[TCP]: Also handle snd_una changes in tcp_cwnd_down

tcp_cwnd_down must check for it too as it should be conservative
in case of collapse stuff and also when receiver is trying to
lie (though that wouldn't be very successful/useful anyway).

Note:
- Separated also is_dupack and do_lost in fast_retransalert
	* Much cleaner look-and-feel now
	* This time it really fixes cumulative ACK with many new
	  SACK blocks recovery entry (I claimed this fixes with
	  last patch but it wasn't). TCP will now call
	  tcp_update_scoreboard regardless of is_dupack when
	  in recovery as long as there is enough fackets_out.
- Introduce FLAG_SND_UNA_ADVANCED
	* Some prior_snd_una arguments are unnecessary after it
- Added helper FLAG_ANY_PROGRESS to avoid long FLAG...|FLAG...
  constructs
Signed-off-by: NIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp_input.c

@@ -102,11 +102,13 @@ int sysctl_tcp_abc __read_mostly;
 #define FLAG_DATA_LOST		0x80 /* SACK detected data lossage.		*/
 #define FLAG_SLOWPATH		0x100 /* Do not skip RFC checks for window update.*/
 #define FLAG_ONLY_ORIG_SACKED	0x200 /* SACKs only non-rexmit sent before RTO */
+#define FLAG_SND_UNA_ADVANCED	0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
 
 #define FLAG_ACKED		(FLAG_DATA_ACKED|FLAG_SYN_ACKED)
 #define FLAG_NOT_DUP		(FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
 #define FLAG_CA_ALERT		(FLAG_DATA_SACKED|FLAG_ECE)
 #define FLAG_FORWARD_PROGRESS	(FLAG_ACKED|FLAG_DATA_SACKED)
+#define FLAG_ANY_PROGRESS	(FLAG_FORWARD_PROGRESS|FLAG_SND_UNA_ADVANCED)
 
 #define IsReno(tp) ((tp)->rx_opt.sack_ok == 0)
 #define IsFack(tp) ((tp)->rx_opt.sack_ok & 2)
@@ -1856,7 +1858,7 @@ static void tcp_cwnd_down(struct sock *sk, int flag)
 	struct tcp_sock *tp = tcp_sk(sk);
 	int decr = tp->snd_cwnd_cnt + 1;
 
-	if ((flag&FLAG_FORWARD_PROGRESS) ||
+	if ((flag&FLAG_ANY_PROGRESS) ||
 	    (IsReno(tp) && !(flag&FLAG_NOT_DUP))) {
 		tp->snd_cwnd_cnt = decr&1;
 		decr >>= 1;
@@ -2107,15 +2109,13 @@ static void tcp_mtup_probe_success(struct sock *sk, struct sk_buff *skb)
  * tcp_xmit_retransmit_queue().
  */
 static void
-tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
-		      int prior_packets, int flag)
+tcp_fastretrans_alert(struct sock *sk, int prior_packets, int flag)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
-	int is_dupack = (tp->snd_una == prior_snd_una &&
-			 (!(flag&FLAG_NOT_DUP) ||
-			  ((flag&FLAG_DATA_SACKED) &&
-			   (tp->fackets_out > tp->reordering))));
+	int is_dupack = !(flag&(FLAG_SND_UNA_ADVANCED|FLAG_NOT_DUP));
+	int do_lost = is_dupack || ((flag&FLAG_DATA_SACKED) &&
+				    (tp->fackets_out > tp->reordering));
 
 	/* Some technical things:
 	 * 1. Reno does not count dupacks (sacked_out) automatically. */
@@ -2192,14 +2192,14 @@ tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
 	/* F. Process state. */
 	switch (icsk->icsk_ca_state) {
 	case TCP_CA_Recovery:
-		if (prior_snd_una == tp->snd_una) {
+		if (!(flag & FLAG_SND_UNA_ADVANCED)) {
 			if (IsReno(tp) && is_dupack)
 				tcp_add_reno_sack(sk);
 		} else {
 			int acked = prior_packets - tp->packets_out;
 			if (IsReno(tp))
 				tcp_remove_reno_sacks(sk, acked);
-			is_dupack = tcp_try_undo_partial(sk, acked);
+			do_lost = tcp_try_undo_partial(sk, acked);
 		}
 		break;
 	case TCP_CA_Loss:
@@ -2215,7 +2215,7 @@ tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
 		/* Loss is undone; fall through to processing in Open state. */
 	default:
 		if (IsReno(tp)) {
-			if (tp->snd_una != prior_snd_una)
+			if (flag & FLAG_SND_UNA_ADVANCED)
 				tcp_reset_reno_sack(tp);
 			if (is_dupack)
 				tcp_add_reno_sack(sk);
@@ -2264,7 +2264,7 @@ tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
 		tcp_set_ca_state(sk, TCP_CA_Recovery);
 	}
 
-	if (is_dupack || tcp_head_timedout(sk))
+	if (do_lost || tcp_head_timedout(sk))
 		tcp_update_scoreboard(sk);
 	tcp_cwnd_down(sk, flag);
 	tcp_xmit_retransmit_queue(sk);
@@ -2684,7 +2684,7 @@ static void tcp_undo_spur_to_response(struct sock *sk, int flag)
  *     to prove that the RTO is indeed spurious. It transfers the control
  *     from F-RTO to the conventional RTO recovery
  */
-static int tcp_process_frto(struct sock *sk, u32 prior_snd_una, int flag)
+static int tcp_process_frto(struct sock *sk, int flag)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 
@@ -2704,8 +2704,7 @@ static int tcp_process_frto(struct sock *sk, u32 prior_snd_una, int flag)
 		 * ACK isn't duplicate nor advances window, e.g., opposite dir
 		 * data, winupdate
 		 */
-		if ((tp->snd_una == prior_snd_una) && (flag&FLAG_NOT_DUP) &&
-		    !(flag&FLAG_FORWARD_PROGRESS))
+		if (!(flag&FLAG_ANY_PROGRESS) && (flag&FLAG_NOT_DUP))
 			return 1;
 
 		if (!(flag&FLAG_DATA_ACKED)) {
@@ -2785,6 +2784,9 @@ static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
 	if (before(ack, prior_snd_una))
 		goto old_ack;
 
+	if (after(ack, prior_snd_una))
+		flag |= FLAG_SND_UNA_ADVANCED;
+
 	if (sysctl_tcp_abc) {
 		if (icsk->icsk_ca_state < TCP_CA_CWR)
 			tp->bytes_acked += ack - prior_snd_una;
@@ -2837,14 +2839,14 @@ static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
 	flag |= tcp_clean_rtx_queue(sk, &seq_rtt);
 
 	if (tp->frto_counter)
-		frto_cwnd = tcp_process_frto(sk, prior_snd_una, flag);
+		frto_cwnd = tcp_process_frto(sk, flag);
 
 	if (tcp_ack_is_dubious(sk, flag)) {
 		/* Advance CWND, if state allows this. */
 		if ((flag & FLAG_DATA_ACKED) && !frto_cwnd &&
 		    tcp_may_raise_cwnd(sk, flag))
 			tcp_cong_avoid(sk, ack, prior_in_flight, 0);
-		tcp_fastretrans_alert(sk, prior_snd_una, prior_packets, flag);
+		tcp_fastretrans_alert(sk, prior_packets, flag);
 	} else {
 		if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
 			tcp_cong_avoid(sk, ack, prior_in_flight, 1);