WARNING: refcount bug in io_wqe

WARNING: refcount bug in io_wqe_worker
Status: upstream: reported C repro on 2020/09/07 21:19
Reported-by: syzbot+956ef5eac18eadd0fb7f@syzkaller.appspotmail.com
First crash: 134d, last: 99d

Cause bisection: failed (bisect log)

Fix bisection: failed (bisect log)

Patch testing requests:
Created	Duration	User	Patch	Repo	Result
2020/09/11 09:34	10m	anant.thazhemadam@gmail.com		https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master	report log

Sample crash report:

------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 1 PID: 11616 at lib/refcount.c:28 refcount_warn_saturate+0x1d1/0x1e0 lib/refcount.c:28
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 11616 Comm: io_wqe_worker-1 Not tainted 5.9.0-rc7-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+0x198/0x1fd lib/dump_stack.c:118
 panic+0x382/0x7fb kernel/panic.c:231
 __warn.cold+0x20/0x4b kernel/panic.c:600
 report_bug+0x1bd/0x210 lib/bug.c:198
 handle_bug+0x38/0x90 arch/x86/kernel/traps.c:234
 exc_invalid_op+0x14/0x40 arch/x86/kernel/traps.c:254
 asm_exc_invalid_op+0x12/0x20 arch/x86/include/asm/idtentry.h:536
RIP: 0010:refcount_warn_saturate+0x1d1/0x1e0 lib/refcount.c:28
Code: e9 db fe ff ff 48 89 df e8 9c 26 f7 fd e9 8a fe ff ff e8 02 4f b6 fd 48 c7 c7 a0 73 d8 88 c6 05 ac 8e 94 07 01 e8 71 8c 86 fd <0f> 0b e9 af fe ff ff 0f 1f 84 00 00 00 00 00 41 56 41 55 41 54 55
RSP: 0018:ffffc90009fafe08 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff8880a88a4500 RSI: ffffffff815f59d5 RDI: fffff520013f5fb3
RBP: 0000000000000003 R08: 0000000000000001 R09: ffff8880ae5318e7
R10: 0000000000000000 R11: 0000000000000000 R12: ffff88809a0f88b8
R13: ffff8880a1ef2930 R14: ffff8880a1ef2900 R15: ffff8880a7930400
 refcount_sub_and_test include/linux/refcount.h:274 [inline]
 refcount_dec_and_test include/linux/refcount.h:294 [inline]
 io_worker_exit fs/io-wq.c:236 [inline]
 io_wqe_worker+0xcdb/0x10e0 fs/io-wq.c:596
 kthread+0x3b5/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
Kernel Offset: disabled
Rebooting in 86400 seconds..

Crashes (6):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	VM info	Maintainers
ci-upstream-kasan-gce-selinux-root	2020/09/28 20:26	upstream	a1b8638b	6bfdbe89	.config	log	report	syz	C		axboe@kernel.dk, io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci-upstream-kasan-gce-root	2020/09/27 16:49	upstream	eeddbe68	5dd8aee8	.config	log	report	syz	C		axboe@kernel.dk, io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci-upstream-kasan-gce-selinux-root	2020/09/12 18:48	upstream	729e3d09	ce441f06	.config	log	report	syz	C		axboe@kernel.dk, io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci-upstream-linux-next-kasan-gce-root	2020/09/06 19:33	linux-next	7a695657	abf9ba4f	.config	log	report	syz			axboe@kernel.dk, io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci-upstream-kasan-gce-root	2020/10/11 13:44	upstream	da690031	4a77ae0b	.config	log	report			info	axboe@kernel.dk, io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
ci-upstream-kasan-gce-root	2020/09/28 01:14	upstream	a1bffa48	5dd8aee8	.config	log	report			info	axboe@kernel.dk, io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk