From: Yuchung Cheng <ycheng@google.com>
Date: Fri, 29 Jan 2016 23:11:50 +0000 (-0800)
Subject: tcp: avoid cwnd undo after receiving ECN
X-Git-Tag: v5.15~14268^2~1
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=99b4dd9f2423130875ac486fe587cd103c64f753;p=platform%2Fkernel%2Flinux-starfive.git

tcp: avoid cwnd undo after receiving ECN

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 <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index d2ad433..1c2a734 100644
--- 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;