KCSAN: data-race in __percpu_ref_switch_mode / io_sq_thread (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: b6505459 Linux 5.10-rc6
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12cc798d500000
kernel config: https://syzkaller.appspot.com/x/.config?x=c949fed53798f819
dashboard link: https://syzkaller.appspot.com/bug?extid=27b23553108c32340251
compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project.git 913f6005669cfb590c99865a90bc51ed0983d09d)
CC: [ax...@kernel.dk io-u...@vger.kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org vi...@zeniv.linux.org.uk]

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+27b235...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __percpu_ref_switch_mode / io_sq_thread

write to 0xffff88810a7b0c00 of 8 bytes by task 18482 on cpu 0:
__percpu_ref_switch_to_atomic lib/percpu-refcount.c:216 [inline]
__percpu_ref_switch_mode+0x19a/0x390 lib/percpu-refcount.c:273
percpu_ref_kill_and_confirm+0x84/0x190 lib/percpu-refcount.c:387
percpu_ref_kill include/linux/percpu-refcount.h:149 [inline]
io_ring_ctx_wait_and_kill+0x31/0x370 fs/io_uring.c:8381
io_uring_release+0x3e/0x50 fs/io_uring.c:8419
__fput+0x243/0x4d0 fs/file_table.c:281
____fput+0x11/0x20 fs/file_table.c:314
task_work_run+0x8e/0x110 kernel/task_work.c:151
exit_task_work include/linux/task_work.h:30 [inline]
do_exit+0x43d/0x1630 kernel/exit.c:809
do_group_exit+0xc8/0x170 kernel/exit.c:906
get_signal+0xf9b/0x1510 kernel/signal.c:2758
arch_do_signal+0x25/0x260 arch/x86/kernel/signal.c:811
exit_to_user_mode_loop kernel/entry/common.c:161 [inline]
exit_to_user_mode_prepare+0xde/0x170 kernel/entry/common.c:191
syscall_exit_to_user_mode+0x16/0x30 kernel/entry/common.c:266
do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88810a7b0c00 of 8 bytes by task 18486 on cpu 1:
percpu_ref_is_dying include/linux/percpu-refcount.h:352 [inline]
__io_sq_thread fs/io_uring.c:6700 [inline]
io_sq_thread+0x50f/0xcd0 fs/io_uring.c:6793
kthread+0x1fd/0x220 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 18486 Comm: io_uring-sq Not tainted 5.10.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================


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[syzbot]

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