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BUG: KCSAN: data-race in skb_queue_tail / unix_dgram_peer_wake_me

write to 0xffff88800beff4e0 of 4 bytes by task 11510 on cpu 0:
 __skb_insert include/linux/skbuff.h:1929 [inline]
 __skb_queue_before include/linux/skbuff.h:2034 [inline]
 __skb_queue_tail include/linux/skbuff.h:2067 [inline]
 skb_queue_tail+0x80/0xa0 net/core/skbuff.c:3200
 unix_dgram_sendmsg+0xfd9/0x1640 net/unix/af_unix.c:1798
 sock_sendmsg_nosec net/socket.c:654 [inline]
 sock_sendmsg net/socket.c:674 [inline]
 ____sys_sendmsg+0x360/0x4d0 net/socket.c:2350
 ___sys_sendmsg net/socket.c:2404 [inline]
 __sys_sendmmsg+0x315/0x4b0 net/socket.c:2490
 __do_sys_sendmmsg net/socket.c:2519 [inline]
 __se_sys_sendmmsg net/socket.c:2516 [inline]
 __x64_sys_sendmmsg+0x53/0x60 net/socket.c:2516
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88800beff4e0 of 4 bytes by task 11516 on cpu 1:
 skb_queue_len include/linux/skbuff.h:1860 [inline]
 unix_recvq_full net/unix/af_unix.c:194 [inline]
 unix_dgram_peer_wake_me+0x180/0x2d0 net/unix/af_unix.c:441
 unix_dgram_poll+0x33c/0x3b0 net/unix/af_unix.c:2726
 sock_poll+0x23e/0x260 net/socket.c:1246
 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:1119 [inline]
 __se_sys_ppoll+0x169/0x1b0 fs/select.c:1099
 __x64_sys_ppoll+0x63/0x70 fs/select.c:1099
 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: 11516 Comm: syz-executor.3 Not tainted 5.12.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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