From: Neal Cardwell <ncardwell@google.com>
Date: Thu, 2 Apr 2015 00:26:46 +0000 (-0400)
Subject: tcp: fix FRTO undo on cumulative ACK of SACKed range
X-Git-Tag: firefly_0821_release~3679^2~567
X-Git-Url: http://plrg.eecs.uci.edu/git/?p=firefly-linux-kernel-4.4.55.git;a=commitdiff_plain;h=c31d60c29774e1c5650f89d5edccfd8314152af6

tcp: fix FRTO undo on cumulative ACK of SACKed range

[ Upstream commit 666b805150efd62f05810ff0db08f44a2370c937 ]

On processing cumulative ACKs, the FRTO code was not checking the
SACKed bit, meaning that there could be a spurious FRTO undo on a
cumulative ACK of a previously SACKed skb.

The FRTO code should only consider a cumulative ACK to indicate that
an original/unretransmitted skb is newly ACKed if the skb was not yet
SACKed.

The effect of the spurious FRTO undo would typically be to make the
connection think that all previously-sent packets were in flight when
they really weren't, leading to a stall and an RTO.

Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Fixes: e33099f96d99c ("tcp: implement RFC5682 F-RTO")
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index ea7f52f3062d..a8be45e4d34f 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3076,10 +3076,11 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
 			if (seq_rtt < 0) {
 				seq_rtt = ca_seq_rtt;
 			}
-			if (!(sacked & TCPCB_SACKED_ACKED))
+			if (!(sacked & TCPCB_SACKED_ACKED)) {
 				reord = min(pkts_acked, reord);
-			if (!after(scb->end_seq, tp->high_seq))
-				flag |= FLAG_ORIG_SACK_ACKED;
+				if (!after(scb->end_seq, tp->high_seq))
+					flag |= FLAG_ORIG_SACK_ACKED;
+			}
 		}
 
 		if (sacked & TCPCB_SACKED_ACKED)