[TCP]: Two RFC3465 Appropriate Byte Count fixes.

1) fix slow start after retransmit timeout
2) fix case of L=2*SMSS acked bytes comparison

Signed-off-by: Daikichi Osuga <osugad@s1.nttdocomo.co.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_cong.c

@@ -189,7 +189,7 @@ void tcp_slow_start(struct tcp_sock *tp)
 			return;
 
 		/* We MAY increase by 2 if discovered delayed ack */
-		if (sysctl_tcp_abc > 1 && tp->bytes_acked > 2*tp->mss_cache) {
+		if (sysctl_tcp_abc > 1 && tp->bytes_acked >= 2*tp->mss_cache) {
 			if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 				tp->snd_cwnd++;
 		}

net/ipv4/tcp_input.c

@@ -2505,8 +2505,13 @@ static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
 	if (before(ack, prior_snd_una))
 		goto old_ack;
 
-	if (sysctl_tcp_abc && icsk->icsk_ca_state < TCP_CA_CWR)
-		tp->bytes_acked += ack - prior_snd_una;
+	if (sysctl_tcp_abc) {
+		if (icsk->icsk_ca_state < TCP_CA_CWR)
+			tp->bytes_acked += ack - prior_snd_una;
+		else if (icsk->icsk_ca_state == TCP_CA_Loss)
+			/* we assume just one segment left network */
+			tp->bytes_acked += min(ack - prior_snd_una, tp->mss_cache);
+	}
 
 	if (!(flag&FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
 		/* Window is constant, pure forward advance.