syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.1.7192/27237 is trying to acquire lock:
ffffffff8e643960 (fs_reclaim){+.+.}-{0:0}, at: might_alloc include/linux/sched/mm.h:318 [inline]
ffffffff8e643960 (fs_reclaim){+.+.}-{0:0}, at: slab_pre_alloc_hook mm/slub.c:4721 [inline]
ffffffff8e643960 (fs_reclaim){+.+.}-{0:0}, at: slab_alloc_node mm/slub.c:5044 [inline]
ffffffff8e643960 (fs_reclaim){+.+.}-{0:0}, at: kmem_cache_alloc_node_noprof+0x48/0x710 mm/slub.c:5120

but task is already holding lock:
ffff88802760b560 (k-sk_lock-AF_INET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1676 [inline]
ffff88802760b560 (k-sk_lock-AF_INET){+.+.}-{0:0}, at: inet_stream_connect+0x51/0xa0 net/ipv4/af_inet.c:747

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #7 (k-sk_lock-AF_INET){+.+.}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       lock_sock_nested+0x48/0x100 net/core/sock.c:3720
       lock_sock include/net/sock.h:1676 [inline]
       mptcp_connect+0x4c3/0x830 net/mptcp/protocol.c:3748
       __inet_stream_connect+0x2ae/0xe80 net/ipv4/af_inet.c:677
       inet_stream_connect+0x66/0xa0 net/ipv4/af_inet.c:748
       __sys_connect_file net/socket.c:2089 [inline]
       __sys_connect+0x316/0x440 net/socket.c:2108
       __do_sys_connect net/socket.c:2114 [inline]
       __se_sys_connect net/socket.c:2111 [inline]
       __x64_sys_connect+0x7a/0x90 net/socket.c:2111
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #6 (sk_lock-AF_INET){+.+.}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       lock_sock_nested+0x48/0x100 net/core/sock.c:3720
       lock_sock include/net/sock.h:1676 [inline]
       inet_shutdown+0x6a/0x390 net/ipv4/af_inet.c:905
       nbd_mark_nsock_dead+0x2e9/0x560 drivers/block/nbd.c:318
       sock_shutdown+0x15e/0x260 drivers/block/nbd.c:411
       nbd_clear_sock drivers/block/nbd.c:1424 [inline]
       nbd_config_put+0x342/0x790 drivers/block/nbd.c:1448
       nbd_release+0xfe/0x140 drivers/block/nbd.c:1753
       bdev_release+0x536/0x650 block/bdev.c:-1
       blkdev_release+0x15/0x20 block/fops.c:702
       __fput+0x44c/0xa70 fs/file_table.c:468
       task_work_run+0x1d4/0x260 kernel/task_work.c:227
       exit_task_work include/linux/task_work.h:40 [inline]
       do_exit+0x6b5/0x2300 kernel/exit.c:966
       do_group_exit+0x21c/0x2d0 kernel/exit.c:1107
       get_signal+0x1286/0x1340 kernel/signal.c:3034
       arch_do_signal_or_restart+0x9a/0x750 arch/x86/kernel/signal.c:337
       exit_to_user_mode_loop+0x75/0x130 kernel/entry/common.c:40
       exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
       syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
       syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
       do_syscall_64+0x2bd/0xfa0 arch/x86/entry/syscall_64.c:100
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #5 (&nsock->tx_lock){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760
       nbd_handle_cmd drivers/block/nbd.c:1140 [inline]
       nbd_queue_rq+0x257/0xf10 drivers/block/nbd.c:1204
       blk_mq_dispatch_rq_list+0x4c0/0x1900 block/blk-mq.c:2129
       __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline]
       blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline]
       __blk_mq_sched_dispatch_requests+0xda4/0x1570 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329
       blk_mq_run_hw_queue+0x348/0x4f0 block/blk-mq.c:2367
       blk_mq_dispatch_list+0xd0c/0xe00 include/linux/spinlock.h:-1
       blk_mq_flush_plug_list+0x469/0x550 block/blk-mq.c:2976
       __blk_flush_plug+0x3d3/0x4b0 block/blk-core.c:1223
       blk_finish_plug block/blk-core.c:1250 [inline]
       __submit_bio+0x2d3/0x5a0 block/blk-core.c:649
       __submit_bio_noacct_mq block/blk-core.c:722 [inline]
       submit_bio_noacct_nocheck+0x2fb/0xa50 block/blk-core.c:753
       submit_bh fs/buffer.c:2829 [inline]
       block_read_full_folio+0x599/0x830 fs/buffer.c:2447
       filemap_read_folio+0x117/0x380 mm/filemap.c:2426
       do_read_cache_folio+0x350/0x590 mm/filemap.c:3991
       read_mapping_folio include/linux/pagemap.h:999 [inline]
       read_part_sector+0xb6/0x2b0 block/partitions/core.c:722
       adfspart_check_ICS+0xa4/0xa50 block/partitions/acorn.c:360
       check_partition block/partitions/core.c:141 [inline]
       blk_add_partitions block/partitions/core.c:589 [inline]
       bdev_disk_changed+0x75f/0x14b0 block/partitions/core.c:693
       blkdev_get_whole+0x380/0x510 block/bdev.c:748
       bdev_open+0x31e/0xd30 block/bdev.c:957
       blkdev_open+0x457/0x600 block/fops.c:694
       do_dentry_open+0x953/0x13f0 fs/open.c:965
       vfs_open+0x3b/0x340 fs/open.c:1095
       do_open fs/namei.c:3895 [inline]
       path_openat+0x2ee5/0x3830 fs/namei.c:4054
       do_filp_open+0x1fa/0x410 fs/namei.c:4081
       do_sys_openat2+0x121/0x1c0 fs/open.c:1435
       do_sys_open fs/open.c:1450 [inline]
       __do_sys_openat fs/open.c:1466 [inline]
       __se_sys_openat fs/open.c:1461 [inline]
       __x64_sys_openat+0x138/0x170 fs/open.c:1461
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #4 (&cmd->lock){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760
       nbd_queue_rq+0xc8/0xf10 drivers/block/nbd.c:1196
       blk_mq_dispatch_rq_list+0x4c0/0x1900 block/blk-mq.c:2129
       __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline]
       blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline]
       __blk_mq_sched_dispatch_requests+0xda4/0x1570 block/blk-mq-sched.c:307
       blk_mq_sched_dispatch_requests+0xd7/0x190 block/blk-mq-sched.c:329
       blk_mq_run_hw_queue+0x348/0x4f0 block/blk-mq.c:2367
       blk_mq_dispatch_list+0xd0c/0xe00 include/linux/spinlock.h:-1
       blk_mq_flush_plug_list+0x469/0x550 block/blk-mq.c:2976
       __blk_flush_plug+0x3d3/0x4b0 block/blk-core.c:1223
       blk_finish_plug block/blk-core.c:1250 [inline]
       __submit_bio+0x2d3/0x5a0 block/blk-core.c:649
       __submit_bio_noacct_mq block/blk-core.c:722 [inline]
       submit_bio_noacct_nocheck+0x2fb/0xa50 block/blk-core.c:753
       submit_bh fs/buffer.c:2829 [inline]
       __bread_slow fs/buffer.c:1272 [inline]
       __bread_gfp+0x216/0x3c0 fs/buffer.c:1518
       sb_bread include/linux/buffer_head.h:346 [inline]
       vxfs_try_sb_magic+0xd7/0x360 fs/freevxfs/vxfs_super.c:134
       vxfs_fill_super+0x17d/0x870 fs/freevxfs/vxfs_super.c:213
       get_tree_bdev_flags+0x40e/0x4d0 fs/super.c:1691
       vfs_get_tree+0x92/0x2b0 fs/super.c:1751
       fc_mount fs/namespace.c:1274 [inline]
       do_new_mount_fc fs/namespace.c:3726 [inline]
       do_new_mount+0x302/0xa10 fs/namespace.c:3802
       do_mount fs/namespace.c:4125 [inline]
       __do_sys_mount fs/namespace.c:4324 [inline]
       __se_sys_mount+0x313/0x410 fs/namespace.c:4301
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (set->srcu){.+.+}-{0:0}:
       lock_sync+0xba/0x160 kernel/locking/lockdep.c:5916
       srcu_lock_sync include/linux/srcu.h:173 [inline]
       __synchronize_srcu+0x96/0x3a0 kernel/rcu/srcutree.c:1429
       elevator_switch+0x12b/0x640 block/elevator.c:588
       elevator_change+0x315/0x4c0 block/elevator.c:691
       elevator_set_default+0x186/0x260 block/elevator.c:767
       blk_register_queue+0x34e/0x3f0 block/blk-sysfs.c:942
       __add_disk+0x677/0xd50 block/genhd.c:528
       add_disk_fwnode+0xfc/0x480 block/genhd.c:597
       add_disk include/linux/blkdev.h:775 [inline]
       nbd_dev_add+0x717/0xae0 drivers/block/nbd.c:1981
       nbd_init+0x168/0x1f0 drivers/block/nbd.c:2688
       do_one_initcall+0x236/0x820 init/main.c:1281
       do_initcall_level+0x104/0x190 init/main.c:1343
       do_initcalls+0x59/0xa0 init/main.c:1359
       kernel_init_freeable+0x334/0x4b0 init/main.c:1591
       kernel_init+0x1d/0x1d0 init/main.c:1481
       ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #2 (&q->elevator_lock){+.+.}-{4:4}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __mutex_lock_common kernel/locking/mutex.c:598 [inline]
       __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760
       elevator_change+0x1e5/0x4c0 block/elevator.c:689
       elevator_set_none+0x42/0xb0 block/elevator.c:782
       blk_mq_elv_switch_none block/blk-mq.c:5034 [inline]
       __blk_mq_update_nr_hw_queues block/blk-mq.c:5077 [inline]
       blk_mq_update_nr_hw_queues+0x598/0x1ab0 block/blk-mq.c:5135
       nbd_start_device+0x17f/0xb10 drivers/block/nbd.c:1486
       nbd_genl_connect+0x135b/0x18f0 drivers/block/nbd.c:2236
       genl_family_rcv_msg_doit+0x215/0x300 net/netlink/genetlink.c:1115
       genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
       genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210
       netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2552
       genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
       netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
       netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1346
       netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
       sock_sendmsg_nosec net/socket.c:714 [inline]
       __sock_sendmsg+0x21c/0x270 net/socket.c:729
       ____sys_sendmsg+0x505/0x830 net/socket.c:2617
       ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2671
       __sys_sendmsg net/socket.c:2703 [inline]
       __do_sys_sendmsg net/socket.c:2708 [inline]
       __se_sys_sendmsg net/socket.c:2706 [inline]
       __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2706
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&q->q_usage_counter(io)#49){++++}-{0:0}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       blk_alloc_queue+0x538/0x620 block/blk-core.c:461
       blk_mq_alloc_queue block/blk-mq.c:4401 [inline]
       __blk_mq_alloc_disk+0x15c/0x340 block/blk-mq.c:4448
       nbd_dev_add+0x46c/0xae0 drivers/block/nbd.c:1951
       nbd_init+0x168/0x1f0 drivers/block/nbd.c:2688
       do_one_initcall+0x236/0x820 init/main.c:1281
       do_initcall_level+0x104/0x190 init/main.c:1343
       do_initcalls+0x59/0xa0 init/main.c:1359
       kernel_init_freeable+0x334/0x4b0 init/main.c:1591
       kernel_init+0x1d/0x1d0 init/main.c:1481
       ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #0 (fs_reclaim){+.+.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __fs_reclaim_acquire mm/page_alloc.c:4245 [inline]
       fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4259
       might_alloc include/linux/sched/mm.h:318 [inline]
       slab_pre_alloc_hook mm/slub.c:4721 [inline]
       slab_alloc_node mm/slub.c:5044 [inline]
       kmem_cache_alloc_node_noprof+0x48/0x710 mm/slub.c:5120
       __alloc_skb+0x112/0x2d0 net/core/skbuff.c:659
       alloc_skb_fclone include/linux/skbuff.h:1427 [inline]
       tcp_stream_alloc_skb+0x3d/0x340 net/ipv4/tcp.c:892
       tcp_connect+0x146f/0x4ef0 net/ipv4/tcp_output.c:4145
       tcp_v4_connect+0x1110/0x1a00 net/ipv4/tcp_ipv4.c:345
       __inet_stream_connect+0x2ae/0xe80 net/ipv4/af_inet.c:677
       inet_stream_connect+0x66/0xa0 net/ipv4/af_inet.c:748
       p9_fd_create_tcp+0x409/0x640 net/9p/trans_fd.c:1027
       p9_client_create+0x85e/0x10b0 net/9p/client.c:1017
       v9fs_session_init+0x1d7/0x19a0 fs/9p/v9fs.c:410
       v9fs_mount+0xc8/0xa50 fs/9p/vfs_super.c:122
       legacy_get_tree+0xfd/0x1a0 fs/fs_context.c:663
       vfs_get_tree+0x92/0x2b0 fs/super.c:1751
       fc_mount fs/namespace.c:1274 [inline]
       do_new_mount_fc fs/namespace.c:3726 [inline]
       do_new_mount+0x302/0xa10 fs/namespace.c:3802
       do_mount fs/namespace.c:4125 [inline]
       __do_sys_mount fs/namespace.c:4324 [inline]
       __se_sys_mount+0x313/0x410 fs/namespace.c:4301
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  fs_reclaim --> sk_lock-AF_INET --> k-sk_lock-AF_INET

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(k-sk_lock-AF_INET);
                               lock(sk_lock-AF_INET);
                               lock(k-sk_lock-AF_INET);
  lock(fs_reclaim);

 *** DEADLOCK ***

1 lock held by syz.1.7192/27237:
 #0: ffff88802760b560 (k-sk_lock-AF_INET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1676 [inline]
 #0: ffff88802760b560 (k-sk_lock-AF_INET){+.+.}-{0:0}, at: inet_stream_connect+0x51/0xa0 net/ipv4/af_inet.c:747

stack backtrace:
CPU: 1 UID: 0 PID: 27237 Comm: syz.1.7192 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
 check_noncircular+0x134/0x160 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+0xb9b/0x2140 kernel/locking/lockdep.c:3908
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 __fs_reclaim_acquire mm/page_alloc.c:4245 [inline]
 fs_reclaim_acquire+0x72/0x100 mm/page_alloc.c:4259
 might_alloc include/linux/sched/mm.h:318 [inline]
 slab_pre_alloc_hook mm/slub.c:4721 [inline]
 slab_alloc_node mm/slub.c:5044 [inline]
 kmem_cache_alloc_node_noprof+0x48/0x710 mm/slub.c:5120
 __alloc_skb+0x112/0x2d0 net/core/skbuff.c:659
 alloc_skb_fclone include/linux/skbuff.h:1427 [inline]
 tcp_stream_alloc_skb+0x3d/0x340 net/ipv4/tcp.c:892
 tcp_connect+0x146f/0x4ef0 net/ipv4/tcp_output.c:4145
 tcp_v4_connect+0x1110/0x1a00 net/ipv4/tcp_ipv4.c:345
 __inet_stream_connect+0x2ae/0xe80 net/ipv4/af_inet.c:677
 inet_stream_connect+0x66/0xa0 net/ipv4/af_inet.c:748
 p9_fd_create_tcp+0x409/0x640 net/9p/trans_fd.c:1027
 p9_client_create+0x85e/0x10b0 net/9p/client.c:1017
 v9fs_session_init+0x1d7/0x19a0 fs/9p/v9fs.c:410
 v9fs_mount+0xc8/0xa50 fs/9p/vfs_super.c:122
 legacy_get_tree+0xfd/0x1a0 fs/fs_context.c:663
 vfs_get_tree+0x92/0x2b0 fs/super.c:1751
 fc_mount fs/namespace.c:1274 [inline]
 do_new_mount_fc fs/namespace.c:3726 [inline]
 do_new_mount+0x302/0xa10 fs/namespace.c:3802
 do_mount fs/namespace.c:4125 [inline]
 __do_sys_mount fs/namespace.c:4324 [inline]
 __se_sys_mount+0x313/0x410 fs/namespace.c:4301
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f81b138eba9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f81b218d038 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f81b15d5fa0 RCX: 00007f81b138eba9
RDX: 0000200000000100 RSI: 00002000000000c0 RDI: 0000200000000080
RBP: 00007f81b1411e19 R08: 0000200000000580 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f81b15d6038 R14: 00007f81b15d5fa0 R15: 00007ffc658fc898
 </TASK>
9pnet_fd: p9_fd_create_tcp (27237): problem connecting socket to 127.0.0.1