1 files changed, 25 insertions, 21 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index bef9f04c22b..ea0d2183df4 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -880,6 +880,11 @@ static void tcp_init_metrics(struct sock *sk)
                 tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
                 if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
                         tp->snd_ssthresh = tp->snd_cwnd_clamp;
+        } else {
+                /* ssthresh may have been reduced unnecessarily during.
+                 * 3WHS. Restore it back to its initial default.
+                 */
+                tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
         }
         if (dst_metric(dst, RTAX_REORDERING) &&
             tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
@@ -887,10 +892,7 @@ static void tcp_init_metrics(struct sock *sk)
                 tp->reordering = dst_metric(dst, RTAX_REORDERING);
         }
 
-        if (dst_metric(dst, RTAX_RTT) == 0)
-                goto reset;
-
-        if (!tp->srtt && dst_metric_rtt(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3))
+        if (dst_metric(dst, RTAX_RTT) == 0 || tp->srtt == 0)
                 goto reset;
 
         /* Initial rtt is determined from SYN,SYN-ACK.
@@ -916,19 +918,26 @@ static void tcp_init_metrics(struct sock *sk)
                 tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
         }
         tcp_set_rto(sk);
-        if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp) {
 reset:
-                /* Play conservative. If timestamps are not
-                 * supported, TCP will fail to recalculate correct
-                 * rtt, if initial rto is too small. FORGET ALL AND RESET!
+        if (tp->srtt == 0) {
+                /* RFC2988bis: We've failed to get a valid RTT sample from
+                 * 3WHS. This is most likely due to retransmission,
+                 * including spurious one. Reset the RTO back to 3secs
+                 * from the more aggressive 1sec to avoid more spurious
+                 * retransmission.
                  */
-                if (!tp->rx_opt.saw_tstamp && tp->srtt) {
-                        tp->srtt = 0;
-                        tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT;
-                        inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
-                }
+                tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_FALLBACK;
+                inet_csk(sk)->icsk_rto = TCP_TIMEOUT_FALLBACK;
         }
-        tp->snd_cwnd = tcp_init_cwnd(tp, dst);
+        /* Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been
+         * retransmitted. In light of RFC2988bis' more aggressive 1sec
+         * initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK
+         * retransmission has occurred.
+         */
+        if (tp->total_retrans > 1)
+                tp->snd_cwnd = 1;
+        else
+                tp->snd_cwnd = tcp_init_cwnd(tp, dst);
         tp->snd_cwnd_stamp = tcp_time_stamp;
 }
 
@@ -3112,12 +3121,13 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked, int flag)
         tcp_xmit_retransmit_queue(sk);
 }
 
-static void tcp_valid_rtt_meas(struct sock *sk, u32 seq_rtt)
+void tcp_valid_rtt_meas(struct sock *sk, u32 seq_rtt)
 {
         tcp_rtt_estimator(sk, seq_rtt);
         tcp_set_rto(sk);
         inet_csk(sk)->icsk_backoff = 0;
 }
+EXPORT_SYMBOL(tcp_valid_rtt_meas);
 
 /* Read draft-ietf-tcplw-high-performance before mucking
  * with this code. (Supersedes RFC1323)
@@ -5806,12 +5816,6 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
                                               tp->rx_opt.snd_wscale;
                                 tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
 
-                                /* tcp_ack considers this ACK as duplicate
-                                 * and does not calculate rtt.
-                                 * Force it here.
-                                 */
-                                tcp_ack_update_rtt(sk, 0, 0);
-
                                 if (tp->rx_opt.tstamp_ok)
                                         tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;