1 files changed, 23 insertions, 3 deletions

diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
index d9dbd9ffe8c..67164bb6ae4 100644
--- a/net/dccp/ccids/ccid2.c
+++ b/net/dccp/ccids/ccid2.c
@@ -101,6 +101,24 @@ static void ccid2_change_l_ack_ratio(struct sock *sk, u32 val)
                                    min_t(u32, val, DCCPF_ACK_RATIO_MAX));
 }
 
+static void ccid2_check_l_ack_ratio(struct sock *sk)
+{
+        struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
+
+        /*
+         * After a loss, idle period, application limited period, or RTO we
+         * need to check that the ack ratio is still less than the congestion
+         * window. Otherwise, we will send an entire congestion window of
+         * packets and got no response because we haven't sent ack ratio
+         * packets yet.
+         * If the ack ratio does need to be reduced, we reduce it to half of
+         * the congestion window (or 1 if that's zero) instead of to the
+         * congestion window. This prevents problems if one ack is lost.
+         */
+        if (dccp_feat_nn_get(sk, DCCPF_ACK_RATIO) > hc->tx_cwnd)
+                ccid2_change_l_ack_ratio(sk, hc->tx_cwnd/2 ? : 1U);
+}
+
 static void ccid2_change_l_seq_window(struct sock *sk, u64 val)
 {
         dccp_feat_signal_nn_change(sk, DCCPF_SEQUENCE_WINDOW,
@@ -187,6 +205,8 @@ static void ccid2_cwnd_application_limited(struct sock *sk, const u32 now)
         }
         hc->tx_cwnd_used  = 0;
         hc->tx_cwnd_stamp = now;
+
+        ccid2_check_l_ack_ratio(sk);
 }
 
 /* This borrows the code of tcp_cwnd_restart() */
@@ -205,6 +225,8 @@ static void ccid2_cwnd_restart(struct sock *sk, const u32 now)
 
         hc->tx_cwnd_stamp = now;
         hc->tx_cwnd_used  = 0;
+
+        ccid2_check_l_ack_ratio(sk);
 }
 
 static void ccid2_hc_tx_packet_sent(struct sock *sk, unsigned int len)
@@ -461,9 +483,7 @@ static void ccid2_congestion_event(struct sock *sk, struct ccid2_seq *seqp)
         hc->tx_cwnd      = hc->tx_cwnd / 2 ? : 1U;
         hc->tx_ssthresh  = max(hc->tx_cwnd, 2U);
 
-        /* Avoid spurious timeouts resulting from Ack Ratio > cwnd */
-        if (dccp_sk(sk)->dccps_l_ack_ratio > hc->tx_cwnd)
-                ccid2_change_l_ack_ratio(sk, hc->tx_cwnd);
+        ccid2_check_l_ack_ratio(sk);
 }
 
 static int ccid2_hc_tx_parse_options(struct sock *sk, u8 packet_type,