On Tue, Nov 24, 2015 at 04:30:01PM -0500, Jason Baron wrote:
> So looking at this trace I think its the other->sk_socket that gets
> freed and then we call sk_wake_async() on it.
>
> We could I think grab the socket reference there with unix_state_lock(),
> since that is held by unix_release_sock() before the final iput() is called.
>
> So something like below might work (compile tested only):
That just adds the performance regression back in. It should be possible
to protect the other socket dereference using RCU. I haven't had time to
look at this yet today, but will try to find some time this evening to come
up with a suggested patch.
-ben
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index aaa0b58..2b014f1 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -196,6 +196,19 @@ static inline int unix_recvq_full(struct sock const
> *sk)
> return skb_queue_len(&sk->sk_receive_queue) > sk->sk_max_ack_backlog;
> }
>
> +struct socket *unix_peer_get_socket(struct sock *s)
> +{
> + struct socket *peer;
> +
> + unix_state_lock(s);
> + peer = s->sk_socket;
> + if (peer)
> + __iget(SOCK_INODE(s->sk_socket));
> + unix_state_unlock(s);
> +
> + return peer;
> +}
> +
> struct sock *unix_peer_get(struct sock *s)
> {
> struct sock *peer;
> @@ -1639,6 +1652,7 @@ static int unix_stream_sendmsg(struct socket
> *sock, struct msghdr *msg,
> {
> struct sock *sk = sock->sk;
> struct sock *other = NULL;
> + struct socket *other_socket = NULL;
> int err, size;
> struct sk_buff *skb;
> int sent = 0;
> @@ -1662,7 +1676,10 @@ static int unix_stream_sendmsg(struct socket
> *sock, struct msghdr *msg,
> } else {
> err = -ENOTCONN;
> other = unix_peer(sk);
> - if (!other)
> + if (other)
> + other_socket = unix_peer_get_socket(other);
> +
> + if (!other_socket)
> goto out_err;
> }
>
> @@ -1721,6 +1738,9 @@ static int unix_stream_sendmsg(struct socket
> *sock, struct msghdr *msg,
> sent += size;
> }
>
> + if (other_socket)
> + iput(SOCK_INODE(other_socket));
> +
> scm_destroy(&scm);
>
> return sent;
> @@ -1733,6 +1753,8 @@ pipe_err:
> send_sig(SIGPIPE, current, 0);
> err = -EPIPE;
> out_err:
> + if (other_socket)
> + iput(SOCK_INODE(other_socket));
> scm_destroy(&scm);
> return sent ? : err;
> }
--
"Thought is the essence of where you are now."
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