syzbot

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BUG: KCSAN: data-race in skb_dequeue / unix_dgram_sendmsg

read to 0xffff88812ae810e0 of 4 bytes by task 15387 on cpu 1:
 unix_recvq_full net/unix/af_unix.c:194 [inline]
 unix_dgram_sendmsg+0xad0/0xdc0 net/unix/af_unix.c:1725
 sock_sendmsg_nosec net/socket.c:639 [inline]
 sock_sendmsg+0x9f/0xc0 net/socket.c:659
 ____sys_sendmsg+0x212/0x4d0 net/socket.c:2330
 ___sys_sendmsg+0xb5/0x100 net/socket.c:2384
 __sys_sendmmsg+0x123/0x350 net/socket.c:2474
 __do_sys_sendmmsg net/socket.c:2503 [inline]
 __se_sys_sendmmsg net/socket.c:2500 [inline]
 __x64_sys_sendmmsg+0x64/0x80 net/socket.c:2500
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffff88812ae810e0 of 4 bytes by task 15391 on cpu 0:
 __skb_unlink include/linux/skbuff.h:2022 [inline]
 __skb_dequeue include/linux/skbuff.h:2042 [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:472
 unix_dgram_connect+0x419/0x5a0 net/unix/af_unix.c:1174
 __sys_connect_file+0xf4/0x100 net/socket.c:1844
 __sys_connect+0x121/0x150 net/socket.c:1861
 __do_sys_connect net/socket.c:1872 [inline]
 __se_sys_connect net/socket.c:1869 [inline]
 __x64_sys_connect+0x4c/0x60 net/socket.c:1869
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 15391 Comm: syz-executor.0 Not tainted 5.5.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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