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    Subject[PATCH 4.2.y-ckt 144/211] tcp: apply Kern's check on RTTs used for congestion control
    Date
    4.2.8-ckt1 -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 77730b4..297b358 100644
    --- a/net/ipv4/tcp_input.c
    +++ b/net/ipv4/tcp_input.c
    @@ -2902,9 +2902,6 @@ 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;

    @@ -3146,7 +3143,7 @@ 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);
    }
    --
    1.9.1


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