1 files changed, 111 insertions, 37 deletions

diff --git a/net/ipv4/tcp_recovery.c b/net/ipv4/tcp_recovery.c
index e36df4fcfeba..4ecb38ae8504 100644
--- a/net/ipv4/tcp_recovery.c
+++ b/net/ipv4/tcp_recovery.c
@@ -1,9 +1,32 @@
 #include <linux/tcp.h>
 #include <net/tcp.h>
 
-int sysctl_tcp_recovery __read_mostly = TCP_RACK_LOST_RETRANS;
+int sysctl_tcp_recovery __read_mostly = TCP_RACK_LOSS_DETECTION;
 
-/* Marks a packet lost, if some packet sent later has been (s)acked.
+static void tcp_rack_mark_skb_lost(struct sock *sk, struct sk_buff *skb)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	tcp_skb_mark_lost_uncond_verify(tp, skb);
+	if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
+		/* Account for retransmits that are lost again */
+		TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
+		tp->retrans_out -= tcp_skb_pcount(skb);
+		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT);
+	}
+}
+
+static bool tcp_rack_sent_after(const struct skb_mstamp *t1,
+				const struct skb_mstamp *t2,
+				u32 seq1, u32 seq2)
+{
+	return skb_mstamp_after(t1, t2) ||
+	       (t1->v64 == t2->v64 && after(seq1, seq2));
+}
+
+/* RACK loss detection (IETF draft draft-ietf-tcpm-rack-01):
+ *
+ * Marks a packet lost, if some packet sent later has been (s)acked.
  * The underlying idea is similar to the traditional dupthresh and FACK
  * but they look at different metrics:
  *
@@ -16,31 +39,26 @@ int sysctl_tcp_recovery __read_mostly = TCP_RACK_LOST_RETRANS;
  * is being more resilient to reordering by simply allowing some
  * "settling delay", instead of tweaking the dupthresh.
  *
- * The current version is only used after recovery starts but can be
- * easily extended to detect the first loss.
+ * When tcp_rack_detect_loss() detects some packets are lost and we
+ * are not already in the CA_Recovery state, either tcp_rack_reo_timeout()
+ * or tcp_time_to_recover()'s "Trick#1: the loss is proven" code path will
+ * make us enter the CA_Recovery state.
  */
-int tcp_rack_mark_lost(struct sock *sk)
+static void tcp_rack_detect_loss(struct sock *sk, const struct skb_mstamp *now,
+				 u32 *reo_timeout)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct sk_buff *skb;
-	u32 reo_wnd, prior_retrans = tp->retrans_out;
-
-	if (inet_csk(sk)->icsk_ca_state < TCP_CA_Recovery || !tp->rack.advanced)
-		return 0;
-
-	/* Reset the advanced flag to avoid unnecessary queue scanning */
-	tp->rack.advanced = 0;
+	u32 reo_wnd;
 
+	*reo_timeout = 0;
 	/* To be more reordering resilient, allow min_rtt/4 settling delay
 	 * (lower-bounded to 1000uS). We use min_rtt instead of the smoothed
 	 * RTT because reordering is often a path property and less related
 	 * to queuing or delayed ACKs.
-	 *
-	 * TODO: measure and adapt to the observed reordering delay, and
-	 * use a timer to retransmit like the delayed early retransmit.
 	 */
 	reo_wnd = 1000;
-	if (tp->rack.reord && tcp_min_rtt(tp) != ~0U)
+	if ((tp->rack.reord || !tp->lost_out) && tcp_min_rtt(tp) != ~0U)
 		reo_wnd = max(tcp_min_rtt(tp) >> 2, reo_wnd);
 
 	tcp_for_write_queue(skb, sk) {
@@ -54,20 +72,29 @@ int tcp_rack_mark_lost(struct sock *sk)
 		    scb->sacked & TCPCB_SACKED_ACKED)
 			continue;
 
-		if (skb_mstamp_after(&tp->rack.mstamp, &skb->skb_mstamp)) {
+		if (tcp_rack_sent_after(&tp->rack.mstamp, &skb->skb_mstamp,
+					tp->rack.end_seq, scb->end_seq)) {
+			/* Step 3 in draft-cheng-tcpm-rack-00.txt:
+			 * A packet is lost if its elapsed time is beyond
+			 * the recent RTT plus the reordering window.
+			 */
+			u32 elapsed = skb_mstamp_us_delta(now,
+							  &skb->skb_mstamp);
+			s32 remaining = tp->rack.rtt_us + reo_wnd - elapsed;
 
-			if (skb_mstamp_us_delta(&tp->rack.mstamp,
-						&skb->skb_mstamp) <= reo_wnd)
+			if (remaining < 0) {
+				tcp_rack_mark_skb_lost(sk, skb);
 				continue;
-
-			/* skb is lost if packet sent later is sacked */
-			tcp_skb_mark_lost_uncond_verify(tp, skb);
-			if (scb->sacked & TCPCB_SACKED_RETRANS) {
-				scb->sacked &= ~TCPCB_SACKED_RETRANS;
-				tp->retrans_out -= tcp_skb_pcount(skb);
-				NET_INC_STATS(sock_net(sk),
-					      LINUX_MIB_TCPLOSTRETRANSMIT);
 			}
+
+			/* Skip ones marked lost but not yet retransmitted */
+			if ((scb->sacked & TCPCB_LOST) &&
+			    !(scb->sacked & TCPCB_SACKED_RETRANS))
+				continue;
+
+			/* Record maximum wait time (+1 to avoid 0) */
+			*reo_timeout = max_t(u32, *reo_timeout, 1 + remaining);
+
 		} else if (!(scb->sacked & TCPCB_RETRANS)) {
 			/* Original data are sent sequentially so stop early
 			 * b/c the rest are all sent after rack_sent
@@ -75,20 +102,43 @@ int tcp_rack_mark_lost(struct sock *sk)
 			break;
 		}
 	}
-	return prior_retrans - tp->retrans_out;
 }
 
-/* Record the most recently (re)sent time among the (s)acked packets */
-void tcp_rack_advance(struct tcp_sock *tp,
-		      const struct skb_mstamp *xmit_time, u8 sacked)
+void tcp_rack_mark_lost(struct sock *sk, const struct skb_mstamp *now)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	u32 timeout;
+
+	if (!tp->rack.advanced)
+		return;
+
+	/* Reset the advanced flag to avoid unnecessary queue scanning */
+	tp->rack.advanced = 0;
+	tcp_rack_detect_loss(sk, now, &timeout);
+	if (timeout) {
+		timeout = usecs_to_jiffies(timeout + TCP_REO_TIMEOUT_MIN);
+		inet_csk_reset_xmit_timer(sk, ICSK_TIME_REO_TIMEOUT,
+					  timeout, inet_csk(sk)->icsk_rto);
+	}
+}
+
+/* Record the most recently (re)sent time among the (s)acked packets
+ * This is "Step 3: Advance RACK.xmit_time and update RACK.RTT" from
+ * draft-cheng-tcpm-rack-00.txt
+ */
+void tcp_rack_advance(struct tcp_sock *tp, u8 sacked, u32 end_seq,
+		      const struct skb_mstamp *xmit_time,
+		      const struct skb_mstamp *ack_time)
 {
+	u32 rtt_us;
+
 	if (tp->rack.mstamp.v64 &&
-	    !skb_mstamp_after(xmit_time, &tp->rack.mstamp))
+	    !tcp_rack_sent_after(xmit_time, &tp->rack.mstamp,
+				 end_seq, tp->rack.end_seq))
 		return;
 
+	rtt_us = skb_mstamp_us_delta(ack_time, xmit_time);
 	if (sacked & TCPCB_RETRANS) {
-		struct skb_mstamp now;
-
 		/* If the sacked packet was retransmitted, it's ambiguous
 		 * whether the retransmission or the original (or the prior
 		 * retransmission) was sacked.
@@ -99,11 +149,35 @@ void tcp_rack_advance(struct tcp_sock *tp,
 		 * so it's at least one RTT (i.e., retransmission is at least
 		 * an RTT later).
 		 */
-		skb_mstamp_get(&now);
-		if (skb_mstamp_us_delta(&now, xmit_time) < tcp_min_rtt(tp))
+		if (rtt_us < tcp_min_rtt(tp))
 			return;
 	}
-
+	tp->rack.rtt_us = rtt_us;
 	tp->rack.mstamp = *xmit_time;
+	tp->rack.end_seq = end_seq;
 	tp->rack.advanced = 1;
 }
+
+/* We have waited long enough to accommodate reordering. Mark the expired
+ * packets lost and retransmit them.
+ */
+void tcp_rack_reo_timeout(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+	struct skb_mstamp now;
+	u32 timeout, prior_inflight;
+
+	skb_mstamp_get(&now);
+	prior_inflight = tcp_packets_in_flight(tp);
+	tcp_rack_detect_loss(sk, &now, &timeout);
+	if (prior_inflight != tcp_packets_in_flight(tp)) {
+		if (inet_csk(sk)->icsk_ca_state != TCP_CA_Recovery) {
+			tcp_enter_recovery(sk, false);
+			if (!inet_csk(sk)->icsk_ca_ops->cong_control)
+				tcp_cwnd_reduction(sk, 1, 0);
+		}
+		tcp_xmit_retransmit_queue(sk);
+	}
+	if (inet_csk(sk)->icsk_pending != ICSK_TIME_RETRANS)
+		tcp_rearm_rto(sk);
+}