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BUG: KCSAN: data-race in __io_cqring_fill_event / io_uring_poll

write to 0xffff8880358ee440 of 4 bytes by task 12558 on cpu 0:
 io_get_cqring fs/io_uring.c:1349 [inline]
 __io_cqring_fill_event+0x135/0x440 fs/io_uring.c:1488
 io_req_complete_post+0x49/0x580 fs/io_uring.c:1528
 __io_req_complete fs/io_uring.c:1576 [inline]
 __io_complete_rw+0x466/0x890 fs/io_uring.c:2512
 io_complete_rw+0x1b/0x20 fs/io_uring.c:2519
 io_rw_done fs/io_uring.c:2746 [inline]
 kiocb_done fs/io_uring.c:2769 [inline]
 io_write+0x7cf/0x970 fs/io_uring.c:3428
 io_issue_sqe+0x7ae/0x5650 fs/io_uring.c:6036
 io_wq_submit_work+0x22d/0x440 fs/io_uring.c:6168
 io_worker_handle_work+0x714/0xee0 fs/io-wq.c:447
 io_wqe_worker+0x1fa/0x550 fs/io-wq.c:497
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

read to 0xffff8880358ee440 of 4 bytes by task 12554 on cpu 1:
 __io_cqring_events fs/io_uring.c:1333 [inline]
 io_cqring_events fs/io_uring.c:2175 [inline]
 io_uring_poll+0xcf/0x160 fs/io_uring.c:8488
 vfs_poll include/linux/poll.h:90 [inline]
 __io_arm_poll_handler+0x18f/0x400 fs/io_uring.c:5127
 io_poll_add fs/io_uring.c:5379 [inline]
 io_issue_sqe+0xce5/0x5650 fs/io_uring.c:6042
 __io_queue_sqe+0xea/0x4e0 fs/io_uring.c:6297
 io_queue_sqe+0x6d/0x160 fs/io_uring.c:6350
 io_submit_sqe+0x15c7/0x3130 fs/io_uring.c:6521
 io_submit_sqes+0x609/0xab0 fs/io_uring.c:6635
 __do_sys_io_uring_enter fs/io_uring.c:9207 [inline]
 __se_sys_io_uring_enter+0x21f/0xb10 fs/io_uring.c:9149
 __x64_sys_io_uring_enter+0x74/0x80 fs/io_uring.c:9149
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 12554 Comm: syz-executor.5 Tainted: G        W         5.12.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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