WARNING: refcount bug in __blkdev_put

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: ae83d0b4 Linux 5.7-rc2
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=157ede73e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=4a2e65056025ac64
dashboard link: https://syzkaller.appspot.com/bug?extid=8eaa11c867408925ef9d
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
CC: [linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+8eaa11...@syzkaller.appspotmail.com

------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 1 PID: 21365 at lib/refcount.c:25 refcount_warn_saturate+0x169/0x1e0 lib/refcount.c:25
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 21365 Comm: syz-executor.4 Not tainted 5.7.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x188/0x20d lib/dump_stack.c:118
panic+0x2e3/0x75c kernel/panic.c:221
__warn.cold+0x2f/0x35 kernel/panic.c:582
report_bug+0x27b/0x2f0 lib/bug.c:195
fixup_bug arch/x86/kernel/traps.c:175 [inline]
fixup_bug arch/x86/kernel/traps.c:170 [inline]
do_error_trap+0x12b/0x220 arch/x86/kernel/traps.c:267
do_invalid_op+0x32/0x40 arch/x86/kernel/traps.c:286
invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027
RIP: 0010:refcount_warn_saturate+0x169/0x1e0 lib/refcount.c:25
Code: 06 31 ff 89 de e8 17 c3 dc fd 84 db 0f 85 36 ff ff ff e8 da c1 dc fd 48 c7 c7 60 5d 72 88 c6 05 51 21 ee 06 01 e8 df fc ad fd <0f> 0b e9 17 ff ff ff e8 bb c1 dc fd 0f b6 1d 36 21 ee 06 31 ff 89
RSP: 0018:ffffc9000d0bfc60 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff815ce161 RDI: fffff52001a17f7e
RBP: 0000000000000002 R08: ffff888064dfe440 R09: ffffed1015ce45f1
R10: ffff8880ae722f83 R11: ffffed1015ce45f0 R12: ffff88808a937220
R13: ffff888064dfe440 R14: 0000000000000001 R15: ffff88808a937218
__mutex_unlock_slowpath+0x3a5/0x660 kernel/locking/mutex.c:1272
__blkdev_put+0x53d/0x690 fs/block_dev.c:1921
blkdev_close+0x8c/0xb0 fs/block_dev.c:1978
__fput+0x33e/0x880 fs/file_table.c:280
task_work_run+0xf4/0x1b0 kernel/task_work.c:123
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop+0x2fa/0x360 arch/x86/entry/common.c:165
prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
do_syscall_64+0x6b1/0x7d0 arch/x86/entry/common.c:305
entry_SYSCALL_64_after_hwframe+0x49/0xb3
RIP: 0033:0x416421
Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 04 1b 00 00 c3 48 83 ec 08 e8 0a fc ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 53 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007ffcdd70f030 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000006 RCX: 0000000000416421
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000005
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
R10: 00007ffcdd70f120 R11: 0000000000000293 R12: 0000000000790488
R13: 000000000015b092 R14: ffffffffffffffff R15: 000000000078bf0c
Kernel Offset: disabled
Rebooting in 86400 seconds..


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.