block nbd2: Receive control failed (result -22)
block nbd1: Receive control failed (result -22)
block nbd1: shutting down sockets
============================================
WARNING: possible recursive locking detected
5.3.0+ #0 Not tainted
--------------------------------------------
kworker/u5:3/8179 is trying to acquire lock:
ffff88809a878668 ((wq_completion)knbd1-recv){+.+.}, at: flush_workqueue+0xf0/0x14c0 kernel/workqueue.c:2774

but task is already holding lock:
ffff88809a878668 ((wq_completion)knbd1-recv){+.+.}, at: spin_unlock_irq include/linux/spinlock.h:388 [inline]
ffff88809a878668 ((wq_completion)knbd1-recv){+.+.}, at: process_one_work+0x75d/0x10e0 kernel/workqueue.c:2242

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock((wq_completion)knbd1-recv);
  lock((wq_completion)knbd1-recv);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

3 locks held by kworker/u5:3/8179:
 #0: ffff88809a878668 ((wq_completion)knbd1-recv){+.+.}, at: spin_unlock_irq include/linux/spinlock.h:388 [inline]
 #0: ffff88809a878668 ((wq_completion)knbd1-recv){+.+.}, at: process_one_work+0x75d/0x10e0 kernel/workqueue.c:2242
 #1: ffff888094cefd78 ((work_completion)(&args->work)){+.+.}, at: process_one_work+0x79f/0x10e0 kernel/workqueue.c:2244
 #2: ffff888218c31e78 (&nbd->config_lock){+.+.}, at: refcount_dec_and_mutex_lock+0x2f/0x60 lib/refcount.c:319

stack backtrace:
CPU: 1 PID: 8179 Comm: kworker/u5:3 Not tainted 5.3.0+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: knbd1-recv recv_work
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1d8/0x2f8 lib/dump_stack.c:113
 print_deadlock_bug kernel/locking/lockdep.c:2371 [inline]
 check_deadlock kernel/locking/lockdep.c:2412 [inline]
 validate_chain+0x6202/0x7c00 kernel/locking/lockdep.c:2955
 __lock_acquire+0xc75/0x1be0 kernel/locking/lockdep.c:3955
 lock_acquire+0x158/0x250 kernel/locking/lockdep.c:4487
 flush_workqueue+0x10c/0x14c0 kernel/workqueue.c:2774
 drain_workqueue+0xb9/0x500 kernel/workqueue.c:2939
 destroy_workqueue+0x2b/0xb00 kernel/workqueue.c:4329
 nbd_config_put+0x525/0x740 drivers/block/nbd.c:1163
 recv_work+0x11eb/0x1250 drivers/block/nbd.c:770
 process_one_work+0x7ef/0x10e0 kernel/workqueue.c:2269
 worker_thread+0xc01/0x1630 kernel/workqueue.c:2415
 kthread+0x332/0x350 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352