5 files changed, 52 insertions, 0 deletions

diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index 4c35911d935f..b6f2ea174898 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -225,6 +225,7 @@ static const struct snmp_mib snmp4_net_list[] = {
         SNMP_MIB_ITEM("TCPSlowStartRetrans", LINUX_MIB_TCPSLOWSTARTRETRANS),
         SNMP_MIB_ITEM("TCPTimeouts", LINUX_MIB_TCPTIMEOUTS),
         SNMP_MIB_ITEM("TCPLossProbes", LINUX_MIB_TCPLOSSPROBES),
+        SNMP_MIB_ITEM("TCPLossProbeRecovery", LINUX_MIB_TCPLOSSPROBERECOVERY),
         SNMP_MIB_ITEM("TCPRenoRecoveryFail", LINUX_MIB_TCPRENORECOVERYFAIL),
         SNMP_MIB_ITEM("TCPSackRecoveryFail", LINUX_MIB_TCPSACKRECOVERYFAIL),
         SNMP_MIB_ITEM("TCPSchedulerFailed", LINUX_MIB_TCPSCHEDULERFAILED),
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:
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index b83a49cc3816..4bdb09fca401 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -440,6 +440,7 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
                 newtp->fackets_out = 0;
                 newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
                 tcp_enable_early_retrans(newtp);
+                newtp->tlp_high_seq = 0;
 
                 /* So many TCP implementations out there (incorrectly) count the
                  * initial SYN frame in their delayed-ACK and congestion control
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index beb63dbc85f5..8e7742f0b5d2 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2132,6 +2132,7 @@ bool tcp_schedule_loss_probe(struct sock *sk)
  */
 void tcp_send_loss_probe(struct sock *sk)
 {
+        struct tcp_sock *tp = tcp_sk(sk);
         struct sk_buff *skb;
         int pcount;
         int mss = tcp_current_mss(sk);
@@ -2142,6 +2143,10 @@ void tcp_send_loss_probe(struct sock *sk)
                 goto rearm_timer;
         }
 
+        /* At most one outstanding TLP retransmission. */
+        if (tp->tlp_high_seq)
+                goto rearm_timer;
+
         /* Retransmit last segment. */
         skb = tcp_write_queue_tail(sk);
         if (WARN_ON(!skb))
@@ -2164,6 +2169,10 @@ void tcp_send_loss_probe(struct sock *sk)
         if (skb->len > 0)
                 err = __tcp_retransmit_skb(sk, skb);
 
+        /* Record snd_nxt for loss detection. */
+        if (likely(!err))
+                tp->tlp_high_seq = tp->snd_nxt;
+
 rearm_timer:
         inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
                                   inet_csk(sk)->icsk_rto,
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index ecd61d54147f..eeccf795e917 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -356,6 +356,8 @@ void tcp_retransmit_timer(struct sock *sk)
 
         WARN_ON(tcp_write_queue_empty(sk));
 
+        tp->tlp_high_seq = 0;
+
         if (!tp->snd_wnd && !sock_flag(sk, SOCK_DEAD) &&
             !((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))) {
                 /* Receiver dastardly shrinks window. Our retransmits