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BUG: KCSAN: data-race in __skb_try_recv_datagram / do_recvmmsg

write to 0xffff8881e03a6a30 of 4 bytes by task 29363 on cpu 0:
 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+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff8881e03a6a30 of 4 bytes by task 29362 on cpu 1:
 sock_error include/net/sock.h:2261 [inline]
 __skb_try_recv_datagram+0x47/0x310 net/core/datagram.c:252
 unix_dgram_recvmsg+0x22f/0x870 net/unix/af_unix.c:2100
 ____sys_recvmsg+0x15d/0x310 include/linux/uio.h:234
 ___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+0x34/0x50 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 29362 Comm: syz-executor.0 Not tainted 5.12.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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