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BUG: KCSAN: data-race in do_epoll_wait / ep_poll_callback

write to 0xffff888024d27168 of 4 bytes by task 29692 on cpu 0:
 ep_send_events fs/eventpoll.c:1692 [inline]
 ep_poll fs/eventpoll.c:1792 [inline]
 do_epoll_wait+0x843/0xf00 fs/eventpoll.c:2220
 __do_sys_epoll_wait fs/eventpoll.c:2232 [inline]
 __se_sys_epoll_wait fs/eventpoll.c:2227 [inline]
 __x64_sys_epoll_wait+0xf6/0x120 fs/eventpoll.c:2227
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888024d27168 of 4 bytes by task 29695 on cpu 1:
 ep_poll_callback+0x415/0x4e0 fs/eventpoll.c:1200
 __wake_up_common+0xbc/0x130 kernel/sched/wait.c:108
 __wake_up_common_lock kernel/sched/wait.c:138 [inline]
 __wake_up+0x80/0xc0 kernel/sched/wait.c:157
 tty_ldisc_lock drivers/tty/tty_ldisc.c:336 [inline]
 tty_ldisc_hangup+0x1b1/0x4b0 drivers/tty/tty_ldisc.c:745
 __tty_hangup+0x467/0x610 drivers/tty/tty_io.c:639
 tty_vhangup drivers/tty/tty_io.c:712 [inline]
 tty_ioctl+0x59a/0x10c0 drivers/tty/tty_io.c:2742
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:739
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:739
 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: 29695 Comm: syz-executor.2 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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