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BUG: KCSAN: data-race in unix_notinflight / wait_for_unix_gc

read to 0xffffffff861ab8d0 of 4 bytes by task 12283 on cpu 0:
 wait_for_unix_gc+0x34/0x150 net/unix/garbage.c:196
 unix_dgram_sendmsg+0x72/0xc80 net/unix/af_unix.c:1586
 unix_seqpacket_sendmsg+0xb5/0x120 net/unix/af_unix.c:2006
 sock_sendmsg_nosec net/socket.c:637 [inline]
 sock_sendmsg+0x9f/0xc0 net/socket.c:657
 ___sys_sendmsg+0x2b7/0x5d0 net/socket.c:2311
 __sys_sendmmsg+0x123/0x350 net/socket.c:2413
 __do_sys_sendmmsg net/socket.c:2442 [inline]
 __se_sys_sendmmsg net/socket.c:2439 [inline]
 __x64_sys_sendmmsg+0x64/0x80 net/socket.c:2439
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

write to 0xffffffff861ab8d0 of 4 bytes by task 12279 on cpu 1:
 unix_notinflight+0xfe/0x220 net/unix/scm.c:82
 unix_detach_fds+0xc0/0xf0 net/unix/scm.c:133
 unix_dgram_recvmsg+0x620/0xba0 net/unix/af_unix.c:2100
 unix_seqpacket_recvmsg+0x6a/0x90 net/unix/af_unix.c:2017
 sock_recvmsg_nosec net/socket.c:871 [inline]
 sock_recvmsg net/socket.c:889 [inline]
 sock_recvmsg+0x92/0xb0 net/socket.c:885
 ___sys_recvmsg+0x1a0/0x3e0 net/socket.c:2480
 do_recvmmsg+0x19a/0x5c0 net/socket.c:2601
 __sys_recvmmsg+0x1ef/0x200 net/socket.c:2680
 __do_sys_recvmmsg net/socket.c:2703 [inline]
 __se_sys_recvmmsg net/socket.c:2696 [inline]
 __x64_sys_recvmmsg+0x89/0xb0 net/socket.c:2696
 do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 12279 Comm: syz-executor.1 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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