KCSAN: data-race in __io_cqring_fill_event / io_req_defer

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 84b13499 Merge tag 'for-linus' of git://git.kernel.org/pub..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=109c0a53900000
kernel config: https://syzkaller.appspot.com/x/.config?x=a5d60aa8b6ca55a0
dashboard link: https://syzkaller.appspot.com/bug?extid=7366b5fb4e738232bc93
compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project.git ca2dcbd030eadbf0aa9b660efe864ff08af6e18b)
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+7366b5...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __io_cqring_fill_event / io_req_defer

write to 0xffff8880305e85c0 of 4 bytes by task 22196 on cpu 0:
io_get_cqring fs/io_uring.c:1301 [inline]
__io_cqring_fill_event+0x116/0x410 fs/io_uring.c:1404
io_cqring_add_event fs/io_uring.c:1437 [inline]
__io_req_complete+0xd8/0x1a0 fs/io_uring.c:1475
io_issue_sqe+0x7249/0x78d0 fs/io_uring.c:3672
io_wq_submit_work+0x23e/0x340 fs/io_uring.c:5939
io_worker_handle_work+0xa69/0xcf0 fs/io-wq.c:527
io_wqe_worker+0x1f2/0x860 fs/io-wq.c:569
kthread+0x20d/0x230 kernel/kthread.c:292
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff8880305e85c0 of 4 bytes by task 22193 on cpu 1:
req_need_defer fs/io_uring.c:1089 [inline]
io_req_defer+0x3b6/0x550 fs/io_uring.c:5580
io_queue_sqe+0x21/0x220 fs/io_uring.c:6206
io_submit_sqe+0x333/0x550 fs/io_uring.c:6299
io_submit_sqes+0x8c6/0xfb0 fs/io_uring.c:6496
__do_sys_io_uring_enter fs/io_uring.c:8322 [inline]
__se_sys_io_uring_enter+0x1c2/0x720 fs/io_uring.c:8281
__x64_sys_io_uring_enter+0x74/0x80 fs/io_uring.c:8281
do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 22193 Comm: syz-executor.3 Not tainted 5.9.0-rc4-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.