====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ syz.5.179/7373 is trying to acquire lock: ffff80008faa22e8 (pcpu_alloc_mutex){+.+.}-{4:4}, at: pcpu_alloc_noprof+0x224/0x18c0 mm/percpu.c:1782 but task is already holding lock: ffff0000ca49bb58 (&q->q_usage_counter(io)#33){++++}-{0:0}, at: nbd_start_device+0x158/0xa48 drivers/block/nbd.c:1478 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&q->q_usage_counter(io)#33){++++}-{0:0}: blk_alloc_queue+0x48c/0x54c block/blk-core.c:461 blk_mq_alloc_queue block/blk-mq.c:4400 [inline] __blk_mq_alloc_disk+0x124/0x304 block/blk-mq.c:4447 nbd_dev_add+0x398/0x820 drivers/block/nbd.c:1943 nbd_init+0x15c/0x174 drivers/block/nbd.c:2680 do_one_initcall+0x250/0x990 init/main.c:1269 do_initcall_level+0x128/0x1c4 init/main.c:1331 do_initcalls+0x70/0xd0 init/main.c:1347 do_basic_setup+0x78/0x8c init/main.c:1366 kernel_init_freeable+0x268/0x39c init/main.c:1579 kernel_init+0x24/0x1dc init/main.c:1469 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844 -> #1 (fs_reclaim){+.+.}-{0:0}: __fs_reclaim_acquire mm/page_alloc.c:4234 [inline] fs_reclaim_acquire+0x8c/0x118 mm/page_alloc.c:4248 might_alloc include/linux/sched/mm.h:318 [inline] prepare_alloc_pages+0x13c/0x50c mm/page_alloc.c:4916 __alloc_frozen_pages_noprof+0x134/0x318 mm/page_alloc.c:5137 __alloc_pages_noprof+0x18/0x100 mm/page_alloc.c:5182 __alloc_pages_node_noprof include/linux/gfp.h:284 [inline] alloc_pages_node_noprof include/linux/gfp.h:311 [inline] pcpu_alloc_pages mm/percpu-vm.c:95 [inline] pcpu_populate_chunk+0x28c/0xa28 mm/percpu-vm.c:285 pcpu_alloc_noprof+0xb40/0x18c0 mm/percpu.c:1870 bpf_map_alloc_percpu+0x1f4/0x4dc kernel/bpf/syscall.c:558 prealloc_init+0x224/0x78c kernel/bpf/hashtab.c:336 htab_map_alloc+0x584/0xa6c kernel/bpf/hashtab.c:561 map_create+0x7a0/0x10e8 kernel/bpf/syscall.c:1480 __sys_bpf+0x210/0x628 kernel/bpf/syscall.c:6011 __do_sys_bpf kernel/bpf/syscall.c:6139 [inline] __se_sys_bpf kernel/bpf/syscall.c:6137 [inline] __arm64_sys_bpf+0x80/0x98 kernel/bpf/syscall.c:6137 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline] invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151 el0_svc+0x58/0x180 arch/arm64/kernel/entry-common.c:879 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596 -> #0 (pcpu_alloc_mutex){+.+.}-{4:4}: check_prev_add kernel/locking/lockdep.c:3165 [inline] check_prevs_add kernel/locking/lockdep.c:3284 [inline] validate_chain kernel/locking/lockdep.c:3908 [inline] __lock_acquire+0x1774/0x30a4 kernel/locking/lockdep.c:5237 lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5868 __mutex_lock_common+0x1d0/0x2678 kernel/locking/mutex.c:598 __mutex_lock kernel/locking/mutex.c:760 [inline] _mutex_lock_killable+0x2c/0x38 kernel/locking/mutex.c:828 pcpu_alloc_noprof+0x224/0x18c0 mm/percpu.c:1782 init_alloc_hint lib/sbitmap.c:16 [inline] sbitmap_init_node+0x1c4/0x578 lib/sbitmap.c:126 sbitmap_queue_init_node+0x54/0x484 lib/sbitmap.c:454 bt_alloc block/blk-mq-tag.c:542 [inline] blk_mq_init_tags+0x104/0x248 block/blk-mq-tag.c:565 blk_mq_alloc_rq_map block/blk-mq.c:3542 [inline] blk_mq_alloc_map_and_rqs+0xc8/0xc30 block/blk-mq.c:4098 __blk_mq_alloc_map_and_rqs block/blk-mq.c:4120 [inline] blk_mq_realloc_tag_set_tags block/blk-mq.c:4759 [inline] __blk_mq_update_nr_hw_queues block/blk-mq.c:5072 [inline] blk_mq_update_nr_hw_queues+0x878/0x15f4 block/blk-mq.c:5124 nbd_start_device+0x158/0xa48 drivers/block/nbd.c:1478 nbd_genl_connect+0xf88/0x158c drivers/block/nbd.c:2228 genl_family_rcv_msg_doit+0x1d8/0x2bc net/netlink/genetlink.c:1115 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline] genl_rcv_msg+0x450/0x624 net/netlink/genetlink.c:1210 netlink_rcv_skb+0x220/0x3fc net/netlink/af_netlink.c:2552 genl_rcv+0x38/0x50 net/netlink/genetlink.c:1219 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline] netlink_unicast+0x694/0x8c4 net/netlink/af_netlink.c:1346 netlink_sendmsg+0x648/0x930 net/netlink/af_netlink.c:1896 sock_sendmsg_nosec net/socket.c:714 [inline] __sock_sendmsg net/socket.c:729 [inline] ____sys_sendmsg+0x490/0x7b8 net/socket.c:2614 ___sys_sendmsg+0x204/0x278 net/socket.c:2668 __sys_sendmsg net/socket.c:2700 [inline] __do_sys_sendmsg net/socket.c:2705 [inline] __se_sys_sendmsg net/socket.c:2703 [inline] __arm64_sys_sendmsg+0x184/0x238 net/socket.c:2703 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline] invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151 el0_svc+0x58/0x180 arch/arm64/kernel/entry-common.c:879 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596 other info that might help us debug this: Chain exists of: pcpu_alloc_mutex --> fs_reclaim --> &q->q_usage_counter(io)#33 Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&q->q_usage_counter(io)#33); lock(fs_reclaim); lock(&q->q_usage_counter(io)#33); lock(pcpu_alloc_mutex); *** DEADLOCK *** 6 locks held by syz.5.179/7373: #0: ffff800092ada670 (cb_lock){++++}-{4:4}, at: genl_rcv+0x28/0x50 net/netlink/genetlink.c:1218 #1: ffff800092ada488 (genl_mutex){+.+.}-{4:4}, at: genl_lock net/netlink/genetlink.c:35 [inline] #1: ffff800092ada488 (genl_mutex){+.+.}-{4:4}, at: genl_op_lock net/netlink/genetlink.c:60 [inline] #1: ffff800092ada488 (genl_mutex){+.+.}-{4:4}, at: genl_rcv_msg+0xf4/0x624 net/netlink/genetlink.c:1209 #2: ffff0000ca517988 (&set->update_nr_hwq_lock){++++}-{4:4}, at: blk_mq_update_nr_hw_queues+0x9c/0x15f4 block/blk-mq.c:5122 #3: ffff0000ca5178d8 (&set->tag_list_lock){+.+.}-{4:4}, at: blk_mq_update_nr_hw_queues+0xa8/0x15f4 block/blk-mq.c:5123 #4: ffff0000ca49bb58 (&q->q_usage_counter(io)#33){++++}-{0:0}, at: nbd_start_device+0x158/0xa48 drivers/block/nbd.c:1478 #5: ffff0000ca49bb90 (&q->q_usage_counter(queue)#17){+.+.}-{0:0}, at: nbd_start_device+0x158/0xa48 drivers/block/nbd.c:1478 stack backtrace: CPU: 1 UID: 0 PID: 7373 Comm: syz.5.179 Not tainted syzkaller #0 PREEMPT Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025 Call trace: show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C) __dump_stack+0x30/0x40 lib/dump_stack.c:94 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120 dump_stack+0x1c/0x28 lib/dump_stack.c:129 print_circular_bug+0x324/0x32c kernel/locking/lockdep.c:2043 check_noncircular+0x154/0x174 kernel/locking/lockdep.c:2175 check_prev_add kernel/locking/lockdep.c:3165 [inline] check_prevs_add kernel/locking/lockdep.c:3284 [inline] validate_chain kernel/locking/lockdep.c:3908 [inline] __lock_acquire+0x1774/0x30a4 kernel/locking/lockdep.c:5237 lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5868 __mutex_lock_common+0x1d0/0x2678 kernel/locking/mutex.c:598 __mutex_lock kernel/locking/mutex.c:760 [inline] _mutex_lock_killable+0x2c/0x38 kernel/locking/mutex.c:828 pcpu_alloc_noprof+0x224/0x18c0 mm/percpu.c:1782 init_alloc_hint lib/sbitmap.c:16 [inline] sbitmap_init_node+0x1c4/0x578 lib/sbitmap.c:126 sbitmap_queue_init_node+0x54/0x484 lib/sbitmap.c:454 bt_alloc block/blk-mq-tag.c:542 [inline] blk_mq_init_tags+0x104/0x248 block/blk-mq-tag.c:565 blk_mq_alloc_rq_map block/blk-mq.c:3542 [inline] blk_mq_alloc_map_and_rqs+0xc8/0xc30 block/blk-mq.c:4098 __blk_mq_alloc_map_and_rqs block/blk-mq.c:4120 [inline] blk_mq_realloc_tag_set_tags block/blk-mq.c:4759 [inline] __blk_mq_update_nr_hw_queues block/blk-mq.c:5072 [inline] blk_mq_update_nr_hw_queues+0x878/0x15f4 block/blk-mq.c:5124 nbd_start_device+0x158/0xa48 drivers/block/nbd.c:1478 nbd_genl_connect+0xf88/0x158c drivers/block/nbd.c:2228 genl_family_rcv_msg_doit+0x1d8/0x2bc net/netlink/genetlink.c:1115 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline] genl_rcv_msg+0x450/0x624 net/netlink/genetlink.c:1210 netlink_rcv_skb+0x220/0x3fc net/netlink/af_netlink.c:2552 genl_rcv+0x38/0x50 net/netlink/genetlink.c:1219 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline] netlink_unicast+0x694/0x8c4 net/netlink/af_netlink.c:1346 netlink_sendmsg+0x648/0x930 net/netlink/af_netlink.c:1896 sock_sendmsg_nosec net/socket.c:714 [inline] __sock_sendmsg net/socket.c:729 [inline] ____sys_sendmsg+0x490/0x7b8 net/socket.c:2614 ___sys_sendmsg+0x204/0x278 net/socket.c:2668 __sys_sendmsg net/socket.c:2700 [inline] __do_sys_sendmsg net/socket.c:2705 [inline] __se_sys_sendmsg net/socket.c:2703 [inline] __arm64_sys_sendmsg+0x184/0x238 net/socket.c:2703 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline] invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151 el0_svc+0x58/0x180 arch/arm64/kernel/entry-common.c:879 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596 nbd0: detected capacity change from 0 to 3