WARNING in nbd_config_put

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    27bba9c5 Merge tag 'scsi-fixes' of git://git.kernel.org/pu..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15ffd94d500000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e7f3c831f4536ec1
dashboard link: https://syzkaller.appspot.com/bug?extid=547e604b2b1c65869d7f
compiler:       gcc (GCC) 10.1.0-syz 20200507
userspace arch: i386

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+547e604b2b1c65869d7f@xxxxxxxxxxxxxxxxxxxxxxxxx

------------[ cut here ]------------
WARNING: CPU: 3 PID: 27869 at kernel/workqueue.c:4396 destroy_workqueue.cold+0x5/0x71 kernel/workqueue.c:4396
Modules linked in:
CPU: 3 PID: 27869 Comm: syz-executor.3 Not tainted 5.10.0-rc4-syzkaller #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
RIP: 0010:destroy_workqueue.cold+0x5/0x71 kernel/workqueue.c:4396
Code: 00 90 4a 89 f7 f1 89 c6 e8 01 80 00 00 c6 44 24 37 01 e9 a1 a7 9b f8 48 c7 c7 80 f1 00 8b e8 9a f4 04 f9 eb c2 e8 63 76 c3 f8 <0f> 0b 48 c7 c6 00 95 4a 89 48 c7 c7 40 90 4a 89 49 8d 96 60 01 00
RSP: 0018:ffffc900009f7a30 EFLAGS: 00010046
RAX: 0000000000040000 RBX: 0000000000000002 RCX: ffffc90023698000
RDX: 0000000000040000 RSI: ffffffff88acb97d RDI: 0000000000000005
RBP: 000000000000000f R08: 0000000000000001 R09: 0000000000000003
R10: 0000000000000001 R11: 0000000000000000 R12: dffffc0000000000
R13: ffff888024e1dc00 R14: ffff88801270a000 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff88802cf00000(0063) knlGS:00000000f5524b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000001991fe8 CR3: 000000001216e000 CR4: 0000000000350ee0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 nbd_config_put+0x3d3/0x870 drivers/block/nbd.c:1231
 nbd_release+0x103/0x190 drivers/block/nbd.c:1523
 __blkdev_put+0x642/0x890 fs/block_dev.c:1782
 blkdev_close+0x8c/0xb0 fs/block_dev.c:1851
 __fput+0x285/0x920 fs/file_table.c:281
 task_work_run+0xdd/0x190 kernel/task_work.c:151
 get_signal+0xd89/0x1f00 kernel/signal.c:2562
 arch_do_signal+0x82/0x2390 arch/x86/kernel/signal.c:811
 exit_to_user_mode_loop kernel/entry/common.c:161 [inline]
 exit_to_user_mode_prepare+0x100/0x1a0 kernel/entry/common.c:191
 syscall_exit_to_user_mode+0x38/0x260 kernel/entry/common.c:266
 __do_fast_syscall_32+0x62/0x80 arch/x86/entry/common.c:138
 do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:160
 entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
RIP: 0023:0xf7f6c549
Code: 03 74 c0 01 10 05 03 74 b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000f55240bc EFLAGS: 00000296 ORIG_RAX: 0000000000000036
RAX: fffffffffffffe00 RBX: 0000000000000003 RCX: 000000000000ab03
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000


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