tcp: fix stretch ACK bugs in Reno

Change Reno to properly handle stretch ACKs in additive increase mode
by passing in the count of ACKed packets to tcp_cong_avoid_ai().

In addition, if snd_cwnd crosses snd_ssthresh during slow start
processing, and we then exit slow start mode, we need to carry over
any remaining "credit" for packets ACKed and apply that to additive
increase by passing this remaining "acked" count to
tcp_cong_avoid_ai().

Reported-by: Eyal Perry <eyalpe@mellanox.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index faaee5338beac17c64389b2dc2998ad43fcd5436..8670e68e2ce67a9c6a8d8185d31ea8a49f81f183 100644 (file)
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -335,11 +335,13 @@ void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
                return;
 
        /* In "safe" area, increase. */
-       if (tp->snd_cwnd <= tp->snd_ssthresh)
-               tcp_slow_start(tp, acked);
+       if (tp->snd_cwnd <= tp->snd_ssthresh) {
+               acked = tcp_slow_start(tp, acked);
+               if (!acked)
+                       return;
+       }
        /* In dangerous area, increase slowly. */
-       else
-               tcp_cong_avoid_ai(tp, tp->snd_cwnd, 1);
+       tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
 }
 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);