======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
kworker/u35:0/67 is trying to acquire lock:
ffff888026b73a60 (&nbd->config_lock){+.+.}-{4:4}, at: refcount_dec_and_mutex_lock+0x51/0x100 lib/refcount.c:118

but task is already holding lock:
ffffc9000082fd08 ((work_completion)(&args->work)){+.+.}-{0:0}, at: process_one_work+0xa2c/0x1b10 kernel/workqueue.c:3372

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 ((work_completion)(&args->work)){+.+.}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5908 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865
       process_one_work+0xa32/0x1b10 kernel/workqueue.c:3372
       process_scheduled_works kernel/workqueue.c:3479 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
       kthread+0x373/0x450 kernel/kthread.c:436
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #1 ((wq_completion)nbd2-recv){+.+.}-{0:0}:
       lock_acquire kernel/locking/lockdep.c:5908 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865
       touch_wq_lockdep_map+0xad/0x1c0 kernel/workqueue.c:4111
       __flush_workqueue+0x131/0x1200 kernel/workqueue.c:4153
       nbd_disconnect_and_put+0x9b/0x1c0 drivers/block/nbd.c:2335
       nbd_genl_disconnect+0x34b/0x4e0 drivers/block/nbd.c:2374
       genl_family_rcv_msg_doit+0x214/0x300 net/netlink/genetlink.c:1114
       genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
       genl_rcv_msg+0x560/0x800 net/netlink/genetlink.c:1209
       netlink_rcv_skb+0x159/0x420 net/netlink/af_netlink.c:2556
       genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
       netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
       netlink_unicast+0x585/0x850 net/netlink/af_netlink.c:1345
       netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1900
       sock_sendmsg_nosec net/socket.c:800 [inline]
       __sock_sendmsg net/socket.c:815 [inline]
       ____sys_sendmsg+0xa4d/0xbe0 net/socket.c:2713
       ___sys_sendmsg+0x190/0x1e0 net/socket.c:2767
       __sys_sendmsg+0x160/0x210 net/socket.c:2799
       do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:79 [inline]
       __do_fast_syscall_32+0x13a/0x8b0 arch/x86/entry/syscall_32.c:291
       do_fast_syscall_32+0x32/0x70 arch/x86/entry/syscall_32.c:316
       entry_SYSENTER_compat_after_hwframe+0x84/0x8e

-> #0 (&nbd->config_lock){+.+.}-{4:4}:
       check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3181
       check_prevs_add kernel/locking/lockdep.c:3300 [inline]
       validate_chain kernel/locking/lockdep.c:3924 [inline]
       __lock_acquire+0x1492/0x1ec0 kernel/locking/lockdep.c:5254
       lock_acquire kernel/locking/lockdep.c:5908 [inline]
       lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
       refcount_dec_and_mutex_lock+0x51/0x100 lib/refcount.c:118
       nbd_config_put+0x98/0x9b0 drivers/block/nbd.c:1470
       recv_work+0x63a/0x8c0 drivers/block/nbd.c:1035
       process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
       process_scheduled_works kernel/workqueue.c:3479 [inline]
       worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
       kthread+0x373/0x450 kernel/kthread.c:436
       ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

other info that might help us debug this:

Chain exists of:
  &nbd->config_lock --> (wq_completion)nbd2-recv --> (work_completion)(&args->work)

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock((work_completion)(&args->work));
                               lock((wq_completion)nbd2-recv);
                               lock((work_completion)(&args->work));
  lock(&nbd->config_lock);

 *** DEADLOCK ***

locks held by kworker/u35:0/67: 2, last CPU#2:
 #0: ffff888026bab140 ((wq_completion)nbd0-recv){+.+.}-{0:0}, at: process_one_work+0x1466/0x1b10 kernel/workqueue.c:3371
 #1: ffffc9000082fd08 ((work_completion)(&args->work)){+.+.}-{0:0}, at: process_one_work+0xa2c/0x1b10 kernel/workqueue.c:3372

stack backtrace:
CPU: 2 UID: 0 PID: 67 Comm: kworker/u35:0 Tainted: G             L      syzkaller #0 PREEMPT(lazy) 
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Workqueue: nbd0-recv recv_work
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_circular_bug.cold+0x178/0x1be kernel/locking/lockdep.c:2059
 check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2191
 check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3181
 check_prevs_add kernel/locking/lockdep.c:3300 [inline]
 validate_chain kernel/locking/lockdep.c:3924 [inline]
 __lock_acquire+0x1492/0x1ec0 kernel/locking/lockdep.c:5254
 lock_acquire kernel/locking/lockdep.c:5908 [inline]
 lock_acquire+0x1d1/0x380 kernel/locking/lockdep.c:5865
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
 refcount_dec_and_mutex_lock+0x51/0x100 lib/refcount.c:118
 nbd_config_put+0x98/0x9b0 drivers/block/nbd.c:1470
 recv_work+0x63a/0x8c0 drivers/block/nbd.c:1035
 process_one_work+0xac7/0x1b10 kernel/workqueue.c:3396
 process_scheduled_works kernel/workqueue.c:3479 [inline]
 worker_thread+0x5ef/0xe50 kernel/workqueue.c:3560
 kthread+0x373/0x450 kernel/kthread.c:436
 ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>