1 files changed, 21 insertions, 18 deletions

diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
index f18235e8ce84..ef19fb834299 100644
--- a/net/dccp/ccids/ccid2.c
+++ b/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)