[TCP] FRTO: remove unnecessary fackets/sacked_out recounting

F-RTO does not touch SACKED_ACKED bits at all, so there is no
need to recount them in tcp_enter_frto_loss. After removal of
the else branch, nested ifs can be combined.

This must also reset sacked_out when SACK is not in use as TCP
could have received some duplicate ACKs prior RTO. To achieve
that in a sane manner, tcp_reset_reno_sack was re-placed by the
previous patch.
Signed-off-by: NIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_input.c

@@ -1474,17 +1474,15 @@ static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct sk_buff *skb;
-	int cnt = 0;
 
-	tp->sacked_out = 0;
 	tp->lost_out = 0;
-	tp->fackets_out = 0;
 	tp->retrans_out = 0;
+	if (IsReno(tp))
+		tcp_reset_reno_sack(tp);
 
 	tcp_for_write_queue(skb, sk) {
 		if (skb == tcp_send_head(sk))
 			break;
-		cnt += tcp_skb_pcount(skb);
 		/*
 		 * Count the retransmission made on RTO correctly (only when
 		 * waiting for the first ACK and did not get it)...
@@ -1498,19 +1496,12 @@ static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
 		} else {
 			TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
 		}
-		if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) {
 
-			/* Do not mark those segments lost that were
-			 * forward transmitted after RTO
-			 */
-			if (!after(TCP_SKB_CB(skb)->end_seq,
-				   tp->frto_highmark)) {
-				TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
-				tp->lost_out += tcp_skb_pcount(skb);
-			}
-		} else {
-			tp->sacked_out += tcp_skb_pcount(skb);
-			tp->fackets_out = cnt;
+		/* Don't lost mark skbs that were fwd transmitted after RTO */
+		if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) &&
+		    !after(TCP_SKB_CB(skb)->end_seq, tp->frto_highmark)) {
+			TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
+			tp->lost_out += tcp_skb_pcount(skb);
 		}
 	}
 	tcp_sync_left_out(tp);