[PATCH net-next 1/2] tcp: notify when a delayed ack is sent

[Lawrence Brakmo <brakmo@fb.com>]

DCTCP depends on the CA_EVENT_NON_DELAYED_ACK and CA_EVENT_DELAYED_ACK
notifications to keep track if it needs to send an ACK for packets that
were received with a particular ECN state but whose ACK was delayed.

Under some circumstances, for example when a delayed ACK is sent with a
data packet, DCTCP state was not being updated due to a lack of
notification that the previously delayed ACK was sent. As a result, it
would sometimes send a duplicate ACK when a new data packet arrived.

This patch insures that DCTCP's state is correctly updated so it will
not send the duplicate ACK.

Signed-off-by: Lawrence Brakmo <brakmo@fb.com>
---
 net/ipv4/tcp_output.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index f8f6129160dd..41f6ad7a21e4 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -172,6 +172,8 @@ static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
 			__sock_put(sk);
 	}
 	tcp_dec_quickack_mode(sk, pkts);
+	if (inet_csk_ack_scheduled(sk))
+		tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK);
 	inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
 }
 
-- 
2.17.1