[TCP]: Restore 2.6.24 mark_head_lost behavior for newreno/fack

The fast retransmission can be forced locally to the rfc3517
branch in tcp_update_scoreboard instead of making such fragile
constructs deeper in tcp_mark_head_lost.

This is necessary for the next patch which must not have
loopholes for cnt > packets check. As one can notice,
readability got some improvements too because of this :-).

Signed-off-by: Ilpo Järvinen <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv4/tcp_input.c

···
 /* Mark head of queue up as lost. With RFC3517 SACK, the packets is
  * is against sacked "cnt", otherwise it's against facked "cnt"
  */
-static void tcp_mark_head_lost(struct sock *sk, int packets, int fast_rexmit)
+static void tcp_mark_head_lost(struct sock *sk, int packets)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct sk_buff *skb;
···
 		    (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
 			cnt += tcp_skb_pcount(skb);
 
-		if (((!fast_rexmit || (tp->lost_out > 0)) && (cnt > packets)) ||
+		if ((cnt > packets) ||
 		    after(TCP_SKB_CB(skb)->end_seq, tp->high_seq))
 			break;
 		if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_SACKED_ACKED|TCPCB_LOST))) {
···
 	struct tcp_sock *tp = tcp_sk(sk);
 
 	if (tcp_is_reno(tp)) {
-		tcp_mark_head_lost(sk, 1, fast_rexmit);
+		tcp_mark_head_lost(sk, 1);
 	} else if (tcp_is_fack(tp)) {
 		int lost = tp->fackets_out - tp->reordering;
 		if (lost <= 0)
 			lost = 1;
-		tcp_mark_head_lost(sk, lost, fast_rexmit);
+		tcp_mark_head_lost(sk, lost);
 	} else {
 		int sacked_upto = tp->sacked_out - tp->reordering;
-		if (sacked_upto < 0)
-			sacked_upto = 0;
-		tcp_mark_head_lost(sk, sacked_upto, fast_rexmit);
+		if (sacked_upto < fast_rexmit)
+			sacked_upto = fast_rexmit;
+		tcp_mark_head_lost(sk, sacked_upto);
 	}
 
 	/* New heuristics: it is possible only after we switched
···
 	    before(tp->snd_una, tp->high_seq) &&
 	    icsk->icsk_ca_state != TCP_CA_Open &&
 	    tp->fackets_out > tp->reordering) {
-		tcp_mark_head_lost(sk, tp->fackets_out - tp->reordering, 0);
+		tcp_mark_head_lost(sk, tp->fackets_out - tp->reordering);
 		NET_INC_STATS_BH(LINUX_MIB_TCPLOSS);
 	}