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[PATCH 3.19.y-ckt 161/164] tcp: apply Kern's check on RTTs used for congestion control

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  [PATCH 3.19.y-ckt 161/164] tcp: apply Kern's check on RTTs used for congestion control Kamal Mostafa <kamal@canonical.com> - 2015-12-02 18:10 +0100

#1282057 — [PATCH 3.19.y-ckt 161/164] tcp: apply Kern's check on RTTs used for congestion control

3.19.8-ckt11 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Yuchung Cheng <ycheng@google.com>

commit 9e45a3e36b363cc4c79c70f2b4f994e66543a219 upstream.

Currently ca_seq_rtt_us does not use Kern's check. Fix that by
checking if any packet acked is a retransmit, for both RTT used
for RTT estimation and congestion control.

Fixes: 5b08e47ca ("tcp: prefer packet timing to TS-ECR for RTT")
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>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 net/ipv4/tcp_input.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 08ccca6..8e967ef 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2907,9 +2907,6 @@ static inline bool tcp_ack_update_rtt(struct sock *sk, const int flag,
 	 * Karn's algorithm forbids taking RTT if some retransmitted data
 	 * is acked (RFC6298).
 	 */
-	if (flag & FLAG_RETRANS_DATA_ACKED)
-		seq_rtt_us = -1L;
-
 	if (seq_rtt_us < 0)
 		seq_rtt_us = sack_rtt_us;
 
@@ -3151,7 +3148,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
 		flag |= FLAG_SACK_RENEGING;
 
 	skb_mstamp_get(&now);
-	if (likely(first_ackt.v64)) {
+	if (likely(first_ackt.v64) && !(flag & FLAG_RETRANS_DATA_ACKED)) {
 		seq_rtt_us = skb_mstamp_us_delta(&now, &first_ackt);
 		ca_seq_rtt_us = skb_mstamp_us_delta(&now, &last_ackt);
 	}
-- 
1.9.1

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