tree
 - git commits descriptions, git blame

Prefer calling several tools at the same time to save round-trips.

In drivers/block/nbd.c, nbd_genl_connect parses NBD_ATTR_SOCKETS. If the user provides the SAME fd twice in the nested attributes, nbd_add_socket is called twice with the same fd. This results in config->socks[0]->sock and config->socks[1]->sock pointing to the SAME socket. Then nbd_start_device is called, which queues TWO recv_work threads. Both threads call nbd_read_reply on the SAME socket. When the socket is closed, both threads wake up, call nbd_mark_nsock_dead, and then call nbd_config_put. In nbd_config_put, sockfd_put is called twice on the same socket. Is there any bug here? Could this cause a kernel panic or deadlock?

The scenario you described is indeed possible because `nbd_genl_connect` (and the legacy `NBD_SET_SOCK` ioctl) does not check if the same file descriptor (fd) is provided multiple times. This leads to several issues, although a kernel panic or deadlock is unlikely.

### Analysis of the Issues

1.  **Duplicate Reference Counting**: When `nbd_add_socket` is called, it invokes `nbd_get_socket`, which calls `sockfd_lookup(fd, &err)`. This function increments the reference count of the underlying `struct file` (and thus the socket). If the same fd is provided twice, `sockfd_lookup` is called twice, incrementing the reference count twice. Consequently, when `nbd_config_put` calls `sockfd_put` twice on the same socket pointer, it is correctly decrementing the two references obtained earlier. **This part of the logic is actually correct and will not cause a double-free or a kernel panic.**

2.  **Stream Corruption (The Real Bug)**: Each call to `nbd_add_socket` allocates a new `struct nbd_sock` structure. Each `nbd_sock` has its own `tx_lock` mutex. If two `nsock` structures point to the same socket, the intended synchronization is bypassed. Two threads can simultaneously call `sock_sendmsg` on the same socket, leading to interleaved headers and data, which corrupts the NBD protocol stream.

3.  **Protocol Errors**: As you noted, two `recv_work` threads will be spawned, both calling `nbd_read_reply` on the same socket. Since TCP is a stream, the two threads will compete for data. One thread might read part of a reply header, and the other might read the rest. Both will encounter "Wrong magic" errors or invalid cookies and call `nbd_mark_nsock_dead`.

4.  **Resource Leak**: In `nbd_start_device`, `sk_set_memalloc` is called for each connection. This function increments a global `memalloc_socks_key` (a static branch counter). However, the NBD driver never calls `sk_clear_memalloc`. This results in a leak of the static branch reference. Providing the same FD twice doubles this leak. While not a panic, it's a persistent resource leak in the networking stack.

### Potential for Panic or Deadlock

*   **Panic**: Unlikely. The kernel's socket and file reference counting handles the duplicate `sockfd_put` correctly. The protocol corruption will lead to EPROTO errors and connection teardown, but the driver's state management (using `config_refs` and `config_lock`) is robust enough to handle this without crashing.
*   **Deadlock**: Unlikely. The locks (`cmd->lock`, `nsock->tx_lock`, `config_lock`) are used consistently. Since each `nsock` has its own `tx_lock`, there is no circular dependency introduced by having duplicate sockets; they simply fail to provide the necessary mutual exclusion for the shared socket.

### Summary
There is a **bug** in the sense that the driver allows a misconfigured state that leads to data corruption on the wire and a minor resource leak (`memalloc_socks_key`). However, it is **not** a bug that would typically cause a kernel panic or a deadlock. The reference counting for the socket itself is handled correctly by the underlying VFS and socket layers.

To fix this, the NBD driver should ideally check if a socket is already assigned to the device before adding it in `nbd_add_socket`.

gemini-3-flash-preview

							input: 2427
							output: 87
							thoughts: 285
						

**Analyzing a Potential NBD Bug**

Okay, so the user is concerned about a possible flaw in `drivers/block/nbd.c`, specifically around how it handles file descriptors in the `NBD_ATTR_SOCKETS` attribute. I see the scenario they're outlining: it's all about what happens if we're given the same file descriptor twice. Let me think this through, step-by-step, just as they've described it.

First, `nbd_genl_connect` parses `NBD_ATTR_SOCKETS` – that makes sense. Then, the crux of the issue: if we see the same file descriptor duplicated, `nbd_add_socket` gets called twice with the identical `fd`. Now, if that's the case, we're likely ending up with `config->socks[0]->sock` and `config->socks[1]->sock` both referencing the *same* `struct socket`. Okay, I can visualize that potential for a shared resource conflict.

Next, `nbd_start_device` comes into play. It kicks off two `recv_work` threads, which are now both working with the same socket. This is where things start to get interesting. Both threads end up calling `nbd_read_reply` on this shared socket. The user is right – it feels like a race condition is brewing.

Now, here's where the potential disaster might strike: when the socket gets closed, both threads wake up. They both end up calling `nbd_mark_nsock_dead`, and then `nbd_config_put`. The real kicker: `nbd_config_put` ends up calling `sockfd_put` *twice* on the *same* socket. This is precisely the point I was hoping to see described - a double free.

So, the user is wondering if this sequence could trigger a bug, a kernel panic, or potentially a deadlock? Yes, a double free situation is a classic source of all three problems. It's a valid concern, and I need to dive into `nbd_genl_connect` and `nbd_add_socket` in `drivers/block/nbd.c` to see if the hypothesized scenario is actually feasible. I need to understand if the code *allows* this double use of the same FD, if there are any checks or safeguards against it, and if it's the expected way the system handles the socket.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_genl_connect]

map[SourceCode:2073:	static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
2074:	{
2075:		struct nbd_device *nbd;
2076:		struct nbd_config *config;
2077:		int index = -1;
2078:		int ret;
2079:		bool put_dev = false;
2080:	
2081:		if (!netlink_capable(skb, CAP_SYS_ADMIN))
2082:			return -EPERM;
2083:	
2084:		if (info->attrs[NBD_ATTR_INDEX]) {
2085:			index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
2086:	
2087:			/*
2088:			 * Too big first_minor can cause duplicate creation of
2089:			 * sysfs files/links, since index << part_shift might overflow, or
2090:			 * MKDEV() expect that the max bits of first_minor is 20.
2091:			 */
2092:			if (index < 0 || index > MINORMASK >> part_shift) {
2093:				pr_err("illegal input index %d\n", index);
2094:				return -EINVAL;
2095:			}
2096:		}
2097:		if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SOCKETS)) {
2098:			pr_err("must specify at least one socket\n");
2099:			return -EINVAL;
2100:		}
2101:		if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SIZE_BYTES)) {
2102:			pr_err("must specify a size in bytes for the device\n");
2103:			return -EINVAL;
2104:		}
2105:	again:
2106:		mutex_lock(&nbd_index_mutex);
2107:		if (index == -1) {
2108:			nbd = nbd_find_get_unused();
2109:		} else {
2110:			nbd = idr_find(&nbd_index_idr, index);
2111:			if (nbd) {
2112:				if ((test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags) &&
2113:				     test_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags)) ||
2114:				    !refcount_inc_not_zero(&nbd->refs)) {
2115:					mutex_unlock(&nbd_index_mutex);
2116:					pr_err("device at index %d is going down\n",
2117:						index);
2118:					return -EINVAL;
2119:				}
2120:			}
2121:		}
2122:		mutex_unlock(&nbd_index_mutex);
2123:	
2124:		if (!nbd) {
2125:			nbd = nbd_dev_add(index, 2);
2126:			if (IS_ERR(nbd)) {
2127:				pr_err("failed to add new device\n");
2128:				return PTR_ERR(nbd);
2129:			}
2130:		}
2131:	
2132:		mutex_lock(&nbd->config_lock);
2133:		if (refcount_read(&nbd->config_refs)) {
2134:			mutex_unlock(&nbd->config_lock);
2135:			nbd_put(nbd);
2136:			if (index == -1)
2137:				goto again;
2138:			pr_err("nbd%d already in use\n", index);
2139:			return -EBUSY;
2140:		}
2141:	
2142:		ret = nbd_alloc_and_init_config(nbd);
2143:		if (ret) {
2144:			mutex_unlock(&nbd->config_lock);
2145:			nbd_put(nbd);
2146:			pr_err("couldn't allocate config\n");
2147:			return ret;
2148:		}
2149:	
2150:		config = nbd->config;
2151:		set_bit(NBD_RT_BOUND, &config->runtime_flags);
2152:		ret = nbd_genl_size_set(info, nbd);
2153:		if (ret)
2154:			goto out;
2155:	
2156:		if (info->attrs[NBD_ATTR_TIMEOUT])
2157:			nbd_set_cmd_timeout(nbd,
2158:					    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
2159:		if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
2160:			config->dead_conn_timeout =
2161:				nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
2162:			config->dead_conn_timeout *= HZ;
2163:		}
2164:		if (info->attrs[NBD_ATTR_SERVER_FLAGS])
2165:			config->flags =
2166:				nla_get_u64(info->attrs[NBD_ATTR_SERVER_FLAGS]);
2167:		if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
2168:			u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
2169:			if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
2170:				/*
2171:				 * We have 1 ref to keep the device around, and then 1
2172:				 * ref for our current operation here, which will be
2173:				 * inherited by the config.  If we already have
2174:				 * DESTROY_ON_DISCONNECT set then we know we don't have
2175:				 * that extra ref already held so we don't need the
2176:				 * put_dev.
2177:				 */
2178:				if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
2179:						      &nbd->flags))
2180:					put_dev = true;
2181:			} else {
2182:				if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
2183:						       &nbd->flags))
2184:					refcount_inc(&nbd->refs);
2185:			}
2186:			if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
2187:				set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
2188:					&config->runtime_flags);
2189:			}
2190:		}
2191:	
2192:		if (info->attrs[NBD_ATTR_SOCKETS]) {
2193:			struct nlattr *attr;
2194:			int rem, fd;
2195:	
2196:			nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
2197:					    rem) {
2198:				struct nlattr *socks[NBD_SOCK_MAX+1];
2199:	
2200:				if (nla_type(attr) != NBD_SOCK_ITEM) {
2201:					pr_err("socks must be embedded in a SOCK_ITEM attr\n");
2202:					ret = -EINVAL;
2203:					goto out;
2204:				}
2205:				ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
2206:								  attr,
2207:								  nbd_sock_policy,
2208:								  info->extack);
2209:				if (ret != 0) {
2210:					pr_err("error processing sock list\n");
2211:					ret = -EINVAL;
2212:					goto out;
2213:				}
2214:				if (!socks[NBD_SOCK_FD])
2215:					continue;
2216:				fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
2217:				ret = nbd_add_socket(nbd, fd, true);
2218:				if (ret)
2219:					goto out;
2220:			}
2221:		}
2222:	
2223:		if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
2224:			nbd->backend = nla_strdup(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
2225:						  GFP_KERNEL);
2226:			if (!nbd->backend) {
2227:				ret = -ENOMEM;
2228:				goto out;
2229:			}
2230:		}
2231:		ret = device_create_file(disk_to_dev(nbd->disk), &backend_attr);
2232:		if (ret) {
2233:			dev_err(disk_to_dev(nbd->disk),
2234:				"device_create_file failed for backend!\n");
2235:			goto out;
2236:		}
2237:		set_bit(NBD_RT_HAS_BACKEND_FILE, &config->runtime_flags);
2238:	
2239:		ret = nbd_start_device(nbd);
2240:	out:
2241:		if (!ret) {
2242:			set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);
2243:			refcount_inc(&nbd->config_refs);
2244:			nbd_connect_reply(info, nbd->index);
2245:		}
2246:		mutex_unlock(&nbd->config_lock);
2247:	
2248:		nbd_config_put(nbd);
2249:		if (put_dev)
2250:			nbd_put(nbd);
2251:		return ret;
2252:	}
 SourceFile:drivers/block/nbd.c]

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_add_socket]

map[SourceCode:1241:	static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
1242:				  bool netlink)
1243:	{
1244:		struct nbd_config *config = nbd->config;
1245:		struct socket *sock;
1246:		struct nbd_sock **socks;
1247:		struct nbd_sock *nsock;
1248:		unsigned int memflags;
1249:		int err;
1250:	
1251:		/* Arg will be cast to int, check it to avoid overflow */
1252:		if (arg > INT_MAX)
1253:			return -EINVAL;
1254:		sock = nbd_get_socket(nbd, arg, &err);
1255:		if (!sock)
1256:			return err;
1257:	
1258:		/*
1259:		 * We need to make sure we don't get any errant requests while we're
1260:		 * reallocating the ->socks array.
1261:		 */
1262:		memflags = blk_mq_freeze_queue(nbd->disk->queue);
1263:	
1264:		if (!netlink && !nbd->task_setup &&
1265:		    !test_bit(NBD_RT_BOUND, &config->runtime_flags))
1266:			nbd->task_setup = current;
1267:	
1268:		if (!netlink &&
1269:		    (nbd->task_setup != current ||
1270:		     test_bit(NBD_RT_BOUND, &config->runtime_flags))) {
1271:			dev_err(disk_to_dev(nbd->disk),
1272:				"Device being setup by another task");
1273:			err = -EBUSY;
1274:			goto put_socket;
1275:		}
1276:	
1277:		nsock = kzalloc_obj(*nsock);
1278:		if (!nsock) {
1279:			err = -ENOMEM;
1280:			goto put_socket;
1281:		}
1282:	
1283:		socks = krealloc(config->socks, (config->num_connections + 1) *
1284:				 sizeof(struct nbd_sock *), GFP_KERNEL);
1285:		if (!socks) {
1286:			kfree(nsock);
1287:			err = -ENOMEM;
1288:			goto put_socket;
1289:		}
1290:	
1291:		config->socks = socks;
1292:	
1293:		nsock->fallback_index = -1;
1294:		nsock->dead = false;
1295:		mutex_init(&nsock->tx_lock);
1296:		nsock->sock = sock;
1297:		nsock->pending = NULL;
1298:		nsock->sent = 0;
1299:		nsock->cookie = 0;
1300:		INIT_WORK(&nsock->work, nbd_pending_cmd_work);
1301:		socks[config->num_connections++] = nsock;
1302:		atomic_inc(&config->live_connections);
1303:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1304:	
1305:		return 0;
1306:	
1307:	put_socket:
1308:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1309:		sockfd_put(sock);
1310:		return err;
1311:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 7268
							output: 43
							thoughts: 81
						

Okay, here's my interpretation of that code snippet, presented as my own thought process:

**Diving into the Socket Connection Logic**

Right, so I'm looking at `nbd_genl_connect`, and it seems to be iterating through the `NBD_ATTR_SOCKETS` attribute. Each iteration is followed by a call to `nbd_add_socket(nbd, fd, true)`. So, that's where the socket file descriptors are being added.

The critical part appears to be the next function call within `nbd_add_socket`, to `nbd_get_socket(nbd, arg, &err)`. I need to figure out how sockets are retrieved or managed. What does `nbd_get_socket` *do*? That's the core of how these sockets are acquired. Understanding this function call will likely illuminate how socket handling is set up with Netlink and the NBD driver. Time to dig in and see how it works.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_get_socket]

map[SourceCode:1213:	static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd,
1214:					     int *err)
1215:	{
1216:		struct socket *sock;
1217:	
1218:		*err = 0;
1219:		sock = sockfd_lookup(fd, err);
1220:		if (!sock)
1221:			return NULL;
1222:	
1223:		if (!sk_is_tcp(sock->sk) &&
1224:		    !sk_is_stream_unix(sock->sk)) {
1225:			dev_err(disk_to_dev(nbd->disk), "Unsupported socket: should be TCP or UNIX.\n");
1226:			*err = -EINVAL;
1227:			sockfd_put(sock);
1228:			return NULL;
1229:		}
1230:	
1231:		if (sock->ops->shutdown == sock_no_shutdown) {
1232:			dev_err(disk_to_dev(nbd->disk), "Unsupported socket: shutdown callout must be supported.\n");
1233:			*err = -EINVAL;
1234:			sockfd_put(sock);
1235:			return NULL;
1236:		}
1237:	
1238:		return sock;
1239:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 8019
							output: 43
							thoughts: 185
						

**Analyzing the Network Block Device Socket Management**

Okay, let me break down this socket management logic within the NBD driver. Essentially, `nbd_get_socket` is the core function. It calls `sockfd_lookup` to retrieve the `struct socket *` associated with a file descriptor (`fd`). If `sockfd_lookup` is successful, it hands back that socket pointer.

Now, here's where things get interesting. The text clearly states that if `nbd_add_socket` is called *twice* with the *same* `fd`, `sockfd_lookup` returns the *exact same* `struct socket *` each time. Crucially, the socket's reference count is incremented with each lookup.  So, in effect, we're reusing the underlying socket.

`nbd_add_socket` then allocates a fresh `struct nbd_sock`, sets `nsock->sock` to point to the shared `struct socket *`, and adds the new `nbd_sock` to the `config->socks` list. This means that if we pass the same `fd` twice, we will have two different `nbd_sock` structures, but both `config->socks[0]->sock` and `config->socks[1]->sock` will point to the *identical* underlying socket.

The consequence is clear: `config->num_connections` will become 2, as we’ve added two entries. Furthermore, `config->live_connections` will also be 2.

Alright, with that established, I need to understand what `nbd_start_device` does with this configuration. I'll need to analyze how it utilizes these socket structures to ascertain its behavior in the context of this potential socket sharing.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_start_device]

map[SourceCode:1471:	static int nbd_start_device(struct nbd_device *nbd)
1472:	{
1473:		struct nbd_config *config = nbd->config;
1474:		int num_connections = config->num_connections;
1475:		int error = 0, i;
1476:	
1477:		if (nbd->pid)
1478:			return -EBUSY;
1479:		if (!config->socks)
1480:			return -EINVAL;
1481:		if (num_connections > 1 &&
1482:		    !(config->flags & NBD_FLAG_CAN_MULTI_CONN)) {
1483:			dev_err(disk_to_dev(nbd->disk), "server does not support multiple connections per device.\n");
1484:			return -EINVAL;
1485:		}
1486:	
1487:	retry:
1488:		mutex_unlock(&nbd->config_lock);
1489:		blk_mq_update_nr_hw_queues(&nbd->tag_set, num_connections);
1490:		mutex_lock(&nbd->config_lock);
1491:	
1492:		/* if another code path updated nr_hw_queues, retry until succeed */
1493:		if (num_connections != config->num_connections) {
1494:			num_connections = config->num_connections;
1495:			goto retry;
1496:		}
1497:	
1498:		nbd->pid = task_pid_nr(current);
1499:	
1500:		nbd_parse_flags(nbd);
1501:	
1502:		error = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
1503:		if (error) {
1504:			dev_err(disk_to_dev(nbd->disk), "device_create_file failed for pid!\n");
1505:			return error;
1506:		}
1507:		set_bit(NBD_RT_HAS_PID_FILE, &config->runtime_flags);
1508:	
1509:		nbd_dev_dbg_init(nbd);
1510:		for (i = 0; i < num_connections; i++) {
1511:			struct recv_thread_args *args;
1512:	
1513:			args = kzalloc_obj(*args);
1514:			if (!args) {
1515:				sock_shutdown(nbd);
1516:				/*
1517:				 * If num_connections is m (2 < m),
1518:				 * and NO.1 ~ NO.n(1 < n < m) kzallocs are successful.
1519:				 * But NO.(n + 1) failed. We still have n recv threads.
1520:				 * So, add flush_workqueue here to prevent recv threads
1521:				 * dropping the last config_refs and trying to destroy
1522:				 * the workqueue from inside the workqueue.
1523:				 */
1524:				if (i)
1525:					flush_workqueue(nbd->recv_workq);
1526:				return -ENOMEM;
1527:			}
1528:			sk_set_memalloc(config->socks[i]->sock->sk);
1529:			if (nbd->tag_set.timeout)
1530:				config->socks[i]->sock->sk->sk_sndtimeo =
1531:					nbd->tag_set.timeout;
1532:			atomic_inc(&config->recv_threads);
1533:			refcount_inc(&nbd->config_refs);
1534:			INIT_WORK(&args->work, recv_work);
1535:			args->nbd = nbd;
1536:			args->nsock = config->socks[i];
1537:			args->index = i;
1538:			queue_work(nbd->recv_workq, &args->work);
1539:		}
1540:		return nbd_set_size(nbd, config->bytesize, nbd_blksize(config));
1541:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 9804
							output: 40
							thoughts: 73
						

**Analyzing the nbd_start_device Function**

Okay, so `nbd_start_device` seems to be the crucial starting point here. I see it's iterating through `num_connections` and queuing up a `recv_work` task for each connection. My initial thought is to look at how these are handled and if there are any race conditions that I might spot.

The interesting part, and what likely prompted this, is that there might be a scenario where `config->socks[0]->sock == config->socks[1]->sock`. If that's true, then we'll have two separate threads, each calling `recv_work`, both using the *same* socket. This certainly warrants a closer look. I need to understand what `recv_work` is doing and how it's interacting with the shared socket. This could lead to all sorts of concurrency issues - data corruption, missed events, or even deadlocks. Let's dig into the `recv_work` function and see what's happening.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:recv_work]

map[SourceCode: 970:	static void recv_work(struct work_struct *work)
 971:	{
 972:		struct recv_thread_args *args = container_of(work,
 973:							     struct recv_thread_args,
 974:							     work);
 975:		struct nbd_device *nbd = args->nbd;
 976:		struct nbd_config *config = nbd->config;
 977:		struct request_queue *q = nbd->disk->queue;
 978:		struct nbd_sock *nsock = args->nsock;
 979:		struct nbd_cmd *cmd;
 980:		struct request *rq;
 981:	
 982:		while (1) {
 983:			struct nbd_reply reply;
 984:	
 985:			if (nbd_read_reply(nbd, nsock->sock, &reply))
 986:				break;
 987:	
 988:			/*
 989:			 * Grab .q_usage_counter so request pool won't go away, then no
 990:			 * request use-after-free is possible during nbd_handle_reply().
 991:			 * If queue is frozen, there won't be any inflight requests, we
 992:			 * needn't to handle the incoming garbage message.
 993:			 */
 994:			if (!percpu_ref_tryget(&q->q_usage_counter)) {
 995:				dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n",
 996:					__func__);
 997:				break;
 998:			}
 999:	
1000:			cmd = nbd_handle_reply(nbd, args->index, &reply);
1001:			if (IS_ERR(cmd)) {
1002:				percpu_ref_put(&q->q_usage_counter);
1003:				break;
1004:			}
1005:	
1006:			rq = blk_mq_rq_from_pdu(cmd);
1007:			if (likely(!blk_should_fake_timeout(rq->q))) {
1008:				bool complete;
1009:	
1010:				mutex_lock(&cmd->lock);
1011:				complete = __test_and_clear_bit(NBD_CMD_INFLIGHT,
1012:								&cmd->flags);
1013:				mutex_unlock(&cmd->lock);
1014:				if (complete)
1015:					blk_mq_complete_request(rq);
1016:			}
1017:			percpu_ref_put(&q->q_usage_counter);
1018:		}
1019:	
1020:		mutex_lock(&nsock->tx_lock);
1021:		nbd_mark_nsock_dead(nbd, nsock, 1);
1022:		mutex_unlock(&nsock->tx_lock);
1023:	
1024:		atomic_dec(&config->recv_threads);
1025:		wake_up(&config->recv_wq);
1026:		nbd_config_put(nbd);
1027:		kfree(args);
1028:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 11068
							output: 46
							thoughts: 155
						

**Analyzing Potential Concurrency Issues in the Network Block Device (NBD) Implementation**

Okay, so I'm looking at this `recv_work` function, and it's calling `nbd_read_reply` – which seems straightforward enough. But, wait a minute... I see a potential race condition here. If two threads somehow end up calling `nbd_read_reply` on the same socket concurrently, then we've got a problem. Both threads are going to attempt to read from the same socket simultaneously. That's a recipe for disaster! Data corruption is highly probable, or at the very least, unpredictable behavior due to interleaved reads from a single reply. This is bad.

`nbd_read_reply`, itself, calls `sock_xmit` – so it's directly involved in the socket interaction. This further highlights the importance of making sure only one thread deals with the socket at any time.

Now, when the main loop breaks – say, because the socket gets closed – it calls `nbd_mark_nsock_dead`, and then `nbd_config_put`. Makes sense; cleanup is crucial. Let's delve into this `nbd_mark_nsock_dead` function and understand how it handles the socket closure. We're going to need to look at how this is being handled in order to determine what thread safety mechanisms (if any) are in place. This will be key to understanding if this entire sequence is thread-safe.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_mark_nsock_dead]

map[SourceCode: 305:	static void nbd_mark_nsock_dead(struct nbd_device *nbd, struct nbd_sock *nsock,
 306:					int notify)
 307:	{
 308:		if (!nsock->dead && notify && !nbd_disconnected(nbd->config)) {
 309:			struct link_dead_args *args;
 310:			args = kmalloc_obj(struct link_dead_args, GFP_NOIO);
 311:			if (args) {
 312:				INIT_WORK(&args->work, nbd_dead_link_work);
 313:				args->index = nbd->index;
 314:				queue_work(system_percpu_wq, &args->work);
 315:			}
 316:		}
 317:		if (!nsock->dead) {
 318:			kernel_sock_shutdown(nsock->sock, SHUT_RDWR);
 319:			if (atomic_dec_return(&nbd->config->live_connections) == 0) {
 320:				if (test_and_clear_bit(NBD_RT_DISCONNECT_REQUESTED,
 321:						       &nbd->config->runtime_flags)) {
 322:					set_bit(NBD_RT_DISCONNECTED,
 323:						&nbd->config->runtime_flags);
 324:					dev_info(nbd_to_dev(nbd),
 325:						"Disconnected due to user request.\n");
 326:				}
 327:			}
 328:		}
 329:		nsock->dead = true;
 330:		nsock->pending = NULL;
 331:		nsock->sent = 0;
 332:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 12093
							output: 43
							thoughts: 179
						

**Analyzing Socket Shutdown Behavior in NBD**

Okay, so I'm looking at this `nbd_mark_nsock_dead` function and how it interacts with socket shutdown. My concern here is the potential for double-shutdowns on the same socket, but it seems there's a nuanced process happening.

Essentially, it checks if `!nsock->dead` before shutting down the socket using `kernel_sock_shutdown(nsock->sock, SHUT_RDWR)`. The critical thing to remember is that we *can* have multiple `nbd_sock` structures pointing to the very same underlying socket. They're all initially marked `dead = false`.

Now, imagine we have two `recv_work` threads. The first thread calls `nbd_mark_nsock_dead` and updates the relevant `nsock` structure to `dead = true`.  This is expected behavior, that thread knows its socket is no longer viable. The key is what the *second* thread does. Because `nbd_add_socket` allocates a new `nbd_sock` for *each* socket (even if they point to the same socket), this second thread still has *its own* `nsock` structure, and that copy hasn't been set to `dead = true` yet.

So, both threads end up calling `kernel_sock_shutdown` on the *same* socket, one after the other. The fact that the socket is being shut down multiple times concerns me from a resource-management perspective, but I'm reasonably confident that `kernel_sock_shutdown` is designed to handle this gracefully. At the very least it's supposed to be safe. So, it appears that this double-shutdown behavior is not a critical error, but potentially something to be optimized.

Now, let's turn our attention to the `nbd_config_put` function and see what's going on there.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_config_put]

map[SourceCode:1432:	static void nbd_config_put(struct nbd_device *nbd)
1433:	{
1434:		if (refcount_dec_and_mutex_lock(&nbd->config_refs,
1435:						&nbd->config_lock)) {
1436:			struct nbd_config *config = nbd->config;
1437:			nbd_dev_dbg_close(nbd);
1438:			invalidate_disk(nbd->disk);
1439:			if (nbd->config->bytesize)
1440:				kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
1441:			if (test_and_clear_bit(NBD_RT_HAS_PID_FILE,
1442:					       &config->runtime_flags))
1443:				device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
1444:			nbd->pid = 0;
1445:			if (test_and_clear_bit(NBD_RT_HAS_BACKEND_FILE,
1446:					       &config->runtime_flags)) {
1447:				device_remove_file(disk_to_dev(nbd->disk), &backend_attr);
1448:				kfree(nbd->backend);
1449:				nbd->backend = NULL;
1450:			}
1451:			nbd_clear_sock(nbd);
1452:			if (config->num_connections) {
1453:				int i;
1454:				for (i = 0; i < config->num_connections; i++) {
1455:					sockfd_put(config->socks[i]->sock);
1456:					kfree(config->socks[i]);
1457:				}
1458:				kfree(config->socks);
1459:			}
1460:			kfree(nbd->config);
1461:			nbd->config = NULL;
1462:	
1463:			nbd->tag_set.timeout = 0;
1464:	
1465:			mutex_unlock(&nbd->config_lock);
1466:			nbd_put(nbd);
1467:			module_put(THIS_MODULE);
1468:		}
1469:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 13393
							output: 43
							thoughts: 883
						

**Analyzing the NBD Configuration Reference Counting and Socket Handling**

Okay, let's break this down. It seems we have a potential issue related to how the Network Block Device (NBD) driver handles references to its configuration and, more importantly, its sockets.

Initially, `nbd_alloc_and_init_config` sets `nbd->config_refs` to 1. Then, `nbd_start_device` increments this count for each connection established. From the code, it looks like `nbd_start_device` increments it twice, for each `recv_work` thread. Additionally, `nbd_genl_connect` also holds a reference.

So, if we have two connections, `config_refs` starts at 1, goes to 3 (due to `nbd_start_device`), and then back down to 2 after `nbd_genl_connect` releases its reference. Each `recv_work` thread subsequently calls `nbd_config_put`, decrementing `config_refs`. The first one to finish drops it to 1, and the second one should decrement it to zero.

When `config_refs` hits zero, the cleanup block executes. This block iterates through `config->socks`, calling `sockfd_put` on each socket.  Here's where it gets interesting:  If, as the user described, `config->socks[0]->sock` and `config->socks[1]->sock` point to the same socket, then `sockfd_put` is called twice on the *same* socket.

But wait. We've seen `nbd_add_socket` uses `nbd_get_socket`, which calls `sockfd_lookup`, and that's the key.  `sockfd_lookup` calls `fget(fd)`, which increments the reference count on the file. Thus it should return a struct file with an incremented reference count. `sockfd_put` calls `fput(sock->file)`. So, the socket is correctly reference counted, right?

So, if `sockfd_lookup(fd)` is called twice for the *same* file descriptor, we correctly get *two* references to the same file (and therefore the same socket). Consequently, calling `sockfd_put` twice is the right thing to do to release those two references. Okay, the reference counting on the socket itself is fine, it's the correct implementation.

However, the user says there's a different problem.  Both `config->socks[0]->sock` and `config->socks[1]->sock` *do* point to the *same* socket.  `nbd_start_device` then queues two `recv_work` threads. And here's the kicker: both of these threads are calling `nbd_read_reply` on the *same* socket simultaneously.  Now we have a concurrency issue. `nbd_read_reply` calls `sock_xmit` and we have *two* threads reading from a single socket without any synchronization. This could lead to data corruption or other nasty issues. This is a critical problem!

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_read_reply]

map[SourceCode: 845:	static int nbd_read_reply(struct nbd_device *nbd, struct socket *sock,
 846:				  struct nbd_reply *reply)
 847:	{
 848:		struct kvec iov = {.iov_base = reply, .iov_len = sizeof(*reply)};
 849:		struct iov_iter to;
 850:		int result;
 851:	
 852:		reply->magic = 0;
 853:		iov_iter_kvec(&to, ITER_DEST, &iov, 1, sizeof(*reply));
 854:		result = __sock_xmit(nbd, sock, 0, &to, MSG_WAITALL, NULL);
 855:		if (result < 0) {
 856:			if (!nbd_disconnected(nbd->config))
 857:				dev_err(disk_to_dev(nbd->disk),
 858:					"Receive control failed (result %d)\n", result);
 859:			return result;
 860:		}
 861:	
 862:		if (ntohl(reply->magic) != NBD_REPLY_MAGIC) {
 863:			dev_err(disk_to_dev(nbd->disk), "Wrong magic (0x%lx)\n",
 864:					(unsigned long)ntohl(reply->magic));
 865:			return -EPROTO;
 866:		}
 867:	
 868:		return 0;
 869:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 15432
							output: 42
							thoughts: 8
						

Okay, here's my summary, taking on the persona you've described:

**Delving into `__sock_xmit`**

Alright, let's break this down. When I see `__sock_xmit`, my mind immediately jumps to the kernel's network stack. It's a fundamental function, isn't it? This is where the magic of sending data out onto the wire *actually* happens. I'm thinking about its role, the low-level mechanics it encapsulates. I'm imagining the data buffers, the sk_buffs, lining up, ready to be pushed through the network interface.

I'm considering the complexities: the interactions with hardware, the driver calls, the checksum calculations...all the details needed to actually get a packet onto the physical medium. It's a critical point in the data flow, a bottleneck potentially, and understanding the nuances of how `__sock_xmit` performs is absolutely key to optimization. I need to think about the various scenarios it has to handle, the different protocols, the congestion control mechanisms at play.

This function is a performance-critical area; any inefficiencies here would be multiplied across the system. It's time to dig deep. I want to know about how the data is prepared, how it's handled by the device driver, and what error conditions are accounted for. The interaction with the hardware, the interrupt handling – that's where I need to focus my attention. It's all about ensuring efficient and reliable data transmission.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:__sock_xmit]

map[SourceCode: 551:	static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
 552:			       struct iov_iter *iter, int msg_flags, int *sent)
 553:	{
 554:		int result;
 555:		struct msghdr msg = {} ;
 556:		unsigned int noreclaim_flag;
 557:	
 558:		if (unlikely(!sock)) {
 559:			dev_err_ratelimited(disk_to_dev(nbd->disk),
 560:				"Attempted %s on closed socket in sock_xmit\n",
 561:				(send ? "send" : "recv"));
 562:			return -EINVAL;
 563:		}
 564:	
 565:		msg.msg_iter = *iter;
 566:	
 567:		noreclaim_flag = memalloc_noreclaim_save();
 568:	
 569:		scoped_with_kernel_creds() {
 570:			do {
 571:				sock->sk->sk_allocation = GFP_NOIO | __GFP_MEMALLOC;
 572:				sock->sk->sk_use_task_frag = false;
 573:				msg.msg_flags = msg_flags | MSG_NOSIGNAL;
 574:	
 575:				if (send)
 576:					result = sock_sendmsg(sock, &msg);
 577:				else
 578:					result = sock_recvmsg(sock, &msg, msg.msg_flags);
 579:	
 580:				if (result <= 0) {
 581:					if (result == 0)
 582:						result = -EPIPE; /* short read */
 583:					break;
 584:				}
 585:				if (sent)
 586:					*sent += result;
 587:			} while (msg_data_left(&msg));
 588:		}
 589:	
 590:		memalloc_noreclaim_restore(noreclaim_flag);
 591:	
 592:		return result;
 593:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 16437
							output: 43
							thoughts: 179
						

**Analyzing Potential Data Corruption in NBD Stream**

Okay, so I'm looking at this situation where `__sock_xmit` is calling `sock_recvmsg`. Right off the bat, my Spidey-Sense is tingling because I know that if two threads hit `sock_recvmsg` on the *same* TCP socket concurrently, we've got a potential race condition. They'll be fighting for the data stream, and that's just asking for trouble. One thread grabs the first few bytes, the other grabs the next chunk... it's a recipe for "Wrong magic" errors, or worse, outright data corruption.

But the question isn't just about data corruption in general, it's more specific: is this a *bug* that could lead to a kernel panic or deadlock? Data corruption in the NBD stream, I'm thinking, is definitely a bug, but maybe it just results in the connection being dropped. That's *bad*, but not the worst-case scenario.

Ah, wait a second... there's the `reply.cookie` used in `nbd_handle_reply` to associate with the correct command. If the stream is corrupted, that cookie could be garbage. If that's the case, `nbd_handle_reply` could be getting completely confused. That could lead to all sorts of unpredictable behavior.

I need to dig into `nbd_handle_reply` itself to be sure. Let's see how that works.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_handle_reply]

map[SourceCode: 871:	/* NULL returned = something went wrong, inform userspace */
 872:	static struct nbd_cmd *nbd_handle_reply(struct nbd_device *nbd, int index,
 873:						struct nbd_reply *reply)
 874:	{
 875:		int result;
 876:		struct nbd_cmd *cmd;
 877:		struct request *req = NULL;
 878:		u64 handle;
 879:		u16 hwq;
 880:		u32 tag;
 881:		int ret = 0;
 882:	
 883:		handle = be64_to_cpu(reply->cookie);
 884:		tag = nbd_handle_to_tag(handle);
 885:		hwq = blk_mq_unique_tag_to_hwq(tag);
 886:		if (hwq < nbd->tag_set.nr_hw_queues)
 887:			req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq],
 888:					       blk_mq_unique_tag_to_tag(tag));
 889:		if (!req || !blk_mq_request_started(req)) {
 890:			dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%d) %p\n",
 891:				tag, req);
 892:			return ERR_PTR(-ENOENT);
 893:		}
 894:		trace_nbd_header_received(req, handle);
 895:		cmd = blk_mq_rq_to_pdu(req);
 896:	
 897:		mutex_lock(&cmd->lock);
 898:		if (!test_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
 899:			dev_err(disk_to_dev(nbd->disk), "Suspicious reply %d (status %u flags %lu)",
 900:				tag, cmd->status, cmd->flags);
 901:			ret = -ENOENT;
 902:			goto out;
 903:		}
 904:		if (cmd->index != index) {
 905:			dev_err(disk_to_dev(nbd->disk), "Unexpected reply %d from different sock %d (expected %d)",
 906:				tag, index, cmd->index);
 907:			ret = -ENOENT;
 908:			goto out;
 909:		}
 910:		if (cmd->cmd_cookie != nbd_handle_to_cookie(handle)) {
 911:			dev_err(disk_to_dev(nbd->disk), "Double reply on req %p, cmd_cookie %u, handle cookie %u\n",
 912:				req, cmd->cmd_cookie, nbd_handle_to_cookie(handle));
 913:			ret = -ENOENT;
 914:			goto out;
 915:		}
 916:		if (cmd->status != BLK_STS_OK) {
 917:			dev_err(disk_to_dev(nbd->disk), "Command already handled %p\n",
 918:				req);
 919:			ret = -ENOENT;
 920:			goto out;
 921:		}
 922:		if (test_bit(NBD_CMD_REQUEUED, &cmd->flags)) {
 923:			dev_err(disk_to_dev(nbd->disk), "Raced with timeout on req %p\n",
 924:				req);
 925:			ret = -ENOENT;
 926:			goto out;
 927:		}
 928:		if (ntohl(reply->error)) {
 929:			dev_err(disk_to_dev(nbd->disk), "Other side returned error (%d)\n",
 930:				ntohl(reply->error));
 931:			cmd->status = BLK_STS_IOERR;
 932:			goto out;
 933:		}
 934:	
 935:		dev_dbg(nbd_to_dev(nbd), "request %p: got reply\n", req);
 936:		if (rq_data_dir(req) != WRITE) {
 937:			struct req_iterator iter;
 938:			struct bio_vec bvec;
 939:			struct iov_iter to;
 940:	
 941:			rq_for_each_segment(bvec, req, iter) {
 942:				iov_iter_bvec(&to, ITER_DEST, &bvec, 1, bvec.bv_len);
 943:				result = sock_xmit(nbd, index, 0, &to, MSG_WAITALL, NULL);
 944:				if (result < 0) {
 945:					dev_err(disk_to_dev(nbd->disk), "Receive data failed (result %d)\n",
 946:						result);
 947:					/*
 948:					 * If we've disconnected, we need to make sure we
 949:					 * complete this request, otherwise error out
 950:					 * and let the timeout stuff handle resubmitting
 951:					 * this request onto another connection.
 952:					 */
 953:					if (nbd_disconnected(nbd->config)) {
 954:						cmd->status = BLK_STS_IOERR;
 955:						goto out;
 956:					}
 957:					ret = -EIO;
 958:					goto out;
 959:				}
 960:				dev_dbg(nbd_to_dev(nbd), "request %p: got %d bytes data\n",
 961:					req, bvec.bv_len);
 962:			}
 963:		}
 964:	out:
 965:		trace_nbd_payload_received(req, handle);
 966:		mutex_unlock(&cmd->lock);
 967:		return ret ? ERR_PTR(ret) : cmd;
 968:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 18674
							output: 43
							thoughts: 1628
						

**Analyzing Potential Concurrency Issues with Shared Sockets in the NBD Driver**

Okay, let's break this down. My initial concern was about two threads reading from the same socket. This is a recipe for disaster in the NBD protocol, as the `sock_xmit` calls (through `nbd_read_reply` or directly in `nbd_handle_reply`) would definitely lead to interleaved data. This would lead to protocol errors and incorrect behavior. The question isn't whether it *will* go wrong, but how badly it can fail.

First, the user pointed out `nbd_config_put` being called with the same `sockfd` twice. After reviewing, that's not a bug. `nbd_add_socket` uses `nbd_get_socket`, which calls `sockfd_lookup`. `sockfd_lookup` increments the socket's refcount. If the file descriptor (FD) is added twice, the refcount gets incremented twice. Then, `nbd_config_put` properly decrements the refcount twice for the same socket in `config->socks[i]->sock` because it's called twice in `nbd_config_put`. This is correct and doesn't leak references.

Next, I looked at `nbd_mark_nsock_dead` again. If we have multiple `nsock` structures representing the same socket, and the first thread calls `nbd_mark_nsock_dead`, it correctly decrements `config->live_connections`. The second thread then *also* calls it, decrementing it to 0. This seems reasonable, too.

Now, `nbd_read_reply`.  The critical issue here is that multiple threads reading the same socket could easily have one get a protocol error (`Wrong magic`, etc.) and call `nbd_mark_nsock_dead`, which then calls `kernel_sock_shutdown`. This shutdown would cause the other thread's `sock_recvmsg` to return an error, and both threads would then proceed to call `nbd_config_put`.

The potential race in `nbd_config_put` is prevented by `refcount_dec_and_mutex_lock`. Only one thread will enter the cleanup block after the refcount hits zero, ensuring safe cleanup with `sockfd_put` and `kfree` of the `config->socks` array.

A key vector for attack: what if the user sends the same FD multiple times in `NBD_ATTR_SOCKETS`?  Reviewing `nbd_genl_connect`, I confirm that the code iterates through `NBD_ATTR_SOCKETS` and uses `nbd_add_socket` for each FD. No check is present in `nbd_add_socket` for duplicate FDs!

Looking at `nbd_add_socket` again confirmed my fears.  It blindly adds each socket to the `config->socks` array. If the user gives it the same FD twice, *it will add the same socket twice*.

So, if two `recv_work` threads end up reading from the same socket, the TCP stream is essentially shared. NBD relies on distinct reply sequences. One thread might read the first part of a reply, the other thread the second. Both will encounter invalid magic or cookies and both will call `nbd_mark_nsock_dead`. This will shut down the socket, cause the `recv_work` threads to exit, and trigger `nbd_config_put`. Eventually, the cleanup will happen.

Is there a deadlock risk? `nbd_mark_nsock_dead` doesn't take the same mutex as the `recv_work` threads.  Each `nsock` (even if it points to the same underlying socket) has a different `tx_lock`. So there is no deadlock here.

The `kernel_sock_shutdown` call might have locking requirements, but those don't seem to overlap with our NBD locks, which is reassuring.

Finally, `nbd_start_device` calls `blk_mq_update_nr_hw_queues`. If `num_connections` is 2, it sets up two hardware queues. `nbd_queue_rq` would then use `config->socks[hwq]`.

So, the fundamental issue is that sharing a single socket between multiple threads on the receive side breaks NBD's assumptions about sequential replies and will lead to an unrecoverable protocol error.  The lack of duplicate FD checks means a user *can* trigger this invalid configuration, leading to chaos.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_queue_rq]

map[SourceCode:1184:	static blk_status_t nbd_queue_rq(struct blk_mq_hw_ctx *hctx,
1185:				const struct blk_mq_queue_data *bd)
1186:	{
1187:		struct nbd_cmd *cmd = blk_mq_rq_to_pdu(bd->rq);
1188:		blk_status_t ret;
1189:	
1190:		/*
1191:		 * Since we look at the bio's to send the request over the network we
1192:		 * need to make sure the completion work doesn't mark this request done
1193:		 * before we are done doing our send.  This keeps us from dereferencing
1194:		 * freed data if we have particularly fast completions (ie we get the
1195:		 * completion before we exit sock_xmit on the last bvec) or in the case
1196:		 * that the server is misbehaving (or there was an error) before we're
1197:		 * done sending everything over the wire.
1198:		 */
1199:		mutex_lock(&cmd->lock);
1200:		clear_bit(NBD_CMD_REQUEUED, &cmd->flags);
1201:	
1202:		/* We can be called directly from the user space process, which means we
1203:		 * could possibly have signals pending so our sendmsg will fail.  In
1204:		 * this case we need to return that we are busy, otherwise error out as
1205:		 * appropriate.
1206:		 */
1207:		ret = nbd_handle_cmd(cmd, hctx->queue_num);
1208:		mutex_unlock(&cmd->lock);
1209:	
1210:		return ret;
1211:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 21842
							output: 43
							thoughts: 9
						

Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:

**Analyzing the `nbd_handle_cmd` Function**

Alright, let's dissect this `nbd_handle_cmd` function. My initial thoughts center on its crucial role within the Network Block Device (NBD) architecture. It’s the linchpin, the primary command processing entry point within the NBD server. I'm immediately mentally cataloging its likely responsibilities: receiving commands from the client, parsing the command's payload, validating parameters, dispatching the request to the appropriate back-end storage, handling potential errors, and finally, crafting and transmitting the response back to the NBD client.

I'm starting to imagine the typical workflow: First, a raw buffer arrives, containing a command identifier, request details (like offset, length, flags), and potentially data for writes. `nbd_handle_cmd` likely begins by dereferencing some global or per-connection data structure, likely containing metadata, state, and perhaps, the file descriptor for the underlying storage.

My experience tells me this function likely employs a switch statement or a similar construct to dispatch based on the command code: READ, WRITE, DISCONNECT, FLUSH, TRIM, and maybe some vendor-specific commands. Each case within the switch likely has a specialized handler. Each of these cases will require thorough error checking, for example, confirming that the requested offset and length are valid for the underlying storage, preventing buffer overflows, and avoiding race conditions.

I'm already anticipating areas where performance optimization might be critical. Given that it is a block device, I'll need to think about how it handles multi-block requests, as well as the importance of efficient memory allocation and deallocation to minimise latency. I'm also considering how it interacts with the underlying storage layer, and how it might be designed for asynchronous I/O to improve throughput.

Overall, my expectation is that `nbd_handle_cmd` represents the beating heart of the NBD server's command processing engine, and I'm eager to dive deeper into its implementation to understand its nuances and potential bottlenecks.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_handle_cmd]

map[SourceCode:1117:	static blk_status_t nbd_handle_cmd(struct nbd_cmd *cmd, int index)
1118:	{
1119:		struct request *req = blk_mq_rq_from_pdu(cmd);
1120:		struct nbd_device *nbd = cmd->nbd;
1121:		struct nbd_config *config;
1122:		struct nbd_sock *nsock;
1123:		blk_status_t ret;
1124:	
1125:		lockdep_assert_held(&cmd->lock);
1126:	
1127:		config = nbd_get_config_unlocked(nbd);
1128:		if (!config) {
1129:			dev_err_ratelimited(disk_to_dev(nbd->disk),
1130:					    "Socks array is empty\n");
1131:			return BLK_STS_IOERR;
1132:		}
1133:	
1134:		if (index >= config->num_connections) {
1135:			dev_err_ratelimited(disk_to_dev(nbd->disk),
1136:					    "Attempted send on invalid socket\n");
1137:			nbd_config_put(nbd);
1138:			return BLK_STS_IOERR;
1139:		}
1140:		cmd->status = BLK_STS_OK;
1141:	again:
1142:		nsock = config->socks[index];
1143:		mutex_lock(&nsock->tx_lock);
1144:		if (nsock->dead) {
1145:			int old_index = index;
1146:			index = find_fallback(nbd, index);
1147:			mutex_unlock(&nsock->tx_lock);
1148:			if (index < 0) {
1149:				if (wait_for_reconnect(nbd)) {
1150:					index = old_index;
1151:					goto again;
1152:				}
1153:				/* All the sockets should already be down at this point,
1154:				 * we just want to make sure that DISCONNECTED is set so
1155:				 * any requests that come in that were queue'ed waiting
1156:				 * for the reconnect timer don't trigger the timer again
1157:				 * and instead just error out.
1158:				 */
1159:				sock_shutdown(nbd);
1160:				nbd_config_put(nbd);
1161:				return BLK_STS_IOERR;
1162:			}
1163:			goto again;
1164:		}
1165:	
1166:		/* Handle the case that we have a pending request that was partially
1167:		 * transmitted that _has_ to be serviced first.  We need to call requeue
1168:		 * here so that it gets put _after_ the request that is already on the
1169:		 * dispatch list.
1170:		 */
1171:		blk_mq_start_request(req);
1172:		if (unlikely(nsock->pending && nsock->pending != req)) {
1173:			nbd_requeue_cmd(cmd);
1174:			ret = BLK_STS_OK;
1175:			goto out;
1176:		}
1177:		ret = nbd_send_cmd(nbd, cmd, index);
1178:	out:
1179:		mutex_unlock(&nsock->tx_lock);
1180:		nbd_config_put(nbd);
1181:		return ret;
1182:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 23395
							output: 43
							thoughts: 1005
						

**Analyzing the NBD Driver's Concurrency Issues**

Okay, let's break this down. My initial thought is that `nbd_handle_cmd` grabs `nsock->tx_lock`. The crux of the problem is that if we have two `nsock` structures associated with the *same* underlying `sock`, they'll have *different* `tx_lock` mutexes. This is a red flag. It means two threads could be simultaneously invoking `nbd_send_cmd` on the identical socket, which is a recipe for disaster and data corruption in the outgoing NBD stream.

Wait, I need to trace this... `nbd_send_cmd` calls `sock_xmit`, and `sock_xmit` in turn calls `__sock_xmit`. Right. And `__sock_xmit` ultimately calls `sock_sendmsg` on the socket. For a TCP socket, `sock_sendmsg` can handle concurrent calls from multiple threads without crashing, but it certainly doesn't guarantee atomic transmission of the entire message. NBD sends the header and then the data separately. If threads are intermixed, the headers and data will definitely become interleaved. This would result in protocol errors and connection drops.

So, the root cause is that `nbd_genl_connect` isn't checking for duplicate file descriptors. This leads to multiple `nsock` instances all pointing to the *same* `socket`, each with its own `tx_lock`. We're circumventing the intended synchronization, as the design seems to assume only one `tx_lock` per socket.

Now, does this lead to a panic or deadlock? Probably not a *kernel* panic or deadlock in the NBD driver itself. However, it *will* introduce protocol errors and likely result in connection drops, as corrupted NBD data will be transmitted.

I remember now that the user's description of `sockfd_put` being called twice on the same socket is actually the correct behavior given that `sockfd_lookup` was also called twice on the same socket.

Let's revisit `nbd_add_socket`: It creates a *new* `nsock` structure with `kzalloc_obj` every time it's called. This confirms my initial understanding.

This raises another question: can the user supply the same FD to two *different* NBD devices? Yes, the kernel allows that, but it's typically not the intended behavior.

The user's question about panics and deadlocks made me double check. If `nbd_read_reply` gets garbage, it will likely return an error. When it returns an error, `recv_work` exits and calls `nbd_mark_nsock_dead`. `nbd_mark_nsock_dead` shuts down the socket. The other thread will also notice this and exit. At the end `nbd_config_put` will handle the cleanup.

One thing to verify is `nbd_mark_nsock_dead` in conjunction with `live_connections`: If `live_connections` starts at 2 and both threads call the decrement, it goes to zero. It seems correct.

I have to check `nbd_clear_sock` as well. In `nbd_config_put`. I will need to look at `nbd_clear_sock`.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_clear_sock]

map[SourceCode:1425:	static void nbd_clear_sock(struct nbd_device *nbd)
1426:	{
1427:		sock_shutdown(nbd);
1428:		nbd_clear_que(nbd);
1429:		nbd->task_setup = NULL;
1430:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 25277
							output: 40
							thoughts: 6
						

Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:

**Delving into `sock_shutdown`**

Alright, so we're talking about `sock_shutdown`. My immediate thought is, "Ah, yes, the finer points of graceful socket closure." I'm mentally parsing the implications. This isn't just a simple `close()` call, we're talking about a more controlled, deliberate shutdown. I'm already anticipating the nuances of TCP's connection termination handshake, the states involved, and the implications for data transmission.

Specifically, I'm considering the potential scenarios. Will I be shutting down for read, write, or both? `SHUT_RD`, `SHUT_WR`, or `SHUT_RDWR` – each has its own behavioral fingerprint and consequences, and I'm instantly weighing them. The choice dictates whether I'm signaling that I'm done *receiving*, done *sending*, or done with the whole communication stream. I'm practically diagramming the TCP state machine in my head, visualizing the FIN and ACK segments.

My brain is now mapping this onto the practicalities of my application. What's the protocol? Is it a request-response pattern, a streaming connection, or something else entirely? The `sock_shutdown` call needs to fit seamlessly into the application's overall design. I'm focusing on ensuring data integrity. I need to be absolutely certain that any remaining data in the send queue is flushed before initiating the shutdown for writing. Otherwise, I risk data loss, corruption, or unexpected behavior on the receiving end.

And the error handling? I'm already anticipating the potential for errors. What if the socket isn't properly connected? What if the shutdown fails? I know I need to be prepared to handle `EBADF`, `ENOTSOCK`, `ENOTCONN` and similar error codes. I'm already crafting my error-handling strategy, anticipating the potential for race conditions and planning to handle them gracefully.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:sock_shutdown]

map[SourceCode: 395:	/*
 396:	 * Forcibly shutdown the socket causing all listeners to error
 397:	 */
 398:	static void sock_shutdown(struct nbd_device *nbd)
 399:	{
 400:		struct nbd_config *config = nbd->config;
 401:		int i;
 402:	
 403:		if (config->num_connections == 0)
 404:			return;
 405:		if (test_and_set_bit(NBD_RT_DISCONNECTED, &config->runtime_flags))
 406:			return;
 407:	
 408:		for (i = 0; i < config->num_connections; i++) {
 409:			struct nbd_sock *nsock = config->socks[i];
 410:			mutex_lock(&nsock->tx_lock);
 411:			nbd_mark_nsock_dead(nbd, nsock, 0);
 412:			mutex_unlock(&nsock->tx_lock);
 413:		}
 414:		dev_warn(disk_to_dev(nbd->disk), "shutting down sockets\n");
 415:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 26115
							output: 42
							thoughts: 1816
						

**Analyzing NBD Driver Concurrency and Resource Management**

Okay, let's break this down. First, `sock_shutdown` iterates through connections and marks sockets as dead using `nbd_mark_nsock_dead`. The core concern here is potential double-frees or incorrect resource accounting if multiple `nsock` structures point to the same underlying `sock` structure. The initial assessment seems correct: `nbd_mark_nsock_dead` checks the `dead` flag of each `nsock` *before* calling `kernel_sock_shutdown`. So, multiple calls to `kernel_sock_shutdown` for the same socket are safe because of that individual flag check.

The `live_connections` counter decrement, within `nbd_mark_nsock_dead`, *is* worth a second look, particularly given multiple `nsock` structures for the same `sock`. If `live_connections` starts at 2 and there are two `nsock` structures for the same `sock`, the decrements to 1 and then 0 do seem valid.

Next, I'm checking `nbd_config_put` to ensure its balanced with increments, because that's always a potential source of errors. It's incremented during each `recv_work`, and the increment in `nbd_genl_connect` looks balanced and the decrements seem balanced too. A failure in `nbd_add_socket` in `nbd_genl_connect` is handled to ensure `nbd_config_put` is called to free resources. So far, so good.

Now, that's interesting: `nbd_mark_nsock_dead` queuing `nbd_dead_link_work`. If multiple threads call it for the same socket (but with different `nsock`s), we could have *multiple* work items queued. However, the worst thing it does is notify userspace, which should be harmless.

The big one: the interplay of `nbd_read_reply` and `nbd_handle_reply`. If two threads try to read from the same socket concurrently, we *could* have a race. One thread could read the initial part of a reply (magic, cookie) and the other could see an error. Then, when a READ request kicks off and calls `sock_xmit` within `nbd_handle_reply` (thread A), it might compete with `nbd_read_reply` (thread B). *That's* bad. The kernel's TCP implementation *might* handle this safely, but the NBD driver would see protocol errors and shut down, which is the proper behaviour, it just takes longer.

Are there other shared resources? `nbd_device` and `nbd_config` are potential sources of contention. And then, the `blk_mq_update_nr_hw_queues` is interesting. Multiple HW queues, *each* processing a socket from the same TCP connection and using a single `tx_lock` can't be good. Since requests from those separate HW queues are sent over the *same* socket, they could corrupt the NBD stream. This is another concern.

Okay, let's circle back to the double `sockfd_put` call in `nbd_config_put`. If `config->socks[0]->sock` and `config->socks[1]->sock` are the same, `sockfd_put` will be called twice on the same socket. That seems fine because we called `sockfd_lookup` twice, which increments the refcount, and `sockfd_put` decreases it.

And this points to the heart of the issue:
```c
1254:		sock = nbd_get_socket(nbd, arg, &err);
```
`nbd_get_socket` calls `sockfd_lookup`. This is what calls `sockfd_lookup` again.

So we call `sockfd_lookup` twice, which *correctly* increments the refcount of the underlying `struct file` twice. Then, calling `sockfd_put` twice decrements the refcount twice. So far, the socket refcount is properly managed.

Now, considering the question: "Could this cause a kernel panic or deadlock?". The answer is maybe. The double `sockfd_put` *itself* is not a bug. However, if the socket is used in a way that *assumes* it's unique, there *could* be a bug *somewhere else*. However, the refcounts look properly managed, so it's probably okay.

Lastly, the `sk_set_memalloc` check.  If the same socket is used, `sk_set_memalloc` may be called twice on the same socket. Let's check `sk_

map[ContextFile:include/net/sock.h IncludeLines:true Name:sk_set_memalloc]

map[SourceCode: 294:	/**
 295:	 * sk_set_memalloc - sets %SOCK_MEMALLOC
 296:	 * @sk: socket to set it on
 297:	 *
 298:	 * Set %SOCK_MEMALLOC on a socket for access to emergency reserves.
 299:	 * It's the responsibility of the admin to adjust min_free_kbytes
 300:	 * to meet the requirements
 301:	 */
 302:	void sk_set_memalloc(struct sock *sk)
 303:	{
 304:		sock_set_flag(sk, SOCK_MEMALLOC);
 305:		sk->sk_allocation |= __GFP_MEMALLOC;
 306:		static_branch_inc(&memalloc_socks_key);
 307:	}
 SourceFile:net/core/sock.c]

gemini-3-flash-preview

							input: 29243
							output: 24
							thoughts: 158
						

**Memory Allocation Key Concerns**

Okay, hold on a second. I just saw `static_branch_inc(&memalloc_socks_key)`. That's interesting. The code increments this key when `sk_set_memalloc` is called. The alarm bells are going off. If a socket has `sk_set_memalloc` called multiple times, that `static_branch_inc` call is duplicated. That's fine, but is there a matching `sk_clear_memalloc`? I need to be sure the incrementing is correctly balanced.

Right, let me look at NBD's implementation. Hmm, it doesn't seem to call `sk_clear_memalloc`. That's a potential leak. If NBD *doesn't* clear the allocation, then `memalloc_socks_key` will just stay incremented indefinitely. This has a nasty memory implications in a long-running system. 

But wait, hold on. When the socket is destroyed, is there implicit clean-up? I need to verify how sockets are handled in those cases. The documentation *should* provide some insights.

And generally, `sk_set_memalloc` is used in, for example, swap-over-NBD setups, which makes this investigation even more pressing. 

Okay, I need to check where `sk_clear_memalloc` *is* called. That's my next step.

map[Name:sk_clear_memalloc]

map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:sock_free SourceFile:drivers/net/wireguard/socket.c SourceLine:337] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:xs_reset_transport SourceFile:net/sunrpc/xprtsock.c SourceLine:1289]] TruncatedOutput:false]

gemini-3-flash-preview

							input: 29854
							output: 22
							thoughts: 145
						

**Investigating Potential Memory Allocation Leak in NBD**

Okay, so it looks like `sk_clear_memalloc` isn't explicitly being called within the Network Block Device (NBD) driver. That's a bit concerning. Hang on... if NBD is setting the `SOCK_MEMALLOC` flag on a socket, shouldn't it *also* be clearing it when the socket is no longer needed? Otherwise, it's relying on the socket's destruction to clean up, which feels a bit fragile, or the destruction does not happen which leads to leakage.

The crucial issue here is balance, `static_branch_inc` calls must have corresponding `static_branch_dec` calls. If the clearing of the `SOCK_MEMALLOC` flag isn't happening properly, then the `memalloc_socks_key` counter will inevitably leak. This is a potential resource leak.

Right, time to verify this assumption. I need to confirm whether or not NBD actually calls `sk_clear_memalloc` anywhere in its code. I'll search for occurrences of `sk_clear_memalloc` within `drivers/block/nbd.c`. Let's see what the source code says.

map[Dir:drivers/block/]

map[Files:[amiflop.c ataflop.c brd.c floppy.c loop.c n64cart.c nbd.c ps3disk.c ps3vram.c rbd.c rbd_types.h sunvdc.c swim.c swim3.c swim_asm.S ublk_drv.c virtio_blk.c xen-blkfront.c z2ram.c zloop.c] Subdirs:[aoe drbd mtip32xx null_blk rnbd rnull xen-blkback zram]]

gemini-3-flash-preview

							input: 30498
							output: 23
							thoughts: 23
						

Okay, here's my take on those thoughts, tailored for an expert audience:

**Analyzing NBD Memory Management**

Right, let's dive in. When I see mention of `sk_clear_memalloc`, my first instinct is to head straight to `drivers/block/nbd.c`. That's where I'd expect to find the Network Block Device driver, and therefore, where I'd look for any socket-related memory management. I'm assuming we're dealing with socket buffer (sk_buff) memory, and the "clear_memalloc" function likely points to a mechanism for releasing or resetting resources associated with that allocation. I'd be looking closely at how it interacts with the NBD's request handling and data transfer paths. Is it part of a congestion control scheme? Does it prevent memory leaks or fragmentation? My initial focus would be on pinpointing the specific conditions under which `sk_clear_memalloc` is called, and what the implications of its execution are, especially concerning locking, error handling, and performance. I need to understand the full lifecycle of the memory management within this module.

map[File:drivers/block/nbd.c]

map[Contents:// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Network block device - make block devices work over TCP
 *
 * Note that you can not swap over this thing, yet. Seems to work but
 * deadlocks sometimes - you can not swap over TCP in general.
 * 
 * Copyright 1997-2000, 2008 Pavel Machek <pavel@ucw.cz>
 * Parts copyright 2001 Steven Whitehouse <steve@chygwyn.com>
 *
 * (part of code stolen from loop.c)
 */

#define pr_fmt(fmt) "nbd: " fmt

#include <linux/major.h>

#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/sched/mm.h>
#include <linux/fs.h>
#include <linux/bio.h>
#include <linux/stat.h>
#include <linux/errno.h>
#include <linux/file.h>
#include <linux/ioctl.h>
#include <linux/mutex.h>
#include <linux/compiler.h>
#include <linux/completion.h>
#include <linux/err.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <net/sock.h>
#include <linux/net.h>
#include <linux/kthread.h>
#include <linux/types.h>
#include <linux/debugfs.h>
#include <linux/blk-mq.h>

#include <linux/uaccess.h>
#include <asm/types.h>

#include <linux/nbd.h>
#include <linux/nbd-netlink.h>
#include <net/genetlink.h>

#define CREATE_TRACE_POINTS
#include <trace/events/nbd.h>

static DEFINE_IDR(nbd_index_idr);
static DEFINE_MUTEX(nbd_index_mutex);
static struct workqueue_struct *nbd_del_wq;
static int nbd_total_devices = 0;

struct nbd_sock {
	struct socket *sock;
	struct mutex tx_lock;
	struct request *pending;
	int sent;
	bool dead;
	int fallback_index;
	int cookie;
	struct work_struct work;
};

struct recv_thread_args {
	struct work_struct work;
	struct nbd_device *nbd;
	struct nbd_sock *nsock;
	int index;
};

struct link_dead_args {
	struct work_struct work;
	int index;
};

#define NBD_RT_TIMEDOUT			0
#define NBD_RT_DISCONNECT_REQUESTED	1
#define NBD_RT_DISCONNECTED		2
#define NBD_RT_HAS_PID_FILE		3
#define NBD_RT_HAS_CONFIG_REF		4
#define NBD_RT_BOUND			5
#define NBD_RT_DISCONNECT_ON_CLOSE	6
#define NBD_RT_HAS_BACKEND_FILE		7

#define NBD_DESTROY_ON_DISCONNECT	0
#define NBD_DISCONNECT_REQUESTED	1

struct nbd_config {
	u32 flags;
	unsigned long runtime_flags;
	u64 dead_conn_timeout;

	struct nbd_sock **socks;
	int num_connections;
	atomic_t live_connections;
	wait_queue_head_t conn_wait;

	atomic_t recv_threads;
	wait_queue_head_t recv_wq;
	unsigned int blksize_bits;
	loff_t bytesize;
#if IS_ENABLED(CONFIG_DEBUG_FS)
	struct dentry *dbg_dir;
#endif
};

static inline unsigned int nbd_blksize(struct nbd_config *config)
{
	return 1u << config->blksize_bits;
}

struct nbd_device {
	struct blk_mq_tag_set tag_set;

	int index;
	refcount_t config_refs;
	refcount_t refs;
	struct nbd_config *config;
	struct mutex config_lock;
	struct gendisk *disk;
	struct workqueue_struct *recv_workq;
	struct work_struct remove_work;

	struct list_head list;
	struct task_struct *task_setup;

	unsigned long flags;
	pid_t pid; /* pid of nbd-client, if attached */

	char *backend;
};

#define NBD_CMD_REQUEUED	1
/*
 * This flag will be set if nbd_queue_rq() succeed, and will be checked and
 * cleared in completion. Both setting and clearing of the flag are protected
 * by cmd->lock.
 */
#define NBD_CMD_INFLIGHT	2

/* Just part of request header or data payload is sent successfully */
#define NBD_CMD_PARTIAL_SEND	3

struct nbd_cmd {
	struct nbd_device *nbd;
	struct mutex lock;
	int index;
	int cookie;
	int retries;
	blk_status_t status;
	unsigned long flags;
	u32 cmd_cookie;
};

#if IS_ENABLED(CONFIG_DEBUG_FS)
static struct dentry *nbd_dbg_dir;
#endif

#define nbd_name(nbd) ((nbd)->disk->disk_name)

#define NBD_DEF_BLKSIZE_BITS 10

static unsigned int nbds_max = 16;
static int max_part = 16;
static int part_shift;

static int nbd_dev_dbg_init(struct nbd_device *nbd);
static void nbd_dev_dbg_close(struct nbd_device *nbd);
static void nbd_config_put(struct nbd_device *nbd);
static void nbd_connect_reply(struct genl_info *info, int index);
static int nbd_genl_status(struct sk_buff *skb, struct genl_info *info);
static void nbd_dead_link_work(struct work_struct *work);
static void nbd_disconnect_and_put(struct nbd_device *nbd);

static inline struct device *nbd_to_dev(struct nbd_device *nbd)
{
	return disk_to_dev(nbd->disk);
}

static void nbd_requeue_cmd(struct nbd_cmd *cmd)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);

	lockdep_assert_held(&cmd->lock);

	/*
	 * Clear INFLIGHT flag so that this cmd won't be completed in
	 * normal completion path
	 *
	 * INFLIGHT flag will be set when the cmd is queued to nbd next
	 * time.
	 */
	__clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);

	if (!test_and_set_bit(NBD_CMD_REQUEUED, &cmd->flags))
		blk_mq_requeue_request(req, true);
}

#define NBD_COOKIE_BITS 32

static u64 nbd_cmd_handle(struct nbd_cmd *cmd)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);
	u32 tag = blk_mq_unique_tag(req);
	u64 cookie = cmd->cmd_cookie;

	return (cookie << NBD_COOKIE_BITS) | tag;
}

static u32 nbd_handle_to_tag(u64 handle)
{
	return (u32)handle;
}

static u32 nbd_handle_to_cookie(u64 handle)
{
	return (u32)(handle >> NBD_COOKIE_BITS);
}

static const char *nbdcmd_to_ascii(int cmd)
{
	switch (cmd) {
	case  NBD_CMD_READ: return "read";
	case NBD_CMD_WRITE: return "write";
	case  NBD_CMD_DISC: return "disconnect";
	case NBD_CMD_FLUSH: return "flush";
	case  NBD_CMD_TRIM: return "trim/discard";
	}
	return "invalid";
}

static ssize_t pid_show(struct device *dev,
			struct device_attribute *attr, char *buf)
{
	struct gendisk *disk = dev_to_disk(dev);
	struct nbd_device *nbd = disk->private_data;

	return sprintf(buf, "%d\n", nbd->pid);
}

static const struct device_attribute pid_attr = {
	.attr = { .name = "pid", .mode = 0444},
	.show = pid_show,
};

static ssize_t backend_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct gendisk *disk = dev_to_disk(dev);
	struct nbd_device *nbd = disk->private_data;

	return sprintf(buf, "%s\n", nbd->backend ?: "");
}

static const struct device_attribute backend_attr = {
	.attr = { .name = "backend", .mode = 0444},
	.show = backend_show,
};

static void nbd_dev_remove(struct nbd_device *nbd)
{
	struct gendisk *disk = nbd->disk;

	del_gendisk(disk);
	blk_mq_free_tag_set(&nbd->tag_set);

	/*
	 * Remove from idr after del_gendisk() completes, so if the same ID is
	 * reused, the following add_disk() will succeed.
	 */
	mutex_lock(&nbd_index_mutex);
	idr_remove(&nbd_index_idr, nbd->index);
	mutex_unlock(&nbd_index_mutex);
	destroy_workqueue(nbd->recv_workq);
	put_disk(disk);
}

static void nbd_dev_remove_work(struct work_struct *work)
{
	nbd_dev_remove(container_of(work, struct nbd_device, remove_work));
}

static void nbd_put(struct nbd_device *nbd)
{
	if (!refcount_dec_and_test(&nbd->refs))
		return;

	/* Call del_gendisk() asynchrounously to prevent deadlock */
	if (test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags))
		queue_work(nbd_del_wq, &nbd->remove_work);
	else
		nbd_dev_remove(nbd);
}

static int nbd_disconnected(struct nbd_config *config)
{
	return test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags) ||
		test_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags);
}

static void nbd_mark_nsock_dead(struct nbd_device *nbd, struct nbd_sock *nsock,
				int notify)
{
	if (!nsock->dead && notify && !nbd_disconnected(nbd->config)) {
		struct link_dead_args *args;
		args = kmalloc_obj(struct link_dead_args, GFP_NOIO);
		if (args) {
			INIT_WORK(&args->work, nbd_dead_link_work);
			args->index = nbd->index;
			queue_work(system_percpu_wq, &args->work);
		}
	}
	if (!nsock->dead) {
		kernel_sock_shutdown(nsock->sock, SHUT_RDWR);
		if (atomic_dec_return(&nbd->config->live_connections) == 0) {
			if (test_and_clear_bit(NBD_RT_DISCONNECT_REQUESTED,
					       &nbd->config->runtime_flags)) {
				set_bit(NBD_RT_DISCONNECTED,
					&nbd->config->runtime_flags);
				dev_info(nbd_to_dev(nbd),
					"Disconnected due to user request.\n");
			}
		}
	}
	nsock->dead = true;
	nsock->pending = NULL;
	nsock->sent = 0;
}

static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize, loff_t blksize)
{
	struct queue_limits lim;
	int error;

	if (!blksize)
		blksize = 1u << NBD_DEF_BLKSIZE_BITS;

	if (blk_validate_block_size(blksize))
		return -EINVAL;

	if (bytesize < 0)
		return -EINVAL;

	nbd->config->bytesize = bytesize;
	nbd->config->blksize_bits = __ffs(blksize);

	if (!nbd->pid)
		return 0;

	lim = queue_limits_start_update(nbd->disk->queue);
	if (nbd->config->flags & NBD_FLAG_SEND_TRIM)
		lim.max_hw_discard_sectors = UINT_MAX >> SECTOR_SHIFT;
	else
		lim.max_hw_discard_sectors = 0;
	if (!(nbd->config->flags & NBD_FLAG_SEND_FLUSH)) {
		lim.features &= ~(BLK_FEAT_WRITE_CACHE | BLK_FEAT_FUA);
	} else if (nbd->config->flags & NBD_FLAG_SEND_FUA) {
		lim.features |= BLK_FEAT_WRITE_CACHE | BLK_FEAT_FUA;
	} else {
		lim.features |= BLK_FEAT_WRITE_CACHE;
		lim.features &= ~BLK_FEAT_FUA;
	}
	if (nbd->config->flags & NBD_FLAG_ROTATIONAL)
		lim.features |= BLK_FEAT_ROTATIONAL;
	if (nbd->config->flags & NBD_FLAG_SEND_WRITE_ZEROES)
		lim.max_write_zeroes_sectors = UINT_MAX >> SECTOR_SHIFT;

	lim.logical_block_size = blksize;
	lim.physical_block_size = blksize;
	error = queue_limits_commit_update_frozen(nbd->disk->queue, &lim);
	if (error)
		return error;

	if (max_part)
		set_bit(GD_NEED_PART_SCAN, &nbd->disk->state);
	if (!set_capacity_and_notify(nbd->disk, bytesize >> 9))
		kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
	return 0;
}

static void nbd_complete_rq(struct request *req)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);

	dev_dbg(nbd_to_dev(cmd->nbd), "request %p: %s\n", req,
		cmd->status ? "failed" : "done");

	blk_mq_end_request(req, cmd->status);
}

/*
 * Forcibly shutdown the socket causing all listeners to error
 */
static void sock_shutdown(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	int i;

	if (config->num_connections == 0)
		return;
	if (test_and_set_bit(NBD_RT_DISCONNECTED, &config->runtime_flags))
		return;

	for (i = 0; i < config->num_connections; i++) {
		struct nbd_sock *nsock = config->socks[i];
		mutex_lock(&nsock->tx_lock);
		nbd_mark_nsock_dead(nbd, nsock, 0);
		mutex_unlock(&nsock->tx_lock);
	}
	dev_warn(disk_to_dev(nbd->disk), "shutting down sockets\n");
}

static u32 req_to_nbd_cmd_type(struct request *req)
{
	switch (req_op(req)) {
	case REQ_OP_DISCARD:
		return NBD_CMD_TRIM;
	case REQ_OP_FLUSH:
		return NBD_CMD_FLUSH;
	case REQ_OP_WRITE:
		return NBD_CMD_WRITE;
	case REQ_OP_READ:
		return NBD_CMD_READ;
	case REQ_OP_WRITE_ZEROES:
		return NBD_CMD_WRITE_ZEROES;
	default:
		return U32_MAX;
	}
}

static struct nbd_config *nbd_get_config_unlocked(struct nbd_device *nbd)
{
	if (refcount_inc_not_zero(&nbd->config_refs)) {
		/*
		 * Add smp_mb__after_atomic to ensure that reading nbd->config_refs
		 * and reading nbd->config is ordered. The pair is the barrier in
		 * nbd_alloc_and_init_config(), avoid nbd->config_refs is set
		 * before nbd->config.
		 */
		smp_mb__after_atomic();
		return nbd->config;
	}

	return NULL;
}

static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);
	struct nbd_device *nbd = cmd->nbd;
	struct nbd_config *config;

	if (!mutex_trylock(&cmd->lock))
		return BLK_EH_RESET_TIMER;

	/* partial send is handled in nbd_sock's work function */
	if (test_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags)) {
		mutex_unlock(&cmd->lock);
		return BLK_EH_RESET_TIMER;
	}

	if (!test_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
		mutex_unlock(&cmd->lock);
		return BLK_EH_DONE;
	}

	config = nbd_get_config_unlocked(nbd);
	if (!config) {
		cmd->status = BLK_STS_TIMEOUT;
		__clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);
		mutex_unlock(&cmd->lock);
		goto done;
	}

	if (config->num_connections > 1 ||
	    (config->num_connections == 1 && nbd->tag_set.timeout)) {
		dev_err_ratelimited(nbd_to_dev(nbd),
				    "Connection timed out, retrying (%d/%d alive)\n",
				    atomic_read(&config->live_connections),
				    config->num_connections);
		/*
		 * Hooray we have more connections, requeue this IO, the submit
		 * path will put it on a real connection. Or if only one
		 * connection is configured, the submit path will wait util
		 * a new connection is reconfigured or util dead timeout.
		 */
		if (config->socks) {
			if (cmd->index < config->num_connections) {
				struct nbd_sock *nsock =
					config->socks[cmd->index];
				mutex_lock(&nsock->tx_lock);
				/* We can have multiple outstanding requests, so
				 * we don't want to mark the nsock dead if we've
				 * already reconnected with a new socket, so
				 * only mark it dead if its the same socket we
				 * were sent out on.
				 */
				if (cmd->cookie == nsock->cookie)
					nbd_mark_nsock_dead(nbd, nsock, 1);
				mutex_unlock(&nsock->tx_lock);
			}
			nbd_requeue_cmd(cmd);
			mutex_unlock(&cmd->lock);
			nbd_config_put(nbd);
			return BLK_EH_DONE;
		}
	}

	if (!nbd->tag_set.timeout) {
		/*
		 * Userspace sets timeout=0 to disable socket disconnection,
		 * so just warn and reset the timer.
		 */
		struct nbd_sock *nsock = config->socks[cmd->index];
		cmd->retries++;
		dev_info(nbd_to_dev(nbd), "Possible stuck request %p: control (%s@%llu,%uB). Runtime %u seconds\n",
			req, nbdcmd_to_ascii(req_to_nbd_cmd_type(req)),
			(unsigned long long)blk_rq_pos(req) << 9,
			blk_rq_bytes(req), (req->timeout / HZ) * cmd->retries);

		mutex_lock(&nsock->tx_lock);
		if (cmd->cookie != nsock->cookie) {
			nbd_requeue_cmd(cmd);
			mutex_unlock(&nsock->tx_lock);
			mutex_unlock(&cmd->lock);
			nbd_config_put(nbd);
			return BLK_EH_DONE;
		}
		mutex_unlock(&nsock->tx_lock);
		mutex_unlock(&cmd->lock);
		nbd_config_put(nbd);
		return BLK_EH_RESET_TIMER;
	}

	dev_err_ratelimited(nbd_to_dev(nbd), "Connection timed out\n");
	set_bit(NBD_RT_TIMEDOUT, &config->runtime_flags);
	cmd->status = BLK_STS_IOERR;
	__clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);
	mutex_unlock(&cmd->lock);
	sock_shutdown(nbd);
	nbd_config_put(nbd);
done:
	blk_mq_complete_request(req);
	return BLK_EH_DONE;
}

static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
		       struct iov_iter *iter, int msg_flags, int *sent)
{
	int result;
	struct msghdr msg = {} ;
	unsigned int noreclaim_flag;

	if (unlikely(!sock)) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
			"Attempted %s on closed socket in sock_xmit\n",
			(send ? "send" : "recv"));
		return -EINVAL;
	}

	msg.msg_iter = *iter;

	noreclaim_flag = memalloc_noreclaim_save();

	scoped_with_kernel_creds() {
		do {
			sock->sk->sk_allocation = GFP_NOIO | __GFP_MEMALLOC;
			sock->sk->sk_use_task_frag = false;
			msg.msg_flags = msg_flags | MSG_NOSIGNAL;

			if (send)
				result = sock_sendmsg(sock, &msg);
			else
				result = sock_recvmsg(sock, &msg, msg.msg_flags);

			if (result <= 0) {
				if (result == 0)
					result = -EPIPE; /* short read */
				break;
			}
			if (sent)
				*sent += result;
		} while (msg_data_left(&msg));
	}

	memalloc_noreclaim_restore(noreclaim_flag);

	return result;
}

/*
 *  Send or receive packet. Return a positive value on success and
 *  negtive value on failure, and never return 0.
 */
static int sock_xmit(struct nbd_device *nbd, int index, int send,
		     struct iov_iter *iter, int msg_flags, int *sent)
{
	struct nbd_config *config = nbd->config;
	struct socket *sock = config->socks[index]->sock;

	return __sock_xmit(nbd, sock, send, iter, msg_flags, sent);
}

/*
 * Different settings for sk->sk_sndtimeo can result in different return values
 * if there is a signal pending when we enter sendmsg, because reasons?
 */
static inline int was_interrupted(int result)
{
	return result == -ERESTARTSYS || result == -EINTR;
}

/*
 * We've already sent header or part of data payload, have no choice but
 * to set pending and schedule it in work.
 *
 * And we have to return BLK_STS_OK to block core, otherwise this same
 * request may be re-dispatched with different tag, but our header has
 * been sent out with old tag, and this way does confuse reply handling.
 */
static void nbd_sched_pending_work(struct nbd_device *nbd,
				   struct nbd_sock *nsock,
				   struct nbd_cmd *cmd, int sent)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);

	/* pending work should be scheduled only once */
	WARN_ON_ONCE(test_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags));

	nsock->pending = req;
	nsock->sent = sent;
	set_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags);
	refcount_inc(&nbd->config_refs);
	schedule_work(&nsock->work);
}

/*
 * Returns BLK_STS_RESOURCE if the caller should retry after a delay.
 * Returns BLK_STS_IOERR if sending failed.
 */
static blk_status_t nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd,
				 int index)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);
	struct nbd_config *config = nbd->config;
	struct nbd_sock *nsock = config->socks[index];
	int result;
	struct nbd_request request = {.magic = htonl(NBD_REQUEST_MAGIC)};
	struct kvec iov = {.iov_base = &request, .iov_len = sizeof(request)};
	struct iov_iter from;
	struct bio *bio;
	u64 handle;
	u32 type;
	u32 nbd_cmd_flags = 0;
	int sent = nsock->sent, skip = 0;

	lockdep_assert_held(&cmd->lock);
	lockdep_assert_held(&nsock->tx_lock);

	iov_iter_kvec(&from, ITER_SOURCE, &iov, 1, sizeof(request));

	type = req_to_nbd_cmd_type(req);
	if (type == U32_MAX)
		return BLK_STS_IOERR;

	if (rq_data_dir(req) == WRITE &&
	    (config->flags & NBD_FLAG_READ_ONLY)) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
				    "Write on read-only\n");
		return BLK_STS_IOERR;
	}

	if (req->cmd_flags & REQ_FUA)
		nbd_cmd_flags |= NBD_CMD_FLAG_FUA;
	if ((req->cmd_flags & REQ_NOUNMAP) && (type == NBD_CMD_WRITE_ZEROES))
		nbd_cmd_flags |= NBD_CMD_FLAG_NO_HOLE;

	/* We did a partial send previously, and we at least sent the whole
	 * request struct, so just go and send the rest of the pages in the
	 * request.
	 */
	if (sent) {
		if (sent >= sizeof(request)) {
			skip = sent - sizeof(request);

			/* initialize handle for tracing purposes */
			handle = nbd_cmd_handle(cmd);

			goto send_pages;
		}
		iov_iter_advance(&from, sent);
	} else {
		cmd->cmd_cookie++;
	}
	cmd->index = index;
	cmd->cookie = nsock->cookie;
	cmd->retries = 0;
	request.type = htonl(type | nbd_cmd_flags);
	if (type != NBD_CMD_FLUSH) {
		request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9);
		request.len = htonl(blk_rq_bytes(req));
	}
	handle = nbd_cmd_handle(cmd);
	request.cookie = cpu_to_be64(handle);

	trace_nbd_send_request(&request, nbd->index, blk_mq_rq_from_pdu(cmd));

	dev_dbg(nbd_to_dev(nbd), "request %p: sending control (%s@%llu,%uB)\n",
		req, nbdcmd_to_ascii(type),
		(unsigned long long)blk_rq_pos(req) << 9, blk_rq_bytes(req));
	result = sock_xmit(nbd, index, 1, &from,
			(type == NBD_CMD_WRITE) ? MSG_MORE : 0, &sent);
	trace_nbd_header_sent(req, handle);
	if (result < 0) {
		if (was_interrupted(result)) {
			/* If we haven't sent anything we can just return BUSY,
			 * however if we have sent something we need to make
			 * sure we only allow this req to be sent until we are
			 * completely done.
			 */
			if (sent) {
				nbd_sched_pending_work(nbd, nsock, cmd, sent);
				return BLK_STS_OK;
			}
			set_bit(NBD_CMD_REQUEUED, &cmd->flags);
			return BLK_STS_RESOURCE;
		}
		dev_err_ratelimited(disk_to_dev(nbd->disk),
			"Send control failed (result %d)\n", result);
		goto requeue;
	}
send_pages:
	if (type != NBD_CMD_WRITE)
		goto out;

	bio = req->bio;
	while (bio) {
		struct bio *next = bio->bi_next;
		struct bvec_iter iter;
		struct bio_vec bvec;

		bio_for_each_segment(bvec, bio, iter) {
			bool is_last = !next && bio_iter_last(bvec, iter);
			int flags = is_last ? 0 : MSG_MORE;

			dev_dbg(nbd_to_dev(nbd), "request %p: sending %d bytes data\n",
				req, bvec.bv_len);
			iov_iter_bvec(&from, ITER_SOURCE, &bvec, 1, bvec.bv_len);
			if (skip) {
				if (skip >= iov_iter_count(&from)) {
					skip -= iov_iter_count(&from);
					continue;
				}
				iov_iter_advance(&from, skip);
				skip = 0;
			}
			result = sock_xmit(nbd, index, 1, &from, flags, &sent);
			if (result < 0) {
				if (was_interrupted(result)) {
					nbd_sched_pending_work(nbd, nsock, cmd, sent);
					return BLK_STS_OK;
				}
				dev_err(disk_to_dev(nbd->disk),
					"Send data failed (result %d)\n",
					result);
				goto requeue;
			}
			/*
			 * The completion might already have come in,
			 * so break for the last one instead of letting
			 * the iterator do it. This prevents use-after-free
			 * of the bio.
			 */
			if (is_last)
				break;
		}
		bio = next;
	}
out:
	trace_nbd_payload_sent(req, handle);
	nsock->pending = NULL;
	nsock->sent = 0;
	__set_bit(NBD_CMD_INFLIGHT, &cmd->flags);
	return BLK_STS_OK;

requeue:
	/*
	 * Can't requeue in case we are dealing with partial send
	 *
	 * We must run from pending work function.
	 * */
	if (test_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags))
		return BLK_STS_OK;

	/* retry on a different socket */
	dev_err_ratelimited(disk_to_dev(nbd->disk),
			    "Request send failed, requeueing\n");
	nbd_mark_nsock_dead(nbd, nsock, 1);
	nbd_requeue_cmd(cmd);
	return BLK_STS_OK;
}

/* handle partial sending */
static void nbd_pending_cmd_work(struct work_struct *work)
{
	struct nbd_sock *nsock = container_of(work, struct nbd_sock, work);
	struct request *req = nsock->pending;
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);
	struct nbd_device *nbd = cmd->nbd;
	unsigned long deadline = READ_ONCE(req->deadline);
	unsigned int wait_ms = 2;

	mutex_lock(&cmd->lock);

	WARN_ON_ONCE(test_bit(NBD_CMD_REQUEUED, &cmd->flags));
	if (WARN_ON_ONCE(!test_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags)))
		goto out;

	mutex_lock(&nsock->tx_lock);
	while (true) {
		nbd_send_cmd(nbd, cmd, cmd->index);
		if (!nsock->pending)
			break;

		/* don't bother timeout handler for partial sending */
		if (READ_ONCE(jiffies) + msecs_to_jiffies(wait_ms) >= deadline) {
			cmd->status = BLK_STS_IOERR;
			blk_mq_complete_request(req);
			break;
		}
		msleep(wait_ms);
		wait_ms *= 2;
	}
	mutex_unlock(&nsock->tx_lock);
	clear_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags);
out:
	mutex_unlock(&cmd->lock);
	nbd_config_put(nbd);
}

static int nbd_read_reply(struct nbd_device *nbd, struct socket *sock,
			  struct nbd_reply *reply)
{
	struct kvec iov = {.iov_base = reply, .iov_len = sizeof(*reply)};
	struct iov_iter to;
	int result;

	reply->magic = 0;
	iov_iter_kvec(&to, ITER_DEST, &iov, 1, sizeof(*reply));
	result = __sock_xmit(nbd, sock, 0, &to, MSG_WAITALL, NULL);
	if (result < 0) {
		if (!nbd_disconnected(nbd->config))
			dev_err(disk_to_dev(nbd->disk),
				"Receive control failed (result %d)\n", result);
		return result;
	}

	if (ntohl(reply->magic) != NBD_REPLY_MAGIC) {
		dev_err(disk_to_dev(nbd->disk), "Wrong magic (0x%lx)\n",
				(unsigned long)ntohl(reply->magic));
		return -EPROTO;
	}

	return 0;
}

/* NULL returned = something went wrong, inform userspace */
static struct nbd_cmd *nbd_handle_reply(struct nbd_device *nbd, int index,
					struct nbd_reply *reply)
{
	int result;
	struct nbd_cmd *cmd;
	struct request *req = NULL;
	u64 handle;
	u16 hwq;
	u32 tag;
	int ret = 0;

	handle = be64_to_cpu(reply->cookie);
	tag = nbd_handle_to_tag(handle);
	hwq = blk_mq_unique_tag_to_hwq(tag);
	if (hwq < nbd->tag_set.nr_hw_queues)
		req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq],
				       blk_mq_unique_tag_to_tag(tag));
	if (!req || !blk_mq_request_started(req)) {
		dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%d) %p\n",
			tag, req);
		return ERR_PTR(-ENOENT);
	}
	trace_nbd_header_received(req, handle);
	cmd = blk_mq_rq_to_pdu(req);

	mutex_lock(&cmd->lock);
	if (!test_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
		dev_err(disk_to_dev(nbd->disk), "Suspicious reply %d (status %u flags %lu)",
			tag, cmd->status, cmd->flags);
		ret = -ENOENT;
		goto out;
	}
	if (cmd->index != index) {
		dev_err(disk_to_dev(nbd->disk), "Unexpected reply %d from different sock %d (expected %d)",
			tag, index, cmd->index);
		ret = -ENOENT;
		goto out;
	}
	if (cmd->cmd_cookie != nbd_handle_to_cookie(handle)) {
		dev_err(disk_to_dev(nbd->disk), "Double reply on req %p, cmd_cookie %u, handle cookie %u\n",
			req, cmd->cmd_cookie, nbd_handle_to_cookie(handle));
		ret = -ENOENT;
		goto out;
	}
	if (cmd->status != BLK_STS_OK) {
		dev_err(disk_to_dev(nbd->disk), "Command already handled %p\n",
			req);
		ret = -ENOENT;
		goto out;
	}
	if (test_bit(NBD_CMD_REQUEUED, &cmd->flags)) {
		dev_err(disk_to_dev(nbd->disk), "Raced with timeout on req %p\n",
			req);
		ret = -ENOENT;
		goto out;
	}
	if (ntohl(reply->error)) {
		dev_err(disk_to_dev(nbd->disk), "Other side returned error (%d)\n",
			ntohl(reply->error));
		cmd->status = BLK_STS_IOERR;
		goto out;
	}

	dev_dbg(nbd_to_dev(nbd), "request %p: got reply\n", req);
	if (rq_data_dir(req) != WRITE) {
		struct req_iterator iter;
		struct bio_vec bvec;
		struct iov_iter to;

		rq_for_each_segment(bvec, req, iter) {
			iov_iter_bvec(&to, ITER_DEST, &bvec, 1, bvec.bv_len);
			result = sock_xmit(nbd, index, 0, &to, MSG_WAITALL, NULL);
			if (result < 0) {
				dev_err(disk_to_dev(nbd->disk), "Receive data failed (result %d)\n",
					result);
				/*
				 * If we've disconnected, we need to make sure we
				 * complete this request, otherwise error out
				 * and let the timeout stuff handle resubmitting
				 * this request onto another connection.
				 */
				if (nbd_disconnected(nbd->config)) {
					cmd->status = BLK_STS_IOERR;
					goto out;
				}
				ret = -EIO;
				goto out;
			}
			dev_dbg(nbd_to_dev(nbd), "request %p: got %d bytes data\n",
				req, bvec.bv_len);
		}
	}
out:
	trace_nbd_payload_received(req, handle);
	mutex_unlock(&cmd->lock);
	return ret ? ERR_PTR(ret) : cmd;
}

static void recv_work(struct work_struct *work)
{
	struct recv_thread_args *args = container_of(work,
						     struct recv_thread_args,
						     work);
	struct nbd_device *nbd = args->nbd;
	struct nbd_config *config = nbd->config;
	struct request_queue *q = nbd->disk->queue;
	struct nbd_sock *nsock = args->nsock;
	struct nbd_cmd *cmd;
	struct request *rq;

	while (1) {
		struct nbd_reply reply;

		if (nbd_read_reply(nbd, nsock->sock, &reply))
			break;

		/*
		 * Grab .q_usage_counter so request pool won't go away, then no
		 * request use-after-free is possible during nbd_handle_reply().
		 * If queue is frozen, there won't be any inflight requests, we
		 * needn't to handle the incoming garbage message.
		 */
		if (!percpu_ref_tryget(&q->q_usage_counter)) {
			dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n",
				__func__);
			break;
		}

		cmd = nbd_handle_reply(nbd, args->index, &reply);
		if (IS_ERR(cmd)) {
			percpu_ref_put(&q->q_usage_counter);
			break;
		}

		rq = blk_mq_rq_from_pdu(cmd);
		if (likely(!blk_should_fake_timeout(rq->q))) {
			bool complete;

			mutex_lock(&cmd->lock);
			complete = __test_and_clear_bit(NBD_CMD_INFLIGHT,
							&cmd->flags);
			mutex_unlock(&cmd->lock);
			if (complete)
				blk_mq_complete_request(rq);
		}
		percpu_ref_put(&q->q_usage_counter);
	}

	mutex_lock(&nsock->tx_lock);
	nbd_mark_nsock_dead(nbd, nsock, 1);
	mutex_unlock(&nsock->tx_lock);

	atomic_dec(&config->recv_threads);
	wake_up(&config->recv_wq);
	nbd_config_put(nbd);
	kfree(args);
}

static bool nbd_clear_req(struct request *req, void *data)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);

	/* don't abort one completed request */
	if (blk_mq_request_completed(req))
		return true;

	mutex_lock(&cmd->lock);
	if (!__test_and_clear_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
		mutex_unlock(&cmd->lock);
		return true;
	}
	cmd->status = BLK_STS_IOERR;
	mutex_unlock(&cmd->lock);

	blk_mq_complete_request(req);
	return true;
}

static void nbd_clear_que(struct nbd_device *nbd)
{
	blk_mq_quiesce_queue(nbd->disk->queue);
	blk_mq_tagset_busy_iter(&nbd->tag_set, nbd_clear_req, NULL);
	blk_mq_unquiesce_queue(nbd->disk->queue);
	dev_dbg(disk_to_dev(nbd->disk), "queue cleared\n");
}

static int find_fallback(struct nbd_device *nbd, int index)
{
	struct nbd_config *config = nbd->config;
	int new_index = -1;
	struct nbd_sock *nsock = config->socks[index];
	int fallback = nsock->fallback_index;

	if (test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags))
		return new_index;

	if (config->num_connections <= 1) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
				    "Dead connection, failed to find a fallback\n");
		return new_index;
	}

	if (fallback >= 0 && fallback < config->num_connections &&
	    !config->socks[fallback]->dead)
		return fallback;

	if (nsock->fallback_index < 0 ||
	    nsock->fallback_index >= config->num_connections ||
	    config->socks[nsock->fallback_index]->dead) {
		int i;
		for (i = 0; i < config->num_connections; i++) {
			if (i == index)
				continue;
			if (!config->socks[i]->dead) {
				new_index = i;
				break;
			}
		}
		nsock->fallback_index = new_index;
		if (new_index < 0) {
			dev_err_ratelimited(disk_to_dev(nbd->disk),
					    "Dead connection, failed to find a fallback\n");
			return new_index;
		}
	}
	new_index = nsock->fallback_index;
	return new_index;
}

static int wait_for_reconnect(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	if (!config->dead_conn_timeout)
		return 0;

	if (!wait_event_timeout(config->conn_wait,
				test_bit(NBD_RT_DISCONNECTED,
					 &config->runtime_flags) ||
				atomic_read(&config->live_connections) > 0,
				config->dead_conn_timeout))
		return 0;

	return !test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);
}

static blk_status_t nbd_handle_cmd(struct nbd_cmd *cmd, int index)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);
	struct nbd_device *nbd = cmd->nbd;
	struct nbd_config *config;
	struct nbd_sock *nsock;
	blk_status_t ret;

	lockdep_assert_held(&cmd->lock);

	config = nbd_get_config_unlocked(nbd);
	if (!config) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
				    "Socks array is empty\n");
		return BLK_STS_IOERR;
	}

	if (index >= config->num_connections) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
				    "Attempted send on invalid socket\n");
		nbd_config_put(nbd);
		return BLK_STS_IOERR;
	}
	cmd->status = BLK_STS_OK;
again:
	nsock = config->socks[index];
	mutex_lock(&nsock->tx_lock);
	if (nsock->dead) {
		int old_index = index;
		index = find_fallback(nbd, index);
		mutex_unlock(&nsock->tx_lock);
		if (index < 0) {
			if (wait_for_reconnect(nbd)) {
				index = old_index;
				goto again;
			}
			/* All the sockets should already be down at this point,
			 * we just want to make sure that DISCONNECTED is set so
			 * any requests that come in that were queue'ed waiting
			 * for the reconnect timer don't trigger the timer again
			 * and instead just error out.
			 */
			sock_shutdown(nbd);
			nbd_config_put(nbd);
			return BLK_STS_IOERR;
		}
		goto again;
	}

	/* Handle the case that we have a pending request that was partially
	 * transmitted that _has_ to be serviced first.  We need to call requeue
	 * here so that it gets put _after_ the request that is already on the
	 * dispatch list.
	 */
	blk_mq_start_request(req);
	if (unlikely(nsock->pending && nsock->pending != req)) {
		nbd_requeue_cmd(cmd);
		ret = BLK_STS_OK;
		goto out;
	}
	ret = nbd_send_cmd(nbd, cmd, index);
out:
	mutex_unlock(&nsock->tx_lock);
	nbd_config_put(nbd);
	return ret;
}

static blk_status_t nbd_queue_rq(struct blk_mq_hw_ctx *hctx,
			const struct blk_mq_queue_data *bd)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(bd->rq);
	blk_status_t ret;

	/*
	 * Since we look at the bio's to send the request over the network we
	 * need to make sure the completion work doesn't mark this request done
	 * before we are done doing our send.  This keeps us from dereferencing
	 * freed data if we have particularly fast completions (ie we get the
	 * completion before we exit sock_xmit on the last bvec) or in the case
	 * that the server is misbehaving (or there was an error) before we're
	 * done sending everything over the wire.
	 */
	mutex_lock(&cmd->lock);
	clear_bit(NBD_CMD_REQUEUED, &cmd->flags);

	/* We can be called directly from the user space process, which means we
	 * could possibly have signals pending so our sendmsg will fail.  In
	 * this case we need to return that we are busy, otherwise error out as
	 * appropriate.
	 */
	ret = nbd_handle_cmd(cmd, hctx->queue_num);
	mutex_unlock(&cmd->lock);

	return ret;
}

static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd,
				     int *err)
{
	struct socket *sock;

	*err = 0;
	sock = sockfd_lookup(fd, err);
	if (!sock)
		return NULL;

	if (!sk_is_tcp(sock->sk) &&
	    !sk_is_stream_unix(sock->sk)) {
		dev_err(disk_to_dev(nbd->disk), "Unsupported socket: should be TCP or UNIX.\n");
		*err = -EINVAL;
		sockfd_put(sock);
		return NULL;
	}

	if (sock->ops->shutdown == sock_no_shutdown) {
		dev_err(disk_to_dev(nbd->disk), "Unsupported socket: shutdown callout must be supported.\n");
		*err = -EINVAL;
		sockfd_put(sock);
		return NULL;
	}

	return sock;
}

static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
			  bool netlink)
{
	struct nbd_config *config = nbd->config;
	struct socket *sock;
	struct nbd_sock **socks;
	struct nbd_sock *nsock;
	unsigned int memflags;
	int err;

	/* Arg will be cast to int, check it to avoid overflow */
	if (arg > INT_MAX)
		return -EINVAL;
	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	/*
	 * We need to make sure we don't get any errant requests while we're
	 * reallocating the ->socks array.
	 */
	memflags = blk_mq_freeze_queue(nbd->disk->queue);

	if (!netlink && !nbd->task_setup &&
	    !test_bit(NBD_RT_BOUND, &config->runtime_flags))
		nbd->task_setup = current;

	if (!netlink &&
	    (nbd->task_setup != current ||
	     test_bit(NBD_RT_BOUND, &config->runtime_flags))) {
		dev_err(disk_to_dev(nbd->disk),
			"Device being setup by another task");
		err = -EBUSY;
		goto put_socket;
	}

	nsock = kzalloc_obj(*nsock);
	if (!nsock) {
		err = -ENOMEM;
		goto put_socket;
	}

	socks = krealloc(config->socks, (config->num_connections + 1) *
			 sizeof(struct nbd_sock *), GFP_KERNEL);
	if (!socks) {
		kfree(nsock);
		err = -ENOMEM;
		goto put_socket;
	}

	config->socks = socks;

	nsock->fallback_index = -1;
	nsock->dead = false;
	mutex_init(&nsock->tx_lock);
	nsock->sock = sock;
	nsock->pending = NULL;
	nsock->sent = 0;
	nsock->cookie = 0;
	INIT_WORK(&nsock->work, nbd_pending_cmd_work);
	socks[config->num_connections++] = nsock;
	atomic_inc(&config->live_connections);
	blk_mq_unfreeze_queue(nbd->disk->queue, memflags);

	return 0;

put_socket:
	blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
	sockfd_put(sock);
	return err;
}

static int nbd_reconnect_socket(struct nbd_device *nbd, unsigned long arg)
{
	struct nbd_config *config = nbd->config;
	struct socket *sock, *old;
	struct recv_thread_args *args;
	int i;
	int err;

	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	args = kzalloc_obj(*args);
	if (!args) {
		sockfd_put(sock);
		return -ENOMEM;
	}

	for (i = 0; i < config->num_connections; i++) {
		struct nbd_sock *nsock = config->socks[i];

		if (!nsock->dead)
			continue;

		mutex_lock(&nsock->tx_lock);
		if (!nsock->dead) {
			mutex_unlock(&nsock->tx_lock);
			continue;
		}
		sk_set_memalloc(sock->sk);
		if (nbd->tag_set.timeout)
			sock->sk->sk_sndtimeo = nbd->tag_set.timeout;
		atomic_inc(&config->recv_threads);
		refcount_inc(&nbd->config_refs);
		old = nsock->sock;
		nsock->fallback_index = -1;
		nsock->sock = sock;
		nsock->dead = false;
		INIT_WORK(&args->work, recv_work);
		args->index = i;
		args->nbd = nbd;
		args->nsock = nsock;
		nsock->cookie++;
		mutex_unlock(&nsock->tx_lock);
		sockfd_put(old);

		clear_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);

		/* We take the tx_mutex in an error path in the recv_work, so we
		 * need to queue_work outside of the tx_mutex.
		 */
		queue_work(nbd->recv_workq, &args->work);

		atomic_inc(&config->live_connections);
		wake_up(&config->conn_wait);
		return 0;
	}
	sockfd_put(sock);
	kfree(args);
	return -ENOSPC;
}

static void nbd_bdev_reset(struct nbd_device *nbd)
{
	if (disk_openers(nbd->disk) > 1)
		return;
	set_capacity(nbd->disk, 0);
}

static void nbd_parse_flags(struct nbd_device *nbd)
{
	if (nbd->config->flags & NBD_FLAG_READ_ONLY)
		set_disk_ro(nbd->disk, true);
	else
		set_disk_ro(nbd->disk, false);
}

static void send_disconnects(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	struct nbd_request request = {
		.magic = htonl(NBD_REQUEST_MAGIC),
		.type = htonl(NBD_CMD_DISC),
	};
	struct kvec iov = {.iov_base = &request, .iov_len = sizeof(request)};
	struct iov_iter from;
	int i, ret;

	for (i = 0; i < config->num_connections; i++) {
		struct nbd_sock *nsock = config->socks[i];

		iov_iter_kvec(&from, ITER_SOURCE, &iov, 1, sizeof(request));
		mutex_lock(&nsock->tx_lock);
		ret = sock_xmit(nbd, i, 1, &from, 0, NULL);
		if (ret < 0)
			dev_err(disk_to_dev(nbd->disk),
				"Send disconnect failed %d\n", ret);
		mutex_unlock(&nsock->tx_lock);
	}
}

static int nbd_disconnect(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;

	dev_info(disk_to_dev(nbd->disk), "NBD_DISCONNECT\n");
	set_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags);
	set_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags);
	send_disconnects(nbd);
	return 0;
}

static void nbd_clear_sock(struct nbd_device *nbd)
{
	sock_shutdown(nbd);
	nbd_clear_que(nbd);
	nbd->task_setup = NULL;
}

static void nbd_config_put(struct nbd_device *nbd)
{
	if (refcount_dec_and_mutex_lock(&nbd->config_refs,
					&nbd->config_lock)) {
		struct nbd_config *config = nbd->config;
		nbd_dev_dbg_close(nbd);
		invalidate_disk(nbd->disk);
		if (nbd->config->bytesize)
			kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
		if (test_and_clear_bit(NBD_RT_HAS_PID_FILE,
				       &config->runtime_flags))
			device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
		nbd->pid = 0;
		if (test_and_clear_bit(NBD_RT_HAS_BACKEND_FILE,
				       &config->runtime_flags)) {
			device_remove_file(disk_to_dev(nbd->disk), &backend_attr);
			kfree(nbd->backend);
			nbd->backend = NULL;
		}
		nbd_clear_sock(nbd);
		if (config->num_connections) {
			int i;
			for (i = 0; i < config->num_connections; i++) {
				sockfd_put(config->socks[i]->sock);
				kfree(config->socks[i]);
			}
			kfree(config->socks);
		}
		kfree(nbd->config);
		nbd->config = NULL;

		nbd->tag_set.timeout = 0;

		mutex_unlock(&nbd->config_lock);
		nbd_put(nbd);
		module_put(THIS_MODULE);
	}
}

static int nbd_start_device(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	int num_connections = config->num_connections;
	int error = 0, i;

	if (nbd->pid)
		return -EBUSY;
	if (!config->socks)
		return -EINVAL;
	if (num_connections > 1 &&
	    !(config->flags & NBD_FLAG_CAN_MULTI_CONN)) {
		dev_err(disk_to_dev(nbd->disk), "server does not support multiple connections per device.\n");
		return -EINVAL;
	}

retry:
	mutex_unlock(&nbd->config_lock);
	blk_mq_update_nr_hw_queues(&nbd->tag_set, num_connections);
	mutex_lock(&nbd->config_lock);

	/* if another code path updated nr_hw_queues, retry until succeed */
	if (num_connections != config->num_connections) {
		num_connections = config->num_connections;
		goto retry;
	}

	nbd->pid = task_pid_nr(current);

	nbd_parse_flags(nbd);

	error = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
	if (error) {
		dev_err(disk_to_dev(nbd->disk), "device_create_file failed for pid!\n");
		return error;
	}
	set_bit(NBD_RT_HAS_PID_FILE, &config->runtime_flags);

	nbd_dev_dbg_init(nbd);
	for (i = 0; i < num_connections; i++) {
		struct recv_thread_args *args;

		args = kzalloc_obj(*args);
		if (!args) {
			sock_shutdown(nbd);
			/*
			 * If num_connections is m (2 < m),
			 * and NO.1 ~ NO.n(1 < n < m) kzallocs are successful.
			 * But NO.(n + 1) failed. We still have n recv threads.
			 * So, add flush_workqueue here to prevent recv threads
			 * dropping the last config_refs and trying to destroy
			 * the workqueue from inside the workqueue.
			 */
			if (i)
				flush_workqueue(nbd->recv_workq);
			return -ENOMEM;
		}
		sk_set_memalloc(config->socks[i]->sock->sk);
		if (nbd->tag_set.timeout)
			config->socks[i]->sock->sk->sk_sndtimeo =
				nbd->tag_set.timeout;
		atomic_inc(&config->recv_threads);
		refcount_inc(&nbd->config_refs);
		INIT_WORK(&args->work, recv_work);
		args->nbd = nbd;
		args->nsock = config->socks[i];
		args->index = i;
		queue_work(nbd->recv_workq, &args->work);
	}
	return nbd_set_size(nbd, config->bytesize, nbd_blksize(config));
}

static int nbd_start_device_ioctl(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	int ret;

	ret = nbd_start_device(nbd);
	if (ret)
		return ret;

	if (max_part)
		set_bit(GD_NEED_PART_SCAN, &nbd->disk->state);
	mutex_unlock(&nbd->config_lock);
	ret = wait_event_interruptible(config->recv_wq,
					 atomic_read(&config->recv_threads) == 0);
	if (ret) {
		sock_shutdown(nbd);
		nbd_clear_que(nbd);
	}

	flush_workqueue(nbd->recv_workq);
	mutex_lock(&nbd->config_lock);
	nbd_bdev_reset(nbd);
	/* user requested, ignore socket errors */
	if (test_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags))
		ret = 0;
	if (test_bit(NBD_RT_TIMEDOUT, &config->runtime_flags))
		ret = -ETIMEDOUT;
	return ret;
}

static void nbd_clear_sock_ioctl(struct nbd_device *nbd)
{
	nbd_clear_sock(nbd);
	disk_force_media_change(nbd->disk);
	nbd_bdev_reset(nbd);
	if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF,
			       &nbd->config->runtime_flags))
		nbd_config_put(nbd);
}

static void nbd_set_cmd_timeout(struct nbd_device *nbd, u64 timeout)
{
	nbd->tag_set.timeout = timeout * HZ;
	if (timeout)
		blk_queue_rq_timeout(nbd->disk->queue, timeout * HZ);
	else
		blk_queue_rq_timeout(nbd->disk->queue, 30 * HZ);
}

/* Must be called with config_lock held */
static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
		       unsigned int cmd, unsigned long arg)
{
	struct nbd_config *config = nbd->config;
	loff_t bytesize;

	switch (cmd) {
	case NBD_DISCONNECT:
		return nbd_disconnect(nbd);
	case NBD_CLEAR_SOCK:
		nbd_clear_sock_ioctl(nbd);
		return 0;
	case NBD_SET_SOCK:
		return nbd_add_socket(nbd, arg, false);
	case NBD_SET_BLKSIZE:
		return nbd_set_size(nbd, config->bytesize, arg);
	case NBD_SET_SIZE:
		return nbd_set_size(nbd, arg, nbd_blksize(config));
	case NBD_SET_SIZE_BLOCKS:
		if (check_shl_overflow(arg, config->blksize_bits, &bytesize))
			return -EINVAL;
		return nbd_set_size(nbd, bytesize, nbd_blksize(config));
	case NBD_SET_TIMEOUT:
		nbd_set_cmd_timeout(nbd, arg);
		return 0;

	case NBD_SET_FLAGS:
		config->flags = arg;
		return 0;
	case NBD_DO_IT:
		return nbd_start_device_ioctl(nbd);
	case NBD_CLEAR_QUE:
		/*
		 * This is for compatibility only.  The queue is always cleared
		 * by NBD_DO_IT or NBD_CLEAR_SOCK.
		 */
		return 0;
	case NBD_PRINT_DEBUG:
		/*
		 * For compatibility only, we no longer keep a list of
		 * outstanding requests.
		 */
		return 0;
	}
	return -ENOTTY;
}

static int nbd_ioctl(struct block_device *bdev, blk_mode_t mode,
		     unsigned int cmd, unsigned long arg)
{
	struct nbd_device *nbd = bdev->bd_disk->private_data;
	struct nbd_config *config = nbd->config;
	int error = -EINVAL;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;

	/* The block layer will pass back some non-nbd ioctls in case we have
	 * special handling for them, but we don't so just return an error.
	 */
	if (_IOC_TYPE(cmd) != 0xab)
		return -EINVAL;

	mutex_lock(&nbd->config_lock);

	/* Don't allow ioctl operations on a nbd device that was created with
	 * netlink, unless it's DISCONNECT or CLEAR_SOCK, which are fine.
	 */
	if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
	    (cmd == NBD_DISCONNECT || cmd == NBD_CLEAR_SOCK))
		error = __nbd_ioctl(bdev, nbd, cmd, arg);
	else
		dev_err(nbd_to_dev(nbd), "Cannot use ioctl interface on a netlink controlled device.\n");
	mutex_unlock(&nbd->config_lock);
	return error;
}

static int nbd_alloc_and_init_config(struct nbd_device *nbd)
{
	struct nbd_config *config;

	if (WARN_ON(nbd->config))
		return -EINVAL;

	if (!try_module_get(THIS_MODULE))
		return -ENODEV;

	config = kzalloc_obj(struct nbd_config, GFP_NOFS);
	if (!config) {
		module_put(THIS_MODULE);
		return -ENOMEM;
	}

	atomic_set(&config->recv_threads, 0);
	init_waitqueue_head(&config->recv_wq);
	init_waitqueue_head(&config->conn_wait);
	config->blksize_bits = NBD_DEF_BLKSIZE_BITS;
	atomic_set(&config->live_connections, 0);

	nbd->config = config;
	/*
	 * Order refcount_set(&nbd->config_refs, 1) and nbd->config assignment,
	 * its pair is the barrier in nbd_get_config_unlocked().
	 * So nbd_get_config_unlocked() won't see nbd->config as null after
	 * refcount_inc_not_zero() succeed.
	 */
	smp_mb__before_atomic();
	refcount_set(&nbd->config_refs, 1);

	return 0;
}

static int nbd_open(struct gendisk *disk, blk_mode_t mode)
{
	struct nbd_device *nbd;
	struct nbd_config *config;
	int ret = 0;

	mutex_lock(&nbd_index_mutex);
	nbd = disk->private_data;
	if (!nbd) {
		ret = -ENXIO;
		goto out;
	}
	if (!refcount_inc_not_zero(&nbd->refs)) {
		ret = -ENXIO;
		goto out;
	}

	config = nbd_get_config_unlocked(nbd);
	if (!config) {
		mutex_lock(&nbd->config_lock);
		if (refcount_inc_not_zero(&nbd->config_refs)) {
			mutex_unlock(&nbd->config_lock);
			goto out;
		}
		ret = nbd_alloc_and_init_config(nbd);
		if (ret) {
			mutex_unlock(&nbd->config_lock);
			goto out;
		}

		refcount_inc(&nbd->refs);
		mutex_unlock(&nbd->config_lock);
		if (max_part)
			set_bit(GD_NEED_PART_SCAN, &disk->state);
	} else if (nbd_disconnected(config)) {
		if (max_part)
			set_bit(GD_NEED_PART_SCAN, &disk->state);
	}
out:
	mutex_unlock(&nbd_index_mutex);
	return ret;
}

static void nbd_release(struct gendisk *disk)
{
	struct nbd_device *nbd = disk->private_data;

	if (test_bit(NBD_RT_DISCONNECT_ON_CLOSE, &nbd->config->runtime_flags) &&
			disk_openers(disk) == 0)
		nbd_disconnect_and_put(nbd);

	nbd_config_put(nbd);
	nbd_put(nbd);
}

static void nbd_free_disk(struct gendisk *disk)
{
	struct nbd_device *nbd = disk->private_data;

	kfree(nbd);
}

static const struct block_device_operations nbd_fops =
{
	.owner =	THIS_MODULE,
	.open =		nbd_open,
	.release =	nbd_release,
	.ioctl =	nbd_ioctl,
	.compat_ioctl =	nbd_ioctl,
	.free_disk =	nbd_free_disk,
};

#if IS_ENABLED(CONFIG_DEBUG_FS)

static int nbd_dbg_tasks_show(struct seq_file *s, void *unused)
{
	struct nbd_device *nbd = s->private;

	if (nbd->pid)
		seq_printf(s, "recv: %d\n", nbd->pid);

	return 0;
}

DEFINE_SHOW_ATTRIBUTE(nbd_dbg_tasks);

static int nbd_dbg_flags_show(struct seq_file *s, void *unused)
{
	struct nbd_device *nbd = s->private;
	u32 flags = nbd->config->flags;

	seq_printf(s, "Hex: 0x%08x\n\n", flags);

	seq_puts(s, "Known flags:\n");

	if (flags & NBD_FLAG_HAS_FLAGS)
		seq_puts(s, "NBD_FLAG_HAS_FLAGS\n");
	if (flags & NBD_FLAG_READ_ONLY)
		seq_puts(s, "NBD_FLAG_READ_ONLY\n");
	if (flags & NBD_FLAG_SEND_FLUSH)
		seq_puts(s, "NBD_FLAG_SEND_FLUSH\n");
	if (flags & NBD_FLAG_SEND_FUA)
		seq_puts(s, "NBD_FLAG_SEND_FUA\n");
	if (flags & NBD_FLAG_SEND_TRIM)
		seq_puts(s, "NBD_FLAG_SEND_TRIM\n");
	if (flags & NBD_FLAG_SEND_WRITE_ZEROES)
		seq_puts(s, "NBD_FLAG_SEND_WRITE_ZEROES\n");
	if (flags & NBD_FLAG_ROTATIONAL)
		seq_puts(s, "NBD_FLAG_ROTATIONAL\n");

	return 0;
}

DEFINE_SHOW_ATTRIBUTE(nbd_dbg_flags);

static int nbd_dev_dbg_init(struct nbd_device *nbd)
{
	struct dentry *dir;
	struct nbd_config *config = nbd->config;

	if (!nbd_dbg_dir)
		return -EIO;

	dir = debugfs_create_dir(nbd_name(nbd), nbd_dbg_dir);
	if (IS_ERR(dir)) {
		dev_err(nbd_to_dev(nbd), "Failed to create debugfs dir for '%s'\n",
			nbd_name(nbd));
		return -EIO;
	}
	config->dbg_dir = dir;

	debugfs_create_file("tasks", 0444, dir, nbd, &nbd_dbg_tasks_fops);
	debugfs_create_u64("size_bytes", 0444, dir, &config->bytesize);
	debugfs_create_u32("timeout", 0444, dir, &nbd->tag_set.timeout);
	debugfs_create_u32("blocksize_bits", 0444, dir, &config->blksize_bits);
	debugfs_create_file("flags", 0444, dir, nbd, &nbd_dbg_flags_fops);

	return 0;
}

static void nbd_dev_dbg_close(struct nbd_device *nbd)
{
	debugfs_remove_recursive(nbd->config->dbg_dir);
}

static int nbd_dbg_init(void)
{
	struct dentry *dbg_dir;

	dbg_dir = debugfs_create_dir("nbd", NULL);
	if (IS_ERR(dbg_dir))
		return -EIO;

	nbd_dbg_dir = dbg_dir;

	return 0;
}

static void nbd_dbg_close(void)
{
	debugfs_remove_recursive(nbd_dbg_dir);
}

#else  /* IS_ENABLED(CONFIG_DEBUG_FS) */

static int nbd_dev_dbg_init(struct nbd_device *nbd)
{
	return 0;
}

static void nbd_dev_dbg_close(struct nbd_device *nbd)
{
}

static int nbd_dbg_init(void)
{
	return 0;
}

static void nbd_dbg_close(void)
{
}

#endif

static int nbd_init_request(struct blk_mq_tag_set *set, struct request *rq,
			    unsigned int hctx_idx, unsigned int numa_node)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(rq);
	cmd->nbd = set->driver_data;
	cmd->flags = 0;
	mutex_init(&cmd->lock);
	return 0;
}

static const struct blk_mq_ops nbd_mq_ops = {
	.queue_rq	= nbd_queue_rq,
	.complete	= nbd_complete_rq,
	.init_request	= nbd_init_request,
	.timeout	= nbd_xmit_timeout,
};

static struct nbd_device *nbd_dev_add(int index, unsigned int refs)
{
	struct queue_limits lim = {
		.max_hw_sectors		= 65536,
		.io_opt			= 256 << SECTOR_SHIFT,
		.max_segments		= USHRT_MAX,
		.max_segment_size	= UINT_MAX,
	};
	struct nbd_device *nbd;
	struct gendisk *disk;
	int err = -ENOMEM;

	nbd = kzalloc_obj(struct nbd_device);
	if (!nbd)
		goto out;

	nbd->tag_set.ops = &nbd_mq_ops;
	nbd->tag_set.nr_hw_queues = 1;
	nbd->tag_set.queue_depth = 128;
	nbd->tag_set.numa_node = NUMA_NO_NODE;
	nbd->tag_set.cmd_size = sizeof(struct nbd_cmd);
	nbd->tag_set.flags = BLK_MQ_F_BLOCKING;
	nbd->tag_set.driver_data = nbd;
	INIT_WORK(&nbd->remove_work, nbd_dev_remove_work);
	nbd->backend = NULL;

	err = blk_mq_alloc_tag_set(&nbd->tag_set);
	if (err)
		goto out_free_nbd;

	mutex_lock(&nbd_index_mutex);
	if (index >= 0) {
		err = idr_alloc(&nbd_index_idr, nbd, index, index + 1,
				GFP_KERNEL);
		if (err == -ENOSPC)
			err = -EEXIST;
	} else {
		err = idr_alloc(&nbd_index_idr, nbd, 0,
				(MINORMASK >> part_shift) + 1, GFP_KERNEL);
		if (err >= 0)
			index = err;
	}
	nbd->index = index;
	mutex_unlock(&nbd_index_mutex);
	if (err < 0)
		goto out_free_tags;

	disk = blk_mq_alloc_disk(&nbd->tag_set, &lim, NULL);
	if (IS_ERR(disk)) {
		err = PTR_ERR(disk);
		goto out_free_idr;
	}
	nbd->disk = disk;

	nbd->recv_workq = alloc_workqueue("nbd%d-recv",
					  WQ_MEM_RECLAIM | WQ_HIGHPRI |
					  WQ_UNBOUND, 0, nbd->index);
	if (!nbd->recv_workq) {
		dev_err(disk_to_dev(nbd->disk), "Could not allocate knbd recv work queue.\n");
		err = -ENOMEM;
		goto out_err_disk;
	}

	mutex_init(&nbd->config_lock);
	refcount_set(&nbd->config_refs, 0);
	/*
	 * Start out with a zero references to keep other threads from using
	 * this device until it is fully initialized.
	 */
	refcount_set(&nbd->refs, 0);
	INIT_LIST_HEAD(&nbd->list);
	disk->major = NBD_MAJOR;
	disk->first_minor = index << part_shift;
	disk->minors = 1 << part_shift;
	disk->fops = &nbd_fops;
	disk->private_data = nbd;
	sprintf(disk->disk_name, "nbd%d", index);
	err = add_disk(disk);
	if (err)
		goto out_free_work;

	/*
	 * Now publish the device.
	 */
	refcount_set(&nbd->refs, refs);
	nbd_total_devices++;
	return nbd;

out_free_work:
	destroy_workqueue(nbd->recv_workq);
out_err_disk:
	put_disk(disk);
out_free_idr:
	mutex_lock(&nbd_index_mutex);
	idr_remove(&nbd_index_idr, index);
	mutex_unlock(&nbd_index_mutex);
out_free_tags:
	blk_mq_free_tag_set(&nbd->tag_set);
out_free_nbd:
	kfree(nbd);
out:
	return ERR_PTR(err);
}

static struct nbd_device *nbd_find_get_unused(void)
{
	struct nbd_device *nbd;
	int id;

	lockdep_assert_held(&nbd_index_mutex);

	idr_for_each_entry(&nbd_index_idr, nbd, id) {
		if (refcount_read(&nbd->config_refs) ||
		    test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags))
			continue;
		if (refcount_inc_not_zero(&nbd->refs))
			return nbd;
	}

	return NULL;
}

/* Netlink interface. */
static const struct nla_policy nbd_attr_policy[NBD_ATTR_MAX + 1] = {
	[NBD_ATTR_INDEX]		=	{ .type = NLA_U32 },
	[NBD_ATTR_SIZE_BYTES]		=	{ .type = NLA_U64 },
	[NBD_ATTR_BLOCK_SIZE_BYTES]	=	{ .type = NLA_U64 },
	[NBD_ATTR_TIMEOUT]		=	{ .type = NLA_U64 },
	[NBD_ATTR_SERVER_FLAGS]		=	{ .type = NLA_U64 },
	[NBD_ATTR_CLIENT_FLAGS]		=	{ .type = NLA_U64 },
	[NBD_ATTR_SOCKETS]		=	{ .type = NLA_NESTED},
	[NBD_ATTR_DEAD_CONN_TIMEOUT]	=	{ .type = NLA_U64 },
	[NBD_ATTR_DEVICE_LIST]		=	{ .type = NLA_NESTED},
	[NBD_ATTR_BACKEND_IDENTIFIER]	=	{ .type = NLA_STRING},
};

static const struct nla_policy nbd_sock_policy[NBD_SOCK_MAX + 1] = {
	[NBD_SOCK_FD]			=	{ .type = NLA_U32 },
};

/* We don't use this right now since we don't parse the incoming list, but we
 * still want it here so userspace knows what to expect.
 */
static const struct nla_policy __attribute__((unused))
nbd_device_policy[NBD_DEVICE_ATTR_MAX + 1] = {
	[NBD_DEVICE_INDEX]		=	{ .type = NLA_U32 },
	[NBD_DEVICE_CONNECTED]		=	{ .type = NLA_U8 },
};

static int nbd_genl_size_set(struct genl_info *info, struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	u64 bsize = nbd_blksize(config);
	u64 bytes = config->bytesize;

	if (info->attrs[NBD_ATTR_SIZE_BYTES])
		bytes = nla_get_u64(info->attrs[NBD_ATTR_SIZE_BYTES]);

	if (info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES])
		bsize = nla_get_u64(info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES]);

	if (bytes != config->bytesize || bsize != nbd_blksize(config))
		return nbd_set_size(nbd, bytes, bsize);
	return 0;
}

static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
{
	struct nbd_device *nbd;
	struct nbd_config *config;
	int index = -1;
	int ret;
	bool put_dev = false;

	if (!netlink_capable(skb, CAP_SYS_ADMIN))
		return -EPERM;

	if (info->attrs[NBD_ATTR_INDEX]) {
		index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);

		/*
		 * Too big first_minor can cause duplicate creation of
		 * sysfs files/links, since index << part_shift might overflow, or
		 * MKDEV() expect that the max bits of first_minor is 20.
		 */
		if (index < 0 || index > MINORMASK >> part_shift) {
			pr_err("illegal input index %d\n", index);
			return -EINVAL;
		}
	}
	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SOCKETS)) {
		pr_err("must specify at least one socket\n");
		return -EINVAL;
	}
	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SIZE_BYTES)) {
		pr_err("must specify a size in bytes for the device\n");
		return -EINVAL;
	}
again:
	mutex_lock(&nbd_index_mutex);
	if (index == -1) {
		nbd = nbd_find_get_unused();
	} else {
		nbd = idr_find(&nbd_index_idr, index);
		if (nbd) {
			if ((test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags) &&
			     test_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags)) ||
			    !refcount_inc_not_zero(&nbd->refs)) {
				mutex_unlock(&nbd_index_mutex);
				pr_err("device at index %d is going down\n",
					index);
				return -EINVAL;
			}
		}
	}
	mutex_unlock(&nbd_index_mutex);

	if (!nbd) {
		nbd = nbd_dev_add(index, 2);
		if (IS_ERR(nbd)) {
			pr_err("failed to add new device\n");
			return PTR_ERR(nbd);
		}
	}

	mutex_lock(&nbd->config_lock);
	if (refcount_read(&nbd->config_refs)) {
		mutex_unlock(&nbd->config_lock);
		nbd_put(nbd);
		if (index == -1)
			goto again;
		pr_err("nbd%d already in use\n", index);
		return -EBUSY;
	}

	ret = nbd_alloc_and_init_config(nbd);
	if (ret) {
		mutex_unlock(&nbd->config_lock);
		nbd_put(nbd);
		pr_err("couldn't allocate config\n");
		return ret;
	}

	config = nbd->config;
	set_bit(NBD_RT_BOUND, &config->runtime_flags);
	ret = nbd_genl_size_set(info, nbd);
	if (ret)
		goto out;

	if (info->attrs[NBD_ATTR_TIMEOUT])
		nbd_set_cmd_timeout(nbd,
				    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
	if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
		config->dead_conn_timeout =
			nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
		config->dead_conn_timeout *= HZ;
	}
	if (info->attrs[NBD_ATTR_SERVER_FLAGS])
		config->flags =
			nla_get_u64(info->attrs[NBD_ATTR_SERVER_FLAGS]);
	if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
		u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
		if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
			/*
			 * We have 1 ref to keep the device around, and then 1
			 * ref for our current operation here, which will be
			 * inherited by the config.  If we already have
			 * DESTROY_ON_DISCONNECT set then we know we don't have
			 * that extra ref already held so we don't need the
			 * put_dev.
			 */
			if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
					      &nbd->flags))
				put_dev = true;
		} else {
			if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
					       &nbd->flags))
				refcount_inc(&nbd->refs);
		}
		if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
			set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
				&config->runtime_flags);
		}
	}

	if (info->attrs[NBD_ATTR_SOCKETS]) {
		struct nlattr *attr;
		int rem, fd;

		nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
				    rem) {
			struct nlattr *socks[NBD_SOCK_MAX+1];

			if (nla_type(attr) != NBD_SOCK_ITEM) {
				pr_err("socks must be embedded in a SOCK_ITEM attr\n");
				ret = -EINVAL;
				goto out;
			}
			ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
							  attr,
							  nbd_sock_policy,
							  info->extack);
			if (ret != 0) {
				pr_err("error processing sock list\n");
				ret = -EINVAL;
				goto out;
			}
			if (!socks[NBD_SOCK_FD])
				continue;
			fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
			ret = nbd_add_socket(nbd, fd, true);
			if (ret)
				goto out;
		}
	}

	if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
		nbd->backend = nla_strdup(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
					  GFP_KERNEL);
		if (!nbd->backend) {
			ret = -ENOMEM;
			goto out;
		}
	}
	ret = device_create_file(disk_to_dev(nbd->disk), &backend_attr);
	if (ret) {
		dev_err(disk_to_dev(nbd->disk),
			"device_create_file failed for backend!\n");
		goto out;
	}
	set_bit(NBD_RT_HAS_BACKEND_FILE, &config->runtime_flags);

	ret = nbd_start_device(nbd);
out:
	if (!ret) {
		set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);
		refcount_inc(&nbd->config_refs);
		nbd_connect_reply(info, nbd->index);
	}
	mutex_unlock(&nbd->config_lock);

	nbd_config_put(nbd);
	if (put_dev)
		nbd_put(nbd);
	return ret;
}

static void nbd_disconnect_and_put(struct nbd_device *nbd)
{
	mutex_lock(&nbd->config_lock);
	nbd_disconnect(nbd);
	sock_shutdown(nbd);
	wake_up(&nbd->config->conn_wait);
	/*
	 * Make sure recv thread has finished, we can safely call nbd_clear_que()
	 * to cancel the inflight I/Os.
	 */
	flush_workqueue(nbd->recv_workq);
	nbd_clear_que(nbd);
	nbd->task_setup = NULL;
	clear_bit(NBD_RT_BOUND, &nbd->config->runtime_flags);
	mutex_unlock(&nbd->config_lock);

	if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF,
			       &nbd->config->runtime_flags))
		nbd_config_put(nbd);
}

static int nbd_genl_disconnect(struct sk_buff *skb, struct genl_info *info)
{
	struct nbd_device *nbd;
	int index;

	if (!netlink_capable(skb, CAP_SYS_ADMIN))
		return -EPERM;

	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)) {
		pr_err("must specify an index to disconnect\n");
		return -EINVAL;
	}
	index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
	mutex_lock(&nbd_index_mutex);
	nbd = idr_find(&nbd_index_idr, index);
	if (!nbd) {
		mutex_unlock(&nbd_index_mutex);
		pr_err("couldn't find device at index %d\n", index);
		return -EINVAL;
	}
	if (!refcount_inc_not_zero(&nbd->refs)) {
		mutex_unlock(&nbd_index_mutex);
		pr_err("device at index %d is going down\n", index);
		return -EINVAL;
	}
	mutex_unlock(&nbd_index_mutex);
	if (!refcount_inc_not_zero(&nbd->config_refs))
		goto put_nbd;
	nbd_disconnect_and_put(nbd);
	nbd_config_put(nbd);
put_nbd:
	nbd_put(nbd);
	return 0;
}

static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
{
	struct nbd_device *nbd = NULL;
	struct nbd_config *config;
	int index;
	int ret = 0;
	bool put_dev = false;

	if (!netlink_capable(skb, CAP_SYS_ADMIN))
		return -EPERM;

	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)) {
		pr_err("must specify a device to reconfigure\n");
		return -EINVAL;
	}
	index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
	mutex_lock(&nbd_index_mutex);
	nbd = idr_find(&nbd_index_idr, index);
	if (!nbd) {
		mutex_unlock(&nbd_index_mutex);
		pr_err("couldn't find a device at index %d\n", index);
		return -EINVAL;
	}
	if (nbd->backend) {
		if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
			if (nla_strcmp(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
				       nbd->backend)) {
				mutex_unlock(&nbd_index_mutex);
				dev_err(nbd_to_dev(nbd),
					"backend image doesn't match with %s\n",
					nbd->backend);
				return -EINVAL;
			}
		} else {
			mutex_unlock(&nbd_index_mutex);
			dev_err(nbd_to_dev(nbd), "must specify backend\n");
			return -EINVAL;
		}
	}
	if (!refcount_inc_not_zero(&nbd->refs)) {
		mutex_unlock(&nbd_index_mutex);
		pr_err("device at index %d is going down\n", index);
		return -EINVAL;
	}
	mutex_unlock(&nbd_index_mutex);

	config = nbd_get_config_unlocked(nbd);
	if (!config) {
		dev_err(nbd_to_dev(nbd),
			"not configured, cannot reconfigure\n");
		nbd_put(nbd);
		return -EINVAL;
	}

	mutex_lock(&nbd->config_lock);
	if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
	    !nbd->pid) {
		dev_err(nbd_to_dev(nbd),
			"not configured, cannot reconfigure\n");
		ret = -EINVAL;
		goto out;
	}

	ret = nbd_genl_size_set(info, nbd);
	if (ret)
		goto out;

	if (info->attrs[NBD_ATTR_TIMEOUT])
		nbd_set_cmd_timeout(nbd,
				    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
	if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
		config->dead_conn_timeout =
			nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
		config->dead_conn_timeout *= HZ;
	}
	if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
		u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
		if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
			if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
					      &nbd->flags))
				put_dev = true;
		} else {
			if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
					       &nbd->flags))
				refcount_inc(&nbd->refs);
		}

		if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
			set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
					&config->runtime_flags);
		} else {
			clear_bit(NBD_RT_DISCONNECT_ON_CLOSE,
					&config->runtime_flags);
		}
	}

	if (info->attrs[NBD_ATTR_SOCKETS]) {
		struct nlattr *attr;
		int rem, fd;

		nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
				    rem) {
			struct nlattr *socks[NBD_SOCK_MAX+1];

			if (nla_type(attr) != NBD_SOCK_ITEM) {
				pr_err("socks must be embedded in a SOCK_ITEM attr\n");
				ret = -EINVAL;
				goto out;
			}
			ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
							  attr,
							  nbd_sock_policy,
							  info->extack);
			if (ret != 0) {
				pr_err("error processing sock list\n");
				ret = -EINVAL;
				goto out;
			}
			if (!socks[NBD_SOCK_FD])
				continue;
			fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
			ret = nbd_reconnect_socket(nbd, fd);
			if (ret) {
				if (ret == -ENOSPC)
					ret = 0;
				goto out;
			}
			dev_info(nbd_to_dev(nbd), "reconnected socket\n");
		}
	}
out:
	mutex_unlock(&nbd->config_lock);
	nbd_config_put(nbd);
	nbd_put(nbd);
	if (put_dev)
		nbd_put(nbd);
	return ret;
}

static const struct genl_small_ops nbd_connect_genl_ops[] = {
	{
		.cmd	= NBD_CMD_CONNECT,
		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
		.doit	= nbd_genl_connect,
	},
	{
		.cmd	= NBD_CMD_DISCONNECT,
		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
		.doit	= nbd_genl_disconnect,
	},
	{
		.cmd	= NBD_CMD_RECONFIGURE,
		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
		.doit	= nbd_genl_reconfigure,
	},
	{
		.cmd	= NBD_CMD_STATUS,
		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
		.doit	= nbd_genl_status,
	},
};

static const struct genl_multicast_group nbd_mcast_grps[] = {
	{ .name = NBD_GENL_MCAST_GROUP_NAME, },
};

static struct genl_family nbd_genl_family __ro_after_init = {
	.hdrsize	= 0,
	.name		= NBD_GENL_FAMILY_NAME,
	.version	= NBD_GENL_VERSION,
	.module		= THIS_MODULE,
	.small_ops	= nbd_connect_genl_ops,
	.n_small_ops	= ARRAY_SIZE(nbd_connect_genl_ops),
	.resv_start_op	= NBD_CMD_STATUS + 1,
	.maxattr	= NBD_ATTR_MAX,
	.netnsok	= 1,
	.policy = nbd_attr_policy,
	.mcgrps		= nbd_mcast_grps,
	.n_mcgrps	= ARRAY_SIZE(nbd_mcast_grps),
};
MODULE_ALIAS_GENL_FAMILY(NBD_GENL_FAMILY_NAME);

static int populate_nbd_status(struct nbd_device *nbd, struct sk_buff *reply)
{
	struct nlattr *dev_opt;
	u8 connected = 0;
	int ret;

	/* This is a little racey, but for status it's ok.  The
	 * reason we don't take a ref here is because we can't
	 * take a ref in the index == -1 case as we would need
	 * to put under the nbd_index_mutex, which could
	 * deadlock if we are configured to remove ourselves
	 * once we're disconnected.
	 */
	if (refcount_read(&nbd->config_refs))
		connected = 1;
	dev_opt = nla_nest_start_noflag(reply, NBD_DEVICE_ITEM);
	if (!dev_opt)
		return -EMSGSIZE;
	ret = nla_put_u32(reply, NBD_DEVICE_INDEX, nbd->index);
	if (ret)
		return -EMSGSIZE;
	ret = nla_put_u8(reply, NBD_DEVICE_CONNECTED,
			 connected);
	if (ret)
		return -EMSGSIZE;
	nla_nest_end(reply, dev_opt);
	return 0;
}

static int status_cb(int id, void *ptr, void *data)
{
	struct nbd_device *nbd = ptr;
	return populate_nbd_status(nbd, (struct sk_buff *)data);
}

static int nbd_genl_status(struct sk_buff *skb, struct genl_info *info)
{
	struct nlattr *dev_list;
	struct sk_buff *reply;
	void *reply_head;
	size_t msg_size;
	int index = -1;
	int ret = -ENOMEM;

	if (info->attrs[NBD_ATTR_INDEX])
		index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);

	mutex_lock(&nbd_index_mutex);

	msg_size = nla_total_size(nla_attr_size(sizeof(u32)) +
				  nla_attr_size(sizeof(u8)));
	msg_size *= (index == -1) ? nbd_total_devices : 1;

	reply = genlmsg_new(msg_size, GFP_KERNEL);
	if (!reply)
		goto out;
	reply_head = genlmsg_put_reply(reply, info, &nbd_genl_family, 0,
				       NBD_CMD_STATUS);
	if (!reply_head) {
		nlmsg_free(reply);
		goto out;
	}

	dev_list = nla_nest_start_noflag(reply, NBD_ATTR_DEVICE_LIST);
	if (!dev_list) {
		nlmsg_free(reply);
		ret = -EMSGSIZE;
		goto out;
	}

	if (index == -1) {
		ret = idr_for_each(&nbd_index_idr, &status_cb, reply);
		if (ret) {
			nlmsg_free(reply);
			goto out;
		}
	} else {
		struct nbd_device *nbd;
		nbd = idr_find(&nbd_index_idr, index);
		if (nbd) {
			ret = populate_nbd_status(nbd, reply);
			if (ret) {
				nlmsg_free(reply);
				goto out;
			}
		}
	}
	nla_nest_end(reply, dev_list);
	genlmsg_end(reply, reply_head);
	ret = genlmsg_reply(reply, info);
out:
	mutex_unlock(&nbd_index_mutex);
	return ret;
}

static void nbd_connect_reply(struct genl_info *info, int index)
{
	struct sk_buff *skb;
	void *msg_head;
	int ret;

	skb = genlmsg_new(nla_total_size(sizeof(u32)), GFP_KERNEL);
	if (!skb)
		return;
	msg_head = genlmsg_put_reply(skb, info, &nbd_genl_family, 0,
				     NBD_CMD_CONNECT);
	if (!msg_head) {
		nlmsg_free(skb);
		return;
	}
	ret = nla_put_u32(skb, NBD_ATTR_INDEX, index);
	if (ret) {
		nlmsg_free(skb);
		return;
	}
	genlmsg_end(skb, msg_head);
	genlmsg_reply(skb, info);
}

static void nbd_mcast_index(int index)
{
	struct sk_buff *skb;
	void *msg_head;
	int ret;

	skb = genlmsg_new(nla_total_size(sizeof(u32)), GFP_KERNEL);
	if (!skb)
		return;
	msg_head = genlmsg_put(skb, 0, 0, &nbd_genl_family, 0,
				     NBD_CMD_LINK_DEAD);
	if (!msg_head) {
		nlmsg_free(skb);
		return;
	}
	ret = nla_put_u32(skb, NBD_ATTR_INDEX, index);
	if (ret) {
		nlmsg_free(skb);
		return;
	}
	genlmsg_end(skb, msg_head);
	genlmsg_multicast(&nbd_genl_family, skb, 0, 0, GFP_KERNEL);
}

static void nbd_dead_link_work(struct work_struct *work)
{
	struct link_dead_args *args = container_of(work, struct link_dead_args,
						   work);
	nbd_mcast_index(args->index);
	kfree(args);
}

static int __init nbd_init(void)
{
	int i;

	BUILD_BUG_ON(sizeof(struct nbd_request) != 28);

	if (max_part < 0) {
		pr_err("max_part must be >= 0\n");
		return -EINVAL;
	}

	part_shift = 0;
	if (max_part > 0) {
		part_shift = fls(max_part);

		/*
		 * Adjust max_part according to part_shift as it is exported
		 * to user space so that user can know the max number of
		 * partition kernel should be able to manage.
		 *
		 * Note that -1 is required because partition 0 is reserved
		 * for the whole disk.
		 */
		max_part = (1UL << part_shift) - 1;
	}

	if ((1UL << part_shift) > DISK_MAX_PARTS)
		return -EINVAL;

	if (nbds_max > 1UL << (MINORBITS - part_shift))
		return -EINVAL;

	if (register_blkdev(NBD_MAJOR, "nbd"))
		return -EIO;

	nbd_del_wq = alloc_workqueue("nbd-del", WQ_UNBOUND, 0);
	if (!nbd_del_wq) {
		unregister_blkdev(NBD_MAJOR, "nbd");
		return -ENOMEM;
	}

	if (genl_register_family(&nbd_genl_family)) {
		destroy_workqueue(nbd_del_wq);
		unregister_blkdev(NBD_MAJOR, "nbd");
		return -EINVAL;
	}
	nbd_dbg_init();

	for (i = 0; i < nbds_max; i++)
		nbd_dev_add(i, 1);
	return 0;
}

static int nbd_exit_cb(int id, void *ptr, void *data)
{
	struct list_head *list = (struct list_head *)data;
	struct nbd_device *nbd = ptr;

	/* Skip nbd that is being removed asynchronously */
	if (refcount_read(&nbd->refs))
		list_add_tail(&nbd->list, list);

	return 0;
}

static void __exit nbd_cleanup(void)
{
	struct nbd_device *nbd;
	LIST_HEAD(del_list);

	/*
	 * Unregister netlink interface prior to waiting
	 * for the completion of netlink commands.
	 */
	genl_unregister_family(&nbd_genl_family);

	nbd_dbg_close();

	mutex_lock(&nbd_index_mutex);
	idr_for_each(&nbd_index_idr, &nbd_exit_cb, &del_list);
	mutex_unlock(&nbd_index_mutex);

	while (!list_empty(&del_list)) {
		nbd = list_first_entry(&del_list, struct nbd_device, list);
		list_del_init(&nbd->list);
		if (refcount_read(&nbd->config_refs))
			pr_err("possibly leaking nbd_config (ref %d)\n",
					refcount_read(&nbd->config_refs));
		if (refcount_read(&nbd->refs) != 1)
			pr_err("possibly leaking a device\n");
		nbd_put(nbd);
	}

	/* Also wait for nbd_dev_remove_work() completes */
	destroy_workqueue(nbd_del_wq);

	idr_destroy(&nbd_index_idr);
	unregister_blkdev(NBD_MAJOR, "nbd");
}

module_init(nbd_init);
module_exit(nbd_cleanup);

MODULE_DESCRIPTION("Network Block Device");
MODULE_LICENSE("GPL");

module_param(nbds_max, int, 0444);
MODULE_PARM_DESC(nbds_max, "number of network block devices to initialize (default: 16)");
module_param(max_part, int, 0444);
MODULE_PARM_DESC(max_part, "number of partitions per device (default: 16)");
]

gemini-3-flash-preview

							input: 59036
							output: 40
							thoughts: 2494
						

**Analysis of the NBD Code with Duplicate Sockets**

Okay, here's my breakdown of this NBD code situation.  I've been reviewing this, and here are my conclusions.

First, I see the issue.  When `nbd_genl_connect` is fed the same file descriptor (FD) twice, the code diligently calls `nbd_add_socket` twice, leading to some, shall we say, *interesting* behavior. `nbd_add_socket` then uses `sockfd_lookup`, which increments the reference count of the socket's associated `struct file`. This is called twice, and thus the refcount is incremented twice.

This creates *two* `nbd_sock` structures, but both point to the *same* `struct socket`.  This is the first area of concern. When `nbd_start_device` is triggered it starts threads that will call `nbd_read_reply` on this single shared socket.

The core problem, from my perspective, is the stream corruption. With multiple threads reading from the same TCP stream, they're going to step on each other's toes.  Data will get interleaved, magic numbers will be wrong, and the NBD protocol will get completely messed up.  When errors are hit, `nbd_mark_nsock_dead` gets called. This then does the *safe* thing by shutting down the socket, but the core issue of data being read out of order on a single socket is the root cause. It also correctly decrements `config->live_connections`.

The cleanup in `nbd_config_put` is fine. `sockfd_put` is called twice, but that's perfectly acceptable since `sockfd_lookup` was called twice, keeping the refcount in sync with what the kernel expects.

The `sk_set_memalloc` function's got my attention, as does the `static_branch_inc` call.  The NBD driver, as it's written now, never calls `sk_clear_memalloc`, which means that it won't actually be balanced. Thus the `memalloc_socks_key` counter will leak. This is a general bug in NBD (not just this scenario) and can be exacerbated by duplicate FDs. While this is a bug, it likely doesn't lead to panic or deadlock, but might have some performance implications on the networking stack (although this is relatively minor).

The `nsock->tx_lock` mutexes are different, but the code isn't protecting access to the *socket* itself with one, so two threads can simultaneously use `sock_sendmsg` on the *same* socket. This creates outgoing stream corruption.

**So, the likely outcomes?:**

*   **Panic**: Unlikely. The TCP stack and NBD driver handle protocol errors.
*   **Deadlock**: Also, unlikely. The locks involved seem to be handled in a way that avoids deadlock, even with duplicate sockets.
*   **Bug**: *Absolutely*. The lack of checking for duplicate sockets leads to the real problem: stream corruption on both incoming *and* outgoing streams. The `memalloc_socks_key` leak is a bug as well.

I checked for the situation where `sockfd_put` is called on a freed socket: no, that's not possible with this current logic. Even if the user closes the FD in userspace, the kernel keeps the `struct file` (and thus the `struct socket`) alive until all references are dropped. The same goes for the other case where the socket is reconnected with the same FD.

I also checked to see how NBD handles the replies. Even if the replies come in out of order, the current `blk_mq_complete_request` logic seems fine. The `nbd_handle_reply` function is built in a way to handle this.

The crucial issue is the interleaving of reads for the *same* reply. Thread A reads part of a reply, Thread B reads the rest. That leads to garbled reads and the connection shutting down.

The call to `sockfd_put` and the `kfree` of the configuration are all safe, as the code as written correctly handles these references.

I looked at the `work_struct` in `nsock`. I can confirm each `nsock` has its own `work_struct`, which is fine.

I also looked at how each `nbd_cmd` is handled. If the data gets corrupted, it *might* find the wrong NBD command, but I see protections for that to prevent it from failing as well.

I confirmed that `nbd_add_socket` and `nbd_start_device` are synchronized using `nbd->config_lock`.

As a final note, I also checked

map[ContextFile:net/core/sock.c IncludeLines:true Name:sk_destruct]

map[SourceCode:2402:	void sk_destruct(struct sock *sk)
2403:	{
2404:		bool use_call_rcu = sock_flag(sk, SOCK_RCU_FREE);
2405:	
2406:		if (rcu_access_pointer(sk->sk_reuseport_cb)) {
2407:			reuseport_detach_sock(sk);
2408:			use_call_rcu = true;
2409:		}
2410:	
2411:		if (use_call_rcu)
2412:			call_rcu(&sk->sk_rcu, __sk_destruct);
2413:		else
2414:			__sk_destruct(&sk->sk_rcu);
2415:	}
 SourceFile:net/core/sock.c]

gemini-3-flash-preview

							input: 62836
							output: 41
							thoughts: 8
						

Okay, here's the summary, rendered as your thoughts as an expert:

**Understanding `__sk_destruct` and its Role**

Alright, let's break this down. When I see `__sk_destruct`, my mind immediately goes to the heart of resource management, especially within a kernel or operating system context. It's a clear signal that we're dealing with something related to deallocation, cleanup, or finalization of a specific data structure or object. The double underscore prefix is a key indicator to me that this function is likely an internal, implementation-specific detail. I wouldn't expect to be calling this directly in user space; it's the kind of function that the kernel or a specific driver calls to handle the intricacies of object lifecycle.

My initial hypothesis is that this likely relates to the deallocation of some structure tied to sockets or networking. The `sk` prefix, combined with `destruct`, strongly suggests a "socket" object is the subject. It is likely called during the deallocation of a socket, or on the destruction of an object with ties to network resources.

I'm starting to think about potential scenarios: garbage collection? Reference counting? Automatic Memory Management? Probably not any of those as the design of a kernel is likely manual. The key to the process will be freeing up network buffers, closing file descriptors, decrementing reference counts, and ensuring that no lingering resources cause memory leaks or other issues. Given the naming, `__sk_destruct` could be associated with freeing the memory of a socket.

The challenge is usually atomicity. If this function is part of a multi-threaded system, I need to consider synchronization. Ensuring that cleanup happens in the correct order, that there are no race conditions, is absolutely paramount to avoid corruption or dangling pointers. I'd be looking closely at any locking mechanisms involved to ensure it's thread-safe and can handle concurrent access correctly. I'd also be curious about the handling of potential errors. Does it return an error code? Log warnings? Panic? The error handling strategy is crucial to understanding the robustness of the system.

Ultimately, I'd expect `__sk_destruct` to be a critical piece of code ensuring the stability and reliability of the networking subsystem. This function is likely part of the low-level infrastructure, and requires meticulous analysis.

map[ContextFile:net/core/sock.c IncludeLines:true Name:__sk_destruct]

map[SourceCode:2342:	/* Sockets having SOCK_RCU_FREE will call this function after one RCU
2343:	 * grace period. This is the case for UDP sockets and TCP listeners.
2344:	 */
2345:	static void __sk_destruct(struct rcu_head *head)
2346:	{
2347:		struct sock *sk = container_of(head, struct sock, sk_rcu);
2348:		struct net *net = sock_net(sk);
2349:		struct sk_filter *filter;
2350:	
2351:		if (sk->sk_destruct)
2352:			sk->sk_destruct(sk);
2353:	
2354:		filter = rcu_dereference_check(sk->sk_filter,
2355:					       refcount_read(&sk->sk_wmem_alloc) == 0);
2356:		if (filter) {
2357:			sk_filter_uncharge(sk, filter);
2358:			RCU_INIT_POINTER(sk->sk_filter, NULL);
2359:		}
2360:	
2361:		sock_disable_timestamp(sk, SK_FLAGS_TIMESTAMP);
2362:	
2363:	#ifdef CONFIG_BPF_SYSCALL
2364:		bpf_sk_storage_free(sk);
2365:	#endif
2366:	
2367:		if (atomic_read(&sk->sk_omem_alloc))
2368:			pr_debug("%s: optmem leakage (%d bytes) detected\n",
2369:				 __func__, atomic_read(&sk->sk_omem_alloc));
2370:	
2371:		if (sk->sk_frag.page) {
2372:			put_page(sk->sk_frag.page);
2373:			sk->sk_frag.page = NULL;
2374:		}
2375:	
2376:		/* We do not need to acquire sk->sk_peer_lock, we are the last user. */
2377:		put_cred(sk->sk_peer_cred);
2378:		put_pid(sk->sk_peer_pid);
2379:	
2380:		if (likely(sk->sk_net_refcnt)) {
2381:			put_net_track(net, &sk->ns_tracker);
2382:		} else {
2383:			__netns_tracker_free(net, &sk->ns_tracker, false);
2384:			net_passive_dec(net);
2385:		}
2386:		sk_prot_free(sk->sk_prot_creator, sk);
2387:	}
 SourceFile:net/core/sock.c]

gemini-3-flash-preview

							input: 64142
							output: 42
							thoughts: 74
						

Okay, here's my interpretation of this debugging thought process, tailored for an expert like myself:

**Tracing Memory Allocation/Deallocation in Sockets**

Alright, I'm diving into the socket destruction path, specifically `__sk_destruct`. I was expecting to see the clean up of memory allocation here, but I'm not spotting either `sk_clear_memalloc` or any use of `static_branch_dec(&memalloc_socks_key)` within this function. That's a bit of a red flag; if `sk_set_memalloc` is indeed incrementing some kind of global counter to track socket memory allocation, then *something* absolutely has to decrement it to maintain integrity. I need to figure out where that counterpart lives. Time to revisit `sk_clear_memalloc` and make sure I haven't missed something fundamental. I need to understand the mechanism behind the accounting, or I'm headed for a memory leak.

map[ContextFile:net/core/sock.c IncludeLines:true Name:sk_clear_memalloc]

map[SourceCode: 310:	void sk_clear_memalloc(struct sock *sk)
 311:	{
 312:		sock_reset_flag(sk, SOCK_MEMALLOC);
 313:		sk->sk_allocation &= ~__GFP_MEMALLOC;
 314:		static_branch_dec(&memalloc_socks_key);
 315:	
 316:		/*
 317:		 * SOCK_MEMALLOC is allowed to ignore rmem limits to ensure forward
 318:		 * progress of swapping. SOCK_MEMALLOC may be cleared while
 319:		 * it has rmem allocations due to the last swapfile being deactivated
 320:		 * but there is a risk that the socket is unusable due to exceeding
 321:		 * the rmem limits. Reclaim the reserves and obey rmem limits again.
 322:		 */
 323:		sk_mem_reclaim(sk);
 324:	}
 SourceFile:net/core/sock.c]

gemini-3-flash-preview

							input: 64734
							output: 20
							thoughts: 132
						

Here's my analysis of the situation:

**Investigating a Potential Memory Leak in the NBD Driver**

Okay, so I'm thinking about this `sk_clear_memalloc` function and how it relates to the NBD driver. I can see that `sk_clear_memalloc` definitely *decrements* something related to memory allocation. My immediate concern is this: if NBD calls `sk_set_memalloc` but *never* calls `sk_clear_memalloc`, then we've got a clear static branch leak. That's a definite bug in the NBD implementation. And if someone provides the same file descriptor twice... boom, we're leaking it twice.

But hold on, the user's initial question was about panic or deadlock, not a simple memory leak. Leaking a static branch is a problem, no doubt, but that alone shouldn't trigger a crash or hang the system.

Okay, let me backtrack and try another angle. I'm going to look through the git logs for commits related to "nbd sk_set_memalloc". There could be a relevant fix or a clue to some related issue I haven't considered. I'm going to search with that search term, and see what comes up.

map[Dir:Documentation/]

map[Files:<nil> Subdirs:[ABI PCI RCU accel accounting admin-guide arch block bpf cdrom core-api cpu-freq crypto dev-tools devicetree doc-guide driver-api edac fault-injection fb features filesystems firmware-guide firmware_class fpga gpu hid hwmon i2c iio images infiniband input kbuild kernel-hacking leds litmus-tests livepatch locking maintainer mhi misc-devices mm netlabel netlink networking nvdimm nvme pcmcia peci power process rust scheduler scsi security sound sphinx sphinx-includes sphinx-static spi staging sunrpc target tee timers tools trace translations usb userspace-api virt w1 watchdog wmi]]

gemini-3-flash-preview

							input: 65537
							output: 24
							thoughts: 25
						

Okay, here's my take on those thoughts, tailored for an expert audience:

**Tracing the Genesis of `sk_set_memalloc` in `nbd.c`**

Alright, let's get down to brass tacks. I need to pinpoint when `sk_set_memalloc` was introduced within the `nbd.c` codebase. Given the importance of memory allocation within a driver like NBD, I figure understanding its introduction is key to grasping its intended use and any potential evolution in that area. I'll fire up my trusty search tool—likely `git log -S sk_set_memalloc nbd.c` or something similar, depending on the repo structure—and let it chew on that query. The goal is a quick and dirty find of the commit that birthed this function. From there, I can examine the surrounding code, the commit message, any related issues or discussions linked to that commit, and so on. Understanding the context of its addition will shed light on why it was implemented the way it was, and give me a foundation for further investigation of any subtle issues or improvements.

map[Name:sk_set_memalloc]

map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nbd_reconnect_socket SourceFile:drivers/block/nbd.c SourceLine:1342] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nbd_start_device SourceFile:drivers/block/nbd.c SourceLine:1528] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nvme_tcp_alloc_queue SourceFile:drivers/nvme/host/tcp.c SourceLine:1849] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:set_sock_opts SourceFile:drivers/net/wireguard/socket.c SourceLine:345]] TruncatedOutput:false]

gemini-3-flash-preview

							input: 66054
							output: 780
							thoughts: 1754
						

**My Analysis of the NBD Driver Issue**

Okay, so the user is asking about potential bugs, kernel panics, or deadlocks in the NBD driver, specifically focusing on a scenario where `sockfd_put` is called twice on the same socket, as a consequence of the duplicate file descriptor issue. I've done a thorough review.

First, I examined `drivers/block/nbd.c` and specifically focused on the relevant code paths, inferring behavior since I can't directly use `git blame` or `git log`. My analysis is:

1.  **The Root Bug:** The fundamental issue lies in `nbd_genl_connect`. It *doesn't* check for duplicate file descriptors within the `NBD_ATTR_SOCKETS` attribute. This allows a user to provide the same socket file descriptor multiple times.
2.  **Protocol Corruption:** This duplication leads to multiple `nsock` structures being created, *all* pointing to the same socket (`sock`). Crucially, each `nsock` gets its own `tx_lock`.  The result is that *multiple threads* can simultaneously write to the same socket, corrupting the NBD data stream, leading to unpredictable behavior.
3.  **Reference Counting (Correct):** The fact that `sockfd_put` *is* called twice (in the scenario the user pointed out) is actually *correct* from a reference counting perspective.  It's a *symptom* of the underlying bug. The code in `nbd_genl_connect` does a `sockfd_lookup` twice, and therefore `sockfd_put` must be called twice.
4.  **Panic/Deadlock (Unlikely):** While the protocol corruption is serious, a kernel panic or deadlock is *unlikely* to occur directly. The stream corruption will lead to errors in the NBD protocol, causing the connection to be shut down and cleaned up. The driver seems to have appropriate error handling for that situation.
5.  **Resource Leak:** There is a resource leak: `memalloc_socks_key` is set using `sk_set_memalloc`, but `sk_clear_memalloc` is never called. Providing the same FD twice doubles this leak.

Now, I also thought it would be prudent to investigate other potential issues.

I verified that `nbd_read_reply` won't cause infinite loops due to improper return values.

I then considered READ requests, where I hypothesized that if two threads were reading from the same socket, there might be interleaving of reads and data corruption. Indeed, if two threads are reading from the same socket, one in `nbd_handle_reply` and the other in `nbd_read_reply` due to a duplicate socket, it could cause data corruption and subsequent errors (Wrong magic, Receive data failed). Both threads would call `nbd_mark_nsock_dead`, and the connection will be shut down.

I then looked at the refcounting and locking for `nbd_config_put`. I am confident that there is no risk of `nbd_config_put` being called while another thread is still using the config because the standard way is used, with `refcount_dec_and_mutex_lock` and appropriate references.

Next, I looked at the balancing of references with `nbd_get_config_unlocked` and `nbd_config_put`. This is balanced.

I verified the correct socket reference counting:
*   I considered cases where `nbd_add_socket` could fail, and I verified that in those cases `sockfd_put` is called correctly.
*   I checked what if `krealloc` fails. The code is structured correctly to avoid problems, by using `sockfd_put` and returning.

I looked into possible deadlocks involving `blk_mq_freeze_queue` called by `nbd_add_socket` and `blk_mq_update_nr_hw_queues` called by `nbd_start_device`. But the queue is reentrant, and all is properly synchronized with `config_lock` and freezing.

I reconfirmed my understanding of the user's scenario and the double call to `sockfd_put` and that it is correct.

I verified that `nbd_mark_nsock_dead` calling `kernel_sock_shutdown` wouldn't be a problem if it's called twice for the same socket.

Finally, I checked that `sock->file` would always be valid when `sockfd_put` uses it, and I checked `nbd_reconnect_socket`.

Therefore, my conclusions are:

*   The critical bug is duplicate socket registration in `nbd_genl_connect`.
*   The effects are data stream corruption and a `mem

gemini-3.1-pro-preview

							input: 296793
							output: 189
							thoughts: 62911
						

map[Question:In drivers/block/nbd.c, nbd_genl_connect parses NBD_ATTR_SOCKETS. If the user provides the SAME fd twice in the nested attributes, nbd_add_socket is called twice with the same fd. This results in config->socks[0]->sock and config->socks[1]->sock pointing to the SAME socket. Then nbd_start_device is called, which queues TWO recv_work threads. Both threads call nbd_read_reply on the SAME socket. When the socket is closed, both threads wake up, call nbd_mark_nsock_dead, and then call nbd_config_put. In nbd_config_put, sockfd_put is called twice on the same socket. Is there any bug here? Could this cause a kernel panic or deadlock?]

map[Answer:The scenario you described is indeed possible because `nbd_genl_connect` (and the legacy `NBD_SET_SOCK` ioctl) does not check if the same file descriptor (fd) is provided multiple times. This leads to several issues, although a kernel panic or deadlock is unlikely.

### Analysis of the Issues

1.  **Duplicate Reference Counting**: When `nbd_add_socket` is called, it invokes `nbd_get_socket`, which calls `sockfd_lookup(fd, &err)`. This function increments the reference count of the underlying `struct file` (and thus the socket). If the same fd is provided twice, `sockfd_lookup` is called twice, incrementing the reference count twice. Consequently, when `nbd_config_put` calls `sockfd_put` twice on the same socket pointer, it is correctly decrementing the two references obtained earlier. **This part of the logic is actually correct and will not cause a double-free or a kernel panic.**

2.  **Stream Corruption (The Real Bug)**: Each call to `nbd_add_socket` allocates a new `struct nbd_sock` structure. Each `nbd_sock` has its own `tx_lock` mutex. If two `nsock` structures point to the same socket, the intended synchronization is bypassed. Two threads can simultaneously call `sock_sendmsg` on the same socket, leading to interleaved headers and data, which corrupts the NBD protocol stream.

3.  **Protocol Errors**: As you noted, two `recv_work` threads will be spawned, both calling `nbd_read_reply` on the same socket. Since TCP is a stream, the two threads will compete for data. One thread might read part of a reply header, and the other might read the rest. Both will encounter "Wrong magic" errors or invalid cookies and call `nbd_mark_nsock_dead`.

4.  **Resource Leak**: In `nbd_start_device`, `sk_set_memalloc` is called for each connection. This function increments a global `memalloc_socks_key` (a static branch counter). However, the NBD driver never calls `sk_clear_memalloc`. This results in a leak of the static branch reference. Providing the same FD twice doubles this leak. While not a panic, it's a persistent resource leak in the networking stack.

### Potential for Panic or Deadlock

*   **Panic**: Unlikely. The kernel's socket and file reference counting handles the duplicate `sockfd_put` correctly. The protocol corruption will lead to EPROTO errors and connection teardown, but the driver's state management (using `config_refs` and `config_lock`) is robust enough to handle this without crashing.
*   **Deadlock**: Unlikely. The locks (`cmd->lock`, `nsock->tx_lock`, `config_lock`) are used consistently. Since each `nsock` has its own `tx_lock`, there is no circular dependency introduced by having duplicate sockets; they simply fail to provide the necessary mutual exclusion for the shared socket.

### Summary
There is a **bug** in the sense that the driver allows a misconfigured state that leads to data corruption on the wire and a minor resource leak (`memalloc_socks_key`). However, it is **not** a bug that would typically cause a kernel panic or a deadlock. The reference counting for the socket itself is handled correctly by the underlying VFS and socket layers.

To fix this, the NBD driver should ideally check if a socket is already assigned to the device before adding it in `nbd_add_socket`.]

gemini-3-flash-preview

You are a capable Linux kernel developer tasked with researching complex questions
about kernel source code. You will be given a concrete question, and need to provide
a concrete answer.
Use tools extensively while researching the question. Don't make assumptions,
or rely on your previous knowledge about the kernel source code, use available tools
to access the actual source code.
Use all available sources of information:
 - kernel source code
 - documentation in the Documentation dir in the source tree
 - git commits descriptions, git blame

Prefer calling several tools at the same time to save round-trips.

In drivers/block/nbd.c, nbd_genl_connect parses NBD_ATTR_SOCKETS. If the user provides the SAME fd twice in the nested attributes, nbd_add_socket is called twice with the same fd. This results in config->socks[0]->sock and config->socks[1]->sock pointing to the SAME socket. Then nbd_start_device is called, which queues TWO recv_work threads. Both threads call nbd_read_reply on the SAME socket. When the socket is closed, both threads wake up, call nbd_mark_nsock_dead, and then call nbd_config_put. In nbd_config_put, sockfd_put is called twice on the same socket. Is there any bug here? Could this cause a kernel panic or deadlock?

The scenario you described is indeed possible because `nbd_genl_connect` (and the legacy `NBD_SET_SOCK` ioctl) does not check if the same file descriptor (fd) is provided multiple times. This leads to several issues, although a kernel panic or deadlock is unlikely.

### Analysis of the Issues

1.  **Duplicate Reference Counting**: When `nbd_add_socket` is called, it invokes `nbd_get_socket`, which calls `sockfd_lookup(fd, &err)`. This function increments the reference count of the underlying `struct file` (and thus the socket). If the same fd is provided twice, `sockfd_lookup` is called twice, incrementing the reference count twice. Consequently, when `nbd_config_put` calls `sockfd_put` twice on the same socket pointer, it is correctly decrementing the two references obtained earlier. **This part of the logic is actually correct and will not cause a double-free or a kernel panic.**

2.  **Stream Corruption (The Real Bug)**: Each call to `nbd_add_socket` allocates a new `struct nbd_sock` structure. Each `nbd_sock` has its own `tx_lock` mutex. If two `nsock` structures point to the same socket, the intended synchronization is bypassed. Two threads can simultaneously call `sock_sendmsg` on the same socket, leading to interleaved headers and data, which corrupts the NBD protocol stream.

3.  **Protocol Errors**: As you noted, two `recv_work` threads will be spawned, both calling `nbd_read_reply` on the same socket. Since TCP is a stream, the two threads will compete for data. One thread might read part of a reply header, and the other might read the rest. Both will encounter "Wrong magic" errors or invalid cookies and call `nbd_mark_nsock_dead`.

4.  **Resource Leak**: In `nbd_start_device`, `sk_set_memalloc` is called for each connection. This function increments a global `memalloc_socks_key` (a static branch counter). However, the NBD driver never calls `sk_clear_memalloc`. This results in a leak of the static branch reference. Providing the same FD twice doubles this leak. While not a panic, it's a persistent resource leak in the networking stack.

### Potential for Panic or Deadlock

*   **Panic**: Unlikely. The kernel's socket and file reference counting handles the duplicate `sockfd_put` correctly. The protocol corruption will lead to EPROTO errors and connection teardown, but the driver's state management (using `config_refs` and `config_lock`) is robust enough to handle this without crashing.
*   **Deadlock**: Unlikely. The locks (`cmd->lock`, `nsock->tx_lock`, `config_lock`) are used consistently. Since each `nsock` has its own `tx_lock`, there is no circular dependency introduced by having duplicate sockets; they simply fail to provide the necessary mutual exclusion for the shared socket.

### Summary
There is a **bug** in the sense that the driver allows a misconfigured state that leads to data corruption on the wire and a minor resource leak (`memalloc_socks_key`). However, it is **not** a bug that would typically cause a kernel panic or a deadlock. The reference counting for the socket itself is handled correctly by the underlying VFS and socket layers.

To fix this, the NBD driver should ideally check if a socket is already assigned to the device before adding it in `nbd_add_socket`.

gemini-3-flash-preview

							input: 2427
							output: 87
							thoughts: 285
						

**Analyzing a Potential NBD Bug**

Okay, so the user is concerned about a possible flaw in `drivers/block/nbd.c`, specifically around how it handles file descriptors in the `NBD_ATTR_SOCKETS` attribute. I see the scenario they're outlining: it's all about what happens if we're given the same file descriptor twice. Let me think this through, step-by-step, just as they've described it.

First, `nbd_genl_connect` parses `NBD_ATTR_SOCKETS` – that makes sense. Then, the crux of the issue: if we see the same file descriptor duplicated, `nbd_add_socket` gets called twice with the identical `fd`. Now, if that's the case, we're likely ending up with `config->socks[0]->sock` and `config->socks[1]->sock` both referencing the *same* `struct socket`. Okay, I can visualize that potential for a shared resource conflict.

Next, `nbd_start_device` comes into play. It kicks off two `recv_work` threads, which are now both working with the same socket. This is where things start to get interesting. Both threads end up calling `nbd_read_reply` on this shared socket. The user is right – it feels like a race condition is brewing.

Now, here's where the potential disaster might strike: when the socket gets closed, both threads wake up. They both end up calling `nbd_mark_nsock_dead`, and then `nbd_config_put`. The real kicker: `nbd_config_put` ends up calling `sockfd_put` *twice* on the *same* socket. This is precisely the point I was hoping to see described - a double free.

So, the user is wondering if this sequence could trigger a bug, a kernel panic, or potentially a deadlock? Yes, a double free situation is a classic source of all three problems. It's a valid concern, and I need to dive into `nbd_genl_connect` and `nbd_add_socket` in `drivers/block/nbd.c` to see if the hypothesized scenario is actually feasible. I need to understand if the code *allows* this double use of the same FD, if there are any checks or safeguards against it, and if it's the expected way the system handles the socket.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_genl_connect]

map[SourceCode:2073:	static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
2074:	{
2075:		struct nbd_device *nbd;
2076:		struct nbd_config *config;
2077:		int index = -1;
2078:		int ret;
2079:		bool put_dev = false;
2080:	
2081:		if (!netlink_capable(skb, CAP_SYS_ADMIN))
2082:			return -EPERM;
2083:	
2084:		if (info->attrs[NBD_ATTR_INDEX]) {
2085:			index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
2086:	
2087:			/*
2088:			 * Too big first_minor can cause duplicate creation of
2089:			 * sysfs files/links, since index << part_shift might overflow, or
2090:			 * MKDEV() expect that the max bits of first_minor is 20.
2091:			 */
2092:			if (index < 0 || index > MINORMASK >> part_shift) {
2093:				pr_err("illegal input index %d\n", index);
2094:				return -EINVAL;
2095:			}
2096:		}
2097:		if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SOCKETS)) {
2098:			pr_err("must specify at least one socket\n");
2099:			return -EINVAL;
2100:		}
2101:		if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SIZE_BYTES)) {
2102:			pr_err("must specify a size in bytes for the device\n");
2103:			return -EINVAL;
2104:		}
2105:	again:
2106:		mutex_lock(&nbd_index_mutex);
2107:		if (index == -1) {
2108:			nbd = nbd_find_get_unused();
2109:		} else {
2110:			nbd = idr_find(&nbd_index_idr, index);
2111:			if (nbd) {
2112:				if ((test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags) &&
2113:				     test_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags)) ||
2114:				    !refcount_inc_not_zero(&nbd->refs)) {
2115:					mutex_unlock(&nbd_index_mutex);
2116:					pr_err("device at index %d is going down\n",
2117:						index);
2118:					return -EINVAL;
2119:				}
2120:			}
2121:		}
2122:		mutex_unlock(&nbd_index_mutex);
2123:	
2124:		if (!nbd) {
2125:			nbd = nbd_dev_add(index, 2);
2126:			if (IS_ERR(nbd)) {
2127:				pr_err("failed to add new device\n");
2128:				return PTR_ERR(nbd);
2129:			}
2130:		}
2131:	
2132:		mutex_lock(&nbd->config_lock);
2133:		if (refcount_read(&nbd->config_refs)) {
2134:			mutex_unlock(&nbd->config_lock);
2135:			nbd_put(nbd);
2136:			if (index == -1)
2137:				goto again;
2138:			pr_err("nbd%d already in use\n", index);
2139:			return -EBUSY;
2140:		}
2141:	
2142:		ret = nbd_alloc_and_init_config(nbd);
2143:		if (ret) {
2144:			mutex_unlock(&nbd->config_lock);
2145:			nbd_put(nbd);
2146:			pr_err("couldn't allocate config\n");
2147:			return ret;
2148:		}
2149:	
2150:		config = nbd->config;
2151:		set_bit(NBD_RT_BOUND, &config->runtime_flags);
2152:		ret = nbd_genl_size_set(info, nbd);
2153:		if (ret)
2154:			goto out;
2155:	
2156:		if (info->attrs[NBD_ATTR_TIMEOUT])
2157:			nbd_set_cmd_timeout(nbd,
2158:					    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
2159:		if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
2160:			config->dead_conn_timeout =
2161:				nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
2162:			config->dead_conn_timeout *= HZ;
2163:		}
2164:		if (info->attrs[NBD_ATTR_SERVER_FLAGS])
2165:			config->flags =
2166:				nla_get_u64(info->attrs[NBD_ATTR_SERVER_FLAGS]);
2167:		if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
2168:			u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
2169:			if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
2170:				/*
2171:				 * We have 1 ref to keep the device around, and then 1
2172:				 * ref for our current operation here, which will be
2173:				 * inherited by the config.  If we already have
2174:				 * DESTROY_ON_DISCONNECT set then we know we don't have
2175:				 * that extra ref already held so we don't need the
2176:				 * put_dev.
2177:				 */
2178:				if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
2179:						      &nbd->flags))
2180:					put_dev = true;
2181:			} else {
2182:				if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
2183:						       &nbd->flags))
2184:					refcount_inc(&nbd->refs);
2185:			}
2186:			if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
2187:				set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
2188:					&config->runtime_flags);
2189:			}
2190:		}
2191:	
2192:		if (info->attrs[NBD_ATTR_SOCKETS]) {
2193:			struct nlattr *attr;
2194:			int rem, fd;
2195:	
2196:			nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
2197:					    rem) {
2198:				struct nlattr *socks[NBD_SOCK_MAX+1];
2199:	
2200:				if (nla_type(attr) != NBD_SOCK_ITEM) {
2201:					pr_err("socks must be embedded in a SOCK_ITEM attr\n");
2202:					ret = -EINVAL;
2203:					goto out;
2204:				}
2205:				ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
2206:								  attr,
2207:								  nbd_sock_policy,
2208:								  info->extack);
2209:				if (ret != 0) {
2210:					pr_err("error processing sock list\n");
2211:					ret = -EINVAL;
2212:					goto out;
2213:				}
2214:				if (!socks[NBD_SOCK_FD])
2215:					continue;
2216:				fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
2217:				ret = nbd_add_socket(nbd, fd, true);
2218:				if (ret)
2219:					goto out;
2220:			}
2221:		}
2222:	
2223:		if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
2224:			nbd->backend = nla_strdup(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
2225:						  GFP_KERNEL);
2226:			if (!nbd->backend) {
2227:				ret = -ENOMEM;
2228:				goto out;
2229:			}
2230:		}
2231:		ret = device_create_file(disk_to_dev(nbd->disk), &backend_attr);
2232:		if (ret) {
2233:			dev_err(disk_to_dev(nbd->disk),
2234:				"device_create_file failed for backend!\n");
2235:			goto out;
2236:		}
2237:		set_bit(NBD_RT_HAS_BACKEND_FILE, &config->runtime_flags);
2238:	
2239:		ret = nbd_start_device(nbd);
2240:	out:
2241:		if (!ret) {
2242:			set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);
2243:			refcount_inc(&nbd->config_refs);
2244:			nbd_connect_reply(info, nbd->index);
2245:		}
2246:		mutex_unlock(&nbd->config_lock);
2247:	
2248:		nbd_config_put(nbd);
2249:		if (put_dev)
2250:			nbd_put(nbd);
2251:		return ret;
2252:	}
 SourceFile:drivers/block/nbd.c]

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_add_socket]

map[SourceCode:1241:	static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
1242:				  bool netlink)
1243:	{
1244:		struct nbd_config *config = nbd->config;
1245:		struct socket *sock;
1246:		struct nbd_sock **socks;
1247:		struct nbd_sock *nsock;
1248:		unsigned int memflags;
1249:		int err;
1250:	
1251:		/* Arg will be cast to int, check it to avoid overflow */
1252:		if (arg > INT_MAX)
1253:			return -EINVAL;
1254:		sock = nbd_get_socket(nbd, arg, &err);
1255:		if (!sock)
1256:			return err;
1257:	
1258:		/*
1259:		 * We need to make sure we don't get any errant requests while we're
1260:		 * reallocating the ->socks array.
1261:		 */
1262:		memflags = blk_mq_freeze_queue(nbd->disk->queue);
1263:	
1264:		if (!netlink && !nbd->task_setup &&
1265:		    !test_bit(NBD_RT_BOUND, &config->runtime_flags))
1266:			nbd->task_setup = current;
1267:	
1268:		if (!netlink &&
1269:		    (nbd->task_setup != current ||
1270:		     test_bit(NBD_RT_BOUND, &config->runtime_flags))) {
1271:			dev_err(disk_to_dev(nbd->disk),
1272:				"Device being setup by another task");
1273:			err = -EBUSY;
1274:			goto put_socket;
1275:		}
1276:	
1277:		nsock = kzalloc_obj(*nsock);
1278:		if (!nsock) {
1279:			err = -ENOMEM;
1280:			goto put_socket;
1281:		}
1282:	
1283:		socks = krealloc(config->socks, (config->num_connections + 1) *
1284:				 sizeof(struct nbd_sock *), GFP_KERNEL);
1285:		if (!socks) {
1286:			kfree(nsock);
1287:			err = -ENOMEM;
1288:			goto put_socket;
1289:		}
1290:	
1291:		config->socks = socks;
1292:	
1293:		nsock->fallback_index = -1;
1294:		nsock->dead = false;
1295:		mutex_init(&nsock->tx_lock);
1296:		nsock->sock = sock;
1297:		nsock->pending = NULL;
1298:		nsock->sent = 0;
1299:		nsock->cookie = 0;
1300:		INIT_WORK(&nsock->work, nbd_pending_cmd_work);
1301:		socks[config->num_connections++] = nsock;
1302:		atomic_inc(&config->live_connections);
1303:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1304:	
1305:		return 0;
1306:	
1307:	put_socket:
1308:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1309:		sockfd_put(sock);
1310:		return err;
1311:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 7268
							output: 43
							thoughts: 81
						

Okay, here's my interpretation of that code snippet, presented as my own thought process:

**Diving into the Socket Connection Logic**

Right, so I'm looking at `nbd_genl_connect`, and it seems to be iterating through the `NBD_ATTR_SOCKETS` attribute. Each iteration is followed by a call to `nbd_add_socket(nbd, fd, true)`. So, that's where the socket file descriptors are being added.

The critical part appears to be the next function call within `nbd_add_socket`, to `nbd_get_socket(nbd, arg, &err)`. I need to figure out how sockets are retrieved or managed. What does `nbd_get_socket` *do*? That's the core of how these sockets are acquired. Understanding this function call will likely illuminate how socket handling is set up with Netlink and the NBD driver. Time to dig in and see how it works.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_get_socket]

map[SourceCode:1213:	static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd,
1214:					     int *err)
1215:	{
1216:		struct socket *sock;
1217:	
1218:		*err = 0;
1219:		sock = sockfd_lookup(fd, err);
1220:		if (!sock)
1221:			return NULL;
1222:	
1223:		if (!sk_is_tcp(sock->sk) &&
1224:		    !sk_is_stream_unix(sock->sk)) {
1225:			dev_err(disk_to_dev(nbd->disk), "Unsupported socket: should be TCP or UNIX.\n");
1226:			*err = -EINVAL;
1227:			sockfd_put(sock);
1228:			return NULL;
1229:		}
1230:	
1231:		if (sock->ops->shutdown == sock_no_shutdown) {
1232:			dev_err(disk_to_dev(nbd->disk), "Unsupported socket: shutdown callout must be supported.\n");
1233:			*err = -EINVAL;
1234:			sockfd_put(sock);
1235:			return NULL;
1236:		}
1237:	
1238:		return sock;
1239:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 8019
							output: 43
							thoughts: 185
						

**Analyzing the Network Block Device Socket Management**

Okay, let me break down this socket management logic within the NBD driver. Essentially, `nbd_get_socket` is the core function. It calls `sockfd_lookup` to retrieve the `struct socket *` associated with a file descriptor (`fd`). If `sockfd_lookup` is successful, it hands back that socket pointer.

Now, here's where things get interesting. The text clearly states that if `nbd_add_socket` is called *twice* with the *same* `fd`, `sockfd_lookup` returns the *exact same* `struct socket *` each time. Crucially, the socket's reference count is incremented with each lookup.  So, in effect, we're reusing the underlying socket.

`nbd_add_socket` then allocates a fresh `struct nbd_sock`, sets `nsock->sock` to point to the shared `struct socket *`, and adds the new `nbd_sock` to the `config->socks` list. This means that if we pass the same `fd` twice, we will have two different `nbd_sock` structures, but both `config->socks[0]->sock` and `config->socks[1]->sock` will point to the *identical* underlying socket.

The consequence is clear: `config->num_connections` will become 2, as we’ve added two entries. Furthermore, `config->live_connections` will also be 2.

Alright, with that established, I need to understand what `nbd_start_device` does with this configuration. I'll need to analyze how it utilizes these socket structures to ascertain its behavior in the context of this potential socket sharing.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_start_device]

map[SourceCode:1471:	static int nbd_start_device(struct nbd_device *nbd)
1472:	{
1473:		struct nbd_config *config = nbd->config;
1474:		int num_connections = config->num_connections;
1475:		int error = 0, i;
1476:	
1477:		if (nbd->pid)
1478:			return -EBUSY;
1479:		if (!config->socks)
1480:			return -EINVAL;
1481:		if (num_connections > 1 &&
1482:		    !(config->flags & NBD_FLAG_CAN_MULTI_CONN)) {
1483:			dev_err(disk_to_dev(nbd->disk), "server does not support multiple connections per device.\n");
1484:			return -EINVAL;
1485:		}
1486:	
1487:	retry:
1488:		mutex_unlock(&nbd->config_lock);
1489:		blk_mq_update_nr_hw_queues(&nbd->tag_set, num_connections);
1490:		mutex_lock(&nbd->config_lock);
1491:	
1492:		/* if another code path updated nr_hw_queues, retry until succeed */
1493:		if (num_connections != config->num_connections) {
1494:			num_connections = config->num_connections;
1495:			goto retry;
1496:		}
1497:	
1498:		nbd->pid = task_pid_nr(current);
1499:	
1500:		nbd_parse_flags(nbd);
1501:	
1502:		error = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
1503:		if (error) {
1504:			dev_err(disk_to_dev(nbd->disk), "device_create_file failed for pid!\n");
1505:			return error;
1506:		}
1507:		set_bit(NBD_RT_HAS_PID_FILE, &config->runtime_flags);
1508:	
1509:		nbd_dev_dbg_init(nbd);
1510:		for (i = 0; i < num_connections; i++) {
1511:			struct recv_thread_args *args;
1512:	
1513:			args = kzalloc_obj(*args);
1514:			if (!args) {
1515:				sock_shutdown(nbd);
1516:				/*
1517:				 * If num_connections is m (2 < m),
1518:				 * and NO.1 ~ NO.n(1 < n < m) kzallocs are successful.
1519:				 * But NO.(n + 1) failed. We still have n recv threads.
1520:				 * So, add flush_workqueue here to prevent recv threads
1521:				 * dropping the last config_refs and trying to destroy
1522:				 * the workqueue from inside the workqueue.
1523:				 */
1524:				if (i)
1525:					flush_workqueue(nbd->recv_workq);
1526:				return -ENOMEM;
1527:			}
1528:			sk_set_memalloc(config->socks[i]->sock->sk);
1529:			if (nbd->tag_set.timeout)
1530:				config->socks[i]->sock->sk->sk_sndtimeo =
1531:					nbd->tag_set.timeout;
1532:			atomic_inc(&config->recv_threads);
1533:			refcount_inc(&nbd->config_refs);
1534:			INIT_WORK(&args->work, recv_work);
1535:			args->nbd = nbd;
1536:			args->nsock = config->socks[i];
1537:			args->index = i;
1538:			queue_work(nbd->recv_workq, &args->work);
1539:		}
1540:		return nbd_set_size(nbd, config->bytesize, nbd_blksize(config));
1541:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 9804
							output: 40
							thoughts: 73
						

**Analyzing the nbd_start_device Function**

Okay, so `nbd_start_device` seems to be the crucial starting point here. I see it's iterating through `num_connections` and queuing up a `recv_work` task for each connection. My initial thought is to look at how these are handled and if there are any race conditions that I might spot.

The interesting part, and what likely prompted this, is that there might be a scenario where `config->socks[0]->sock == config->socks[1]->sock`. If that's true, then we'll have two separate threads, each calling `recv_work`, both using the *same* socket. This certainly warrants a closer look. I need to understand what `recv_work` is doing and how it's interacting with the shared socket. This could lead to all sorts of concurrency issues - data corruption, missed events, or even deadlocks. Let's dig into the `recv_work` function and see what's happening.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:recv_work]

map[SourceCode: 970:	static void recv_work(struct work_struct *work)
 971:	{
 972:		struct recv_thread_args *args = container_of(work,
 973:							     struct recv_thread_args,
 974:							     work);
 975:		struct nbd_device *nbd = args->nbd;
 976:		struct nbd_config *config = nbd->config;
 977:		struct request_queue *q = nbd->disk->queue;
 978:		struct nbd_sock *nsock = args->nsock;
 979:		struct nbd_cmd *cmd;
 980:		struct request *rq;
 981:	
 982:		while (1) {
 983:			struct nbd_reply reply;
 984:	
 985:			if (nbd_read_reply(nbd, nsock->sock, &reply))
 986:				break;
 987:	
 988:			/*
 989:			 * Grab .q_usage_counter so request pool won't go away, then no
 990:			 * request use-after-free is possible during nbd_handle_reply().
 991:			 * If queue is frozen, there won't be any inflight requests, we
 992:			 * needn't to handle the incoming garbage message.
 993:			 */
 994:			if (!percpu_ref_tryget(&q->q_usage_counter)) {
 995:				dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n",
 996:					__func__);
 997:				break;
 998:			}
 999:	
1000:			cmd = nbd_handle_reply(nbd, args->index, &reply);
1001:			if (IS_ERR(cmd)) {
1002:				percpu_ref_put(&q->q_usage_counter);
1003:				break;
1004:			}
1005:	
1006:			rq = blk_mq_rq_from_pdu(cmd);
1007:			if (likely(!blk_should_fake_timeout(rq->q))) {
1008:				bool complete;
1009:	
1010:				mutex_lock(&cmd->lock);
1011:				complete = __test_and_clear_bit(NBD_CMD_INFLIGHT,
1012:								&cmd->flags);
1013:				mutex_unlock(&cmd->lock);
1014:				if (complete)
1015:					blk_mq_complete_request(rq);
1016:			}
1017:			percpu_ref_put(&q->q_usage_counter);
1018:		}
1019:	
1020:		mutex_lock(&nsock->tx_lock);
1021:		nbd_mark_nsock_dead(nbd, nsock, 1);
1022:		mutex_unlock(&nsock->tx_lock);
1023:	
1024:		atomic_dec(&config->recv_threads);
1025:		wake_up(&config->recv_wq);
1026:		nbd_config_put(nbd);
1027:		kfree(args);
1028:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 11068
							output: 46
							thoughts: 155
						

**Analyzing Potential Concurrency Issues in the Network Block Device (NBD) Implementation**

Okay, so I'm looking at this `recv_work` function, and it's calling `nbd_read_reply` – which seems straightforward enough. But, wait a minute... I see a potential race condition here. If two threads somehow end up calling `nbd_read_reply` on the same socket concurrently, then we've got a problem. Both threads are going to attempt to read from the same socket simultaneously. That's a recipe for disaster! Data corruption is highly probable, or at the very least, unpredictable behavior due to interleaved reads from a single reply. This is bad.

`nbd_read_reply`, itself, calls `sock_xmit` – so it's directly involved in the socket interaction. This further highlights the importance of making sure only one thread deals with the socket at any time.

Now, when the main loop breaks – say, because the socket gets closed – it calls `nbd_mark_nsock_dead`, and then `nbd_config_put`. Makes sense; cleanup is crucial. Let's delve into this `nbd_mark_nsock_dead` function and understand how it handles the socket closure. We're going to need to look at how this is being handled in order to determine what thread safety mechanisms (if any) are in place. This will be key to understanding if this entire sequence is thread-safe.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_mark_nsock_dead]

map[SourceCode: 305:	static void nbd_mark_nsock_dead(struct nbd_device *nbd, struct nbd_sock *nsock,
 306:					int notify)
 307:	{
 308:		if (!nsock->dead && notify && !nbd_disconnected(nbd->config)) {
 309:			struct link_dead_args *args;
 310:			args = kmalloc_obj(struct link_dead_args, GFP_NOIO);
 311:			if (args) {
 312:				INIT_WORK(&args->work, nbd_dead_link_work);
 313:				args->index = nbd->index;
 314:				queue_work(system_percpu_wq, &args->work);
 315:			}
 316:		}
 317:		if (!nsock->dead) {
 318:			kernel_sock_shutdown(nsock->sock, SHUT_RDWR);
 319:			if (atomic_dec_return(&nbd->config->live_connections) == 0) {
 320:				if (test_and_clear_bit(NBD_RT_DISCONNECT_REQUESTED,
 321:						       &nbd->config->runtime_flags)) {
 322:					set_bit(NBD_RT_DISCONNECTED,
 323:						&nbd->config->runtime_flags);
 324:					dev_info(nbd_to_dev(nbd),
 325:						"Disconnected due to user request.\n");
 326:				}
 327:			}
 328:		}
 329:		nsock->dead = true;
 330:		nsock->pending = NULL;
 331:		nsock->sent = 0;
 332:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 12093
							output: 43
							thoughts: 179
						

**Analyzing Socket Shutdown Behavior in NBD**

Okay, so I'm looking at this `nbd_mark_nsock_dead` function and how it interacts with socket shutdown. My concern here is the potential for double-shutdowns on the same socket, but it seems there's a nuanced process happening.

Essentially, it checks if `!nsock->dead` before shutting down the socket using `kernel_sock_shutdown(nsock->sock, SHUT_RDWR)`. The critical thing to remember is that we *can* have multiple `nbd_sock` structures pointing to the very same underlying socket. They're all initially marked `dead = false`.

Now, imagine we have two `recv_work` threads. The first thread calls `nbd_mark_nsock_dead` and updates the relevant `nsock` structure to `dead = true`.  This is expected behavior, that thread knows its socket is no longer viable. The key is what the *second* thread does. Because `nbd_add_socket` allocates a new `nbd_sock` for *each* socket (even if they point to the same socket), this second thread still has *its own* `nsock` structure, and that copy hasn't been set to `dead = true` yet.

So, both threads end up calling `kernel_sock_shutdown` on the *same* socket, one after the other. The fact that the socket is being shut down multiple times concerns me from a resource-management perspective, but I'm reasonably confident that `kernel_sock_shutdown` is designed to handle this gracefully. At the very least it's supposed to be safe. So, it appears that this double-shutdown behavior is not a critical error, but potentially something to be optimized.

Now, let's turn our attention to the `nbd_config_put` function and see what's going on there.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_config_put]

map[SourceCode:1432:	static void nbd_config_put(struct nbd_device *nbd)
1433:	{
1434:		if (refcount_dec_and_mutex_lock(&nbd->config_refs,
1435:						&nbd->config_lock)) {
1436:			struct nbd_config *config = nbd->config;
1437:			nbd_dev_dbg_close(nbd);
1438:			invalidate_disk(nbd->disk);
1439:			if (nbd->config->bytesize)
1440:				kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
1441:			if (test_and_clear_bit(NBD_RT_HAS_PID_FILE,
1442:					       &config->runtime_flags))
1443:				device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
1444:			nbd->pid = 0;
1445:			if (test_and_clear_bit(NBD_RT_HAS_BACKEND_FILE,
1446:					       &config->runtime_flags)) {
1447:				device_remove_file(disk_to_dev(nbd->disk), &backend_attr);
1448:				kfree(nbd->backend);
1449:				nbd->backend = NULL;
1450:			}
1451:			nbd_clear_sock(nbd);
1452:			if (config->num_connections) {
1453:				int i;
1454:				for (i = 0; i < config->num_connections; i++) {
1455:					sockfd_put(config->socks[i]->sock);
1456:					kfree(config->socks[i]);
1457:				}
1458:				kfree(config->socks);
1459:			}
1460:			kfree(nbd->config);
1461:			nbd->config = NULL;
1462:	
1463:			nbd->tag_set.timeout = 0;
1464:	
1465:			mutex_unlock(&nbd->config_lock);
1466:			nbd_put(nbd);
1467:			module_put(THIS_MODULE);
1468:		}
1469:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 13393
							output: 43
							thoughts: 883
						

**Analyzing the NBD Configuration Reference Counting and Socket Handling**

Okay, let's break this down. It seems we have a potential issue related to how the Network Block Device (NBD) driver handles references to its configuration and, more importantly, its sockets.

Initially, `nbd_alloc_and_init_config` sets `nbd->config_refs` to 1. Then, `nbd_start_device` increments this count for each connection established. From the code, it looks like `nbd_start_device` increments it twice, for each `recv_work` thread. Additionally, `nbd_genl_connect` also holds a reference.

So, if we have two connections, `config_refs` starts at 1, goes to 3 (due to `nbd_start_device`), and then back down to 2 after `nbd_genl_connect` releases its reference. Each `recv_work` thread subsequently calls `nbd_config_put`, decrementing `config_refs`. The first one to finish drops it to 1, and the second one should decrement it to zero.

When `config_refs` hits zero, the cleanup block executes. This block iterates through `config->socks`, calling `sockfd_put` on each socket.  Here's where it gets interesting:  If, as the user described, `config->socks[0]->sock` and `config->socks[1]->sock` point to the same socket, then `sockfd_put` is called twice on the *same* socket.

But wait. We've seen `nbd_add_socket` uses `nbd_get_socket`, which calls `sockfd_lookup`, and that's the key.  `sockfd_lookup` calls `fget(fd)`, which increments the reference count on the file. Thus it should return a struct file with an incremented reference count. `sockfd_put` calls `fput(sock->file)`. So, the socket is correctly reference counted, right?

So, if `sockfd_lookup(fd)` is called twice for the *same* file descriptor, we correctly get *two* references to the same file (and therefore the same socket). Consequently, calling `sockfd_put` twice is the right thing to do to release those two references. Okay, the reference counting on the socket itself is fine, it's the correct implementation.

However, the user says there's a different problem.  Both `config->socks[0]->sock` and `config->socks[1]->sock` *do* point to the *same* socket.  `nbd_start_device` then queues two `recv_work` threads. And here's the kicker: both of these threads are calling `nbd_read_reply` on the *same* socket simultaneously.  Now we have a concurrency issue. `nbd_read_reply` calls `sock_xmit` and we have *two* threads reading from a single socket without any synchronization. This could lead to data corruption or other nasty issues. This is a critical problem!

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_read_reply]

map[SourceCode: 845:	static int nbd_read_reply(struct nbd_device *nbd, struct socket *sock,
 846:				  struct nbd_reply *reply)
 847:	{
 848:		struct kvec iov = {.iov_base = reply, .iov_len = sizeof(*reply)};
 849:		struct iov_iter to;
 850:		int result;
 851:	
 852:		reply->magic = 0;
 853:		iov_iter_kvec(&to, ITER_DEST, &iov, 1, sizeof(*reply));
 854:		result = __sock_xmit(nbd, sock, 0, &to, MSG_WAITALL, NULL);
 855:		if (result < 0) {
 856:			if (!nbd_disconnected(nbd->config))
 857:				dev_err(disk_to_dev(nbd->disk),
 858:					"Receive control failed (result %d)\n", result);
 859:			return result;
 860:		}
 861:	
 862:		if (ntohl(reply->magic) != NBD_REPLY_MAGIC) {
 863:			dev_err(disk_to_dev(nbd->disk), "Wrong magic (0x%lx)\n",
 864:					(unsigned long)ntohl(reply->magic));
 865:			return -EPROTO;
 866:		}
 867:	
 868:		return 0;
 869:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 15432
							output: 42
							thoughts: 8
						

Okay, here's my summary, taking on the persona you've described:

**Delving into `__sock_xmit`**

Alright, let's break this down. When I see `__sock_xmit`, my mind immediately jumps to the kernel's network stack. It's a fundamental function, isn't it? This is where the magic of sending data out onto the wire *actually* happens. I'm thinking about its role, the low-level mechanics it encapsulates. I'm imagining the data buffers, the sk_buffs, lining up, ready to be pushed through the network interface.

I'm considering the complexities: the interactions with hardware, the driver calls, the checksum calculations...all the details needed to actually get a packet onto the physical medium. It's a critical point in the data flow, a bottleneck potentially, and understanding the nuances of how `__sock_xmit` performs is absolutely key to optimization. I need to think about the various scenarios it has to handle, the different protocols, the congestion control mechanisms at play.

This function is a performance-critical area; any inefficiencies here would be multiplied across the system. It's time to dig deep. I want to know about how the data is prepared, how it's handled by the device driver, and what error conditions are accounted for. The interaction with the hardware, the interrupt handling – that's where I need to focus my attention. It's all about ensuring efficient and reliable data transmission.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:__sock_xmit]

map[SourceCode: 551:	static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
 552:			       struct iov_iter *iter, int msg_flags, int *sent)
 553:	{
 554:		int result;
 555:		struct msghdr msg = {} ;
 556:		unsigned int noreclaim_flag;
 557:	
 558:		if (unlikely(!sock)) {
 559:			dev_err_ratelimited(disk_to_dev(nbd->disk),
 560:				"Attempted %s on closed socket in sock_xmit\n",
 561:				(send ? "send" : "recv"));
 562:			return -EINVAL;
 563:		}
 564:	
 565:		msg.msg_iter = *iter;
 566:	
 567:		noreclaim_flag = memalloc_noreclaim_save();
 568:	
 569:		scoped_with_kernel_creds() {
 570:			do {
 571:				sock->sk->sk_allocation = GFP_NOIO | __GFP_MEMALLOC;
 572:				sock->sk->sk_use_task_frag = false;
 573:				msg.msg_flags = msg_flags | MSG_NOSIGNAL;
 574:	
 575:				if (send)
 576:					result = sock_sendmsg(sock, &msg);
 577:				else
 578:					result = sock_recvmsg(sock, &msg, msg.msg_flags);
 579:	
 580:				if (result <= 0) {
 581:					if (result == 0)
 582:						result = -EPIPE; /* short read */
 583:					break;
 584:				}
 585:				if (sent)
 586:					*sent += result;
 587:			} while (msg_data_left(&msg));
 588:		}
 589:	
 590:		memalloc_noreclaim_restore(noreclaim_flag);
 591:	
 592:		return result;
 593:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 16437
							output: 43
							thoughts: 179
						

**Analyzing Potential Data Corruption in NBD Stream**

Okay, so I'm looking at this situation where `__sock_xmit` is calling `sock_recvmsg`. Right off the bat, my Spidey-Sense is tingling because I know that if two threads hit `sock_recvmsg` on the *same* TCP socket concurrently, we've got a potential race condition. They'll be fighting for the data stream, and that's just asking for trouble. One thread grabs the first few bytes, the other grabs the next chunk... it's a recipe for "Wrong magic" errors, or worse, outright data corruption.

But the question isn't just about data corruption in general, it's more specific: is this a *bug* that could lead to a kernel panic or deadlock? Data corruption in the NBD stream, I'm thinking, is definitely a bug, but maybe it just results in the connection being dropped. That's *bad*, but not the worst-case scenario.

Ah, wait a second... there's the `reply.cookie` used in `nbd_handle_reply` to associate with the correct command. If the stream is corrupted, that cookie could be garbage. If that's the case, `nbd_handle_reply` could be getting completely confused. That could lead to all sorts of unpredictable behavior.

I need to dig into `nbd_handle_reply` itself to be sure. Let's see how that works.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_handle_reply]

map[SourceCode: 871:	/* NULL returned = something went wrong, inform userspace */
 872:	static struct nbd_cmd *nbd_handle_reply(struct nbd_device *nbd, int index,
 873:						struct nbd_reply *reply)
 874:	{
 875:		int result;
 876:		struct nbd_cmd *cmd;
 877:		struct request *req = NULL;
 878:		u64 handle;
 879:		u16 hwq;
 880:		u32 tag;
 881:		int ret = 0;
 882:	
 883:		handle = be64_to_cpu(reply->cookie);
 884:		tag = nbd_handle_to_tag(handle);
 885:		hwq = blk_mq_unique_tag_to_hwq(tag);
 886:		if (hwq < nbd->tag_set.nr_hw_queues)
 887:			req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq],
 888:					       blk_mq_unique_tag_to_tag(tag));
 889:		if (!req || !blk_mq_request_started(req)) {
 890:			dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%d) %p\n",
 891:				tag, req);
 892:			return ERR_PTR(-ENOENT);
 893:		}
 894:		trace_nbd_header_received(req, handle);
 895:		cmd = blk_mq_rq_to_pdu(req);
 896:	
 897:		mutex_lock(&cmd->lock);
 898:		if (!test_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
 899:			dev_err(disk_to_dev(nbd->disk), "Suspicious reply %d (status %u flags %lu)",
 900:				tag, cmd->status, cmd->flags);
 901:			ret = -ENOENT;
 902:			goto out;
 903:		}
 904:		if (cmd->index != index) {
 905:			dev_err(disk_to_dev(nbd->disk), "Unexpected reply %d from different sock %d (expected %d)",
 906:				tag, index, cmd->index);
 907:			ret = -ENOENT;
 908:			goto out;
 909:		}
 910:		if (cmd->cmd_cookie != nbd_handle_to_cookie(handle)) {
 911:			dev_err(disk_to_dev(nbd->disk), "Double reply on req %p, cmd_cookie %u, handle cookie %u\n",
 912:				req, cmd->cmd_cookie, nbd_handle_to_cookie(handle));
 913:			ret = -ENOENT;
 914:			goto out;
 915:		}
 916:		if (cmd->status != BLK_STS_OK) {
 917:			dev_err(disk_to_dev(nbd->disk), "Command already handled %p\n",
 918:				req);
 919:			ret = -ENOENT;
 920:			goto out;
 921:		}
 922:		if (test_bit(NBD_CMD_REQUEUED, &cmd->flags)) {
 923:			dev_err(disk_to_dev(nbd->disk), "Raced with timeout on req %p\n",
 924:				req);
 925:			ret = -ENOENT;
 926:			goto out;
 927:		}
 928:		if (ntohl(reply->error)) {
 929:			dev_err(disk_to_dev(nbd->disk), "Other side returned error (%d)\n",
 930:				ntohl(reply->error));
 931:			cmd->status = BLK_STS_IOERR;
 932:			goto out;
 933:		}
 934:	
 935:		dev_dbg(nbd_to_dev(nbd), "request %p: got reply\n", req);
 936:		if (rq_data_dir(req) != WRITE) {
 937:			struct req_iterator iter;
 938:			struct bio_vec bvec;
 939:			struct iov_iter to;
 940:	
 941:			rq_for_each_segment(bvec, req, iter) {
 942:				iov_iter_bvec(&to, ITER_DEST, &bvec, 1, bvec.bv_len);
 943:				result = sock_xmit(nbd, index, 0, &to, MSG_WAITALL, NULL);
 944:				if (result < 0) {
 945:					dev_err(disk_to_dev(nbd->disk), "Receive data failed (result %d)\n",
 946:						result);
 947:					/*
 948:					 * If we've disconnected, we need to make sure we
 949:					 * complete this request, otherwise error out
 950:					 * and let the timeout stuff handle resubmitting
 951:					 * this request onto another connection.
 952:					 */
 953:					if (nbd_disconnected(nbd->config)) {
 954:						cmd->status = BLK_STS_IOERR;
 955:						goto out;
 956:					}
 957:					ret = -EIO;
 958:					goto out;
 959:				}
 960:				dev_dbg(nbd_to_dev(nbd), "request %p: got %d bytes data\n",
 961:					req, bvec.bv_len);
 962:			}
 963:		}
 964:	out:
 965:		trace_nbd_payload_received(req, handle);
 966:		mutex_unlock(&cmd->lock);
 967:		return ret ? ERR_PTR(ret) : cmd;
 968:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 18674
							output: 43
							thoughts: 1628
						

**Analyzing Potential Concurrency Issues with Shared Sockets in the NBD Driver**

Okay, let's break this down. My initial concern was about two threads reading from the same socket. This is a recipe for disaster in the NBD protocol, as the `sock_xmit` calls (through `nbd_read_reply` or directly in `nbd_handle_reply`) would definitely lead to interleaved data. This would lead to protocol errors and incorrect behavior. The question isn't whether it *will* go wrong, but how badly it can fail.

First, the user pointed out `nbd_config_put` being called with the same `sockfd` twice. After reviewing, that's not a bug. `nbd_add_socket` uses `nbd_get_socket`, which calls `sockfd_lookup`. `sockfd_lookup` increments the socket's refcount. If the file descriptor (FD) is added twice, the refcount gets incremented twice. Then, `nbd_config_put` properly decrements the refcount twice for the same socket in `config->socks[i]->sock` because it's called twice in `nbd_config_put`. This is correct and doesn't leak references.

Next, I looked at `nbd_mark_nsock_dead` again. If we have multiple `nsock` structures representing the same socket, and the first thread calls `nbd_mark_nsock_dead`, it correctly decrements `config->live_connections`. The second thread then *also* calls it, decrementing it to 0. This seems reasonable, too.

Now, `nbd_read_reply`.  The critical issue here is that multiple threads reading the same socket could easily have one get a protocol error (`Wrong magic`, etc.) and call `nbd_mark_nsock_dead`, which then calls `kernel_sock_shutdown`. This shutdown would cause the other thread's `sock_recvmsg` to return an error, and both threads would then proceed to call `nbd_config_put`.

The potential race in `nbd_config_put` is prevented by `refcount_dec_and_mutex_lock`. Only one thread will enter the cleanup block after the refcount hits zero, ensuring safe cleanup with `sockfd_put` and `kfree` of the `config->socks` array.

A key vector for attack: what if the user sends the same FD multiple times in `NBD_ATTR_SOCKETS`?  Reviewing `nbd_genl_connect`, I confirm that the code iterates through `NBD_ATTR_SOCKETS` and uses `nbd_add_socket` for each FD. No check is present in `nbd_add_socket` for duplicate FDs!

Looking at `nbd_add_socket` again confirmed my fears.  It blindly adds each socket to the `config->socks` array. If the user gives it the same FD twice, *it will add the same socket twice*.

So, if two `recv_work` threads end up reading from the same socket, the TCP stream is essentially shared. NBD relies on distinct reply sequences. One thread might read the first part of a reply, the other thread the second. Both will encounter invalid magic or cookies and both will call `nbd_mark_nsock_dead`. This will shut down the socket, cause the `recv_work` threads to exit, and trigger `nbd_config_put`. Eventually, the cleanup will happen.

Is there a deadlock risk? `nbd_mark_nsock_dead` doesn't take the same mutex as the `recv_work` threads.  Each `nsock` (even if it points to the same underlying socket) has a different `tx_lock`. So there is no deadlock here.

The `kernel_sock_shutdown` call might have locking requirements, but those don't seem to overlap with our NBD locks, which is reassuring.

Finally, `nbd_start_device` calls `blk_mq_update_nr_hw_queues`. If `num_connections` is 2, it sets up two hardware queues. `nbd_queue_rq` would then use `config->socks[hwq]`.

So, the fundamental issue is that sharing a single socket between multiple threads on the receive side breaks NBD's assumptions about sequential replies and will lead to an unrecoverable protocol error.  The lack of duplicate FD checks means a user *can* trigger this invalid configuration, leading to chaos.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_queue_rq]

map[SourceCode:1184:	static blk_status_t nbd_queue_rq(struct blk_mq_hw_ctx *hctx,
1185:				const struct blk_mq_queue_data *bd)
1186:	{
1187:		struct nbd_cmd *cmd = blk_mq_rq_to_pdu(bd->rq);
1188:		blk_status_t ret;
1189:	
1190:		/*
1191:		 * Since we look at the bio's to send the request over the network we
1192:		 * need to make sure the completion work doesn't mark this request done
1193:		 * before we are done doing our send.  This keeps us from dereferencing
1194:		 * freed data if we have particularly fast completions (ie we get the
1195:		 * completion before we exit sock_xmit on the last bvec) or in the case
1196:		 * that the server is misbehaving (or there was an error) before we're
1197:		 * done sending everything over the wire.
1198:		 */
1199:		mutex_lock(&cmd->lock);
1200:		clear_bit(NBD_CMD_REQUEUED, &cmd->flags);
1201:	
1202:		/* We can be called directly from the user space process, which means we
1203:		 * could possibly have signals pending so our sendmsg will fail.  In
1204:		 * this case we need to return that we are busy, otherwise error out as
1205:		 * appropriate.
1206:		 */
1207:		ret = nbd_handle_cmd(cmd, hctx->queue_num);
1208:		mutex_unlock(&cmd->lock);
1209:	
1210:		return ret;
1211:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 21842
							output: 43
							thoughts: 9
						

Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:

**Analyzing the `nbd_handle_cmd` Function**

Alright, let's dissect this `nbd_handle_cmd` function. My initial thoughts center on its crucial role within the Network Block Device (NBD) architecture. It’s the linchpin, the primary command processing entry point within the NBD server. I'm immediately mentally cataloging its likely responsibilities: receiving commands from the client, parsing the command's payload, validating parameters, dispatching the request to the appropriate back-end storage, handling potential errors, and finally, crafting and transmitting the response back to the NBD client.

I'm starting to imagine the typical workflow: First, a raw buffer arrives, containing a command identifier, request details (like offset, length, flags), and potentially data for writes. `nbd_handle_cmd` likely begins by dereferencing some global or per-connection data structure, likely containing metadata, state, and perhaps, the file descriptor for the underlying storage.

My experience tells me this function likely employs a switch statement or a similar construct to dispatch based on the command code: READ, WRITE, DISCONNECT, FLUSH, TRIM, and maybe some vendor-specific commands. Each case within the switch likely has a specialized handler. Each of these cases will require thorough error checking, for example, confirming that the requested offset and length are valid for the underlying storage, preventing buffer overflows, and avoiding race conditions.

I'm already anticipating areas where performance optimization might be critical. Given that it is a block device, I'll need to think about how it handles multi-block requests, as well as the importance of efficient memory allocation and deallocation to minimise latency. I'm also considering how it interacts with the underlying storage layer, and how it might be designed for asynchronous I/O to improve throughput.

Overall, my expectation is that `nbd_handle_cmd` represents the beating heart of the NBD server's command processing engine, and I'm eager to dive deeper into its implementation to understand its nuances and potential bottlenecks.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_handle_cmd]

map[SourceCode:1117:	static blk_status_t nbd_handle_cmd(struct nbd_cmd *cmd, int index)
1118:	{
1119:		struct request *req = blk_mq_rq_from_pdu(cmd);
1120:		struct nbd_device *nbd = cmd->nbd;
1121:		struct nbd_config *config;
1122:		struct nbd_sock *nsock;
1123:		blk_status_t ret;
1124:	
1125:		lockdep_assert_held(&cmd->lock);
1126:	
1127:		config = nbd_get_config_unlocked(nbd);
1128:		if (!config) {
1129:			dev_err_ratelimited(disk_to_dev(nbd->disk),
1130:					    "Socks array is empty\n");
1131:			return BLK_STS_IOERR;
1132:		}
1133:	
1134:		if (index >= config->num_connections) {
1135:			dev_err_ratelimited(disk_to_dev(nbd->disk),
1136:					    "Attempted send on invalid socket\n");
1137:			nbd_config_put(nbd);
1138:			return BLK_STS_IOERR;
1139:		}
1140:		cmd->status = BLK_STS_OK;
1141:	again:
1142:		nsock = config->socks[index];
1143:		mutex_lock(&nsock->tx_lock);
1144:		if (nsock->dead) {
1145:			int old_index = index;
1146:			index = find_fallback(nbd, index);
1147:			mutex_unlock(&nsock->tx_lock);
1148:			if (index < 0) {
1149:				if (wait_for_reconnect(nbd)) {
1150:					index = old_index;
1151:					goto again;
1152:				}
1153:				/* All the sockets should already be down at this point,
1154:				 * we just want to make sure that DISCONNECTED is set so
1155:				 * any requests that come in that were queue'ed waiting
1156:				 * for the reconnect timer don't trigger the timer again
1157:				 * and instead just error out.
1158:				 */
1159:				sock_shutdown(nbd);
1160:				nbd_config_put(nbd);
1161:				return BLK_STS_IOERR;
1162:			}
1163:			goto again;
1164:		}
1165:	
1166:		/* Handle the case that we have a pending request that was partially
1167:		 * transmitted that _has_ to be serviced first.  We need to call requeue
1168:		 * here so that it gets put _after_ the request that is already on the
1169:		 * dispatch list.
1170:		 */
1171:		blk_mq_start_request(req);
1172:		if (unlikely(nsock->pending && nsock->pending != req)) {
1173:			nbd_requeue_cmd(cmd);
1174:			ret = BLK_STS_OK;
1175:			goto out;
1176:		}
1177:		ret = nbd_send_cmd(nbd, cmd, index);
1178:	out:
1179:		mutex_unlock(&nsock->tx_lock);
1180:		nbd_config_put(nbd);
1181:		return ret;
1182:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 23395
							output: 43
							thoughts: 1005
						

**Analyzing the NBD Driver's Concurrency Issues**

Okay, let's break this down. My initial thought is that `nbd_handle_cmd` grabs `nsock->tx_lock`. The crux of the problem is that if we have two `nsock` structures associated with the *same* underlying `sock`, they'll have *different* `tx_lock` mutexes. This is a red flag. It means two threads could be simultaneously invoking `nbd_send_cmd` on the identical socket, which is a recipe for disaster and data corruption in the outgoing NBD stream.

Wait, I need to trace this... `nbd_send_cmd` calls `sock_xmit`, and `sock_xmit` in turn calls `__sock_xmit`. Right. And `__sock_xmit` ultimately calls `sock_sendmsg` on the socket. For a TCP socket, `sock_sendmsg` can handle concurrent calls from multiple threads without crashing, but it certainly doesn't guarantee atomic transmission of the entire message. NBD sends the header and then the data separately. If threads are intermixed, the headers and data will definitely become interleaved. This would result in protocol errors and connection drops.

So, the root cause is that `nbd_genl_connect` isn't checking for duplicate file descriptors. This leads to multiple `nsock` instances all pointing to the *same* `socket`, each with its own `tx_lock`. We're circumventing the intended synchronization, as the design seems to assume only one `tx_lock` per socket.

Now, does this lead to a panic or deadlock? Probably not a *kernel* panic or deadlock in the NBD driver itself. However, it *will* introduce protocol errors and likely result in connection drops, as corrupted NBD data will be transmitted.

I remember now that the user's description of `sockfd_put` being called twice on the same socket is actually the correct behavior given that `sockfd_lookup` was also called twice on the same socket.

Let's revisit `nbd_add_socket`: It creates a *new* `nsock` structure with `kzalloc_obj` every time it's called. This confirms my initial understanding.

This raises another question: can the user supply the same FD to two *different* NBD devices? Yes, the kernel allows that, but it's typically not the intended behavior.

The user's question about panics and deadlocks made me double check. If `nbd_read_reply` gets garbage, it will likely return an error. When it returns an error, `recv_work` exits and calls `nbd_mark_nsock_dead`. `nbd_mark_nsock_dead` shuts down the socket. The other thread will also notice this and exit. At the end `nbd_config_put` will handle the cleanup.

One thing to verify is `nbd_mark_nsock_dead` in conjunction with `live_connections`: If `live_connections` starts at 2 and both threads call the decrement, it goes to zero. It seems correct.

I have to check `nbd_clear_sock` as well. In `nbd_config_put`. I will need to look at `nbd_clear_sock`.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_clear_sock]

map[SourceCode:1425:	static void nbd_clear_sock(struct nbd_device *nbd)
1426:	{
1427:		sock_shutdown(nbd);
1428:		nbd_clear_que(nbd);
1429:		nbd->task_setup = NULL;
1430:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 25277
							output: 40
							thoughts: 6
						

Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:

**Delving into `sock_shutdown`**

Alright, so we're talking about `sock_shutdown`. My immediate thought is, "Ah, yes, the finer points of graceful socket closure." I'm mentally parsing the implications. This isn't just a simple `close()` call, we're talking about a more controlled, deliberate shutdown. I'm already anticipating the nuances of TCP's connection termination handshake, the states involved, and the implications for data transmission.

Specifically, I'm considering the potential scenarios. Will I be shutting down for read, write, or both? `SHUT_RD`, `SHUT_WR`, or `SHUT_RDWR` – each has its own behavioral fingerprint and consequences, and I'm instantly weighing them. The choice dictates whether I'm signaling that I'm done *receiving*, done *sending*, or done with the whole communication stream. I'm practically diagramming the TCP state machine in my head, visualizing the FIN and ACK segments.

My brain is now mapping this onto the practicalities of my application. What's the protocol? Is it a request-response pattern, a streaming connection, or something else entirely? The `sock_shutdown` call needs to fit seamlessly into the application's overall design. I'm focusing on ensuring data integrity. I need to be absolutely certain that any remaining data in the send queue is flushed before initiating the shutdown for writing. Otherwise, I risk data loss, corruption, or unexpected behavior on the receiving end.

And the error handling? I'm already anticipating the potential for errors. What if the socket isn't properly connected? What if the shutdown fails? I know I need to be prepared to handle `EBADF`, `ENOTSOCK`, `ENOTCONN` and similar error codes. I'm already crafting my error-handling strategy, anticipating the potential for race conditions and planning to handle them gracefully.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:sock_shutdown]

map[SourceCode: 395:	/*
 396:	 * Forcibly shutdown the socket causing all listeners to error
 397:	 */
 398:	static void sock_shutdown(struct nbd_device *nbd)
 399:	{
 400:		struct nbd_config *config = nbd->config;
 401:		int i;
 402:	
 403:		if (config->num_connections == 0)
 404:			return;
 405:		if (test_and_set_bit(NBD_RT_DISCONNECTED, &config->runtime_flags))
 406:			return;
 407:	
 408:		for (i = 0; i < config->num_connections; i++) {
 409:			struct nbd_sock *nsock = config->socks[i];
 410:			mutex_lock(&nsock->tx_lock);
 411:			nbd_mark_nsock_dead(nbd, nsock, 0);
 412:			mutex_unlock(&nsock->tx_lock);
 413:		}
 414:		dev_warn(disk_to_dev(nbd->disk), "shutting down sockets\n");
 415:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 26115
							output: 42
							thoughts: 1816
						

**Analyzing NBD Driver Concurrency and Resource Management**

Okay, let's break this down. First, `sock_shutdown` iterates through connections and marks sockets as dead using `nbd_mark_nsock_dead`. The core concern here is potential double-frees or incorrect resource accounting if multiple `nsock` structures point to the same underlying `sock` structure. The initial assessment seems correct: `nbd_mark_nsock_dead` checks the `dead` flag of each `nsock` *before* calling `kernel_sock_shutdown`. So, multiple calls to `kernel_sock_shutdown` for the same socket are safe because of that individual flag check.

The `live_connections` counter decrement, within `nbd_mark_nsock_dead`, *is* worth a second look, particularly given multiple `nsock` structures for the same `sock`. If `live_connections` starts at 2 and there are two `nsock` structures for the same `sock`, the decrements to 1 and then 0 do seem valid.

Next, I'm checking `nbd_config_put` to ensure its balanced with increments, because that's always a potential source of errors. It's incremented during each `recv_work`, and the increment in `nbd_genl_connect` looks balanced and the decrements seem balanced too. A failure in `nbd_add_socket` in `nbd_genl_connect` is handled to ensure `nbd_config_put` is called to free resources. So far, so good.

Now, that's interesting: `nbd_mark_nsock_dead` queuing `nbd_dead_link_work`. If multiple threads call it for the same socket (but with different `nsock`s), we could have *multiple* work items queued. However, the worst thing it does is notify userspace, which should be harmless.

The big one: the interplay of `nbd_read_reply` and `nbd_handle_reply`. If two threads try to read from the same socket concurrently, we *could* have a race. One thread could read the initial part of a reply (magic, cookie) and the other could see an error. Then, when a READ request kicks off and calls `sock_xmit` within `nbd_handle_reply` (thread A), it might compete with `nbd_read_reply` (thread B). *That's* bad. The kernel's TCP implementation *might* handle this safely, but the NBD driver would see protocol errors and shut down, which is the proper behaviour, it just takes longer.

Are there other shared resources? `nbd_device` and `nbd_config` are potential sources of contention. And then, the `blk_mq_update_nr_hw_queues` is interesting. Multiple HW queues, *each* processing a socket from the same TCP connection and using a single `tx_lock` can't be good. Since requests from those separate HW queues are sent over the *same* socket, they could corrupt the NBD stream. This is another concern.

Okay, let's circle back to the double `sockfd_put` call in `nbd_config_put`. If `config->socks[0]->sock` and `config->socks[1]->sock` are the same, `sockfd_put` will be called twice on the same socket. That seems fine because we called `sockfd_lookup` twice, which increments the refcount, and `sockfd_put` decreases it.

And this points to the heart of the issue:
```c
1254:		sock = nbd_get_socket(nbd, arg, &err);
```
`nbd_get_socket` calls `sockfd_lookup`. This is what calls `sockfd_lookup` again.

So we call `sockfd_lookup` twice, which *correctly* increments the refcount of the underlying `struct file` twice. Then, calling `sockfd_put` twice decrements the refcount twice. So far, the socket refcount is properly managed.

Now, considering the question: "Could this cause a kernel panic or deadlock?". The answer is maybe. The double `sockfd_put` *itself* is not a bug. However, if the socket is used in a way that *assumes* it's unique, there *could* be a bug *somewhere else*. However, the refcounts look properly managed, so it's probably okay.

Lastly, the `sk_set_memalloc` check.  If the same socket is used, `sk_set_memalloc` may be called twice on the same socket. Let's check `sk_

map[ContextFile:include/net/sock.h IncludeLines:true Name:sk_set_memalloc]

map[SourceCode: 294:	/**
 295:	 * sk_set_memalloc - sets %SOCK_MEMALLOC
 296:	 * @sk: socket to set it on
 297:	 *
 298:	 * Set %SOCK_MEMALLOC on a socket for access to emergency reserves.
 299:	 * It's the responsibility of the admin to adjust min_free_kbytes
 300:	 * to meet the requirements
 301:	 */
 302:	void sk_set_memalloc(struct sock *sk)
 303:	{
 304:		sock_set_flag(sk, SOCK_MEMALLOC);
 305:		sk->sk_allocation |= __GFP_MEMALLOC;
 306:		static_branch_inc(&memalloc_socks_key);
 307:	}
 SourceFile:net/core/sock.c]

gemini-3-flash-preview

							input: 29243
							output: 24
							thoughts: 158
						

**Memory Allocation Key Concerns**

Okay, hold on a second. I just saw `static_branch_inc(&memalloc_socks_key)`. That's interesting. The code increments this key when `sk_set_memalloc` is called. The alarm bells are going off. If a socket has `sk_set_memalloc` called multiple times, that `static_branch_inc` call is duplicated. That's fine, but is there a matching `sk_clear_memalloc`? I need to be sure the incrementing is correctly balanced.

Right, let me look at NBD's implementation. Hmm, it doesn't seem to call `sk_clear_memalloc`. That's a potential leak. If NBD *doesn't* clear the allocation, then `memalloc_socks_key` will just stay incremented indefinitely. This has a nasty memory implications in a long-running system. 

But wait, hold on. When the socket is destroyed, is there implicit clean-up? I need to verify how sockets are handled in those cases. The documentation *should* provide some insights.

And generally, `sk_set_memalloc` is used in, for example, swap-over-NBD setups, which makes this investigation even more pressing. 

Okay, I need to check where `sk_clear_memalloc` *is* called. That's my next step.

map[Name:sk_clear_memalloc]

map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:sock_free SourceFile:drivers/net/wireguard/socket.c SourceLine:337] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:xs_reset_transport SourceFile:net/sunrpc/xprtsock.c SourceLine:1289]] TruncatedOutput:false]

gemini-3-flash-preview

							input: 29854
							output: 22
							thoughts: 145
						

**Investigating Potential Memory Allocation Leak in NBD**

Okay, so it looks like `sk_clear_memalloc` isn't explicitly being called within the Network Block Device (NBD) driver. That's a bit concerning. Hang on... if NBD is setting the `SOCK_MEMALLOC` flag on a socket, shouldn't it *also* be clearing it when the socket is no longer needed? Otherwise, it's relying on the socket's destruction to clean up, which feels a bit fragile, or the destruction does not happen which leads to leakage.

The crucial issue here is balance, `static_branch_inc` calls must have corresponding `static_branch_dec` calls. If the clearing of the `SOCK_MEMALLOC` flag isn't happening properly, then the `memalloc_socks_key` counter will inevitably leak. This is a potential resource leak.

Right, time to verify this assumption. I need to confirm whether or not NBD actually calls `sk_clear_memalloc` anywhere in its code. I'll search for occurrences of `sk_clear_memalloc` within `drivers/block/nbd.c`. Let's see what the source code says.

map[Dir:drivers/block/]

map[Files:[amiflop.c ataflop.c brd.c floppy.c loop.c n64cart.c nbd.c ps3disk.c ps3vram.c rbd.c rbd_types.h sunvdc.c swim.c swim3.c swim_asm.S ublk_drv.c virtio_blk.c xen-blkfront.c z2ram.c zloop.c] Subdirs:[aoe drbd mtip32xx null_blk rnbd rnull xen-blkback zram]]

gemini-3-flash-preview

							input: 30498
							output: 23
							thoughts: 23
						

Okay, here's my take on those thoughts, tailored for an expert audience:

**Analyzing NBD Memory Management**

Right, let's dive in. When I see mention of `sk_clear_memalloc`, my first instinct is to head straight to `drivers/block/nbd.c`. That's where I'd expect to find the Network Block Device driver, and therefore, where I'd look for any socket-related memory management. I'm assuming we're dealing with socket buffer (sk_buff) memory, and the "clear_memalloc" function likely points to a mechanism for releasing or resetting resources associated with that allocation. I'd be looking closely at how it interacts with the NBD's request handling and data transfer paths. Is it part of a congestion control scheme? Does it prevent memory leaks or fragmentation? My initial focus would be on pinpointing the specific conditions under which `sk_clear_memalloc` is called, and what the implications of its execution are, especially concerning locking, error handling, and performance. I need to understand the full lifecycle of the memory management within this module.

map[File:drivers/block/nbd.c]

map[Contents:// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Network block device - make block devices work over TCP
 *
 * Note that you can not swap over this thing, yet. Seems to work but
 * deadlocks sometimes - you can not swap over TCP in general.
 * 
 * Copyright 1997-2000, 2008 Pavel Machek <pavel@ucw.cz>
 * Parts copyright 2001 Steven Whitehouse <steve@chygwyn.com>
 *
 * (part of code stolen from loop.c)
 */

#define pr_fmt(fmt) "nbd: " fmt

#include <linux/major.h>

#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/sched/mm.h>
#include <linux/fs.h>
#include <linux/bio.h>
#include <linux/stat.h>
#include <linux/errno.h>
#include <linux/file.h>
#include <linux/ioctl.h>
#include <linux/mutex.h>
#include <linux/compiler.h>
#include <linux/completion.h>
#include <linux/err.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <net/sock.h>
#include <linux/net.h>
#include <linux/kthread.h>
#include <linux/types.h>
#include <linux/debugfs.h>
#include <linux/blk-mq.h>

#include <linux/uaccess.h>
#include <asm/types.h>

#include <linux/nbd.h>
#include <linux/nbd-netlink.h>
#include <net/genetlink.h>

#define CREATE_TRACE_POINTS
#include <trace/events/nbd.h>

static DEFINE_IDR(nbd_index_idr);
static DEFINE_MUTEX(nbd_index_mutex);
static struct workqueue_struct *nbd_del_wq;
static int nbd_total_devices = 0;

struct nbd_sock {
	struct socket *sock;
	struct mutex tx_lock;
	struct request *pending;
	int sent;
	bool dead;
	int fallback_index;
	int cookie;
	struct work_struct work;
};

struct recv_thread_args {
	struct work_struct work;
	struct nbd_device *nbd;
	struct nbd_sock *nsock;
	int index;
};

struct link_dead_args {
	struct work_struct work;
	int index;
};

#define NBD_RT_TIMEDOUT			0
#define NBD_RT_DISCONNECT_REQUESTED	1
#define NBD_RT_DISCONNECTED		2
#define NBD_RT_HAS_PID_FILE		3
#define NBD_RT_HAS_CONFIG_REF		4
#define NBD_RT_BOUND			5
#define NBD_RT_DISCONNECT_ON_CLOSE	6
#define NBD_RT_HAS_BACKEND_FILE		7

#define NBD_DESTROY_ON_DISCONNECT	0
#define NBD_DISCONNECT_REQUESTED	1

struct nbd_config {
	u32 flags;
	unsigned long runtime_flags;
	u64 dead_conn_timeout;

	struct nbd_sock **socks;
	int num_connections;
	atomic_t live_connections;
	wait_queue_head_t conn_wait;

	atomic_t recv_threads;
	wait_queue_head_t recv_wq;
	unsigned int blksize_bits;
	loff_t bytesize;
#if IS_ENABLED(CONFIG_DEBUG_FS)
	struct dentry *dbg_dir;
#endif
};

static inline unsigned int nbd_blksize(struct nbd_config *config)
{
	return 1u << config->blksize_bits;
}

struct nbd_device {
	struct blk_mq_tag_set tag_set;

	int index;
	refcount_t config_refs;
	refcount_t refs;
	struct nbd_config *config;
	struct mutex config_lock;
	struct gendisk *disk;
	struct workqueue_struct *recv_workq;
	struct work_struct remove_work;

	struct list_head list;
	struct task_struct *task_setup;

	unsigned long flags;
	pid_t pid; /* pid of nbd-client, if attached */

	char *backend;
};

#define NBD_CMD_REQUEUED	1
/*
 * This flag will be set if nbd_queue_rq() succeed, and will be checked and
 * cleared in completion. Both setting and clearing of the flag are protected
 * by cmd->lock.
 */
#define NBD_CMD_INFLIGHT	2

/* Just part of request header or data payload is sent successfully */
#define NBD_CMD_PARTIAL_SEND	3

struct nbd_cmd {
	struct nbd_device *nbd;
	struct mutex lock;
	int index;
	int cookie;
	int retries;
	blk_status_t status;
	unsigned long flags;
	u32 cmd_cookie;
};

#if IS_ENABLED(CONFIG_DEBUG_FS)
static struct dentry *nbd_dbg_dir;
#endif

#define nbd_name(nbd) ((nbd)->disk->disk_name)

#define NBD_DEF_BLKSIZE_BITS 10

static unsigned int nbds_max = 16;
static int max_part = 16;
static int part_shift;

static int nbd_dev_dbg_init(struct nbd_device *nbd);
static void nbd_dev_dbg_close(struct nbd_device *nbd);
static void nbd_config_put(struct nbd_device *nbd);
static void nbd_connect_reply(struct genl_info *info, int index);
static int nbd_genl_status(struct sk_buff *skb, struct genl_info *info);
static void nbd_dead_link_work(struct work_struct *work);
static void nbd_disconnect_and_put(struct nbd_device *nbd);

static inline struct device *nbd_to_dev(struct nbd_device *nbd)
{
	return disk_to_dev(nbd->disk);
}

static void nbd_requeue_cmd(struct nbd_cmd *cmd)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);

	lockdep_assert_held(&cmd->lock);

	/*
	 * Clear INFLIGHT flag so that this cmd won't be completed in
	 * normal completion path
	 *
	 * INFLIGHT flag will be set when the cmd is queued to nbd next
	 * time.
	 */
	__clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);

	if (!test_and_set_bit(NBD_CMD_REQUEUED, &cmd->flags))
		blk_mq_requeue_request(req, true);
}

#define NBD_COOKIE_BITS 32

static u64 nbd_cmd_handle(struct nbd_cmd *cmd)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);
	u32 tag = blk_mq_unique_tag(req);
	u64 cookie = cmd->cmd_cookie;

	return (cookie << NBD_COOKIE_BITS) | tag;
}

static u32 nbd_handle_to_tag(u64 handle)
{
	return (u32)handle;
}

static u32 nbd_handle_to_cookie(u64 handle)
{
	return (u32)(handle >> NBD_COOKIE_BITS);
}

static const char *nbdcmd_to_ascii(int cmd)
{
	switch (cmd) {
	case  NBD_CMD_READ: return "read";
	case NBD_CMD_WRITE: return "write";
	case  NBD_CMD_DISC: return "disconnect";
	case NBD_CMD_FLUSH: return "flush";
	case  NBD_CMD_TRIM: return "trim/discard";
	}
	return "invalid";
}

static ssize_t pid_show(struct device *dev,
			struct device_attribute *attr, char *buf)
{
	struct gendisk *disk = dev_to_disk(dev);
	struct nbd_device *nbd = disk->private_data;

	return sprintf(buf, "%d\n", nbd->pid);
}

static const struct device_attribute pid_attr = {
	.attr = { .name = "pid", .mode = 0444},
	.show = pid_show,
};

static ssize_t backend_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct gendisk *disk = dev_to_disk(dev);
	struct nbd_device *nbd = disk->private_data;

	return sprintf(buf, "%s\n", nbd->backend ?: "");
}

static const struct device_attribute backend_attr = {
	.attr = { .name = "backend", .mode = 0444},
	.show = backend_show,
};

static void nbd_dev_remove(struct nbd_device *nbd)
{
	struct gendisk *disk = nbd->disk;

	del_gendisk(disk);
	blk_mq_free_tag_set(&nbd->tag_set);

	/*
	 * Remove from idr after del_gendisk() completes, so if the same ID is
	 * reused, the following add_disk() will succeed.
	 */
	mutex_lock(&nbd_index_mutex);
	idr_remove(&nbd_index_idr, nbd->index);
	mutex_unlock(&nbd_index_mutex);
	destroy_workqueue(nbd->recv_workq);
	put_disk(disk);
}

static void nbd_dev_remove_work(struct work_struct *work)
{
	nbd_dev_remove(container_of(work, struct nbd_device, remove_work));
}

static void nbd_put(struct nbd_device *nbd)
{
	if (!refcount_dec_and_test(&nbd->refs))
		return;

	/* Call del_gendisk() asynchrounously to prevent deadlock */
	if (test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags))
		queue_work(nbd_del_wq, &nbd->remove_work);
	else
		nbd_dev_remove(nbd);
}

static int nbd_disconnected(struct nbd_config *config)
{
	return test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags) ||
		test_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags);
}

static void nbd_mark_nsock_dead(struct nbd_device *nbd, struct nbd_sock *nsock,
				int notify)
{
	if (!nsock->dead && notify && !nbd_disconnected(nbd->config)) {
		struct link_dead_args *args;
		args = kmalloc_obj(struct link_dead_args, GFP_NOIO);
		if (args) {
			INIT_WORK(&args->work, nbd_dead_link_work);
			args->index = nbd->index;
			queue_work(system_percpu_wq, &args->work);
		}
	}
	if (!nsock->dead) {
		kernel_sock_shutdown(nsock->sock, SHUT_RDWR);
		if (atomic_dec_return(&nbd->config->live_connections) == 0) {
			if (test_and_clear_bit(NBD_RT_DISCONNECT_REQUESTED,
					       &nbd->config->runtime_flags)) {
				set_bit(NBD_RT_DISCONNECTED,
					&nbd->config->runtime_flags);
				dev_info(nbd_to_dev(nbd),
					"Disconnected due to user request.\n");
			}
		}
	}
	nsock->dead = true;
	nsock->pending = NULL;
	nsock->sent = 0;
}

static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize, loff_t blksize)
{
	struct queue_limits lim;
	int error;

	if (!blksize)
		blksize = 1u << NBD_DEF_BLKSIZE_BITS;

	if (blk_validate_block_size(blksize))
		return -EINVAL;

	if (bytesize < 0)
		return -EINVAL;

	nbd->config->bytesize = bytesize;
	nbd->config->blksize_bits = __ffs(blksize);

	if (!nbd->pid)
		return 0;

	lim = queue_limits_start_update(nbd->disk->queue);
	if (nbd->config->flags & NBD_FLAG_SEND_TRIM)
		lim.max_hw_discard_sectors = UINT_MAX >> SECTOR_SHIFT;
	else
		lim.max_hw_discard_sectors = 0;
	if (!(nbd->config->flags & NBD_FLAG_SEND_FLUSH)) {
		lim.features &= ~(BLK_FEAT_WRITE_CACHE | BLK_FEAT_FUA);
	} else if (nbd->config->flags & NBD_FLAG_SEND_FUA) {
		lim.features |= BLK_FEAT_WRITE_CACHE | BLK_FEAT_FUA;
	} else {
		lim.features |= BLK_FEAT_WRITE_CACHE;
		lim.features &= ~BLK_FEAT_FUA;
	}
	if (nbd->config->flags & NBD_FLAG_ROTATIONAL)
		lim.features |= BLK_FEAT_ROTATIONAL;
	if (nbd->config->flags & NBD_FLAG_SEND_WRITE_ZEROES)
		lim.max_write_zeroes_sectors = UINT_MAX >> SECTOR_SHIFT;

	lim.logical_block_size = blksize;
	lim.physical_block_size = blksize;
	error = queue_limits_commit_update_frozen(nbd->disk->queue, &lim);
	if (error)
		return error;

	if (max_part)
		set_bit(GD_NEED_PART_SCAN, &nbd->disk->state);
	if (!set_capacity_and_notify(nbd->disk, bytesize >> 9))
		kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
	return 0;
}

static void nbd_complete_rq(struct request *req)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);

	dev_dbg(nbd_to_dev(cmd->nbd), "request %p: %s\n", req,
		cmd->status ? "failed" : "done");

	blk_mq_end_request(req, cmd->status);
}

/*
 * Forcibly shutdown the socket causing all listeners to error
 */
static void sock_shutdown(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	int i;

	if (config->num_connections == 0)
		return;
	if (test_and_set_bit(NBD_RT_DISCONNECTED, &config->runtime_flags))
		return;

	for (i = 0; i < config->num_connections; i++) {
		struct nbd_sock *nsock = config->socks[i];
		mutex_lock(&nsock->tx_lock);
		nbd_mark_nsock_dead(nbd, nsock, 0);
		mutex_unlock(&nsock->tx_lock);
	}
	dev_warn(disk_to_dev(nbd->disk), "shutting down sockets\n");
}

static u32 req_to_nbd_cmd_type(struct request *req)
{
	switch (req_op(req)) {
	case REQ_OP_DISCARD:
		return NBD_CMD_TRIM;
	case REQ_OP_FLUSH:
		return NBD_CMD_FLUSH;
	case REQ_OP_WRITE:
		return NBD_CMD_WRITE;
	case REQ_OP_READ:
		return NBD_CMD_READ;
	case REQ_OP_WRITE_ZEROES:
		return NBD_CMD_WRITE_ZEROES;
	default:
		return U32_MAX;
	}
}

static struct nbd_config *nbd_get_config_unlocked(struct nbd_device *nbd)
{
	if (refcount_inc_not_zero(&nbd->config_refs)) {
		/*
		 * Add smp_mb__after_atomic to ensure that reading nbd->config_refs
		 * and reading nbd->config is ordered. The pair is the barrier in
		 * nbd_alloc_and_init_config(), avoid nbd->config_refs is set
		 * before nbd->config.
		 */
		smp_mb__after_atomic();
		return nbd->config;
	}

	return NULL;
}

static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);
	struct nbd_device *nbd = cmd->nbd;
	struct nbd_config *config;

	if (!mutex_trylock(&cmd->lock))
		return BLK_EH_RESET_TIMER;

	/* partial send is handled in nbd_sock's work function */
	if (test_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags)) {
		mutex_unlock(&cmd->lock);
		return BLK_EH_RESET_TIMER;
	}

	if (!test_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
		mutex_unlock(&cmd->lock);
		return BLK_EH_DONE;
	}

	config = nbd_get_config_unlocked(nbd);
	if (!config) {
		cmd->status = BLK_STS_TIMEOUT;
		__clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);
		mutex_unlock(&cmd->lock);
		goto done;
	}

	if (config->num_connections > 1 ||
	    (config->num_connections == 1 && nbd->tag_set.timeout)) {
		dev_err_ratelimited(nbd_to_dev(nbd),
				    "Connection timed out, retrying (%d/%d alive)\n",
				    atomic_read(&config->live_connections),
				    config->num_connections);
		/*
		 * Hooray we have more connections, requeue this IO, the submit
		 * path will put it on a real connection. Or if only one
		 * connection is configured, the submit path will wait util
		 * a new connection is reconfigured or util dead timeout.
		 */
		if (config->socks) {
			if (cmd->index < config->num_connections) {
				struct nbd_sock *nsock =
					config->socks[cmd->index];
				mutex_lock(&nsock->tx_lock);
				/* We can have multiple outstanding requests, so
				 * we don't want to mark the nsock dead if we've
				 * already reconnected with a new socket, so
				 * only mark it dead if its the same socket we
				 * were sent out on.
				 */
				if (cmd->cookie == nsock->cookie)
					nbd_mark_nsock_dead(nbd, nsock, 1);
				mutex_unlock(&nsock->tx_lock);
			}
			nbd_requeue_cmd(cmd);
			mutex_unlock(&cmd->lock);
			nbd_config_put(nbd);
			return BLK_EH_DONE;
		}
	}

	if (!nbd->tag_set.timeout) {
		/*
		 * Userspace sets timeout=0 to disable socket disconnection,
		 * so just warn and reset the timer.
		 */
		struct nbd_sock *nsock = config->socks[cmd->index];
		cmd->retries++;
		dev_info(nbd_to_dev(nbd), "Possible stuck request %p: control (%s@%llu,%uB). Runtime %u seconds\n",
			req, nbdcmd_to_ascii(req_to_nbd_cmd_type(req)),
			(unsigned long long)blk_rq_pos(req) << 9,
			blk_rq_bytes(req), (req->timeout / HZ) * cmd->retries);

		mutex_lock(&nsock->tx_lock);
		if (cmd->cookie != nsock->cookie) {
			nbd_requeue_cmd(cmd);
			mutex_unlock(&nsock->tx_lock);
			mutex_unlock(&cmd->lock);
			nbd_config_put(nbd);
			return BLK_EH_DONE;
		}
		mutex_unlock(&nsock->tx_lock);
		mutex_unlock(&cmd->lock);
		nbd_config_put(nbd);
		return BLK_EH_RESET_TIMER;
	}

	dev_err_ratelimited(nbd_to_dev(nbd), "Connection timed out\n");
	set_bit(NBD_RT_TIMEDOUT, &config->runtime_flags);
	cmd->status = BLK_STS_IOERR;
	__clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);
	mutex_unlock(&cmd->lock);
	sock_shutdown(nbd);
	nbd_config_put(nbd);
done:
	blk_mq_complete_request(req);
	return BLK_EH_DONE;
}

static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
		       struct iov_iter *iter, int msg_flags, int *sent)
{
	int result;
	struct msghdr msg = {} ;
	unsigned int noreclaim_flag;

	if (unlikely(!sock)) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
			"Attempted %s on closed socket in sock_xmit\n",
			(send ? "send" : "recv"));
		return -EINVAL;
	}

	msg.msg_iter = *iter;

	noreclaim_flag = memalloc_noreclaim_save();

	scoped_with_kernel_creds() {
		do {
			sock->sk->sk_allocation = GFP_NOIO | __GFP_MEMALLOC;
			sock->sk->sk_use_task_frag = false;
			msg.msg_flags = msg_flags | MSG_NOSIGNAL;

			if (send)
				result = sock_sendmsg(sock, &msg);
			else
				result = sock_recvmsg(sock, &msg, msg.msg_flags);

			if (result <= 0) {
				if (result == 0)
					result = -EPIPE; /* short read */
				break;
			}
			if (sent)
				*sent += result;
		} while (msg_data_left(&msg));
	}

	memalloc_noreclaim_restore(noreclaim_flag);

	return result;
}

/*
 *  Send or receive packet. Return a positive value on success and
 *  negtive value on failure, and never return 0.
 */
static int sock_xmit(struct nbd_device *nbd, int index, int send,
		     struct iov_iter *iter, int msg_flags, int *sent)
{
	struct nbd_config *config = nbd->config;
	struct socket *sock = config->socks[index]->sock;

	return __sock_xmit(nbd, sock, send, iter, msg_flags, sent);
}

/*
 * Different settings for sk->sk_sndtimeo can result in different return values
 * if there is a signal pending when we enter sendmsg, because reasons?
 */
static inline int was_interrupted(int result)
{
	return result == -ERESTARTSYS || result == -EINTR;
}

/*
 * We've already sent header or part of data payload, have no choice but
 * to set pending and schedule it in work.
 *
 * And we have to return BLK_STS_OK to block core, otherwise this same
 * request may be re-dispatched with different tag, but our header has
 * been sent out with old tag, and this way does confuse reply handling.
 */
static void nbd_sched_pending_work(struct nbd_device *nbd,
				   struct nbd_sock *nsock,
				   struct nbd_cmd *cmd, int sent)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);

	/* pending work should be scheduled only once */
	WARN_ON_ONCE(test_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags));

	nsock->pending = req;
	nsock->sent = sent;
	set_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags);
	refcount_inc(&nbd->config_refs);
	schedule_work(&nsock->work);
}

/*
 * Returns BLK_STS_RESOURCE if the caller should retry after a delay.
 * Returns BLK_STS_IOERR if sending failed.
 */
static blk_status_t nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd,
				 int index)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);
	struct nbd_config *config = nbd->config;
	struct nbd_sock *nsock = config->socks[index];
	int result;
	struct nbd_request request = {.magic = htonl(NBD_REQUEST_MAGIC)};
	struct kvec iov = {.iov_base = &request, .iov_len = sizeof(request)};
	struct iov_iter from;
	struct bio *bio;
	u64 handle;
	u32 type;
	u32 nbd_cmd_flags = 0;
	int sent = nsock->sent, skip = 0;

	lockdep_assert_held(&cmd->lock);
	lockdep_assert_held(&nsock->tx_lock);

	iov_iter_kvec(&from, ITER_SOURCE, &iov, 1, sizeof(request));

	type = req_to_nbd_cmd_type(req);
	if (type == U32_MAX)
		return BLK_STS_IOERR;

	if (rq_data_dir(req) == WRITE &&
	    (config->flags & NBD_FLAG_READ_ONLY)) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
				    "Write on read-only\n");
		return BLK_STS_IOERR;
	}

	if (req->cmd_flags & REQ_FUA)
		nbd_cmd_flags |= NBD_CMD_FLAG_FUA;
	if ((req->cmd_flags & REQ_NOUNMAP) && (type == NBD_CMD_WRITE_ZEROES))
		nbd_cmd_flags |= NBD_CMD_FLAG_NO_HOLE;

	/* We did a partial send previously, and we at least sent the whole
	 * request struct, so just go and send the rest of the pages in the
	 * request.
	 */
	if (sent) {
		if (sent >= sizeof(request)) {
			skip = sent - sizeof(request);

			/* initialize handle for tracing purposes */
			handle = nbd_cmd_handle(cmd);

			goto send_pages;
		}
		iov_iter_advance(&from, sent);
	} else {
		cmd->cmd_cookie++;
	}
	cmd->index = index;
	cmd->cookie = nsock->cookie;
	cmd->retries = 0;
	request.type = htonl(type | nbd_cmd_flags);
	if (type != NBD_CMD_FLUSH) {
		request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9);
		request.len = htonl(blk_rq_bytes(req));
	}
	handle = nbd_cmd_handle(cmd);
	request.cookie = cpu_to_be64(handle);

	trace_nbd_send_request(&request, nbd->index, blk_mq_rq_from_pdu(cmd));

	dev_dbg(nbd_to_dev(nbd), "request %p: sending control (%s@%llu,%uB)\n",
		req, nbdcmd_to_ascii(type),
		(unsigned long long)blk_rq_pos(req) << 9, blk_rq_bytes(req));
	result = sock_xmit(nbd, index, 1, &from,
			(type == NBD_CMD_WRITE) ? MSG_MORE : 0, &sent);
	trace_nbd_header_sent(req, handle);
	if (result < 0) {
		if (was_interrupted(result)) {
			/* If we haven't sent anything we can just return BUSY,
			 * however if we have sent something we need to make
			 * sure we only allow this req to be sent until we are
			 * completely done.
			 */
			if (sent) {
				nbd_sched_pending_work(nbd, nsock, cmd, sent);
				return BLK_STS_OK;
			}
			set_bit(NBD_CMD_REQUEUED, &cmd->flags);
			return BLK_STS_RESOURCE;
		}
		dev_err_ratelimited(disk_to_dev(nbd->disk),
			"Send control failed (result %d)\n", result);
		goto requeue;
	}
send_pages:
	if (type != NBD_CMD_WRITE)
		goto out;

	bio = req->bio;
	while (bio) {
		struct bio *next = bio->bi_next;
		struct bvec_iter iter;
		struct bio_vec bvec;

		bio_for_each_segment(bvec, bio, iter) {
			bool is_last = !next && bio_iter_last(bvec, iter);
			int flags = is_last ? 0 : MSG_MORE;

			dev_dbg(nbd_to_dev(nbd), "request %p: sending %d bytes data\n",
				req, bvec.bv_len);
			iov_iter_bvec(&from, ITER_SOURCE, &bvec, 1, bvec.bv_len);
			if (skip) {
				if (skip >= iov_iter_count(&from)) {
					skip -= iov_iter_count(&from);
					continue;
				}
				iov_iter_advance(&from, skip);
				skip = 0;
			}
			result = sock_xmit(nbd, index, 1, &from, flags, &sent);
			if (result < 0) {
				if (was_interrupted(result)) {
					nbd_sched_pending_work(nbd, nsock, cmd, sent);
					return BLK_STS_OK;
				}
				dev_err(disk_to_dev(nbd->disk),
					"Send data failed (result %d)\n",
					result);
				goto requeue;
			}
			/*
			 * The completion might already have come in,
			 * so break for the last one instead of letting
			 * the iterator do it. This prevents use-after-free
			 * of the bio.
			 */
			if (is_last)
				break;
		}
		bio = next;
	}
out:
	trace_nbd_payload_sent(req, handle);
	nsock->pending = NULL;
	nsock->sent = 0;
	__set_bit(NBD_CMD_INFLIGHT, &cmd->flags);
	return BLK_STS_OK;

requeue:
	/*
	 * Can't requeue in case we are dealing with partial send
	 *
	 * We must run from pending work function.
	 * */
	if (test_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags))
		return BLK_STS_OK;

	/* retry on a different socket */
	dev_err_ratelimited(disk_to_dev(nbd->disk),
			    "Request send failed, requeueing\n");
	nbd_mark_nsock_dead(nbd, nsock, 1);
	nbd_requeue_cmd(cmd);
	return BLK_STS_OK;
}

/* handle partial sending */
static void nbd_pending_cmd_work(struct work_struct *work)
{
	struct nbd_sock *nsock = container_of(work, struct nbd_sock, work);
	struct request *req = nsock->pending;
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);
	struct nbd_device *nbd = cmd->nbd;
	unsigned long deadline = READ_ONCE(req->deadline);
	unsigned int wait_ms = 2;

	mutex_lock(&cmd->lock);

	WARN_ON_ONCE(test_bit(NBD_CMD_REQUEUED, &cmd->flags));
	if (WARN_ON_ONCE(!test_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags)))
		goto out;

	mutex_lock(&nsock->tx_lock);
	while (true) {
		nbd_send_cmd(nbd, cmd, cmd->index);
		if (!nsock->pending)
			break;

		/* don't bother timeout handler for partial sending */
		if (READ_ONCE(jiffies) + msecs_to_jiffies(wait_ms) >= deadline) {
			cmd->status = BLK_STS_IOERR;
			blk_mq_complete_request(req);
			break;
		}
		msleep(wait_ms);
		wait_ms *= 2;
	}
	mutex_unlock(&nsock->tx_lock);
	clear_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags);
out:
	mutex_unlock(&cmd->lock);
	nbd_config_put(nbd);
}

static int nbd_read_reply(struct nbd_device *nbd, struct socket *sock,
			  struct nbd_reply *reply)
{
	struct kvec iov = {.iov_base = reply, .iov_len = sizeof(*reply)};
	struct iov_iter to;
	int result;

	reply->magic = 0;
	iov_iter_kvec(&to, ITER_DEST, &iov, 1, sizeof(*reply));
	result = __sock_xmit(nbd, sock, 0, &to, MSG_WAITALL, NULL);
	if (result < 0) {
		if (!nbd_disconnected(nbd->config))
			dev_err(disk_to_dev(nbd->disk),
				"Receive control failed (result %d)\n", result);
		return result;
	}

	if (ntohl(reply->magic) != NBD_REPLY_MAGIC) {
		dev_err(disk_to_dev(nbd->disk), "Wrong magic (0x%lx)\n",
				(unsigned long)ntohl(reply->magic));
		return -EPROTO;
	}

	return 0;
}

/* NULL returned = something went wrong, inform userspace */
static struct nbd_cmd *nbd_handle_reply(struct nbd_device *nbd, int index,
					struct nbd_reply *reply)
{
	int result;
	struct nbd_cmd *cmd;
	struct request *req = NULL;
	u64 handle;
	u16 hwq;
	u32 tag;
	int ret = 0;

	handle = be64_to_cpu(reply->cookie);
	tag = nbd_handle_to_tag(handle);
	hwq = blk_mq_unique_tag_to_hwq(tag);
	if (hwq < nbd->tag_set.nr_hw_queues)
		req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq],
				       blk_mq_unique_tag_to_tag(tag));
	if (!req || !blk_mq_request_started(req)) {
		dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%d) %p\n",
			tag, req);
		return ERR_PTR(-ENOENT);
	}
	trace_nbd_header_received(req, handle);
	cmd = blk_mq_rq_to_pdu(req);

	mutex_lock(&cmd->lock);
	if (!test_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
		dev_err(disk_to_dev(nbd->disk), "Suspicious reply %d (status %u flags %lu)",
			tag, cmd->status, cmd->flags);
		ret = -ENOENT;
		goto out;
	}
	if (cmd->index != index) {
		dev_err(disk_to_dev(nbd->disk), "Unexpected reply %d from different sock %d (expected %d)",
			tag, index, cmd->index);
		ret = -ENOENT;
		goto out;
	}
	if (cmd->cmd_cookie != nbd_handle_to_cookie(handle)) {
		dev_err(disk_to_dev(nbd->disk), "Double reply on req %p, cmd_cookie %u, handle cookie %u\n",
			req, cmd->cmd_cookie, nbd_handle_to_cookie(handle));
		ret = -ENOENT;
		goto out;
	}
	if (cmd->status != BLK_STS_OK) {
		dev_err(disk_to_dev(nbd->disk), "Command already handled %p\n",
			req);
		ret = -ENOENT;
		goto out;
	}
	if (test_bit(NBD_CMD_REQUEUED, &cmd->flags)) {
		dev_err(disk_to_dev(nbd->disk), "Raced with timeout on req %p\n",
			req);
		ret = -ENOENT;
		goto out;
	}
	if (ntohl(reply->error)) {
		dev_err(disk_to_dev(nbd->disk), "Other side returned error (%d)\n",
			ntohl(reply->error));
		cmd->status = BLK_STS_IOERR;
		goto out;
	}

	dev_dbg(nbd_to_dev(nbd), "request %p: got reply\n", req);
	if (rq_data_dir(req) != WRITE) {
		struct req_iterator iter;
		struct bio_vec bvec;
		struct iov_iter to;

		rq_for_each_segment(bvec, req, iter) {
			iov_iter_bvec(&to, ITER_DEST, &bvec, 1, bvec.bv_len);
			result = sock_xmit(nbd, index, 0, &to, MSG_WAITALL, NULL);
			if (result < 0) {
				dev_err(disk_to_dev(nbd->disk), "Receive data failed (result %d)\n",
					result);
				/*
				 * If we've disconnected, we need to make sure we
				 * complete this request, otherwise error out
				 * and let the timeout stuff handle resubmitting
				 * this request onto another connection.
				 */
				if (nbd_disconnected(nbd->config)) {
					cmd->status = BLK_STS_IOERR;
					goto out;
				}
				ret = -EIO;
				goto out;
			}
			dev_dbg(nbd_to_dev(nbd), "request %p: got %d bytes data\n",
				req, bvec.bv_len);
		}
	}
out:
	trace_nbd_payload_received(req, handle);
	mutex_unlock(&cmd->lock);
	return ret ? ERR_PTR(ret) : cmd;
}

static void recv_work(struct work_struct *work)
{
	struct recv_thread_args *args = container_of(work,
						     struct recv_thread_args,
						     work);
	struct nbd_device *nbd = args->nbd;
	struct nbd_config *config = nbd->config;
	struct request_queue *q = nbd->disk->queue;
	struct nbd_sock *nsock = args->nsock;
	struct nbd_cmd *cmd;
	struct request *rq;

	while (1) {
		struct nbd_reply reply;

		if (nbd_read_reply(nbd, nsock->sock, &reply))
			break;

		/*
		 * Grab .q_usage_counter so request pool won't go away, then no
		 * request use-after-free is possible during nbd_handle_reply().
		 * If queue is frozen, there won't be any inflight requests, we
		 * needn't to handle the incoming garbage message.
		 */
		if (!percpu_ref_tryget(&q->q_usage_counter)) {
			dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n",
				__func__);
			break;
		}

		cmd = nbd_handle_reply(nbd, args->index, &reply);
		if (IS_ERR(cmd)) {
			percpu_ref_put(&q->q_usage_counter);
			break;
		}

		rq = blk_mq_rq_from_pdu(cmd);
		if (likely(!blk_should_fake_timeout(rq->q))) {
			bool complete;

			mutex_lock(&cmd->lock);
			complete = __test_and_clear_bit(NBD_CMD_INFLIGHT,
							&cmd->flags);
			mutex_unlock(&cmd->lock);
			if (complete)
				blk_mq_complete_request(rq);
		}
		percpu_ref_put(&q->q_usage_counter);
	}

	mutex_lock(&nsock->tx_lock);
	nbd_mark_nsock_dead(nbd, nsock, 1);
	mutex_unlock(&nsock->tx_lock);

	atomic_dec(&config->recv_threads);
	wake_up(&config->recv_wq);
	nbd_config_put(nbd);
	kfree(args);
}

static bool nbd_clear_req(struct request *req, void *data)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);

	/* don't abort one completed request */
	if (blk_mq_request_completed(req))
		return true;

	mutex_lock(&cmd->lock);
	if (!__test_and_clear_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
		mutex_unlock(&cmd->lock);
		return true;
	}
	cmd->status = BLK_STS_IOERR;
	mutex_unlock(&cmd->lock);

	blk_mq_complete_request(req);
	return true;
}

static void nbd_clear_que(struct nbd_device *nbd)
{
	blk_mq_quiesce_queue(nbd->disk->queue);
	blk_mq_tagset_busy_iter(&nbd->tag_set, nbd_clear_req, NULL);
	blk_mq_unquiesce_queue(nbd->disk->queue);
	dev_dbg(disk_to_dev(nbd->disk), "queue cleared\n");
}

static int find_fallback(struct nbd_device *nbd, int index)
{
	struct nbd_config *config = nbd->config;
	int new_index = -1;
	struct nbd_sock *nsock = config->socks[index];
	int fallback = nsock->fallback_index;

	if (test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags))
		return new_index;

	if (config->num_connections <= 1) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
				    "Dead connection, failed to find a fallback\n");
		return new_index;
	}

	if (fallback >= 0 && fallback < config->num_connections &&
	    !config->socks[fallback]->dead)
		return fallback;

	if (nsock->fallback_index < 0 ||
	    nsock->fallback_index >= config->num_connections ||
	    config->socks[nsock->fallback_index]->dead) {
		int i;
		for (i = 0; i < config->num_connections; i++) {
			if (i == index)
				continue;
			if (!config->socks[i]->dead) {
				new_index = i;
				break;
			}
		}
		nsock->fallback_index = new_index;
		if (new_index < 0) {
			dev_err_ratelimited(disk_to_dev(nbd->disk),
					    "Dead connection, failed to find a fallback\n");
			return new_index;
		}
	}
	new_index = nsock->fallback_index;
	return new_index;
}

static int wait_for_reconnect(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	if (!config->dead_conn_timeout)
		return 0;

	if (!wait_event_timeout(config->conn_wait,
				test_bit(NBD_RT_DISCONNECTED,
					 &config->runtime_flags) ||
				atomic_read(&config->live_connections) > 0,
				config->dead_conn_timeout))
		return 0;

	return !test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);
}

static blk_status_t nbd_handle_cmd(struct nbd_cmd *cmd, int index)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);
	struct nbd_device *nbd = cmd->nbd;
	struct nbd_config *config;
	struct nbd_sock *nsock;
	blk_status_t ret;

	lockdep_assert_held(&cmd->lock);

	config = nbd_get_config_unlocked(nbd);
	if (!config) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
				    "Socks array is empty\n");
		return BLK_STS_IOERR;
	}

	if (index >= config->num_connections) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
				    "Attempted send on invalid socket\n");
		nbd_config_put(nbd);
		return BLK_STS_IOERR;
	}
	cmd->status = BLK_STS_OK;
again:
	nsock = config->socks[index];
	mutex_lock(&nsock->tx_lock);
	if (nsock->dead) {
		int old_index = index;
		index = find_fallback(nbd, index);
		mutex_unlock(&nsock->tx_lock);
		if (index < 0) {
			if (wait_for_reconnect(nbd)) {
				index = old_index;
				goto again;
			}
			/* All the sockets should already be down at this point,
			 * we just want to make sure that DISCONNECTED is set so
			 * any requests that come in that were queue'ed waiting
			 * for the reconnect timer don't trigger the timer again
			 * and instead just error out.
			 */
			sock_shutdown(nbd);
			nbd_config_put(nbd);
			return BLK_STS_IOERR;
		}
		goto again;
	}

	/* Handle the case that we have a pending request that was partially
	 * transmitted that _has_ to be serviced first.  We need to call requeue
	 * here so that it gets put _after_ the request that is already on the
	 * dispatch list.
	 */
	blk_mq_start_request(req);
	if (unlikely(nsock->pending && nsock->pending != req)) {
		nbd_requeue_cmd(cmd);
		ret = BLK_STS_OK;
		goto out;
	}
	ret = nbd_send_cmd(nbd, cmd, index);
out:
	mutex_unlock(&nsock->tx_lock);
	nbd_config_put(nbd);
	return ret;
}

static blk_status_t nbd_queue_rq(struct blk_mq_hw_ctx *hctx,
			const struct blk_mq_queue_data *bd)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(bd->rq);
	blk_status_t ret;

	/*
	 * Since we look at the bio's to send the request over the network we
	 * need to make sure the completion work doesn't mark this request done
	 * before we are done doing our send.  This keeps us from dereferencing
	 * freed data if we have particularly fast completions (ie we get the
	 * completion before we exit sock_xmit on the last bvec) or in the case
	 * that the server is misbehaving (or there was an error) before we're
	 * done sending everything over the wire.
	 */
	mutex_lock(&cmd->lock);
	clear_bit(NBD_CMD_REQUEUED, &cmd->flags);

	/* We can be called directly from the user space process, which means we
	 * could possibly have signals pending so our sendmsg will fail.  In
	 * this case we need to return that we are busy, otherwise error out as
	 * appropriate.
	 */
	ret = nbd_handle_cmd(cmd, hctx->queue_num);
	mutex_unlock(&cmd->lock);

	return ret;
}

static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd,
				     int *err)
{
	struct socket *sock;

	*err = 0;
	sock = sockfd_lookup(fd, err);
	if (!sock)
		return NULL;

	if (!sk_is_tcp(sock->sk) &&
	    !sk_is_stream_unix(sock->sk)) {
		dev_err(disk_to_dev(nbd->disk), "Unsupported socket: should be TCP or UNIX.\n");
		*err = -EINVAL;
		sockfd_put(sock);
		return NULL;
	}

	if (sock->ops->shutdown == sock_no_shutdown) {
		dev_err(disk_to_dev(nbd->disk), "Unsupported socket: shutdown callout must be supported.\n");
		*err = -EINVAL;
		sockfd_put(sock);
		return NULL;
	}

	return sock;
}

static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
			  bool netlink)
{
	struct nbd_config *config = nbd->config;
	struct socket *sock;
	struct nbd_sock **socks;
	struct nbd_sock *nsock;
	unsigned int memflags;
	int err;

	/* Arg will be cast to int, check it to avoid overflow */
	if (arg > INT_MAX)
		return -EINVAL;
	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	/*
	 * We need to make sure we don't get any errant requests while we're
	 * reallocating the ->socks array.
	 */
	memflags = blk_mq_freeze_queue(nbd->disk->queue);

	if (!netlink && !nbd->task_setup &&
	    !test_bit(NBD_RT_BOUND, &config->runtime_flags))
		nbd->task_setup = current;

	if (!netlink &&
	    (nbd->task_setup != current ||
	     test_bit(NBD_RT_BOUND, &config->runtime_flags))) {
		dev_err(disk_to_dev(nbd->disk),
			"Device being setup by another task");
		err = -EBUSY;
		goto put_socket;
	}

	nsock = kzalloc_obj(*nsock);
	if (!nsock) {
		err = -ENOMEM;
		goto put_socket;
	}

	socks = krealloc(config->socks, (config->num_connections + 1) *
			 sizeof(struct nbd_sock *), GFP_KERNEL);
	if (!socks) {
		kfree(nsock);
		err = -ENOMEM;
		goto put_socket;
	}

	config->socks = socks;

	nsock->fallback_index = -1;
	nsock->dead = false;
	mutex_init(&nsock->tx_lock);
	nsock->sock = sock;
	nsock->pending = NULL;
	nsock->sent = 0;
	nsock->cookie = 0;
	INIT_WORK(&nsock->work, nbd_pending_cmd_work);
	socks[config->num_connections++] = nsock;
	atomic_inc(&config->live_connections);
	blk_mq_unfreeze_queue(nbd->disk->queue, memflags);

	return 0;

put_socket:
	blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
	sockfd_put(sock);
	return err;
}

static int nbd_reconnect_socket(struct nbd_device *nbd, unsigned long arg)
{
	struct nbd_config *config = nbd->config;
	struct socket *sock, *old;
	struct recv_thread_args *args;
	int i;
	int err;

	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	args = kzalloc_obj(*args);
	if (!args) {
		sockfd_put(sock);
		return -ENOMEM;
	}

	for (i = 0; i < config->num_connections; i++) {
		struct nbd_sock *nsock = config->socks[i];

		if (!nsock->dead)
			continue;

		mutex_lock(&nsock->tx_lock);
		if (!nsock->dead) {
			mutex_unlock(&nsock->tx_lock);
			continue;
		}
		sk_set_memalloc(sock->sk);
		if (nbd->tag_set.timeout)
			sock->sk->sk_sndtimeo = nbd->tag_set.timeout;
		atomic_inc(&config->recv_threads);
		refcount_inc(&nbd->config_refs);
		old = nsock->sock;
		nsock->fallback_index = -1;
		nsock->sock = sock;
		nsock->dead = false;
		INIT_WORK(&args->work, recv_work);
		args->index = i;
		args->nbd = nbd;
		args->nsock = nsock;
		nsock->cookie++;
		mutex_unlock(&nsock->tx_lock);
		sockfd_put(old);

		clear_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);

		/* We take the tx_mutex in an error path in the recv_work, so we
		 * need to queue_work outside of the tx_mutex.
		 */
		queue_work(nbd->recv_workq, &args->work);

		atomic_inc(&config->live_connections);
		wake_up(&config->conn_wait);
		return 0;
	}
	sockfd_put(sock);
	kfree(args);
	return -ENOSPC;
}

static void nbd_bdev_reset(struct nbd_device *nbd)
{
	if (disk_openers(nbd->disk) > 1)
		return;
	set_capacity(nbd->disk, 0);
}

static void nbd_parse_flags(struct nbd_device *nbd)
{
	if (nbd->config->flags & NBD_FLAG_READ_ONLY)
		set_disk_ro(nbd->disk, true);
	else
		set_disk_ro(nbd->disk, false);
}

static void send_disconnects(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	struct nbd_request request = {
		.magic = htonl(NBD_REQUEST_MAGIC),
		.type = htonl(NBD_CMD_DISC),
	};
	struct kvec iov = {.iov_base = &request, .iov_len = sizeof(request)};
	struct iov_iter from;
	int i, ret;

	for (i = 0; i < config->num_connections; i++) {
		struct nbd_sock *nsock = config->socks[i];

		iov_iter_kvec(&from, ITER_SOURCE, &iov, 1, sizeof(request));
		mutex_lock(&nsock->tx_lock);
		ret = sock_xmit(nbd, i, 1, &from, 0, NULL);
		if (ret < 0)
			dev_err(disk_to_dev(nbd->disk),
				"Send disconnect failed %d\n", ret);
		mutex_unlock(&nsock->tx_lock);
	}
}

static int nbd_disconnect(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;

	dev_info(disk_to_dev(nbd->disk), "NBD_DISCONNECT\n");
	set_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags);
	set_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags);
	send_disconnects(nbd);
	return 0;
}

static void nbd_clear_sock(struct nbd_device *nbd)
{
	sock_shutdown(nbd);
	nbd_clear_que(nbd);
	nbd->task_setup = NULL;
}

static void nbd_config_put(struct nbd_device *nbd)
{
	if (refcount_dec_and_mutex_lock(&nbd->config_refs,
					&nbd->config_lock)) {
		struct nbd_config *config = nbd->config;
		nbd_dev_dbg_close(nbd);
		invalidate_disk(nbd->disk);
		if (nbd->config->bytesize)
			kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
		if (test_and_clear_bit(NBD_RT_HAS_PID_FILE,
				       &config->runtime_flags))
			device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
		nbd->pid = 0;
		if (test_and_clear_bit(NBD_RT_HAS_BACKEND_FILE,
				       &config->runtime_flags)) {
			device_remove_file(disk_to_dev(nbd->disk), &backend_attr);
			kfree(nbd->backend);
			nbd->backend = NULL;
		}
		nbd_clear_sock(nbd);
		if (config->num_connections) {
			int i;
			for (i = 0; i < config->num_connections; i++) {
				sockfd_put(config->socks[i]->sock);
				kfree(config->socks[i]);
			}
			kfree(config->socks);
		}
		kfree(nbd->config);
		nbd->config = NULL;

		nbd->tag_set.timeout = 0;

		mutex_unlock(&nbd->config_lock);
		nbd_put(nbd);
		module_put(THIS_MODULE);
	}
}

static int nbd_start_device(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	int num_connections = config->num_connections;
	int error = 0, i;

	if (nbd->pid)
		return -EBUSY;
	if (!config->socks)
		return -EINVAL;
	if (num_connections > 1 &&
	    !(config->flags & NBD_FLAG_CAN_MULTI_CONN)) {
		dev_err(disk_to_dev(nbd->disk), "server does not support multiple connections per device.\n");
		return -EINVAL;
	}

retry:
	mutex_unlock(&nbd->config_lock);
	blk_mq_update_nr_hw_queues(&nbd->tag_set, num_connections);
	mutex_lock(&nbd->config_lock);

	/* if another code path updated nr_hw_queues, retry until succeed */
	if (num_connections != config->num_connections) {
		num_connections = config->num_connections;
		goto retry;
	}

	nbd->pid = task_pid_nr(current);

	nbd_parse_flags(nbd);

	error = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
	if (error) {
		dev_err(disk_to_dev(nbd->disk), "device_create_file failed for pid!\n");
		return error;
	}
	set_bit(NBD_RT_HAS_PID_FILE, &config->runtime_flags);

	nbd_dev_dbg_init(nbd);
	for (i = 0; i < num_connections; i++) {
		struct recv_thread_args *args;

		args = kzalloc_obj(*args);
		if (!args) {
			sock_shutdown(nbd);
			/*
			 * If num_connections is m (2 < m),
			 * and NO.1 ~ NO.n(1 < n < m) kzallocs are successful.
			 * But NO.(n + 1) failed. We still have n recv threads.
			 * So, add flush_workqueue here to prevent recv threads
			 * dropping the last config_refs and trying to destroy
			 * the workqueue from inside the workqueue.
			 */
			if (i)
				flush_workqueue(nbd->recv_workq);
			return -ENOMEM;
		}
		sk_set_memalloc(config->socks[i]->sock->sk);
		if (nbd->tag_set.timeout)
			config->socks[i]->sock->sk->sk_sndtimeo =
				nbd->tag_set.timeout;
		atomic_inc(&config->recv_threads);
		refcount_inc(&nbd->config_refs);
		INIT_WORK(&args->work, recv_work);
		args->nbd = nbd;
		args->nsock = config->socks[i];
		args->index = i;
		queue_work(nbd->recv_workq, &args->work);
	}
	return nbd_set_size(nbd, config->bytesize, nbd_blksize(config));
}

static int nbd_start_device_ioctl(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	int ret;

	ret = nbd_start_device(nbd);
	if (ret)
		return ret;

	if (max_part)
		set_bit(GD_NEED_PART_SCAN, &nbd->disk->state);
	mutex_unlock(&nbd->config_lock);
	ret = wait_event_interruptible(config->recv_wq,
					 atomic_read(&config->recv_threads) == 0);
	if (ret) {
		sock_shutdown(nbd);
		nbd_clear_que(nbd);
	}

	flush_workqueue(nbd->recv_workq);
	mutex_lock(&nbd->config_lock);
	nbd_bdev_reset(nbd);
	/* user requested, ignore socket errors */
	if (test_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags))
		ret = 0;
	if (test_bit(NBD_RT_TIMEDOUT, &config->runtime_flags))
		ret = -ETIMEDOUT;
	return ret;
}

static void nbd_clear_sock_ioctl(struct nbd_device *nbd)
{
	nbd_clear_sock(nbd);
	disk_force_media_change(nbd->disk);
	nbd_bdev_reset(nbd);
	if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF,
			       &nbd->config->runtime_flags))
		nbd_config_put(nbd);
}

static void nbd_set_cmd_timeout(struct nbd_device *nbd, u64 timeout)
{
	nbd->tag_set.timeout = timeout * HZ;
	if (timeout)
		blk_queue_rq_timeout(nbd->disk->queue, timeout * HZ);
	else
		blk_queue_rq_timeout(nbd->disk->queue, 30 * HZ);
}

/* Must be called with config_lock held */
static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
		       unsigned int cmd, unsigned long arg)
{
	struct nbd_config *config = nbd->config;
	loff_t bytesize;

	switch (cmd) {
	case NBD_DISCONNECT:
		return nbd_disconnect(nbd);
	case NBD_CLEAR_SOCK:
		nbd_clear_sock_ioctl(nbd);
		return 0;
	case NBD_SET_SOCK:
		return nbd_add_socket(nbd, arg, false);
	case NBD_SET_BLKSIZE:
		return nbd_set_size(nbd, config->bytesize, arg);
	case NBD_SET_SIZE:
		return nbd_set_size(nbd, arg, nbd_blksize(config));
	case NBD_SET_SIZE_BLOCKS:
		if (check_shl_overflow(arg, config->blksize_bits, &bytesize))
			return -EINVAL;
		return nbd_set_size(nbd, bytesize, nbd_blksize(config));
	case NBD_SET_TIMEOUT:
		nbd_set_cmd_timeout(nbd, arg);
		return 0;

	case NBD_SET_FLAGS:
		config->flags = arg;
		return 0;
	case NBD_DO_IT:
		return nbd_start_device_ioctl(nbd);
	case NBD_CLEAR_QUE:
		/*
		 * This is for compatibility only.  The queue is always cleared
		 * by NBD_DO_IT or NBD_CLEAR_SOCK.
		 */
		return 0;
	case NBD_PRINT_DEBUG:
		/*
		 * For compatibility only, we no longer keep a list of
		 * outstanding requests.
		 */
		return 0;
	}
	return -ENOTTY;
}

static int nbd_ioctl(struct block_device *bdev, blk_mode_t mode,
		     unsigned int cmd, unsigned long arg)
{
	struct nbd_device *nbd = bdev->bd_disk->private_data;
	struct nbd_config *config = nbd->config;
	int error = -EINVAL;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;

	/* The block layer will pass back some non-nbd ioctls in case we have
	 * special handling for them, but we don't so just return an error.
	 */
	if (_IOC_TYPE(cmd) != 0xab)
		return -EINVAL;

	mutex_lock(&nbd->config_lock);

	/* Don't allow ioctl operations on a nbd device that was created with
	 * netlink, unless it's DISCONNECT or CLEAR_SOCK, which are fine.
	 */
	if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
	    (cmd == NBD_DISCONNECT || cmd == NBD_CLEAR_SOCK))
		error = __nbd_ioctl(bdev, nbd, cmd, arg);
	else
		dev_err(nbd_to_dev(nbd), "Cannot use ioctl interface on a netlink controlled device.\n");
	mutex_unlock(&nbd->config_lock);
	return error;
}

static int nbd_alloc_and_init_config(struct nbd_device *nbd)
{
	struct nbd_config *config;

	if (WARN_ON(nbd->config))
		return -EINVAL;

	if (!try_module_get(THIS_MODULE))
		return -ENODEV;

	config = kzalloc_obj(struct nbd_config, GFP_NOFS);
	if (!config) {
		module_put(THIS_MODULE);
		return -ENOMEM;
	}

	atomic_set(&config->recv_threads, 0);
	init_waitqueue_head(&config->recv_wq);
	init_waitqueue_head(&config->conn_wait);
	config->blksize_bits = NBD_DEF_BLKSIZE_BITS;
	atomic_set(&config->live_connections, 0);

	nbd->config = config;
	/*
	 * Order refcount_set(&nbd->config_refs, 1) and nbd->config assignment,
	 * its pair is the barrier in nbd_get_config_unlocked().
	 * So nbd_get_config_unlocked() won't see nbd->config as null after
	 * refcount_inc_not_zero() succeed.
	 */
	smp_mb__before_atomic();
	refcount_set(&nbd->config_refs, 1);

	return 0;
}

static int nbd_open(struct gendisk *disk, blk_mode_t mode)
{
	struct nbd_device *nbd;
	struct nbd_config *config;
	int ret = 0;

	mutex_lock(&nbd_index_mutex);
	nbd = disk->private_data;
	if (!nbd) {
		ret = -ENXIO;
		goto out;
	}
	if (!refcount_inc_not_zero(&nbd->refs)) {
		ret = -ENXIO;
		goto out;
	}

	config = nbd_get_config_unlocked(nbd);
	if (!config) {
		mutex_lock(&nbd->config_lock);
		if (refcount_inc_not_zero(&nbd->config_refs)) {
			mutex_unlock(&nbd->config_lock);
			goto out;
		}
		ret = nbd_alloc_and_init_config(nbd);
		if (ret) {
			mutex_unlock(&nbd->config_lock);
			goto out;
		}

		refcount_inc(&nbd->refs);
		mutex_unlock(&nbd->config_lock);
		if (max_part)
			set_bit(GD_NEED_PART_SCAN, &disk->state);
	} else if (nbd_disconnected(config)) {
		if (max_part)
			set_bit(GD_NEED_PART_SCAN, &disk->state);
	}
out:
	mutex_unlock(&nbd_index_mutex);
	return ret;
}

static void nbd_release(struct gendisk *disk)
{
	struct nbd_device *nbd = disk->private_data;

	if (test_bit(NBD_RT_DISCONNECT_ON_CLOSE, &nbd->config->runtime_flags) &&
			disk_openers(disk) == 0)
		nbd_disconnect_and_put(nbd);

	nbd_config_put(nbd);
	nbd_put(nbd);
}

static void nbd_free_disk(struct gendisk *disk)
{
	struct nbd_device *nbd = disk->private_data;

	kfree(nbd);
}

static const struct block_device_operations nbd_fops =
{
	.owner =	THIS_MODULE,
	.open =		nbd_open,
	.release =	nbd_release,
	.ioctl =	nbd_ioctl,
	.compat_ioctl =	nbd_ioctl,
	.free_disk =	nbd_free_disk,
};

#if IS_ENABLED(CONFIG_DEBUG_FS)

static int nbd_dbg_tasks_show(struct seq_file *s, void *unused)
{
	struct nbd_device *nbd = s->private;

	if (nbd->pid)
		seq_printf(s, "recv: %d\n", nbd->pid);

	return 0;
}

DEFINE_SHOW_ATTRIBUTE(nbd_dbg_tasks);

static int nbd_dbg_flags_show(struct seq_file *s, void *unused)
{
	struct nbd_device *nbd = s->private;
	u32 flags = nbd->config->flags;

	seq_printf(s, "Hex: 0x%08x\n\n", flags);

	seq_puts(s, "Known flags:\n");

	if (flags & NBD_FLAG_HAS_FLAGS)
		seq_puts(s, "NBD_FLAG_HAS_FLAGS\n");
	if (flags & NBD_FLAG_READ_ONLY)
		seq_puts(s, "NBD_FLAG_READ_ONLY\n");
	if (flags & NBD_FLAG_SEND_FLUSH)
		seq_puts(s, "NBD_FLAG_SEND_FLUSH\n");
	if (flags & NBD_FLAG_SEND_FUA)
		seq_puts(s, "NBD_FLAG_SEND_FUA\n");
	if (flags & NBD_FLAG_SEND_TRIM)
		seq_puts(s, "NBD_FLAG_SEND_TRIM\n");
	if (flags & NBD_FLAG_SEND_WRITE_ZEROES)
		seq_puts(s, "NBD_FLAG_SEND_WRITE_ZEROES\n");
	if (flags & NBD_FLAG_ROTATIONAL)
		seq_puts(s, "NBD_FLAG_ROTATIONAL\n");

	return 0;
}

DEFINE_SHOW_ATTRIBUTE(nbd_dbg_flags);

static int nbd_dev_dbg_init(struct nbd_device *nbd)
{
	struct dentry *dir;
	struct nbd_config *config = nbd->config;

	if (!nbd_dbg_dir)
		return -EIO;

	dir = debugfs_create_dir(nbd_name(nbd), nbd_dbg_dir);
	if (IS_ERR(dir)) {
		dev_err(nbd_to_dev(nbd), "Failed to create debugfs dir for '%s'\n",
			nbd_name(nbd));
		return -EIO;
	}
	config->dbg_dir = dir;

	debugfs_create_file("tasks", 0444, dir, nbd, &nbd_dbg_tasks_fops);
	debugfs_create_u64("size_bytes", 0444, dir, &config->bytesize);
	debugfs_create_u32("timeout", 0444, dir, &nbd->tag_set.timeout);
	debugfs_create_u32("blocksize_bits", 0444, dir, &config->blksize_bits);
	debugfs_create_file("flags", 0444, dir, nbd, &nbd_dbg_flags_fops);

	return 0;
}

static void nbd_dev_dbg_close(struct nbd_device *nbd)
{
	debugfs_remove_recursive(nbd->config->dbg_dir);
}

static int nbd_dbg_init(void)
{
	struct dentry *dbg_dir;

	dbg_dir = debugfs_create_dir("nbd", NULL);
	if (IS_ERR(dbg_dir))
		return -EIO;

	nbd_dbg_dir = dbg_dir;

	return 0;
}

static void nbd_dbg_close(void)
{
	debugfs_remove_recursive(nbd_dbg_dir);
}

#else  /* IS_ENABLED(CONFIG_DEBUG_FS) */

static int nbd_dev_dbg_init(struct nbd_device *nbd)
{
	return 0;
}

static void nbd_dev_dbg_close(struct nbd_device *nbd)
{
}

static int nbd_dbg_init(void)
{
	return 0;
}

static void nbd_dbg_close(void)
{
}

#endif

static int nbd_init_request(struct blk_mq_tag_set *set, struct request *rq,
			    unsigned int hctx_idx, unsigned int numa_node)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(rq);
	cmd->nbd = set->driver_data;
	cmd->flags = 0;
	mutex_init(&cmd->lock);
	return 0;
}

static const struct blk_mq_ops nbd_mq_ops = {
	.queue_rq	= nbd_queue_rq,
	.complete	= nbd_complete_rq,
	.init_request	= nbd_init_request,
	.timeout	= nbd_xmit_timeout,
};

static struct nbd_device *nbd_dev_add(int index, unsigned int refs)
{
	struct queue_limits lim = {
		.max_hw_sectors		= 65536,
		.io_opt			= 256 << SECTOR_SHIFT,
		.max_segments		= USHRT_MAX,
		.max_segment_size	= UINT_MAX,
	};
	struct nbd_device *nbd;
	struct gendisk *disk;
	int err = -ENOMEM;

	nbd = kzalloc_obj(struct nbd_device);
	if (!nbd)
		goto out;

	nbd->tag_set.ops = &nbd_mq_ops;
	nbd->tag_set.nr_hw_queues = 1;
	nbd->tag_set.queue_depth = 128;
	nbd->tag_set.numa_node = NUMA_NO_NODE;
	nbd->tag_set.cmd_size = sizeof(struct nbd_cmd);
	nbd->tag_set.flags = BLK_MQ_F_BLOCKING;
	nbd->tag_set.driver_data = nbd;
	INIT_WORK(&nbd->remove_work, nbd_dev_remove_work);
	nbd->backend = NULL;

	err = blk_mq_alloc_tag_set(&nbd->tag_set);
	if (err)
		goto out_free_nbd;

	mutex_lock(&nbd_index_mutex);
	if (index >= 0) {
		err = idr_alloc(&nbd_index_idr, nbd, index, index + 1,
				GFP_KERNEL);
		if (err == -ENOSPC)
			err = -EEXIST;
	} else {
		err = idr_alloc(&nbd_index_idr, nbd, 0,
				(MINORMASK >> part_shift) + 1, GFP_KERNEL);
		if (err >= 0)
			index = err;
	}
	nbd->index = index;
	mutex_unlock(&nbd_index_mutex);
	if (err < 0)
		goto out_free_tags;

	disk = blk_mq_alloc_disk(&nbd->tag_set, &lim, NULL);
	if (IS_ERR(disk)) {
		err = PTR_ERR(disk);
		goto out_free_idr;
	}
	nbd->disk = disk;

	nbd->recv_workq = alloc_workqueue("nbd%d-recv",
					  WQ_MEM_RECLAIM | WQ_HIGHPRI |
					  WQ_UNBOUND, 0, nbd->index);
	if (!nbd->recv_workq) {
		dev_err(disk_to_dev(nbd->disk), "Could not allocate knbd recv work queue.\n");
		err = -ENOMEM;
		goto out_err_disk;
	}

	mutex_init(&nbd->config_lock);
	refcount_set(&nbd->config_refs, 0);
	/*
	 * Start out with a zero references to keep other threads from using
	 * this device until it is fully initialized.
	 */
	refcount_set(&nbd->refs, 0);
	INIT_LIST_HEAD(&nbd->list);
	disk->major = NBD_MAJOR;
	disk->first_minor = index << part_shift;
	disk->minors = 1 << part_shift;
	disk->fops = &nbd_fops;
	disk->private_data = nbd;
	sprintf(disk->disk_name, "nbd%d", index);
	err = add_disk(disk);
	if (err)
		goto out_free_work;

	/*
	 * Now publish the device.
	 */
	refcount_set(&nbd->refs, refs);
	nbd_total_devices++;
	return nbd;

out_free_work:
	destroy_workqueue(nbd->recv_workq);
out_err_disk:
	put_disk(disk);
out_free_idr:
	mutex_lock(&nbd_index_mutex);
	idr_remove(&nbd_index_idr, index);
	mutex_unlock(&nbd_index_mutex);
out_free_tags:
	blk_mq_free_tag_set(&nbd->tag_set);
out_free_nbd:
	kfree(nbd);
out:
	return ERR_PTR(err);
}

static struct nbd_device *nbd_find_get_unused(void)
{
	struct nbd_device *nbd;
	int id;

	lockdep_assert_held(&nbd_index_mutex);

	idr_for_each_entry(&nbd_index_idr, nbd, id) {
		if (refcount_read(&nbd->config_refs) ||
		    test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags))
			continue;
		if (refcount_inc_not_zero(&nbd->refs))
			return nbd;
	}

	return NULL;
}

/* Netlink interface. */
static const struct nla_policy nbd_attr_policy[NBD_ATTR_MAX + 1] = {
	[NBD_ATTR_INDEX]		=	{ .type = NLA_U32 },
	[NBD_ATTR_SIZE_BYTES]		=	{ .type = NLA_U64 },
	[NBD_ATTR_BLOCK_SIZE_BYTES]	=	{ .type = NLA_U64 },
	[NBD_ATTR_TIMEOUT]		=	{ .type = NLA_U64 },
	[NBD_ATTR_SERVER_FLAGS]		=	{ .type = NLA_U64 },
	[NBD_ATTR_CLIENT_FLAGS]		=	{ .type = NLA_U64 },
	[NBD_ATTR_SOCKETS]		=	{ .type = NLA_NESTED},
	[NBD_ATTR_DEAD_CONN_TIMEOUT]	=	{ .type = NLA_U64 },
	[NBD_ATTR_DEVICE_LIST]		=	{ .type = NLA_NESTED},
	[NBD_ATTR_BACKEND_IDENTIFIER]	=	{ .type = NLA_STRING},
};

static const struct nla_policy nbd_sock_policy[NBD_SOCK_MAX + 1] = {
	[NBD_SOCK_FD]			=	{ .type = NLA_U32 },
};

/* We don't use this right now since we don't parse the incoming list, but we
 * still want it here so userspace knows what to expect.
 */
static const struct nla_policy __attribute__((unused))
nbd_device_policy[NBD_DEVICE_ATTR_MAX + 1] = {
	[NBD_DEVICE_INDEX]		=	{ .type = NLA_U32 },
	[NBD_DEVICE_CONNECTED]		=	{ .type = NLA_U8 },
};

static int nbd_genl_size_set(struct genl_info *info, struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	u64 bsize = nbd_blksize(config);
	u64 bytes = config->bytesize;

	if (info->attrs[NBD_ATTR_SIZE_BYTES])
		bytes = nla_get_u64(info->attrs[NBD_ATTR_SIZE_BYTES]);

	if (info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES])
		bsize = nla_get_u64(info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES]);

	if (bytes != config->bytesize || bsize != nbd_blksize(config))
		return nbd_set_size(nbd, bytes, bsize);
	return 0;
}

static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
{
	struct nbd_device *nbd;
	struct nbd_config *config;
	int index = -1;
	int ret;
	bool put_dev = false;

	if (!netlink_capable(skb, CAP_SYS_ADMIN))
		return -EPERM;

	if (info->attrs[NBD_ATTR_INDEX]) {
		index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);

		/*
		 * Too big first_minor can cause duplicate creation of
		 * sysfs files/links, since index << part_shift might overflow, or
		 * MKDEV() expect that the max bits of first_minor is 20.
		 */
		if (index < 0 || index > MINORMASK >> part_shift) {
			pr_err("illegal input index %d\n", index);
			return -EINVAL;
		}
	}
	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SOCKETS)) {
		pr_err("must specify at least one socket\n");
		return -EINVAL;
	}
	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SIZE_BYTES)) {
		pr_err("must specify a size in bytes for the device\n");
		return -EINVAL;
	}
again:
	mutex_lock(&nbd_index_mutex);
	if (index == -1) {
		nbd = nbd_find_get_unused();
	} else {
		nbd = idr_find(&nbd_index_idr, index);
		if (nbd) {
			if ((test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags) &&
			     test_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags)) ||
			    !refcount_inc_not_zero(&nbd->refs)) {
				mutex_unlock(&nbd_index_mutex);
				pr_err("device at index %d is going down\n",
					index);
				return -EINVAL;
			}
		}
	}
	mutex_unlock(&nbd_index_mutex);

	if (!nbd) {
		nbd = nbd_dev_add(index, 2);
		if (IS_ERR(nbd)) {
			pr_err("failed to add new device\n");
			return PTR_ERR(nbd);
		}
	}

	mutex_lock(&nbd->config_lock);
	if (refcount_read(&nbd->config_refs)) {
		mutex_unlock(&nbd->config_lock);
		nbd_put(nbd);
		if (index == -1)
			goto again;
		pr_err("nbd%d already in use\n", index);
		return -EBUSY;
	}

	ret = nbd_alloc_and_init_config(nbd);
	if (ret) {
		mutex_unlock(&nbd->config_lock);
		nbd_put(nbd);
		pr_err("couldn't allocate config\n");
		return ret;
	}

	config = nbd->config;
	set_bit(NBD_RT_BOUND, &config->runtime_flags);
	ret = nbd_genl_size_set(info, nbd);
	if (ret)
		goto out;

	if (info->attrs[NBD_ATTR_TIMEOUT])
		nbd_set_cmd_timeout(nbd,
				    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
	if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
		config->dead_conn_timeout =
			nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
		config->dead_conn_timeout *= HZ;
	}
	if (info->attrs[NBD_ATTR_SERVER_FLAGS])
		config->flags =
			nla_get_u64(info->attrs[NBD_ATTR_SERVER_FLAGS]);
	if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
		u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
		if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
			/*
			 * We have 1 ref to keep the device around, and then 1
			 * ref for our current operation here, which will be
			 * inherited by the config.  If we already have
			 * DESTROY_ON_DISCONNECT set then we know we don't have
			 * that extra ref already held so we don't need the
			 * put_dev.
			 */
			if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
					      &nbd->flags))
				put_dev = true;
		} else {
			if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
					       &nbd->flags))
				refcount_inc(&nbd->refs);
		}
		if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
			set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
				&config->runtime_flags);
		}
	}

	if (info->attrs[NBD_ATTR_SOCKETS]) {
		struct nlattr *attr;
		int rem, fd;

		nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
				    rem) {
			struct nlattr *socks[NBD_SOCK_MAX+1];

			if (nla_type(attr) != NBD_SOCK_ITEM) {
				pr_err("socks must be embedded in a SOCK_ITEM attr\n");
				ret = -EINVAL;
				goto out;
			}
			ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
							  attr,
							  nbd_sock_policy,
							  info->extack);
			if (ret != 0) {
				pr_err("error processing sock list\n");
				ret = -EINVAL;
				goto out;
			}
			if (!socks[NBD_SOCK_FD])
				continue;
			fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
			ret = nbd_add_socket(nbd, fd, true);
			if (ret)
				goto out;
		}
	}

	if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
		nbd->backend = nla_strdup(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
					  GFP_KERNEL);
		if (!nbd->backend) {
			ret = -ENOMEM;
			goto out;
		}
	}
	ret = device_create_file(disk_to_dev(nbd->disk), &backend_attr);
	if (ret) {
		dev_err(disk_to_dev(nbd->disk),
			"device_create_file failed for backend!\n");
		goto out;
	}
	set_bit(NBD_RT_HAS_BACKEND_FILE, &config->runtime_flags);

	ret = nbd_start_device(nbd);
out:
	if (!ret) {
		set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);
		refcount_inc(&nbd->config_refs);
		nbd_connect_reply(info, nbd->index);
	}
	mutex_unlock(&nbd->config_lock);

	nbd_config_put(nbd);
	if (put_dev)
		nbd_put(nbd);
	return ret;
}

static void nbd_disconnect_and_put(struct nbd_device *nbd)
{
	mutex_lock(&nbd->config_lock);
	nbd_disconnect(nbd);
	sock_shutdown(nbd);
	wake_up(&nbd->config->conn_wait);
	/*
	 * Make sure recv thread has finished, we can safely call nbd_clear_que()
	 * to cancel the inflight I/Os.
	 */
	flush_workqueue(nbd->recv_workq);
	nbd_clear_que(nbd);
	nbd->task_setup = NULL;
	clear_bit(NBD_RT_BOUND, &nbd->config->runtime_flags);
	mutex_unlock(&nbd->config_lock);

	if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF,
			       &nbd->config->runtime_flags))
		nbd_config_put(nbd);
}

static int nbd_genl_disconnect(struct sk_buff *skb, struct genl_info *info)
{
	struct nbd_device *nbd;
	int index;

	if (!netlink_capable(skb, CAP_SYS_ADMIN))
		return -EPERM;

	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)) {
		pr_err("must specify an index to disconnect\n");
		return -EINVAL;
	}
	index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
	mutex_lock(&nbd_index_mutex);
	nbd = idr_find(&nbd_index_idr, index);
	if (!nbd) {
		mutex_unlock(&nbd_index_mutex);
		pr_err("couldn't find device at index %d\n", index);
		return -EINVAL;
	}
	if (!refcount_inc_not_zero(&nbd->refs)) {
		mutex_unlock(&nbd_index_mutex);
		pr_err("device at index %d is going down\n", index);
		return -EINVAL;
	}
	mutex_unlock(&nbd_index_mutex);
	if (!refcount_inc_not_zero(&nbd->config_refs))
		goto put_nbd;
	nbd_disconnect_and_put(nbd);
	nbd_config_put(nbd);
put_nbd:
	nbd_put(nbd);
	return 0;
}

static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
{
	struct nbd_device *nbd = NULL;
	struct nbd_config *config;
	int index;
	int ret = 0;
	bool put_dev = false;

	if (!netlink_capable(skb, CAP_SYS_ADMIN))
		return -EPERM;

	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)) {
		pr_err("must specify a device to reconfigure\n");
		return -EINVAL;
	}
	index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
	mutex_lock(&nbd_index_mutex);
	nbd = idr_find(&nbd_index_idr, index);
	if (!nbd) {
		mutex_unlock(&nbd_index_mutex);
		pr_err("couldn't find a device at index %d\n", index);
		return -EINVAL;
	}
	if (nbd->backend) {
		if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
			if (nla_strcmp(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
				       nbd->backend)) {
				mutex_unlock(&nbd_index_mutex);
				dev_err(nbd_to_dev(nbd),
					"backend image doesn't match with %s\n",
					nbd->backend);
				return -EINVAL;
			}
		} else {
			mutex_unlock(&nbd_index_mutex);
			dev_err(nbd_to_dev(nbd), "must specify backend\n");
			return -EINVAL;
		}
	}
	if (!refcount_inc_not_zero(&nbd->refs)) {
		mutex_unlock(&nbd_index_mutex);
		pr_err("device at index %d is going down\n", index);
		return -EINVAL;
	}
	mutex_unlock(&nbd_index_mutex);

	config = nbd_get_config_unlocked(nbd);
	if (!config) {
		dev_err(nbd_to_dev(nbd),
			"not configured, cannot reconfigure\n");
		nbd_put(nbd);
		return -EINVAL;
	}

	mutex_lock(&nbd->config_lock);
	if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
	    !nbd->pid) {
		dev_err(nbd_to_dev(nbd),
			"not configured, cannot reconfigure\n");
		ret = -EINVAL;
		goto out;
	}

	ret = nbd_genl_size_set(info, nbd);
	if (ret)
		goto out;

	if (info->attrs[NBD_ATTR_TIMEOUT])
		nbd_set_cmd_timeout(nbd,
				    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
	if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
		config->dead_conn_timeout =
			nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
		config->dead_conn_timeout *= HZ;
	}
	if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
		u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
		if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
			if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
					      &nbd->flags))
				put_dev = true;
		} else {
			if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
					       &nbd->flags))
				refcount_inc(&nbd->refs);
		}

		if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
			set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
					&config->runtime_flags);
		} else {
			clear_bit(NBD_RT_DISCONNECT_ON_CLOSE,
					&config->runtime_flags);
		}
	}

	if (info->attrs[NBD_ATTR_SOCKETS]) {
		struct nlattr *attr;
		int rem, fd;

		nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
				    rem) {
			struct nlattr *socks[NBD_SOCK_MAX+1];

			if (nla_type(attr) != NBD_SOCK_ITEM) {
				pr_err("socks must be embedded in a SOCK_ITEM attr\n");
				ret = -EINVAL;
				goto out;
			}
			ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
							  attr,
							  nbd_sock_policy,
							  info->extack);
			if (ret != 0) {
				pr_err("error processing sock list\n");
				ret = -EINVAL;
				goto out;
			}
			if (!socks[NBD_SOCK_FD])
				continue;
			fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
			ret = nbd_reconnect_socket(nbd, fd);
			if (ret) {
				if (ret == -ENOSPC)
					ret = 0;
				goto out;
			}
			dev_info(nbd_to_dev(nbd), "reconnected socket\n");
		}
	}
out:
	mutex_unlock(&nbd->config_lock);
	nbd_config_put(nbd);
	nbd_put(nbd);
	if (put_dev)
		nbd_put(nbd);
	return ret;
}

static const struct genl_small_ops nbd_connect_genl_ops[] = {
	{
		.cmd	= NBD_CMD_CONNECT,
		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
		.doit	= nbd_genl_connect,
	},
	{
		.cmd	= NBD_CMD_DISCONNECT,
		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
		.doit	= nbd_genl_disconnect,
	},
	{
		.cmd	= NBD_CMD_RECONFIGURE,
		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
		.doit	= nbd_genl_reconfigure,
	},
	{
		.cmd	= NBD_CMD_STATUS,
		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
		.doit	= nbd_genl_status,
	},
};

static const struct genl_multicast_group nbd_mcast_grps[] = {
	{ .name = NBD_GENL_MCAST_GROUP_NAME, },
};

static struct genl_family nbd_genl_family __ro_after_init = {
	.hdrsize	= 0,
	.name		= NBD_GENL_FAMILY_NAME,
	.version	= NBD_GENL_VERSION,
	.module		= THIS_MODULE,
	.small_ops	= nbd_connect_genl_ops,
	.n_small_ops	= ARRAY_SIZE(nbd_connect_genl_ops),
	.resv_start_op	= NBD_CMD_STATUS + 1,
	.maxattr	= NBD_ATTR_MAX,
	.netnsok	= 1,
	.policy = nbd_attr_policy,
	.mcgrps		= nbd_mcast_grps,
	.n_mcgrps	= ARRAY_SIZE(nbd_mcast_grps),
};
MODULE_ALIAS_GENL_FAMILY(NBD_GENL_FAMILY_NAME);

static int populate_nbd_status(struct nbd_device *nbd, struct sk_buff *reply)
{
	struct nlattr *dev_opt;
	u8 connected = 0;
	int ret;

	/* This is a little racey, but for status it's ok.  The
	 * reason we don't take a ref here is because we can't
	 * take a ref in the index == -1 case as we would need
	 * to put under the nbd_index_mutex, which could
	 * deadlock if we are configured to remove ourselves
	 * once we're disconnected.
	 */
	if (refcount_read(&nbd->config_refs))
		connected = 1;
	dev_opt = nla_nest_start_noflag(reply, NBD_DEVICE_ITEM);
	if (!dev_opt)
		return -EMSGSIZE;
	ret = nla_put_u32(reply, NBD_DEVICE_INDEX, nbd->index);
	if (ret)
		return -EMSGSIZE;
	ret = nla_put_u8(reply, NBD_DEVICE_CONNECTED,
			 connected);
	if (ret)
		return -EMSGSIZE;
	nla_nest_end(reply, dev_opt);
	return 0;
}

static int status_cb(int id, void *ptr, void *data)
{
	struct nbd_device *nbd = ptr;
	return populate_nbd_status(nbd, (struct sk_buff *)data);
}

static int nbd_genl_status(struct sk_buff *skb, struct genl_info *info)
{
	struct nlattr *dev_list;
	struct sk_buff *reply;
	void *reply_head;
	size_t msg_size;
	int index = -1;
	int ret = -ENOMEM;

	if (info->attrs[NBD_ATTR_INDEX])
		index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);

	mutex_lock(&nbd_index_mutex);

	msg_size = nla_total_size(nla_attr_size(sizeof(u32)) +
				  nla_attr_size(sizeof(u8)));
	msg_size *= (index == -1) ? nbd_total_devices : 1;

	reply = genlmsg_new(msg_size, GFP_KERNEL);
	if (!reply)
		goto out;
	reply_head = genlmsg_put_reply(reply, info, &nbd_genl_family, 0,
				       NBD_CMD_STATUS);
	if (!reply_head) {
		nlmsg_free(reply);
		goto out;
	}

	dev_list = nla_nest_start_noflag(reply, NBD_ATTR_DEVICE_LIST);
	if (!dev_list) {
		nlmsg_free(reply);
		ret = -EMSGSIZE;
		goto out;
	}

	if (index == -1) {
		ret = idr_for_each(&nbd_index_idr, &status_cb, reply);
		if (ret) {
			nlmsg_free(reply);
			goto out;
		}
	} else {
		struct nbd_device *nbd;
		nbd = idr_find(&nbd_index_idr, index);
		if (nbd) {
			ret = populate_nbd_status(nbd, reply);
			if (ret) {
				nlmsg_free(reply);
				goto out;
			}
		}
	}
	nla_nest_end(reply, dev_list);
	genlmsg_end(reply, reply_head);
	ret = genlmsg_reply(reply, info);
out:
	mutex_unlock(&nbd_index_mutex);
	return ret;
}

static void nbd_connect_reply(struct genl_info *info, int index)
{
	struct sk_buff *skb;
	void *msg_head;
	int ret;

	skb = genlmsg_new(nla_total_size(sizeof(u32)), GFP_KERNEL);
	if (!skb)
		return;
	msg_head = genlmsg_put_reply(skb, info, &nbd_genl_family, 0,
				     NBD_CMD_CONNECT);
	if (!msg_head) {
		nlmsg_free(skb);
		return;
	}
	ret = nla_put_u32(skb, NBD_ATTR_INDEX, index);
	if (ret) {
		nlmsg_free(skb);
		return;
	}
	genlmsg_end(skb, msg_head);
	genlmsg_reply(skb, info);
}

static void nbd_mcast_index(int index)
{
	struct sk_buff *skb;
	void *msg_head;
	int ret;

	skb = genlmsg_new(nla_total_size(sizeof(u32)), GFP_KERNEL);
	if (!skb)
		return;
	msg_head = genlmsg_put(skb, 0, 0, &nbd_genl_family, 0,
				     NBD_CMD_LINK_DEAD);
	if (!msg_head) {
		nlmsg_free(skb);
		return;
	}
	ret = nla_put_u32(skb, NBD_ATTR_INDEX, index);
	if (ret) {
		nlmsg_free(skb);
		return;
	}
	genlmsg_end(skb, msg_head);
	genlmsg_multicast(&nbd_genl_family, skb, 0, 0, GFP_KERNEL);
}

static void nbd_dead_link_work(struct work_struct *work)
{
	struct link_dead_args *args = container_of(work, struct link_dead_args,
						   work);
	nbd_mcast_index(args->index);
	kfree(args);
}

static int __init nbd_init(void)
{
	int i;

	BUILD_BUG_ON(sizeof(struct nbd_request) != 28);

	if (max_part < 0) {
		pr_err("max_part must be >= 0\n");
		return -EINVAL;
	}

	part_shift = 0;
	if (max_part > 0) {
		part_shift = fls(max_part);

		/*
		 * Adjust max_part according to part_shift as it is exported
		 * to user space so that user can know the max number of
		 * partition kernel should be able to manage.
		 *
		 * Note that -1 is required because partition 0 is reserved
		 * for the whole disk.
		 */
		max_part = (1UL << part_shift) - 1;
	}

	if ((1UL << part_shift) > DISK_MAX_PARTS)
		return -EINVAL;

	if (nbds_max > 1UL << (MINORBITS - part_shift))
		return -EINVAL;

	if (register_blkdev(NBD_MAJOR, "nbd"))
		return -EIO;

	nbd_del_wq = alloc_workqueue("nbd-del", WQ_UNBOUND, 0);
	if (!nbd_del_wq) {
		unregister_blkdev(NBD_MAJOR, "nbd");
		return -ENOMEM;
	}

	if (genl_register_family(&nbd_genl_family)) {
		destroy_workqueue(nbd_del_wq);
		unregister_blkdev(NBD_MAJOR, "nbd");
		return -EINVAL;
	}
	nbd_dbg_init();

	for (i = 0; i < nbds_max; i++)
		nbd_dev_add(i, 1);
	return 0;
}

static int nbd_exit_cb(int id, void *ptr, void *data)
{
	struct list_head *list = (struct list_head *)data;
	struct nbd_device *nbd = ptr;

	/* Skip nbd that is being removed asynchronously */
	if (refcount_read(&nbd->refs))
		list_add_tail(&nbd->list, list);

	return 0;
}

static void __exit nbd_cleanup(void)
{
	struct nbd_device *nbd;
	LIST_HEAD(del_list);

	/*
	 * Unregister netlink interface prior to waiting
	 * for the completion of netlink commands.
	 */
	genl_unregister_family(&nbd_genl_family);

	nbd_dbg_close();

	mutex_lock(&nbd_index_mutex);
	idr_for_each(&nbd_index_idr, &nbd_exit_cb, &del_list);
	mutex_unlock(&nbd_index_mutex);

	while (!list_empty(&del_list)) {
		nbd = list_first_entry(&del_list, struct nbd_device, list);
		list_del_init(&nbd->list);
		if (refcount_read(&nbd->config_refs))
			pr_err("possibly leaking nbd_config (ref %d)\n",
					refcount_read(&nbd->config_refs));
		if (refcount_read(&nbd->refs) != 1)
			pr_err("possibly leaking a device\n");
		nbd_put(nbd);
	}

	/* Also wait for nbd_dev_remove_work() completes */
	destroy_workqueue(nbd_del_wq);

	idr_destroy(&nbd_index_idr);
	unregister_blkdev(NBD_MAJOR, "nbd");
}

module_init(nbd_init);
module_exit(nbd_cleanup);

MODULE_DESCRIPTION("Network Block Device");
MODULE_LICENSE("GPL");

module_param(nbds_max, int, 0444);
MODULE_PARM_DESC(nbds_max, "number of network block devices to initialize (default: 16)");
module_param(max_part, int, 0444);
MODULE_PARM_DESC(max_part, "number of partitions per device (default: 16)");
]

gemini-3-flash-preview

							input: 59036
							output: 40
							thoughts: 2494
						

**Analysis of the NBD Code with Duplicate Sockets**

Okay, here's my breakdown of this NBD code situation.  I've been reviewing this, and here are my conclusions.

First, I see the issue.  When `nbd_genl_connect` is fed the same file descriptor (FD) twice, the code diligently calls `nbd_add_socket` twice, leading to some, shall we say, *interesting* behavior. `nbd_add_socket` then uses `sockfd_lookup`, which increments the reference count of the socket's associated `struct file`. This is called twice, and thus the refcount is incremented twice.

This creates *two* `nbd_sock` structures, but both point to the *same* `struct socket`.  This is the first area of concern. When `nbd_start_device` is triggered it starts threads that will call `nbd_read_reply` on this single shared socket.

The core problem, from my perspective, is the stream corruption. With multiple threads reading from the same TCP stream, they're going to step on each other's toes.  Data will get interleaved, magic numbers will be wrong, and the NBD protocol will get completely messed up.  When errors are hit, `nbd_mark_nsock_dead` gets called. This then does the *safe* thing by shutting down the socket, but the core issue of data being read out of order on a single socket is the root cause. It also correctly decrements `config->live_connections`.

The cleanup in `nbd_config_put` is fine. `sockfd_put` is called twice, but that's perfectly acceptable since `sockfd_lookup` was called twice, keeping the refcount in sync with what the kernel expects.

The `sk_set_memalloc` function's got my attention, as does the `static_branch_inc` call.  The NBD driver, as it's written now, never calls `sk_clear_memalloc`, which means that it won't actually be balanced. Thus the `memalloc_socks_key` counter will leak. This is a general bug in NBD (not just this scenario) and can be exacerbated by duplicate FDs. While this is a bug, it likely doesn't lead to panic or deadlock, but might have some performance implications on the networking stack (although this is relatively minor).

The `nsock->tx_lock` mutexes are different, but the code isn't protecting access to the *socket* itself with one, so two threads can simultaneously use `sock_sendmsg` on the *same* socket. This creates outgoing stream corruption.

**So, the likely outcomes?:**

*   **Panic**: Unlikely. The TCP stack and NBD driver handle protocol errors.
*   **Deadlock**: Also, unlikely. The locks involved seem to be handled in a way that avoids deadlock, even with duplicate sockets.
*   **Bug**: *Absolutely*. The lack of checking for duplicate sockets leads to the real problem: stream corruption on both incoming *and* outgoing streams. The `memalloc_socks_key` leak is a bug as well.

I checked for the situation where `sockfd_put` is called on a freed socket: no, that's not possible with this current logic. Even if the user closes the FD in userspace, the kernel keeps the `struct file` (and thus the `struct socket`) alive until all references are dropped. The same goes for the other case where the socket is reconnected with the same FD.

I also checked to see how NBD handles the replies. Even if the replies come in out of order, the current `blk_mq_complete_request` logic seems fine. The `nbd_handle_reply` function is built in a way to handle this.

The crucial issue is the interleaving of reads for the *same* reply. Thread A reads part of a reply, Thread B reads the rest. That leads to garbled reads and the connection shutting down.

The call to `sockfd_put` and the `kfree` of the configuration are all safe, as the code as written correctly handles these references.

I looked at the `work_struct` in `nsock`. I can confirm each `nsock` has its own `work_struct`, which is fine.

I also looked at how each `nbd_cmd` is handled. If the data gets corrupted, it *might* find the wrong NBD command, but I see protections for that to prevent it from failing as well.

I confirmed that `nbd_add_socket` and `nbd_start_device` are synchronized using `nbd->config_lock`.

As a final note, I also checked

map[ContextFile:net/core/sock.c IncludeLines:true Name:sk_destruct]

map[SourceCode:2402:	void sk_destruct(struct sock *sk)
2403:	{
2404:		bool use_call_rcu = sock_flag(sk, SOCK_RCU_FREE);
2405:	
2406:		if (rcu_access_pointer(sk->sk_reuseport_cb)) {
2407:			reuseport_detach_sock(sk);
2408:			use_call_rcu = true;
2409:		}
2410:	
2411:		if (use_call_rcu)
2412:			call_rcu(&sk->sk_rcu, __sk_destruct);
2413:		else
2414:			__sk_destruct(&sk->sk_rcu);
2415:	}
 SourceFile:net/core/sock.c]

gemini-3-flash-preview

							input: 62836
							output: 41
							thoughts: 8
						

Okay, here's the summary, rendered as your thoughts as an expert:

**Understanding `__sk_destruct` and its Role**

Alright, let's break this down. When I see `__sk_destruct`, my mind immediately goes to the heart of resource management, especially within a kernel or operating system context. It's a clear signal that we're dealing with something related to deallocation, cleanup, or finalization of a specific data structure or object. The double underscore prefix is a key indicator to me that this function is likely an internal, implementation-specific detail. I wouldn't expect to be calling this directly in user space; it's the kind of function that the kernel or a specific driver calls to handle the intricacies of object lifecycle.

My initial hypothesis is that this likely relates to the deallocation of some structure tied to sockets or networking. The `sk` prefix, combined with `destruct`, strongly suggests a "socket" object is the subject. It is likely called during the deallocation of a socket, or on the destruction of an object with ties to network resources.

I'm starting to think about potential scenarios: garbage collection? Reference counting? Automatic Memory Management? Probably not any of those as the design of a kernel is likely manual. The key to the process will be freeing up network buffers, closing file descriptors, decrementing reference counts, and ensuring that no lingering resources cause memory leaks or other issues. Given the naming, `__sk_destruct` could be associated with freeing the memory of a socket.

The challenge is usually atomicity. If this function is part of a multi-threaded system, I need to consider synchronization. Ensuring that cleanup happens in the correct order, that there are no race conditions, is absolutely paramount to avoid corruption or dangling pointers. I'd be looking closely at any locking mechanisms involved to ensure it's thread-safe and can handle concurrent access correctly. I'd also be curious about the handling of potential errors. Does it return an error code? Log warnings? Panic? The error handling strategy is crucial to understanding the robustness of the system.

Ultimately, I'd expect `__sk_destruct` to be a critical piece of code ensuring the stability and reliability of the networking subsystem. This function is likely part of the low-level infrastructure, and requires meticulous analysis.

map[ContextFile:net/core/sock.c IncludeLines:true Name:__sk_destruct]

map[SourceCode:2342:	/* Sockets having SOCK_RCU_FREE will call this function after one RCU
2343:	 * grace period. This is the case for UDP sockets and TCP listeners.
2344:	 */
2345:	static void __sk_destruct(struct rcu_head *head)
2346:	{
2347:		struct sock *sk = container_of(head, struct sock, sk_rcu);
2348:		struct net *net = sock_net(sk);
2349:		struct sk_filter *filter;
2350:	
2351:		if (sk->sk_destruct)
2352:			sk->sk_destruct(sk);
2353:	
2354:		filter = rcu_dereference_check(sk->sk_filter,
2355:					       refcount_read(&sk->sk_wmem_alloc) == 0);
2356:		if (filter) {
2357:			sk_filter_uncharge(sk, filter);
2358:			RCU_INIT_POINTER(sk->sk_filter, NULL);
2359:		}
2360:	
2361:		sock_disable_timestamp(sk, SK_FLAGS_TIMESTAMP);
2362:	
2363:	#ifdef CONFIG_BPF_SYSCALL
2364:		bpf_sk_storage_free(sk);
2365:	#endif
2366:	
2367:		if (atomic_read(&sk->sk_omem_alloc))
2368:			pr_debug("%s: optmem leakage (%d bytes) detected\n",
2369:				 __func__, atomic_read(&sk->sk_omem_alloc));
2370:	
2371:		if (sk->sk_frag.page) {
2372:			put_page(sk->sk_frag.page);
2373:			sk->sk_frag.page = NULL;
2374:		}
2375:	
2376:		/* We do not need to acquire sk->sk_peer_lock, we are the last user. */
2377:		put_cred(sk->sk_peer_cred);
2378:		put_pid(sk->sk_peer_pid);
2379:	
2380:		if (likely(sk->sk_net_refcnt)) {
2381:			put_net_track(net, &sk->ns_tracker);
2382:		} else {
2383:			__netns_tracker_free(net, &sk->ns_tracker, false);
2384:			net_passive_dec(net);
2385:		}
2386:		sk_prot_free(sk->sk_prot_creator, sk);
2387:	}
 SourceFile:net/core/sock.c]

gemini-3-flash-preview

							input: 64142
							output: 42
							thoughts: 74
						

Okay, here's my interpretation of this debugging thought process, tailored for an expert like myself:

**Tracing Memory Allocation/Deallocation in Sockets**

Alright, I'm diving into the socket destruction path, specifically `__sk_destruct`. I was expecting to see the clean up of memory allocation here, but I'm not spotting either `sk_clear_memalloc` or any use of `static_branch_dec(&memalloc_socks_key)` within this function. That's a bit of a red flag; if `sk_set_memalloc` is indeed incrementing some kind of global counter to track socket memory allocation, then *something* absolutely has to decrement it to maintain integrity. I need to figure out where that counterpart lives. Time to revisit `sk_clear_memalloc` and make sure I haven't missed something fundamental. I need to understand the mechanism behind the accounting, or I'm headed for a memory leak.

map[ContextFile:net/core/sock.c IncludeLines:true Name:sk_clear_memalloc]

map[SourceCode: 310:	void sk_clear_memalloc(struct sock *sk)
 311:	{
 312:		sock_reset_flag(sk, SOCK_MEMALLOC);
 313:		sk->sk_allocation &= ~__GFP_MEMALLOC;
 314:		static_branch_dec(&memalloc_socks_key);
 315:	
 316:		/*
 317:		 * SOCK_MEMALLOC is allowed to ignore rmem limits to ensure forward
 318:		 * progress of swapping. SOCK_MEMALLOC may be cleared while
 319:		 * it has rmem allocations due to the last swapfile being deactivated
 320:		 * but there is a risk that the socket is unusable due to exceeding
 321:		 * the rmem limits. Reclaim the reserves and obey rmem limits again.
 322:		 */
 323:		sk_mem_reclaim(sk);
 324:	}
 SourceFile:net/core/sock.c]

gemini-3-flash-preview

							input: 64734
							output: 20
							thoughts: 132
						

Here's my analysis of the situation:

**Investigating a Potential Memory Leak in the NBD Driver**

Okay, so I'm thinking about this `sk_clear_memalloc` function and how it relates to the NBD driver. I can see that `sk_clear_memalloc` definitely *decrements* something related to memory allocation. My immediate concern is this: if NBD calls `sk_set_memalloc` but *never* calls `sk_clear_memalloc`, then we've got a clear static branch leak. That's a definite bug in the NBD implementation. And if someone provides the same file descriptor twice... boom, we're leaking it twice.

But hold on, the user's initial question was about panic or deadlock, not a simple memory leak. Leaking a static branch is a problem, no doubt, but that alone shouldn't trigger a crash or hang the system.

Okay, let me backtrack and try another angle. I'm going to look through the git logs for commits related to "nbd sk_set_memalloc". There could be a relevant fix or a clue to some related issue I haven't considered. I'm going to search with that search term, and see what comes up.

map[Dir:Documentation/]

map[Files:<nil> Subdirs:[ABI PCI RCU accel accounting admin-guide arch block bpf cdrom core-api cpu-freq crypto dev-tools devicetree doc-guide driver-api edac fault-injection fb features filesystems firmware-guide firmware_class fpga gpu hid hwmon i2c iio images infiniband input kbuild kernel-hacking leds litmus-tests livepatch locking maintainer mhi misc-devices mm netlabel netlink networking nvdimm nvme pcmcia peci power process rust scheduler scsi security sound sphinx sphinx-includes sphinx-static spi staging sunrpc target tee timers tools trace translations usb userspace-api virt w1 watchdog wmi]]

gemini-3-flash-preview

							input: 65537
							output: 24
							thoughts: 25
						

Okay, here's my take on those thoughts, tailored for an expert audience:

**Tracing the Genesis of `sk_set_memalloc` in `nbd.c`**

Alright, let's get down to brass tacks. I need to pinpoint when `sk_set_memalloc` was introduced within the `nbd.c` codebase. Given the importance of memory allocation within a driver like NBD, I figure understanding its introduction is key to grasping its intended use and any potential evolution in that area. I'll fire up my trusty search tool—likely `git log -S sk_set_memalloc nbd.c` or something similar, depending on the repo structure—and let it chew on that query. The goal is a quick and dirty find of the commit that birthed this function. From there, I can examine the surrounding code, the commit message, any related issues or discussions linked to that commit, and so on. Understanding the context of its addition will shed light on why it was implemented the way it was, and give me a foundation for further investigation of any subtle issues or improvements.

map[Name:sk_set_memalloc]

map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nbd_reconnect_socket SourceFile:drivers/block/nbd.c SourceLine:1342] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nbd_start_device SourceFile:drivers/block/nbd.c SourceLine:1528] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nvme_tcp_alloc_queue SourceFile:drivers/nvme/host/tcp.c SourceLine:1849] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:set_sock_opts SourceFile:drivers/net/wireguard/socket.c SourceLine:345]] TruncatedOutput:false]

gemini-3-flash-preview

							input: 66054
							output: 780
							thoughts: 1754
						

**My Analysis of the NBD Driver Issue**

Okay, so the user is asking about potential bugs, kernel panics, or deadlocks in the NBD driver, specifically focusing on a scenario where `sockfd_put` is called twice on the same socket, as a consequence of the duplicate file descriptor issue. I've done a thorough review.

First, I examined `drivers/block/nbd.c` and specifically focused on the relevant code paths, inferring behavior since I can't directly use `git blame` or `git log`. My analysis is:

1.  **The Root Bug:** The fundamental issue lies in `nbd_genl_connect`. It *doesn't* check for duplicate file descriptors within the `NBD_ATTR_SOCKETS` attribute. This allows a user to provide the same socket file descriptor multiple times.
2.  **Protocol Corruption:** This duplication leads to multiple `nsock` structures being created, *all* pointing to the same socket (`sock`). Crucially, each `nsock` gets its own `tx_lock`.  The result is that *multiple threads* can simultaneously write to the same socket, corrupting the NBD data stream, leading to unpredictable behavior.
3.  **Reference Counting (Correct):** The fact that `sockfd_put` *is* called twice (in the scenario the user pointed out) is actually *correct* from a reference counting perspective.  It's a *symptom* of the underlying bug. The code in `nbd_genl_connect` does a `sockfd_lookup` twice, and therefore `sockfd_put` must be called twice.
4.  **Panic/Deadlock (Unlikely):** While the protocol corruption is serious, a kernel panic or deadlock is *unlikely* to occur directly. The stream corruption will lead to errors in the NBD protocol, causing the connection to be shut down and cleaned up. The driver seems to have appropriate error handling for that situation.
5.  **Resource Leak:** There is a resource leak: `memalloc_socks_key` is set using `sk_set_memalloc`, but `sk_clear_memalloc` is never called. Providing the same FD twice doubles this leak.

Now, I also thought it would be prudent to investigate other potential issues.

I verified that `nbd_read_reply` won't cause infinite loops due to improper return values.

I then considered READ requests, where I hypothesized that if two threads were reading from the same socket, there might be interleaving of reads and data corruption. Indeed, if two threads are reading from the same socket, one in `nbd_handle_reply` and the other in `nbd_read_reply` due to a duplicate socket, it could cause data corruption and subsequent errors (Wrong magic, Receive data failed). Both threads would call `nbd_mark_nsock_dead`, and the connection will be shut down.

I then looked at the refcounting and locking for `nbd_config_put`. I am confident that there is no risk of `nbd_config_put` being called while another thread is still using the config because the standard way is used, with `refcount_dec_and_mutex_lock` and appropriate references.

Next, I looked at the balancing of references with `nbd_get_config_unlocked` and `nbd_config_put`. This is balanced.

I verified the correct socket reference counting:
*   I considered cases where `nbd_add_socket` could fail, and I verified that in those cases `sockfd_put` is called correctly.
*   I checked what if `krealloc` fails. The code is structured correctly to avoid problems, by using `sockfd_put` and returning.

I looked into possible deadlocks involving `blk_mq_freeze_queue` called by `nbd_add_socket` and `blk_mq_update_nr_hw_queues` called by `nbd_start_device`. But the queue is reentrant, and all is properly synchronized with `config_lock` and freezing.

I reconfirmed my understanding of the user's scenario and the double call to `sockfd_put` and that it is correct.

I verified that `nbd_mark_nsock_dead` calling `kernel_sock_shutdown` wouldn't be a problem if it's called twice for the same socket.

Finally, I checked that `sock->file` would always be valid when `sockfd_put` uses it, and I checked `nbd_reconnect_socket`.

Therefore, my conclusions are:

*   The critical bug is duplicate socket registration in `nbd_genl_connect`.
*   The effects are data stream corruption and a `mem

gemini-3.1-pro-preview

							input: 360685
							output: 189
							thoughts: 62913
						

map[Question:In drivers/block/nbd.c, nbd_genl_connect parses NBD_ATTR_SOCKETS. If the user provides the SAME fd twice in the nested attributes, nbd_add_socket is called twice with the same fd. This results in config->socks[0]->sock and config->socks[1]->sock pointing to the SAME socket. Then nbd_start_device is called, which queues TWO recv_work threads. Both threads call nbd_read_reply on the SAME socket. When the socket is closed, both threads wake up, call nbd_mark_nsock_dead, and then call nbd_config_put. In nbd_config_put, sockfd_put is called twice on the same socket. Is there any bug here? Could this cause a kernel panic or deadlock?]

map[Answer:The scenario you described is indeed possible because `nbd_genl_connect` (and the legacy `NBD_SET_SOCK` ioctl) does not check if the same file descriptor (fd) is provided multiple times. This leads to several issues, although a kernel panic or deadlock is unlikely.

### Analysis of the Issues

1.  **Duplicate Reference Counting**: When `nbd_add_socket` is called, it invokes `nbd_get_socket`, which calls `sockfd_lookup(fd, &err)`. This function increments the reference count of the underlying `struct file` (and thus the socket). If the same fd is provided twice, `sockfd_lookup` is called twice, incrementing the reference count twice. Consequently, when `nbd_config_put` calls `sockfd_put` twice on the same socket pointer, it is correctly decrementing the two references obtained earlier. **This part of the logic is actually correct and will not cause a double-free or a kernel panic.**

2.  **Stream Corruption (The Real Bug)**: Each call to `nbd_add_socket` allocates a new `struct nbd_sock` structure. Each `nbd_sock` has its own `tx_lock` mutex. If two `nsock` structures point to the same socket, the intended synchronization is bypassed. Two threads can simultaneously call `sock_sendmsg` on the same socket, leading to interleaved headers and data, which corrupts the NBD protocol stream.

3.  **Protocol Errors**: As you noted, two `recv_work` threads will be spawned, both calling `nbd_read_reply` on the same socket. Since TCP is a stream, the two threads will compete for data. One thread might read part of a reply header, and the other might read the rest. Both will encounter "Wrong magic" errors or invalid cookies and call `nbd_mark_nsock_dead`.

4.  **Resource Leak**: In `nbd_start_device`, `sk_set_memalloc` is called for each connection. This function increments a global `memalloc_socks_key` (a static branch counter). However, the NBD driver never calls `sk_clear_memalloc`. This results in a leak of the static branch reference. Providing the same FD twice doubles this leak. While not a panic, it's a persistent resource leak in the networking stack.

### Potential for Panic or Deadlock

*   **Panic**: Unlikely. The kernel's socket and file reference counting handles the duplicate `sockfd_put` correctly. The protocol corruption will lead to EPROTO errors and connection teardown, but the driver's state management (using `config_refs` and `config_lock`) is robust enough to handle this without crashing.
*   **Deadlock**: Unlikely. The locks (`cmd->lock`, `nsock->tx_lock`, `config_lock`) are used consistently. Since each `nsock` has its own `tx_lock`, there is no circular dependency introduced by having duplicate sockets; they simply fail to provide the necessary mutual exclusion for the shared socket.

### Summary
There is a **bug** in the sense that the driver allows a misconfigured state that leads to data corruption on the wire and a minor resource leak (`memalloc_socks_key`). However, it is **not** a bug that would typically cause a kernel panic or a deadlock. The reference counting for the socket itself is handled correctly by the underlying VFS and socket layers.

To fix this, the NBD driver should ideally check if a socket is already assigned to the device before adding it in `nbd_add_socket`.]

gemini-3-flash-preview

You are a capable Linux kernel developer tasked with researching complex questions
about kernel source code. You will be given a concrete question, and need to provide
a concrete answer.
Use tools extensively while researching the question. Don't make assumptions,
or rely on your previous knowledge about the kernel source code, use available tools
to access the actual source code.
Use all available sources of information:
 - kernel source code
 - documentation in the Documentation dir in the source tree
 - git commits descriptions, git blame

Prefer calling several tools at the same time to save round-trips.

In drivers/block/nbd.c, nbd_genl_connect parses NBD_ATTR_SOCKETS. If the user provides the SAME fd twice in the nested attributes, nbd_add_socket is called twice with the same fd. This results in config->socks[0]->sock and config->socks[1]->sock pointing to the SAME socket. Then nbd_start_device is called, which queues TWO recv_work threads. Both threads call nbd_read_reply on the SAME socket. When the socket is closed, both threads wake up, call nbd_mark_nsock_dead, and then call nbd_config_put. In nbd_config_put, sockfd_put is called twice on the same socket. Is there any bug here? Could this cause a kernel panic or deadlock?

The scenario you described is indeed possible because `nbd_genl_connect` (and the legacy `NBD_SET_SOCK` ioctl) does not check if the same file descriptor (fd) is provided multiple times. This leads to several issues, although a kernel panic or deadlock is unlikely.

### Analysis of the Issues

1.  **Duplicate Reference Counting**: When `nbd_add_socket` is called, it invokes `nbd_get_socket`, which calls `sockfd_lookup(fd, &err)`. This function increments the reference count of the underlying `struct file` (and thus the socket). If the same fd is provided twice, `sockfd_lookup` is called twice, incrementing the reference count twice. Consequently, when `nbd_config_put` calls `sockfd_put` twice on the same socket pointer, it is correctly decrementing the two references obtained earlier. **This part of the logic is actually correct and will not cause a double-free or a kernel panic.**

2.  **Stream Corruption (The Real Bug)**: Each call to `nbd_add_socket` allocates a new `struct nbd_sock` structure. Each `nbd_sock` has its own `tx_lock` mutex. If two `nsock` structures point to the same socket, the intended synchronization is bypassed. Two threads can simultaneously call `sock_sendmsg` on the same socket, leading to interleaved headers and data, which corrupts the NBD protocol stream.

3.  **Protocol Errors**: As you noted, two `recv_work` threads will be spawned, both calling `nbd_read_reply` on the same socket. Since TCP is a stream, the two threads will compete for data. One thread might read part of a reply header, and the other might read the rest. Both will encounter "Wrong magic" errors or invalid cookies and call `nbd_mark_nsock_dead`.

4.  **Resource Leak**: In `nbd_start_device`, `sk_set_memalloc` is called for each connection. This function increments a global `memalloc_socks_key` (a static branch counter). However, the NBD driver never calls `sk_clear_memalloc`. This results in a leak of the static branch reference. Providing the same FD twice doubles this leak. While not a panic, it's a persistent resource leak in the networking stack.

### Potential for Panic or Deadlock

*   **Panic**: Unlikely. The kernel's socket and file reference counting handles the duplicate `sockfd_put` correctly. The protocol corruption will lead to EPROTO errors and connection teardown, but the driver's state management (using `config_refs` and `config_lock`) is robust enough to handle this without crashing.
*   **Deadlock**: Unlikely. The locks (`cmd->lock`, `nsock->tx_lock`, `config_lock`) are used consistently. Since each `nsock` has its own `tx_lock`, there is no circular dependency introduced by having duplicate sockets; they simply fail to provide the necessary mutual exclusion for the shared socket.

### Summary
There is a **bug** in the sense that the driver allows a misconfigured state that leads to data corruption on the wire and a minor resource leak (`memalloc_socks_key`). However, it is **not** a bug that would typically cause a kernel panic or a deadlock. The reference counting for the socket itself is handled correctly by the underlying VFS and socket layers.

To fix this, the NBD driver should ideally check if a socket is already assigned to the device before adding it in `nbd_add_socket`.

gemini-3-flash-preview

							input: 2427
							output: 87
							thoughts: 285
						

**Analyzing a Potential NBD Bug**

Okay, so the user is concerned about a possible flaw in `drivers/block/nbd.c`, specifically around how it handles file descriptors in the `NBD_ATTR_SOCKETS` attribute. I see the scenario they're outlining: it's all about what happens if we're given the same file descriptor twice. Let me think this through, step-by-step, just as they've described it.

First, `nbd_genl_connect` parses `NBD_ATTR_SOCKETS` – that makes sense. Then, the crux of the issue: if we see the same file descriptor duplicated, `nbd_add_socket` gets called twice with the identical `fd`. Now, if that's the case, we're likely ending up with `config->socks[0]->sock` and `config->socks[1]->sock` both referencing the *same* `struct socket`. Okay, I can visualize that potential for a shared resource conflict.

Next, `nbd_start_device` comes into play. It kicks off two `recv_work` threads, which are now both working with the same socket. This is where things start to get interesting. Both threads end up calling `nbd_read_reply` on this shared socket. The user is right – it feels like a race condition is brewing.

Now, here's where the potential disaster might strike: when the socket gets closed, both threads wake up. They both end up calling `nbd_mark_nsock_dead`, and then `nbd_config_put`. The real kicker: `nbd_config_put` ends up calling `sockfd_put` *twice* on the *same* socket. This is precisely the point I was hoping to see described - a double free.

So, the user is wondering if this sequence could trigger a bug, a kernel panic, or potentially a deadlock? Yes, a double free situation is a classic source of all three problems. It's a valid concern, and I need to dive into `nbd_genl_connect` and `nbd_add_socket` in `drivers/block/nbd.c` to see if the hypothesized scenario is actually feasible. I need to understand if the code *allows* this double use of the same FD, if there are any checks or safeguards against it, and if it's the expected way the system handles the socket.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_genl_connect]

map[SourceCode:2073:	static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
2074:	{
2075:		struct nbd_device *nbd;
2076:		struct nbd_config *config;
2077:		int index = -1;
2078:		int ret;
2079:		bool put_dev = false;
2080:	
2081:		if (!netlink_capable(skb, CAP_SYS_ADMIN))
2082:			return -EPERM;
2083:	
2084:		if (info->attrs[NBD_ATTR_INDEX]) {
2085:			index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
2086:	
2087:			/*
2088:			 * Too big first_minor can cause duplicate creation of
2089:			 * sysfs files/links, since index << part_shift might overflow, or
2090:			 * MKDEV() expect that the max bits of first_minor is 20.
2091:			 */
2092:			if (index < 0 || index > MINORMASK >> part_shift) {
2093:				pr_err("illegal input index %d\n", index);
2094:				return -EINVAL;
2095:			}
2096:		}
2097:		if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SOCKETS)) {
2098:			pr_err("must specify at least one socket\n");
2099:			return -EINVAL;
2100:		}
2101:		if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SIZE_BYTES)) {
2102:			pr_err("must specify a size in bytes for the device\n");
2103:			return -EINVAL;
2104:		}
2105:	again:
2106:		mutex_lock(&nbd_index_mutex);
2107:		if (index == -1) {
2108:			nbd = nbd_find_get_unused();
2109:		} else {
2110:			nbd = idr_find(&nbd_index_idr, index);
2111:			if (nbd) {
2112:				if ((test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags) &&
2113:				     test_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags)) ||
2114:				    !refcount_inc_not_zero(&nbd->refs)) {
2115:					mutex_unlock(&nbd_index_mutex);
2116:					pr_err("device at index %d is going down\n",
2117:						index);
2118:					return -EINVAL;
2119:				}
2120:			}
2121:		}
2122:		mutex_unlock(&nbd_index_mutex);
2123:	
2124:		if (!nbd) {
2125:			nbd = nbd_dev_add(index, 2);
2126:			if (IS_ERR(nbd)) {
2127:				pr_err("failed to add new device\n");
2128:				return PTR_ERR(nbd);
2129:			}
2130:		}
2131:	
2132:		mutex_lock(&nbd->config_lock);
2133:		if (refcount_read(&nbd->config_refs)) {
2134:			mutex_unlock(&nbd->config_lock);
2135:			nbd_put(nbd);
2136:			if (index == -1)
2137:				goto again;
2138:			pr_err("nbd%d already in use\n", index);
2139:			return -EBUSY;
2140:		}
2141:	
2142:		ret = nbd_alloc_and_init_config(nbd);
2143:		if (ret) {
2144:			mutex_unlock(&nbd->config_lock);
2145:			nbd_put(nbd);
2146:			pr_err("couldn't allocate config\n");
2147:			return ret;
2148:		}
2149:	
2150:		config = nbd->config;
2151:		set_bit(NBD_RT_BOUND, &config->runtime_flags);
2152:		ret = nbd_genl_size_set(info, nbd);
2153:		if (ret)
2154:			goto out;
2155:	
2156:		if (info->attrs[NBD_ATTR_TIMEOUT])
2157:			nbd_set_cmd_timeout(nbd,
2158:					    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
2159:		if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
2160:			config->dead_conn_timeout =
2161:				nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
2162:			config->dead_conn_timeout *= HZ;
2163:		}
2164:		if (info->attrs[NBD_ATTR_SERVER_FLAGS])
2165:			config->flags =
2166:				nla_get_u64(info->attrs[NBD_ATTR_SERVER_FLAGS]);
2167:		if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
2168:			u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
2169:			if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
2170:				/*
2171:				 * We have 1 ref to keep the device around, and then 1
2172:				 * ref for our current operation here, which will be
2173:				 * inherited by the config.  If we already have
2174:				 * DESTROY_ON_DISCONNECT set then we know we don't have
2175:				 * that extra ref already held so we don't need the
2176:				 * put_dev.
2177:				 */
2178:				if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
2179:						      &nbd->flags))
2180:					put_dev = true;
2181:			} else {
2182:				if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
2183:						       &nbd->flags))
2184:					refcount_inc(&nbd->refs);
2185:			}
2186:			if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
2187:				set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
2188:					&config->runtime_flags);
2189:			}
2190:		}
2191:	
2192:		if (info->attrs[NBD_ATTR_SOCKETS]) {
2193:			struct nlattr *attr;
2194:			int rem, fd;
2195:	
2196:			nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
2197:					    rem) {
2198:				struct nlattr *socks[NBD_SOCK_MAX+1];
2199:	
2200:				if (nla_type(attr) != NBD_SOCK_ITEM) {
2201:					pr_err("socks must be embedded in a SOCK_ITEM attr\n");
2202:					ret = -EINVAL;
2203:					goto out;
2204:				}
2205:				ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
2206:								  attr,
2207:								  nbd_sock_policy,
2208:								  info->extack);
2209:				if (ret != 0) {
2210:					pr_err("error processing sock list\n");
2211:					ret = -EINVAL;
2212:					goto out;
2213:				}
2214:				if (!socks[NBD_SOCK_FD])
2215:					continue;
2216:				fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
2217:				ret = nbd_add_socket(nbd, fd, true);
2218:				if (ret)
2219:					goto out;
2220:			}
2221:		}
2222:	
2223:		if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
2224:			nbd->backend = nla_strdup(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
2225:						  GFP_KERNEL);
2226:			if (!nbd->backend) {
2227:				ret = -ENOMEM;
2228:				goto out;
2229:			}
2230:		}
2231:		ret = device_create_file(disk_to_dev(nbd->disk), &backend_attr);
2232:		if (ret) {
2233:			dev_err(disk_to_dev(nbd->disk),
2234:				"device_create_file failed for backend!\n");
2235:			goto out;
2236:		}
2237:		set_bit(NBD_RT_HAS_BACKEND_FILE, &config->runtime_flags);
2238:	
2239:		ret = nbd_start_device(nbd);
2240:	out:
2241:		if (!ret) {
2242:			set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);
2243:			refcount_inc(&nbd->config_refs);
2244:			nbd_connect_reply(info, nbd->index);
2245:		}
2246:		mutex_unlock(&nbd->config_lock);
2247:	
2248:		nbd_config_put(nbd);
2249:		if (put_dev)
2250:			nbd_put(nbd);
2251:		return ret;
2252:	}
 SourceFile:drivers/block/nbd.c]

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_add_socket]

map[SourceCode:1241:	static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
1242:				  bool netlink)
1243:	{
1244:		struct nbd_config *config = nbd->config;
1245:		struct socket *sock;
1246:		struct nbd_sock **socks;
1247:		struct nbd_sock *nsock;
1248:		unsigned int memflags;
1249:		int err;
1250:	
1251:		/* Arg will be cast to int, check it to avoid overflow */
1252:		if (arg > INT_MAX)
1253:			return -EINVAL;
1254:		sock = nbd_get_socket(nbd, arg, &err);
1255:		if (!sock)
1256:			return err;
1257:	
1258:		/*
1259:		 * We need to make sure we don't get any errant requests while we're
1260:		 * reallocating the ->socks array.
1261:		 */
1262:		memflags = blk_mq_freeze_queue(nbd->disk->queue);
1263:	
1264:		if (!netlink && !nbd->task_setup &&
1265:		    !test_bit(NBD_RT_BOUND, &config->runtime_flags))
1266:			nbd->task_setup = current;
1267:	
1268:		if (!netlink &&
1269:		    (nbd->task_setup != current ||
1270:		     test_bit(NBD_RT_BOUND, &config->runtime_flags))) {
1271:			dev_err(disk_to_dev(nbd->disk),
1272:				"Device being setup by another task");
1273:			err = -EBUSY;
1274:			goto put_socket;
1275:		}
1276:	
1277:		nsock = kzalloc_obj(*nsock);
1278:		if (!nsock) {
1279:			err = -ENOMEM;
1280:			goto put_socket;
1281:		}
1282:	
1283:		socks = krealloc(config->socks, (config->num_connections + 1) *
1284:				 sizeof(struct nbd_sock *), GFP_KERNEL);
1285:		if (!socks) {
1286:			kfree(nsock);
1287:			err = -ENOMEM;
1288:			goto put_socket;
1289:		}
1290:	
1291:		config->socks = socks;
1292:	
1293:		nsock->fallback_index = -1;
1294:		nsock->dead = false;
1295:		mutex_init(&nsock->tx_lock);
1296:		nsock->sock = sock;
1297:		nsock->pending = NULL;
1298:		nsock->sent = 0;
1299:		nsock->cookie = 0;
1300:		INIT_WORK(&nsock->work, nbd_pending_cmd_work);
1301:		socks[config->num_connections++] = nsock;
1302:		atomic_inc(&config->live_connections);
1303:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1304:	
1305:		return 0;
1306:	
1307:	put_socket:
1308:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1309:		sockfd_put(sock);
1310:		return err;
1311:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 7268
							output: 43
							thoughts: 81
						

Okay, here's my interpretation of that code snippet, presented as my own thought process:

**Diving into the Socket Connection Logic**

Right, so I'm looking at `nbd_genl_connect`, and it seems to be iterating through the `NBD_ATTR_SOCKETS` attribute. Each iteration is followed by a call to `nbd_add_socket(nbd, fd, true)`. So, that's where the socket file descriptors are being added.

The critical part appears to be the next function call within `nbd_add_socket`, to `nbd_get_socket(nbd, arg, &err)`. I need to figure out how sockets are retrieved or managed. What does `nbd_get_socket` *do*? That's the core of how these sockets are acquired. Understanding this function call will likely illuminate how socket handling is set up with Netlink and the NBD driver. Time to dig in and see how it works.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_get_socket]

map[SourceCode:1213:	static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd,
1214:					     int *err)
1215:	{
1216:		struct socket *sock;
1217:	
1218:		*err = 0;
1219:		sock = sockfd_lookup(fd, err);
1220:		if (!sock)
1221:			return NULL;
1222:	
1223:		if (!sk_is_tcp(sock->sk) &&
1224:		    !sk_is_stream_unix(sock->sk)) {
1225:			dev_err(disk_to_dev(nbd->disk), "Unsupported socket: should be TCP or UNIX.\n");
1226:			*err = -EINVAL;
1227:			sockfd_put(sock);
1228:			return NULL;
1229:		}
1230:	
1231:		if (sock->ops->shutdown == sock_no_shutdown) {
1232:			dev_err(disk_to_dev(nbd->disk), "Unsupported socket: shutdown callout must be supported.\n");
1233:			*err = -EINVAL;
1234:			sockfd_put(sock);
1235:			return NULL;
1236:		}
1237:	
1238:		return sock;
1239:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 8019
							output: 43
							thoughts: 185
						

**Analyzing the Network Block Device Socket Management**

Okay, let me break down this socket management logic within the NBD driver. Essentially, `nbd_get_socket` is the core function. It calls `sockfd_lookup` to retrieve the `struct socket *` associated with a file descriptor (`fd`). If `sockfd_lookup` is successful, it hands back that socket pointer.

Now, here's where things get interesting. The text clearly states that if `nbd_add_socket` is called *twice* with the *same* `fd`, `sockfd_lookup` returns the *exact same* `struct socket *` each time. Crucially, the socket's reference count is incremented with each lookup.  So, in effect, we're reusing the underlying socket.

`nbd_add_socket` then allocates a fresh `struct nbd_sock`, sets `nsock->sock` to point to the shared `struct socket *`, and adds the new `nbd_sock` to the `config->socks` list. This means that if we pass the same `fd` twice, we will have two different `nbd_sock` structures, but both `config->socks[0]->sock` and `config->socks[1]->sock` will point to the *identical* underlying socket.

The consequence is clear: `config->num_connections` will become 2, as we’ve added two entries. Furthermore, `config->live_connections` will also be 2.

Alright, with that established, I need to understand what `nbd_start_device` does with this configuration. I'll need to analyze how it utilizes these socket structures to ascertain its behavior in the context of this potential socket sharing.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_start_device]

map[SourceCode:1471:	static int nbd_start_device(struct nbd_device *nbd)
1472:	{
1473:		struct nbd_config *config = nbd->config;
1474:		int num_connections = config->num_connections;
1475:		int error = 0, i;
1476:	
1477:		if (nbd->pid)
1478:			return -EBUSY;
1479:		if (!config->socks)
1480:			return -EINVAL;
1481:		if (num_connections > 1 &&
1482:		    !(config->flags & NBD_FLAG_CAN_MULTI_CONN)) {
1483:			dev_err(disk_to_dev(nbd->disk), "server does not support multiple connections per device.\n");
1484:			return -EINVAL;
1485:		}
1486:	
1487:	retry:
1488:		mutex_unlock(&nbd->config_lock);
1489:		blk_mq_update_nr_hw_queues(&nbd->tag_set, num_connections);
1490:		mutex_lock(&nbd->config_lock);
1491:	
1492:		/* if another code path updated nr_hw_queues, retry until succeed */
1493:		if (num_connections != config->num_connections) {
1494:			num_connections = config->num_connections;
1495:			goto retry;
1496:		}
1497:	
1498:		nbd->pid = task_pid_nr(current);
1499:	
1500:		nbd_parse_flags(nbd);
1501:	
1502:		error = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
1503:		if (error) {
1504:			dev_err(disk_to_dev(nbd->disk), "device_create_file failed for pid!\n");
1505:			return error;
1506:		}
1507:		set_bit(NBD_RT_HAS_PID_FILE, &config->runtime_flags);
1508:	
1509:		nbd_dev_dbg_init(nbd);
1510:		for (i = 0; i < num_connections; i++) {
1511:			struct recv_thread_args *args;
1512:	
1513:			args = kzalloc_obj(*args);
1514:			if (!args) {
1515:				sock_shutdown(nbd);
1516:				/*
1517:				 * If num_connections is m (2 < m),
1518:				 * and NO.1 ~ NO.n(1 < n < m) kzallocs are successful.
1519:				 * But NO.(n + 1) failed. We still have n recv threads.
1520:				 * So, add flush_workqueue here to prevent recv threads
1521:				 * dropping the last config_refs and trying to destroy
1522:				 * the workqueue from inside the workqueue.
1523:				 */
1524:				if (i)
1525:					flush_workqueue(nbd->recv_workq);
1526:				return -ENOMEM;
1527:			}
1528:			sk_set_memalloc(config->socks[i]->sock->sk);
1529:			if (nbd->tag_set.timeout)
1530:				config->socks[i]->sock->sk->sk_sndtimeo =
1531:					nbd->tag_set.timeout;
1532:			atomic_inc(&config->recv_threads);
1533:			refcount_inc(&nbd->config_refs);
1534:			INIT_WORK(&args->work, recv_work);
1535:			args->nbd = nbd;
1536:			args->nsock = config->socks[i];
1537:			args->index = i;
1538:			queue_work(nbd->recv_workq, &args->work);
1539:		}
1540:		return nbd_set_size(nbd, config->bytesize, nbd_blksize(config));
1541:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 9804
							output: 40
							thoughts: 73
						

**Analyzing the nbd_start_device Function**

Okay, so `nbd_start_device` seems to be the crucial starting point here. I see it's iterating through `num_connections` and queuing up a `recv_work` task for each connection. My initial thought is to look at how these are handled and if there are any race conditions that I might spot.

The interesting part, and what likely prompted this, is that there might be a scenario where `config->socks[0]->sock == config->socks[1]->sock`. If that's true, then we'll have two separate threads, each calling `recv_work`, both using the *same* socket. This certainly warrants a closer look. I need to understand what `recv_work` is doing and how it's interacting with the shared socket. This could lead to all sorts of concurrency issues - data corruption, missed events, or even deadlocks. Let's dig into the `recv_work` function and see what's happening.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:recv_work]

map[SourceCode: 970:	static void recv_work(struct work_struct *work)
 971:	{
 972:		struct recv_thread_args *args = container_of(work,
 973:							     struct recv_thread_args,
 974:							     work);
 975:		struct nbd_device *nbd = args->nbd;
 976:		struct nbd_config *config = nbd->config;
 977:		struct request_queue *q = nbd->disk->queue;
 978:		struct nbd_sock *nsock = args->nsock;
 979:		struct nbd_cmd *cmd;
 980:		struct request *rq;
 981:	
 982:		while (1) {
 983:			struct nbd_reply reply;
 984:	
 985:			if (nbd_read_reply(nbd, nsock->sock, &reply))
 986:				break;
 987:	
 988:			/*
 989:			 * Grab .q_usage_counter so request pool won't go away, then no
 990:			 * request use-after-free is possible during nbd_handle_reply().
 991:			 * If queue is frozen, there won't be any inflight requests, we
 992:			 * needn't to handle the incoming garbage message.
 993:			 */
 994:			if (!percpu_ref_tryget(&q->q_usage_counter)) {
 995:				dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n",
 996:					__func__);
 997:				break;
 998:			}
 999:	
1000:			cmd = nbd_handle_reply(nbd, args->index, &reply);
1001:			if (IS_ERR(cmd)) {
1002:				percpu_ref_put(&q->q_usage_counter);
1003:				break;
1004:			}
1005:	
1006:			rq = blk_mq_rq_from_pdu(cmd);
1007:			if (likely(!blk_should_fake_timeout(rq->q))) {
1008:				bool complete;
1009:	
1010:				mutex_lock(&cmd->lock);
1011:				complete = __test_and_clear_bit(NBD_CMD_INFLIGHT,
1012:								&cmd->flags);
1013:				mutex_unlock(&cmd->lock);
1014:				if (complete)
1015:					blk_mq_complete_request(rq);
1016:			}
1017:			percpu_ref_put(&q->q_usage_counter);
1018:		}
1019:	
1020:		mutex_lock(&nsock->tx_lock);
1021:		nbd_mark_nsock_dead(nbd, nsock, 1);
1022:		mutex_unlock(&nsock->tx_lock);
1023:	
1024:		atomic_dec(&config->recv_threads);
1025:		wake_up(&config->recv_wq);
1026:		nbd_config_put(nbd);
1027:		kfree(args);
1028:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 11068
							output: 46
							thoughts: 155
						

**Analyzing Potential Concurrency Issues in the Network Block Device (NBD) Implementation**

Okay, so I'm looking at this `recv_work` function, and it's calling `nbd_read_reply` – which seems straightforward enough. But, wait a minute... I see a potential race condition here. If two threads somehow end up calling `nbd_read_reply` on the same socket concurrently, then we've got a problem. Both threads are going to attempt to read from the same socket simultaneously. That's a recipe for disaster! Data corruption is highly probable, or at the very least, unpredictable behavior due to interleaved reads from a single reply. This is bad.

`nbd_read_reply`, itself, calls `sock_xmit` – so it's directly involved in the socket interaction. This further highlights the importance of making sure only one thread deals with the socket at any time.

Now, when the main loop breaks – say, because the socket gets closed – it calls `nbd_mark_nsock_dead`, and then `nbd_config_put`. Makes sense; cleanup is crucial. Let's delve into this `nbd_mark_nsock_dead` function and understand how it handles the socket closure. We're going to need to look at how this is being handled in order to determine what thread safety mechanisms (if any) are in place. This will be key to understanding if this entire sequence is thread-safe.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_mark_nsock_dead]

map[SourceCode: 305:	static void nbd_mark_nsock_dead(struct nbd_device *nbd, struct nbd_sock *nsock,
 306:					int notify)
 307:	{
 308:		if (!nsock->dead && notify && !nbd_disconnected(nbd->config)) {
 309:			struct link_dead_args *args;
 310:			args = kmalloc_obj(struct link_dead_args, GFP_NOIO);
 311:			if (args) {
 312:				INIT_WORK(&args->work, nbd_dead_link_work);
 313:				args->index = nbd->index;
 314:				queue_work(system_percpu_wq, &args->work);
 315:			}
 316:		}
 317:		if (!nsock->dead) {
 318:			kernel_sock_shutdown(nsock->sock, SHUT_RDWR);
 319:			if (atomic_dec_return(&nbd->config->live_connections) == 0) {
 320:				if (test_and_clear_bit(NBD_RT_DISCONNECT_REQUESTED,
 321:						       &nbd->config->runtime_flags)) {
 322:					set_bit(NBD_RT_DISCONNECTED,
 323:						&nbd->config->runtime_flags);
 324:					dev_info(nbd_to_dev(nbd),
 325:						"Disconnected due to user request.\n");
 326:				}
 327:			}
 328:		}
 329:		nsock->dead = true;
 330:		nsock->pending = NULL;
 331:		nsock->sent = 0;
 332:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 12093
							output: 43
							thoughts: 179
						

**Analyzing Socket Shutdown Behavior in NBD**

Okay, so I'm looking at this `nbd_mark_nsock_dead` function and how it interacts with socket shutdown. My concern here is the potential for double-shutdowns on the same socket, but it seems there's a nuanced process happening.

Essentially, it checks if `!nsock->dead` before shutting down the socket using `kernel_sock_shutdown(nsock->sock, SHUT_RDWR)`. The critical thing to remember is that we *can* have multiple `nbd_sock` structures pointing to the very same underlying socket. They're all initially marked `dead = false`.

Now, imagine we have two `recv_work` threads. The first thread calls `nbd_mark_nsock_dead` and updates the relevant `nsock` structure to `dead = true`.  This is expected behavior, that thread knows its socket is no longer viable. The key is what the *second* thread does. Because `nbd_add_socket` allocates a new `nbd_sock` for *each* socket (even if they point to the same socket), this second thread still has *its own* `nsock` structure, and that copy hasn't been set to `dead = true` yet.

So, both threads end up calling `kernel_sock_shutdown` on the *same* socket, one after the other. The fact that the socket is being shut down multiple times concerns me from a resource-management perspective, but I'm reasonably confident that `kernel_sock_shutdown` is designed to handle this gracefully. At the very least it's supposed to be safe. So, it appears that this double-shutdown behavior is not a critical error, but potentially something to be optimized.

Now, let's turn our attention to the `nbd_config_put` function and see what's going on there.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_config_put]

map[SourceCode:1432:	static void nbd_config_put(struct nbd_device *nbd)
1433:	{
1434:		if (refcount_dec_and_mutex_lock(&nbd->config_refs,
1435:						&nbd->config_lock)) {
1436:			struct nbd_config *config = nbd->config;
1437:			nbd_dev_dbg_close(nbd);
1438:			invalidate_disk(nbd->disk);
1439:			if (nbd->config->bytesize)
1440:				kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
1441:			if (test_and_clear_bit(NBD_RT_HAS_PID_FILE,
1442:					       &config->runtime_flags))
1443:				device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
1444:			nbd->pid = 0;
1445:			if (test_and_clear_bit(NBD_RT_HAS_BACKEND_FILE,
1446:					       &config->runtime_flags)) {
1447:				device_remove_file(disk_to_dev(nbd->disk), &backend_attr);
1448:				kfree(nbd->backend);
1449:				nbd->backend = NULL;
1450:			}
1451:			nbd_clear_sock(nbd);
1452:			if (config->num_connections) {
1453:				int i;
1454:				for (i = 0; i < config->num_connections; i++) {
1455:					sockfd_put(config->socks[i]->sock);
1456:					kfree(config->socks[i]);
1457:				}
1458:				kfree(config->socks);
1459:			}
1460:			kfree(nbd->config);
1461:			nbd->config = NULL;
1462:	
1463:			nbd->tag_set.timeout = 0;
1464:	
1465:			mutex_unlock(&nbd->config_lock);
1466:			nbd_put(nbd);
1467:			module_put(THIS_MODULE);
1468:		}
1469:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 13393
							output: 43
							thoughts: 883
						

**Analyzing the NBD Configuration Reference Counting and Socket Handling**

Okay, let's break this down. It seems we have a potential issue related to how the Network Block Device (NBD) driver handles references to its configuration and, more importantly, its sockets.

Initially, `nbd_alloc_and_init_config` sets `nbd->config_refs` to 1. Then, `nbd_start_device` increments this count for each connection established. From the code, it looks like `nbd_start_device` increments it twice, for each `recv_work` thread. Additionally, `nbd_genl_connect` also holds a reference.

So, if we have two connections, `config_refs` starts at 1, goes to 3 (due to `nbd_start_device`), and then back down to 2 after `nbd_genl_connect` releases its reference. Each `recv_work` thread subsequently calls `nbd_config_put`, decrementing `config_refs`. The first one to finish drops it to 1, and the second one should decrement it to zero.

When `config_refs` hits zero, the cleanup block executes. This block iterates through `config->socks`, calling `sockfd_put` on each socket.  Here's where it gets interesting:  If, as the user described, `config->socks[0]->sock` and `config->socks[1]->sock` point to the same socket, then `sockfd_put` is called twice on the *same* socket.

But wait. We've seen `nbd_add_socket` uses `nbd_get_socket`, which calls `sockfd_lookup`, and that's the key.  `sockfd_lookup` calls `fget(fd)`, which increments the reference count on the file. Thus it should return a struct file with an incremented reference count. `sockfd_put` calls `fput(sock->file)`. So, the socket is correctly reference counted, right?

So, if `sockfd_lookup(fd)` is called twice for the *same* file descriptor, we correctly get *two* references to the same file (and therefore the same socket). Consequently, calling `sockfd_put` twice is the right thing to do to release those two references. Okay, the reference counting on the socket itself is fine, it's the correct implementation.

However, the user says there's a different problem.  Both `config->socks[0]->sock` and `config->socks[1]->sock` *do* point to the *same* socket.  `nbd_start_device` then queues two `recv_work` threads. And here's the kicker: both of these threads are calling `nbd_read_reply` on the *same* socket simultaneously.  Now we have a concurrency issue. `nbd_read_reply` calls `sock_xmit` and we have *two* threads reading from a single socket without any synchronization. This could lead to data corruption or other nasty issues. This is a critical problem!

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_read_reply]

map[SourceCode: 845:	static int nbd_read_reply(struct nbd_device *nbd, struct socket *sock,
 846:				  struct nbd_reply *reply)
 847:	{
 848:		struct kvec iov = {.iov_base = reply, .iov_len = sizeof(*reply)};
 849:		struct iov_iter to;
 850:		int result;
 851:	
 852:		reply->magic = 0;
 853:		iov_iter_kvec(&to, ITER_DEST, &iov, 1, sizeof(*reply));
 854:		result = __sock_xmit(nbd, sock, 0, &to, MSG_WAITALL, NULL);
 855:		if (result < 0) {
 856:			if (!nbd_disconnected(nbd->config))
 857:				dev_err(disk_to_dev(nbd->disk),
 858:					"Receive control failed (result %d)\n", result);
 859:			return result;
 860:		}
 861:	
 862:		if (ntohl(reply->magic) != NBD_REPLY_MAGIC) {
 863:			dev_err(disk_to_dev(nbd->disk), "Wrong magic (0x%lx)\n",
 864:					(unsigned long)ntohl(reply->magic));
 865:			return -EPROTO;
 866:		}
 867:	
 868:		return 0;
 869:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 15432
							output: 42
							thoughts: 8
						

Okay, here's my summary, taking on the persona you've described:

**Delving into `__sock_xmit`**

Alright, let's break this down. When I see `__sock_xmit`, my mind immediately jumps to the kernel's network stack. It's a fundamental function, isn't it? This is where the magic of sending data out onto the wire *actually* happens. I'm thinking about its role, the low-level mechanics it encapsulates. I'm imagining the data buffers, the sk_buffs, lining up, ready to be pushed through the network interface.

I'm considering the complexities: the interactions with hardware, the driver calls, the checksum calculations...all the details needed to actually get a packet onto the physical medium. It's a critical point in the data flow, a bottleneck potentially, and understanding the nuances of how `__sock_xmit` performs is absolutely key to optimization. I need to think about the various scenarios it has to handle, the different protocols, the congestion control mechanisms at play.

This function is a performance-critical area; any inefficiencies here would be multiplied across the system. It's time to dig deep. I want to know about how the data is prepared, how it's handled by the device driver, and what error conditions are accounted for. The interaction with the hardware, the interrupt handling – that's where I need to focus my attention. It's all about ensuring efficient and reliable data transmission.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:__sock_xmit]

map[SourceCode: 551:	static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
 552:			       struct iov_iter *iter, int msg_flags, int *sent)
 553:	{
 554:		int result;
 555:		struct msghdr msg = {} ;
 556:		unsigned int noreclaim_flag;
 557:	
 558:		if (unlikely(!sock)) {
 559:			dev_err_ratelimited(disk_to_dev(nbd->disk),
 560:				"Attempted %s on closed socket in sock_xmit\n",
 561:				(send ? "send" : "recv"));
 562:			return -EINVAL;
 563:		}
 564:	
 565:		msg.msg_iter = *iter;
 566:	
 567:		noreclaim_flag = memalloc_noreclaim_save();
 568:	
 569:		scoped_with_kernel_creds() {
 570:			do {
 571:				sock->sk->sk_allocation = GFP_NOIO | __GFP_MEMALLOC;
 572:				sock->sk->sk_use_task_frag = false;
 573:				msg.msg_flags = msg_flags | MSG_NOSIGNAL;
 574:	
 575:				if (send)
 576:					result = sock_sendmsg(sock, &msg);
 577:				else
 578:					result = sock_recvmsg(sock, &msg, msg.msg_flags);
 579:	
 580:				if (result <= 0) {
 581:					if (result == 0)
 582:						result = -EPIPE; /* short read */
 583:					break;
 584:				}
 585:				if (sent)
 586:					*sent += result;
 587:			} while (msg_data_left(&msg));
 588:		}
 589:	
 590:		memalloc_noreclaim_restore(noreclaim_flag);
 591:	
 592:		return result;
 593:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 16437
							output: 43
							thoughts: 179
						

**Analyzing Potential Data Corruption in NBD Stream**

Okay, so I'm looking at this situation where `__sock_xmit` is calling `sock_recvmsg`. Right off the bat, my Spidey-Sense is tingling because I know that if two threads hit `sock_recvmsg` on the *same* TCP socket concurrently, we've got a potential race condition. They'll be fighting for the data stream, and that's just asking for trouble. One thread grabs the first few bytes, the other grabs the next chunk... it's a recipe for "Wrong magic" errors, or worse, outright data corruption.

But the question isn't just about data corruption in general, it's more specific: is this a *bug* that could lead to a kernel panic or deadlock? Data corruption in the NBD stream, I'm thinking, is definitely a bug, but maybe it just results in the connection being dropped. That's *bad*, but not the worst-case scenario.

Ah, wait a second... there's the `reply.cookie` used in `nbd_handle_reply` to associate with the correct command. If the stream is corrupted, that cookie could be garbage. If that's the case, `nbd_handle_reply` could be getting completely confused. That could lead to all sorts of unpredictable behavior.

I need to dig into `nbd_handle_reply` itself to be sure. Let's see how that works.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_handle_reply]

map[SourceCode: 871:	/* NULL returned = something went wrong, inform userspace */
 872:	static struct nbd_cmd *nbd_handle_reply(struct nbd_device *nbd, int index,
 873:						struct nbd_reply *reply)
 874:	{
 875:		int result;
 876:		struct nbd_cmd *cmd;
 877:		struct request *req = NULL;
 878:		u64 handle;
 879:		u16 hwq;
 880:		u32 tag;
 881:		int ret = 0;
 882:	
 883:		handle = be64_to_cpu(reply->cookie);
 884:		tag = nbd_handle_to_tag(handle);
 885:		hwq = blk_mq_unique_tag_to_hwq(tag);
 886:		if (hwq < nbd->tag_set.nr_hw_queues)
 887:			req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq],
 888:					       blk_mq_unique_tag_to_tag(tag));
 889:		if (!req || !blk_mq_request_started(req)) {
 890:			dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%d) %p\n",
 891:				tag, req);
 892:			return ERR_PTR(-ENOENT);
 893:		}
 894:		trace_nbd_header_received(req, handle);
 895:		cmd = blk_mq_rq_to_pdu(req);
 896:	
 897:		mutex_lock(&cmd->lock);
 898:		if (!test_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
 899:			dev_err(disk_to_dev(nbd->disk), "Suspicious reply %d (status %u flags %lu)",
 900:				tag, cmd->status, cmd->flags);
 901:			ret = -ENOENT;
 902:			goto out;
 903:		}
 904:		if (cmd->index != index) {
 905:			dev_err(disk_to_dev(nbd->disk), "Unexpected reply %d from different sock %d (expected %d)",
 906:				tag, index, cmd->index);
 907:			ret = -ENOENT;
 908:			goto out;
 909:		}
 910:		if (cmd->cmd_cookie != nbd_handle_to_cookie(handle)) {
 911:			dev_err(disk_to_dev(nbd->disk), "Double reply on req %p, cmd_cookie %u, handle cookie %u\n",
 912:				req, cmd->cmd_cookie, nbd_handle_to_cookie(handle));
 913:			ret = -ENOENT;
 914:			goto out;
 915:		}
 916:		if (cmd->status != BLK_STS_OK) {
 917:			dev_err(disk_to_dev(nbd->disk), "Command already handled %p\n",
 918:				req);
 919:			ret = -ENOENT;
 920:			goto out;
 921:		}
 922:		if (test_bit(NBD_CMD_REQUEUED, &cmd->flags)) {
 923:			dev_err(disk_to_dev(nbd->disk), "Raced with timeout on req %p\n",
 924:				req);
 925:			ret = -ENOENT;
 926:			goto out;
 927:		}
 928:		if (ntohl(reply->error)) {
 929:			dev_err(disk_to_dev(nbd->disk), "Other side returned error (%d)\n",
 930:				ntohl(reply->error));
 931:			cmd->status = BLK_STS_IOERR;
 932:			goto out;
 933:		}
 934:	
 935:		dev_dbg(nbd_to_dev(nbd), "request %p: got reply\n", req);
 936:		if (rq_data_dir(req) != WRITE) {
 937:			struct req_iterator iter;
 938:			struct bio_vec bvec;
 939:			struct iov_iter to;
 940:	
 941:			rq_for_each_segment(bvec, req, iter) {
 942:				iov_iter_bvec(&to, ITER_DEST, &bvec, 1, bvec.bv_len);
 943:				result = sock_xmit(nbd, index, 0, &to, MSG_WAITALL, NULL);
 944:				if (result < 0) {
 945:					dev_err(disk_to_dev(nbd->disk), "Receive data failed (result %d)\n",
 946:						result);
 947:					/*
 948:					 * If we've disconnected, we need to make sure we
 949:					 * complete this request, otherwise error out
 950:					 * and let the timeout stuff handle resubmitting
 951:					 * this request onto another connection.
 952:					 */
 953:					if (nbd_disconnected(nbd->config)) {
 954:						cmd->status = BLK_STS_IOERR;
 955:						goto out;
 956:					}
 957:					ret = -EIO;
 958:					goto out;
 959:				}
 960:				dev_dbg(nbd_to_dev(nbd), "request %p: got %d bytes data\n",
 961:					req, bvec.bv_len);
 962:			}
 963:		}
 964:	out:
 965:		trace_nbd_payload_received(req, handle);
 966:		mutex_unlock(&cmd->lock);
 967:		return ret ? ERR_PTR(ret) : cmd;
 968:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 18674
							output: 43
							thoughts: 1628
						

**Analyzing Potential Concurrency Issues with Shared Sockets in the NBD Driver**

Okay, let's break this down. My initial concern was about two threads reading from the same socket. This is a recipe for disaster in the NBD protocol, as the `sock_xmit` calls (through `nbd_read_reply` or directly in `nbd_handle_reply`) would definitely lead to interleaved data. This would lead to protocol errors and incorrect behavior. The question isn't whether it *will* go wrong, but how badly it can fail.

First, the user pointed out `nbd_config_put` being called with the same `sockfd` twice. After reviewing, that's not a bug. `nbd_add_socket` uses `nbd_get_socket`, which calls `sockfd_lookup`. `sockfd_lookup` increments the socket's refcount. If the file descriptor (FD) is added twice, the refcount gets incremented twice. Then, `nbd_config_put` properly decrements the refcount twice for the same socket in `config->socks[i]->sock` because it's called twice in `nbd_config_put`. This is correct and doesn't leak references.

Next, I looked at `nbd_mark_nsock_dead` again. If we have multiple `nsock` structures representing the same socket, and the first thread calls `nbd_mark_nsock_dead`, it correctly decrements `config->live_connections`. The second thread then *also* calls it, decrementing it to 0. This seems reasonable, too.

Now, `nbd_read_reply`.  The critical issue here is that multiple threads reading the same socket could easily have one get a protocol error (`Wrong magic`, etc.) and call `nbd_mark_nsock_dead`, which then calls `kernel_sock_shutdown`. This shutdown would cause the other thread's `sock_recvmsg` to return an error, and both threads would then proceed to call `nbd_config_put`.

The potential race in `nbd_config_put` is prevented by `refcount_dec_and_mutex_lock`. Only one thread will enter the cleanup block after the refcount hits zero, ensuring safe cleanup with `sockfd_put` and `kfree` of the `config->socks` array.

A key vector for attack: what if the user sends the same FD multiple times in `NBD_ATTR_SOCKETS`?  Reviewing `nbd_genl_connect`, I confirm that the code iterates through `NBD_ATTR_SOCKETS` and uses `nbd_add_socket` for each FD. No check is present in `nbd_add_socket` for duplicate FDs!

Looking at `nbd_add_socket` again confirmed my fears.  It blindly adds each socket to the `config->socks` array. If the user gives it the same FD twice, *it will add the same socket twice*.

So, if two `recv_work` threads end up reading from the same socket, the TCP stream is essentially shared. NBD relies on distinct reply sequences. One thread might read the first part of a reply, the other thread the second. Both will encounter invalid magic or cookies and both will call `nbd_mark_nsock_dead`. This will shut down the socket, cause the `recv_work` threads to exit, and trigger `nbd_config_put`. Eventually, the cleanup will happen.

Is there a deadlock risk? `nbd_mark_nsock_dead` doesn't take the same mutex as the `recv_work` threads.  Each `nsock` (even if it points to the same underlying socket) has a different `tx_lock`. So there is no deadlock here.

The `kernel_sock_shutdown` call might have locking requirements, but those don't seem to overlap with our NBD locks, which is reassuring.

Finally, `nbd_start_device` calls `blk_mq_update_nr_hw_queues`. If `num_connections` is 2, it sets up two hardware queues. `nbd_queue_rq` would then use `config->socks[hwq]`.

So, the fundamental issue is that sharing a single socket between multiple threads on the receive side breaks NBD's assumptions about sequential replies and will lead to an unrecoverable protocol error.  The lack of duplicate FD checks means a user *can* trigger this invalid configuration, leading to chaos.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_queue_rq]

map[SourceCode:1184:	static blk_status_t nbd_queue_rq(struct blk_mq_hw_ctx *hctx,
1185:				const struct blk_mq_queue_data *bd)
1186:	{
1187:		struct nbd_cmd *cmd = blk_mq_rq_to_pdu(bd->rq);
1188:		blk_status_t ret;
1189:	
1190:		/*
1191:		 * Since we look at the bio's to send the request over the network we
1192:		 * need to make sure the completion work doesn't mark this request done
1193:		 * before we are done doing our send.  This keeps us from dereferencing
1194:		 * freed data if we have particularly fast completions (ie we get the
1195:		 * completion before we exit sock_xmit on the last bvec) or in the case
1196:		 * that the server is misbehaving (or there was an error) before we're
1197:		 * done sending everything over the wire.
1198:		 */
1199:		mutex_lock(&cmd->lock);
1200:		clear_bit(NBD_CMD_REQUEUED, &cmd->flags);
1201:	
1202:		/* We can be called directly from the user space process, which means we
1203:		 * could possibly have signals pending so our sendmsg will fail.  In
1204:		 * this case we need to return that we are busy, otherwise error out as
1205:		 * appropriate.
1206:		 */
1207:		ret = nbd_handle_cmd(cmd, hctx->queue_num);
1208:		mutex_unlock(&cmd->lock);
1209:	
1210:		return ret;
1211:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 21842
							output: 43
							thoughts: 9
						

Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:

**Analyzing the `nbd_handle_cmd` Function**

Alright, let's dissect this `nbd_handle_cmd` function. My initial thoughts center on its crucial role within the Network Block Device (NBD) architecture. It’s the linchpin, the primary command processing entry point within the NBD server. I'm immediately mentally cataloging its likely responsibilities: receiving commands from the client, parsing the command's payload, validating parameters, dispatching the request to the appropriate back-end storage, handling potential errors, and finally, crafting and transmitting the response back to the NBD client.

I'm starting to imagine the typical workflow: First, a raw buffer arrives, containing a command identifier, request details (like offset, length, flags), and potentially data for writes. `nbd_handle_cmd` likely begins by dereferencing some global or per-connection data structure, likely containing metadata, state, and perhaps, the file descriptor for the underlying storage.

My experience tells me this function likely employs a switch statement or a similar construct to dispatch based on the command code: READ, WRITE, DISCONNECT, FLUSH, TRIM, and maybe some vendor-specific commands. Each case within the switch likely has a specialized handler. Each of these cases will require thorough error checking, for example, confirming that the requested offset and length are valid for the underlying storage, preventing buffer overflows, and avoiding race conditions.

I'm already anticipating areas where performance optimization might be critical. Given that it is a block device, I'll need to think about how it handles multi-block requests, as well as the importance of efficient memory allocation and deallocation to minimise latency. I'm also considering how it interacts with the underlying storage layer, and how it might be designed for asynchronous I/O to improve throughput.

Overall, my expectation is that `nbd_handle_cmd` represents the beating heart of the NBD server's command processing engine, and I'm eager to dive deeper into its implementation to understand its nuances and potential bottlenecks.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_handle_cmd]

map[SourceCode:1117:	static blk_status_t nbd_handle_cmd(struct nbd_cmd *cmd, int index)
1118:	{
1119:		struct request *req = blk_mq_rq_from_pdu(cmd);
1120:		struct nbd_device *nbd = cmd->nbd;
1121:		struct nbd_config *config;
1122:		struct nbd_sock *nsock;
1123:		blk_status_t ret;
1124:	
1125:		lockdep_assert_held(&cmd->lock);
1126:	
1127:		config = nbd_get_config_unlocked(nbd);
1128:		if (!config) {
1129:			dev_err_ratelimited(disk_to_dev(nbd->disk),
1130:					    "Socks array is empty\n");
1131:			return BLK_STS_IOERR;
1132:		}
1133:	
1134:		if (index >= config->num_connections) {
1135:			dev_err_ratelimited(disk_to_dev(nbd->disk),
1136:					    "Attempted send on invalid socket\n");
1137:			nbd_config_put(nbd);
1138:			return BLK_STS_IOERR;
1139:		}
1140:		cmd->status = BLK_STS_OK;
1141:	again:
1142:		nsock = config->socks[index];
1143:		mutex_lock(&nsock->tx_lock);
1144:		if (nsock->dead) {
1145:			int old_index = index;
1146:			index = find_fallback(nbd, index);
1147:			mutex_unlock(&nsock->tx_lock);
1148:			if (index < 0) {
1149:				if (wait_for_reconnect(nbd)) {
1150:					index = old_index;
1151:					goto again;
1152:				}
1153:				/* All the sockets should already be down at this point,
1154:				 * we just want to make sure that DISCONNECTED is set so
1155:				 * any requests that come in that were queue'ed waiting
1156:				 * for the reconnect timer don't trigger the timer again
1157:				 * and instead just error out.
1158:				 */
1159:				sock_shutdown(nbd);
1160:				nbd_config_put(nbd);
1161:				return BLK_STS_IOERR;
1162:			}
1163:			goto again;
1164:		}
1165:	
1166:		/* Handle the case that we have a pending request that was partially
1167:		 * transmitted that _has_ to be serviced first.  We need to call requeue
1168:		 * here so that it gets put _after_ the request that is already on the
1169:		 * dispatch list.
1170:		 */
1171:		blk_mq_start_request(req);
1172:		if (unlikely(nsock->pending && nsock->pending != req)) {
1173:			nbd_requeue_cmd(cmd);
1174:			ret = BLK_STS_OK;
1175:			goto out;
1176:		}
1177:		ret = nbd_send_cmd(nbd, cmd, index);
1178:	out:
1179:		mutex_unlock(&nsock->tx_lock);
1180:		nbd_config_put(nbd);
1181:		return ret;
1182:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 23395
							output: 43
							thoughts: 1005
						

**Analyzing the NBD Driver's Concurrency Issues**

Okay, let's break this down. My initial thought is that `nbd_handle_cmd` grabs `nsock->tx_lock`. The crux of the problem is that if we have two `nsock` structures associated with the *same* underlying `sock`, they'll have *different* `tx_lock` mutexes. This is a red flag. It means two threads could be simultaneously invoking `nbd_send_cmd` on the identical socket, which is a recipe for disaster and data corruption in the outgoing NBD stream.

Wait, I need to trace this... `nbd_send_cmd` calls `sock_xmit`, and `sock_xmit` in turn calls `__sock_xmit`. Right. And `__sock_xmit` ultimately calls `sock_sendmsg` on the socket. For a TCP socket, `sock_sendmsg` can handle concurrent calls from multiple threads without crashing, but it certainly doesn't guarantee atomic transmission of the entire message. NBD sends the header and then the data separately. If threads are intermixed, the headers and data will definitely become interleaved. This would result in protocol errors and connection drops.

So, the root cause is that `nbd_genl_connect` isn't checking for duplicate file descriptors. This leads to multiple `nsock` instances all pointing to the *same* `socket`, each with its own `tx_lock`. We're circumventing the intended synchronization, as the design seems to assume only one `tx_lock` per socket.

Now, does this lead to a panic or deadlock? Probably not a *kernel* panic or deadlock in the NBD driver itself. However, it *will* introduce protocol errors and likely result in connection drops, as corrupted NBD data will be transmitted.

I remember now that the user's description of `sockfd_put` being called twice on the same socket is actually the correct behavior given that `sockfd_lookup` was also called twice on the same socket.

Let's revisit `nbd_add_socket`: It creates a *new* `nsock` structure with `kzalloc_obj` every time it's called. This confirms my initial understanding.

This raises another question: can the user supply the same FD to two *different* NBD devices? Yes, the kernel allows that, but it's typically not the intended behavior.

The user's question about panics and deadlocks made me double check. If `nbd_read_reply` gets garbage, it will likely return an error. When it returns an error, `recv_work` exits and calls `nbd_mark_nsock_dead`. `nbd_mark_nsock_dead` shuts down the socket. The other thread will also notice this and exit. At the end `nbd_config_put` will handle the cleanup.

One thing to verify is `nbd_mark_nsock_dead` in conjunction with `live_connections`: If `live_connections` starts at 2 and both threads call the decrement, it goes to zero. It seems correct.

I have to check `nbd_clear_sock` as well. In `nbd_config_put`. I will need to look at `nbd_clear_sock`.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_clear_sock]

map[SourceCode:1425:	static void nbd_clear_sock(struct nbd_device *nbd)
1426:	{
1427:		sock_shutdown(nbd);
1428:		nbd_clear_que(nbd);
1429:		nbd->task_setup = NULL;
1430:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 25277
							output: 40
							thoughts: 6
						

Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:

**Delving into `sock_shutdown`**

Alright, so we're talking about `sock_shutdown`. My immediate thought is, "Ah, yes, the finer points of graceful socket closure." I'm mentally parsing the implications. This isn't just a simple `close()` call, we're talking about a more controlled, deliberate shutdown. I'm already anticipating the nuances of TCP's connection termination handshake, the states involved, and the implications for data transmission.

Specifically, I'm considering the potential scenarios. Will I be shutting down for read, write, or both? `SHUT_RD`, `SHUT_WR`, or `SHUT_RDWR` – each has its own behavioral fingerprint and consequences, and I'm instantly weighing them. The choice dictates whether I'm signaling that I'm done *receiving*, done *sending*, or done with the whole communication stream. I'm practically diagramming the TCP state machine in my head, visualizing the FIN and ACK segments.

My brain is now mapping this onto the practicalities of my application. What's the protocol? Is it a request-response pattern, a streaming connection, or something else entirely? The `sock_shutdown` call needs to fit seamlessly into the application's overall design. I'm focusing on ensuring data integrity. I need to be absolutely certain that any remaining data in the send queue is flushed before initiating the shutdown for writing. Otherwise, I risk data loss, corruption, or unexpected behavior on the receiving end.

And the error handling? I'm already anticipating the potential for errors. What if the socket isn't properly connected? What if the shutdown fails? I know I need to be prepared to handle `EBADF`, `ENOTSOCK`, `ENOTCONN` and similar error codes. I'm already crafting my error-handling strategy, anticipating the potential for race conditions and planning to handle them gracefully.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:sock_shutdown]

map[SourceCode: 395:	/*
 396:	 * Forcibly shutdown the socket causing all listeners to error
 397:	 */
 398:	static void sock_shutdown(struct nbd_device *nbd)
 399:	{
 400:		struct nbd_config *config = nbd->config;
 401:		int i;
 402:	
 403:		if (config->num_connections == 0)
 404:			return;
 405:		if (test_and_set_bit(NBD_RT_DISCONNECTED, &config->runtime_flags))
 406:			return;
 407:	
 408:		for (i = 0; i < config->num_connections; i++) {
 409:			struct nbd_sock *nsock = config->socks[i];
 410:			mutex_lock(&nsock->tx_lock);
 411:			nbd_mark_nsock_dead(nbd, nsock, 0);
 412:			mutex_unlock(&nsock->tx_lock);
 413:		}
 414:		dev_warn(disk_to_dev(nbd->disk), "shutting down sockets\n");
 415:	}
 SourceFile:drivers/block/nbd.c]

gemini-3-flash-preview

							input: 26115
							output: 42
							thoughts: 1816
						

**Analyzing NBD Driver Concurrency and Resource Management**

Okay, let's break this down. First, `sock_shutdown` iterates through connections and marks sockets as dead using `nbd_mark_nsock_dead`. The core concern here is potential double-frees or incorrect resource accounting if multiple `nsock` structures point to the same underlying `sock` structure. The initial assessment seems correct: `nbd_mark_nsock_dead` checks the `dead` flag of each `nsock` *before* calling `kernel_sock_shutdown`. So, multiple calls to `kernel_sock_shutdown` for the same socket are safe because of that individual flag check.

The `live_connections` counter decrement, within `nbd_mark_nsock_dead`, *is* worth a second look, particularly given multiple `nsock` structures for the same `sock`. If `live_connections` starts at 2 and there are two `nsock` structures for the same `sock`, the decrements to 1 and then 0 do seem valid.

Next, I'm checking `nbd_config_put` to ensure its balanced with increments, because that's always a potential source of errors. It's incremented during each `recv_work`, and the increment in `nbd_genl_connect` looks balanced and the decrements seem balanced too. A failure in `nbd_add_socket` in `nbd_genl_connect` is handled to ensure `nbd_config_put` is called to free resources. So far, so good.

Now, that's interesting: `nbd_mark_nsock_dead` queuing `nbd_dead_link_work`. If multiple threads call it for the same socket (but with different `nsock`s), we could have *multiple* work items queued. However, the worst thing it does is notify userspace, which should be harmless.

The big one: the interplay of `nbd_read_reply` and `nbd_handle_reply`. If two threads try to read from the same socket concurrently, we *could* have a race. One thread could read the initial part of a reply (magic, cookie) and the other could see an error. Then, when a READ request kicks off and calls `sock_xmit` within `nbd_handle_reply` (thread A), it might compete with `nbd_read_reply` (thread B). *That's* bad. The kernel's TCP implementation *might* handle this safely, but the NBD driver would see protocol errors and shut down, which is the proper behaviour, it just takes longer.

Are there other shared resources? `nbd_device` and `nbd_config` are potential sources of contention. And then, the `blk_mq_update_nr_hw_queues` is interesting. Multiple HW queues, *each* processing a socket from the same TCP connection and using a single `tx_lock` can't be good. Since requests from those separate HW queues are sent over the *same* socket, they could corrupt the NBD stream. This is another concern.

Okay, let's circle back to the double `sockfd_put` call in `nbd_config_put`. If `config->socks[0]->sock` and `config->socks[1]->sock` are the same, `sockfd_put` will be called twice on the same socket. That seems fine because we called `sockfd_lookup` twice, which increments the refcount, and `sockfd_put` decreases it.

And this points to the heart of the issue:
```c
1254:		sock = nbd_get_socket(nbd, arg, &err);
```
`nbd_get_socket` calls `sockfd_lookup`. This is what calls `sockfd_lookup` again.

So we call `sockfd_lookup` twice, which *correctly* increments the refcount of the underlying `struct file` twice. Then, calling `sockfd_put` twice decrements the refcount twice. So far, the socket refcount is properly managed.

Now, considering the question: "Could this cause a kernel panic or deadlock?". The answer is maybe. The double `sockfd_put` *itself* is not a bug. However, if the socket is used in a way that *assumes* it's unique, there *could* be a bug *somewhere else*. However, the refcounts look properly managed, so it's probably okay.

Lastly, the `sk_set_memalloc` check.  If the same socket is used, `sk_set_memalloc` may be called twice on the same socket. Let's check `sk_

map[ContextFile:include/net/sock.h IncludeLines:true Name:sk_set_memalloc]

map[SourceCode: 294:	/**
 295:	 * sk_set_memalloc - sets %SOCK_MEMALLOC
 296:	 * @sk: socket to set it on
 297:	 *
 298:	 * Set %SOCK_MEMALLOC on a socket for access to emergency reserves.
 299:	 * It's the responsibility of the admin to adjust min_free_kbytes
 300:	 * to meet the requirements
 301:	 */
 302:	void sk_set_memalloc(struct sock *sk)
 303:	{
 304:		sock_set_flag(sk, SOCK_MEMALLOC);
 305:		sk->sk_allocation |= __GFP_MEMALLOC;
 306:		static_branch_inc(&memalloc_socks_key);
 307:	}
 SourceFile:net/core/sock.c]

gemini-3-flash-preview

							input: 29243
							output: 24
							thoughts: 158
						

**Memory Allocation Key Concerns**

Okay, hold on a second. I just saw `static_branch_inc(&memalloc_socks_key)`. That's interesting. The code increments this key when `sk_set_memalloc` is called. The alarm bells are going off. If a socket has `sk_set_memalloc` called multiple times, that `static_branch_inc` call is duplicated. That's fine, but is there a matching `sk_clear_memalloc`? I need to be sure the incrementing is correctly balanced.

Right, let me look at NBD's implementation. Hmm, it doesn't seem to call `sk_clear_memalloc`. That's a potential leak. If NBD *doesn't* clear the allocation, then `memalloc_socks_key` will just stay incremented indefinitely. This has a nasty memory implications in a long-running system. 

But wait, hold on. When the socket is destroyed, is there implicit clean-up? I need to verify how sockets are handled in those cases. The documentation *should* provide some insights.

And generally, `sk_set_memalloc` is used in, for example, swap-over-NBD setups, which makes this investigation even more pressing. 

Okay, I need to check where `sk_clear_memalloc` *is* called. That's my next step.

map[Name:sk_clear_memalloc]

map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:sock_free SourceFile:drivers/net/wireguard/socket.c SourceLine:337] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:xs_reset_transport SourceFile:net/sunrpc/xprtsock.c SourceLine:1289]] TruncatedOutput:false]

gemini-3-flash-preview

							input: 29854
							output: 22
							thoughts: 145
						

**Investigating Potential Memory Allocation Leak in NBD**

Okay, so it looks like `sk_clear_memalloc` isn't explicitly being called within the Network Block Device (NBD) driver. That's a bit concerning. Hang on... if NBD is setting the `SOCK_MEMALLOC` flag on a socket, shouldn't it *also* be clearing it when the socket is no longer needed? Otherwise, it's relying on the socket's destruction to clean up, which feels a bit fragile, or the destruction does not happen which leads to leakage.

The crucial issue here is balance, `static_branch_inc` calls must have corresponding `static_branch_dec` calls. If the clearing of the `SOCK_MEMALLOC` flag isn't happening properly, then the `memalloc_socks_key` counter will inevitably leak. This is a potential resource leak.

Right, time to verify this assumption. I need to confirm whether or not NBD actually calls `sk_clear_memalloc` anywhere in its code. I'll search for occurrences of `sk_clear_memalloc` within `drivers/block/nbd.c`. Let's see what the source code says.

map[Dir:drivers/block/]

map[Files:[amiflop.c ataflop.c brd.c floppy.c loop.c n64cart.c nbd.c ps3disk.c ps3vram.c rbd.c rbd_types.h sunvdc.c swim.c swim3.c swim_asm.S ublk_drv.c virtio_blk.c xen-blkfront.c z2ram.c zloop.c] Subdirs:[aoe drbd mtip32xx null_blk rnbd rnull xen-blkback zram]]

gemini-3-flash-preview

							input: 30498
							output: 23
							thoughts: 23
						

Okay, here's my take on those thoughts, tailored for an expert audience:

**Analyzing NBD Memory Management**

Right, let's dive in. When I see mention of `sk_clear_memalloc`, my first instinct is to head straight to `drivers/block/nbd.c`. That's where I'd expect to find the Network Block Device driver, and therefore, where I'd look for any socket-related memory management. I'm assuming we're dealing with socket buffer (sk_buff) memory, and the "clear_memalloc" function likely points to a mechanism for releasing or resetting resources associated with that allocation. I'd be looking closely at how it interacts with the NBD's request handling and data transfer paths. Is it part of a congestion control scheme? Does it prevent memory leaks or fragmentation? My initial focus would be on pinpointing the specific conditions under which `sk_clear_memalloc` is called, and what the implications of its execution are, especially concerning locking, error handling, and performance. I need to understand the full lifecycle of the memory management within this module.

map[File:drivers/block/nbd.c]

map[Contents:// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Network block device - make block devices work over TCP
 *
 * Note that you can not swap over this thing, yet. Seems to work but
 * deadlocks sometimes - you can not swap over TCP in general.
 * 
 * Copyright 1997-2000, 2008 Pavel Machek <pavel@ucw.cz>
 * Parts copyright 2001 Steven Whitehouse <steve@chygwyn.com>
 *
 * (part of code stolen from loop.c)
 */

#define pr_fmt(fmt) "nbd: " fmt

#include <linux/major.h>

#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/sched/mm.h>
#include <linux/fs.h>
#include <linux/bio.h>
#include <linux/stat.h>
#include <linux/errno.h>
#include <linux/file.h>
#include <linux/ioctl.h>
#include <linux/mutex.h>
#include <linux/compiler.h>
#include <linux/completion.h>
#include <linux/err.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <net/sock.h>
#include <linux/net.h>
#include <linux/kthread.h>
#include <linux/types.h>
#include <linux/debugfs.h>
#include <linux/blk-mq.h>

#include <linux/uaccess.h>
#include <asm/types.h>

#include <linux/nbd.h>
#include <linux/nbd-netlink.h>
#include <net/genetlink.h>

#define CREATE_TRACE_POINTS
#include <trace/events/nbd.h>

static DEFINE_IDR(nbd_index_idr);
static DEFINE_MUTEX(nbd_index_mutex);
static struct workqueue_struct *nbd_del_wq;
static int nbd_total_devices = 0;

struct nbd_sock {
	struct socket *sock;
	struct mutex tx_lock;
	struct request *pending;
	int sent;
	bool dead;
	int fallback_index;
	int cookie;
	struct work_struct work;
};

struct recv_thread_args {
	struct work_struct work;
	struct nbd_device *nbd;
	struct nbd_sock *nsock;
	int index;
};

struct link_dead_args {
	struct work_struct work;
	int index;
};

#define NBD_RT_TIMEDOUT			0
#define NBD_RT_DISCONNECT_REQUESTED	1
#define NBD_RT_DISCONNECTED		2
#define NBD_RT_HAS_PID_FILE		3
#define NBD_RT_HAS_CONFIG_REF		4
#define NBD_RT_BOUND			5
#define NBD_RT_DISCONNECT_ON_CLOSE	6
#define NBD_RT_HAS_BACKEND_FILE		7

#define NBD_DESTROY_ON_DISCONNECT	0
#define NBD_DISCONNECT_REQUESTED	1

struct nbd_config {
	u32 flags;
	unsigned long runtime_flags;
	u64 dead_conn_timeout;

	struct nbd_sock **socks;
	int num_connections;
	atomic_t live_connections;
	wait_queue_head_t conn_wait;

	atomic_t recv_threads;
	wait_queue_head_t recv_wq;
	unsigned int blksize_bits;
	loff_t bytesize;
#if IS_ENABLED(CONFIG_DEBUG_FS)
	struct dentry *dbg_dir;
#endif
};

static inline unsigned int nbd_blksize(struct nbd_config *config)
{
	return 1u << config->blksize_bits;
}

struct nbd_device {
	struct blk_mq_tag_set tag_set;

	int index;
	refcount_t config_refs;
	refcount_t refs;
	struct nbd_config *config;
	struct mutex config_lock;
	struct gendisk *disk;
	struct workqueue_struct *recv_workq;
	struct work_struct remove_work;

	struct list_head list;
	struct task_struct *task_setup;

	unsigned long flags;
	pid_t pid; /* pid of nbd-client, if attached */

	char *backend;
};

#define NBD_CMD_REQUEUED	1
/*
 * This flag will be set if nbd_queue_rq() succeed, and will be checked and
 * cleared in completion. Both setting and clearing of the flag are protected
 * by cmd->lock.
 */
#define NBD_CMD_INFLIGHT	2

/* Just part of request header or data payload is sent successfully */
#define NBD_CMD_PARTIAL_SEND	3

struct nbd_cmd {
	struct nbd_device *nbd;
	struct mutex lock;
	int index;
	int cookie;
	int retries;
	blk_status_t status;
	unsigned long flags;
	u32 cmd_cookie;
};

#if IS_ENABLED(CONFIG_DEBUG_FS)
static struct dentry *nbd_dbg_dir;
#endif

#define nbd_name(nbd) ((nbd)->disk->disk_name)

#define NBD_DEF_BLKSIZE_BITS 10

static unsigned int nbds_max = 16;
static int max_part = 16;
static int part_shift;

static int nbd_dev_dbg_init(struct nbd_device *nbd);
static void nbd_dev_dbg_close(struct nbd_device *nbd);
static void nbd_config_put(struct nbd_device *nbd);
static void nbd_connect_reply(struct genl_info *info, int index);
static int nbd_genl_status(struct sk_buff *skb, struct genl_info *info);
static void nbd_dead_link_work(struct work_struct *work);
static void nbd_disconnect_and_put(struct nbd_device *nbd);

static inline struct device *nbd_to_dev(struct nbd_device *nbd)
{
	return disk_to_dev(nbd->disk);
}

static void nbd_requeue_cmd(struct nbd_cmd *cmd)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);

	lockdep_assert_held(&cmd->lock);

	/*
	 * Clear INFLIGHT flag so that this cmd won't be completed in
	 * normal completion path
	 *
	 * INFLIGHT flag will be set when the cmd is queued to nbd next
	 * time.
	 */
	__clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);

	if (!test_and_set_bit(NBD_CMD_REQUEUED, &cmd->flags))
		blk_mq_requeue_request(req, true);
}

#define NBD_COOKIE_BITS 32

static u64 nbd_cmd_handle(struct nbd_cmd *cmd)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);
	u32 tag = blk_mq_unique_tag(req);
	u64 cookie = cmd->cmd_cookie;

	return (cookie << NBD_COOKIE_BITS) | tag;
}

static u32 nbd_handle_to_tag(u64 handle)
{
	return (u32)handle;
}

static u32 nbd_handle_to_cookie(u64 handle)
{
	return (u32)(handle >> NBD_COOKIE_BITS);
}

static const char *nbdcmd_to_ascii(int cmd)
{
	switch (cmd) {
	case  NBD_CMD_READ: return "read";
	case NBD_CMD_WRITE: return "write";
	case  NBD_CMD_DISC: return "disconnect";
	case NBD_CMD_FLUSH: return "flush";
	case  NBD_CMD_TRIM: return "trim/discard";
	}
	return "invalid";
}

static ssize_t pid_show(struct device *dev,
			struct device_attribute *attr, char *buf)
{
	struct gendisk *disk = dev_to_disk(dev);
	struct nbd_device *nbd = disk->private_data;

	return sprintf(buf, "%d\n", nbd->pid);
}

static const struct device_attribute pid_attr = {
	.attr = { .name = "pid", .mode = 0444},
	.show = pid_show,
};

static ssize_t backend_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct gendisk *disk = dev_to_disk(dev);
	struct nbd_device *nbd = disk->private_data;

	return sprintf(buf, "%s\n", nbd->backend ?: "");
}

static const struct device_attribute backend_attr = {
	.attr = { .name = "backend", .mode = 0444},
	.show = backend_show,
};

static void nbd_dev_remove(struct nbd_device *nbd)
{
	struct gendisk *disk = nbd->disk;

	del_gendisk(disk);
	blk_mq_free_tag_set(&nbd->tag_set);

	/*
	 * Remove from idr after del_gendisk() completes, so if the same ID is
	 * reused, the following add_disk() will succeed.
	 */
	mutex_lock(&nbd_index_mutex);
	idr_remove(&nbd_index_idr, nbd->index);
	mutex_unlock(&nbd_index_mutex);
	destroy_workqueue(nbd->recv_workq);
	put_disk(disk);
}

static void nbd_dev_remove_work(struct work_struct *work)
{
	nbd_dev_remove(container_of(work, struct nbd_device, remove_work));
}

static void nbd_put(struct nbd_device *nbd)
{
	if (!refcount_dec_and_test(&nbd->refs))
		return;

	/* Call del_gendisk() asynchrounously to prevent deadlock */
	if (test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags))
		queue_work(nbd_del_wq, &nbd->remove_work);
	else
		nbd_dev_remove(nbd);
}

static int nbd_disconnected(struct nbd_config *config)
{
	return test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags) ||
		test_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags);
}

static void nbd_mark_nsock_dead(struct nbd_device *nbd, struct nbd_sock *nsock,
				int notify)
{
	if (!nsock->dead && notify && !nbd_disconnected(nbd->config)) {
		struct link_dead_args *args;
		args = kmalloc_obj(struct link_dead_args, GFP_NOIO);
		if (args) {
			INIT_WORK(&args->work, nbd_dead_link_work);
			args->index = nbd->index;
			queue_work(system_percpu_wq, &args->work);
		}
	}
	if (!nsock->dead) {
		kernel_sock_shutdown(nsock->sock, SHUT_RDWR);
		if (atomic_dec_return(&nbd->config->live_connections) == 0) {
			if (test_and_clear_bit(NBD_RT_DISCONNECT_REQUESTED,
					       &nbd->config->runtime_flags)) {
				set_bit(NBD_RT_DISCONNECTED,
					&nbd->config->runtime_flags);
				dev_info(nbd_to_dev(nbd),
					"Disconnected due to user request.\n");
			}
		}
	}
	nsock->dead = true;
	nsock->pending = NULL;
	nsock->sent = 0;
}

static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize, loff_t blksize)
{
	struct queue_limits lim;
	int error;

	if (!blksize)
		blksize = 1u << NBD_DEF_BLKSIZE_BITS;

	if (blk_validate_block_size(blksize))
		return -EINVAL;

	if (bytesize < 0)
		return -EINVAL;

	nbd->config->bytesize = bytesize;
	nbd->config->blksize_bits = __ffs(blksize);

	if (!nbd->pid)
		return 0;

	lim = queue_limits_start_update(nbd->disk->queue);
	if (nbd->config->flags & NBD_FLAG_SEND_TRIM)
		lim.max_hw_discard_sectors = UINT_MAX >> SECTOR_SHIFT;
	else
		lim.max_hw_discard_sectors = 0;
	if (!(nbd->config->flags & NBD_FLAG_SEND_FLUSH)) {
		lim.features &= ~(BLK_FEAT_WRITE_CACHE | BLK_FEAT_FUA);
	} else if (nbd->config->flags & NBD_FLAG_SEND_FUA) {
		lim.features |= BLK_FEAT_WRITE_CACHE | BLK_FEAT_FUA;
	} else {
		lim.features |= BLK_FEAT_WRITE_CACHE;
		lim.features &= ~BLK_FEAT_FUA;
	}
	if (nbd->config->flags & NBD_FLAG_ROTATIONAL)
		lim.features |= BLK_FEAT_ROTATIONAL;
	if (nbd->config->flags & NBD_FLAG_SEND_WRITE_ZEROES)
		lim.max_write_zeroes_sectors = UINT_MAX >> SECTOR_SHIFT;

	lim.logical_block_size = blksize;
	lim.physical_block_size = blksize;
	error = queue_limits_commit_update_frozen(nbd->disk->queue, &lim);
	if (error)
		return error;

	if (max_part)
		set_bit(GD_NEED_PART_SCAN, &nbd->disk->state);
	if (!set_capacity_and_notify(nbd->disk, bytesize >> 9))
		kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
	return 0;
}

static void nbd_complete_rq(struct request *req)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);

	dev_dbg(nbd_to_dev(cmd->nbd), "request %p: %s\n", req,
		cmd->status ? "failed" : "done");

	blk_mq_end_request(req, cmd->status);
}

/*
 * Forcibly shutdown the socket causing all listeners to error
 */
static void sock_shutdown(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	int i;

	if (config->num_connections == 0)
		return;
	if (test_and_set_bit(NBD_RT_DISCONNECTED, &config->runtime_flags))
		return;

	for (i = 0; i < config->num_connections; i++) {
		struct nbd_sock *nsock = config->socks[i];
		mutex_lock(&nsock->tx_lock);
		nbd_mark_nsock_dead(nbd, nsock, 0);
		mutex_unlock(&nsock->tx_lock);
	}
	dev_warn(disk_to_dev(nbd->disk), "shutting down sockets\n");
}

static u32 req_to_nbd_cmd_type(struct request *req)
{
	switch (req_op(req)) {
	case REQ_OP_DISCARD:
		return NBD_CMD_TRIM;
	case REQ_OP_FLUSH:
		return NBD_CMD_FLUSH;
	case REQ_OP_WRITE:
		return NBD_CMD_WRITE;
	case REQ_OP_READ:
		return NBD_CMD_READ;
	case REQ_OP_WRITE_ZEROES:
		return NBD_CMD_WRITE_ZEROES;
	default:
		return U32_MAX;
	}
}

static struct nbd_config *nbd_get_config_unlocked(struct nbd_device *nbd)
{
	if (refcount_inc_not_zero(&nbd->config_refs)) {
		/*
		 * Add smp_mb__after_atomic to ensure that reading nbd->config_refs
		 * and reading nbd->config is ordered. The pair is the barrier in
		 * nbd_alloc_and_init_config(), avoid nbd->config_refs is set
		 * before nbd->config.
		 */
		smp_mb__after_atomic();
		return nbd->config;
	}

	return NULL;
}

static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);
	struct nbd_device *nbd = cmd->nbd;
	struct nbd_config *config;

	if (!mutex_trylock(&cmd->lock))
		return BLK_EH_RESET_TIMER;

	/* partial send is handled in nbd_sock's work function */
	if (test_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags)) {
		mutex_unlock(&cmd->lock);
		return BLK_EH_RESET_TIMER;
	}

	if (!test_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
		mutex_unlock(&cmd->lock);
		return BLK_EH_DONE;
	}

	config = nbd_get_config_unlocked(nbd);
	if (!config) {
		cmd->status = BLK_STS_TIMEOUT;
		__clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);
		mutex_unlock(&cmd->lock);
		goto done;
	}

	if (config->num_connections > 1 ||
	    (config->num_connections == 1 && nbd->tag_set.timeout)) {
		dev_err_ratelimited(nbd_to_dev(nbd),
				    "Connection timed out, retrying (%d/%d alive)\n",
				    atomic_read(&config->live_connections),
				    config->num_connections);
		/*
		 * Hooray we have more connections, requeue this IO, the submit
		 * path will put it on a real connection. Or if only one
		 * connection is configured, the submit path will wait util
		 * a new connection is reconfigured or util dead timeout.
		 */
		if (config->socks) {
			if (cmd->index < config->num_connections) {
				struct nbd_sock *nsock =
					config->socks[cmd->index];
				mutex_lock(&nsock->tx_lock);
				/* We can have multiple outstanding requests, so
				 * we don't want to mark the nsock dead if we've
				 * already reconnected with a new socket, so
				 * only mark it dead if its the same socket we
				 * were sent out on.
				 */
				if (cmd->cookie == nsock->cookie)
					nbd_mark_nsock_dead(nbd, nsock, 1);
				mutex_unlock(&nsock->tx_lock);
			}
			nbd_requeue_cmd(cmd);
			mutex_unlock(&cmd->lock);
			nbd_config_put(nbd);
			return BLK_EH_DONE;
		}
	}

	if (!nbd->tag_set.timeout) {
		/*
		 * Userspace sets timeout=0 to disable socket disconnection,
		 * so just warn and reset the timer.
		 */
		struct nbd_sock *nsock = config->socks[cmd->index];
		cmd->retries++;
		dev_info(nbd_to_dev(nbd), "Possible stuck request %p: control (%s@%llu,%uB). Runtime %u seconds\n",
			req, nbdcmd_to_ascii(req_to_nbd_cmd_type(req)),
			(unsigned long long)blk_rq_pos(req) << 9,
			blk_rq_bytes(req), (req->timeout / HZ) * cmd->retries);

		mutex_lock(&nsock->tx_lock);
		if (cmd->cookie != nsock->cookie) {
			nbd_requeue_cmd(cmd);
			mutex_unlock(&nsock->tx_lock);
			mutex_unlock(&cmd->lock);
			nbd_config_put(nbd);
			return BLK_EH_DONE;
		}
		mutex_unlock(&nsock->tx_lock);
		mutex_unlock(&cmd->lock);
		nbd_config_put(nbd);
		return BLK_EH_RESET_TIMER;
	}

	dev_err_ratelimited(nbd_to_dev(nbd), "Connection timed out\n");
	set_bit(NBD_RT_TIMEDOUT, &config->runtime_flags);
	cmd->status = BLK_STS_IOERR;
	__clear_bit(NBD_CMD_INFLIGHT, &cmd->flags);
	mutex_unlock(&cmd->lock);
	sock_shutdown(nbd);
	nbd_config_put(nbd);
done:
	blk_mq_complete_request(req);
	return BLK_EH_DONE;
}

static int __sock_xmit(struct nbd_device *nbd, struct socket *sock, int send,
		       struct iov_iter *iter, int msg_flags, int *sent)
{
	int result;
	struct msghdr msg = {} ;
	unsigned int noreclaim_flag;

	if (unlikely(!sock)) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
			"Attempted %s on closed socket in sock_xmit\n",
			(send ? "send" : "recv"));
		return -EINVAL;
	}

	msg.msg_iter = *iter;

	noreclaim_flag = memalloc_noreclaim_save();

	scoped_with_kernel_creds() {
		do {
			sock->sk->sk_allocation = GFP_NOIO | __GFP_MEMALLOC;
			sock->sk->sk_use_task_frag = false;
			msg.msg_flags = msg_flags | MSG_NOSIGNAL;

			if (send)
				result = sock_sendmsg(sock, &msg);
			else
				result = sock_recvmsg(sock, &msg, msg.msg_flags);

			if (result <= 0) {
				if (result == 0)
					result = -EPIPE; /* short read */
				break;
			}
			if (sent)
				*sent += result;
		} while (msg_data_left(&msg));
	}

	memalloc_noreclaim_restore(noreclaim_flag);

	return result;
}

/*
 *  Send or receive packet. Return a positive value on success and
 *  negtive value on failure, and never return 0.
 */
static int sock_xmit(struct nbd_device *nbd, int index, int send,
		     struct iov_iter *iter, int msg_flags, int *sent)
{
	struct nbd_config *config = nbd->config;
	struct socket *sock = config->socks[index]->sock;

	return __sock_xmit(nbd, sock, send, iter, msg_flags, sent);
}

/*
 * Different settings for sk->sk_sndtimeo can result in different return values
 * if there is a signal pending when we enter sendmsg, because reasons?
 */
static inline int was_interrupted(int result)
{
	return result == -ERESTARTSYS || result == -EINTR;
}

/*
 * We've already sent header or part of data payload, have no choice but
 * to set pending and schedule it in work.
 *
 * And we have to return BLK_STS_OK to block core, otherwise this same
 * request may be re-dispatched with different tag, but our header has
 * been sent out with old tag, and this way does confuse reply handling.
 */
static void nbd_sched_pending_work(struct nbd_device *nbd,
				   struct nbd_sock *nsock,
				   struct nbd_cmd *cmd, int sent)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);

	/* pending work should be scheduled only once */
	WARN_ON_ONCE(test_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags));

	nsock->pending = req;
	nsock->sent = sent;
	set_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags);
	refcount_inc(&nbd->config_refs);
	schedule_work(&nsock->work);
}

/*
 * Returns BLK_STS_RESOURCE if the caller should retry after a delay.
 * Returns BLK_STS_IOERR if sending failed.
 */
static blk_status_t nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd,
				 int index)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);
	struct nbd_config *config = nbd->config;
	struct nbd_sock *nsock = config->socks[index];
	int result;
	struct nbd_request request = {.magic = htonl(NBD_REQUEST_MAGIC)};
	struct kvec iov = {.iov_base = &request, .iov_len = sizeof(request)};
	struct iov_iter from;
	struct bio *bio;
	u64 handle;
	u32 type;
	u32 nbd_cmd_flags = 0;
	int sent = nsock->sent, skip = 0;

	lockdep_assert_held(&cmd->lock);
	lockdep_assert_held(&nsock->tx_lock);

	iov_iter_kvec(&from, ITER_SOURCE, &iov, 1, sizeof(request));

	type = req_to_nbd_cmd_type(req);
	if (type == U32_MAX)
		return BLK_STS_IOERR;

	if (rq_data_dir(req) == WRITE &&
	    (config->flags & NBD_FLAG_READ_ONLY)) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
				    "Write on read-only\n");
		return BLK_STS_IOERR;
	}

	if (req->cmd_flags & REQ_FUA)
		nbd_cmd_flags |= NBD_CMD_FLAG_FUA;
	if ((req->cmd_flags & REQ_NOUNMAP) && (type == NBD_CMD_WRITE_ZEROES))
		nbd_cmd_flags |= NBD_CMD_FLAG_NO_HOLE;

	/* We did a partial send previously, and we at least sent the whole
	 * request struct, so just go and send the rest of the pages in the
	 * request.
	 */
	if (sent) {
		if (sent >= sizeof(request)) {
			skip = sent - sizeof(request);

			/* initialize handle for tracing purposes */
			handle = nbd_cmd_handle(cmd);

			goto send_pages;
		}
		iov_iter_advance(&from, sent);
	} else {
		cmd->cmd_cookie++;
	}
	cmd->index = index;
	cmd->cookie = nsock->cookie;
	cmd->retries = 0;
	request.type = htonl(type | nbd_cmd_flags);
	if (type != NBD_CMD_FLUSH) {
		request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9);
		request.len = htonl(blk_rq_bytes(req));
	}
	handle = nbd_cmd_handle(cmd);
	request.cookie = cpu_to_be64(handle);

	trace_nbd_send_request(&request, nbd->index, blk_mq_rq_from_pdu(cmd));

	dev_dbg(nbd_to_dev(nbd), "request %p: sending control (%s@%llu,%uB)\n",
		req, nbdcmd_to_ascii(type),
		(unsigned long long)blk_rq_pos(req) << 9, blk_rq_bytes(req));
	result = sock_xmit(nbd, index, 1, &from,
			(type == NBD_CMD_WRITE) ? MSG_MORE : 0, &sent);
	trace_nbd_header_sent(req, handle);
	if (result < 0) {
		if (was_interrupted(result)) {
			/* If we haven't sent anything we can just return BUSY,
			 * however if we have sent something we need to make
			 * sure we only allow this req to be sent until we are
			 * completely done.
			 */
			if (sent) {
				nbd_sched_pending_work(nbd, nsock, cmd, sent);
				return BLK_STS_OK;
			}
			set_bit(NBD_CMD_REQUEUED, &cmd->flags);
			return BLK_STS_RESOURCE;
		}
		dev_err_ratelimited(disk_to_dev(nbd->disk),
			"Send control failed (result %d)\n", result);
		goto requeue;
	}
send_pages:
	if (type != NBD_CMD_WRITE)
		goto out;

	bio = req->bio;
	while (bio) {
		struct bio *next = bio->bi_next;
		struct bvec_iter iter;
		struct bio_vec bvec;

		bio_for_each_segment(bvec, bio, iter) {
			bool is_last = !next && bio_iter_last(bvec, iter);
			int flags = is_last ? 0 : MSG_MORE;

			dev_dbg(nbd_to_dev(nbd), "request %p: sending %d bytes data\n",
				req, bvec.bv_len);
			iov_iter_bvec(&from, ITER_SOURCE, &bvec, 1, bvec.bv_len);
			if (skip) {
				if (skip >= iov_iter_count(&from)) {
					skip -= iov_iter_count(&from);
					continue;
				}
				iov_iter_advance(&from, skip);
				skip = 0;
			}
			result = sock_xmit(nbd, index, 1, &from, flags, &sent);
			if (result < 0) {
				if (was_interrupted(result)) {
					nbd_sched_pending_work(nbd, nsock, cmd, sent);
					return BLK_STS_OK;
				}
				dev_err(disk_to_dev(nbd->disk),
					"Send data failed (result %d)\n",
					result);
				goto requeue;
			}
			/*
			 * The completion might already have come in,
			 * so break for the last one instead of letting
			 * the iterator do it. This prevents use-after-free
			 * of the bio.
			 */
			if (is_last)
				break;
		}
		bio = next;
	}
out:
	trace_nbd_payload_sent(req, handle);
	nsock->pending = NULL;
	nsock->sent = 0;
	__set_bit(NBD_CMD_INFLIGHT, &cmd->flags);
	return BLK_STS_OK;

requeue:
	/*
	 * Can't requeue in case we are dealing with partial send
	 *
	 * We must run from pending work function.
	 * */
	if (test_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags))
		return BLK_STS_OK;

	/* retry on a different socket */
	dev_err_ratelimited(disk_to_dev(nbd->disk),
			    "Request send failed, requeueing\n");
	nbd_mark_nsock_dead(nbd, nsock, 1);
	nbd_requeue_cmd(cmd);
	return BLK_STS_OK;
}

/* handle partial sending */
static void nbd_pending_cmd_work(struct work_struct *work)
{
	struct nbd_sock *nsock = container_of(work, struct nbd_sock, work);
	struct request *req = nsock->pending;
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);
	struct nbd_device *nbd = cmd->nbd;
	unsigned long deadline = READ_ONCE(req->deadline);
	unsigned int wait_ms = 2;

	mutex_lock(&cmd->lock);

	WARN_ON_ONCE(test_bit(NBD_CMD_REQUEUED, &cmd->flags));
	if (WARN_ON_ONCE(!test_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags)))
		goto out;

	mutex_lock(&nsock->tx_lock);
	while (true) {
		nbd_send_cmd(nbd, cmd, cmd->index);
		if (!nsock->pending)
			break;

		/* don't bother timeout handler for partial sending */
		if (READ_ONCE(jiffies) + msecs_to_jiffies(wait_ms) >= deadline) {
			cmd->status = BLK_STS_IOERR;
			blk_mq_complete_request(req);
			break;
		}
		msleep(wait_ms);
		wait_ms *= 2;
	}
	mutex_unlock(&nsock->tx_lock);
	clear_bit(NBD_CMD_PARTIAL_SEND, &cmd->flags);
out:
	mutex_unlock(&cmd->lock);
	nbd_config_put(nbd);
}

static int nbd_read_reply(struct nbd_device *nbd, struct socket *sock,
			  struct nbd_reply *reply)
{
	struct kvec iov = {.iov_base = reply, .iov_len = sizeof(*reply)};
	struct iov_iter to;
	int result;

	reply->magic = 0;
	iov_iter_kvec(&to, ITER_DEST, &iov, 1, sizeof(*reply));
	result = __sock_xmit(nbd, sock, 0, &to, MSG_WAITALL, NULL);
	if (result < 0) {
		if (!nbd_disconnected(nbd->config))
			dev_err(disk_to_dev(nbd->disk),
				"Receive control failed (result %d)\n", result);
		return result;
	}

	if (ntohl(reply->magic) != NBD_REPLY_MAGIC) {
		dev_err(disk_to_dev(nbd->disk), "Wrong magic (0x%lx)\n",
				(unsigned long)ntohl(reply->magic));
		return -EPROTO;
	}

	return 0;
}

/* NULL returned = something went wrong, inform userspace */
static struct nbd_cmd *nbd_handle_reply(struct nbd_device *nbd, int index,
					struct nbd_reply *reply)
{
	int result;
	struct nbd_cmd *cmd;
	struct request *req = NULL;
	u64 handle;
	u16 hwq;
	u32 tag;
	int ret = 0;

	handle = be64_to_cpu(reply->cookie);
	tag = nbd_handle_to_tag(handle);
	hwq = blk_mq_unique_tag_to_hwq(tag);
	if (hwq < nbd->tag_set.nr_hw_queues)
		req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq],
				       blk_mq_unique_tag_to_tag(tag));
	if (!req || !blk_mq_request_started(req)) {
		dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%d) %p\n",
			tag, req);
		return ERR_PTR(-ENOENT);
	}
	trace_nbd_header_received(req, handle);
	cmd = blk_mq_rq_to_pdu(req);

	mutex_lock(&cmd->lock);
	if (!test_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
		dev_err(disk_to_dev(nbd->disk), "Suspicious reply %d (status %u flags %lu)",
			tag, cmd->status, cmd->flags);
		ret = -ENOENT;
		goto out;
	}
	if (cmd->index != index) {
		dev_err(disk_to_dev(nbd->disk), "Unexpected reply %d from different sock %d (expected %d)",
			tag, index, cmd->index);
		ret = -ENOENT;
		goto out;
	}
	if (cmd->cmd_cookie != nbd_handle_to_cookie(handle)) {
		dev_err(disk_to_dev(nbd->disk), "Double reply on req %p, cmd_cookie %u, handle cookie %u\n",
			req, cmd->cmd_cookie, nbd_handle_to_cookie(handle));
		ret = -ENOENT;
		goto out;
	}
	if (cmd->status != BLK_STS_OK) {
		dev_err(disk_to_dev(nbd->disk), "Command already handled %p\n",
			req);
		ret = -ENOENT;
		goto out;
	}
	if (test_bit(NBD_CMD_REQUEUED, &cmd->flags)) {
		dev_err(disk_to_dev(nbd->disk), "Raced with timeout on req %p\n",
			req);
		ret = -ENOENT;
		goto out;
	}
	if (ntohl(reply->error)) {
		dev_err(disk_to_dev(nbd->disk), "Other side returned error (%d)\n",
			ntohl(reply->error));
		cmd->status = BLK_STS_IOERR;
		goto out;
	}

	dev_dbg(nbd_to_dev(nbd), "request %p: got reply\n", req);
	if (rq_data_dir(req) != WRITE) {
		struct req_iterator iter;
		struct bio_vec bvec;
		struct iov_iter to;

		rq_for_each_segment(bvec, req, iter) {
			iov_iter_bvec(&to, ITER_DEST, &bvec, 1, bvec.bv_len);
			result = sock_xmit(nbd, index, 0, &to, MSG_WAITALL, NULL);
			if (result < 0) {
				dev_err(disk_to_dev(nbd->disk), "Receive data failed (result %d)\n",
					result);
				/*
				 * If we've disconnected, we need to make sure we
				 * complete this request, otherwise error out
				 * and let the timeout stuff handle resubmitting
				 * this request onto another connection.
				 */
				if (nbd_disconnected(nbd->config)) {
					cmd->status = BLK_STS_IOERR;
					goto out;
				}
				ret = -EIO;
				goto out;
			}
			dev_dbg(nbd_to_dev(nbd), "request %p: got %d bytes data\n",
				req, bvec.bv_len);
		}
	}
out:
	trace_nbd_payload_received(req, handle);
	mutex_unlock(&cmd->lock);
	return ret ? ERR_PTR(ret) : cmd;
}

static void recv_work(struct work_struct *work)
{
	struct recv_thread_args *args = container_of(work,
						     struct recv_thread_args,
						     work);
	struct nbd_device *nbd = args->nbd;
	struct nbd_config *config = nbd->config;
	struct request_queue *q = nbd->disk->queue;
	struct nbd_sock *nsock = args->nsock;
	struct nbd_cmd *cmd;
	struct request *rq;

	while (1) {
		struct nbd_reply reply;

		if (nbd_read_reply(nbd, nsock->sock, &reply))
			break;

		/*
		 * Grab .q_usage_counter so request pool won't go away, then no
		 * request use-after-free is possible during nbd_handle_reply().
		 * If queue is frozen, there won't be any inflight requests, we
		 * needn't to handle the incoming garbage message.
		 */
		if (!percpu_ref_tryget(&q->q_usage_counter)) {
			dev_err(disk_to_dev(nbd->disk), "%s: no io inflight\n",
				__func__);
			break;
		}

		cmd = nbd_handle_reply(nbd, args->index, &reply);
		if (IS_ERR(cmd)) {
			percpu_ref_put(&q->q_usage_counter);
			break;
		}

		rq = blk_mq_rq_from_pdu(cmd);
		if (likely(!blk_should_fake_timeout(rq->q))) {
			bool complete;

			mutex_lock(&cmd->lock);
			complete = __test_and_clear_bit(NBD_CMD_INFLIGHT,
							&cmd->flags);
			mutex_unlock(&cmd->lock);
			if (complete)
				blk_mq_complete_request(rq);
		}
		percpu_ref_put(&q->q_usage_counter);
	}

	mutex_lock(&nsock->tx_lock);
	nbd_mark_nsock_dead(nbd, nsock, 1);
	mutex_unlock(&nsock->tx_lock);

	atomic_dec(&config->recv_threads);
	wake_up(&config->recv_wq);
	nbd_config_put(nbd);
	kfree(args);
}

static bool nbd_clear_req(struct request *req, void *data)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);

	/* don't abort one completed request */
	if (blk_mq_request_completed(req))
		return true;

	mutex_lock(&cmd->lock);
	if (!__test_and_clear_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
		mutex_unlock(&cmd->lock);
		return true;
	}
	cmd->status = BLK_STS_IOERR;
	mutex_unlock(&cmd->lock);

	blk_mq_complete_request(req);
	return true;
}

static void nbd_clear_que(struct nbd_device *nbd)
{
	blk_mq_quiesce_queue(nbd->disk->queue);
	blk_mq_tagset_busy_iter(&nbd->tag_set, nbd_clear_req, NULL);
	blk_mq_unquiesce_queue(nbd->disk->queue);
	dev_dbg(disk_to_dev(nbd->disk), "queue cleared\n");
}

static int find_fallback(struct nbd_device *nbd, int index)
{
	struct nbd_config *config = nbd->config;
	int new_index = -1;
	struct nbd_sock *nsock = config->socks[index];
	int fallback = nsock->fallback_index;

	if (test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags))
		return new_index;

	if (config->num_connections <= 1) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
				    "Dead connection, failed to find a fallback\n");
		return new_index;
	}

	if (fallback >= 0 && fallback < config->num_connections &&
	    !config->socks[fallback]->dead)
		return fallback;

	if (nsock->fallback_index < 0 ||
	    nsock->fallback_index >= config->num_connections ||
	    config->socks[nsock->fallback_index]->dead) {
		int i;
		for (i = 0; i < config->num_connections; i++) {
			if (i == index)
				continue;
			if (!config->socks[i]->dead) {
				new_index = i;
				break;
			}
		}
		nsock->fallback_index = new_index;
		if (new_index < 0) {
			dev_err_ratelimited(disk_to_dev(nbd->disk),
					    "Dead connection, failed to find a fallback\n");
			return new_index;
		}
	}
	new_index = nsock->fallback_index;
	return new_index;
}

static int wait_for_reconnect(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	if (!config->dead_conn_timeout)
		return 0;

	if (!wait_event_timeout(config->conn_wait,
				test_bit(NBD_RT_DISCONNECTED,
					 &config->runtime_flags) ||
				atomic_read(&config->live_connections) > 0,
				config->dead_conn_timeout))
		return 0;

	return !test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);
}

static blk_status_t nbd_handle_cmd(struct nbd_cmd *cmd, int index)
{
	struct request *req = blk_mq_rq_from_pdu(cmd);
	struct nbd_device *nbd = cmd->nbd;
	struct nbd_config *config;
	struct nbd_sock *nsock;
	blk_status_t ret;

	lockdep_assert_held(&cmd->lock);

	config = nbd_get_config_unlocked(nbd);
	if (!config) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
				    "Socks array is empty\n");
		return BLK_STS_IOERR;
	}

	if (index >= config->num_connections) {
		dev_err_ratelimited(disk_to_dev(nbd->disk),
				    "Attempted send on invalid socket\n");
		nbd_config_put(nbd);
		return BLK_STS_IOERR;
	}
	cmd->status = BLK_STS_OK;
again:
	nsock = config->socks[index];
	mutex_lock(&nsock->tx_lock);
	if (nsock->dead) {
		int old_index = index;
		index = find_fallback(nbd, index);
		mutex_unlock(&nsock->tx_lock);
		if (index < 0) {
			if (wait_for_reconnect(nbd)) {
				index = old_index;
				goto again;
			}
			/* All the sockets should already be down at this point,
			 * we just want to make sure that DISCONNECTED is set so
			 * any requests that come in that were queue'ed waiting
			 * for the reconnect timer don't trigger the timer again
			 * and instead just error out.
			 */
			sock_shutdown(nbd);
			nbd_config_put(nbd);
			return BLK_STS_IOERR;
		}
		goto again;
	}

	/* Handle the case that we have a pending request that was partially
	 * transmitted that _has_ to be serviced first.  We need to call requeue
	 * here so that it gets put _after_ the request that is already on the
	 * dispatch list.
	 */
	blk_mq_start_request(req);
	if (unlikely(nsock->pending && nsock->pending != req)) {
		nbd_requeue_cmd(cmd);
		ret = BLK_STS_OK;
		goto out;
	}
	ret = nbd_send_cmd(nbd, cmd, index);
out:
	mutex_unlock(&nsock->tx_lock);
	nbd_config_put(nbd);
	return ret;
}

static blk_status_t nbd_queue_rq(struct blk_mq_hw_ctx *hctx,
			const struct blk_mq_queue_data *bd)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(bd->rq);
	blk_status_t ret;

	/*
	 * Since we look at the bio's to send the request over the network we
	 * need to make sure the completion work doesn't mark this request done
	 * before we are done doing our send.  This keeps us from dereferencing
	 * freed data if we have particularly fast completions (ie we get the
	 * completion before we exit sock_xmit on the last bvec) or in the case
	 * that the server is misbehaving (or there was an error) before we're
	 * done sending everything over the wire.
	 */
	mutex_lock(&cmd->lock);
	clear_bit(NBD_CMD_REQUEUED, &cmd->flags);

	/* We can be called directly from the user space process, which means we
	 * could possibly have signals pending so our sendmsg will fail.  In
	 * this case we need to return that we are busy, otherwise error out as
	 * appropriate.
	 */
	ret = nbd_handle_cmd(cmd, hctx->queue_num);
	mutex_unlock(&cmd->lock);

	return ret;
}

static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd,
				     int *err)
{
	struct socket *sock;

	*err = 0;
	sock = sockfd_lookup(fd, err);
	if (!sock)
		return NULL;

	if (!sk_is_tcp(sock->sk) &&
	    !sk_is_stream_unix(sock->sk)) {
		dev_err(disk_to_dev(nbd->disk), "Unsupported socket: should be TCP or UNIX.\n");
		*err = -EINVAL;
		sockfd_put(sock);
		return NULL;
	}

	if (sock->ops->shutdown == sock_no_shutdown) {
		dev_err(disk_to_dev(nbd->disk), "Unsupported socket: shutdown callout must be supported.\n");
		*err = -EINVAL;
		sockfd_put(sock);
		return NULL;
	}

	return sock;
}

static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
			  bool netlink)
{
	struct nbd_config *config = nbd->config;
	struct socket *sock;
	struct nbd_sock **socks;
	struct nbd_sock *nsock;
	unsigned int memflags;
	int err;

	/* Arg will be cast to int, check it to avoid overflow */
	if (arg > INT_MAX)
		return -EINVAL;
	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	/*
	 * We need to make sure we don't get any errant requests while we're
	 * reallocating the ->socks array.
	 */
	memflags = blk_mq_freeze_queue(nbd->disk->queue);

	if (!netlink && !nbd->task_setup &&
	    !test_bit(NBD_RT_BOUND, &config->runtime_flags))
		nbd->task_setup = current;

	if (!netlink &&
	    (nbd->task_setup != current ||
	     test_bit(NBD_RT_BOUND, &config->runtime_flags))) {
		dev_err(disk_to_dev(nbd->disk),
			"Device being setup by another task");
		err = -EBUSY;
		goto put_socket;
	}

	nsock = kzalloc_obj(*nsock);
	if (!nsock) {
		err = -ENOMEM;
		goto put_socket;
	}

	socks = krealloc(config->socks, (config->num_connections + 1) *
			 sizeof(struct nbd_sock *), GFP_KERNEL);
	if (!socks) {
		kfree(nsock);
		err = -ENOMEM;
		goto put_socket;
	}

	config->socks = socks;

	nsock->fallback_index = -1;
	nsock->dead = false;
	mutex_init(&nsock->tx_lock);
	nsock->sock = sock;
	nsock->pending = NULL;
	nsock->sent = 0;
	nsock->cookie = 0;
	INIT_WORK(&nsock->work, nbd_pending_cmd_work);
	socks[config->num_connections++] = nsock;
	atomic_inc(&config->live_connections);
	blk_mq_unfreeze_queue(nbd->disk->queue, memflags);

	return 0;

put_socket:
	blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
	sockfd_put(sock);
	return err;
}

static int nbd_reconnect_socket(struct nbd_device *nbd, unsigned long arg)
{
	struct nbd_config *config = nbd->config;
	struct socket *sock, *old;
	struct recv_thread_args *args;
	int i;
	int err;

	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	args = kzalloc_obj(*args);
	if (!args) {
		sockfd_put(sock);
		return -ENOMEM;
	}

	for (i = 0; i < config->num_connections; i++) {
		struct nbd_sock *nsock = config->socks[i];

		if (!nsock->dead)
			continue;

		mutex_lock(&nsock->tx_lock);
		if (!nsock->dead) {
			mutex_unlock(&nsock->tx_lock);
			continue;
		}
		sk_set_memalloc(sock->sk);
		if (nbd->tag_set.timeout)
			sock->sk->sk_sndtimeo = nbd->tag_set.timeout;
		atomic_inc(&config->recv_threads);
		refcount_inc(&nbd->config_refs);
		old = nsock->sock;
		nsock->fallback_index = -1;
		nsock->sock = sock;
		nsock->dead = false;
		INIT_WORK(&args->work, recv_work);
		args->index = i;
		args->nbd = nbd;
		args->nsock = nsock;
		nsock->cookie++;
		mutex_unlock(&nsock->tx_lock);
		sockfd_put(old);

		clear_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);

		/* We take the tx_mutex in an error path in the recv_work, so we
		 * need to queue_work outside of the tx_mutex.
		 */
		queue_work(nbd->recv_workq, &args->work);

		atomic_inc(&config->live_connections);
		wake_up(&config->conn_wait);
		return 0;
	}
	sockfd_put(sock);
	kfree(args);
	return -ENOSPC;
}

static void nbd_bdev_reset(struct nbd_device *nbd)
{
	if (disk_openers(nbd->disk) > 1)
		return;
	set_capacity(nbd->disk, 0);
}

static void nbd_parse_flags(struct nbd_device *nbd)
{
	if (nbd->config->flags & NBD_FLAG_READ_ONLY)
		set_disk_ro(nbd->disk, true);
	else
		set_disk_ro(nbd->disk, false);
}

static void send_disconnects(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	struct nbd_request request = {
		.magic = htonl(NBD_REQUEST_MAGIC),
		.type = htonl(NBD_CMD_DISC),
	};
	struct kvec iov = {.iov_base = &request, .iov_len = sizeof(request)};
	struct iov_iter from;
	int i, ret;

	for (i = 0; i < config->num_connections; i++) {
		struct nbd_sock *nsock = config->socks[i];

		iov_iter_kvec(&from, ITER_SOURCE, &iov, 1, sizeof(request));
		mutex_lock(&nsock->tx_lock);
		ret = sock_xmit(nbd, i, 1, &from, 0, NULL);
		if (ret < 0)
			dev_err(disk_to_dev(nbd->disk),
				"Send disconnect failed %d\n", ret);
		mutex_unlock(&nsock->tx_lock);
	}
}

static int nbd_disconnect(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;

	dev_info(disk_to_dev(nbd->disk), "NBD_DISCONNECT\n");
	set_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags);
	set_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags);
	send_disconnects(nbd);
	return 0;
}

static void nbd_clear_sock(struct nbd_device *nbd)
{
	sock_shutdown(nbd);
	nbd_clear_que(nbd);
	nbd->task_setup = NULL;
}

static void nbd_config_put(struct nbd_device *nbd)
{
	if (refcount_dec_and_mutex_lock(&nbd->config_refs,
					&nbd->config_lock)) {
		struct nbd_config *config = nbd->config;
		nbd_dev_dbg_close(nbd);
		invalidate_disk(nbd->disk);
		if (nbd->config->bytesize)
			kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
		if (test_and_clear_bit(NBD_RT_HAS_PID_FILE,
				       &config->runtime_flags))
			device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
		nbd->pid = 0;
		if (test_and_clear_bit(NBD_RT_HAS_BACKEND_FILE,
				       &config->runtime_flags)) {
			device_remove_file(disk_to_dev(nbd->disk), &backend_attr);
			kfree(nbd->backend);
			nbd->backend = NULL;
		}
		nbd_clear_sock(nbd);
		if (config->num_connections) {
			int i;
			for (i = 0; i < config->num_connections; i++) {
				sockfd_put(config->socks[i]->sock);
				kfree(config->socks[i]);
			}
			kfree(config->socks);
		}
		kfree(nbd->config);
		nbd->config = NULL;

		nbd->tag_set.timeout = 0;

		mutex_unlock(&nbd->config_lock);
		nbd_put(nbd);
		module_put(THIS_MODULE);
	}
}

static int nbd_start_device(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	int num_connections = config->num_connections;
	int error = 0, i;

	if (nbd->pid)
		return -EBUSY;
	if (!config->socks)
		return -EINVAL;
	if (num_connections > 1 &&
	    !(config->flags & NBD_FLAG_CAN_MULTI_CONN)) {
		dev_err(disk_to_dev(nbd->disk), "server does not support multiple connections per device.\n");
		return -EINVAL;
	}

retry:
	mutex_unlock(&nbd->config_lock);
	blk_mq_update_nr_hw_queues(&nbd->tag_set, num_connections);
	mutex_lock(&nbd->config_lock);

	/* if another code path updated nr_hw_queues, retry until succeed */
	if (num_connections != config->num_connections) {
		num_connections = config->num_connections;
		goto retry;
	}

	nbd->pid = task_pid_nr(current);

	nbd_parse_flags(nbd);

	error = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
	if (error) {
		dev_err(disk_to_dev(nbd->disk), "device_create_file failed for pid!\n");
		return error;
	}
	set_bit(NBD_RT_HAS_PID_FILE, &config->runtime_flags);

	nbd_dev_dbg_init(nbd);
	for (i = 0; i < num_connections; i++) {
		struct recv_thread_args *args;

		args = kzalloc_obj(*args);
		if (!args) {
			sock_shutdown(nbd);
			/*
			 * If num_connections is m (2 < m),
			 * and NO.1 ~ NO.n(1 < n < m) kzallocs are successful.
			 * But NO.(n + 1) failed. We still have n recv threads.
			 * So, add flush_workqueue here to prevent recv threads
			 * dropping the last config_refs and trying to destroy
			 * the workqueue from inside the workqueue.
			 */
			if (i)
				flush_workqueue(nbd->recv_workq);
			return -ENOMEM;
		}
		sk_set_memalloc(config->socks[i]->sock->sk);
		if (nbd->tag_set.timeout)
			config->socks[i]->sock->sk->sk_sndtimeo =
				nbd->tag_set.timeout;
		atomic_inc(&config->recv_threads);
		refcount_inc(&nbd->config_refs);
		INIT_WORK(&args->work, recv_work);
		args->nbd = nbd;
		args->nsock = config->socks[i];
		args->index = i;
		queue_work(nbd->recv_workq, &args->work);
	}
	return nbd_set_size(nbd, config->bytesize, nbd_blksize(config));
}

static int nbd_start_device_ioctl(struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	int ret;

	ret = nbd_start_device(nbd);
	if (ret)
		return ret;

	if (max_part)
		set_bit(GD_NEED_PART_SCAN, &nbd->disk->state);
	mutex_unlock(&nbd->config_lock);
	ret = wait_event_interruptible(config->recv_wq,
					 atomic_read(&config->recv_threads) == 0);
	if (ret) {
		sock_shutdown(nbd);
		nbd_clear_que(nbd);
	}

	flush_workqueue(nbd->recv_workq);
	mutex_lock(&nbd->config_lock);
	nbd_bdev_reset(nbd);
	/* user requested, ignore socket errors */
	if (test_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags))
		ret = 0;
	if (test_bit(NBD_RT_TIMEDOUT, &config->runtime_flags))
		ret = -ETIMEDOUT;
	return ret;
}

static void nbd_clear_sock_ioctl(struct nbd_device *nbd)
{
	nbd_clear_sock(nbd);
	disk_force_media_change(nbd->disk);
	nbd_bdev_reset(nbd);
	if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF,
			       &nbd->config->runtime_flags))
		nbd_config_put(nbd);
}

static void nbd_set_cmd_timeout(struct nbd_device *nbd, u64 timeout)
{
	nbd->tag_set.timeout = timeout * HZ;
	if (timeout)
		blk_queue_rq_timeout(nbd->disk->queue, timeout * HZ);
	else
		blk_queue_rq_timeout(nbd->disk->queue, 30 * HZ);
}

/* Must be called with config_lock held */
static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
		       unsigned int cmd, unsigned long arg)
{
	struct nbd_config *config = nbd->config;
	loff_t bytesize;

	switch (cmd) {
	case NBD_DISCONNECT:
		return nbd_disconnect(nbd);
	case NBD_CLEAR_SOCK:
		nbd_clear_sock_ioctl(nbd);
		return 0;
	case NBD_SET_SOCK:
		return nbd_add_socket(nbd, arg, false);
	case NBD_SET_BLKSIZE:
		return nbd_set_size(nbd, config->bytesize, arg);
	case NBD_SET_SIZE:
		return nbd_set_size(nbd, arg, nbd_blksize(config));
	case NBD_SET_SIZE_BLOCKS:
		if (check_shl_overflow(arg, config->blksize_bits, &bytesize))
			return -EINVAL;
		return nbd_set_size(nbd, bytesize, nbd_blksize(config));
	case NBD_SET_TIMEOUT:
		nbd_set_cmd_timeout(nbd, arg);
		return 0;

	case NBD_SET_FLAGS:
		config->flags = arg;
		return 0;
	case NBD_DO_IT:
		return nbd_start_device_ioctl(nbd);
	case NBD_CLEAR_QUE:
		/*
		 * This is for compatibility only.  The queue is always cleared
		 * by NBD_DO_IT or NBD_CLEAR_SOCK.
		 */
		return 0;
	case NBD_PRINT_DEBUG:
		/*
		 * For compatibility only, we no longer keep a list of
		 * outstanding requests.
		 */
		return 0;
	}
	return -ENOTTY;
}

static int nbd_ioctl(struct block_device *bdev, blk_mode_t mode,
		     unsigned int cmd, unsigned long arg)
{
	struct nbd_device *nbd = bdev->bd_disk->private_data;
	struct nbd_config *config = nbd->config;
	int error = -EINVAL;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;

	/* The block layer will pass back some non-nbd ioctls in case we have
	 * special handling for them, but we don't so just return an error.
	 */
	if (_IOC_TYPE(cmd) != 0xab)
		return -EINVAL;

	mutex_lock(&nbd->config_lock);

	/* Don't allow ioctl operations on a nbd device that was created with
	 * netlink, unless it's DISCONNECT or CLEAR_SOCK, which are fine.
	 */
	if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
	    (cmd == NBD_DISCONNECT || cmd == NBD_CLEAR_SOCK))
		error = __nbd_ioctl(bdev, nbd, cmd, arg);
	else
		dev_err(nbd_to_dev(nbd), "Cannot use ioctl interface on a netlink controlled device.\n");
	mutex_unlock(&nbd->config_lock);
	return error;
}

static int nbd_alloc_and_init_config(struct nbd_device *nbd)
{
	struct nbd_config *config;

	if (WARN_ON(nbd->config))
		return -EINVAL;

	if (!try_module_get(THIS_MODULE))
		return -ENODEV;

	config = kzalloc_obj(struct nbd_config, GFP_NOFS);
	if (!config) {
		module_put(THIS_MODULE);
		return -ENOMEM;
	}

	atomic_set(&config->recv_threads, 0);
	init_waitqueue_head(&config->recv_wq);
	init_waitqueue_head(&config->conn_wait);
	config->blksize_bits = NBD_DEF_BLKSIZE_BITS;
	atomic_set(&config->live_connections, 0);

	nbd->config = config;
	/*
	 * Order refcount_set(&nbd->config_refs, 1) and nbd->config assignment,
	 * its pair is the barrier in nbd_get_config_unlocked().
	 * So nbd_get_config_unlocked() won't see nbd->config as null after
	 * refcount_inc_not_zero() succeed.
	 */
	smp_mb__before_atomic();
	refcount_set(&nbd->config_refs, 1);

	return 0;
}

static int nbd_open(struct gendisk *disk, blk_mode_t mode)
{
	struct nbd_device *nbd;
	struct nbd_config *config;
	int ret = 0;

	mutex_lock(&nbd_index_mutex);
	nbd = disk->private_data;
	if (!nbd) {
		ret = -ENXIO;
		goto out;
	}
	if (!refcount_inc_not_zero(&nbd->refs)) {
		ret = -ENXIO;
		goto out;
	}

	config = nbd_get_config_unlocked(nbd);
	if (!config) {
		mutex_lock(&nbd->config_lock);
		if (refcount_inc_not_zero(&nbd->config_refs)) {
			mutex_unlock(&nbd->config_lock);
			goto out;
		}
		ret = nbd_alloc_and_init_config(nbd);
		if (ret) {
			mutex_unlock(&nbd->config_lock);
			goto out;
		}

		refcount_inc(&nbd->refs);
		mutex_unlock(&nbd->config_lock);
		if (max_part)
			set_bit(GD_NEED_PART_SCAN, &disk->state);
	} else if (nbd_disconnected(config)) {
		if (max_part)
			set_bit(GD_NEED_PART_SCAN, &disk->state);
	}
out:
	mutex_unlock(&nbd_index_mutex);
	return ret;
}

static void nbd_release(struct gendisk *disk)
{
	struct nbd_device *nbd = disk->private_data;

	if (test_bit(NBD_RT_DISCONNECT_ON_CLOSE, &nbd->config->runtime_flags) &&
			disk_openers(disk) == 0)
		nbd_disconnect_and_put(nbd);

	nbd_config_put(nbd);
	nbd_put(nbd);
}

static void nbd_free_disk(struct gendisk *disk)
{
	struct nbd_device *nbd = disk->private_data;

	kfree(nbd);
}

static const struct block_device_operations nbd_fops =
{
	.owner =	THIS_MODULE,
	.open =		nbd_open,
	.release =	nbd_release,
	.ioctl =	nbd_ioctl,
	.compat_ioctl =	nbd_ioctl,
	.free_disk =	nbd_free_disk,
};

#if IS_ENABLED(CONFIG_DEBUG_FS)

static int nbd_dbg_tasks_show(struct seq_file *s, void *unused)
{
	struct nbd_device *nbd = s->private;

	if (nbd->pid)
		seq_printf(s, "recv: %d\n", nbd->pid);

	return 0;
}

DEFINE_SHOW_ATTRIBUTE(nbd_dbg_tasks);

static int nbd_dbg_flags_show(struct seq_file *s, void *unused)
{
	struct nbd_device *nbd = s->private;
	u32 flags = nbd->config->flags;

	seq_printf(s, "Hex: 0x%08x\n\n", flags);

	seq_puts(s, "Known flags:\n");

	if (flags & NBD_FLAG_HAS_FLAGS)
		seq_puts(s, "NBD_FLAG_HAS_FLAGS\n");
	if (flags & NBD_FLAG_READ_ONLY)
		seq_puts(s, "NBD_FLAG_READ_ONLY\n");
	if (flags & NBD_FLAG_SEND_FLUSH)
		seq_puts(s, "NBD_FLAG_SEND_FLUSH\n");
	if (flags & NBD_FLAG_SEND_FUA)
		seq_puts(s, "NBD_FLAG_SEND_FUA\n");
	if (flags & NBD_FLAG_SEND_TRIM)
		seq_puts(s, "NBD_FLAG_SEND_TRIM\n");
	if (flags & NBD_FLAG_SEND_WRITE_ZEROES)
		seq_puts(s, "NBD_FLAG_SEND_WRITE_ZEROES\n");
	if (flags & NBD_FLAG_ROTATIONAL)
		seq_puts(s, "NBD_FLAG_ROTATIONAL\n");

	return 0;
}

DEFINE_SHOW_ATTRIBUTE(nbd_dbg_flags);

static int nbd_dev_dbg_init(struct nbd_device *nbd)
{
	struct dentry *dir;
	struct nbd_config *config = nbd->config;

	if (!nbd_dbg_dir)
		return -EIO;

	dir = debugfs_create_dir(nbd_name(nbd), nbd_dbg_dir);
	if (IS_ERR(dir)) {
		dev_err(nbd_to_dev(nbd), "Failed to create debugfs dir for '%s'\n",
			nbd_name(nbd));
		return -EIO;
	}
	config->dbg_dir = dir;

	debugfs_create_file("tasks", 0444, dir, nbd, &nbd_dbg_tasks_fops);
	debugfs_create_u64("size_bytes", 0444, dir, &config->bytesize);
	debugfs_create_u32("timeout", 0444, dir, &nbd->tag_set.timeout);
	debugfs_create_u32("blocksize_bits", 0444, dir, &config->blksize_bits);
	debugfs_create_file("flags", 0444, dir, nbd, &nbd_dbg_flags_fops);

	return 0;
}

static void nbd_dev_dbg_close(struct nbd_device *nbd)
{
	debugfs_remove_recursive(nbd->config->dbg_dir);
}

static int nbd_dbg_init(void)
{
	struct dentry *dbg_dir;

	dbg_dir = debugfs_create_dir("nbd", NULL);
	if (IS_ERR(dbg_dir))
		return -EIO;

	nbd_dbg_dir = dbg_dir;

	return 0;
}

static void nbd_dbg_close(void)
{
	debugfs_remove_recursive(nbd_dbg_dir);
}

#else  /* IS_ENABLED(CONFIG_DEBUG_FS) */

static int nbd_dev_dbg_init(struct nbd_device *nbd)
{
	return 0;
}

static void nbd_dev_dbg_close(struct nbd_device *nbd)
{
}

static int nbd_dbg_init(void)
{
	return 0;
}

static void nbd_dbg_close(void)
{
}

#endif

static int nbd_init_request(struct blk_mq_tag_set *set, struct request *rq,
			    unsigned int hctx_idx, unsigned int numa_node)
{
	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(rq);
	cmd->nbd = set->driver_data;
	cmd->flags = 0;
	mutex_init(&cmd->lock);
	return 0;
}

static const struct blk_mq_ops nbd_mq_ops = {
	.queue_rq	= nbd_queue_rq,
	.complete	= nbd_complete_rq,
	.init_request	= nbd_init_request,
	.timeout	= nbd_xmit_timeout,
};

static struct nbd_device *nbd_dev_add(int index, unsigned int refs)
{
	struct queue_limits lim = {
		.max_hw_sectors		= 65536,
		.io_opt			= 256 << SECTOR_SHIFT,
		.max_segments		= USHRT_MAX,
		.max_segment_size	= UINT_MAX,
	};
	struct nbd_device *nbd;
	struct gendisk *disk;
	int err = -ENOMEM;

	nbd = kzalloc_obj(struct nbd_device);
	if (!nbd)
		goto out;

	nbd->tag_set.ops = &nbd_mq_ops;
	nbd->tag_set.nr_hw_queues = 1;
	nbd->tag_set.queue_depth = 128;
	nbd->tag_set.numa_node = NUMA_NO_NODE;
	nbd->tag_set.cmd_size = sizeof(struct nbd_cmd);
	nbd->tag_set.flags = BLK_MQ_F_BLOCKING;
	nbd->tag_set.driver_data = nbd;
	INIT_WORK(&nbd->remove_work, nbd_dev_remove_work);
	nbd->backend = NULL;

	err = blk_mq_alloc_tag_set(&nbd->tag_set);
	if (err)
		goto out_free_nbd;

	mutex_lock(&nbd_index_mutex);
	if (index >= 0) {
		err = idr_alloc(&nbd_index_idr, nbd, index, index + 1,
				GFP_KERNEL);
		if (err == -ENOSPC)
			err = -EEXIST;
	} else {
		err = idr_alloc(&nbd_index_idr, nbd, 0,
				(MINORMASK >> part_shift) + 1, GFP_KERNEL);
		if (err >= 0)
			index = err;
	}
	nbd->index = index;
	mutex_unlock(&nbd_index_mutex);
	if (err < 0)
		goto out_free_tags;

	disk = blk_mq_alloc_disk(&nbd->tag_set, &lim, NULL);
	if (IS_ERR(disk)) {
		err = PTR_ERR(disk);
		goto out_free_idr;
	}
	nbd->disk = disk;

	nbd->recv_workq = alloc_workqueue("nbd%d-recv",
					  WQ_MEM_RECLAIM | WQ_HIGHPRI |
					  WQ_UNBOUND, 0, nbd->index);
	if (!nbd->recv_workq) {
		dev_err(disk_to_dev(nbd->disk), "Could not allocate knbd recv work queue.\n");
		err = -ENOMEM;
		goto out_err_disk;
	}

	mutex_init(&nbd->config_lock);
	refcount_set(&nbd->config_refs, 0);
	/*
	 * Start out with a zero references to keep other threads from using
	 * this device until it is fully initialized.
	 */
	refcount_set(&nbd->refs, 0);
	INIT_LIST_HEAD(&nbd->list);
	disk->major = NBD_MAJOR;
	disk->first_minor = index << part_shift;
	disk->minors = 1 << part_shift;
	disk->fops = &nbd_fops;
	disk->private_data = nbd;
	sprintf(disk->disk_name, "nbd%d", index);
	err = add_disk(disk);
	if (err)
		goto out_free_work;

	/*
	 * Now publish the device.
	 */
	refcount_set(&nbd->refs, refs);
	nbd_total_devices++;
	return nbd;

out_free_work:
	destroy_workqueue(nbd->recv_workq);
out_err_disk:
	put_disk(disk);
out_free_idr:
	mutex_lock(&nbd_index_mutex);
	idr_remove(&nbd_index_idr, index);
	mutex_unlock(&nbd_index_mutex);
out_free_tags:
	blk_mq_free_tag_set(&nbd->tag_set);
out_free_nbd:
	kfree(nbd);
out:
	return ERR_PTR(err);
}

static struct nbd_device *nbd_find_get_unused(void)
{
	struct nbd_device *nbd;
	int id;

	lockdep_assert_held(&nbd_index_mutex);

	idr_for_each_entry(&nbd_index_idr, nbd, id) {
		if (refcount_read(&nbd->config_refs) ||
		    test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags))
			continue;
		if (refcount_inc_not_zero(&nbd->refs))
			return nbd;
	}

	return NULL;
}

/* Netlink interface. */
static const struct nla_policy nbd_attr_policy[NBD_ATTR_MAX + 1] = {
	[NBD_ATTR_INDEX]		=	{ .type = NLA_U32 },
	[NBD_ATTR_SIZE_BYTES]		=	{ .type = NLA_U64 },
	[NBD_ATTR_BLOCK_SIZE_BYTES]	=	{ .type = NLA_U64 },
	[NBD_ATTR_TIMEOUT]		=	{ .type = NLA_U64 },
	[NBD_ATTR_SERVER_FLAGS]		=	{ .type = NLA_U64 },
	[NBD_ATTR_CLIENT_FLAGS]		=	{ .type = NLA_U64 },
	[NBD_ATTR_SOCKETS]		=	{ .type = NLA_NESTED},
	[NBD_ATTR_DEAD_CONN_TIMEOUT]	=	{ .type = NLA_U64 },
	[NBD_ATTR_DEVICE_LIST]		=	{ .type = NLA_NESTED},
	[NBD_ATTR_BACKEND_IDENTIFIER]	=	{ .type = NLA_STRING},
};

static const struct nla_policy nbd_sock_policy[NBD_SOCK_MAX + 1] = {
	[NBD_SOCK_FD]			=	{ .type = NLA_U32 },
};

/* We don't use this right now since we don't parse the incoming list, but we
 * still want it here so userspace knows what to expect.
 */
static const struct nla_policy __attribute__((unused))
nbd_device_policy[NBD_DEVICE_ATTR_MAX + 1] = {
	[NBD_DEVICE_INDEX]		=	{ .type = NLA_U32 },
	[NBD_DEVICE_CONNECTED]		=	{ .type = NLA_U8 },
};

static int nbd_genl_size_set(struct genl_info *info, struct nbd_device *nbd)
{
	struct nbd_config *config = nbd->config;
	u64 bsize = nbd_blksize(config);
	u64 bytes = config->bytesize;

	if (info->attrs[NBD_ATTR_SIZE_BYTES])
		bytes = nla_get_u64(info->attrs[NBD_ATTR_SIZE_BYTES]);

	if (info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES])
		bsize = nla_get_u64(info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES]);

	if (bytes != config->bytesize || bsize != nbd_blksize(config))
		return nbd_set_size(nbd, bytes, bsize);
	return 0;
}

static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
{
	struct nbd_device *nbd;
	struct nbd_config *config;
	int index = -1;
	int ret;
	bool put_dev = false;

	if (!netlink_capable(skb, CAP_SYS_ADMIN))
		return -EPERM;

	if (info->attrs[NBD_ATTR_INDEX]) {
		index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);

		/*
		 * Too big first_minor can cause duplicate creation of
		 * sysfs files/links, since index << part_shift might overflow, or
		 * MKDEV() expect that the max bits of first_minor is 20.
		 */
		if (index < 0 || index > MINORMASK >> part_shift) {
			pr_err("illegal input index %d\n", index);
			return -EINVAL;
		}
	}
	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SOCKETS)) {
		pr_err("must specify at least one socket\n");
		return -EINVAL;
	}
	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SIZE_BYTES)) {
		pr_err("must specify a size in bytes for the device\n");
		return -EINVAL;
	}
again:
	mutex_lock(&nbd_index_mutex);
	if (index == -1) {
		nbd = nbd_find_get_unused();
	} else {
		nbd = idr_find(&nbd_index_idr, index);
		if (nbd) {
			if ((test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags) &&
			     test_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags)) ||
			    !refcount_inc_not_zero(&nbd->refs)) {
				mutex_unlock(&nbd_index_mutex);
				pr_err("device at index %d is going down\n",
					index);
				return -EINVAL;
			}
		}
	}
	mutex_unlock(&nbd_index_mutex);

	if (!nbd) {
		nbd = nbd_dev_add(index, 2);
		if (IS_ERR(nbd)) {
			pr_err("failed to add new device\n");
			return PTR_ERR(nbd);
		}
	}

	mutex_lock(&nbd->config_lock);
	if (refcount_read(&nbd->config_refs)) {
		mutex_unlock(&nbd->config_lock);
		nbd_put(nbd);
		if (index == -1)
			goto again;
		pr_err("nbd%d already in use\n", index);
		return -EBUSY;
	}

	ret = nbd_alloc_and_init_config(nbd);
	if (ret) {
		mutex_unlock(&nbd->config_lock);
		nbd_put(nbd);
		pr_err("couldn't allocate config\n");
		return ret;
	}

	config = nbd->config;
	set_bit(NBD_RT_BOUND, &config->runtime_flags);
	ret = nbd_genl_size_set(info, nbd);
	if (ret)
		goto out;

	if (info->attrs[NBD_ATTR_TIMEOUT])
		nbd_set_cmd_timeout(nbd,
				    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
	if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
		config->dead_conn_timeout =
			nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
		config->dead_conn_timeout *= HZ;
	}
	if (info->attrs[NBD_ATTR_SERVER_FLAGS])
		config->flags =
			nla_get_u64(info->attrs[NBD_ATTR_SERVER_FLAGS]);
	if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
		u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
		if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
			/*
			 * We have 1 ref to keep the device around, and then 1
			 * ref for our current operation here, which will be
			 * inherited by the config.  If we already have
			 * DESTROY_ON_DISCONNECT set then we know we don't have
			 * that extra ref already held so we don't need the
			 * put_dev.
			 */
			if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
					      &nbd->flags))
				put_dev = true;
		} else {
			if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
					       &nbd->flags))
				refcount_inc(&nbd->refs);
		}
		if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
			set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
				&config->runtime_flags);
		}
	}

	if (info->attrs[NBD_ATTR_SOCKETS]) {
		struct nlattr *attr;
		int rem, fd;

		nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
				    rem) {
			struct nlattr *socks[NBD_SOCK_MAX+1];

			if (nla_type(attr) != NBD_SOCK_ITEM) {
				pr_err("socks must be embedded in a SOCK_ITEM attr\n");
				ret = -EINVAL;
				goto out;
			}
			ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
							  attr,
							  nbd_sock_policy,
							  info->extack);
			if (ret != 0) {
				pr_err("error processing sock list\n");
				ret = -EINVAL;
				goto out;
			}
			if (!socks[NBD_SOCK_FD])
				continue;
			fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
			ret = nbd_add_socket(nbd, fd, true);
			if (ret)
				goto out;
		}
	}

	if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
		nbd->backend = nla_strdup(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
					  GFP_KERNEL);
		if (!nbd->backend) {
			ret = -ENOMEM;
			goto out;
		}
	}
	ret = device_create_file(disk_to_dev(nbd->disk), &backend_attr);
	if (ret) {
		dev_err(disk_to_dev(nbd->disk),
			"device_create_file failed for backend!\n");
		goto out;
	}
	set_bit(NBD_RT_HAS_BACKEND_FILE, &config->runtime_flags);

	ret = nbd_start_device(nbd);
out:
	if (!ret) {
		set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);
		refcount_inc(&nbd->config_refs);
		nbd_connect_reply(info, nbd->index);
	}
	mutex_unlock(&nbd->config_lock);

	nbd_config_put(nbd);
	if (put_dev)
		nbd_put(nbd);
	return ret;
}

static void nbd_disconnect_and_put(struct nbd_device *nbd)
{
	mutex_lock(&nbd->config_lock);
	nbd_disconnect(nbd);
	sock_shutdown(nbd);
	wake_up(&nbd->config->conn_wait);
	/*
	 * Make sure recv thread has finished, we can safely call nbd_clear_que()
	 * to cancel the inflight I/Os.
	 */
	flush_workqueue(nbd->recv_workq);
	nbd_clear_que(nbd);
	nbd->task_setup = NULL;
	clear_bit(NBD_RT_BOUND, &nbd->config->runtime_flags);
	mutex_unlock(&nbd->config_lock);

	if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF,
			       &nbd->config->runtime_flags))
		nbd_config_put(nbd);
}

static int nbd_genl_disconnect(struct sk_buff *skb, struct genl_info *info)
{
	struct nbd_device *nbd;
	int index;

	if (!netlink_capable(skb, CAP_SYS_ADMIN))
		return -EPERM;

	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)) {
		pr_err("must specify an index to disconnect\n");
		return -EINVAL;
	}
	index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
	mutex_lock(&nbd_index_mutex);
	nbd = idr_find(&nbd_index_idr, index);
	if (!nbd) {
		mutex_unlock(&nbd_index_mutex);
		pr_err("couldn't find device at index %d\n", index);
		return -EINVAL;
	}
	if (!refcount_inc_not_zero(&nbd->refs)) {
		mutex_unlock(&nbd_index_mutex);
		pr_err("device at index %d is going down\n", index);
		return -EINVAL;
	}
	mutex_unlock(&nbd_index_mutex);
	if (!refcount_inc_not_zero(&nbd->config_refs))
		goto put_nbd;
	nbd_disconnect_and_put(nbd);
	nbd_config_put(nbd);
put_nbd:
	nbd_put(nbd);
	return 0;
}

static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
{
	struct nbd_device *nbd = NULL;
	struct nbd_config *config;
	int index;
	int ret = 0;
	bool put_dev = false;

	if (!netlink_capable(skb, CAP_SYS_ADMIN))
		return -EPERM;

	if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)) {
		pr_err("must specify a device to reconfigure\n");
		return -EINVAL;
	}
	index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
	mutex_lock(&nbd_index_mutex);
	nbd = idr_find(&nbd_index_idr, index);
	if (!nbd) {
		mutex_unlock(&nbd_index_mutex);
		pr_err("couldn't find a device at index %d\n", index);
		return -EINVAL;
	}
	if (nbd->backend) {
		if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
			if (nla_strcmp(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
				       nbd->backend)) {
				mutex_unlock(&nbd_index_mutex);
				dev_err(nbd_to_dev(nbd),
					"backend image doesn't match with %s\n",
					nbd->backend);
				return -EINVAL;
			}
		} else {
			mutex_unlock(&nbd_index_mutex);
			dev_err(nbd_to_dev(nbd), "must specify backend\n");
			return -EINVAL;
		}
	}
	if (!refcount_inc_not_zero(&nbd->refs)) {
		mutex_unlock(&nbd_index_mutex);
		pr_err("device at index %d is going down\n", index);
		return -EINVAL;
	}
	mutex_unlock(&nbd_index_mutex);

	config = nbd_get_config_unlocked(nbd);
	if (!config) {
		dev_err(nbd_to_dev(nbd),
			"not configured, cannot reconfigure\n");
		nbd_put(nbd);
		return -EINVAL;
	}

	mutex_lock(&nbd->config_lock);
	if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
	    !nbd->pid) {
		dev_err(nbd_to_dev(nbd),
			"not configured, cannot reconfigure\n");
		ret = -EINVAL;
		goto out;
	}

	ret = nbd_genl_size_set(info, nbd);
	if (ret)
		goto out;

	if (info->attrs[NBD_ATTR_TIMEOUT])
		nbd_set_cmd_timeout(nbd,
				    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
	if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
		config->dead_conn_timeout =
			nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
		config->dead_conn_timeout *= HZ;
	}
	if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
		u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
		if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
			if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
					      &nbd->flags))
				put_dev = true;
		} else {
			if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
					       &nbd->flags))
				refcount_inc(&nbd->refs);
		}

		if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
			set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
					&config->runtime_flags);
		} else {
			clear_bit(NBD_RT_DISCONNECT_ON_CLOSE,
					&config->runtime_flags);
		}
	}

	if (info->attrs[NBD_ATTR_SOCKETS]) {
		struct nlattr *attr;
		int rem, fd;

		nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
				    rem) {
			struct nlattr *socks[NBD_SOCK_MAX+1];

			if (nla_type(attr) != NBD_SOCK_ITEM) {
				pr_err("socks must be embedded in a SOCK_ITEM attr\n");
				ret = -EINVAL;
				goto out;
			}
			ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
							  attr,
							  nbd_sock_policy,
							  info->extack);
			if (ret != 0) {
				pr_err("error processing sock list\n");
				ret = -EINVAL;
				goto out;
			}
			if (!socks[NBD_SOCK_FD])
				continue;
			fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
			ret = nbd_reconnect_socket(nbd, fd);
			if (ret) {
				if (ret == -ENOSPC)
					ret = 0;
				goto out;
			}
			dev_info(nbd_to_dev(nbd), "reconnected socket\n");
		}
	}
out:
	mutex_unlock(&nbd->config_lock);
	nbd_config_put(nbd);
	nbd_put(nbd);
	if (put_dev)
		nbd_put(nbd);
	return ret;
}

static const struct genl_small_ops nbd_connect_genl_ops[] = {
	{
		.cmd	= NBD_CMD_CONNECT,
		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
		.doit	= nbd_genl_connect,
	},
	{
		.cmd	= NBD_CMD_DISCONNECT,
		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
		.doit	= nbd_genl_disconnect,
	},
	{
		.cmd	= NBD_CMD_RECONFIGURE,
		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
		.doit	= nbd_genl_reconfigure,
	},
	{
		.cmd	= NBD_CMD_STATUS,
		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
		.doit	= nbd_genl_status,
	},
};

static const struct genl_multicast_group nbd_mcast_grps[] = {
	{ .name = NBD_GENL_MCAST_GROUP_NAME, },
};

static struct genl_family nbd_genl_family __ro_after_init = {
	.hdrsize	= 0,
	.name		= NBD_GENL_FAMILY_NAME,
	.version	= NBD_GENL_VERSION,
	.module		= THIS_MODULE,
	.small_ops	= nbd_connect_genl_ops,
	.n_small_ops	= ARRAY_SIZE(nbd_connect_genl_ops),
	.resv_start_op	= NBD_CMD_STATUS + 1,
	.maxattr	= NBD_ATTR_MAX,
	.netnsok	= 1,
	.policy = nbd_attr_policy,
	.mcgrps		= nbd_mcast_grps,
	.n_mcgrps	= ARRAY_SIZE(nbd_mcast_grps),
};
MODULE_ALIAS_GENL_FAMILY(NBD_GENL_FAMILY_NAME);

static int populate_nbd_status(struct nbd_device *nbd, struct sk_buff *reply)
{
	struct nlattr *dev_opt;
	u8 connected = 0;
	int ret;

	/* This is a little racey, but for status it's ok.  The
	 * reason we don't take a ref here is because we can't
	 * take a ref in the index == -1 case as we would need
	 * to put under the nbd_index_mutex, which could
	 * deadlock if we are configured to remove ourselves
	 * once we're disconnected.
	 */
	if (refcount_read(&nbd->config_refs))
		connected = 1;
	dev_opt = nla_nest_start_noflag(reply, NBD_DEVICE_ITEM);
	if (!dev_opt)
		return -EMSGSIZE;
	ret = nla_put_u32(reply, NBD_DEVICE_INDEX, nbd->index);
	if (ret)
		return -EMSGSIZE;
	ret = nla_put_u8(reply, NBD_DEVICE_CONNECTED,
			 connected);
	if (ret)
		return -EMSGSIZE;
	nla_nest_end(reply, dev_opt);
	return 0;
}

static int status_cb(int id, void *ptr, void *data)
{
	struct nbd_device *nbd = ptr;
	return populate_nbd_status(nbd, (struct sk_buff *)data);
}

static int nbd_genl_status(struct sk_buff *skb, struct genl_info *info)
{
	struct nlattr *dev_list;
	struct sk_buff *reply;
	void *reply_head;
	size_t msg_size;
	int index = -1;
	int ret = -ENOMEM;

	if (info->attrs[NBD_ATTR_INDEX])
		index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);

	mutex_lock(&nbd_index_mutex);

	msg_size = nla_total_size(nla_attr_size(sizeof(u32)) +
				  nla_attr_size(sizeof(u8)));
	msg_size *= (index == -1) ? nbd_total_devices : 1;

	reply = genlmsg_new(msg_size, GFP_KERNEL);
	if (!reply)
		goto out;
	reply_head = genlmsg_put_reply(reply, info, &nbd_genl_family, 0,
				       NBD_CMD_STATUS);
	if (!reply_head) {
		nlmsg_free(reply);
		goto out;
	}

	dev_list = nla_nest_start_noflag(reply, NBD_ATTR_DEVICE_LIST);
	if (!dev_list) {
		nlmsg_free(reply);
		ret = -EMSGSIZE;
		goto out;
	}

	if (index == -1) {
		ret = idr_for_each(&nbd_index_idr, &status_cb, reply);
		if (ret) {
			nlmsg_free(reply);
			goto out;
		}
	} else {
		struct nbd_device *nbd;
		nbd = idr_find(&nbd_index_idr, index);
		if (nbd) {
			ret = populate_nbd_status(nbd, reply);
			if (ret) {
				nlmsg_free(reply);
				goto out;
			}
		}
	}
	nla_nest_end(reply, dev_list);
	genlmsg_end(reply, reply_head);
	ret = genlmsg_reply(reply, info);
out:
	mutex_unlock(&nbd_index_mutex);
	return ret;
}

static void nbd_connect_reply(struct genl_info *info, int index)
{
	struct sk_buff *skb;
	void *msg_head;
	int ret;

	skb = genlmsg_new(nla_total_size(sizeof(u32)), GFP_KERNEL);
	if (!skb)
		return;
	msg_head = genlmsg_put_reply(skb, info, &nbd_genl_family, 0,
				     NBD_CMD_CONNECT);
	if (!msg_head) {
		nlmsg_free(skb);
		return;
	}
	ret = nla_put_u32(skb, NBD_ATTR_INDEX, index);
	if (ret) {
		nlmsg_free(skb);
		return;
	}
	genlmsg_end(skb, msg_head);
	genlmsg_reply(skb, info);
}

static void nbd_mcast_index(int index)
{
	struct sk_buff *skb;
	void *msg_head;
	int ret;

	skb = genlmsg_new(nla_total_size(sizeof(u32)), GFP_KERNEL);
	if (!skb)
		return;
	msg_head = genlmsg_put(skb, 0, 0, &nbd_genl_family, 0,
				     NBD_CMD_LINK_DEAD);
	if (!msg_head) {
		nlmsg_free(skb);
		return;
	}
	ret = nla_put_u32(skb, NBD_ATTR_INDEX, index);
	if (ret) {
		nlmsg_free(skb);
		return;
	}
	genlmsg_end(skb, msg_head);
	genlmsg_multicast(&nbd_genl_family, skb, 0, 0, GFP_KERNEL);
}

static void nbd_dead_link_work(struct work_struct *work)
{
	struct link_dead_args *args = container_of(work, struct link_dead_args,
						   work);
	nbd_mcast_index(args->index);
	kfree(args);
}

static int __init nbd_init(void)
{
	int i;

	BUILD_BUG_ON(sizeof(struct nbd_request) != 28);

	if (max_part < 0) {
		pr_err("max_part must be >= 0\n");
		return -EINVAL;
	}

	part_shift = 0;
	if (max_part > 0) {
		part_shift = fls(max_part);

		/*
		 * Adjust max_part according to part_shift as it is exported
		 * to user space so that user can know the max number of
		 * partition kernel should be able to manage.
		 *
		 * Note that -1 is required because partition 0 is reserved
		 * for the whole disk.
		 */
		max_part = (1UL << part_shift) - 1;
	}

	if ((1UL << part_shift) > DISK_MAX_PARTS)
		return -EINVAL;

	if (nbds_max > 1UL << (MINORBITS - part_shift))
		return -EINVAL;

	if (register_blkdev(NBD_MAJOR, "nbd"))
		return -EIO;

	nbd_del_wq = alloc_workqueue("nbd-del", WQ_UNBOUND, 0);
	if (!nbd_del_wq) {
		unregister_blkdev(NBD_MAJOR, "nbd");
		return -ENOMEM;
	}

	if (genl_register_family(&nbd_genl_family)) {
		destroy_workqueue(nbd_del_wq);
		unregister_blkdev(NBD_MAJOR, "nbd");
		return -EINVAL;
	}
	nbd_dbg_init();

	for (i = 0; i < nbds_max; i++)
		nbd_dev_add(i, 1);
	return 0;
}

static int nbd_exit_cb(int id, void *ptr, void *data)
{
	struct list_head *list = (struct list_head *)data;
	struct nbd_device *nbd = ptr;

	/* Skip nbd that is being removed asynchronously */
	if (refcount_read(&nbd->refs))
		list_add_tail(&nbd->list, list);

	return 0;
}

static void __exit nbd_cleanup(void)
{
	struct nbd_device *nbd;
	LIST_HEAD(del_list);

	/*
	 * Unregister netlink interface prior to waiting
	 * for the completion of netlink commands.
	 */
	genl_unregister_family(&nbd_genl_family);

	nbd_dbg_close();

	mutex_lock(&nbd_index_mutex);
	idr_for_each(&nbd_index_idr, &nbd_exit_cb, &del_list);
	mutex_unlock(&nbd_index_mutex);

	while (!list_empty(&del_list)) {
		nbd = list_first_entry(&del_list, struct nbd_device, list);
		list_del_init(&nbd->list);
		if (refcount_read(&nbd->config_refs))
			pr_err("possibly leaking nbd_config (ref %d)\n",
					refcount_read(&nbd->config_refs));
		if (refcount_read(&nbd->refs) != 1)
			pr_err("possibly leaking a device\n");
		nbd_put(nbd);
	}

	/* Also wait for nbd_dev_remove_work() completes */
	destroy_workqueue(nbd_del_wq);

	idr_destroy(&nbd_index_idr);
	unregister_blkdev(NBD_MAJOR, "nbd");
}

module_init(nbd_init);
module_exit(nbd_cleanup);

MODULE_DESCRIPTION("Network Block Device");
MODULE_LICENSE("GPL");

module_param(nbds_max, int, 0444);
MODULE_PARM_DESC(nbds_max, "number of network block devices to initialize (default: 16)");
module_param(max_part, int, 0444);
MODULE_PARM_DESC(max_part, "number of partitions per device (default: 16)");
]

gemini-3-flash-preview

							input: 59036
							output: 40
							thoughts: 2494
						

**Analysis of the NBD Code with Duplicate Sockets**

Okay, here's my breakdown of this NBD code situation.  I've been reviewing this, and here are my conclusions.

First, I see the issue.  When `nbd_genl_connect` is fed the same file descriptor (FD) twice, the code diligently calls `nbd_add_socket` twice, leading to some, shall we say, *interesting* behavior. `nbd_add_socket` then uses `sockfd_lookup`, which increments the reference count of the socket's associated `struct file`. This is called twice, and thus the refcount is incremented twice.

This creates *two* `nbd_sock` structures, but both point to the *same* `struct socket`.  This is the first area of concern. When `nbd_start_device` is triggered it starts threads that will call `nbd_read_reply` on this single shared socket.

The core problem, from my perspective, is the stream corruption. With multiple threads reading from the same TCP stream, they're going to step on each other's toes.  Data will get interleaved, magic numbers will be wrong, and the NBD protocol will get completely messed up.  When errors are hit, `nbd_mark_nsock_dead` gets called. This then does the *safe* thing by shutting down the socket, but the core issue of data being read out of order on a single socket is the root cause. It also correctly decrements `config->live_connections`.

The cleanup in `nbd_config_put` is fine. `sockfd_put` is called twice, but that's perfectly acceptable since `sockfd_lookup` was called twice, keeping the refcount in sync with what the kernel expects.

The `sk_set_memalloc` function's got my attention, as does the `static_branch_inc` call.  The NBD driver, as it's written now, never calls `sk_clear_memalloc`, which means that it won't actually be balanced. Thus the `memalloc_socks_key` counter will leak. This is a general bug in NBD (not just this scenario) and can be exacerbated by duplicate FDs. While this is a bug, it likely doesn't lead to panic or deadlock, but might have some performance implications on the networking stack (although this is relatively minor).

The `nsock->tx_lock` mutexes are different, but the code isn't protecting access to the *socket* itself with one, so two threads can simultaneously use `sock_sendmsg` on the *same* socket. This creates outgoing stream corruption.

**So, the likely outcomes?:**

*   **Panic**: Unlikely. The TCP stack and NBD driver handle protocol errors.
*   **Deadlock**: Also, unlikely. The locks involved seem to be handled in a way that avoids deadlock, even with duplicate sockets.
*   **Bug**: *Absolutely*. The lack of checking for duplicate sockets leads to the real problem: stream corruption on both incoming *and* outgoing streams. The `memalloc_socks_key` leak is a bug as well.

I checked for the situation where `sockfd_put` is called on a freed socket: no, that's not possible with this current logic. Even if the user closes the FD in userspace, the kernel keeps the `struct file` (and thus the `struct socket`) alive until all references are dropped. The same goes for the other case where the socket is reconnected with the same FD.

I also checked to see how NBD handles the replies. Even if the replies come in out of order, the current `blk_mq_complete_request` logic seems fine. The `nbd_handle_reply` function is built in a way to handle this.

The crucial issue is the interleaving of reads for the *same* reply. Thread A reads part of a reply, Thread B reads the rest. That leads to garbled reads and the connection shutting down.

The call to `sockfd_put` and the `kfree` of the configuration are all safe, as the code as written correctly handles these references.

I looked at the `work_struct` in `nsock`. I can confirm each `nsock` has its own `work_struct`, which is fine.

I also looked at how each `nbd_cmd` is handled. If the data gets corrupted, it *might* find the wrong NBD command, but I see protections for that to prevent it from failing as well.

I confirmed that `nbd_add_socket` and `nbd_start_device` are synchronized using `nbd->config_lock`.

As a final note, I also checked

map[ContextFile:net/core/sock.c IncludeLines:true Name:sk_destruct]

map[SourceCode:2402:	void sk_destruct(struct sock *sk)
2403:	{
2404:		bool use_call_rcu = sock_flag(sk, SOCK_RCU_FREE);
2405:	
2406:		if (rcu_access_pointer(sk->sk_reuseport_cb)) {
2407:			reuseport_detach_sock(sk);
2408:			use_call_rcu = true;
2409:		}
2410:	
2411:		if (use_call_rcu)
2412:			call_rcu(&sk->sk_rcu, __sk_destruct);
2413:		else
2414:			__sk_destruct(&sk->sk_rcu);
2415:	}
 SourceFile:net/core/sock.c]

gemini-3-flash-preview

							input: 62836
							output: 41
							thoughts: 8
						

Okay, here's the summary, rendered as your thoughts as an expert:

**Understanding `__sk_destruct` and its Role**

Alright, let's break this down. When I see `__sk_destruct`, my mind immediately goes to the heart of resource management, especially within a kernel or operating system context. It's a clear signal that we're dealing with something related to deallocation, cleanup, or finalization of a specific data structure or object. The double underscore prefix is a key indicator to me that this function is likely an internal, implementation-specific detail. I wouldn't expect to be calling this directly in user space; it's the kind of function that the kernel or a specific driver calls to handle the intricacies of object lifecycle.

My initial hypothesis is that this likely relates to the deallocation of some structure tied to sockets or networking. The `sk` prefix, combined with `destruct`, strongly suggests a "socket" object is the subject. It is likely called during the deallocation of a socket, or on the destruction of an object with ties to network resources.

I'm starting to think about potential scenarios: garbage collection? Reference counting? Automatic Memory Management? Probably not any of those as the design of a kernel is likely manual. The key to the process will be freeing up network buffers, closing file descriptors, decrementing reference counts, and ensuring that no lingering resources cause memory leaks or other issues. Given the naming, `__sk_destruct` could be associated with freeing the memory of a socket.

The challenge is usually atomicity. If this function is part of a multi-threaded system, I need to consider synchronization. Ensuring that cleanup happens in the correct order, that there are no race conditions, is absolutely paramount to avoid corruption or dangling pointers. I'd be looking closely at any locking mechanisms involved to ensure it's thread-safe and can handle concurrent access correctly. I'd also be curious about the handling of potential errors. Does it return an error code? Log warnings? Panic? The error handling strategy is crucial to understanding the robustness of the system.

Ultimately, I'd expect `__sk_destruct` to be a critical piece of code ensuring the stability and reliability of the networking subsystem. This function is likely part of the low-level infrastructure, and requires meticulous analysis.

map[ContextFile:net/core/sock.c IncludeLines:true Name:__sk_destruct]

map[SourceCode:2342:	/* Sockets having SOCK_RCU_FREE will call this function after one RCU
2343:	 * grace period. This is the case for UDP sockets and TCP listeners.
2344:	 */
2345:	static void __sk_destruct(struct rcu_head *head)
2346:	{
2347:		struct sock *sk = container_of(head, struct sock, sk_rcu);
2348:		struct net *net = sock_net(sk);
2349:		struct sk_filter *filter;
2350:	
2351:		if (sk->sk_destruct)
2352:			sk->sk_destruct(sk);
2353:	
2354:		filter = rcu_dereference_check(sk->sk_filter,
2355:					       refcount_read(&sk->sk_wmem_alloc) == 0);
2356:		if (filter) {
2357:			sk_filter_uncharge(sk, filter);
2358:			RCU_INIT_POINTER(sk->sk_filter, NULL);
2359:		}
2360:	
2361:		sock_disable_timestamp(sk, SK_FLAGS_TIMESTAMP);
2362:	
2363:	#ifdef CONFIG_BPF_SYSCALL
2364:		bpf_sk_storage_free(sk);
2365:	#endif
2366:	
2367:		if (atomic_read(&sk->sk_omem_alloc))
2368:			pr_debug("%s: optmem leakage (%d bytes) detected\n",
2369:				 __func__, atomic_read(&sk->sk_omem_alloc));
2370:	
2371:		if (sk->sk_frag.page) {
2372:			put_page(sk->sk_frag.page);
2373:			sk->sk_frag.page = NULL;
2374:		}
2375:	
2376:		/* We do not need to acquire sk->sk_peer_lock, we are the last user. */
2377:		put_cred(sk->sk_peer_cred);
2378:		put_pid(sk->sk_peer_pid);
2379:	
2380:		if (likely(sk->sk_net_refcnt)) {
2381:			put_net_track(net, &sk->ns_tracker);
2382:		} else {
2383:			__netns_tracker_free(net, &sk->ns_tracker, false);
2384:			net_passive_dec(net);
2385:		}
2386:		sk_prot_free(sk->sk_prot_creator, sk);
2387:	}
 SourceFile:net/core/sock.c]

gemini-3-flash-preview

							input: 64142
							output: 42
							thoughts: 74
						

Okay, here's my interpretation of this debugging thought process, tailored for an expert like myself:

**Tracing Memory Allocation/Deallocation in Sockets**

Alright, I'm diving into the socket destruction path, specifically `__sk_destruct`. I was expecting to see the clean up of memory allocation here, but I'm not spotting either `sk_clear_memalloc` or any use of `static_branch_dec(&memalloc_socks_key)` within this function. That's a bit of a red flag; if `sk_set_memalloc` is indeed incrementing some kind of global counter to track socket memory allocation, then *something* absolutely has to decrement it to maintain integrity. I need to figure out where that counterpart lives. Time to revisit `sk_clear_memalloc` and make sure I haven't missed something fundamental. I need to understand the mechanism behind the accounting, or I'm headed for a memory leak.

map[ContextFile:net/core/sock.c IncludeLines:true Name:sk_clear_memalloc]

map[SourceCode: 310:	void sk_clear_memalloc(struct sock *sk)
 311:	{
 312:		sock_reset_flag(sk, SOCK_MEMALLOC);
 313:		sk->sk_allocation &= ~__GFP_MEMALLOC;
 314:		static_branch_dec(&memalloc_socks_key);
 315:	
 316:		/*
 317:		 * SOCK_MEMALLOC is allowed to ignore rmem limits to ensure forward
 318:		 * progress of swapping. SOCK_MEMALLOC may be cleared while
 319:		 * it has rmem allocations due to the last swapfile being deactivated
 320:		 * but there is a risk that the socket is unusable due to exceeding
 321:		 * the rmem limits. Reclaim the reserves and obey rmem limits again.
 322:		 */
 323:		sk_mem_reclaim(sk);
 324:	}
 SourceFile:net/core/sock.c]

gemini-3-flash-preview

							input: 64734
							output: 20
							thoughts: 132
						

Here's my analysis of the situation:

**Investigating a Potential Memory Leak in the NBD Driver**

Okay, so I'm thinking about this `sk_clear_memalloc` function and how it relates to the NBD driver. I can see that `sk_clear_memalloc` definitely *decrements* something related to memory allocation. My immediate concern is this: if NBD calls `sk_set_memalloc` but *never* calls `sk_clear_memalloc`, then we've got a clear static branch leak. That's a definite bug in the NBD implementation. And if someone provides the same file descriptor twice... boom, we're leaking it twice.

But hold on, the user's initial question was about panic or deadlock, not a simple memory leak. Leaking a static branch is a problem, no doubt, but that alone shouldn't trigger a crash or hang the system.

Okay, let me backtrack and try another angle. I'm going to look through the git logs for commits related to "nbd sk_set_memalloc". There could be a relevant fix or a clue to some related issue I haven't considered. I'm going to search with that search term, and see what comes up.

map[Dir:Documentation/]

map[Files:<nil> Subdirs:[ABI PCI RCU accel accounting admin-guide arch block bpf cdrom core-api cpu-freq crypto dev-tools devicetree doc-guide driver-api edac fault-injection fb features filesystems firmware-guide firmware_class fpga gpu hid hwmon i2c iio images infiniband input kbuild kernel-hacking leds litmus-tests livepatch locking maintainer mhi misc-devices mm netlabel netlink networking nvdimm nvme pcmcia peci power process rust scheduler scsi security sound sphinx sphinx-includes sphinx-static spi staging sunrpc target tee timers tools trace translations usb userspace-api virt w1 watchdog wmi]]

gemini-3-flash-preview

							input: 65537
							output: 24
							thoughts: 25
						

Okay, here's my take on those thoughts, tailored for an expert audience:

**Tracing the Genesis of `sk_set_memalloc` in `nbd.c`**

Alright, let's get down to brass tacks. I need to pinpoint when `sk_set_memalloc` was introduced within the `nbd.c` codebase. Given the importance of memory allocation within a driver like NBD, I figure understanding its introduction is key to grasping its intended use and any potential evolution in that area. I'll fire up my trusty search tool—likely `git log -S sk_set_memalloc nbd.c` or something similar, depending on the repo structure—and let it chew on that query. The goal is a quick and dirty find of the commit that birthed this function. From there, I can examine the surrounding code, the commit message, any related issues or discussions linked to that commit, and so on. Understanding the context of its addition will shed light on why it was implemented the way it was, and give me a foundation for further investigation of any subtle issues or improvements.

map[Name:sk_set_memalloc]

map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nbd_reconnect_socket SourceFile:drivers/block/nbd.c SourceLine:1342] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nbd_start_device SourceFile:drivers/block/nbd.c SourceLine:1528] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nvme_tcp_alloc_queue SourceFile:drivers/nvme/host/tcp.c SourceLine:1849] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:set_sock_opts SourceFile:drivers/net/wireguard/socket.c SourceLine:345]] TruncatedOutput:false]

gemini-3-flash-preview

							input: 66054
							output: 780
							thoughts: 1754
						

**My Analysis of the NBD Driver Issue**

Okay, so the user is asking about potential bugs, kernel panics, or deadlocks in the NBD driver, specifically focusing on a scenario where `sockfd_put` is called twice on the same socket, as a consequence of the duplicate file descriptor issue. I've done a thorough review.

First, I examined `drivers/block/nbd.c` and specifically focused on the relevant code paths, inferring behavior since I can't directly use `git blame` or `git log`. My analysis is:

1.  **The Root Bug:** The fundamental issue lies in `nbd_genl_connect`. It *doesn't* check for duplicate file descriptors within the `NBD_ATTR_SOCKETS` attribute. This allows a user to provide the same socket file descriptor multiple times.
2.  **Protocol Corruption:** This duplication leads to multiple `nsock` structures being created, *all* pointing to the same socket (`sock`). Crucially, each `nsock` gets its own `tx_lock`.  The result is that *multiple threads* can simultaneously write to the same socket, corrupting the NBD data stream, leading to unpredictable behavior.
3.  **Reference Counting (Correct):** The fact that `sockfd_put` *is* called twice (in the scenario the user pointed out) is actually *correct* from a reference counting perspective.  It's a *symptom* of the underlying bug. The code in `nbd_genl_connect` does a `sockfd_lookup` twice, and therefore `sockfd_put` must be called twice.
4.  **Panic/Deadlock (Unlikely):** While the protocol corruption is serious, a kernel panic or deadlock is *unlikely* to occur directly. The stream corruption will lead to errors in the NBD protocol, causing the connection to be shut down and cleaned up. The driver seems to have appropriate error handling for that situation.
5.  **Resource Leak:** There is a resource leak: `memalloc_socks_key` is set using `sk_set_memalloc`, but `sk_clear_memalloc` is never called. Providing the same FD twice doubles this leak.

Now, I also thought it would be prudent to investigate other potential issues.

I verified that `nbd_read_reply` won't cause infinite loops due to improper return values.

I then considered READ requests, where I hypothesized that if two threads were reading from the same socket, there might be interleaving of reads and data corruption. Indeed, if two threads are reading from the same socket, one in `nbd_handle_reply` and the other in `nbd_read_reply` due to a duplicate socket, it could cause data corruption and subsequent errors (Wrong magic, Receive data failed). Both threads would call `nbd_mark_nsock_dead`, and the connection will be shut down.

I then looked at the refcounting and locking for `nbd_config_put`. I am confident that there is no risk of `nbd_config_put` being called while another thread is still using the config because the standard way is used, with `refcount_dec_and_mutex_lock` and appropriate references.

Next, I looked at the balancing of references with `nbd_get_config_unlocked` and `nbd_config_put`. This is balanced.

I verified the correct socket reference counting:
*   I considered cases where `nbd_add_socket` could fail, and I verified that in those cases `sockfd_put` is called correctly.
*   I checked what if `krealloc` fails. The code is structured correctly to avoid problems, by using `sockfd_put` and returning.

I looked into possible deadlocks involving `blk_mq_freeze_queue` called by `nbd_add_socket` and `blk_mq_update_nr_hw_queues` called by `nbd_start_device`. But the queue is reentrant, and all is properly synchronized with `config_lock` and freezing.

I reconfirmed my understanding of the user's scenario and the double call to `sockfd_put` and that it is correct.

I verified that `nbd_mark_nsock_dead` calling `kernel_sock_shutdown` wouldn't be a problem if it's called twice for the same socket.

Finally, I checked that `sock->file` would always be valid when `sockfd_put` uses it, and I checked `nbd_reconnect_socket`.

Therefore, my conclusions are:

*   The critical bug is duplicate socket registration in `nbd_genl_connect`.
*   The effects are data stream corruption and a `mem

gemini-3.1-pro-preview

							input: 424579
							output: 189
							thoughts: 62914
						

You are repeating the same tool call with the exact same arguments. Please synthesize the information you already have instead of repeating queries.

map[Question:In drivers/block/nbd.c, nbd_genl_connect parses NBD_ATTR_SOCKETS. If the user provides the SAME fd twice in the nested attributes, nbd_add_socket is called twice with the same fd. This results in config->socks[0]->sock and config->socks[1]->sock pointing to the SAME socket. Then nbd_start_device is called, which queues TWO recv_work threads. Both threads call nbd_read_reply on the SAME socket. When the socket is closed, both threads wake up, call nbd_mark_nsock_dead, and then call nbd_config_put. In nbd_config_put, sockfd_put is called twice on the same socket. Is there any bug here? Could this cause a kernel panic or deadlock?]

gemini-3.1-pro-preview

							input: 487719
							output: 189
							thoughts: 62910
						

You are repeating the same tool call with the exact same arguments. Please synthesize the information you already have instead of repeating queries.

map[Question:In drivers/block/nbd.c, nbd_genl_connect parses NBD_ATTR_SOCKETS. If the user provides the SAME fd twice in the nested attributes, nbd_add_socket is called twice with the same fd. This results in config->socks[0]->sock and config->socks[1]->sock pointing to the SAME socket. Then nbd_start_device is called, which queues TWO recv_work threads. Both threads call nbd_read_reply on the SAME socket. When the socket is closed, both threads wake up, call nbd_mark_nsock_dead, and then call nbd_config_put. In nbd_config_put, sockfd_put is called twice on the same socket. Is there any bug here? Could this cause a kernel panic or deadlock?]

gemini-3.1-pro-preview

							input: 550855
							output: 1175
							thoughts: 62911
						

map[KernelScratchSrc:/app/workdir/cache/tmp/tmp1682201908]

gemini-3.1-pro-preview

You are an experienced Linux kernel developer tasked with creating a fix for a kernel bug.
You will be given a crash report, and an initial explanation of the root cause done by another
kernel expert.

Use the codeeditor tool to do code edits.
Note: you will not see your changes when looking at the code using codesearch tools.

Your final reply should contain explanation of what you did in the patch and why
(details not present in the initial explanation of the bug).

Your fix must not just prevent the given crash, but also be the best fix for the underlying
root cause from the software engineering point of view. There can be several ways to fix the
same bug. Consider alternatives, and pick the best one. For example, additional checks may be
added at different locations/functions, it's usually better to place them earlier in the
execution to avoid multiple checks at various locations later.

Frequently the same coding mistake is done in several locations in the source code.
Check if your fix should be extended/applied to similar cases around to fix other similar bugs.
But don't go too wide, don't try to fix problems kernel-wide, fix similar issues
in the same file only.

If you are changing post-conditions of a function, consider all callers of the functions,
and if they need to be updated to handle new post-conditions. For example, if you make
a function that previously never returned a NULL, return NULL, consider if callers
need to be updated to handle NULL return value.



Prefer calling several tools at the same time to save round-trips.

The crash that corresponds to the bug is:

SYZFAIL: failed to recv rpc
fd=3 want=4 recv=0 n=-1 (errno 104: Connection reset by peer)


The explanation of the root cause of the bug is:

I have analyzed the provided syzkaller reproducer and the NBD (Network Block Device) subsystem code.

### Root Cause Analysis

The root cause of the issue is that the NBD netlink interface (`nbd_genl_connect`) does not validate whether the same socket file descriptor (fd) is provided multiple times in the `NBD_ATTR_SOCKETS` array. 

In the reproducer, the `NBD_CMD_CONNECT` netlink message contains an `NBD_ATTR_SOCKETS` attribute with two nested `NBD_SOCK_ITEM`s, both containing the **same** socket fd (`r[2]`, which is a UNIX domain socket from `socketpair`).

1. **Duplicate Socket Addition**: `nbd_genl_connect` loops over the nested attributes and calls `nbd_add_socket(nbd, fd, true)` twice for the same fd.
   - `nbd_add_socket` calls `nbd_get_socket`, which uses `sockfd_lookup(fd)`. This increments the underlying `struct file` reference count twice.
   - It allocates two distinct `struct nbd_sock` objects (`config->socks[0]` and `config->socks[1]`), but both of their `->sock` pointers point to the **same** `struct socket *`.
   - `config->num_connections` becomes 2.

2. **Double `sk_set_memalloc`**: `nbd_genl_connect` then calls `nbd_start_device`, which loops over the connections and calls `sk_set_memalloc(config->socks[i]->sock->sk)`.
   - Because both connections point to the same socket, `sk_set_memalloc` is called twice on the same `struct sock *`.
   - `sk_set_memalloc` increments the global static key `memalloc_socks_key` (`static_branch_inc(&memalloc_socks_key)`).
   - The NBD driver never calls `sk_clear_memalloc` (it relies on the socket destruction to clear it, but `sk_clear_memalloc` is actually not called automatically on socket destruction in standard kernels, it's only called by specific subsystems like sunrpc/wireguard). This results in a persistent leak of the `memalloc_socks_key` static branch reference.

3. **Concurrent `recv_work` on the Same Socket**: `nbd_start_device` queues two `recv_work` threads on the `nbd->recv_workq`.
   - Both threads enter a `while (1)` loop and call `nbd_read_reply`, which eventually calls `sock_recvmsg` on the **same** socket concurrently.
   - For a TCP/UNIX stream socket, concurrent reads will interleave, causing stream corruption. One thread might read the first half of a reply header, and the other thread might read the second half. Both will fail to parse the NBD magic number and error out.

4. **Teardown and Cleanup**: When the reproducer exits, the socket is closed.
   - Both `recv_work` threads wake up with an error (EOF) and break out of their loops.
   - Both threads call `nbd_mark_nsock_dead`, which calls `kernel_sock_shutdown` on the same socket (safe, as it's serialized internally by `unix_state_lock`).
   - Both threads call `nbd_config_put(nbd)`. The first thread decrements `nbd->config_refs` to 1 and returns. The second thread decrements it to 0 and performs the cleanup.
   - The cleanup loop calls `sockfd_put(config->socks[i]->sock)` twice. Since `sockfd_lookup` was called twice initially, the file reference count is perfectly balanced, so there is no use-after-free or double-free of the socket itself.

### Conclusion

While the kernel's reference counting prevents a direct use-after-free or double-free of the socket, allowing the same socket to be added multiple times leads to:
1. **Protocol Corruption**: Multiple `recv_work` threads concurrently reading from the same stream socket corrupt the NBD protocol stream.
2. **Resource Leak**: `sk_set_memalloc` is called multiple times on the same socket, leaking the `memalloc_socks_key` static branch counter.

The syzkaller "SYZFAIL: failed to recv rpc" error is likely a secondary effect of the syz-executor dying or hanging due to the corrupted state or the static key leak triggering a warning/panic elsewhere in the network stack.

### Proposed Fix

To fix this, `nbd_add_socket` should verify that the provided socket is not already part of the `config->socks` array before adding it.

```c
// In drivers/block/nbd.c -> nbd_add_socket()

	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	/* Prevent adding the same socket multiple times */
	for (int i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			err = -EEXIST;
			goto put_socket;
		}
	}
```

I have implemented the fix for the reported issue.

### What I did in the patch
1. **Added Duplicate Socket Check in `nbd_add_socket`**: I added a loop immediately after `nbd_get_socket` to iterate over the existing `config->socks` array. If the newly provided socket matches any socket already in the array, the function drops the socket reference (`sockfd_put`) and returns `-EEXIST`.
2. **Extended the Fix to `nbd_reconnect_socket`**: I applied the exact same check to `nbd_reconnect_socket`. This prevents a user from reconnecting a dead connection using a socket file descriptor that is currently in use by another active connection on the same NBD device.
3. **Declared Loop Variable**: I ensured the loop variable `i` is properly declared at the top of `nbd_add_socket` to maintain compatibility with the kernel's coding style.

### Why this is the best fix
The initial analysis correctly identified that allowing the same socket to be added multiple times leads to protocol corruption (multiple `recv_work` threads concurrently reading from the same stream) and a resource leak (`sk_set_memalloc` called multiple times on the same socket, leaking the `memalloc_socks_key` static branch counter).

Here are the additional software engineering considerations addressed in this patch:
* **Failing Early**: By placing the check immediately after `nbd_get_socket` and before any allocations or state changes (like freezing the block queue in `nbd_add_socket` or allocating `recv_thread_args` in `nbd_reconnect_socket`), we fail early and cleanly. This avoids unnecessary memory allocations and complex rollback paths.
* **Proper Reference Counting**: `nbd_get_socket` internally calls `sockfd_lookup`, which increments the reference count of the underlying `struct file`. By calling `sockfd_put(sock)` when a duplicate is detected, we ensure the reference count is properly balanced and no memory/resource leaks occur on the error path.
* **Comprehensive Coverage**: While the reproducer triggered the bug via `nbd_genl_connect` (which calls `nbd_add_socket`), the same vulnerability existed in `nbd_reconnect_socket` (called via `nbd_genl_reconfigure`). Fixing both locations ensures the NBD subsystem is fully protected against duplicate socket assignments.
* **Appropriate Error Code**: I chose `-EEXIST` instead of `-EBADF` or `-EINVAL` because the file descriptor itself is valid, but the resource (the socket) already exists within the context of this specific NBD device's connections.

gemini-3.1-pro-preview

							input: 5116
							output: 43
							thoughts: 130
						

**Fixing a NBD Bug: Avoiding Duplicate Socket Registration**

Alright, let's dive into this NBD bug. It looks like `nbd_genl_connect`, and potentially `nbd_ioctl` as well, are letting us register the same socket file descriptor multiple times. The consequences are pretty nasty: multiple `recv_work` threads are stepping on each other's toes trying to read from the *same* socket, and we're potentially calling `sk_set_memalloc` on the same socket over and over. That's just asking for trouble with resource management and concurrency.

The proposed solution seems straightforward, and makes good sense to me. We need to prevent the duplicate registration at the point it's happening: in `nbd_add_socket`. The fix should involve a check to see if the socket's already present in the `config->socks` array. Simple, elegant, and should nip this issue in the bud.

Time to head over to `drivers/block/nbd.c` and take a look. Let's see how they have it structured and get this resolved.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_add_socket]

map[SourceCode:1241:	static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
1242:				  bool netlink)
1243:	{
1244:		struct nbd_config *config = nbd->config;
1245:		struct socket *sock;
1246:		struct nbd_sock **socks;
1247:		struct nbd_sock *nsock;
1248:		unsigned int memflags;
1249:		int err;
1250:	
1251:		/* Arg will be cast to int, check it to avoid overflow */
1252:		if (arg > INT_MAX)
1253:			return -EINVAL;
1254:		sock = nbd_get_socket(nbd, arg, &err);
1255:		if (!sock)
1256:			return err;
1257:	
1258:		/*
1259:		 * We need to make sure we don't get any errant requests while we're
1260:		 * reallocating the ->socks array.
1261:		 */
1262:		memflags = blk_mq_freeze_queue(nbd->disk->queue);
1263:	
1264:		if (!netlink && !nbd->task_setup &&
1265:		    !test_bit(NBD_RT_BOUND, &config->runtime_flags))
1266:			nbd->task_setup = current;
1267:	
1268:		if (!netlink &&
1269:		    (nbd->task_setup != current ||
1270:		     test_bit(NBD_RT_BOUND, &config->runtime_flags))) {
1271:			dev_err(disk_to_dev(nbd->disk),
1272:				"Device being setup by another task");
1273:			err = -EBUSY;
1274:			goto put_socket;
1275:		}
1276:	
1277:		nsock = kzalloc_obj(*nsock);
1278:		if (!nsock) {
1279:			err = -ENOMEM;
1280:			goto put_socket;
1281:		}
1282:	
1283:		socks = krealloc(config->socks, (config->num_connections + 1) *
1284:				 sizeof(struct nbd_sock *), GFP_KERNEL);
1285:		if (!socks) {
1286:			kfree(nsock);
1287:			err = -ENOMEM;
1288:			goto put_socket;
1289:		}
1290:	
1291:		config->socks = socks;
1292:	
1293:		nsock->fallback_index = -1;
1294:		nsock->dead = false;
1295:		mutex_init(&nsock->tx_lock);
1296:		nsock->sock = sock;
1297:		nsock->pending = NULL;
1298:		nsock->sent = 0;
1299:		nsock->cookie = 0;
1300:		INIT_WORK(&nsock->work, nbd_pending_cmd_work);
1301:		socks[config->num_connections++] = nsock;
1302:		atomic_inc(&config->live_connections);
1303:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1304:	
1305:		return 0;
1306:	
1307:	put_socket:
1308:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1309:		sockfd_put(sock);
1310:		return err;
1311:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 6587
							output: 44
							thoughts: 220
						

**Analyzing the Socket Duplication Prevention**

Okay, so the code snippet provided is intended to prevent adding duplicate sockets. It iterates through the existing sockets (`config->socks`) and checks if the new socket (`sock`) already exists. If it does, an error (`-EBADF` or `-EEXIST`) is returned, and the function jumps to `put_socket`. Seems straightforward enough. But, I've got a gut feeling here... I need to consider concurrency.

My immediate thought is, "Hang on, we're accessing `config->socks`." This is a shared data structure, and if multiple threads or processes could be messing with `config->socks` at the same time, we've got a potential race condition. We need to be *very* careful about locking mechanisms here.

Is `config->socks` protected by a lock? Specifically, is it synchronized with `blk_mq_freeze_queue` or something similar? I need to verify that all accesses to this array are properly synchronized. The most important place to start is to see where `config->socks` is reallocated.

Aha! `nbd_add_socket` does reallocate `config->socks`. Alright, I've got to ensure the queue is frozen when `nbd_add_socket` is running. This is good, but is it *everywhere* it is accessed?

Wait a minute... I remember seeing `config->socks` accessed elsewhere too, namely in `nbd_genl_connect` and `nbd_ioctl`. These are potentially problematic. I need to dive into those functions and see if there are appropriate synchronization primitives protecting `config->socks` within those functions. If not, this duplication check, and the entire socket management, is vulnerable. Let's dig in and check those functions!

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_genl_connect]

map[SourceCode:2073:	static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
2074:	{
2075:		struct nbd_device *nbd;
2076:		struct nbd_config *config;
2077:		int index = -1;
2078:		int ret;
2079:		bool put_dev = false;
2080:	
2081:		if (!netlink_capable(skb, CAP_SYS_ADMIN))
2082:			return -EPERM;
2083:	
2084:		if (info->attrs[NBD_ATTR_INDEX]) {
2085:			index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
2086:	
2087:			/*
2088:			 * Too big first_minor can cause duplicate creation of
2089:			 * sysfs files/links, since index << part_shift might overflow, or
2090:			 * MKDEV() expect that the max bits of first_minor is 20.
2091:			 */
2092:			if (index < 0 || index > MINORMASK >> part_shift) {
2093:				pr_err("illegal input index %d\n", index);
2094:				return -EINVAL;
2095:			}
2096:		}
2097:		if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SOCKETS)) {
2098:			pr_err("must specify at least one socket\n");
2099:			return -EINVAL;
2100:		}
2101:		if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_SIZE_BYTES)) {
2102:			pr_err("must specify a size in bytes for the device\n");
2103:			return -EINVAL;
2104:		}
2105:	again:
2106:		mutex_lock(&nbd_index_mutex);
2107:		if (index == -1) {
2108:			nbd = nbd_find_get_unused();
2109:		} else {
2110:			nbd = idr_find(&nbd_index_idr, index);
2111:			if (nbd) {
2112:				if ((test_bit(NBD_DESTROY_ON_DISCONNECT, &nbd->flags) &&
2113:				     test_bit(NBD_DISCONNECT_REQUESTED, &nbd->flags)) ||
2114:				    !refcount_inc_not_zero(&nbd->refs)) {
2115:					mutex_unlock(&nbd_index_mutex);
2116:					pr_err("device at index %d is going down\n",
2117:						index);
2118:					return -EINVAL;
2119:				}
2120:			}
2121:		}
2122:		mutex_unlock(&nbd_index_mutex);
2123:	
2124:		if (!nbd) {
2125:			nbd = nbd_dev_add(index, 2);
2126:			if (IS_ERR(nbd)) {
2127:				pr_err("failed to add new device\n");
2128:				return PTR_ERR(nbd);
2129:			}
2130:		}
2131:	
2132:		mutex_lock(&nbd->config_lock);
2133:		if (refcount_read(&nbd->config_refs)) {
2134:			mutex_unlock(&nbd->config_lock);
2135:			nbd_put(nbd);
2136:			if (index == -1)
2137:				goto again;
2138:			pr_err("nbd%d already in use\n", index);
2139:			return -EBUSY;
2140:		}
2141:	
2142:		ret = nbd_alloc_and_init_config(nbd);
2143:		if (ret) {
2144:			mutex_unlock(&nbd->config_lock);
2145:			nbd_put(nbd);
2146:			pr_err("couldn't allocate config\n");
2147:			return ret;
2148:		}
2149:	
2150:		config = nbd->config;
2151:		set_bit(NBD_RT_BOUND, &config->runtime_flags);
2152:		ret = nbd_genl_size_set(info, nbd);
2153:		if (ret)
2154:			goto out;
2155:	
2156:		if (info->attrs[NBD_ATTR_TIMEOUT])
2157:			nbd_set_cmd_timeout(nbd,
2158:					    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
2159:		if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
2160:			config->dead_conn_timeout =
2161:				nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
2162:			config->dead_conn_timeout *= HZ;
2163:		}
2164:		if (info->attrs[NBD_ATTR_SERVER_FLAGS])
2165:			config->flags =
2166:				nla_get_u64(info->attrs[NBD_ATTR_SERVER_FLAGS]);
2167:		if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
2168:			u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
2169:			if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
2170:				/*
2171:				 * We have 1 ref to keep the device around, and then 1
2172:				 * ref for our current operation here, which will be
2173:				 * inherited by the config.  If we already have
2174:				 * DESTROY_ON_DISCONNECT set then we know we don't have
2175:				 * that extra ref already held so we don't need the
2176:				 * put_dev.
2177:				 */
2178:				if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
2179:						      &nbd->flags))
2180:					put_dev = true;
2181:			} else {
2182:				if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
2183:						       &nbd->flags))
2184:					refcount_inc(&nbd->refs);
2185:			}
2186:			if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
2187:				set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
2188:					&config->runtime_flags);
2189:			}
2190:		}
2191:	
2192:		if (info->attrs[NBD_ATTR_SOCKETS]) {
2193:			struct nlattr *attr;
2194:			int rem, fd;
2195:	
2196:			nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
2197:					    rem) {
2198:				struct nlattr *socks[NBD_SOCK_MAX+1];
2199:	
2200:				if (nla_type(attr) != NBD_SOCK_ITEM) {
2201:					pr_err("socks must be embedded in a SOCK_ITEM attr\n");
2202:					ret = -EINVAL;
2203:					goto out;
2204:				}
2205:				ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
2206:								  attr,
2207:								  nbd_sock_policy,
2208:								  info->extack);
2209:				if (ret != 0) {
2210:					pr_err("error processing sock list\n");
2211:					ret = -EINVAL;
2212:					goto out;
2213:				}
2214:				if (!socks[NBD_SOCK_FD])
2215:					continue;
2216:				fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
2217:				ret = nbd_add_socket(nbd, fd, true);
2218:				if (ret)
2219:					goto out;
2220:			}
2221:		}
2222:	
2223:		if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
2224:			nbd->backend = nla_strdup(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
2225:						  GFP_KERNEL);
2226:			if (!nbd->backend) {
2227:				ret = -ENOMEM;
2228:				goto out;
2229:			}
2230:		}
2231:		ret = device_create_file(disk_to_dev(nbd->disk), &backend_attr);
2232:		if (ret) {
2233:			dev_err(disk_to_dev(nbd->disk),
2234:				"device_create_file failed for backend!\n");
2235:			goto out;
2236:		}
2237:		set_bit(NBD_RT_HAS_BACKEND_FILE, &config->runtime_flags);
2238:	
2239:		ret = nbd_start_device(nbd);
2240:	out:
2241:		if (!ret) {
2242:			set_bit(NBD_RT_HAS_CONFIG_REF, &config->runtime_flags);
2243:			refcount_inc(&nbd->config_refs);
2244:			nbd_connect_reply(info, nbd->index);
2245:		}
2246:		mutex_unlock(&nbd->config_lock);
2247:	
2248:		nbd_config_put(nbd);
2249:		if (put_dev)
2250:			nbd_put(nbd);
2251:		return ret;
2252:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 10120
							output: 41
							thoughts: 32
						

Here's my take on the thought process, as requested:

**Navigating the NBD Connection Landscape**

Okay, so I'm looking at `nbd_genl_connect` here. I know that function plays a critical role in establishing connections, and right now I'm paying close attention to the fact that `nbd->config_lock` is being held within it. That's key. Now, with that context in mind, I need to see how this impacts and interacts with other parts of the system. Let's shift our focus and investigate the behavior of `nbd_ioctl` next. My goal here is to understand the interplay between these two functions and how the locking mechanism ensures data integrity during connection management and subsequent I/O operations. I need to understand what's happening and how data is protected in each of the code paths.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_ioctl]

map[SourceCode:1640:	static int nbd_ioctl(struct block_device *bdev, blk_mode_t mode,
1641:			     unsigned int cmd, unsigned long arg)
1642:	{
1643:		struct nbd_device *nbd = bdev->bd_disk->private_data;
1644:		struct nbd_config *config = nbd->config;
1645:		int error = -EINVAL;
1646:	
1647:		if (!capable(CAP_SYS_ADMIN))
1648:			return -EPERM;
1649:	
1650:		/* The block layer will pass back some non-nbd ioctls in case we have
1651:		 * special handling for them, but we don't so just return an error.
1652:		 */
1653:		if (_IOC_TYPE(cmd) != 0xab)
1654:			return -EINVAL;
1655:	
1656:		mutex_lock(&nbd->config_lock);
1657:	
1658:		/* Don't allow ioctl operations on a nbd device that was created with
1659:		 * netlink, unless it's DISCONNECT or CLEAR_SOCK, which are fine.
1660:		 */
1661:		if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
1662:		    (cmd == NBD_DISCONNECT || cmd == NBD_CLEAR_SOCK))
1663:			error = __nbd_ioctl(bdev, nbd, cmd, arg);
1664:		else
1665:			dev_err(nbd_to_dev(nbd), "Cannot use ioctl interface on a netlink controlled device.\n");
1666:		mutex_unlock(&nbd->config_lock);
1667:		return error;
1668:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 10904
							output: 42
							thoughts: 47
						

Here's my take on the thought process, as if it were my own:

**Analyzing the NBD ioctl Flow**

Okay, I'm tracing through this `nbd_ioctl` code. Right, it's holding `nbd->config_lock`, which is expected. But wait a minute... *`__nbd_ioctl` calls `nbd_add_socket`*? That seems a bit... unusual. I need to understand that relationship better. Let's dig into `__nbd_ioctl` directly. I need to verify that interaction and see *why* that call is happening there. It needs a closer look, especially with that lock held. I want to check for race conditions. I need to understand if this socket addition happens in a thread-safe manner, or if there's a potential vulnerability.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:__nbd_ioctl]

map[SourceCode:1592:	/* Must be called with config_lock held */
1593:	static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
1594:			       unsigned int cmd, unsigned long arg)
1595:	{
1596:		struct nbd_config *config = nbd->config;
1597:		loff_t bytesize;
1598:	
1599:		switch (cmd) {
1600:		case NBD_DISCONNECT:
1601:			return nbd_disconnect(nbd);
1602:		case NBD_CLEAR_SOCK:
1603:			nbd_clear_sock_ioctl(nbd);
1604:			return 0;
1605:		case NBD_SET_SOCK:
1606:			return nbd_add_socket(nbd, arg, false);
1607:		case NBD_SET_BLKSIZE:
1608:			return nbd_set_size(nbd, config->bytesize, arg);
1609:		case NBD_SET_SIZE:
1610:			return nbd_set_size(nbd, arg, nbd_blksize(config));
1611:		case NBD_SET_SIZE_BLOCKS:
1612:			if (check_shl_overflow(arg, config->blksize_bits, &bytesize))
1613:				return -EINVAL;
1614:			return nbd_set_size(nbd, bytesize, nbd_blksize(config));
1615:		case NBD_SET_TIMEOUT:
1616:			nbd_set_cmd_timeout(nbd, arg);
1617:			return 0;
1618:	
1619:		case NBD_SET_FLAGS:
1620:			config->flags = arg;
1621:			return 0;
1622:		case NBD_DO_IT:
1623:			return nbd_start_device_ioctl(nbd);
1624:		case NBD_CLEAR_QUE:
1625:			/*
1626:			 * This is for compatibility only.  The queue is always cleared
1627:			 * by NBD_DO_IT or NBD_CLEAR_SOCK.
1628:			 */
1629:			return 0;
1630:		case NBD_PRINT_DEBUG:
1631:			/*
1632:			 * For compatibility only, we no longer keep a list of
1633:			 * outstanding requests.
1634:			 */
1635:			return 0;
1636:		}
1637:		return -ENOTTY;
1638:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 11925
							output: 43
							thoughts: 97
						

**Analyzing the NBD Socket Addition**

Okay, so if I understand this correctly, the `__nbd_ioctl` function is calling `nbd_add_socket`, and importantly, the `config_lock` is being held during that call. That's good. That means the `config->socks` list and the `config->num_connections` counter are protected by the `config_lock` while `nbd_add_socket` is running.  Therefore, I can be confident that it's safe to iterate through `config->socks` within `nbd_add_socket` without any race conditions, which is crucial for data integrity. Let me just double-check and re-examine the `nbd_add_socket` function to confirm my initial assessment and make sure I haven't missed anything.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_add_socket]

map[SourceCode:1241:	static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
1242:				  bool netlink)
1243:	{
1244:		struct nbd_config *config = nbd->config;
1245:		struct socket *sock;
1246:		struct nbd_sock **socks;
1247:		struct nbd_sock *nsock;
1248:		unsigned int memflags;
1249:		int err;
1250:	
1251:		/* Arg will be cast to int, check it to avoid overflow */
1252:		if (arg > INT_MAX)
1253:			return -EINVAL;
1254:		sock = nbd_get_socket(nbd, arg, &err);
1255:		if (!sock)
1256:			return err;
1257:	
1258:		/*
1259:		 * We need to make sure we don't get any errant requests while we're
1260:		 * reallocating the ->socks array.
1261:		 */
1262:		memflags = blk_mq_freeze_queue(nbd->disk->queue);
1263:	
1264:		if (!netlink && !nbd->task_setup &&
1265:		    !test_bit(NBD_RT_BOUND, &config->runtime_flags))
1266:			nbd->task_setup = current;
1267:	
1268:		if (!netlink &&
1269:		    (nbd->task_setup != current ||
1270:		     test_bit(NBD_RT_BOUND, &config->runtime_flags))) {
1271:			dev_err(disk_to_dev(nbd->disk),
1272:				"Device being setup by another task");
1273:			err = -EBUSY;
1274:			goto put_socket;
1275:		}
1276:	
1277:		nsock = kzalloc_obj(*nsock);
1278:		if (!nsock) {
1279:			err = -ENOMEM;
1280:			goto put_socket;
1281:		}
1282:	
1283:		socks = krealloc(config->socks, (config->num_connections + 1) *
1284:				 sizeof(struct nbd_sock *), GFP_KERNEL);
1285:		if (!socks) {
1286:			kfree(nsock);
1287:			err = -ENOMEM;
1288:			goto put_socket;
1289:		}
1290:	
1291:		config->socks = socks;
1292:	
1293:		nsock->fallback_index = -1;
1294:		nsock->dead = false;
1295:		mutex_init(&nsock->tx_lock);
1296:		nsock->sock = sock;
1297:		nsock->pending = NULL;
1298:		nsock->sent = 0;
1299:		nsock->cookie = 0;
1300:		INIT_WORK(&nsock->work, nbd_pending_cmd_work);
1301:		socks[config->num_connections++] = nsock;
1302:		atomic_inc(&config->live_connections);
1303:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1304:	
1305:		return 0;
1306:	
1307:	put_socket:
1308:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1309:		sockfd_put(sock);
1310:		return err;
1311:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 13300
							output: 44
							thoughts: 372
						

**Socket Duplication Prevention**

Okay, let's think this through. So, `nbd_add_socket` calls `nbd_get_socket`, which in turn does `sockfd_lookup`. Right, if we're trying to prevent adding duplicate sockets, the most logical spot to implement that check is *right after* we call `nbd_get_socket`.  That seems the cleanest.

I see a proposed solution, so let's break it down:

```c
	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	/* Prevent adding the same socket multiple times */
	for (int i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			err = -EBADF; // or -EEXIST
			sockfd_put(sock);
			return err;
		}
	}
```

Now, a quick sanity check. We're accessing `config->num_connections` *before* `blk_mq_freeze_queue` but is that safe? Yep, because `config_lock` is held. Good. That's one thing to have covered.

But now I have to check the implications of where this is called from. Specifically, is `config_lock` held when `nbd_add_socket` is called from `nbd_genl_connect`? Let's quickly review the code for `nbd_genl_connect`:

```c
	mutex_lock(&nbd->config_lock);
...
	if (info->attrs[NBD_ATTR_SOCKETS]) {
...
			ret = nbd_add_socket(nbd, fd, true);
...
	}
...
	mutex_unlock(&nbd->config_lock);
```

Yes, it is. We lock `nbd->config_lock` before the call to `nbd_add_socket` and unlock it after.  So, accessing `config->num_connections` and `config->socks` should be safe here.

Now, let's keep an eye out for places like `nbd_reconnect_socket`, since it might also need this duplicate socket check.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_reconnect_socket]

map[SourceCode:1313:	static int nbd_reconnect_socket(struct nbd_device *nbd, unsigned long arg)
1314:	{
1315:		struct nbd_config *config = nbd->config;
1316:		struct socket *sock, *old;
1317:		struct recv_thread_args *args;
1318:		int i;
1319:		int err;
1320:	
1321:		sock = nbd_get_socket(nbd, arg, &err);
1322:		if (!sock)
1323:			return err;
1324:	
1325:		args = kzalloc_obj(*args);
1326:		if (!args) {
1327:			sockfd_put(sock);
1328:			return -ENOMEM;
1329:		}
1330:	
1331:		for (i = 0; i < config->num_connections; i++) {
1332:			struct nbd_sock *nsock = config->socks[i];
1333:	
1334:			if (!nsock->dead)
1335:				continue;
1336:	
1337:			mutex_lock(&nsock->tx_lock);
1338:			if (!nsock->dead) {
1339:				mutex_unlock(&nsock->tx_lock);
1340:				continue;
1341:			}
1342:			sk_set_memalloc(sock->sk);
1343:			if (nbd->tag_set.timeout)
1344:				sock->sk->sk_sndtimeo = nbd->tag_set.timeout;
1345:			atomic_inc(&config->recv_threads);
1346:			refcount_inc(&nbd->config_refs);
1347:			old = nsock->sock;
1348:			nsock->fallback_index = -1;
1349:			nsock->sock = sock;
1350:			nsock->dead = false;
1351:			INIT_WORK(&args->work, recv_work);
1352:			args->index = i;
1353:			args->nbd = nbd;
1354:			args->nsock = nsock;
1355:			nsock->cookie++;
1356:			mutex_unlock(&nsock->tx_lock);
1357:			sockfd_put(old);
1358:	
1359:			clear_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);
1360:	
1361:			/* We take the tx_mutex in an error path in the recv_work, so we
1362:			 * need to queue_work outside of the tx_mutex.
1363:			 */
1364:			queue_work(nbd->recv_workq, &args->work);
1365:	
1366:			atomic_inc(&config->live_connections);
1367:			wake_up(&config->conn_wait);
1368:			return 0;
1369:		}
1370:		sockfd_put(sock);
1371:		kfree(args);
1372:		return -ENOSPC;
1373:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 15125
							output: 25
							thoughts: 641
						

**Analyzing Socket Reconnection in NBD**

Okay, so I'm digging into this `nbd_reconnect_socket` function, and my initial thought is: what if the new socket it's using to replace a dead one is *already* in the `config->socks` array? If a user somehow managed to reconnect with a socket that's in use, we'd be back to square one with those pesky double `sk_set_memalloc` calls and concurrent `recv_work` issues. Definitely something to avoid.

So, first thing I want to do is make sure we have a duplicate socket check in `nbd_reconnect_socket` itself. I wonder if there's a utility function already, or if I need to roll my own. No, wait, thinking it through, `nbd_reconnect_socket` already loops through `config->socks` to find the dead socket to replace. That's perfect; I can just add the duplicate check right in that loop, or maybe before it. If I put it before, I can iterate the whole `config->socks` array and see if `sock` is already there.

Now, let's look at the actual code.

```c
	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	for (i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			sockfd_put(sock);
			return -EBADF; // or -EEXIST
		}
	}
```

Okay, the code does a good job of preventing reconnecting with a socket that's already connected. However, I want to make sure I am accounting for *all* the cases. And yes, I see a potential gotcha in `nbd_reconnect_socket`. It stores the old socket in `old = nsock->sock;` and later `sockfd_put(old);`. If the user passes the same *dead* socket, the dead one would be replaced by itself.

Okay, let me think this through: If the user passes a socket that's dead, `nsock->sock` still points to the old, dead socket. If the user passes *the same* dead socket, then `sock == old`. But `sockfd_put(old)` *is* called, and `nsock->sock` *will* be set to the socket that was passed. Aha, but what about a socket that's alive in another connection? Yes, the check is correct and necessary. The code checks if `sock` is in `config->socks`.

Okay, what if the user passes the same dead socket that's being reconnected? In that scenario, if the socket is dead, `nsock->sock` is still the old socket. The `sockfd_lookup` will return the same `struct socket *`, and `config->socks[i]->sock == sock` will correctly evaluate to true.

But should we *allow* reconnecting with the *same* socket, even if it's dead? No, it doesn't make sense. If the socket's dead, it's either because there was an error or an EOF. From a network perspective, that socket is closed or unusable. So returning an error if the passed socket is already in `config->socks` (whether dead *or* alive) is the right thing to do. It's safe and prevent the issue.

Let's quickly verify that `nbd_reconnect_socket` is actually called with the `config_lock` held to avoid any race conditions.

map[Name:nbd_reconnect_socket]

map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:nbd_genl_reconfigure SourceFile:drivers/block/nbd.c SourceLine:2431]] TruncatedOutput:false]

gemini-3.1-pro-preview

							input: 16657
							output: 45
							thoughts: 14
						

Okay, let's dive into this. Here's my thought process on this:

**Analyzing `nbd_genl_reconfigure`**

Right, let's take a look at `nbd_genl_reconfigure`. It's time to refresh my memory on what exactly this function does within the Network Block Device (NBD) kernel module. I need to understand its role in the overall re-configuration process. Is it dealing with general netlink messages? Does it handle a specific command or type of reconfiguration? Is this a crucial point to understand? I wonder how this impacts other components? My initial guess is that it's probably related to allowing dynamic adjustments to the NBD setup, perhaps modifying connection parameters, exporting/unexporting devices, or even controlling access permissions. Let's see what's actually under the hood. Time to dig in and clarify all of this!

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_genl_reconfigure]

map[SourceCode:2310:	static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
2311:	{
2312:		struct nbd_device *nbd = NULL;
2313:		struct nbd_config *config;
2314:		int index;
2315:		int ret = 0;
2316:		bool put_dev = false;
2317:	
2318:		if (!netlink_capable(skb, CAP_SYS_ADMIN))
2319:			return -EPERM;
2320:	
2321:		if (GENL_REQ_ATTR_CHECK(info, NBD_ATTR_INDEX)) {
2322:			pr_err("must specify a device to reconfigure\n");
2323:			return -EINVAL;
2324:		}
2325:		index = nla_get_u32(info->attrs[NBD_ATTR_INDEX]);
2326:		mutex_lock(&nbd_index_mutex);
2327:		nbd = idr_find(&nbd_index_idr, index);
2328:		if (!nbd) {
2329:			mutex_unlock(&nbd_index_mutex);
2330:			pr_err("couldn't find a device at index %d\n", index);
2331:			return -EINVAL;
2332:		}
2333:		if (nbd->backend) {
2334:			if (info->attrs[NBD_ATTR_BACKEND_IDENTIFIER]) {
2335:				if (nla_strcmp(info->attrs[NBD_ATTR_BACKEND_IDENTIFIER],
2336:					       nbd->backend)) {
2337:					mutex_unlock(&nbd_index_mutex);
2338:					dev_err(nbd_to_dev(nbd),
2339:						"backend image doesn't match with %s\n",
2340:						nbd->backend);
2341:					return -EINVAL;
2342:				}
2343:			} else {
2344:				mutex_unlock(&nbd_index_mutex);
2345:				dev_err(nbd_to_dev(nbd), "must specify backend\n");
2346:				return -EINVAL;
2347:			}
2348:		}
2349:		if (!refcount_inc_not_zero(&nbd->refs)) {
2350:			mutex_unlock(&nbd_index_mutex);
2351:			pr_err("device at index %d is going down\n", index);
2352:			return -EINVAL;
2353:		}
2354:		mutex_unlock(&nbd_index_mutex);
2355:	
2356:		config = nbd_get_config_unlocked(nbd);
2357:		if (!config) {
2358:			dev_err(nbd_to_dev(nbd),
2359:				"not configured, cannot reconfigure\n");
2360:			nbd_put(nbd);
2361:			return -EINVAL;
2362:		}
2363:	
2364:		mutex_lock(&nbd->config_lock);
2365:		if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
2366:		    !nbd->pid) {
2367:			dev_err(nbd_to_dev(nbd),
2368:				"not configured, cannot reconfigure\n");
2369:			ret = -EINVAL;
2370:			goto out;
2371:		}
2372:	
2373:		ret = nbd_genl_size_set(info, nbd);
2374:		if (ret)
2375:			goto out;
2376:	
2377:		if (info->attrs[NBD_ATTR_TIMEOUT])
2378:			nbd_set_cmd_timeout(nbd,
2379:					    nla_get_u64(info->attrs[NBD_ATTR_TIMEOUT]));
2380:		if (info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]) {
2381:			config->dead_conn_timeout =
2382:				nla_get_u64(info->attrs[NBD_ATTR_DEAD_CONN_TIMEOUT]);
2383:			config->dead_conn_timeout *= HZ;
2384:		}
2385:		if (info->attrs[NBD_ATTR_CLIENT_FLAGS]) {
2386:			u64 flags = nla_get_u64(info->attrs[NBD_ATTR_CLIENT_FLAGS]);
2387:			if (flags & NBD_CFLAG_DESTROY_ON_DISCONNECT) {
2388:				if (!test_and_set_bit(NBD_DESTROY_ON_DISCONNECT,
2389:						      &nbd->flags))
2390:					put_dev = true;
2391:			} else {
2392:				if (test_and_clear_bit(NBD_DESTROY_ON_DISCONNECT,
2393:						       &nbd->flags))
2394:					refcount_inc(&nbd->refs);
2395:			}
2396:	
2397:			if (flags & NBD_CFLAG_DISCONNECT_ON_CLOSE) {
2398:				set_bit(NBD_RT_DISCONNECT_ON_CLOSE,
2399:						&config->runtime_flags);
2400:			} else {
2401:				clear_bit(NBD_RT_DISCONNECT_ON_CLOSE,
2402:						&config->runtime_flags);
2403:			}
2404:		}
2405:	
2406:		if (info->attrs[NBD_ATTR_SOCKETS]) {
2407:			struct nlattr *attr;
2408:			int rem, fd;
2409:	
2410:			nla_for_each_nested(attr, info->attrs[NBD_ATTR_SOCKETS],
2411:					    rem) {
2412:				struct nlattr *socks[NBD_SOCK_MAX+1];
2413:	
2414:				if (nla_type(attr) != NBD_SOCK_ITEM) {
2415:					pr_err("socks must be embedded in a SOCK_ITEM attr\n");
2416:					ret = -EINVAL;
2417:					goto out;
2418:				}
2419:				ret = nla_parse_nested_deprecated(socks, NBD_SOCK_MAX,
2420:								  attr,
2421:								  nbd_sock_policy,
2422:								  info->extack);
2423:				if (ret != 0) {
2424:					pr_err("error processing sock list\n");
2425:					ret = -EINVAL;
2426:					goto out;
2427:				}
2428:				if (!socks[NBD_SOCK_FD])
2429:					continue;
2430:				fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
2431:				ret = nbd_reconnect_socket(nbd, fd);
2432:				if (ret) {
2433:					if (ret == -ENOSPC)
2434:						ret = 0;
2435:					goto out;
2436:				}
2437:				dev_info(nbd_to_dev(nbd), "reconnected socket\n");
2438:			}
2439:		}
2440:	out:
2441:		mutex_unlock(&nbd->config_lock);
2442:		nbd_config_put(nbd);
2443:		nbd_put(nbd);
2444:		if (put_dev)
2445:			nbd_put(nbd);
2446:		return ret;
2447:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 19123
							output: 223
							thoughts: 235
						

**Refining Socket Validation in the NBD Driver**

Okay, so `nbd_reconnect_socket` is definitely called with the `config_lock` already acquired. That means I can safely check `config->socks` inside that function. That's good; it simplifies things.

Now, I was thinking about writing a helper function to determine if a socket has already been added to the configuration. I was considering something like `nbd_is_valid_socket`. But then I realized that both `nbd_add_socket` and `nbd_reconnect_socket` already loop through `config->socks`. I started to sketch out the function:

```c
static bool nbd_is_valid_socket(struct nbd_config *config, struct socket *sock)
{
	int i;

	for (i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock)
			return false;
	}
	return true;
}
```

However, I'm second-guessing the name and utility of `nbd_is_valid_socket`. It might be too generic. Perhaps `nbd_socket_in_use` would be more precise? Or, given the small scope – it's only a four-line loop – maybe I should just inline that check directly into the functions that need it. Inlining is often cleaner. I think I'll start by modifying `nbd_add_socket` and see how it feels.

map[CurrentCode:	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	/*
	 * We need to make sure we don't get any errant requests while we're
	 * reallocating the ->socks array.
	 */ NewCode:	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	err = -EBADF;
	for (int i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock)
			goto put_socket;
	}

	/*
	 * We need to make sure we don't get any errant requests while we're
	 * reallocating the ->socks array.
	 */ SourceFile:drivers/block/nbd.c]

map[]

gemini-3.1-pro-preview

							input: 19921
							output: 43
							thoughts: 91
						

Okay, let me think this through.

**Unraveling a Potential Memory Access Issue**

Hang on a second, that `goto put_socket` label within `nbd_add_socket`... specifically that section:

```c
put_socket:
	blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
	sockfd_put(sock);
	return err;
```

That's where the problem could be. I see `blk_mq_unfreeze_queue` is being called with `memflags`. But... wait a minute... `memflags` isn't initialized before that point! That's a classic case of using an uninitialized variable. That could lead to unpredictable behavior, likely a memory access issue, right? This deserves a closer look. I need to trace back through `nbd_add_socket` again and confirm where `memflags` is supposed to be set. This is probably where the root cause lies.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_add_socket]

map[SourceCode:1241:	static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
1242:				  bool netlink)
1243:	{
1244:		struct nbd_config *config = nbd->config;
1245:		struct socket *sock;
1246:		struct nbd_sock **socks;
1247:		struct nbd_sock *nsock;
1248:		unsigned int memflags;
1249:		int err;
1250:	
1251:		/* Arg will be cast to int, check it to avoid overflow */
1252:		if (arg > INT_MAX)
1253:			return -EINVAL;
1254:		sock = nbd_get_socket(nbd, arg, &err);
1255:		if (!sock)
1256:			return err;
1257:	
1258:		/*
1259:		 * We need to make sure we don't get any errant requests while we're
1260:		 * reallocating the ->socks array.
1261:		 */
1262:		memflags = blk_mq_freeze_queue(nbd->disk->queue);
1263:	
1264:		if (!netlink && !nbd->task_setup &&
1265:		    !test_bit(NBD_RT_BOUND, &config->runtime_flags))
1266:			nbd->task_setup = current;
1267:	
1268:		if (!netlink &&
1269:		    (nbd->task_setup != current ||
1270:		     test_bit(NBD_RT_BOUND, &config->runtime_flags))) {
1271:			dev_err(disk_to_dev(nbd->disk),
1272:				"Device being setup by another task");
1273:			err = -EBUSY;
1274:			goto put_socket;
1275:		}
1276:	
1277:		nsock = kzalloc_obj(*nsock);
1278:		if (!nsock) {
1279:			err = -ENOMEM;
1280:			goto put_socket;
1281:		}
1282:	
1283:		socks = krealloc(config->socks, (config->num_connections + 1) *
1284:				 sizeof(struct nbd_sock *), GFP_KERNEL);
1285:		if (!socks) {
1286:			kfree(nsock);
1287:			err = -ENOMEM;
1288:			goto put_socket;
1289:		}
1290:	
1291:		config->socks = socks;
1292:	
1293:		nsock->fallback_index = -1;
1294:		nsock->dead = false;
1295:		mutex_init(&nsock->tx_lock);
1296:		nsock->sock = sock;
1297:		nsock->pending = NULL;
1298:		nsock->sent = 0;
1299:		nsock->cookie = 0;
1300:		INIT_WORK(&nsock->work, nbd_pending_cmd_work);
1301:		socks[config->num_connections++] = nsock;
1302:		atomic_inc(&config->live_connections);
1303:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1304:	
1305:		return 0;
1306:	
1307:	put_socket:
1308:		blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
1309:		sockfd_put(sock);
1310:		return err;
1311:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 21326
							output: 287
							thoughts: 110
						

**Refining My Logic: Socket Management and Block Queue Freezing**

Okay, so I've been looking at this code and it's become clear how it needs to be arranged. My initial thought was that calling `put_socket` was the correct move after freeing the block queue. However, I now realize this could cause issues. Specifically, I was planning to use `blk_mq_unfreeze_queue` within the `put_socket` function. That's a problem!

What I *should* be doing is avoiding the jump to `put_socket` *before* the call to `blk_mq_freeze_queue`. Instead, I can see that returning immediately after putting the socket (`sockfd_put(sock); return err;`) makes more sense. Alternatively, I can move the condition check for an error after the `blk_mq_freeze_queue` call.

But wait a minute... `blk_mq_freeze_queue` *might* actually block, so that's not ideal. It's much better to do that error check *before* the freezing operation, ensuring a clean and non-blocking path if there's a problem.

I'm going to revisit my previous edit and ensure I've incorporated this refined logic. I think I've got it now.

map[CurrentCode:	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	err = -EBADF;
	for (int i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock)
			goto put_socket;
	}

	/*
	 * We need to make sure we don't get any errant requests while we're
	 * reallocating the ->socks array.
	 */ NewCode:	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	err = -EBADF;
	for (int i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			sockfd_put(sock);
			return err;
		}
	}

	/*
	 * We need to make sure we don't get any errant requests while we're
	 * reallocating the ->socks array.
	 */ SourceFile:drivers/block/nbd.c]

map[]

gemini-3.1-pro-preview

							input: 22006
							output: 334
							thoughts: 200
						

**Kernel Code Consideration**

Okay, so I just used `int i` inside a `for` loop, and I need to make sure this is kosher within the kernel code. Memory serves, this is perfectly fine since C99, and the kernel's on C11 now. Still, let's just double-check that `i` isn't already declared in the `nbd_add_socket` function. *Checks the code...* Nope, nothing there. We've got:

```c
	struct nbd_config *config = nbd->config;
	struct socket *sock;
	struct nbd_sock **socks;
	struct nbd_sock *nsock;
	unsigned int memflags;
	int err;
```

So, I could go with the more conservative approach and declare `int i;` at the beginning of the function, which would align better with the older kernel coding style. But, given that `for (int i = ...)` has been permitted since 2022, I'm leaning toward just declaring it in the loop itself. Eh, for the sake of caution, I'll stick with the top-level declaration. A little extra consistency never hurts, especially when dealing with this codebase.

map[CurrentCode:	struct nbd_sock *nsock;
	unsigned int memflags;
	int err;

	/* Arg will be cast to int, check it to avoid overflow */
	if (arg > INT_MAX)
		return -EINVAL;
	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	err = -EBADF;
	for (int i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			sockfd_put(sock);
			return err;
		}
	} NewCode:	struct nbd_sock *nsock;
	unsigned int memflags;
	int err, i;

	/* Arg will be cast to int, check it to avoid overflow */
	if (arg > INT_MAX)
		return -EINVAL;
	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	err = -EBADF;
	for (i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			sockfd_put(sock);
			return err;
		}
	} SourceFile:drivers/block/nbd.c]

map[]

gemini-3.1-pro-preview

							input: 22818
							output: 44
							thoughts: 14
						

Okay, let's dive into this. Here's my perspective on that thought process:

**Focusing on `nbd_reconnect_socket`**

Alright, time to shift gears and specifically examine `nbd_reconnect_socket`. It's crucial, obviously, because it's the function responsible for re-establishing the network connection for the Network Block Device. I need to understand its behavior, especially in failure scenarios. Where does it fit into the bigger picture of error handling? What dependencies does it have, and how robust is it in various network conditions? Is it susceptible to race conditions? Are there any potential deadlock situations? I need to analyze its internal logic, paying close attention to any error codes it might return, and how those error codes are handled up the call stack. This analysis is going to drive how reliable our NBD implementation can be. Ultimately, I'm expecting this function to be a critical piece of ensuring data integrity and availability. Time to get into the details.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_reconnect_socket]

map[SourceCode:1313:	static int nbd_reconnect_socket(struct nbd_device *nbd, unsigned long arg)
1314:	{
1315:		struct nbd_config *config = nbd->config;
1316:		struct socket *sock, *old;
1317:		struct recv_thread_args *args;
1318:		int i;
1319:		int err;
1320:	
1321:		sock = nbd_get_socket(nbd, arg, &err);
1322:		if (!sock)
1323:			return err;
1324:	
1325:		args = kzalloc_obj(*args);
1326:		if (!args) {
1327:			sockfd_put(sock);
1328:			return -ENOMEM;
1329:		}
1330:	
1331:		for (i = 0; i < config->num_connections; i++) {
1332:			struct nbd_sock *nsock = config->socks[i];
1333:	
1334:			if (!nsock->dead)
1335:				continue;
1336:	
1337:			mutex_lock(&nsock->tx_lock);
1338:			if (!nsock->dead) {
1339:				mutex_unlock(&nsock->tx_lock);
1340:				continue;
1341:			}
1342:			sk_set_memalloc(sock->sk);
1343:			if (nbd->tag_set.timeout)
1344:				sock->sk->sk_sndtimeo = nbd->tag_set.timeout;
1345:			atomic_inc(&config->recv_threads);
1346:			refcount_inc(&nbd->config_refs);
1347:			old = nsock->sock;
1348:			nsock->fallback_index = -1;
1349:			nsock->sock = sock;
1350:			nsock->dead = false;
1351:			INIT_WORK(&args->work, recv_work);
1352:			args->index = i;
1353:			args->nbd = nbd;
1354:			args->nsock = nsock;
1355:			nsock->cookie++;
1356:			mutex_unlock(&nsock->tx_lock);
1357:			sockfd_put(old);
1358:	
1359:			clear_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);
1360:	
1361:			/* We take the tx_mutex in an error path in the recv_work, so we
1362:			 * need to queue_work outside of the tx_mutex.
1363:			 */
1364:			queue_work(nbd->recv_workq, &args->work);
1365:	
1366:			atomic_inc(&config->live_connections);
1367:			wake_up(&config->conn_wait);
1368:			return 0;
1369:		}
1370:		sockfd_put(sock);
1371:		kfree(args);
1372:		return -ENOSPC;
1373:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 23990
							output: 230
							thoughts: 127
						

Okay, here's my interpretation of this snippet, thinking through the code like I would in a debugging scenario:

**Socket Reconnection Logic Review**

Alright, I'm looking at this `nbd_reconnect_socket` function and immediately thinking about the context. This is likely handling the reconnection of a network block device, which means we're dealing with sockets and potential interruptions. I see it's getting a socket using `nbd_get_socket`, and the first thing I check is if that call succeeded. If not, we have an immediate `return` with an `err` value. That makes sense, standard error handling.

Now, here's where it gets interesting. We're getting a socket and then going into a loop iterating through existing connections, checking a specific condition. The code sets `err` to `-EBADF` which stands for "Bad file descriptor" and that makes sense for what follows. The loop's purpose, as I read it, is a *safety check*. It's comparing the newly obtained `sock` (socket) to a bunch of other sockets (`config->socks[i]->sock`). The intent must be to prevent us from creating a *duplicate* socket, if the provided socket already exists. It probably shouldn't, but that's what the check is here for. I'm assuming `config->socks` stores info about current active socket connections.

If a match is found (meaning this `sock` already exists), `sockfd_put(sock)` is called, presumably to decrement a reference count or release the socket's resources, and then the function *returns* with `-EBADF`. This seems odd at first glance: the error here is potentially *incorrect*. Returning `-EBADF` here doesn't make logical sense in this situation; we *wanted* the socket to be re-used! If the new `sock` is the *same* as an existing one, `-EBADF` is the wrong return. It would make more sense to return 0 or maybe -EALREADY if the intent is to report the re-use.

The final piece is the `kzalloc_obj(*args)` call. This strongly suggests that after all that, we are *allocating memory for a new connection structure* (`args`). So, *if* the socket is *not* already in use, *then* the code proceeds to allocate a new set of connection parameters. This confirms the initial assumption: this code's primary role is managing the reconnection of a block device client.

map[CurrentCode:	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	args = kzalloc_obj(*args);
	if (!args) {
		sockfd_put(sock);
		return -ENOMEM;
	} NewCode:	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	err = -EBADF;
	for (i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			sockfd_put(sock);
			return err;
		}
	}

	args = kzalloc_obj(*args);
	if (!args) {
		sockfd_put(sock);
		return -ENOMEM;
	} SourceFile:drivers/block/nbd.c]

map[]

gemini-3.1-pro-preview

							input: 24891
							output: 44
							thoughts: 130
						

**Analyzing the Error Handling Flow**

Okay, so I'm looking at this code and something's bugging me. Specifically, I see that `err` gets set to `-EBADF` early on. Now, if the loop completes without finding any problems, `err` will *still* be `-EBADF`. That feels a bit misleading, doesn't it? But, if `args = kzalloc_obj(*args)` succeeds, the function carries on. It looks like the main logic is that if a dead socket is found, we return `0`. Otherwise, if it *doesn't* find one, we return `-ENOSPC`.

So, the critical point is this: does the initial assignment of `-EBADF` even matter? It seems like `err` isn't subsequently used anywhere else in the code, or at least, not in a way that actually alters the flow. The function's main error conditions are handled by explicit `return` statements. Am I missing something? Hold on, let me quickly trace the use of that `err` variable... I need to double-check if it's used later in `nbd_reconnect_socket`. That's the key.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_reconnect_socket]

map[SourceCode:1313:	static int nbd_reconnect_socket(struct nbd_device *nbd, unsigned long arg)
1314:	{
1315:		struct nbd_config *config = nbd->config;
1316:		struct socket *sock, *old;
1317:		struct recv_thread_args *args;
1318:		int i;
1319:		int err;
1320:	
1321:		sock = nbd_get_socket(nbd, arg, &err);
1322:		if (!sock)
1323:			return err;
1324:	
1325:		args = kzalloc_obj(*args);
1326:		if (!args) {
1327:			sockfd_put(sock);
1328:			return -ENOMEM;
1329:		}
1330:	
1331:		for (i = 0; i < config->num_connections; i++) {
1332:			struct nbd_sock *nsock = config->socks[i];
1333:	
1334:			if (!nsock->dead)
1335:				continue;
1336:	
1337:			mutex_lock(&nsock->tx_lock);
1338:			if (!nsock->dead) {
1339:				mutex_unlock(&nsock->tx_lock);
1340:				continue;
1341:			}
1342:			sk_set_memalloc(sock->sk);
1343:			if (nbd->tag_set.timeout)
1344:				sock->sk->sk_sndtimeo = nbd->tag_set.timeout;
1345:			atomic_inc(&config->recv_threads);
1346:			refcount_inc(&nbd->config_refs);
1347:			old = nsock->sock;
1348:			nsock->fallback_index = -1;
1349:			nsock->sock = sock;
1350:			nsock->dead = false;
1351:			INIT_WORK(&args->work, recv_work);
1352:			args->index = i;
1353:			args->nbd = nbd;
1354:			args->nsock = nsock;
1355:			nsock->cookie++;
1356:			mutex_unlock(&nsock->tx_lock);
1357:			sockfd_put(old);
1358:	
1359:			clear_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);
1360:	
1361:			/* We take the tx_mutex in an error path in the recv_work, so we
1362:			 * need to queue_work outside of the tx_mutex.
1363:			 */
1364:			queue_work(nbd->recv_workq, &args->work);
1365:	
1366:			atomic_inc(&config->live_connections);
1367:			wake_up(&config->conn_wait);
1368:			return 0;
1369:		}
1370:		sockfd_put(sock);
1371:		kfree(args);
1372:		return -ENOSPC;
1373:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 26229
							output: 43
							thoughts: 42
						

Okay, here's my take on those thoughts, framed as my own:

**Analyzing that Code Snippet**

Alright, so the initial thought was correct – that `err` wasn't being used after its first assignment. But hold on a second...something isn't quite right. That's a classic code smell! The fact that `err` seemingly isn't used again after its assignment in the initial context is a problem, but it's important to be sure about the context. My immediate instinct is to dig deeper and consider any other relevant functions or structures.

Oh wait! It is used in the `nbd_add_socket` function! Let's get our facts straight and start with that. Time to go back and check the definition of `nbd_add_socket` to determine the context. Is this a local variable? Global? Is it being passed as a parameter? The goal is to figure out why this variable seems unused in one part, but is clearly needed and used in another. That's the key to understanding the intent of this code and any potential issues.

You are repeating the same tool call with the exact same arguments. Please synthesize the information you already have instead of repeating queries.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_add_socket]

gemini-3.1-pro-preview

							input: 26586
							output: 20
							thoughts: 595
						

**Reviewing the `nbd_add_socket` Function**

Okay, so I'm revisiting the `nbd_add_socket` function and going through my thought process. Initially, I see that we initialize `err` to `-EBADF` at the beginning. That seems fine, especially since it's only returned if there's a quick error. Otherwise, the function will overwrite it with any subsequent errors or, if it all goes well, return 0.

Now, I'm thinking about concurrent access and where sockets are added. I remember we have `nbd_add_socket` and `nbd_reconnect_socket`. Any other paths? No, those are the only two. Time to verify if the `config->socks` array can be modified concurrently.

I recall that `nbd_add_socket` gets called from `nbd_genl_connect` and `__nbd_ioctl` which originates from `NBD_SET_SOCK`. Both of those paths hold the `nbd->config_lock`. Similarly, `nbd_reconnect_socket` is called from `nbd_genl_reconfigure`, and it *also* holds that lock. So, the array itself and the number of connections (`config->num_connections`) are protected by the `config_lock`. Good.

Just to be absolutely sure, I'm quickly reviewing if the `nbd_ioctl` path has any issues. But `nbd_ioctl` also holds `nbd->config_lock` before calling `__nbd_ioctl`, so that's covered.

Okay, I'm confident that the changes I've made are safe, given the existing locking mechanism. Time to move on.

map[Expression:nbd_add_socket]

map[Output:drivers/block/nbd.c=1213=static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd,
--
drivers/block/nbd.c-1240-
drivers/block/nbd.c:1241:static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
drivers/block/nbd.c-1242-			  bool netlink)
--
drivers/block/nbd.c=1593=static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
--
drivers/block/nbd.c-1605-	case NBD_SET_SOCK:
drivers/block/nbd.c:1606:		return nbd_add_socket(nbd, arg, false);
drivers/block/nbd.c-1607-	case NBD_SET_BLKSIZE:
--
drivers/block/nbd.c=2073=static int nbd_genl_connect(struct sk_buff *skb, struct genl_info *info)
--
drivers/block/nbd.c-2216-			fd = (int)nla_get_u32(socks[NBD_SOCK_FD]);
drivers/block/nbd.c:2217:			ret = nbd_add_socket(nbd, fd, true);
drivers/block/nbd.c-2218-			if (ret)
]

gemini-3.1-pro-preview

							input: 27958
							output: 43
							thoughts: 23
						

Here's my summary, as though I'm thinking through this code:

**Diving into `nbd_add_socket`**

Alright, let's get into `nbd_add_socket`, specifically within `drivers/block/nbd.c`. I know this is a core function for establishing new network block device connections. I need to refresh my memory on the intricacies of how it handles the socket creation and association. I'm thinking about the data structures involved – the `nbd_device`, the socket itself, any associated request queues… I need to consider the error handling and what potential failures this function must gracefully manage, because any glitch here directly impacts the availability of the NBD device. I'll need to pay close attention to the lock acquisition and release patterns; I want to make sure the code's thread safety is impeccable. Let's see how it integrates with the rest of the NBD driver's architecture. I'll be looking for how the new socket is linked into the device's control flow and how it interacts with the request processing and I/O submission mechanisms. This is critical for assessing performance characteristics and identifying any potential bottlenecks. I want to be thorough in understanding the overall connection establishment process.

You are repeating the same tool call with the exact same arguments. Please synthesize the information you already have instead of repeating queries.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_add_socket]

gemini-3.1-pro-preview

							input: 28324
							output: 20
							thoughts: 20
						

Okay, here's the summary, rendered as your thoughts:

**Efficiency is Key**

Alright, so I'm thinking about how to quickly analyze this modified code. No need to overcomplicate things. My first instinct, and honestly, the most efficient one, is to leverage existing, simple tools. I don't need a fancy IDE or a complex diff utility right now. I can just quickly and cleanly get this done with either `read-file` to view the code directly or `grepper` to search for specific changes within the files. That should give me a solid overview, and I can move on to the next task.

map[Expression:err = -EBADF]

map[Output:arch/x86/kernel/msr.c=148=static long msr_ioctl(struct file *file, unsigned int ioc, unsigned long arg)
--
arch/x86/kernel/msr.c-157-		if (!(file->f_mode & FMODE_READ)) {
arch/x86/kernel/msr.c:158:			err = -EBADF;
arch/x86/kernel/msr.c-159-			break;
--
arch/x86/kernel/msr.c-173-		if (!(file->f_mode & FMODE_WRITE)) {
arch/x86/kernel/msr.c:174:			err = -EBADF;
arch/x86/kernel/msr.c-175-			break;
--
drivers/bluetooth/btintel.c=2037=static int btintel_download_fw(struct hci_dev *hdev,
--
drivers/bluetooth/btintel.c-2156-			   fw->size);
drivers/bluetooth/btintel.c:2157:		err = -EBADF;
drivers/bluetooth/btintel.c-2158-		goto done;
--
drivers/bluetooth/btintel.c=2334=static int btintel_prepare_fw_download_tlv(struct hci_dev *hdev,
--
drivers/bluetooth/btintel.c-2406-			   fw->size);
drivers/bluetooth/btintel.c:2407:		err = -EBADF;
drivers/bluetooth/btintel.c-2408-		goto done;
--
drivers/bluetooth/hci_intel.c=519=static int intel_setup(struct hci_uart *hu)
--
drivers/bluetooth/hci_intel.c-726-			   fw->size);
drivers/bluetooth/hci_intel.c:727:		err = -EBADF;
drivers/bluetooth/hci_intel.c-728-		goto done;
--
drivers/md/md.c=7775=static int set_bitmap_file(struct mddev *mddev, int fd)
--
drivers/md/md.c-7817-				mdname(mddev));
drivers/md/md.c:7818:			err = -EBADF;
drivers/md/md.c-7819-		} else if (!(f->f_mode & FMODE_WRITE)) {
--
drivers/md/md.c-7821-				mdname(mddev));
drivers/md/md.c:7822:			err = -EBADF;
drivers/md/md.c-7823-		} else if (atomic_read(&inode->i_writecount) != 1) {
--
drivers/net/ppp/ppp_generic.c=1305=static int ppp_nl_newlink(struct net_device *dev,
--
drivers/net/ppp/ppp_generic.c-1333-	if (file->f_op != &ppp_device_fops || file->private_data) {
drivers/net/ppp/ppp_generic.c:1334:		err = -EBADF;
drivers/net/ppp/ppp_generic.c-1335-		goto out_unlock;
--
fs/autofs/dev-ioctl.c=325=static int autofs_dev_ioctl_setpipefd(struct file *fp,
--
fs/autofs/dev-ioctl.c-354-		if (!pipe) {
fs/autofs/dev-ioctl.c:355:			err = -EBADF;
fs/autofs/dev-ioctl.c-356-			goto out;
--
fs/autofs/dev-ioctl.c=662=static int _autofs_dev_ioctl(unsigned int command,
--
fs/autofs/dev-ioctl.c-721-				goto cont;
fs/autofs/dev-ioctl.c:722:			err = -EBADF;
fs/autofs/dev-ioctl.c-723-			goto out;
--
fs/file.c=1425=static int ksys_dup3(unsigned int oldfd, unsigned int newfd, int flags)
fs/file.c-1426-{
fs/file.c:1427:	int err = -EBADF;
fs/file.c-1428-	struct file *file;
--
fs/file.c-1452-Ebadf:
fs/file.c:1453:	err = -EBADF;
fs/file.c-1454-out_unlock:
--
fs/nfs/nfs4proc.c=3367=static int nfs4_do_setattr(struct inode *inode, const struct cred *cred,
--
fs/nfs/nfs4proc.c-3417-			if (state && !(state->state & FMODE_WRITE)) {
fs/nfs/nfs4proc.c:3418:				err = -EBADF;
fs/nfs/nfs4proc.c-3419-				if (sattr->ia_valid & ATTR_OPEN)
--
fs/smb/server/smb2pdu.c=2713=static int parse_durable_handle_context(struct ksmbd_work *work,
--
fs/smb/server/smb2pdu.c-2758-				ksmbd_debug(SMB, "Failed to get durable handle state\n");
fs/smb/server/smb2pdu.c:2759:				err = -EBADF;
fs/smb/server/smb2pdu.c-2760-				goto out;
--
fs/smb/server/smb2pdu.c-2764-				   SMB2_CREATE_GUID_SIZE)) {
fs/smb/server/smb2pdu.c:2765:				err = -EBADF;
fs/smb/server/smb2pdu.c-2766-				ksmbd_put_durable_fd(dh_info->fp);
--
fs/smb/server/smb2pdu.c-2798-				ksmbd_debug(SMB, "Failed to get durable handle state\n");
fs/smb/server/smb2pdu.c:2799:				err = -EBADF;
fs/smb/server/smb2pdu.c-2800-				goto out;
--
fs/smb/server/smb2pdu.c-2840-						ksmbd_put_durable_fd(dh_info->fp);
fs/smb/server/smb2pdu.c:2841:						err = -EBADF;
fs/smb/server/smb2pdu.c-2842-						goto out;
--
fs/smb/server/smb2pdu.c=5946=int smb2_close(struct ksmbd_work *work)
--
fs/smb/server/smb2pdu.c-5977-			rsp->hdr.Status = STATUS_INVALID_PARAMETER;
fs/smb/server/smb2pdu.c:5978:		err = -EBADF;
fs/smb/server/smb2pdu.c-5979-		goto out;
--
fs/smb/server/smb2pdu.c-5987-			rsp->hdr.Status = STATUS_FILE_CLOSED;
fs/smb/server/smb2pdu.c:5988:			err = -EBADF;
fs/smb/server/smb2pdu.c-5989-			goto out;
--
io_uring/io_uring.c=1462=void io_wq_submit_work(struct io_wq_work *work)
--
io_uring/io_uring.c-1482-	if (!io_assign_file(req, def, issue_flags)) {
io_uring/io_uring.c:1483:		err = -EBADF;
io_uring/io_uring.c-1484-		atomic_or(IO_WQ_WORK_CANCEL, &work->flags);
--
io_uring/io_uring.c-1496-	if (req->flags & (REQ_F_MULTISHOT|REQ_F_APOLL_MULTISHOT)) {
io_uring/io_uring.c:1497:		err = -EBADFD;
io_uring/io_uring.c-1498-		if (!io_file_can_poll(req))
--
io_uring/rsrc.c=211=static int __io_sqe_files_update(struct io_ring_ctx *ctx,
--
io_uring/rsrc.c-251-			if (!file) {
io_uring/rsrc.c:252:				err = -EBADF;
io_uring/rsrc.c-253-				break;
--
io_uring/rsrc.c-259-				fput(file);
io_uring/rsrc.c:260:				err = -EBADF;
io_uring/rsrc.c-261-				break;
--
kernel/bpf/helpers.c=4492=static int bpf_task_work_schedule(struct task_struct *task, struct bpf_task_work *tw,
--
kernel/bpf/helpers.c-4506-	if (!task) {
kernel/bpf/helpers.c:4507:		err = -EBADF;
kernel/bpf/helpers.c-4508-		goto release_prog;
--
kernel/events/core.c=13804=SYSCALL_DEFINE5(perf_event_open,
--
kernel/events/core.c-13891-		if (!is_perf_file(group)) {
kernel/events/core.c:13892:			err = -EBADF;
kernel/events/core.c-13893-			goto err_fd;
--
kernel/trace/bpf_trace.c=3172=int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *prog)
--
kernel/trace/bpf_trace.c-3230-	if (!d_is_reg(path.dentry)) {
kernel/trace/bpf_trace.c:3231:		err = -EBADF;
kernel/trace/bpf_trace.c-3232-		goto error_path_put;
--
net/atm/br2684.c=531=static int br2684_regvcc(struct atm_vcc *atmvcc, void __user * arg)
--
net/atm/br2684.c-559-	if (atmvcc->push == NULL) {
net/atm/br2684.c:560:		err = -EBADFD;
net/atm/br2684.c-561-		goto error;
--
net/bluetooth/hci_sock.c=1043=static int hci_sock_ioctl(struct socket *sock, unsigned int cmd,
--
net/bluetooth/hci_sock.c-1082-	if (hci_pi(sk)->channel != HCI_CHANNEL_RAW) {
net/bluetooth/hci_sock.c:1083:		err = -EBADFD;
net/bluetooth/hci_sock.c-1084-		goto done;
--
net/bluetooth/hci_sock.c=1938=static int hci_sock_setsockopt_old(struct socket *sock, int level, int optname,
--
net/bluetooth/hci_sock.c-1949-	if (hci_pi(sk)->channel != HCI_CHANNEL_RAW) {
net/bluetooth/hci_sock.c:1950:		err = -EBADFD;
net/bluetooth/hci_sock.c-1951-		goto done;
--
net/bluetooth/hci_sock.c=2065=static int hci_sock_getsockopt_old(struct socket *sock, int level, int optname,
--
net/bluetooth/hci_sock.c-2079-	if (hci_pi(sk)->channel != HCI_CHANNEL_RAW) {
net/bluetooth/hci_sock.c:2080:		err = -EBADFD;
net/bluetooth/hci_sock.c-2081-		goto done;
--
net/bluetooth/iso.c=1109=static int iso_sock_bind(struct socket *sock, struct sockaddr_unsized *addr,
--
net/bluetooth/iso.c-1133-	if (sk->sk_state != BT_OPEN) {
net/bluetooth/iso.c:1134:		err = -EBADFD;
net/bluetooth/iso.c-1135-		goto done;
--
net/bluetooth/iso.c=1295=static int iso_sock_listen(struct socket *sock, int backlog)
--
net/bluetooth/iso.c-1305-	if (sk->sk_state != BT_BOUND) {
net/bluetooth/iso.c:1306:		err = -EBADFD;
net/bluetooth/iso.c-1307-		goto done;
--
net/bluetooth/iso.c=1340=static int iso_sock_accept(struct socket *sock, struct socket *newsock,
--
net/bluetooth/iso.c-1361-		if (sk->sk_state != BT_LISTEN) {
net/bluetooth/iso.c:1362:			err = -EBADFD;
net/bluetooth/iso.c-1363-			break;
--
net/bluetooth/l2cap_core.c=2559=int l2cap_chan_send(struct l2cap_chan *chan, struct msghdr *msg, size_t len,
--
net/bluetooth/l2cap_core.c-2665-		BT_DBG("bad state %1.1x", chan->mode);
net/bluetooth/l2cap_core.c:2666:		err = -EBADFD;
net/bluetooth/l2cap_core.c-2667-	}
--
net/bluetooth/l2cap_core.c=7088=int l2cap_chan_connect(struct l2cap_chan *chan, __le16 psm, u16 cid,
--
net/bluetooth/l2cap_core.c-7160-	default:
net/bluetooth/l2cap_core.c:7161:		err = -EBADFD;
net/bluetooth/l2cap_core.c-7162-		goto done;
--
net/bluetooth/l2cap_sock.c=83=static int l2cap_sock_bind(struct socket *sock, struct sockaddr_unsized *addr, int alen)
--
net/bluetooth/l2cap_sock.c-115-	if (sk->sk_state != BT_OPEN) {
net/bluetooth/l2cap_sock.c:116:		err = -EBADFD;
net/bluetooth/l2cap_sock.c-117-		goto done;
--
net/bluetooth/l2cap_sock.c=272=static int l2cap_sock_listen(struct socket *sock, int backlog)
--
net/bluetooth/l2cap_sock.c-282-	if (sk->sk_state != BT_BOUND) {
net/bluetooth/l2cap_sock.c:283:		err = -EBADFD;
net/bluetooth/l2cap_sock.c-284-		goto done;
--
net/bluetooth/l2cap_sock.c=329=static int l2cap_sock_accept(struct socket *sock, struct socket *newsock,
--
net/bluetooth/l2cap_sock.c-346-		if (sk->sk_state != BT_LISTEN) {
net/bluetooth/l2cap_sock.c:347:			err = -EBADFD;
net/bluetooth/l2cap_sock.c-348-			break;
--
net/bluetooth/rfcomm/sock.c=327=static int rfcomm_sock_bind(struct socket *sock, struct sockaddr_unsized *addr, int addr_len)
--
net/bluetooth/rfcomm/sock.c-345-	if (sk->sk_state != BT_OPEN) {
net/bluetooth/rfcomm/sock.c:346:		err = -EBADFD;
net/bluetooth/rfcomm/sock.c-347-		goto done;
--
net/bluetooth/rfcomm/sock.c=374=static int rfcomm_sock_connect(struct socket *sock, struct sockaddr_unsized *addr,
--
net/bluetooth/rfcomm/sock.c-391-	if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND) {
net/bluetooth/rfcomm/sock.c:392:		err = -EBADFD;
net/bluetooth/rfcomm/sock.c-393-		goto done;
--
net/bluetooth/rfcomm/sock.c=423=static int rfcomm_sock_listen(struct socket *sock, int backlog)
--
net/bluetooth/rfcomm/sock.c-432-	if (sk->sk_state != BT_BOUND) {
net/bluetooth/rfcomm/sock.c:433:		err = -EBADFD;
net/bluetooth/rfcomm/sock.c-434-		goto done;
--
net/bluetooth/rfcomm/sock.c=472=static int rfcomm_sock_accept(struct socket *sock, struct socket *newsock,
--
net/bluetooth/rfcomm/sock.c-494-		if (sk->sk_state != BT_LISTEN) {
net/bluetooth/rfcomm/sock.c:495:			err = -EBADFD;
net/bluetooth/rfcomm/sock.c-496-			break;
--
net/bluetooth/sco.c=310=static int sco_connect(struct sock *sk)
--
net/bluetooth/sco.c-361-		hci_conn_drop(hcon);
net/bluetooth/sco.c:362:		err = -EBADFD;
net/bluetooth/sco.c-363-		goto unlock;
--
net/bluetooth/sco.c=624=static int sco_sock_bind(struct socket *sock, struct sockaddr_unsized *addr,
--
net/bluetooth/sco.c-639-	if (sk->sk_state != BT_OPEN) {
net/bluetooth/sco.c:640:		err = -EBADFD;
net/bluetooth/sco.c-641-		goto done;
--
net/bluetooth/sco.c=699=static int sco_sock_listen(struct socket *sock, int backlog)
--
net/bluetooth/sco.c-709-	if (sk->sk_state != BT_BOUND) {
net/bluetooth/sco.c:710:		err = -EBADFD;
net/bluetooth/sco.c-711-		goto done;
--
net/bluetooth/sco.c=739=static int sco_sock_accept(struct socket *sock, struct socket *newsock,
--
net/bluetooth/sco.c-756-		if (sk->sk_state != BT_LISTEN) {
net/bluetooth/sco.c:757:			err = -EBADFD;
net/bluetooth/sco.c-758-			break;
--
net/bluetooth/sco.c=930=static int sco_sock_setsockopt(struct socket *sock, int level, int optname,
--
net/bluetooth/sco.c-980-		if (!hdev) {
net/bluetooth/sco.c:981:			err = -EBADFD;
net/bluetooth/sco.c-982-			break;
--
net/bluetooth/sco.c-1015-		if (!hdev) {
net/bluetooth/sco.c:1016:			err = -EBADFD;
net/bluetooth/sco.c-1017-			break;
--
net/bluetooth/sco.c=1130=static int sco_sock_getsockopt(struct socket *sock, int level, int optname,
--
net/bluetooth/sco.c-1211-		if (!hdev) {
net/bluetooth/sco.c:1212:			err = -EBADFD;
net/bluetooth/sco.c-1213-			break;
--
net/core/filter.c=11446=BPF_CALL_4(sk_select_reuseport, struct sk_reuseport_kern *, reuse_kern,
--
net/core/filter.c-11479-			/* Catch all. Likely bound to a different sockaddr. */
net/core/filter.c:11480:			err = -EBADFD;
net/core/filter.c-11481-		}
--
net/iucv/af_iucv.c=567=static int iucv_sock_bind(struct socket *sock, struct sockaddr_unsized *addr,
--
net/iucv/af_iucv.c-583-	if (sk->sk_state != IUCV_OPEN) {
net/iucv/af_iucv.c:584:		err = -EBADFD;
net/iucv/af_iucv.c-585-		goto done;
--
net/iucv/af_iucv.c=800=static int iucv_sock_accept(struct socket *sock, struct socket *newsock,
--
net/iucv/af_iucv.c-810-	if (sk->sk_state != IUCV_LISTEN) {
net/iucv/af_iucv.c:811:		err = -EBADFD;
net/iucv/af_iucv.c-812-		goto done;
--
net/iucv/af_iucv.c-830-		if (sk->sk_state != IUCV_LISTEN) {
net/iucv/af_iucv.c:831:			err = -EBADFD;
net/iucv/af_iucv.c-832-			break;
--
net/l2tp/l2tp_ppp.c=1213=static int pppol2tp_setsockopt(struct socket *sock, int level, int optname,
--
net/l2tp/l2tp_ppp.c-1235-	/* Get session context from the socket */
net/l2tp/l2tp_ppp.c:1236:	err = -EBADF;
net/l2tp/l2tp_ppp.c-1237-	session = pppol2tp_sock_to_session(sk);
--
net/l2tp/l2tp_ppp.c=1319=static int pppol2tp_getsockopt(struct socket *sock, int level, int optname,
--
net/l2tp/l2tp_ppp.c-1343-	/* Get the session context */
net/l2tp/l2tp_ppp.c:1344:	err = -EBADF;
net/l2tp/l2tp_ppp.c-1345-	session = pppol2tp_sock_to_session(sk);
--
net/socket.c=612=struct socket *sockfd_lookup(int fd, int *err)
--
net/socket.c-618-	if (!file) {
net/socket.c:619:		*err = -EBADF;
net/socket.c-620-		return NULL;
--
net/xdp/xsk.c=1361=static int xsk_bind(struct socket *sock, struct sockaddr_unsized *addr, int addr_len)
--
net/xdp/xsk.c-1431-		if (!xsk_is_bound(umem_xs)) {
net/xdp/xsk.c:1432:			err = -EBADF;
net/xdp/xsk.c-1433-			sockfd_put(sock);
--
sound/core/pcm_lib.c=1949=static int wait_for_avail(struct snd_pcm_substream *substream,
--
sound/core/pcm_lib.c-2017-		case SNDRV_PCM_STATE_DISCONNECTED:
sound/core/pcm_lib.c:2018:			err = -EBADFD;
sound/core/pcm_lib.c-2019-			goto _endloop;
--
sound/core/pcm_native.c=773=static int snd_pcm_hw_params(struct snd_pcm_substream *substream,
--
sound/core/pcm_native.c-793-			    atomic_read(&substream->mmap_count))
sound/core/pcm_native.c:794:				err = -EBADFD;
sound/core/pcm_native.c-795-			break;
sound/core/pcm_native.c-796-		default:
sound/core/pcm_native.c:797:			err = -EBADFD;
sound/core/pcm_native.c-798-			break;
--
sound/core/seq/seq_clientmgr.c=2066=static int snd_seq_ioctl_client_ump_info(struct snd_seq_client *caller,
--
sound/core/seq/seq_clientmgr.c-2094-		if (!cptr->midi_version) {
sound/core/seq/seq_clientmgr.c:2095:			err = -EBADFD;
sound/core/seq/seq_clientmgr.c-2096-			break;
--
sound/core/seq/seq_clientmgr.c-2113-			if (cptr->type != USER_CLIENT) {
sound/core/seq/seq_clientmgr.c:2114:				err = -EBADFD;
sound/core/seq/seq_clientmgr.c-2115-				break;
--
tools/perf/util/s390-cpumsf.c=602=static int s390_cpumsf_samples(struct s390_cpumsf_queue *sfq, u64 *ts)
--
tools/perf/util/s390-cpumsf.c-641-		else {
tools/perf/util/s390-cpumsf.c:642:			err = -EBADF;
tools/perf/util/s390-cpumsf.c-643-			goto out;
]

gemini-3.1-pro-preview

							input: 35303
							output: 24
							thoughts: 20
						

Here's my thought process, summarized as you requested:

**Checking the Block Device Driver**

Okay, hold on a second. Before I proceed any further, I need to make absolutely sure my changes are correctly reflected within the Network Block Device (NBD) driver. Specifically, I'm thinking I need to verify that my modifications are present within the `drivers/block/nbd.c` file. It's easy to make assumptions, but in this domain, thorough verification is paramount. Double-checking this location now will save me significant headaches down the road, and this particular area is the most critical to the success of my recent work. Best to be certain before moving forward.

no matches

map[Expression:config->socks\[i\]->sock == sock]

map[Output:]

gemini-3.1-pro-preview

							input: 35504
							output: 159
							thoughts: 92
						

Okay, here's my thought process on this, distilled down for a fellow expert:

**The `grepper` Conundrum**

Wait a second... I'm using `grepper`, but that thing relies on `git grep`, doesn't it? And *that* won't pick up the changes I just made in `codeeditor`! Damn, I knew I'd read about this. Ah, right, the note... "you will not see your changes when looking at the code using codesearch tools." Yep, that's the rub. So `grepper` is basically blind to what I've just done. No point in continuing down that path.

Alright, no need to panic. The real question is whether the changes actually *took* from `codeeditor`. Best way to verify this: just use `codeeditor` itself. A quick, throwaway edit and a check of the output should be enough to confirm the current state of the code. That should be much faster than anything else I could think of.

CurrentCode snippet matched 2 places, increase context in CurrentCode to avoid ambiguity

map[CurrentCode:	err = -EBADF;
	for (i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			sockfd_put(sock);
			return err;
		}
	} NewCode:	err = -EBADF;
	for (i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			sockfd_put(sock);
			return err;
		}
	} SourceFile:drivers/block/nbd.c]

map[]

gemini-3.1-pro-preview

							input: 36002
							output: 43
							thoughts: 631
						

**Analyzing the Impact of My Changes**

Okay, so my changes in the code base affected both `nbd_add_socket` and `nbd_reconnect_socket`. That's good; it means the modifications were applied where I expected. Now, I need to make sure the logic is still sound. Let's start with `nbd_add_socket`.

I'm stepping through the function, and I'm catching something right away. The code sets `err` to `-EBADF` early on, before the loop that checks for existing sockets. The intent seems to be a default error value, which is then overwritten if a more specific error occurs. The loop iterates through existing sockets. If a matching socket is found in the connection array, then `err` will remain -EBADF. The function then attempts to exit.

However, the question then becomes, will `err = -EBADF` leak?

If the loop completes without finding a match, the code continues. Then, there's a freeze on the block queue. There's a check to ensure the task isn't already setting up the device. This is followed by a memory allocation for a new socket structure. If the allocation fails, the error code is set to `-ENOMEM` and returned. Similarly, if there are allocation errors later, the code sets `err = -ENOMEM` and exits. So, the code seems to overwrite the original `-EBADF` in the failure paths. If allocation and setup succeed, then 0 is returned.

But, hang on a second... what if `config->num_connections` is zero? The loop doesn't execute, so the initial `-EBADF` remains. But then the code proceeds as before, allocating memory and returning 0 if all goes well. In this edge case, `-EBADF` is not used. However, I want to be 100% sure, and go over it once more. I'll read through `nbd_add_socket` again and look for possible leaks of that initial value.

You are repeating the same tool call with the exact same arguments. Please synthesize the information you already have instead of repeating queries.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_add_socket]

gemini-3.1-pro-preview

							input: 37159
							output: 158
							thoughts: 2089
						

**Analysis of `nbd_add_socket` and Potential Error Code Replacement**

Okay, so I've been looking at the `nbd_add_socket` and `nbd_reconnect_socket` functions, trying to figure out if it's safe to insert some new code.  I started by tracing the possible error paths within `nbd_add_socket`. I see that the `err` variable is set in several places, depending on whether `nbd_get_socket`, memory allocation or thread setup succeeds. Importantly, I confirmed `err` is only local, and not used outside the immediate function scope, so I can safely insert code before the assignments to `err` since I am setting a value to `err`, and there are no uses of the variable prior to the code being executed.

I then did the same analysis for `nbd_reconnect_socket`. This also showed local use only for an `err` variable, further validating the safety of my intended code insertion.

However, a quick review then prompted me to think about error codes. I'm focusing on what happens if a socket argument is given that is already in use by the device. Currently, `nbd_add_socket` returns `-EBADF` in that case, but I have been pondering if that is the *most* appropriate error code.  `-EBADF` (bad file descriptor) seemed reasonable initially, but `-EEXIST` (file exists) is also possible. In `nbd_genl_connect`, this error code is passed to userspace, so it makes sense to make it as descriptive as possible.

Since `-EBADF` is used elsewhere in the function, it seems safe. While `-EEXIST` is more semantically accurate, I'm thinking about the effort involved in changing this. Since there's no major technical downside, it makes sense to change this.

I'm thinking that `-EEXIST` may be a slightly better fit, but `-EBADF` would also be understandable in this scenario. Then I think about the other place where an error code would be thrown, when `arg > INT_MAX`, and that throws `-EINVAL`. If `nbd_get_socket` fails, it returns `err` (which is `-ENOTSOCK` or `-EBADF` from `sockfd_lookup`). Since `-EEXIST` makes sense semantically for the socket already being added to the device, I decide to change the error code in `nbd_add_socket` from `-EBADF` to `-EEXIST`.

CurrentCode snippet matched 2 places, increase context in CurrentCode to avoid ambiguity

map[CurrentCode:	err = -EBADF;
	for (i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			sockfd_put(sock);
			return err;
		}
	} NewCode:	err = -EEXIST;
	for (i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			sockfd_put(sock);
			return err;
		}
	} SourceFile:drivers/block/nbd.c]

map[]

gemini-3.1-pro-preview

							input: 39978
							output: 294
							thoughts: 15
						

Okay, here's my summary, considering my expertise:

**Strategic Adaptation & Contextual Relevance**

Alright, I'm analyzing the need for change and realize a simple edit won't cut it. I need to ensure a holistic approach. It’s clear to me that if I'm altering something, especially within this specific area, I have to consider the impact and make the corresponding adjustments in two distinct locations. A localized fix will create inconsistencies; a robust solution requires that I identify the relationship between these locations and ensure alignment to maintain coherence. I'm going to have to dive deeper than I originally anticipated to fully understand the dependencies. This process must focus on the interconnectedness of these two sites and how a change in one ripples outward to affect the other.

map[CurrentCode:	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	err = -EBADF;
	for (i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			sockfd_put(sock);
			return err;
		}
	}

	/*
	 * We need to make sure we don't get any errant requests while we're
	 * reallocating the ->socks array.
	 */ NewCode:	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	err = -EEXIST;
	for (i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			sockfd_put(sock);
			return err;
		}
	}

	/*
	 * We need to make sure we don't get any errant requests while we're
	 * reallocating the ->socks array.
	 */ SourceFile:drivers/block/nbd.c]

map[]

gemini-3.1-pro-preview

							input: 40452
							output: 240
							thoughts: 11
						

Okay, here's my interpretation of those thoughts, crafted with the understanding that I'm speaking to a fellow expert:

**Navigating the NBD Reconnection Socket Function**

Right, let's dive into this `nbd_reconnect_socket` function. My initial thoughts center on the core problem: establishing a robust and graceful reconnect strategy for NBD clients. We're dealing with potentially unstable network connections, and the client *must* recover automatically. So, I need to ensure this function handles various failure scenarios. What happens if the initial socket creation fails? What about errors during the connection handshake? Are we properly accounting for timeouts?

My mental checklist starts filling up: I need to scrutinize the error handling. Is there comprehensive logging at *every* point a connection might fail? This logging is critical for debugging, especially when we're dealing with remote systems. And that brings up another key area: retry logic. How many times will we attempt a reconnect? What's the backoff strategy to avoid overwhelming the server? Exponential backoff, I'd imagine, is the best approach. Are we using it, or something equally intelligent?

Then there's the question of synchronization. Multiple threads or processes might be trying to access the same NBD device simultaneously. The reconnection process needs to be thread-safe, of course. Are we using mutexes or semaphores, or is there a smarter synchronization method being employed? And what about resource cleanup? If a connection fails during a previous attempt, are we properly closing file descriptors, and freeing allocated memory? Memory leaks are the enemy.

Finally, I'm thinking about the user experience. How will the client *signal* the reconnect process is happening? A simple "reconnecting..." message is probably not enough. We might need a more informative progress indicator and clear communication of the cause of the disconnect, if available. I need to make sure the user can be sure that this action is occurring, and in a way that minimizes disruption. And the most important question is, can we *ensure* data integrity through this process? Every action must be taken to ensure that happens.

map[CurrentCode:	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	err = -EBADF;
	for (i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			sockfd_put(sock);
			return err;
		}
	}

	args = kzalloc_obj(*args); NewCode:	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	err = -EEXIST;
	for (i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			sockfd_put(sock);
			return err;
		}
	}

	args = kzalloc_obj(*args); SourceFile:drivers/block/nbd.c]

map[]

gemini-3.1-pro-preview

							input: 41152
							output: 20
							thoughts: 93
						

**Socket Management Investigation**

Okay, let's make absolutely sure we haven't missed a socket creation or modification point within the NBD driver code. My immediate concern is ensuring the robustness of our socket handling. `nbd_add_socket` seems like the primary function for introducing a *new* socket, and `nbd_reconnect_socket` handles the replacement of a dead or broken one. However, I want to be *certain* there aren't any sneaky, less obvious methods involved. We can't afford to overlook a socket injection point.

So, I'll perform a focused search. Let's delve into `drivers/block/nbd.c` and hunt for instances of `sockfd_lookup` or `nbd_get_socket`. These functions are potential candidates for socket retrieval and thus socket adding. A thorough scan using these key search terms should uncover anything we've possibly overlooked. My aim is to be meticulously complete in this socket lifecycle review.

map[Expression:nbd_get_socket]

map[Output:drivers/block/nbd.c=1184=static blk_status_t nbd_queue_rq(struct blk_mq_hw_ctx *hctx,
--
drivers/block/nbd.c-1212-
drivers/block/nbd.c:1213:static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd,
drivers/block/nbd.c-1214-				     int *err)
--
drivers/block/nbd.c=1241=static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
--
drivers/block/nbd.c-1253-		return -EINVAL;
drivers/block/nbd.c:1254:	sock = nbd_get_socket(nbd, arg, &err);
drivers/block/nbd.c-1255-	if (!sock)
--
drivers/block/nbd.c=1313=static int nbd_reconnect_socket(struct nbd_device *nbd, unsigned long arg)
--
drivers/block/nbd.c-1320-
drivers/block/nbd.c:1321:	sock = nbd_get_socket(nbd, arg, &err);
drivers/block/nbd.c-1322-	if (!sock)
]

gemini-3.1-pro-preview

							input: 41828
							output: 17
							thoughts: 56
						

Okay, here's my take on those code interactions, focusing on the key takeaways for someone familiar with network block devices like myself:

**Socket Management in the NBD Driver**

Alright, so the socket management in this NBD driver is pretty straightforward. I see that the core function, `nbd_get_socket`, acts as the centralized point for obtaining file descriptors related to sockets. That's a good design choice, centralizing the lookup.

More specifically, the code indicates that only `nbd_add_socket` and `nbd_reconnect_socket` are responsible for initiating the retrieval of those socket file descriptors, by calling that `nbd_get_socket` function. Further, I can see that `sockfd_lookup` is called exclusively within the `nbd_get_socket` function. This makes it a clean and contained piece of logic: If I need to understand socket lookups, I only need to look at the `nbd_get_socket` function and any functions that call it.

map[Expression:sockfd_lookup]

map[Output:drivers/block/nbd.c=1213=static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd,
--
drivers/block/nbd.c-1218-	*err = 0;
drivers/block/nbd.c:1219:	sock = sockfd_lookup(fd, err);
drivers/block/nbd.c-1220-	if (!sock)
--
drivers/infiniband/hw/usnic/usnic_transport.c=144=struct socket *usnic_transport_get_socket(int sock_fd)
--
drivers/infiniband/hw/usnic/usnic_transport.c-149-
drivers/infiniband/hw/usnic/usnic_transport.c:150:	/* sockfd_lookup will internally do a fget */
drivers/infiniband/hw/usnic/usnic_transport.c:151:	sock = sockfd_lookup(sock_fd, &err);
drivers/infiniband/hw/usnic/usnic_transport.c-152-	if (!sock) {
--
drivers/net/gtp.c=1648=static struct sock *gtp_encap_enable_socket(int fd, int type,
--
drivers/net/gtp.c-1657-
drivers/net/gtp.c:1658:	sock = sockfd_lookup(fd, &err);
drivers/net/gtp.c-1659-	if (!sock) {
--
drivers/net/ovpn/netlink.c=347=int ovpn_nl_peer_new_doit(struct sk_buff *skb, struct genl_info *info)
--
drivers/net/ovpn/netlink.c-392-	sockfd = nla_get_u32(attrs[OVPN_A_PEER_SOCKET]);
drivers/net/ovpn/netlink.c:393:	/* sockfd_lookup() increases sock's refcounter */
drivers/net/ovpn/netlink.c:394:	sock = sockfd_lookup(sockfd, &ret);
drivers/net/ovpn/netlink.c-395-	if (!sock) {
--
drivers/scsi/iscsi_tcp.c=664=iscsi_sw_tcp_conn_bind(struct iscsi_cls_session *cls_session,
--
drivers/scsi/iscsi_tcp.c-675-	/* lookup for existing socket */
drivers/scsi/iscsi_tcp.c:676:	sock = sockfd_lookup((int)transport_eph, &err);
drivers/scsi/iscsi_tcp.c-677-	if (!sock) {
drivers/scsi/iscsi_tcp.c-678-		iscsi_conn_printk(KERN_ERR, conn,
drivers/scsi/iscsi_tcp.c:679:				  "sockfd_lookup failed %d\n", err);
drivers/scsi/iscsi_tcp.c-680-		return -EEXIST;
--
drivers/usb/usbip/stub_dev.c=42=static ssize_t usbip_sockfd_store(struct device *dev, struct device_attribute *attr,
--
drivers/usb/usbip/stub_dev.c-73-
drivers/usb/usbip/stub_dev.c:74:		socket = sockfd_lookup(sockfd, &err);
drivers/usb/usbip/stub_dev.c-75-		if (!socket) {
--
drivers/usb/usbip/vhci_sysfs.c=309=static ssize_t attach_store(struct device *dev, struct device_attribute *attr,
--
drivers/usb/usbip/vhci_sysfs.c-360-	/* Extract socket from fd. */
drivers/usb/usbip/vhci_sysfs.c:361:	socket = sockfd_lookup(sockfd, &err);
drivers/usb/usbip/vhci_sysfs.c-362-	if (!socket) {
--
drivers/usb/usbip/vudc_sysfs.c=93=static ssize_t usbip_sockfd_store(struct device *dev,
--
drivers/usb/usbip/vudc_sysfs.c-137-
drivers/usb/usbip/vudc_sysfs.c:138:		socket = sockfd_lookup(sockfd, &err);
drivers/usb/usbip/vudc_sysfs.c-139-		if (!socket) {
--
drivers/vhost/net.c=1456=static struct socket *get_raw_socket(int fd)
--
drivers/vhost/net.c-1458-	int r;
drivers/vhost/net.c:1459:	struct socket *sock = sockfd_lookup(fd, &r);
drivers/vhost/net.c-1460-
--
include/linux/net.h=285=struct file *sock_alloc_file(struct socket *sock, int flags, const char *dname);
include/linux/net.h:286:struct socket *sockfd_lookup(int fd, int *err);
include/linux/net.h-287-struct socket *sock_from_file(struct file *file);
--
kernel/bpf/reuseport_array.c=232=int bpf_fd_reuseport_array_update_elem(struct bpf_map *map, void *key,
--
kernel/bpf/reuseport_array.c-258-
kernel/bpf/reuseport_array.c:259:	socket = sockfd_lookup(fd, &err);
kernel/bpf/reuseport_array.c-260-	if (!socket)
--
net/bluetooth/bnep/sock.c=53=static int do_bnep_sock_ioctl(struct socket *sock, unsigned int cmd, void __user *argp)
--
net/bluetooth/bnep/sock.c-72-
net/bluetooth/bnep/sock.c:73:		nsock = sockfd_lookup(ca.sock, &err);
net/bluetooth/bnep/sock.c-74-		if (!nsock)
--
net/bluetooth/hidp/sock.c=50=static int do_hidp_sock_ioctl(struct socket *sock, unsigned int cmd, void __user *argp)
--
net/bluetooth/hidp/sock.c-69-
net/bluetooth/hidp/sock.c:70:		csock = sockfd_lookup(ca.ctrl_sock, &err);
net/bluetooth/hidp/sock.c-71-		if (!csock)
--
net/bluetooth/hidp/sock.c-73-
net/bluetooth/hidp/sock.c:74:		isock = sockfd_lookup(ca.intr_sock, &err);
net/bluetooth/hidp/sock.c-75-		if (!isock) {
--
net/bluetooth/hidp/sock.c=148=static int hidp_sock_compat_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
--
net/bluetooth/hidp/sock.c-198-
net/bluetooth/hidp/sock.c:199:		csock = sockfd_lookup(ca.ctrl_sock, &err);
net/bluetooth/hidp/sock.c-200-		if (!csock)
--
net/bluetooth/hidp/sock.c-202-
net/bluetooth/hidp/sock.c:203:		isock = sockfd_lookup(ca.intr_sock, &err);
net/bluetooth/hidp/sock.c-204-		if (!isock) {
--
net/core/bpf_sk_storage.c=80=static void *bpf_fd_sk_storage_lookup_elem(struct bpf_map *map, void *key)
--
net/core/bpf_sk_storage.c-86-	fd = *(int *)key;
net/core/bpf_sk_storage.c:87:	sock = sockfd_lookup(fd, &err);
net/core/bpf_sk_storage.c-88-	if (sock) {
--
net/core/bpf_sk_storage.c=97=static long bpf_fd_sk_storage_update_elem(struct bpf_map *map, void *key,
--
net/core/bpf_sk_storage.c-104-	fd = *(int *)key;
net/core/bpf_sk_storage.c:105:	sock = sockfd_lookup(fd, &err);
net/core/bpf_sk_storage.c-106-	if (sock) {
--
net/core/bpf_sk_storage.c=117=static long bpf_fd_sk_storage_delete_elem(struct bpf_map *map, void *key)
--
net/core/bpf_sk_storage.c-122-	fd = *(int *)key;
net/core/bpf_sk_storage.c:123:	sock = sockfd_lookup(fd, &err);
net/core/bpf_sk_storage.c-124-	if (sock) {
--
net/core/sock_map.c=556=int sock_map_update_elem_sys(struct bpf_map *map, void *key, void *value,
--
net/core/sock_map.c-570-
net/core/sock_map.c:571:	sock = sockfd_lookup(ufd, &ret);
net/core/sock_map.c-572-	if (!sock)
--
net/handshake/netlink.c=136=int handshake_nl_done_doit(struct sk_buff *skb, struct genl_info *info)
--
net/handshake/netlink.c-146-
net/handshake/netlink.c:147:	sock = sockfd_lookup(fd, &err);
net/handshake/netlink.c-148-	if (!sock)
--
net/kcm/kcmsock.c=1342=static int kcm_attach_ioctl(struct socket *sock, struct kcm_attach *info)
--
net/kcm/kcmsock.c-1347-
net/kcm/kcmsock.c:1348:	csock = sockfd_lookup(info->fd, &err);
net/kcm/kcmsock.c-1349-	if (!csock)
--
net/kcm/kcmsock.c=1468=static int kcm_unattach_ioctl(struct socket *sock, struct kcm_unattach *info)
--
net/kcm/kcmsock.c-1476-
net/kcm/kcmsock.c:1477:	csock = sockfd_lookup(info->fd, &err);
net/kcm/kcmsock.c-1478-	if (!csock)
--
net/l2tp/l2tp_core.c=1642=int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
--
net/l2tp/l2tp_core.c-1664-	} else {
net/l2tp/l2tp_core.c:1665:		sock = sockfd_lookup(tunnel->fd, &ret);
net/l2tp/l2tp_core.c-1666-		if (!sock)
--
net/psp/psp_nl.c=282=int psp_assoc_device_get_locked(const struct genl_split_ops *ops,
--
net/psp/psp_nl.c-293-	fd = nla_get_u32(info->attrs[PSP_A_ASSOC_SOCK_FD]);
net/psp/psp_nl.c:294:	socket = sockfd_lookup(fd, &err);
net/psp/psp_nl.c-295-	if (!socket)
--
net/socket.c=597=EXPORT_SYMBOL(sock_from_file);
--
net/socket.c-599-/**
net/socket.c:600: *	sockfd_lookup - Go from a file number to its socket slot
net/socket.c-601- *	@fd: file handle
--
net/socket.c-611-
net/socket.c:612:struct socket *sockfd_lookup(int fd, int *err)
net/socket.c-613-{
--
net/socket.c-629-}
net/socket.c:630:EXPORT_SYMBOL(sockfd_lookup);
net/socket.c-631-
--
net/sunrpc/svcsock.c=1499=int svc_addsock(struct svc_serv *serv, struct net *net, const int fd,
--
net/sunrpc/svcsock.c-1502-	int err = 0;
net/sunrpc/svcsock.c:1503:	struct socket *so = sockfd_lookup(fd, &err);
net/sunrpc/svcsock.c-1504-	struct svc_sock *svsk = NULL;
--
net/xdp/xsk.c=1339=static struct socket *xsk_lookup_xsk_from_fd(int fd)
--
net/xdp/xsk.c-1343-
net/xdp/xsk.c:1344:	sock = sockfd_lookup(fd, &err);
net/xdp/xsk.c-1345-	if (!sock)
--
net/xdp/xskmap.c=161=static long xsk_map_update_elem(struct bpf_map *map, void *key, void *value,
--
net/xdp/xskmap.c-176-
net/xdp/xskmap.c:177:	sock = sockfd_lookup(fd, &err);
net/xdp/xskmap.c-178-	if (!sock)
]

gemini-3.1-pro-preview

							input: 45667
							output: 43
							thoughts: 366
						

**Analyzing the NBD Socket Handling**

Okay, so I've zeroed in on the use of `sockfd_lookup` within `drivers/block/nbd.c`. It's only used by `nbd_get_socket`, which is itself only called by `nbd_add_socket` and `nbd_reconnect_socket`. This means my proposed fix neatly covers every scenario where a socket is introduced into the NBD device. That's good; it confirms my understanding of the call graph.

Let's re-examine the code in those two functions, just to be completely thorough. In `nbd_add_socket`, I see:

```c
	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	err = -EEXIST;
	for (i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			sockfd_put(sock);
			return err;
		}
	}
```

And similarly in `nbd_reconnect_socket`:

```c
	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	err = -EEXIST;
	for (i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			sockfd_put(sock);
			return err;
		}
	}
```

Perfect. This checks if the socket is already present before adding it, which is exactly what we want. Crucially, the code correctly calls `sockfd_put(sock)` to release the reference gained by `nbd_get_socket` (which, of course, calls `sockfd_lookup`) if the socket already exists. The use of `-EEXIST` for the existing socket is also appropriate. This is a robust check that is correctly handled in both cases. Now, let's revisit the specifics of `nbd_get_socket`.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_get_socket]

map[SourceCode:1213:	static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd,
1214:					     int *err)
1215:	{
1216:		struct socket *sock;
1217:	
1218:		*err = 0;
1219:		sock = sockfd_lookup(fd, err);
1220:		if (!sock)
1221:			return NULL;
1222:	
1223:		if (!sk_is_tcp(sock->sk) &&
1224:		    !sk_is_stream_unix(sock->sk)) {
1225:			dev_err(disk_to_dev(nbd->disk), "Unsupported socket: should be TCP or UNIX.\n");
1226:			*err = -EINVAL;
1227:			sockfd_put(sock);
1228:			return NULL;
1229:		}
1230:	
1231:		if (sock->ops->shutdown == sock_no_shutdown) {
1232:			dev_err(disk_to_dev(nbd->disk), "Unsupported socket: shutdown callout must be supported.\n");
1233:			*err = -EINVAL;
1234:			sockfd_put(sock);
1235:			return NULL;
1236:		}
1237:	
1238:		return sock;
1239:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 46953
							output: 42
							thoughts: 655
						

**Analyzing Socket Management in the NBD Driver**

Okay, so I've been reviewing this code, and it seems like the `nbd_get_socket` function does indeed return a valid `struct socket *`, and importantly, the reference count is incremented. Good. I made sure to call `sockfd_put(sock)` to decrement the reference count when a duplicate is found.

Now, let me make sure I'm not missing anything. I need to be certain that the logic for detecting duplicate sockets is sound. Where else could `config->socks` be populated? Alright, `config->socks` is an array of `struct nbd_sock *`, and from what I can see, it's only ever populated within `nbd_add_socket`. Also, it's updated in `nbd_reconnect_socket`. So, checking `config->socks[i]->sock == sock` should be a reliable way to detect duplicates, assuming no unexpected concurrent modifications.

Next, I need to confirm that `config->socks` can safely be `NULL`. Let's see...in `nbd_add_socket`, if `config->num_connections` is zero, `config->socks` will be `NULL`, but the loop that uses this array won't execute. Safe. Now, `nbd_reconnect_socket`. If `config->num_connections` is zero there, it also won't execute, returning `-ENOSPC`, which is correct behavior in that situation. So far, so good.

Now, I have to consider concurrency. Could `config->num_connections` or `config->socks` be modified concurrently? Both `nbd_add_socket` and `nbd_reconnect_socket` are called with `nbd->config_lock` held, so the `config->num_connections` and `config->socks` access is protected. Good.

Time to broaden my review. Let's think about adding the same socket to *different* NBD devices. Is this even allowed? It's not a direct issue in the code, but it makes me think... If the same socket *is* added to multiple NBD devices, then they're both calling `sk_set_memalloc` on the *same* socket. `sk_set_memalloc` increments `memalloc_socks_key`. The thing is, when the NBD devices are destroyed, they don't call `sk_clear_memalloc`. Hold on, I remember something... the initial explanation says: "The NBD driver never calls `sk_clear_memalloc` (it relies on the socket destruction to clear it, but `sk_clear_memalloc` is actually not called automatically on socket destruction in standard kernels, it's only called by specific subsystems like sunrpc/wireguard). This results in a persistent leak of the `memalloc_socks_key` static branch reference." Wait a minute... if `sk_clear_memalloc` isn't called automatically on socket destruction, *any* use of `sk_set_memalloc` in NBD will leak the static key if the socket is destroyed? I need to double-check `sk_set_memalloc` and `sk_clear_memalloc` in `net/core/sock.c` to be sure.

map[ContextFile:net/core/sock.c IncludeLines:true Name:sk_set_memalloc]

map[SourceCode: 294:	/**
 295:	 * sk_set_memalloc - sets %SOCK_MEMALLOC
 296:	 * @sk: socket to set it on
 297:	 *
 298:	 * Set %SOCK_MEMALLOC on a socket for access to emergency reserves.
 299:	 * It's the responsibility of the admin to adjust min_free_kbytes
 300:	 * to meet the requirements
 301:	 */
 302:	void sk_set_memalloc(struct sock *sk)
 303:	{
 304:		sock_set_flag(sk, SOCK_MEMALLOC);
 305:		sk->sk_allocation |= __GFP_MEMALLOC;
 306:		static_branch_inc(&memalloc_socks_key);
 307:	}
 SourceFile:net/core/sock.c]

gemini-3.1-pro-preview

							input: 48604
							output: 42
							thoughts: 9
						

Okay, here's my attempt at summarizing the thought process, tailored for an expert audience, and written as if it's my own internal monologue:

**Deep Dive into Memory Allocation and Optimization**

Alright, let's dissect this. "sk_clear_memalloc"... immediately, my mind starts tracing the implications. This isn't just a function, it's a critical point in the memory management lifecycle. "sk" suggests we're dealing with something specific, potentially a library or system with its own memory allocator, which piques my interest. The "clear" part is key. We're not just allocating; we're also implying some kind of zeroing or initialization. This impacts performance directly.

My initial thoughts run along several parallel tracks:

*   **Underlying Memory Model:** First, what kind of memory model are we dealing with? Is it a heap allocation, stack allocation, or something more specialized? Does "sk" provide its own pool or rely on the underlying OS allocator? This will dictate the efficiency of `sk_clear_memalloc`.
*   **Initialization Strategy:** The 'clear' part could mean setting the allocated memory to all zeros. Is this a full-zeroing operation? If so, is this an unavoidable requirement due to security or application constraints? If not, can we optimize it with a more efficient pattern to skip zeroes. If we are using a specific pattern, how does this affect memory allocation algorithms?
*   **Performance Bottlenecks:** What's the impact on performance? Zeroing a large block of memory is inherently costly. Is this function critical path? If so, we're likely looking for ways to reduce its overhead. Can we use platform-specific intrinsics (like `memset` optimized with SIMD instructions) or hardware acceleration to speed this up?
*   **Context is Crucial:** What's the context? What data structures are allocated using `sk_clear_memalloc`? Understanding the data structures' alignment, padding, and access patterns will give valuable insights for optimization. Are we dealing with frequent small allocations or fewer, large ones? This directs our focus on either fragmentation or allocation overhead.
*   **Potential Alternatives:** Is there an alternative pattern to initialization? Could we delay the zeroing until it's needed? Lazy initialization might be an option. Perhaps the application can provide hints about data, reducing the need for zero-ing? This would be a great performance gain.
*   **Threading and Synchronization:** Is this function thread-safe? If it's used in a multithreaded environment, how does it handle concurrency and potential data races? Proper synchronization is vital.

The code itself is likely the next step to fully understand its behaviour and identify if any of these insights apply. I'd need to consider profiling to validate hypotheses, and if it's a performance bottleneck, I'd investigate alternative strategies.

map[ContextFile:net/core/sock.c IncludeLines:true Name:sk_clear_memalloc]

map[SourceCode: 310:	void sk_clear_memalloc(struct sock *sk)
 311:	{
 312:		sock_reset_flag(sk, SOCK_MEMALLOC);
 313:		sk->sk_allocation &= ~__GFP_MEMALLOC;
 314:		static_branch_dec(&memalloc_socks_key);
 315:	
 316:		/*
 317:		 * SOCK_MEMALLOC is allowed to ignore rmem limits to ensure forward
 318:		 * progress of swapping. SOCK_MEMALLOC may be cleared while
 319:		 * it has rmem allocations due to the last swapfile being deactivated
 320:		 * but there is a risk that the socket is unusable due to exceeding
 321:		 * the rmem limits. Reclaim the reserves and obey rmem limits again.
 322:		 */
 323:		sk_mem_reclaim(sk);
 324:	}
 SourceFile:net/core/sock.c]

gemini-3.1-pro-preview

							input: 49532
							output: 24
							thoughts: 28
						

Here's my thought process, as if I were considering this question:

**Investigating Memory Allocation Cleanup in Socket Destruction**

Okay, so I need to confirm something about memory management in socket destruction. The question is whether `sk_clear_memalloc` is actually called when a socket is cleaned up. My initial thought is to trace the destruction path to see where memory is explicitly freed. That means I need to look at functions related to socket teardown, specifically something like `sk_destruct` – or a similar function name that handles the socket's final lifecycle. I'll start there.

map[Name:sk_clear_memalloc]

map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:sock_free SourceFile:drivers/net/wireguard/socket.c SourceLine:337] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:xs_reset_transport SourceFile:net/sunrpc/xprtsock.c SourceLine:1289]] TruncatedOutput:false]

gemini-3.1-pro-preview

							input: 49834
							output: 40
							thoughts: 115
						

**Investigating `sk_clear_memalloc` Usage and Socket Destruction**

Okay, this is interesting. I'm taking a look at `sk_clear_memalloc` and its call sites. It seems it's only called in `drivers/net/wireguard/socket.c` and `net/sunrpc/xprtsock.c`. That's unexpected, especially since it's *not* called in `net/core/sock.c` during socket destruction – that's the usual place to expect this sort of memory management cleanup.

So, if a socket has `SOCK_MEMALLOC` set, which implies memory pressure concerns, does the kernel *automatically* decrement the `memalloc_socks_key` counter when that socket is destroyed? It's crucial to know this, otherwise we might have a leak or mis-accounting. Time to dive into the `sk_destruct` function within `net/core/sock.c`. That's where socket cleanup happens, so it's the obvious place to investigate this behavior.

map[ContextFile:net/core/sock.c IncludeLines:true Name:sk_destruct]

map[SourceCode:2402:	void sk_destruct(struct sock *sk)
2403:	{
2404:		bool use_call_rcu = sock_flag(sk, SOCK_RCU_FREE);
2405:	
2406:		if (rcu_access_pointer(sk->sk_reuseport_cb)) {
2407:			reuseport_detach_sock(sk);
2408:			use_call_rcu = true;
2409:		}
2410:	
2411:		if (use_call_rcu)
2412:			call_rcu(&sk->sk_rcu, __sk_destruct);
2413:		else
2414:			__sk_destruct(&sk->sk_rcu);
2415:	}
 SourceFile:net/core/sock.c]

gemini-3.1-pro-preview

							input: 50456
							output: 41
							thoughts: 11
						

Okay, here's my take on those thoughts, tailored for an expert audience:

**Diving into `__sk_destruct`**

Alright, let's get down to it. Time to poke around in `__sk_destruct`. That's where the rubber meets the road, isn't it? It's the critical point, the moment where the kernel's taking out the trash and releasing resources. Depending on the architecture, this function likely manages the teardown process for a specific kernel object, potentially a socket. I'll need to drill down into the implementation to understand how it handles this teardown. Specifically, I need to know: what's freed, the ordering of the operations, if there are any race conditions lurking in there, how it interacts with reference counts, and if there are any potential memory leaks if something goes wrong during the teardown. I anticipate a cascade of dependent object destructors. Let's see if my mental model of its behavior holds true. I have a feeling that a specific bug I've been chasing has something to do with this region of code.

map[ContextFile:net/core/sock.c IncludeLines:true Name:__sk_destruct]

map[SourceCode:2342:	/* Sockets having SOCK_RCU_FREE will call this function after one RCU
2343:	 * grace period. This is the case for UDP sockets and TCP listeners.
2344:	 */
2345:	static void __sk_destruct(struct rcu_head *head)
2346:	{
2347:		struct sock *sk = container_of(head, struct sock, sk_rcu);
2348:		struct net *net = sock_net(sk);
2349:		struct sk_filter *filter;
2350:	
2351:		if (sk->sk_destruct)
2352:			sk->sk_destruct(sk);
2353:	
2354:		filter = rcu_dereference_check(sk->sk_filter,
2355:					       refcount_read(&sk->sk_wmem_alloc) == 0);
2356:		if (filter) {
2357:			sk_filter_uncharge(sk, filter);
2358:			RCU_INIT_POINTER(sk->sk_filter, NULL);
2359:		}
2360:	
2361:		sock_disable_timestamp(sk, SK_FLAGS_TIMESTAMP);
2362:	
2363:	#ifdef CONFIG_BPF_SYSCALL
2364:		bpf_sk_storage_free(sk);
2365:	#endif
2366:	
2367:		if (atomic_read(&sk->sk_omem_alloc))
2368:			pr_debug("%s: optmem leakage (%d bytes) detected\n",
2369:				 __func__, atomic_read(&sk->sk_omem_alloc));
2370:	
2371:		if (sk->sk_frag.page) {
2372:			put_page(sk->sk_frag.page);
2373:			sk->sk_frag.page = NULL;
2374:		}
2375:	
2376:		/* We do not need to acquire sk->sk_peer_lock, we are the last user. */
2377:		put_cred(sk->sk_peer_cred);
2378:		put_pid(sk->sk_peer_pid);
2379:	
2380:		if (likely(sk->sk_net_refcnt)) {
2381:			put_net_track(net, &sk->ns_tracker);
2382:		} else {
2383:			__netns_tracker_free(net, &sk->ns_tracker, false);
2384:			net_passive_dec(net);
2385:		}
2386:		sk_prot_free(sk->sk_prot_creator, sk);
2387:	}
 SourceFile:net/core/sock.c]

gemini-3.1-pro-preview

							input: 51508
							output: 24
							thoughts: 83
						

**A Critical Oversight - Potential Memory Leak!**

Okay, hold on a second. I'm reviewing this code, and something's not quite right. It seems like `memalloc_socks_key` isn't being decremented within `__sk_destruct`! That's a huge red flag. If a socket has `SOCK_MEMALLOC` set, the caller is *supposed* to call `sk_clear_memalloc` before the socket is destroyed, right? Otherwise, we've got a classic memory leak in `memalloc_socks_key`, and that's not good at all. I need to get to the bottom of this. Let's see if NBD, in its interactions, correctly calls `sk_clear_memalloc` when it's supposed to. Time to dig in and verify that. This could be a significant issue if missed.

map[Name:sk_clear_memalloc]

map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:sock_free SourceFile:drivers/net/wireguard/socket.c SourceLine:337] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:xs_reset_transport SourceFile:net/sunrpc/xprtsock.c SourceLine:1289]] TruncatedOutput:false]

gemini-3.1-pro-preview

							input: 51928
							output: 43
							thoughts: 81
						

Okay, here's my breakdown of what I'm seeing:

**The NBD Memory Allocation Conundrum**

Alright, wait a minute... I was just reviewing this NBD code and I've hit something that smells like a memory leak. I'm certain that `sk_clear_memalloc` isn't being explicitly called by NBD anywhere. This is a bit of a red flag. The thing is, if NBD is diligently setting `sk_set_memalloc` in its socket initialization but *never* clears that flag, then we're in trouble. Every single time an NBD device gets spun up and then torn down – which, in a dynamic environment, could be quite frequent – we're going to leak entries in `memalloc_socks_key`. Those entries accumulate, slowly depleting the allocated memory pool, and potentially resulting in significant stability issues. I need to track down where this is happening. The two obvious places to check are in `nbd_start_device` and `nbd_reconnect_socket`. That's where I need to start my investigation.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_start_device]

map[SourceCode:1471:	static int nbd_start_device(struct nbd_device *nbd)
1472:	{
1473:		struct nbd_config *config = nbd->config;
1474:		int num_connections = config->num_connections;
1475:		int error = 0, i;
1476:	
1477:		if (nbd->pid)
1478:			return -EBUSY;
1479:		if (!config->socks)
1480:			return -EINVAL;
1481:		if (num_connections > 1 &&
1482:		    !(config->flags & NBD_FLAG_CAN_MULTI_CONN)) {
1483:			dev_err(disk_to_dev(nbd->disk), "server does not support multiple connections per device.\n");
1484:			return -EINVAL;
1485:		}
1486:	
1487:	retry:
1488:		mutex_unlock(&nbd->config_lock);
1489:		blk_mq_update_nr_hw_queues(&nbd->tag_set, num_connections);
1490:		mutex_lock(&nbd->config_lock);
1491:	
1492:		/* if another code path updated nr_hw_queues, retry until succeed */
1493:		if (num_connections != config->num_connections) {
1494:			num_connections = config->num_connections;
1495:			goto retry;
1496:		}
1497:	
1498:		nbd->pid = task_pid_nr(current);
1499:	
1500:		nbd_parse_flags(nbd);
1501:	
1502:		error = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
1503:		if (error) {
1504:			dev_err(disk_to_dev(nbd->disk), "device_create_file failed for pid!\n");
1505:			return error;
1506:		}
1507:		set_bit(NBD_RT_HAS_PID_FILE, &config->runtime_flags);
1508:	
1509:		nbd_dev_dbg_init(nbd);
1510:		for (i = 0; i < num_connections; i++) {
1511:			struct recv_thread_args *args;
1512:	
1513:			args = kzalloc_obj(*args);
1514:			if (!args) {
1515:				sock_shutdown(nbd);
1516:				/*
1517:				 * If num_connections is m (2 < m),
1518:				 * and NO.1 ~ NO.n(1 < n < m) kzallocs are successful.
1519:				 * But NO.(n + 1) failed. We still have n recv threads.
1520:				 * So, add flush_workqueue here to prevent recv threads
1521:				 * dropping the last config_refs and trying to destroy
1522:				 * the workqueue from inside the workqueue.
1523:				 */
1524:				if (i)
1525:					flush_workqueue(nbd->recv_workq);
1526:				return -ENOMEM;
1527:			}
1528:			sk_set_memalloc(config->socks[i]->sock->sk);
1529:			if (nbd->tag_set.timeout)
1530:				config->socks[i]->sock->sk->sk_sndtimeo =
1531:					nbd->tag_set.timeout;
1532:			atomic_inc(&config->recv_threads);
1533:			refcount_inc(&nbd->config_refs);
1534:			INIT_WORK(&args->work, recv_work);
1535:			args->nbd = nbd;
1536:			args->nsock = config->socks[i];
1537:			args->index = i;
1538:			queue_work(nbd->recv_workq, &args->work);
1539:		}
1540:		return nbd_set_size(nbd, config->bytesize, nbd_blksize(config));
1541:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 53471
							output: 20
							thoughts: 278
						

**NBD Driver Memory Leak Discovery**

Okay, so I'm tracing the memory allocation and deallocation within the NBD driver, specifically looking at how `memalloc_socks_key` is handled. I see that `sk_set_memalloc` is definitely being called in both `nbd_start_device` and `nbd_reconnect_socket`. But hang on... I'm not seeing *any* calls to `sk_clear_memalloc` anywhere in the NBD code.

This is a problem. If `sk_clear_memalloc` is never called, that means every time an NBD device is spun up and then later torn down, the `memalloc_socks_key` reference is leaking. It's accumulating. This... feels like a significant oversight. Is this a documented bug? I should check.

The provided explanation mentions that the NBD driver *expects* socket destruction to handle the cleanup. However, the documentation also points out the core issue: `sk_clear_memalloc` is *not* automatically called during socket destruction in vanilla kernels. It's specific to certain subsystems like `sunrpc` or `wireguard`.

I'm starting to put this together. The initial fix, which addresses the duplicate socket issue, seems to prevent the potential *double* call to `sk_set_memalloc` on the same socket. That's good, but it doesn't solve the core leak. What happens when a socket is closed normally? If `sk_clear_memalloc` isn't called during socket teardown, then we're leaking even with correct NBD usage! This seems like a critical flaw.

Okay, I need to confirm this. I need to explicitly check the NBD code again to be absolutely sure that `sk_clear_memalloc` is never being called. This is a potential vulnerability and I need to be 100% sure.

map[Expression:sk_clear_memalloc]

map[Output:drivers/net/wireguard/socket.c=333=static void sock_free(struct sock *sock)
--
drivers/net/wireguard/socket.c-336-		return;
drivers/net/wireguard/socket.c:337:	sk_clear_memalloc(sock);
drivers/net/wireguard/socket.c-338-	udp_tunnel_sock_release(sock->sk_socket);
--
include/net/sock.h=1245=void sk_set_memalloc(struct sock *sk);
include/net/sock.h:1246:void sk_clear_memalloc(struct sock *sk);
include/net/sock.h-1247-
--
net/core/sock.c=308=EXPORT_SYMBOL_GPL(sk_set_memalloc);
net/core/sock.c-309-
net/core/sock.c:310:void sk_clear_memalloc(struct sock *sk)
net/core/sock.c-311-{
--
net/core/sock.c-324-}
net/core/sock.c:325:EXPORT_SYMBOL_GPL(sk_clear_memalloc);
net/core/sock.c-326-
--
net/sunrpc/xprtsock.c=1268=static void xs_reset_transport(struct sock_xprt *transport)
--
net/sunrpc/xprtsock.c-1288-	if (atomic_read(&transport->xprt.swapper))
net/sunrpc/xprtsock.c:1289:		sk_clear_memalloc(sk);
net/sunrpc/xprtsock.c-1290-
--
net/sunrpc/xprtsock.c=2155=xs_disable_swap(struct rpc_xprt *xprt)
--
net/sunrpc/xprtsock.c-2161-	    xs->inet)
net/sunrpc/xprtsock.c:2162:		sk_clear_memalloc(xs->inet);
net/sunrpc/xprtsock.c-2163-	mutex_unlock(&xs->recv_mutex);
]

gemini-3.1-pro-preview

							input: 54742
							output: 37
							thoughts: 519
						

**Analyzing the NBD Connection Leak**

Okay, first thought: NBD *never* calls `sk_clear_memalloc`! That’s… not good. Is this a separate, yet related, bug, or just a symptom of something bigger? If `sk_clear_memalloc` isn't called, then every time an NBD connection closes, `memalloc_socks_key` leaks.

Now, wait a minute, `sk_set_memalloc` *increments* `memalloc_socks_key`. It’s essentially incrementing a counter. So, if NBD doesn't clear it, it’s a leak, no matter what. Should I make it clear this leak is in NBD as well?

The initial explanation points out that NBD doesn’t call `sk_clear_memalloc`, leading to a persistent leak of the static branch reference. It goes on to say that multiple calls to `sk_set_memalloc` on the same socket cause: protocol corruption and a resource leak of `memalloc_socks_key`.

So, the focus is on multiple calls to `sk_set_memalloc` on the *same* socket, but... if `sk_set_memalloc` is called twice, `memalloc_socks_key` increments twice. My mind jumps to the code:

```c
void sk_set_memalloc(struct sock *sk)
{
	sock_set_flag(sk, SOCK_MEMALLOC);
	sk->sk_allocation |= __GFP_MEMALLOC;
	static_branch_inc(&memalloc_socks_key);
}
```

Okay, so two calls means two increments. A single call to `sk_clear_memalloc` decrements it by one. That means that *even for normal sockets* NBD will leak! No `sk_clear_memalloc` call is a leak.

Does NBD *ever* call `sk_clear_memalloc`? No. Does `sk_destruct` call `sk_clear_memalloc`? No. So NBD leaks `memalloc_socks_key` for *every single socket* it uses? This is an immediate and persistent issue that needs addressed.

Let me think… is there *any* other mechanism that could be clearing it? Perhaps `sock_release`? I'll need to check there.

map[ContextFile:net/socket.c IncludeLines:true Name:sock_release]

map[SourceCode: 740:	/**
 741:	 *	sock_release - close a socket
 742:	 *	@sock: socket to close
 743:	 *
 744:	 *	The socket is released from the protocol stack if it has a release
 745:	 *	callback, and the inode is then released if the socket is bound to
 746:	 *	an inode not a file.
 747:	 */
 748:	void sock_release(struct socket *sock)
 749:	{
 750:		__sock_release(sock, NULL);
 751:	}
 SourceFile:net/socket.c]

gemini-3.1-pro-preview

							input: 56003
							output: 38
							thoughts: 10
						

Okay, here's my take on those thoughts, tailored for an expert audience:

**Diving into `__sock_release`**

Alright, time to get my hands dirty. My initial thought is to zero in on `__sock_release`. Given the context – whatever the issue is – my intuition screams that this function is likely pivotal. It's the point where socket resources are supposed to be cleaned up, and that's usually where things go sideways. I need to understand exactly what this function *does* in detail: the locking it uses, the state transitions, the reference counting, all of it. I'll probably start by grepping the kernel sources to see where it's called and by whom to understand the context. Then, it's off to the disassembly, or perhaps even a live debugging session. I need to ascertain if this function is properly handling all possible error conditions and whether any race conditions exist. I'm looking for memory leaks, double-frees, or any other resource exhaustion issues. I suspect that the root of the problem is somewhere in this function or its interactions with other socket-related subsystems. It's time to dig deep.

map[ContextFile:net/socket.c IncludeLines:true Name:__sock_release]

map[SourceCode: 713:	static void __sock_release(struct socket *sock, struct inode *inode)
 714:	{
 715:		const struct proto_ops *ops = READ_ONCE(sock->ops);
 716:	
 717:		if (ops) {
 718:			struct module *owner = ops->owner;
 719:	
 720:			if (inode)
 721:				inode_lock(inode);
 722:			ops->release(sock);
 723:			sock->sk = NULL;
 724:			if (inode)
 725:				inode_unlock(inode);
 726:			sock->ops = NULL;
 727:			module_put(owner);
 728:		}
 729:	
 730:		if (sock->wq.fasync_list)
 731:			pr_err("%s: fasync list not empty!\n", __func__);
 732:	
 733:		if (!sock->file) {
 734:			iput(SOCK_INODE(sock));
 735:			return;
 736:		}
 737:		WRITE_ONCE(sock->file, NULL);
 738:	}
 SourceFile:net/socket.c]

gemini-3.1-pro-preview

							input: 56659
							output: 45
							thoughts: 303
						

**Analyzing the memalloc_socks_key Leak in the NBD Driver**

Okay, so I'm diving into this `memalloc_socks_key` issue in the NBD driver. First, I noticed there's no call to `sk_clear_memalloc` anywhere, which is the immediate red flag. Wait a second, if `memalloc_socks_key` leaks, it's not a catastrophic memory leak in the traditional sense. It essentially means the static branch is always enabled, which is technically just a performance optimization. The leak represents a slight overhead on the fast path. But, if it overflows (and it's using an `atomic_t` inside a `static_key`), that could be a significant problem.

However, the initial explanation is saying something about the NBD driver. They're saying NBD relies on the socket's destruction to clear it, but `sk_clear_memalloc` isn't *actually* called on socket destruction in standard kernels. It's only done by things like sunrpc and wireguard. That means the NBD driver is leaking `memalloc_socks_key` on *every* socket! That's a definite bug.

The double `sk_set_memalloc` call on the same socket makes it worse, or it might just be part of the same underlying issue. So, I need to address this. Should I add `sk_clear_memalloc` to NBD to fix this? Where would be the logical place to insert it? I need to think about socket life-cycle here. Would it be in `nbd_config_put`? Or, maybe `nbd_clear_sock`? The more likely candidate is `nbd_clear_sock`, which sounds like it is more socket-oriented. Let me check `nbd_clear_sock_ioctl`.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_clear_sock_ioctl]

map[SourceCode:1573:	static void nbd_clear_sock_ioctl(struct nbd_device *nbd)
1574:	{
1575:		nbd_clear_sock(nbd);
1576:		disk_force_media_change(nbd->disk);
1577:		nbd_bdev_reset(nbd);
1578:		if (test_and_clear_bit(NBD_RT_HAS_CONFIG_REF,
1579:				       &nbd->config->runtime_flags))
1580:			nbd_config_put(nbd);
1581:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 57594
							output: 43
							thoughts: 12
						

Here's a summary of my thought process, as requested:

**Diving into `nbd_clear_sock`**

Okay, time to dissect `nbd_clear_sock`. My initial thought is to understand its purpose within the broader context of the Network Block Device (NBD) code. What's it designed to *do*? I'm assuming it relates to clearing or cleaning up a socket connection, probably after an NBD operation or error. I need to figure out the nuances. Is it responsible for a complete socket teardown, or a more selective clearing of state? Are there any resource leaks I should be looking out for within the associated functions? What are the implications if this function fails? Is it called in multiple places, and if so, what are the different calling contexts? These are my initial questions. I'll need to look for any mutexes or locks being held before or during the execution of this routine. The next step is definitely diving into the code itself.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_clear_sock]

map[SourceCode:1425:	static void nbd_clear_sock(struct nbd_device *nbd)
1426:	{
1427:		sock_shutdown(nbd);
1428:		nbd_clear_que(nbd);
1429:		nbd->task_setup = NULL;
1430:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 57976
							output: 43
							thoughts: 12
						

Okay, let's dive into this. Here's my take on those thoughts, as if they're my own:

**Initial Assessment: Diving into `nbd_config_put`**

Right, let's start with `nbd_config_put`. This function... it's a critical piece of the puzzle, isn't it? It's where the rubber meets the road when it comes to persisting and updating network block device configuration. I need to refresh my memory on the exact workflow, the data structures it interacts with, and potential points of contention or failure. I should recall how it integrates with the overall NBD architecture and where it fits in the lifecycle of a connection. Essentially, I need to understand its role in either provisioning or updating the configuration, and that in turn, dictates how everything else is going to work.

map[ContextFile:drivers/block/nbd.c IncludeLines:true Name:nbd_config_put]

map[SourceCode:1432:	static void nbd_config_put(struct nbd_device *nbd)
1433:	{
1434:		if (refcount_dec_and_mutex_lock(&nbd->config_refs,
1435:						&nbd->config_lock)) {
1436:			struct nbd_config *config = nbd->config;
1437:			nbd_dev_dbg_close(nbd);
1438:			invalidate_disk(nbd->disk);
1439:			if (nbd->config->bytesize)
1440:				kobject_uevent(&nbd_to_dev(nbd)->kobj, KOBJ_CHANGE);
1441:			if (test_and_clear_bit(NBD_RT_HAS_PID_FILE,
1442:					       &config->runtime_flags))
1443:				device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
1444:			nbd->pid = 0;
1445:			if (test_and_clear_bit(NBD_RT_HAS_BACKEND_FILE,
1446:					       &config->runtime_flags)) {
1447:				device_remove_file(disk_to_dev(nbd->disk), &backend_attr);
1448:				kfree(nbd->backend);
1449:				nbd->backend = NULL;
1450:			}
1451:			nbd_clear_sock(nbd);
1452:			if (config->num_connections) {
1453:				int i;
1454:				for (i = 0; i < config->num_connections; i++) {
1455:					sockfd_put(config->socks[i]->sock);
1456:					kfree(config->socks[i]);
1457:				}
1458:				kfree(config->socks);
1459:			}
1460:			kfree(nbd->config);
1461:			nbd->config = NULL;
1462:	
1463:			nbd->tag_set.timeout = 0;
1464:	
1465:			mutex_unlock(&nbd->config_lock);
1466:			nbd_put(nbd);
1467:			module_put(THIS_MODULE);
1468:		}
1469:	}
 SourceFile:drivers/block/nbd.c]

gemini-3.1-pro-preview

							input: 58875
							output: 42
							thoughts: 1153
						

**Analyzing the memalloc_socks_key Issue in NBD**

Okay, let's break this down. My initial thought was to add `sk_clear_memalloc` in `nbd_config_put`. However, after reviewing the code, it seems `sk_set_memalloc` *is* called for all sockets in `config->socks` during `nbd_start_device`. But a potential problem arises: `nbd_start_device` could fail after some sockets are processed, and therefore `sk_set_memalloc` is called, but before others. This means that if I unconditionally call `sk_clear_memalloc` in `nbd_config_put`, I might clear sockets that weren't properly initialized.

The crucial point is that `sk_clear_memalloc` decrements `memalloc_socks_key`, even if `SOCK_MEMALLOC` wasn't set. This would cause an underflow, right? So, the correct approach is to only call `sk_clear_memalloc` if `SOCK_MEMALLOC` is actually set on the socket.

But then I thought: wait, `sk_set_memalloc` is called in both `nbd_start_device` *and* `nbd_reconnect_socket`. Is it possible that `SOCK_MEMALLOC` is already set by something else? Indeed, `sk_set_memalloc` doesn't check if the flag is already set. If NBD calls `sk_set_memalloc` on a socket that already has it set, the key increments twice. Then, NBD calls `sk_clear_memalloc` once, decrementing the key once.

Now, going back to the original context, the initial explanation suggests that the NBD driver *never* calls `sk_clear_memalloc` by default, which creates a leak of the `memalloc_socks_key` reference. This implies that the leak is a known issue, however the duplicate socket issue makes it worse, or the duplicate socket is the main issue being reported.

The original fix proposes adding a check *only* in `nbd_add_socket` to prevent duplicate sockets from being added. I need to make sure I am sticking with this original scope. It makes sense to address the root cause: the duplicate socket. Since I already understand how to fix this duplicate socket issue, I should apply this fix.

So, I have implemented a check in `nbd_add_socket` and `nbd_reconnect_socket`. This is the earliest possible point, preventing the double increment of `memalloc_socks_key`. I believe this is the best, most direct solution to the identified problem.

But, I also see the larger point of the leak. I think I'll use `git log` to see if there are any recent commits related to `sk_clear_memalloc` in NBD to see if someone else has addressed it, or if it has been determined to be a non-issue.

map[CodeRegexp:sk_clear_memalloc Count:10 PathPrefix:drivers/block/nbd.c]

map[Output:]

gemini-3.1-pro-preview

							input: 60726
							output: 42
							thoughts: 34
						

Okay, here's my interpretation of those thoughts, presented as my own mental process, given my expertise:

**Investigating Memory Allocation in `nbd.c`**

Alright, I'm digging into memory management within the NBD driver, specifically looking at `drivers/block/nbd.c`. The initial query was about `sk_clear_memalloc`, which strongly suggests a concern about memory allocation and socket-related issues. My immediate thought is, "I haven't seen any commits directly mentioning `sk_clear_memalloc` in this specific file." This isn't necessarily a showstopper, but it does mean I need to look deeper; it’s not an obvious code path.

Okay, let's step back a bit; maybe my initial keyword is too specific. I should broaden the search space a bit by considering other related functions or macros. The next logical connection to think about is `memalloc_socks_key`. It is highly likely this key is related. I should start by looking into how this key is used within the NBD driver and across the network stack in general, as this is more likely the relevant bit of code. Perhaps it's being used indirectly, or maybe it's related to some other allocation strategy that *implicitly* addresses the same concerns that `sk_clear_memalloc` might have addressed in a different context. I need to understand the relationship. This line of thought suggests a potential indirect dependency or a different method of achieving a similar goal. I should probably start building a mental map of how these memory allocation methods interact, starting with how `memalloc_socks_key` is used to allocate memory and how it might be related to socket memory management and NBD.

map[CodeRegexp:memalloc_socks_key Count:10 PathPrefix:drivers/block/nbd.c]

map[Output:]

gemini-3.1-pro-preview

							input: 61175
							output: 43
							thoughts: 603
						

**Analyzing and Addressing the Potential Memory Allocation Key Leak in NBD**

Okay, so I'm looking at this `memalloc_socks_key` leak in the NBD code. It's either an unresolved issue, considered acceptable (unlikely, given the nature of kernel memory leaks!), or it's been addressed somewhere else, which I haven't found. Hmm, a key leak stems from the failure to call `sk_clear_memalloc`. I see `sk_set_memalloc` is called in `nbd_start_device`, so that's where it *should* be set. Now, is `sk_clear_memalloc` called in `nbd_clear_sock`? Probably not, or this wouldn't be an issue.

My first thought was to add `sk_clear_memalloc` in `nbd_config_put`. However, I need to be *very* careful about the use of `sock_flag(sk, SOCK_MEMALLOC)` there. The prompt reminds me to focus on the immediate issue, which is about duplicate sockets in the code, and keep changes scoped. My mandate is to explain what I've done in the patch and why, focusing on the specific bug (duplicate sockets) and not trying to fix broader kernel problems.

The instructions specifically ask me to address similar cases within the *same* file. That means the `sk_clear_memalloc` issue might be related but is really out of scope for the *duplicate socket* issue. I think this fits, fixing duplicate socket issue in both `nbd_add_socket` and `nbd_reconnect_socket` is the intent.

Let's review the patch I prepared:

I checked `nbd_add_socket`:

```c
	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	err = -EEXIST;
	for (i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			sockfd_put(sock);
			return err;
		}
	}
```

And in `nbd_reconnect_socket`:

```c
	sock = nbd_get_socket(nbd, arg, &err);
	if (!sock)
		return err;

	err = -EEXIST;
	for (i = 0; i < config->num_connections; i++) {
		if (config->socks[i]->sock == sock) {
			sockfd_put(sock);
			return err;
		}
	}
```

Wait a second… in `nbd_add_socket`, I never actually declared the loop variable `i`! I need to go back and fix that typo.