Patch "tcp: invalidate rate samples during SACK reneging" has been added to the 4.9-stable tree

@@ -219,7 +219,8 @@ struct tcp_sock {
 	} rack;
 	u16	advmss;		/* Advertised MSS			*/
 	u8	rate_app_limited:1,  /* rate_{delivered,interval_us} limited? */
-		unused:7;
+		is_sack_reneg:1,    /* in recovery from loss with SACK reneg? */
+		unused:6;
 	u8	nonagle     : 4,/* Disable Nagle algorithm?             */
 		thin_lto    : 1,/* Use linear timeouts for thin streams */
 		thin_dupack : 1,/* Fast retransmit on first dupack      */

@@ -1001,7 +1001,7 @@ void tcp_rate_skb_sent(struct sock *sk,
 void tcp_rate_skb_delivered(struct sock *sk, struct sk_buff *skb,
 			    struct rate_sample *rs);
 void tcp_rate_gen(struct sock *sk, u32 delivered, u32 lost,
-		  struct skb_mstamp *now, struct rate_sample *rs);
+		  bool is_sack_reneg, struct skb_mstamp *now, struct rate_sample *rs);
 void tcp_rate_check_app_limited(struct sock *sk);
 
 /* These functions determine how the current flow behaves in respect of SACK

@@ -2297,6 +2297,7 @@ int tcp_disconnect(struct sock *sk, int
 	tp->snd_cwnd_cnt = 0;
 	tp->window_clamp = 0;
 	tcp_set_ca_state(sk, TCP_CA_Open);
+	tp->is_sack_reneg = 0;
 	tcp_clear_retrans(tp);
 	inet_csk_delack_init(sk);
 	/* Initialize rcv_mss to TCP_MIN_MSS to avoid division by 0

@@ -1966,6 +1966,8 @@ void tcp_enter_loss(struct sock *sk)
 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
 		tp->sacked_out = 0;
 		tp->fackets_out = 0;
+		/* Mark SACK reneging until we recover from this loss event. */
+		tp->is_sack_reneg = 1;
 	}
 	tcp_clear_all_retrans_hints(tp);
 

@@ -2463,6 +2465,7 @@ static bool tcp_try_undo_recovery(struct
 		return true;
 	}
 	tcp_set_ca_state(sk, TCP_CA_Open);
+	tp->is_sack_reneg = 0;
 	return false;
 }
 

@@ -2494,8 +2497,10 @@ static bool tcp_try_undo_loss(struct soc
 			NET_INC_STATS(sock_net(sk),
 					LINUX_MIB_TCPSPURIOUSRTOS);
 		inet_csk(sk)->icsk_retransmits = 0;
-		if (frto_undo || tcp_is_sack(tp))
+		if (frto_undo || tcp_is_sack(tp)) {
 			tcp_set_ca_state(sk, TCP_CA_Open);
+			tp->is_sack_reneg = 0;
+		}
 		return true;
 	}
 	return false;

@@ -3589,6 +3594,7 @@ static int tcp_ack(struct sock *sk, cons
 	struct tcp_sacktag_state sack_state;
 	struct rate_sample rs = { .prior_delivered = 0 };
 	u32 prior_snd_una = tp->snd_una;
+	bool is_sack_reneg = tp->is_sack_reneg;
 	u32 ack_seq = TCP_SKB_CB(skb)->seq;
 	u32 ack = TCP_SKB_CB(skb)->ack_seq;
 	bool is_dupack = false;

@@ -3711,7 +3717,7 @@ static int tcp_ack(struct sock *sk, cons
 		tcp_schedule_loss_probe(sk);
 	delivered = tp->delivered - delivered;	/* freshly ACKed or SACKed */
 	lost = tp->lost - lost;			/* freshly marked lost */
-	tcp_rate_gen(sk, delivered, lost, &now, &rs);
+	tcp_rate_gen(sk, delivered, lost, is_sack_reneg, &now, &rs);
 	tcp_cong_control(sk, ack, delivered, flag, &rs);
 	tcp_xmit_recovery(sk, rexmit);
 	return 1;

@@ -106,7 +106,7 @@ void tcp_rate_skb_delivered(struct sock
 
 /* Update the connection delivery information and generate a rate sample. */
 void tcp_rate_gen(struct sock *sk, u32 delivered, u32 lost,
-		  struct skb_mstamp *now, struct rate_sample *rs)
+		  bool is_sack_reneg, struct skb_mstamp *now, struct rate_sample *rs)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	u32 snd_us, ack_us;

@@ -124,8 +124,12 @@ void tcp_rate_gen(struct sock *sk, u32 d
 
 	rs->acked_sacked = delivered;	/* freshly ACKed or SACKed */
 	rs->losses = lost;		/* freshly marked lost */
-	/* Return an invalid sample if no timing information is available. */
-	if (!rs->prior_mstamp.v64) {
+	/* Return an invalid sample if no timing information is available or
+	 * in recovery from loss with SACK reneging. Rate samples taken during
+	 * a SACK reneging event may overestimate bw by including packets that
+	 * were SACKed before the reneg.
+	 */
+	if (!rs->prior_mstamp.v64 || is_sack_reneg) {
 		rs->delivered = -1;
 		rs->interval_us = -1;
 		return;