[syzbot] [io-uring?] WARNING in io_sq_thread_stop

[syzbot] [io-uring?] WARNING in io_sq_thread_stop

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    bd5c762ac051 Merge tag 'scsi-misc' of git://git.kernel.org..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=176b0981580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=27aa0e260943f70b
dashboard link: https://syzkaller.appspot.com/bug?extid=675af112519ca34f5502
compiler:       Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1096ccb1580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1496ccb1580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/63d7454ecf30/disk-bd5c762a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/07607d1cf7ed/vmlinux-bd5c762a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/2eb94eb9d0af/bzImage-bd5c762a.xz

The issue was bisected to:

commit 22d9db9fd64a493525d692b32c556875b7254665
Author: Jens Axboe <axboe@kernel.dk>
Date:   Fri Oct 30 13:27:28 2026 +0000

    io_uring/sqpoll: don't attach to a thread that is canceling

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1024562d580000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=1224562d580000
console output: https://syzkaller.appspot.com/x/log.txt?x=1424562d580000

AI-generated root cause summary:
When an io_uring SQPOLL thread terminates prematurely (e.g., due to a fatal
signal), io_sq_thread() sets the IO_SQ_THREAD_SHOULD_STOP bit in sqd->state
before exiting. Later, when the ring is cleaned up during io_ring_exit_work(),
io_put_sq_data() calls io_sq_thread_stop(), which checks
WARN_ON_ONCE(test_bit(IO_SQ_THREAD_SHOULD_STOP, &sqd->state)) under the
assumption that the stop bit is not yet set. This causes a benign WARN_ON_ONCE
to trigger; subsequent cleanup proceeds normally without leaking memory or
corrupting state.

full analysis:  https://syzkaller.appspot.com/x/ai_root_cause?x=675af112519ca34f5502

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+675af112519ca34f5502@syzkaller.appspotmail.com
Fixes: 22d9db9fd64a ("io_uring/sqpoll: don't attach to a thread that is canceling")

------------[ cut here ]------------
test_bit(IO_SQ_THREAD_SHOULD_STOP, &sqd->state)
WARNING: io_uring/sqpoll.c:88 at io_sq_thread_stop+0x17e/0x1a0 io_uring/sqpoll.c:88, CPU#0: kworker/u8:2/48
Modules linked in:
CPU: 0 UID: 0 PID: 48 Comm: kworker/u8:2 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/07/2026
Workqueue: iou_exit io_ring_exit_work
RIP: 0010:io_sq_thread_stop+0x17e/0x1a0 io_uring/sqpoll.c:88
Code: c6 05 cb df e9 0b 01 48 c7 c7 a0 da ea 8b be 26 00 00 00 48 c7 c2 e0 da ea 8b e8 dd 05 ce fc e9 4f ff ff ff e8 e3 d8 f2 fc 90 <0f> 0b 90 e9 e1 fe ff ff e8 d5 d8 f2 fc 90 0f 0b 90 e9 6e ff ff ff
RSP: 0018:ffffc90000ba7890 EFLAGS: 00010293
RAX: ffffffff84d5061d RBX: ffff888030ac3400 RCX: ffff888022291f40
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffed10061586ab R12: 0000000000000001
R13: 0000000000000000 R14: ffff888030ac3550 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff888124718000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055556aef1340 CR3: 000000003f44e000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 io_put_sq_data+0x8a/0x150 io_uring/sqpoll.c:105
 io_sq_thread_finish+0x1fd/0x240 io_uring/sqpoll.c:130
 io_ring_ctx_free+0x2d/0x5e0 io_uring/io_uring.c:2322
 io_ring_exit_work+0x5b1/0x640 io_uring/io_uring.c:2658
 process_one_work kernel/workqueue.c:3495 [inline]
 process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3578
 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3659
 kthread+0x38b/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>


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