KCSAN: data-race in io_sq_thread / percpu_ref_kill_and_confirm

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 7c3cd68e Merge remote-tracking branch 'linux-rcu/kcsan' in..
git tree: https://github.com/google/ktsan.git kcsan
console output: https://syzkaller.appspot.com/x/log.txt?x=177c4151100000
kernel config: https://syzkaller.appspot.com/x/.config?x=ff291dc25f22cdda
dashboard link: https://syzkaller.appspot.com/bug?extid=a5a066a41083b8c5e929
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
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 crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a5a066...@syzkaller.appspotmail.com

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

write to 0xffff8880b2e69408 of 8 bytes by task 16302 on cpu 1:
percpu_ref_kill_and_confirm+0x7d/0x1d0 lib/percpu-refcount.c:349
percpu_ref_kill include/linux/percpu-refcount.h:136 [inline]
io_ring_ctx_wait_and_kill+0x50/0x3a0 fs/io_uring.c:7291
io_uring_release+0x47/0x60 fs/io_uring.c:7324
__fput+0x1e9/0x500 fs/file_table.c:280
____fput+0x1b/0x30 fs/file_table.c:313
task_work_run+0xba/0x120 kernel/task_work.c:123
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop+0x2ae/0x2c0 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+0x38b/0x3b0 arch/x86/entry/common.c:305
entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff8880b2e69408 of 8 bytes by task 16311 on cpu 0:
io_sq_thread+0x41d/0x7d0 fs/io_uring.c:5966
kthread+0x203/0x230 kernel/kthread.c:268
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 16311 Comm: io_uring-sq Not tainted 5.7.0-rc1-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.