Techwizz/kernel-fxtec-pro1x
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity

tcp: ensure epoll edge trigger wakeup when write queue is empty

Browse source 
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>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jason Baron 2015-05-20 15:52:53 +00:00 committed by David S. Miller
parent b92d581499
commit ce5ec44099
1 changed files with 6 additions and 0 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

6
net/ipv4/tcp.c
View file

@ -999,6 +999,9 @@ static ssize_t do_tcp_sendpages(struct sock *sk, struct page *page, int offset,
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);
}
@ -1288,6 +1291,9 @@ int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
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;
}