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

[syzbot <syzbot+9f32706bfd7c4ff81434@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    36aad21d50d1 Merge tag 'ksmbd-for-7.4-rc1-part2' of git://..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13ebf981580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=bd712e5dbce1d1a0
dashboard link: https://syzkaller.appspot.com/bug?extid=9f32706bfd7c4ff81434
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
userspace arch: i386

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

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-36aad21d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f5ef884eedc9/vmlinux-36aad21d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7e4771aa5ca4/bzImage-36aad21d.xz

AI-generated root cause summary:
In io_uring/sqpoll.c, io_sq_thread() sets the IO_SQ_THREAD_SHOULD_STOP bit on
sqd->state when the SQPOLL thread terminates (e.g., due to a fatal signal) to
prevent new rings from attaching during cancelation. However,
io_sq_thread_stop() still contains an assertion
WARN_ON_ONCE(test_bit(IO_SQ_THREAD_SHOULD_STOP, &sqd->state)) under the earlier
invariant that only io_sq_thread_stop() ever sets this bit when rings release
their references. When the ring is subsequently torn down during process
cleanup, io_put_sq_data() calls io_sq_thread_stop() on the already-stopped sqd,
tripping the warning.

full analysis:  https://syzkaller.appspot.com/x/ai_root_cause?x=9f32706bfd7c4ff81434

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9f32706bfd7c4ff81434@syzkaller.appspotmail.com

------------[ cut here ]------------
test_bit(IO_SQ_THREAD_SHOULD_STOP, &sqd->state)
WARNING: io_uring/sqpoll.c:88 at io_sq_thread_stop+0x18b/0x1c0 io_uring/sqpoll.c:88, CPU#2: kworker/u33:12/1172
Modules linked in:
CPU: 2 UID: 0 PID: 1172 Comm: kworker/u33:12 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Workqueue: iou_exit io_ring_exit_work
RIP: 001qemu-system-x86_64: warning: 9p: degraded performance: a reasonable high msize should be chosen on client/guest side (chosen msize is <= 8192). See https://wiki.qemu.org/Documentation/9psetup#msize for details.
Code: 48 c7 c2 c0 cc 80 8c be 25 00 00 00 48 c7 c7 20 cd 80 8c c6 05 29 56 22 0d 01 e8 f0 3f b8 fc e9 12 ff ff ff e8 36 a9 dd fc 90 <0f> 0b 90 e9 c8 fe ff ff e8 28 a9 dd fc 90 0f 0b 90 e9 3c ff ff ff
RSP: 0000:ffffc90006627a28 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff888052edb400 RCX: 0000000000000000
RDX: ffff888022a90000 RSI: ffffffff852ffcea RDI: 0000000000000001
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000001
R10: ffff888052edb51f R11: 0000000000000000 R12: ffff888052edb518
R13: 0000000000000000 R14: ffff88806ebfe4e0 R15: ffff888052edafc0
FS:  0000000000000000(0000) GS:ffff888095481000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000057f2b470 CR3: 000000004f385000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 io_put_sq_data io_uring/sqpoll.c:105 [inline]
 io_put_sq_data+0xb0/0x100 io_uring/sqpoll.c:100
 io_sq_thread_finish+0x252/0x320 io_uring/sqpoll.c:130
 io_ring_ctx_free io_uring/io_uring.c:2322 [inline]
 io_ring_exit_work+0x40a/0x9f5 io_uring/io_uring.c:2658
 process_one_work+0xac7/0x1b10 kernel/workqueue.c:3495
 process_scheduled_works kernel/workqueue.c:3578 [inline]
 worker_thread+0x5ef/0xe50 kernel/workqueue.c:3659
 kthread+0x373/0x450 kernel/kthread.c:436
 ret_from_fork+0x730/0xd60 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>


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