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af_unix: Don't hold unix_state_lock() in __unix_dgram_recvmsg().

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When __skb_try_recv_datagram() returns NULL in __unix_dgram_recvmsg(),
we hold unix_state_lock() unconditionally.

This is because SOCK_SEQPACKET sk needs to return EOF in case its peer
has been close()d concurrently.

This behaviour totally depends on the timing of the peer's close() and
reading sk->sk_shutdown, and taking the lock does not play a role.

Let's drop the lock from __unix_dgram_recvmsg() and use READ_ONCE().

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20250702223606.1054680-2-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Kuniyuki Iwashima 2025-07-02 22:35:13 +00:00 committed by Jakub Kicinski
parent d18e43dddf
commit b429a5ad19
1 changed files with 1 additions and 3 deletions
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4
net/unix/af_unix.c
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@ -2527,12 +2527,10 @@ int __unix_dgram_recvmsg(struct sock *sk, struct msghdr *msg, size_t size,
&err, &timeo, last));
if (!skb) { /* implies iolock unlocked */
unix_state_lock(sk);
/* Signal EOF on disconnected non-blocking SEQPACKET socket. */
if (sk->sk_type == SOCK_SEQPACKET && err == -EAGAIN &&
(sk->sk_shutdown & RCV_SHUTDOWN))
(READ_ONCE(sk->sk_shutdown) & RCV_SHUTDOWN))
err = 0;
unix_state_unlock(sk);
goto out;
}