2 files changed, 22 insertions, 5 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 572a77bb6907..7fd6b77519c3 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -341,7 +341,7 @@ extern struct sock *		tcp_check_req(struct sock *sk,struct sk_buff *skb,
 extern int                      tcp_child_process(struct sock *parent,
                                                   struct sock *child,
                                                   struct sk_buff *skb);
-extern int                      tcp_use_frto(const struct sock *sk);
+extern int                      tcp_use_frto(struct sock *sk);
 extern void                     tcp_enter_frto(struct sock *sk);
 extern void                     tcp_enter_loss(struct sock *sk, int how);
 extern void                     tcp_clear_retrans(struct tcp_sock *tp);
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 723cee63791f..a283fc12186e 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1239,14 +1239,31 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_
 /* 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
  */
-int tcp_use_frto(const struct sock *sk)
+int tcp_use_frto(struct sock *sk)
 {
         const struct tcp_sock *tp = tcp_sk(sk);
+        struct sk_buff *skb;
+
+        if (!sysctl_tcp_frto || !sk->sk_send_head ||
+                after(TCP_SKB_CB(sk->sk_send_head)->end_seq,
+                      tp->snd_una + tp->snd_wnd))
+                return 0;
 
-        return (sysctl_tcp_frto && sk->sk_send_head &&
-                !after(TCP_SKB_CB(sk->sk_send_head)->end_seq,
-                       tp->snd_una + tp->snd_wnd));
+        /* Avoid expensive walking of rexmit queue if possible */
+        if (tp->retrans_out > 1)
+                return 0;
+
+        skb = skb_peek(&sk->sk_write_queue)->next;      /* Skips head */
+        sk_stream_for_retrans_queue_from(skb, sk) {
+                if (TCP_SKB_CB(skb)->sacked&TCPCB_RETRANS)
+                        return 0;
+                /* Short-circuit when first non-SACKed skb has been checked */
+                if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED))
+                        break;
+        }
+        return 1;
 }
 
 /* RTO occurred, but do not yet enter Loss state. Instead, defer RTO