tcp: apply Kern's check on RTTs used for congestion control

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>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 0cdaa633059b6c90d62285eaae14b4f9203774dd..e3d40a303b8f0382ab4ea044cad122b1affd8232 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2891,9 +2891,6 @@ 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;
 
@@ -3115,7 +3112,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
                flag |= FLAG_SACK_RENEGING;
 
        skb_mstamp_get(&now);
-       if (first_ackt.v64) {
+       if (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);
        }