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BUG: KCSAN: data-race in skb_dequeue / unix_dgram_poll

read to 0xffff8880ae490ce0 of 4 bytes by task 27518 on cpu 1:
 unix_recvq_full net/unix/af_unix.c:194 [inline]
 unix_dgram_poll+0x2ea/0x410 net/unix/af_unix.c:2663
 sock_poll+0xed/0x250 net/socket.c:1256
 vfs_poll include/linux/poll.h:90 [inline]
 ep_item_poll.isra.0+0x90/0x190 fs/eventpoll.c:892
 ep_send_events_proc+0x113/0x590 fs/eventpoll.c:1749
 ep_scan_ready_list.constprop.0+0x189/0x500 fs/eventpoll.c:704
 ep_send_events fs/eventpoll.c:1793 [inline]
 ep_poll+0xe3/0x900 fs/eventpoll.c:1930
 do_epoll_wait+0x162/0x180 fs/eventpoll.c:2294
 __do_sys_epoll_wait fs/eventpoll.c:2304 [inline]
 __se_sys_epoll_wait fs/eventpoll.c:2301 [inline]
 __x64_sys_epoll_wait+0x5e/0x80 fs/eventpoll.c:2301
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff8880ae490ce0 of 4 bytes by task 27524 on cpu 0:
 __skb_unlink include/linux/skbuff.h:2020 [inline]
 __skb_dequeue include/linux/skbuff.h:2040 [inline]
 skb_dequeue+0x84/0x150 net/core/skbuff.c:3040
 skb_queue_purge+0x2f/0x50 net/core/skbuff.c:3077
 unix_dgram_disconnected+0x42/0xe0 net/unix/af_unix.c:474
 unix_dgram_connect+0x210/0x490 net/unix/af_unix.c:1164
 __sys_connect+0x1e9/0x250 net/socket.c:1828
 __do_sys_connect net/socket.c:1839 [inline]
 __se_sys_connect net/socket.c:1836 [inline]
 __x64_sys_connect+0x4c/0x60 net/socket.c:1836
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 27524 Comm: syz-executor.2 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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