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BUG: KCSAN: data-race in do_epoll_wait / ep_poll_callback

write to 0xffff8881018cc768 of 4 bytes by task 9837 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+0x44/0xa9

read to 0xffff8881018cc768 of 4 bytes by task 9850 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_sync_key+0x83/0xc0 kernel/sched/wait.c:205
 unix_write_space+0xc9/0x140 net/unix/af_unix.c:464
 sock_wfree+0xaf/0x150 net/core/sock.c:2052
 unix_destruct_scm+0x164/0x190 net/unix/scm.c:150
 skb_release_head_state+0xb3/0x170 net/core/skbuff.c:665
 skb_release_all net/core/skbuff.c:676 [inline]
 __kfree_skb+0x14/0x150 net/core/skbuff.c:692
 kfree_skb+0x50/0x170 net/core/skbuff.c:710
 unix_release_sock+0x505/0x650 net/unix/af_unix.c:568
 unix_release+0x2f/0x50 net/unix/af_unix.c:859
 __sock_release net/socket.c:597 [inline]
 sock_close+0x6c/0x150 net/socket.c:1256
 __fput+0x24e/0x4e0 fs/file_table.c:280
 ____fput+0x11/0x20 fs/file_table.c:313
 task_work_run+0x8e/0x110 kernel/task_work.c:140
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
 exit_to_user_mode_prepare+0x17c/0x1b0 kernel/entry/common.c:201
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:302
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 9850 Comm: syz-executor.0 Not tainted 5.11.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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