tcp: invoke pkts_acked hook on every ACK

Invoking pkts_acked is currently conditioned on FLAG_ACKED:
receiving a cumulative ACK of new data, or ACK with SYN flag set.

Remove this condition so that CC may get RTT measurements from all SACKs.

Cc: Yuchung Cheng <ycheng@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Kenneth Klette Jonassen <kennetkl@ifi.uio.no>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_input.c

@@ -3159,9 +3159,6 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
 	rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us);
 
 	if (flag & FLAG_ACKED) {
-		const struct tcp_congestion_ops *ca_ops
-			= inet_csk(sk)->icsk_ca_ops;
-
 		tcp_rearm_rto(sk);
 		if (unlikely(icsk->icsk_mtup.probe_size &&
 			     !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
@@ -3184,9 +3181,6 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
 
 		tp->fackets_out -= min(pkts_acked, tp->fackets_out);
 
-		if (ca_ops->pkts_acked)
-			ca_ops->pkts_acked(sk, pkts_acked, ca_rtt_us);
-
 	} else if (skb && rtt_update && sack_rtt_us >= 0 &&
 		   sack_rtt_us > skb_mstamp_us_delta(&now, &skb->skb_mstamp)) {
 		/* Do not re-arm RTO if the sack RTT is measured from data sent
@@ -3196,6 +3190,9 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
 		tcp_rearm_rto(sk);
 	}
 
+	if (icsk->icsk_ca_ops->pkts_acked)
+		icsk->icsk_ca_ops->pkts_acked(sk, pkts_acked, ca_rtt_us);
+
 #if FASTRETRANS_DEBUG > 0
 	WARN_ON((int)tp->sacked_out < 0);
 	WARN_ON((int)tp->lost_out < 0);