tcp: make is_dupack a parameter to tcp_fastretrans_alert()

Allow callers to decide whether an ACK is a duplicate ACK. This is a
prerequisite to allowing fastretrans_alert to be called from new
contexts, such as the no_queue and old_ack code paths, from which we
have extra info that tells us whether an ACK is a dupack.

Signed-off-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_input.c

@@ -3009,11 +3009,11 @@ static void tcp_update_cwnd_in_recovery(struct sock *sk, int newly_acked_sacked,
  * tcp_xmit_retransmit_queue().
  */
 static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
-				  int newly_acked_sacked, int flag)
+				  int newly_acked_sacked, bool is_dupack,
+				  int flag)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
-	int is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
 	int do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
 				    (tcp_fackets_out(tp) > tp->reordering));
 	int fast_rexmit = 0, mib_idx;
@@ -3681,10 +3681,12 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 	u32 prior_snd_una = tp->snd_una;
 	u32 ack_seq = TCP_SKB_CB(skb)->seq;
 	u32 ack = TCP_SKB_CB(skb)->ack_seq;
+	bool is_dupack = false;
 	u32 prior_in_flight;
 	u32 prior_fackets;
 	int prior_packets;
 	int prior_sacked = tp->sacked_out;
+	int pkts_acked = 0;
 	int newly_acked_sacked = 0;
 	int frto_cwnd = 0;
 
@@ -3757,6 +3759,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 	/* See if we can take anything off of the retransmit queue. */
 	flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una);
 
+	pkts_acked = prior_packets - tp->packets_out;
 	newly_acked_sacked = (prior_packets - prior_sacked) -
 			     (tp->packets_out - tp->sacked_out);
 
@@ -3771,8 +3774,9 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 		if ((flag & FLAG_DATA_ACKED) && !frto_cwnd &&
 		    tcp_may_raise_cwnd(sk, flag))
 			tcp_cong_avoid(sk, ack, prior_in_flight);
-		tcp_fastretrans_alert(sk, prior_packets - tp->packets_out,
-				      newly_acked_sacked, flag);
+		is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
+		tcp_fastretrans_alert(sk, pkts_acked, newly_acked_sacked,
+				      is_dupack, flag);
 	} else {
 		if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
 			tcp_cong_avoid(sk, ack, prior_in_flight);