2 files changed, 12 insertions, 16 deletions

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index fa5258f322e7..e567f0dbf282 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -276,7 +276,7 @@ struct tcp_sock {
         u32     retrans_stamp;  /* Timestamp of the last retransmit,
                                  * also used in SYN-SENT to remember stamp of
                                  * the first SYN. */
-        u32     undo_marker;    /* tracking retrans started here. */
+        u32     undo_marker;    /* snd_una upon a new recovery episode. */
         int     undo_retrans;   /* number of undoable retransmissions. */
         u32     total_retrans;  /* Total retransmits for entire connection */
 
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index a906e0200ff2..aba4926ca095 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1888,21 +1888,21 @@ static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
         tp->sacked_out = 0;
 }
 
-static void tcp_clear_retrans_partial(struct tcp_sock *tp)
+void tcp_clear_retrans(struct tcp_sock *tp)
 {
         tp->retrans_out = 0;
         tp->lost_out = 0;
-
         tp->undo_marker = 0;
         tp->undo_retrans = -1;
+        tp->fackets_out = 0;
+        tp->sacked_out = 0;
 }
 
-void tcp_clear_retrans(struct tcp_sock *tp)
+static inline void tcp_init_undo(struct tcp_sock *tp)
 {
-        tcp_clear_retrans_partial(tp);
-
-        tp->fackets_out = 0;
-        tp->sacked_out = 0;
+        tp->undo_marker = tp->snd_una;
+        /* Retransmission still in flight may cause DSACKs later. */
+        tp->undo_retrans = tp->retrans_out ? : -1;
 }
 
 /* Enter Loss state. If we detect SACK reneging, forget all SACK information
@@ -1925,18 +1925,18 @@ void tcp_enter_loss(struct sock *sk)
                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
                 tcp_ca_event(sk, CA_EVENT_LOSS);
+                tcp_init_undo(tp);
         }
         tp->snd_cwnd       = 1;
         tp->snd_cwnd_cnt   = 0;
         tp->snd_cwnd_stamp = tcp_time_stamp;
 
-        tcp_clear_retrans_partial(tp);
+        tp->retrans_out = 0;
+        tp->lost_out = 0;
 
         if (tcp_is_reno(tp))
                 tcp_reset_reno_sack(tp);
 
-        tp->undo_marker = tp->snd_una;
-
         skb = tcp_write_queue_head(sk);
         is_reneg = skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED);
         if (is_reneg) {
@@ -1950,9 +1950,6 @@ void tcp_enter_loss(struct sock *sk)
                 if (skb == tcp_send_head(sk))
                         break;
 
-                if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
-                        tp->undo_marker = 0;
-
                 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || is_reneg) {
                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
@@ -2671,8 +2668,7 @@ static void tcp_enter_recovery(struct sock *sk, bool ece_ack)
         NET_INC_STATS_BH(sock_net(sk), mib_idx);
 
         tp->prior_ssthresh = 0;
-        tp->undo_marker = tp->snd_una;
-        tp->undo_retrans = tp->retrans_out ? : -1;
+        tcp_init_undo(tp);
 
         if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
                 if (!ece_ack)