Handle snd_una in tcp_cwnd_down()

commit 6ee8009e38006da81d2a53da1aaa27365552553e in mainline

Subject: [PATCH 1/1] [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 it wouldn't be successful 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 + 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

This is a reduced version of a mainline patch.
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

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;
@@ -2112,10 +2114,9 @@ tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
 {
 	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. */
@@ -2199,7 +2200,7 @@ tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
 			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:
@@ -2264,7 +2265,7 @@ 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);
@@ -2774,6 +2775,9 @@ 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;