1 files changed, 12 insertions, 9 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 4b255fe999d9..41163ddc312c 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1851,19 +1851,22 @@ static inline u32 tcp_cwnd_min(const struct sock *sk)
 }
 
 /* Decrease cwnd each second ack. */
-static void tcp_cwnd_down(struct sock *sk)
+static void tcp_cwnd_down(struct sock *sk, int flag)
 {
         struct tcp_sock *tp = tcp_sk(sk);
         int decr = tp->snd_cwnd_cnt + 1;
 
-        tp->snd_cwnd_cnt = decr&1;
-        decr >>= 1;
+        if ((flag&FLAG_FORWARD_PROGRESS) ||
+            (IsReno(tp) && !(flag&FLAG_NOT_DUP))) {
+                tp->snd_cwnd_cnt = decr&1;
+                decr >>= 1;
 
-        if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
-                tp->snd_cwnd -= decr;
+                if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
+                        tp->snd_cwnd -= decr;
 
-        tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+1);
-        tp->snd_cwnd_stamp = tcp_time_stamp;
+                tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+1);
+                tp->snd_cwnd_stamp = tcp_time_stamp;
+        }
 }
 
 /* Nothing was retransmitted or returned timestamp is less
@@ -2060,7 +2063,7 @@ static void tcp_try_to_open(struct sock *sk, int flag)
                 }
                 tcp_moderate_cwnd(tp);
         } else {
-                tcp_cwnd_down(sk);
+                tcp_cwnd_down(sk, flag);
         }
 }
 
@@ -2260,7 +2263,7 @@ tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
 
         if (is_dupack || tcp_head_timedout(sk))
                 tcp_update_scoreboard(sk);
-        tcp_cwnd_down(sk);
+        tcp_cwnd_down(sk, flag);
         tcp_xmit_retransmit_queue(sk);
 }