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BUG: KCSAN: data-race in unix_gc / wait_for_unix_gc

write to 0xffffffff88c49c23 of 1 bytes by task 8468 on cpu 1:
 unix_gc+0x815/0x880 net/unix/garbage.c:302
 unix_release_sock+0x5c3/0x650 net/unix/af_unix.c:590
 unix_release+0x2f/0x50 net/unix/af_unix.c:859
 __sock_release net/socket.c:597 [inline]
 sock_close+0x6c/0x150 net/socket.c:1256
 __fput+0x24b/0x4e0 fs/file_table.c:280
 ____fput+0x11/0x20 fs/file_table.c:313
 task_work_run+0x8e/0x110 kernel/task_work.c:140
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
 exit_to_user_mode_prepare+0x16b/0x1a0 kernel/entry/common.c:201
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:302
 do_syscall_64+0x45/0x80 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffffffff88c49c23 of 1 bytes by task 9931 on cpu 0:
 wait_for_unix_gc+0x77/0x140 net/unix/garbage.c:198
 unix_dgram_sendmsg+0x5f/0x1660 net/unix/af_unix.c:1631
 unix_seqpacket_sendmsg+0xc2/0x100 net/unix/af_unix.c:2054
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg net/socket.c:672 [inline]
 ____sys_sendmsg+0x352/0x4c0 net/socket.c:2345
 ___sys_sendmsg net/socket.c:2399 [inline]
 __sys_sendmmsg+0x335/0x4b0 net/socket.c:2489
 __do_sys_sendmmsg net/socket.c:2518 [inline]
 __se_sys_sendmmsg net/socket.c:2515 [inline]
 __x64_sys_sendmmsg+0x53/0x60 net/socket.c:2515
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 9931 Comm: syz-executor.2 Not tainted 5.11.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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