1 files changed, 39 insertions, 0 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index b794f89ac1f2..836d74dd0187 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2682,6 +2682,7 @@ static void tcp_init_cwnd_reduction(struct sock *sk, const bool set_ssthresh)
         struct tcp_sock *tp = tcp_sk(sk);
 
         tp->high_seq = tp->snd_nxt;
+        tp->tlp_high_seq = 0;
         tp->snd_cwnd_cnt = 0;
         tp->prior_cwnd = tp->snd_cwnd;
         tp->prr_delivered = 0;
@@ -3569,6 +3570,38 @@ static void tcp_send_challenge_ack(struct sock *sk)
         }
 }
 
+/* This routine deals with acks during a TLP episode.
+ * Ref: loss detection algorithm in draft-dukkipati-tcpm-tcp-loss-probe.
+ */
+static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
+{
+        struct tcp_sock *tp = tcp_sk(sk);
+        bool is_tlp_dupack = (ack == tp->tlp_high_seq) &&
+                             !(flag & (FLAG_SND_UNA_ADVANCED |
+                                       FLAG_NOT_DUP | FLAG_DATA_SACKED));
+
+        /* Mark the end of TLP episode on receiving TLP dupack or when
+         * ack is after tlp_high_seq.
+         */
+        if (is_tlp_dupack) {
+                tp->tlp_high_seq = 0;
+                return;
+        }
+
+        if (after(ack, tp->tlp_high_seq)) {
+                tp->tlp_high_seq = 0;
+                /* Don't reduce cwnd if DSACK arrives for TLP retrans. */
+                if (!(flag & FLAG_DSACKING_ACK)) {
+                        tcp_init_cwnd_reduction(sk, true);
+                        tcp_set_ca_state(sk, TCP_CA_CWR);
+                        tcp_end_cwnd_reduction(sk);
+                        tcp_set_ca_state(sk, TCP_CA_Open);
+                        NET_INC_STATS_BH(sock_net(sk),
+                                         LINUX_MIB_TCPLOSSPROBERECOVERY);
+                }
+        }
+}
+
 /* This routine deals with incoming acks, but not outgoing ones. */
 static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 {
@@ -3676,6 +3709,9 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
                         tcp_cong_avoid(sk, ack, prior_in_flight);
         }
 
+        if (tp->tlp_high_seq)
+                tcp_process_tlp_ack(sk, ack, flag);
+
         if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP)) {
                 struct dst_entry *dst = __sk_dst_get(sk);
                 if (dst)
@@ -3697,6 +3733,9 @@ no_queue:
          */
         if (tcp_send_head(sk))
                 tcp_ack_probe(sk);
+
+        if (tp->tlp_high_seq)
+                tcp_process_tlp_ack(sk, ack, flag);
         return 1;
 
 invalid_ack: