diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 4b255fe999d918870573bf5bfd239cfbc32d6203..41163ddc312cce05cd6f28515adc2b9cdf48937a 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);
 }