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BUG: KCSAN: data-race in do_recvmmsg / unix_dgram_poll

write to 0xffff88813ddb7520 of 4 bytes by task 20915 on cpu 1:
 do_recvmmsg+0x973/0xa30 net/socket.c:2903
 __sys_recvmmsg net/socket.c:2926 [inline]
 __do_sys_recvmmsg net/socket.c:2949 [inline]
 __se_sys_recvmmsg net/socket.c:2942 [inline]
 __x64_sys_recvmmsg+0xde/0x160 net/socket.c:2942
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x46/0xb0

read to 0xffff88813ddb7520 of 4 bytes by task 20919 on cpu 0:
 unix_dgram_poll+0x6e/0x3e0 net/unix/af_unix.c:3168
 sock_poll+0x23e/0x260 net/socket.c:1353
 vfs_poll include/linux/poll.h:88 [inline]
 do_pollfd fs/select.c:873 [inline]
 do_poll fs/select.c:921 [inline]
 do_sys_poll+0x6d5/0xca0 fs/select.c:1015
 __do_sys_ppoll fs/select.c:1121 [inline]
 __se_sys_ppoll+0x195/0x1d0 fs/select.c:1101
 __x64_sys_ppoll+0x63/0x70 fs/select.c:1101
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x46/0xb0

value changed: 0x00000000 -> 0x0000000e

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 20919 Comm: syz-executor.2 Not tainted 5.19.0-rc3-syzkaller-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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