1 files changed, 25 insertions, 21 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index bef9f04..ea0d218 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;