5.15-stable review patch. If anyone has any objections, please let me know.
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From: Kuniyuki Iwashima kuniyu@amazon.com
[ Upstream commit 45d872f0e65593176d880ec148f41ad7c02e40a7 ]
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: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Kuniyuki Iwashima kuniyu@amazon.com Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- net/unix/af_unix.c | 10 ++-------- 1 file changed, 2 insertions(+), 8 deletions(-)
--- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -190,15 +190,9 @@ static inline int unix_may_send(struct s 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) @@ -1387,7 +1381,7 @@ restart: 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;