1 files changed, 20 insertions, 10 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 8ac15a604e0..b54d9d37b63 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -114,8 +114,6 @@ int sysctl_tcp_abc __read_mostly;
 #define FLAG_FORWARD_PROGRESS	(FLAG_ACKED|FLAG_DATA_SACKED)
 #define FLAG_ANY_PROGRESS	(FLAG_FORWARD_PROGRESS|FLAG_SND_UNA_ADVANCED)
 
-#define IsSackFrto() (sysctl_tcp_frto == 0x2)
-
 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
 
@@ -1686,6 +1684,11 @@ static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
 	tp->sacked_out = 0;
 }
 
+static int tcp_is_sackfrto(const struct tcp_sock *tp)
+{
+	return (sysctl_tcp_frto == 0x2) && !tcp_is_reno(tp);
+}
+
 /* F-RTO can only be used if TCP has never retransmitted anything other than
  * head (SACK enhanced variant from Appendix B of RFC4138 is more robust here)
  */
@@ -1702,7 +1705,7 @@ int tcp_use_frto(struct sock *sk)
 	if (icsk->icsk_mtup.probe_size)
 		return 0;
 
-	if (IsSackFrto())
+	if (tcp_is_sackfrto(tp))
 		return 1;
 
 	/* Avoid expensive walking of rexmit queue if possible */
@@ -1792,7 +1795,7 @@ void tcp_enter_frto(struct sock *sk)
 	/* Earlier loss recovery underway (see RFC4138; Appendix B).
 	 * The last condition is necessary at least in tp->frto_counter case.
 	 */
-	if (IsSackFrto() && (tp->frto_counter ||
+	if (tcp_is_sackfrto(tp) && (tp->frto_counter ||
 	    ((1 << icsk->icsk_ca_state) & (TCPF_CA_Recovery|TCPF_CA_Loss))) &&
 	    after(tp->high_seq, tp->snd_una)) {
 		tp->frto_highmark = tp->high_seq;
@@ -1839,9 +1842,16 @@ static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
 		}
 
-		/* Don't lost mark skbs that were fwd transmitted after RTO */
-		if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) &&
-		    !after(TCP_SKB_CB(skb)->end_seq, tp->frto_highmark)) {
+		/* Marking forward transmissions that were made after RTO lost
+		 * can cause unnecessary retransmissions in some scenarios,
+		 * SACK blocks will mitigate that in some but not in all cases.
+		 * We used to not mark them but it was causing break-ups with
+		 * receivers that do only in-order receival.
+		 *
+		 * TODO: we could detect presence of such receiver and select
+		 * different behavior per flow.
+		 */
+		if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
 			TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
 			tp->lost_out += tcp_skb_pcount(skb);
 		}
@@ -1857,7 +1867,7 @@ static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
 	tp->reordering = min_t(unsigned int, tp->reordering,
 			       sysctl_tcp_reordering);
 	tcp_set_ca_state(sk, TCP_CA_Loss);
-	tp->high_seq = tp->frto_highmark;
+	tp->high_seq = tp->snd_nxt;
 	TCP_ECN_queue_cwr(tp);
 
 	tcp_clear_retrans_hints_partial(tp);
@@ -2479,7 +2489,7 @@ static void tcp_try_to_open(struct sock *sk, int flag)
 
 	tcp_verify_left_out(tp);
 
-	if (tp->retrans_out == 0)
+	if (!tp->frto_counter && tp->retrans_out == 0)
 		tp->retrans_stamp = 0;
 
 	if (flag & FLAG_ECE)
@@ -3124,7 +3134,7 @@ static int tcp_process_frto(struct sock *sk, int flag)
 		return 1;
 	}
 
-	if (!IsSackFrto() || tcp_is_reno(tp)) {
+	if (!tcp_is_sackfrto(tp)) {
 		/* RFC4138 shortcoming in step 2; should also have case c):
 		 * ACK isn't duplicate nor advances window, e.g., opposite dir
 		 * data, winupdate