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af_unix: Use unix_recvq_full_lockless() in unix_stream_connect().

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Once sk->sk_state is changed to TCP_LISTEN, it never changes.

unix_accept() takes advantage of this characteristics; it does not
hold the listener's unix_state_lock() and only acquires recvq lock
to pop one skb.

It means unix_state_lock() does not prevent the queue length from
changing in unix_stream_connect().

Thus, we need to use unix_recvq_full_lockless() to avoid data-race.

Now we remove unix_recvq_full() as no one uses it.

Note that we can remove READ_ONCE() for sk->sk_max_ack_backlog in
unix_recvq_full_lockless() because of the following reasons:

  (1) For SOCK_DGRAM, it is a written-once field in unix_create1()

  (2) For SOCK_STREAM and SOCK_SEQPACKET, it is changed under the
      listener's unix_state_lock() in unix_listen(), and we hold
      the lock in unix_stream_connect()

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Kuniyuki Iwashima 2024-06-04 09:52:38 -07:00 committed by Paolo Abeni
parent bd9f2d0573
commit 45d872f0e6
1 changed files with 2 additions and 8 deletions
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10
net/unix/af_unix.c
View file

@ -221,15 +221,9 @@ static inline int unix_may_send(struct sock *sk, struct sock *osk)
return unix_peer(osk) == NULL || unix_our_peer(sk, osk);
}
static inline int unix_recvq_full(const struct sock *sk)
{
return skb_queue_len(&sk->sk_receive_queue) > sk->sk_max_ack_backlog;
}
static inline int unix_recvq_full_lockless(const struct sock *sk)
{
return skb_queue_len_lockless(&sk->sk_receive_queue) >
READ_ONCE(sk->sk_max_ack_backlog);
return skb_queue_len_lockless(&sk->sk_receive_queue) > sk->sk_max_ack_backlog;
}
struct sock *unix_peer_get(struct sock *s)
@ -1545,7 +1539,7 @@ static int unix_stream_connect(struct socket *sock, struct sockaddr *uaddr,
if (other->sk_shutdown & RCV_SHUTDOWN)
goto out_unlock;
if (unix_recvq_full(other)) {
if (unix_recvq_full_lockless(other)) {
err = -EAGAIN;
if (!timeo)
goto out_unlock;