1 files changed, 18 insertions, 11 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 7832d941dbcd..6a2984507755 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1904,16 +1904,17 @@ void tcp_clear_retrans(struct tcp_sock *tp)
 	tp->sacked_out = 0;
 }
 
-/* Enter Loss state. If "how" is not zero, forget all SACK information
+/* Enter Loss state. If we detect SACK reneging, forget all SACK information
  * and reset tags completely, otherwise preserve SACKs. If receiver
  * dropped its ofo queue, we will know this due to reneging detection.
  */
-void tcp_enter_loss(struct sock *sk, int how)
+void tcp_enter_loss(struct sock *sk)
 {
 	const struct inet_connection_sock *icsk = inet_csk(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct sk_buff *skb;
 	bool new_recovery = false;
+	bool is_reneg;			/* is receiver reneging on SACKs? */
 
 	/* Reduce ssthresh if it has not yet been made inside this window. */
 	if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
@@ -1934,7 +1935,11 @@ void tcp_enter_loss(struct sock *sk, int how)
 		tcp_reset_reno_sack(tp);
 
 	tp->undo_marker = tp->snd_una;
-	if (how) {
+
+	skb = tcp_write_queue_head(sk);
+	is_reneg = skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED);
+	if (is_reneg) {
+		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
 		tp->sacked_out = 0;
 		tp->fackets_out = 0;
 	}
@@ -1948,7 +1953,7 @@ void tcp_enter_loss(struct sock *sk, int how)
 			tp->undo_marker = 0;
 
 		TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
-		if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
+		if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || is_reneg) {
 			TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
 			TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
 			tp->lost_out += tcp_skb_pcount(skb);
@@ -1981,19 +1986,21 @@ void tcp_enter_loss(struct sock *sk, int how)
  * remembered SACKs do not reflect real state of receiver i.e.
  * receiver _host_ is heavily congested (or buggy).
  *
- * Do processing similar to RTO timeout.
+ * To avoid big spurious retransmission bursts due to transient SACK
+ * scoreboard oddities that look like reneging, we give the receiver a
+ * little time (max(RTT/2, 10ms)) to send us some more ACKs that will
+ * restore sanity to the SACK scoreboard. If the apparent reneging
+ * persists until this RTO then we'll clear the SACK scoreboard.
  */
 static bool tcp_check_sack_reneging(struct sock *sk, int flag)
 {
 	if (flag & FLAG_SACK_RENEGING) {
-		struct inet_connection_sock *icsk = inet_csk(sk);
-		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
+		struct tcp_sock *tp = tcp_sk(sk);
+		unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
+					  msecs_to_jiffies(10));
 
-		tcp_enter_loss(sk, 1);
-		icsk->icsk_retransmits++;
-		tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
 		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
-					  icsk->icsk_rto, TCP_RTO_MAX);
+					  delay, TCP_RTO_MAX);
 		return true;
 	}
 	return false;