On Fri, Oct 02, 2015 at 08:44:02PM +0000, Jason Baron wrote:
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index f789423..b8ed1bc 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -1079,6 +1079,9 @@ static long unix_wait_for_peer(struct sock *other, long
> timeo)
>
> prepare_to_wait_exclusive(&u->peer_wait, &wait, TASK_INTERRUPTIBLE);
>
> + set_bit(UNIX_NOSPACE, &u->flags);
> + /* pairs with mb in unix_dgram_recv */
> + smp_mb__after_atomic();
> sched = !sock_flag(other, SOCK_DEAD) &&
> !(other->sk_shutdown & RCV_SHUTDOWN) &&
> unix_recvq_full(other);
> @@ -1623,17 +1626,22 @@ restart:
>
> if (unix_peer(other) != sk && unix_recvq_full(other)) {
> if (!timeo) {
> + set_bit(UNIX_NOSPACE, &unix_sk(other)->flags);
> + /* pairs with mb in unix_dgram_recv */
> + smp_mb__after_atomic();
> + if (unix_recvq_full(other)) {
> + err = -EAGAIN;
> + goto out_unlock;
> + }
> + } else {
> @@ -1939,8 +1947,14 @@ static int unix_dgram_recvmsg(struct socket *sock,
> struct msghdr *msg,
> goto out_unlock;
> }
>
> + /* pairs with unix_dgram_poll() and wait_for_peer() */
> + smp_mb();
> + if (test_bit(UNIX_NOSPACE, &u->flags)) {
> + clear_bit(UNIX_NOSPACE, &u->flags);
> + wake_up_interruptible_sync_poll(&u->peer_wait,
> + POLLOUT | POLLWRNORM |
> + POLLWRBAND);
> + }
>
> if (msg->msg_name)
> unix_copy_addr(msg, skb->sk);
> @@ -2468,20 +2493,19 @@ static unsigned int unix_dgram_poll(struct file
> *file, struct socket *sock,
> if (!(poll_requested_events(wait) & (POLLWRBAND|POLLWRNORM|POLLOUT)))
> return mask;
>
> other = unix_peer_get(sk);
> + if (unix_dgram_writable(sk, other)) {
> mask |= POLLOUT | POLLWRNORM | POLLWRBAND;
> + } else {
> set_bit(SOCK_ASYNC_NOSPACE, &sk->sk_socket->flags);
> + set_bit(UNIX_NOSPACE, &unix_sk(other)->flags);
> + /* pairs with mb in unix_dgram_recv */
> + smp_mb__after_atomic();
> + if (unix_dgram_writable(sk, other))
> + mask |= POLLOUT | POLLWRNORM | POLLWRBAND;
> + }
> + if (other)
> + sock_put(other);
>
> return mask;
> }
So I must object to these barrier comments; stating which other barrier
they pair with is indeed good and required, but its not sufficient.
A barrier comment should also explain the data ordering -- the most
important part.
As it stands its not clear to me these barriers are required at all, but
this is not code I understand so I might well miss something obvious.
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