On 8/26/19 9:56 PM, Jason Baron wrote:
>
>
> On 8/26/19 12:19 PM, Eric Dumazet wrote:
>> Vladimir Rutsky reported stuck TCP sessions after memory pressure
>> events. Edge Trigger epoll() user would never receive an EPOLLOUT
>> notification allowing them to retry a sendmsg().
>>
>> Jason tested the case of sk_stream_alloc_skb() returning NULL,
>> but there are other paths that could lead both sendmsg() and sendpage()
>> to return -1 (EAGAIN), with an empty skb queued on the write queue.
>>
>> This patch makes sure we remove this empty skb so that
>> Jason code can detect that the queue is empty, and
>> call sk->sk_write_space(sk) accordingly.
>>
>
> Makes sense, thanks. I think this check for empty queue could also
> benefit from and update to use tcp_write_queue_empty(). I will send a
> follow-up for that.
>
My plan (for net-next) is to submit something more like this one instead.
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 051ef10374f6..908dbe91e04b 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1068,7 +1068,7 @@ ssize_t do_tcp_sendpages(struct sock *sk, struct page
*page, int offset,
goto out;
out_err:
/* make sure we wake any epoll edge trigger waiter */
- if (unlikely(skb_queue_len(&sk->sk_write_queue) == 0 &&
+ if (unlikely(tcp_rtx_and_write_queues_empty(sk) &&
err == -EAGAIN)) {
sk->sk_write_space(sk);
tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED);
@@ -1407,7 +1407,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr
*msg, size_t size)
sock_zerocopy_put_abort(uarg, true);
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 &&
+ if (unlikely(tcp_rtx_and_write_queues_empty(sk) &&
err == -EAGAIN)) {
sk->sk_write_space(sk);
tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED);
