[TCP]: Prevent unrelated cwnd adjustment while using FRTO

FRTO controls cwnd when it still processes the ACK input or it
has just reverted back to conventional RTO recovery; the normal
rules apply when FRTO has reverted to standard congestion
control.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 7 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 9dc5754141e9..723cee63791f 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2522,7 +2522,7 @@ static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
  *     to prove that the RTO is indeed spurious. It transfers the control
  *     from F-RTO to the conventional RTO recovery
  */
-static void tcp_process_frto(struct sock *sk, u32 prior_snd_una, int flag)
+static int tcp_process_frto(struct sock *sk, u32 prior_snd_una, int flag)
 {
         struct tcp_sock *tp = tcp_sk(sk);
 
@@ -2534,7 +2534,7 @@ static void tcp_process_frto(struct sock *sk, u32 prior_snd_una, int flag)
 
         if (!before(tp->snd_una, tp->frto_highmark)) {
                 tcp_enter_frto_loss(sk, tp->frto_counter + 1);
-                return;
+                return 1;
         }
 
         /* RFC4138 shortcoming in step 2; should also have case c): ACK isn't
@@ -2542,20 +2542,22 @@ static void tcp_process_frto(struct sock *sk, u32 prior_snd_una, int flag)
          */
         if ((tp->snd_una == prior_snd_una) && (flag&FLAG_NOT_DUP) &&
             !(flag&FLAG_FORWARD_PROGRESS))
-                return;
+                return 1;
 
         if (!(flag&FLAG_DATA_ACKED)) {
                 tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3));
-                return;
+                return 1;
         }
 
         if (tp->frto_counter == 1) {
                 tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
                 tp->frto_counter = 2;
+                return 1;
         } else /* frto_counter == 2 */ {
                 tcp_conservative_spur_to_response(tp);
                 tp->frto_counter = 0;
         }
+        return 0;
 }
 
 /* This routine deals with incoming acks, but not outgoing ones. */
@@ -2569,6 +2571,7 @@ static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
         u32 prior_in_flight;
         s32 seq_rtt;
         int prior_packets;
+        int frto_cwnd = 0;
 
         /* If the ack is newer than sent or older than previous acks
          * then we can probably ignore it.
@@ -2631,15 +2634,16 @@ static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
         flag |= tcp_clean_rtx_queue(sk, &seq_rtt);
 
         if (tp->frto_counter)
-                tcp_process_frto(sk, prior_snd_una, flag);
+                frto_cwnd = tcp_process_frto(sk, prior_snd_una, flag);
 
         if (tcp_ack_is_dubious(sk, flag)) {
                 /* Advance CWND, if state allows this. */
-                if ((flag & FLAG_DATA_ACKED) && tcp_may_raise_cwnd(sk, flag))
+                if ((flag & FLAG_DATA_ACKED) && !frto_cwnd &&
+                    tcp_may_raise_cwnd(sk, flag))
                         tcp_cong_avoid(sk, ack,  seq_rtt, prior_in_flight, 0);
                 tcp_fastretrans_alert(sk, prior_snd_una, prior_packets, flag);
         } else {
-                if ((flag & FLAG_DATA_ACKED))
+                if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
                         tcp_cong_avoid(sk, ack, seq_rtt, prior_in_flight, 1);
         }