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af_unix: fix unix_dgram_poll() behavior for EPOLLOUT event

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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>
This commit is contained in:
Eric Dumazet 2010-10-31 05:36:23 +00:00 committed by David S. Miller
parent 67426b756c
commit 5456f09aaf
1 changed files with 9 additions and 15 deletions
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24
net/unix/af_unix.c
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@ -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 */
@ -2092,20 +2091,15 @@ 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);
if (unix_recvq_full(other))
writable = 0;
}
sock_put(other);
other = unix_peer_get(sk);
if (other) {
if (unix_peer(other) != sk) {
sock_poll_wait(file, &unix_sk(other)->peer_wait, wait);
if (unix_recvq_full(other))
writable = 0;
}
sock_put(other);
}
if (writable)