af_unix: fix unix_dgram_poll() behavior for EPOLLOUT event (5456f09a) · Commits · 戴 / test

Alban Crequy reported a problem with connected dgram af_unix sockets and provided a test program. epoll() would miss to send an EPOLLOUT event when a thread unqueues a packet from the other peer, making its receive queue not full. This is because unix_dgram_poll() fails to call sock_poll_wait(file, &unix_sk(other)->peer_wait, wait); if the socket is not writeable at the time epoll_ctl(ADD) is called. We must call sock_poll_wait(), regardless of 'writable' status, so that epoll can be notified later of states changes. Misc: avoids testing twice (sk->sk_shutdown & RCV_SHUTDOWN) Reported-by:

Alban Crequy <alban.crequy@collabora.co.uk> Cc: Davide Libenzi <davidel@xmailserver.org> Signed-off-by:

Eric Dumazet <eric.dumazet@gmail.com> Acked-by:

Davide Libenzi <davidel@xmailserver.org> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/unix/af_unix.c

+9 −15

Original line number	Diff line number	Diff line
		@@ -2074,13 +2074,12 @@ static unsigned int unix_dgram_poll(struct file file, struct socket sock,
		if (sk->sk_err \|\| !skb_queue_empty(&sk->sk_error_queue))
		mask \|= POLLERR;
		if (sk->sk_shutdown & RCV_SHUTDOWN)
		mask \|= POLLRDHUP;
		mask \|= POLLRDHUP \| POLLIN \| POLLRDNORM;
		if (sk->sk_shutdown == SHUTDOWN_MASK)
		mask \|= POLLHUP;

		/* readable? */
		if (!skb_queue_empty(&sk->sk_receive_queue) \|\|
		(sk->sk_shutdown & RCV_SHUTDOWN))
		if (!skb_queue_empty(&sk->sk_receive_queue))
		mask \|= POLLIN \| POLLRDNORM;

		/* Connection-based need to check for termination and startup */
		@@ -2092,21 +2091,16 @@ static unsigned int unix_dgram_poll(struct file file, struct socket sock,
		return mask;
		}

		/* writable? */
		writable = unix_writable(sk);
		if (writable) {
		other = unix_peer_get(sk);
		if (other) {
		if (unix_peer(other) != sk) {
		sock_poll_wait(file, &unix_sk(other)->peer_wait,
		wait);
		sock_poll_wait(file, &unix_sk(other)->peer_wait, wait);
		if (unix_recvq_full(other))
		writable = 0;
		}

		sock_put(other);
		}
		}

		if (writable)
		mask \|= POLLOUT \| POLLWRNORM \| POLLWRBAND;

Admin message