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BUG: KCSAN: data-race in __io_cqring_fill_event / io_uring_poll

write to 0xffff888157d9ec40 of 4 bytes by task 2169 on cpu 1:
 io_get_cqring fs/io_uring.c:1352 [inline]
 __io_cqring_fill_event+0x135/0x400 fs/io_uring.c:1491
 io_submit_flush_completions+0xb1/0x3c0 fs/io_uring.c:2105
 __io_queue_sqe+0x277/0x3a0 fs/io_uring.c:6344
 io_queue_sqe+0x6d/0x160 fs/io_uring.c:6375
 io_submit_sqe+0x15c7/0x30c0 fs/io_uring.c:6546
 io_submit_sqes+0x61f/0xaf0 fs/io_uring.c:6660
 __do_sys_io_uring_enter fs/io_uring.c:9237 [inline]
 __se_sys_io_uring_enter+0x217/0xb20 fs/io_uring.c:9179
 __x64_sys_io_uring_enter+0x74/0x80 fs/io_uring.c:9179
 do_syscall_64+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888157d9ec40 of 4 bytes by task 2152 on cpu 0:
 __io_cqring_events fs/io_uring.c:1336 [inline]
 io_cqring_events fs/io_uring.c:2178 [inline]
 io_uring_poll+0xcf/0x160 fs/io_uring.c:8516
 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+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 2152 Comm: syz-executor.1 Not tainted 5.12.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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