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BUG: KCSAN: data-race in unix_attach_fds / unix_inflight

write to 0xffffffff83a498c8 of 8 bytes by task 13701 on cpu 1:
 unix_inflight+0x22a/0x280 net/unix/scm.c:65
 unix_attach_fds+0x10c/0x1e0 net/unix/scm.c:121
 unix_scm_to_skb net/unix/af_unix.c:1534 [inline]
 unix_dgram_sendmsg+0x5cb/0x1610 net/unix/af_unix.c:1677
 unix_seqpacket_sendmsg+0xc2/0x100 net/unix/af_unix.c:2055
 sock_sendmsg_nosec net/socket.c:654 [inline]
 sock_sendmsg net/socket.c:674 [inline]
 ____sys_sendmsg+0x360/0x4d0 net/socket.c:2350
 __sys_sendmsg_sock+0x25/0x30 net/socket.c:2416
 io_sendmsg fs/io_uring.c:4367 [inline]
 io_issue_sqe+0x231a/0x6750 fs/io_uring.c:6135
 __io_queue_sqe+0xe9/0x360 fs/io_uring.c:6414
 io_queue_sqe fs/io_uring.c:6463 [inline]
 io_submit_sqe+0x1887/0x3360 fs/io_uring.c:6626
 io_submit_sqes+0x5bd/0xbd0 fs/io_uring.c:6734
 __do_sys_io_uring_enter fs/io_uring.c:9319 [inline]
 __se_sys_io_uring_enter+0x1e1/0xa80 fs/io_uring.c:9261
 __x64_sys_io_uring_enter+0x74/0x80 fs/io_uring.c:9261
 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffffffff83a498c8 of 8 bytes by task 13700 on cpu 0:
 too_many_unix_fds net/unix/scm.c:99 [inline]
 unix_attach_fds+0x4d/0x1e0 net/unix/scm.c:108
 unix_scm_to_skb net/unix/af_unix.c:1534 [inline]
 unix_dgram_sendmsg+0x5cb/0x1610 net/unix/af_unix.c:1677
 unix_seqpacket_sendmsg+0xc2/0x100 net/unix/af_unix.c:2055
 sock_sendmsg_nosec net/socket.c:654 [inline]
 sock_sendmsg net/socket.c:674 [inline]
 ____sys_sendmsg+0x360/0x4d0 net/socket.c:2350
 __sys_sendmsg_sock+0x25/0x30 net/socket.c:2416
 io_sendmsg fs/io_uring.c:4367 [inline]
 io_issue_sqe+0x231a/0x6750 fs/io_uring.c:6135
 __io_queue_sqe+0xe9/0x360 fs/io_uring.c:6414
 io_queue_sqe fs/io_uring.c:6463 [inline]
 io_submit_sqe+0x1887/0x3360 fs/io_uring.c:6626
 io_submit_sqes+0x5bd/0xbd0 fs/io_uring.c:6734
 __do_sys_io_uring_enter fs/io_uring.c:9319 [inline]
 __se_sys_io_uring_enter+0x1e1/0xa80 fs/io_uring.c:9261
 __x64_sys_io_uring_enter+0x74/0x80 fs/io_uring.c:9261
 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: 13700 Comm: syz-executor.5 Not tainted 5.13.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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