| Message ID | 20150520155253.86202203D@prod-mail-relay06.akamai.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
On Wed, 2015-05-20 at 15:52 +0000, Jason Baron wrote: > From: Jason Baron <jbaron@akamai.com> > > We currently rely on the setting of SOCK_NOSPACE in the write() > path to ensure that we wake up any epoll edge trigger waiters when > acks return to free space in the write queue. However, if we fail > to allocate even a single skb in the write queue, we could end up > waiting indefinitely. > > Fix this by explicitly issuing a wakeup when we detect the condition > of an empty write queue and a return value of -EAGAIN. This allows > userspace to re-try as we expect this to be a temporary failure. > > I've tested this approach by artificially making > sk_stream_alloc_skb() return NULL periodically. In that case, > epoll edge trigger waiters will hang indefinitely in epoll_wait() > without this patch. > > Signed-off-by: Jason Baron <jbaron@akamai.com> > --- Acked-by: Eric Dumazet <edumazet@google.com> -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Jason Baron <jbaron@akamai.com> Date: Wed, 20 May 2015 15:52:53 +0000 (GMT) > From: Jason Baron <jbaron@akamai.com> > > We currently rely on the setting of SOCK_NOSPACE in the write() > path to ensure that we wake up any epoll edge trigger waiters when > acks return to free space in the write queue. However, if we fail > to allocate even a single skb in the write queue, we could end up > waiting indefinitely. > > Fix this by explicitly issuing a wakeup when we detect the condition > of an empty write queue and a return value of -EAGAIN. This allows > userspace to re-try as we expect this to be a temporary failure. > > I've tested this approach by artificially making > sk_stream_alloc_skb() return NULL periodically. In that case, > epoll edge trigger waiters will hang indefinitely in epoll_wait() > without this patch. > > Signed-off-by: Jason Baron <jbaron@akamai.com> > --- > v2: > - ensure it compiles :) Applied, thanks Jason :) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index c724195..6247c24 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -997,6 +997,9 @@ do_error: if (copied) goto out; out_err: + /* make sure we wake any epoll edge trigger waiter */ + if (unlikely(skb_queue_len(&sk->sk_write_queue) == 0 && err == -EAGAIN)) + sk->sk_write_space(sk); return sk_stream_error(sk, flags, err); } @@ -1285,6 +1288,9 @@ do_error: goto out; out_err: err = sk_stream_error(sk, flags, err); + /* make sure we wake any epoll edge trigger waiter */ + if (unlikely(skb_queue_len(&sk->sk_write_queue) == 0 && err == -EAGAIN)) + sk->sk_write_space(sk); release_sock(sk); return err; }