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BUG: KCSAN: data-race in __io_cqring_fill_event / io_uring_poll

write to 0xffff888120d56480 of 4 bytes by task 19261 on cpu 0:
 io_get_cqring fs/io_uring.c:1384 [inline]
 __io_cqring_fill_event+0xfd/0x350 fs/io_uring.c:1566
 io_submit_flush_completions+0xd2/0x3e0 fs/io_uring.c:2142
 __io_queue_sqe+0x1fe/0x360 fs/io_uring.c:6433
 io_queue_sqe fs/io_uring.c:6468 [inline]
 io_submit_sqe+0x1887/0x3360 fs/io_uring.c:6631
 io_submit_sqes+0x5bd/0xbd0 fs/io_uring.c:6739
 __do_sys_io_uring_enter fs/io_uring.c:9336 [inline]
 __se_sys_io_uring_enter+0x1e1/0xa80 fs/io_uring.c:9278
 __x64_sys_io_uring_enter+0x74/0x80 fs/io_uring.c:9278
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888120d56480 of 4 bytes by task 19260 on cpu 1:
 __io_cqring_events fs/io_uring.c:1368 [inline]
 io_cqring_events fs/io_uring.c:2206 [inline]
 io_uring_poll+0xcf/0x160 fs/io_uring.c:8668
 vfs_poll include/linux/poll.h:90 [inline]
 do_pollfd fs/select.c:869 [inline]
 do_poll fs/select.c:917 [inline]
 do_sys_poll+0x622/0xc40 fs/select.c:1011
 __do_sys_ppoll fs/select.c:1117 [inline]
 __se_sys_ppoll+0x169/0x1b0 fs/select.c:1097
 __x64_sys_ppoll+0x63/0x70 fs/select.c:1097
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x000005a0 -> 0x000005c0

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 19260 Comm: syz-executor.2 Not tainted 5.13.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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