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

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>

1 files changed, 1 insertions, 4 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 944eaca69115..62ee71efd1ce 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2925,9 +2925,6 @@ 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;
 
@@ -3169,7 +3166,7 @@ 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_rtt_us = skb_mstamp_us_delta(&now, &last_ackt);
         }