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BUG: KCSAN: data-race in do_epoll_wait / ep_done_scan

write to 0xffff8881027071d8 of 8 bytes by task 1767 on cpu 1:
 __list_add include/linux/list.h:70 [inline]
 list_add include/linux/list.h:86 [inline]
 ep_done_scan+0xab/0x270 fs/eventpoll.c:644
 ep_send_events fs/eventpoll.c:1715 [inline]
 ep_poll fs/eventpoll.c:1798 [inline]
 do_epoll_wait+0x91c/0xf00 fs/eventpoll.c:2226
 do_epoll_pwait fs/eventpoll.c:2260 [inline]
 __do_sys_epoll_pwait fs/eventpoll.c:2273 [inline]
 __se_sys_epoll_pwait+0xfb/0x210 fs/eventpoll.c:2267
 __x64_sys_epoll_pwait+0x74/0x80 fs/eventpoll.c:2267
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff8881027071d8 of 8 bytes by task 1754 on cpu 0:
 list_empty_careful include/linux/list.h:319 [inline]
 ep_events_available fs/eventpoll.c:374 [inline]
 ep_poll fs/eventpoll.c:1789 [inline]
 do_epoll_wait+0x292/0xf00 fs/eventpoll.c:2226
 do_epoll_pwait fs/eventpoll.c:2260 [inline]
 __do_sys_epoll_pwait fs/eventpoll.c:2273 [inline]
 __se_sys_epoll_pwait+0xfb/0x210 fs/eventpoll.c:2267
 __x64_sys_epoll_pwait+0x74/0x80 fs/eventpoll.c:2267
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 1754 Comm: syz-fuzzer Not tainted 5.13.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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