From cafc31d81142127656d75d87c3e80276794b5ee0 Mon Sep 17 00:00:00 2001
From: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Date: Sat, 24 Nov 2007 21:40:24 -0200
Subject: [PATCH] --- yaml --- r: 78197 b: refs/heads/master c:
 d50ad163e6db2dcc365b8d02b30350220f86df04 h: refs/heads/master i:   78195:
 40b3b72e304d40f6318f4da8bc04fec68aca06d4 v: v3

---
 [refs]                       |  2 +-
 trunk/net/dccp/ccids/ccid2.c | 39 +++++++++++++++++++-----------------
 2 files changed, 22 insertions(+), 19 deletions(-)

diff --git a/[refs] b/[refs]
index b5b3962ffbf8..f34301ac723a 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: df054e1d00fdafa2e2920319df326ddb3f0d0413
+refs/heads/master: d50ad163e6db2dcc365b8d02b30350220f86df04
diff --git a/trunk/net/dccp/ccids/ccid2.c b/trunk/net/dccp/ccids/ccid2.c
index f18235e8ce84..ef19fb834299 100644
--- a/trunk/net/dccp/ccids/ccid2.c
+++ b/trunk/net/dccp/ccids/ccid2.c
@@ -143,32 +143,30 @@ static int ccid2_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
 static void ccid2_change_l_ack_ratio(struct sock *sk, u32 val)
 {
 	struct dccp_sock *dp = dccp_sk(sk);
+	u32 max_ratio = DIV_ROUND_UP(ccid2_hc_tx_sk(sk)->ccid2hctx_cwnd, 2);
+
 	/*
-	 * XXX I don't really agree with val != 2.  If cwnd is 1, ack ratio
-	 * should be 1... it shouldn't be allowed to become 2.
-	 * -sorbo.
+	 * Ensure that Ack Ratio does not exceed ceil(cwnd/2), which is (2) from
+	 * RFC 4341, 6.1.2. We ignore the statement that Ack Ratio 2 is always
+	 * acceptable since this causes starvation/deadlock whenever cwnd < 2.
+	 * The same problem arises when Ack Ratio is 0 (ie. Ack Ratio disabled).
 	 */
-	if (val != 2) {
-		const struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);
-		int max = hctx->ccid2hctx_cwnd / 2;
-
-		/* round up */
-		if (hctx->ccid2hctx_cwnd & 1)
-			max++;
-
-		if (val > max)
-			val = max;
+	if (val == 0 || val > max_ratio) {
+		DCCP_WARN("Limiting Ack Ratio (%u) to %u\n", val, max_ratio);
+		val = max_ratio;
 	}
 	if (val > 0xFFFF)		/* RFC 4340, 11.3 */
 		val = 0xFFFF;
 
+	if (val == dp->dccps_l_ack_ratio)
+		return;
+
 	ccid2_pr_debug("changing local ack ratio to %u\n", val);
 	dp->dccps_l_ack_ratio = val;
 }
 
 static void ccid2_change_cwnd(struct ccid2_hc_tx_sock *hctx, u32 val)
 {
-	/* XXX do we need to change ack ratio? */
 	hctx->ccid2hctx_cwnd = val? : 1;
 	ccid2_pr_debug("changed cwnd to %u\n", hctx->ccid2hctx_cwnd);
 }
@@ -519,9 +517,10 @@ static void ccid2_hc_tx_dec_pipe(struct sock *sk)
 		ccid2_hc_tx_kill_rto_timer(sk);
 }
 
-static void ccid2_congestion_event(struct ccid2_hc_tx_sock *hctx,
-				   struct ccid2_seq *seqp)
+static void ccid2_congestion_event(struct sock *sk, struct ccid2_seq *seqp)
 {
+	struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);
+
 	if (time_before(seqp->ccid2s_sent, hctx->ccid2hctx_last_cong)) {
 		ccid2_pr_debug("Multiple losses in an RTT---treating as one\n");
 		return;
@@ -533,6 +532,10 @@ static void ccid2_congestion_event(struct ccid2_hc_tx_sock *hctx,
 	hctx->ccid2hctx_ssthresh = hctx->ccid2hctx_cwnd;
 	if (hctx->ccid2hctx_ssthresh < 2)
 		hctx->ccid2hctx_ssthresh = 2;
+
+	/* Avoid spurious timeouts resulting from Ack Ratio > cwnd */
+	if (dccp_sk(sk)->dccps_l_ack_ratio > hctx->ccid2hctx_cwnd)
+		ccid2_change_l_ack_ratio(sk, hctx->ccid2hctx_cwnd);
 }
 
 static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
@@ -648,7 +651,7 @@ static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
 				    !seqp->ccid2s_acked) {
 					if (state ==
 					    DCCP_ACKVEC_STATE_ECN_MARKED) {
-						ccid2_congestion_event(hctx,
+						ccid2_congestion_event(sk,
 								       seqp);
 					} else
 						ccid2_new_ack(sk, seqp,
@@ -713,7 +716,7 @@ static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
 				 * order to detect multiple congestion events in
 				 * one ack vector.
 				 */
-				ccid2_congestion_event(hctx, seqp);
+				ccid2_congestion_event(sk, seqp);
 				ccid2_hc_tx_dec_pipe(sk);
 			}
 			if (seqp == hctx->ccid2hctx_seqt)