tcp: avoid cwnd undo after receiving ECN

yuchungcheng · davem330 · commit 99b4dd9f2423 · 2016-01-29T23:03:56.000-08:00
RFC 4015 section 3.4 says the TCP sender MUST refrain from
reversing the congestion control state when the ACK signals
congestion through the ECN-Echo flag. Currently we may not
always do that when prior_ssthresh is reset upon receiving
ACKs with ECE marks. This patch fixes that.

Signed-off-by: Yuchung Cheng &lt;ycheng@google.com&gt;
Signed-off-by: Neal Cardwell &lt;ncardwell@google.com&gt;
Signed-off-by: Eric Dumazet &lt;edumazet@google.com&gt;
Signed-off-by: David S. Miller &lt;davem@davemloft.net&gt;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
@@ -2366,8 +2366,6 @@ static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
 			tp->snd_ssthresh = tp->prior_ssthresh;
 			tcp_ecn_withdraw_cwr(tp);
 		}
-	} else {
-		tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
 	}
 	tp->snd_cwnd_stamp = tcp_time_stamp;
 	tp->undo_marker = 0;

Original file line number	Diff line number	Diff line change
`@@ -2366,8 +2366,6 @@ static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)`
`2366`	`2366`	`tp->snd_ssthresh = tp->prior_ssthresh;`
`2367`	`2367`	`tcp_ecn_withdraw_cwr(tp);`
`2368`	`2368`	`}`
`2369`		`- } else {`
`2370`		`- tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);`
`2371`	`2369`	`}`
`2372`	`2370`	`tp->snd_cwnd_stamp = tcp_time_stamp;`
`2373`	`2371`	`tp->undo_marker = 0;`