1 files changed, 33 insertions, 26 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index fcb668d..c35b227 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2243,8 +2243,7 @@ static void DBGUNDO(struct sock *sk, const char *msg)
 #define DBGUNDO(x...) do { } while (0)
 #endif
 
-static void tcp_undo_cwnd_reduction(struct sock *sk, const bool undo_ssthresh,
-				    bool unmark_loss)
+static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 
@@ -2268,7 +2267,7 @@ static void tcp_undo_cwnd_reduction(struct sock *sk, const bool undo_ssthresh,
 		else
 			tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
 
-		if (undo_ssthresh && tp->prior_ssthresh > tp->snd_ssthresh) {
+		if (tp->prior_ssthresh > tp->snd_ssthresh) {
 			tp->snd_ssthresh = tp->prior_ssthresh;
 			TCP_ECN_withdraw_cwr(tp);
 		}
@@ -2276,9 +2275,7 @@ static void tcp_undo_cwnd_reduction(struct sock *sk, const bool undo_ssthresh,
 		tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
 	}
 	tp->snd_cwnd_stamp = tcp_time_stamp;
-
-	if (undo_ssthresh)
-		tp->undo_marker = 0;
+	tp->undo_marker = 0;
 }
 
 static inline bool tcp_may_undo(const struct tcp_sock *tp)
@@ -2298,7 +2295,7 @@ static bool tcp_try_undo_recovery(struct sock *sk)
 		 * or our original transmission succeeded.
 		 */
 		DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
-		tcp_undo_cwnd_reduction(sk, true, false);
+		tcp_undo_cwnd_reduction(sk, false);
 		if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
 			mib_idx = LINUX_MIB_TCPLOSSUNDO;
 		else
@@ -2324,7 +2321,7 @@ static void tcp_try_undo_dsack(struct sock *sk)
 
 	if (tp->undo_marker && !tp->undo_retrans) {
 		DBGUNDO(sk, "D-SACK");
-		tcp_undo_cwnd_reduction(sk, true, false);
+		tcp_undo_cwnd_reduction(sk, false);
 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
 	}
 }
@@ -2364,7 +2361,7 @@ static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
 	struct tcp_sock *tp = tcp_sk(sk);
 
 	if (frto_undo || tcp_may_undo(tp)) {
-		tcp_undo_cwnd_reduction(sk, true, true);
+		tcp_undo_cwnd_reduction(sk, true);
 
 		DBGUNDO(sk, "partial loss");
 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
@@ -2644,32 +2641,37 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack)
 }
 
 /* Undo during fast recovery after partial ACK. */
-static bool tcp_try_undo_partial(struct sock *sk, int acked)
+static bool tcp_try_undo_partial(struct sock *sk, const int acked,
+				 const int prior_unsacked)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
-	/* Partial ACK arrived. Force Hoe's retransmit. */
-	bool failed = tcp_is_reno(tp) || (tcp_fackets_out(tp) > tp->reordering);
 
-	if (tcp_may_undo(tp)) {
+	if (tp->undo_marker && tcp_packet_delayed(tp)) {
 		/* Plain luck! Hole if filled with delayed
 		 * packet, rather than with a retransmit.
 		 */
+		tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
+
+		/* We are getting evidence that the reordering degree is higher
+		 * than we realized. If there are no retransmits out then we
+		 * can undo. Otherwise we clock out new packets but do not
+		 * mark more packets lost or retransmit more.
+		 */
+		if (tp->retrans_out) {
+			tcp_cwnd_reduction(sk, prior_unsacked, 0);
+			return true;
+		}
+
 		if (!tcp_any_retrans_done(sk))
 			tp->retrans_stamp = 0;
 
-		tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
-
-		DBGUNDO(sk, "Hoe");
-		tcp_undo_cwnd_reduction(sk, false, false);
+		DBGUNDO(sk, "partial recovery");
+		tcp_undo_cwnd_reduction(sk, true);
 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
-
-		/* So... Do not make Hoe's retransmit yet.
-		 * If the first packet was delayed, the rest
-		 * ones are most probably delayed as well.
-		 */
-		failed = false;
+		tcp_try_keep_open(sk);
+		return true;
 	}
-	return failed;
+	return false;
 }
 
 /* Process an event, which can update packets-in-flight not trivially.
@@ -2742,8 +2744,13 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked,
 		if (!(flag & FLAG_SND_UNA_ADVANCED)) {
 			if (tcp_is_reno(tp) && is_dupack)
 				tcp_add_reno_sack(sk);
-		} else
-			do_lost = tcp_try_undo_partial(sk, acked);
+		} else {
+			if (tcp_try_undo_partial(sk, acked, prior_unsacked))
+				return;
+			/* Partial ACK arrived. Force fast retransmit. */
+			do_lost = tcp_is_reno(tp) ||
+				  tcp_fackets_out(tp) > tp->reordering;
+		}
 		break;
 	case TCP_CA_Loss:
 		tcp_process_loss(sk, flag, is_dupack);