syzbot

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BUG: KCSAN: data-race in __skb_try_recv_from_queue / unix_dgram_sendmsg

write to 0xffff88809a499ce0 of 4 bytes by task 8248 on cpu 0:
 __skb_unlink include/linux/skbuff.h:2022 [inline]
 __skb_try_recv_from_queue+0x407/0x4e0 net/core/datagram.c:199
 __skb_try_recv_datagram+0xfa/0x2c0 net/core/datagram.c:269
 unix_dgram_recvmsg+0xfd/0xbf0 net/unix/af_unix.c:2061
 sock_recvmsg_nosec net/socket.c:873 [inline]
 ____sys_recvmsg+0x387/0x3a0 net/socket.c:2551
 ___sys_recvmsg+0xb2/0x100 net/socket.c:2595
 do_recvmmsg+0x19a/0x5c0 net/socket.c:2693
 __sys_recvmmsg+0x1ef/0x200 net/socket.c:2772
 __do_sys_recvmmsg net/socket.c:2795 [inline]
 __se_sys_recvmmsg net/socket.c:2788 [inline]
 __x64_sys_recvmmsg+0x89/0xb0 net/socket.c:2788
 do_syscall_64+0xcc/0x3a0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88809a499ce0 of 4 bytes by task 8234 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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 8234 Comm: syz-executor.4 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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