tcp: fix RTO calculated from cached RTT

Commit 1b7fdd2ab5852 ("tcp: do not use cached RTT for RTT estimation")
did not correctly account for the fact that crtt is the RTT shifted
left 3 bits. Fix the calculation to consistently reflect this fact.

Signed-off-by: Neal Cardwell <ncardwell@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Acked-By: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 1 deletions

diff --git a/net/ipv4/tcp_metrics.c b/net/ipv4/tcp_metrics.c
index 4a22f3e715df..52f3c6b971d2 100644
--- a/net/ipv4/tcp_metrics.c
+++ b/net/ipv4/tcp_metrics.c
@@ -502,7 +502,9 @@ reset:
          * ACKs, wait for troubles.
          */
         if (crtt > tp->srtt) {
-                inet_csk(sk)->icsk_rto = crtt + max(crtt >> 2, tcp_rto_min(sk));
+                /* Set RTO like tcp_rtt_estimator(), but from cached RTT. */
+                crtt >>= 3;
+                inet_csk(sk)->icsk_rto = crtt + max(2 * crtt, tcp_rto_min(sk));
         } else if (tp->srtt == 0) {
                 /* RFC6298: 5.7 We've failed to get a valid RTT sample from
                  * 3WHS. This is most likely due to retransmission,