[TCP] FRTO: Delay skb available check until it's mandatory

No new data is needed until the first ACK comes, so no need to check
for application limitedness until then.

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

1 files changed, 11 insertions, 8 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 051f0f815f17..6b669898b197 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1265,20 +1265,15 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
         return flag;
 }
 
-/* F-RTO can only be used if these conditions are satisfied:
- *  - there must be some unsent new data
- *  - the advertised window should allow sending it
- *  - TCP has never retransmitted anything other than head (SACK enhanced
- *    variant from Appendix B of RFC4138 is more robust here)
+/* 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)
  */
 int tcp_use_frto(struct sock *sk)
 {
         const struct tcp_sock *tp = tcp_sk(sk);
         struct sk_buff *skb;
 
-        if (!sysctl_tcp_frto || !tcp_send_head(sk) ||
-                after(TCP_SKB_CB(tcp_send_head(sk))->end_seq,
-                      tp->snd_una + tp->snd_wnd))
+        if (!sysctl_tcp_frto)
                 return 0;
 
         if (IsSackFrto())
@@ -2710,6 +2705,14 @@ static int tcp_process_frto(struct sock *sk, u32 prior_snd_una, int flag)
         }
 
         if (tp->frto_counter == 1) {
+                /* Sending of the next skb must be allowed or no FRTO */
+                if (!tcp_send_head(sk) ||
+                    after(TCP_SKB_CB(tcp_send_head(sk))->end_seq,
+                                     tp->snd_una + tp->snd_wnd)) {
+                        tcp_enter_frto_loss(sk, tp->frto_counter + 1, flag);
+                        return 1;
+                }
+
                 tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
                 tp->frto_counter = 2;
                 return 1;