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BUG: KCSAN: data-race in __skb_wait_for_more_packets / do_recvmmsg

write to 0xffff88812d636230 of 4 bytes by task 4101 on cpu 1:
 do_recvmmsg+0x923/0x9e0 net/socket.c:2761
 __sys_recvmmsg net/socket.c:2784 [inline]
 __do_sys_recvmmsg net/socket.c:2807 [inline]
 __se_sys_recvmmsg net/socket.c:2800 [inline]
 __x64_sys_recvmmsg+0xcf/0x150 net/socket.c:2800
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88812d636230 of 4 bytes by task 4095 on cpu 0:
 sock_error include/net/sock.h:2261 [inline]
 __skb_wait_for_more_packets+0x97/0x2e0 net/core/datagram.c:98
 unix_dgram_recvmsg+0x1d2/0x870 net/unix/af_unix.c:2113
 ____sys_recvmsg+0x15d/0x310 include/linux/uio.h:244
 ___sys_recvmsg net/socket.c:2611 [inline]
 do_recvmmsg+0x34c/0x9e0 net/socket.c:2705
 __sys_recvmmsg net/socket.c:2784 [inline]
 __do_sys_recvmmsg net/socket.c:2807 [inline]
 __se_sys_recvmmsg net/socket.c:2800 [inline]
 __x64_sys_recvmmsg+0xcf/0x150 net/socket.c:2800
 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: 4095 Comm: syz-executor.4 Not tainted 5.12.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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