git: c21b7b55bea2 - main - tcp: finish SACK loss recovery on sudden lack of SACK blocks

The branch main has been updated by rscheff:

URL: https://cgit.FreeBSD.org/src/commit/?id=c21b7b55bea2cc2bf3b420c70a9018e703ed6f00

commit c21b7b55bea2cc2bf3b420c70a9018e703ed6f00
Author:     Richard Scheffenegger <rscheff@FreeBSD.org>
AuthorDate: 2022-08-31 12:49:25 +0000
Commit:     Richard Scheffenegger <rscheff@FreeBSD.org>
CommitDate: 2022-08-31 12:49:47 +0000

    tcp: finish SACK loss recovery on sudden lack of SACK blocks
    
    While a receiver should continue sending SACK blocks for the
    duration of a SACK loss recovery, if for some reason the
    TCP options no longer contain these SACK blocks, but we
    already started maintaining the Scoreboard, keep on handling
    incoming ACKs (without SACK) as belonging to the SACK recovery.
    
    Reported by:            thj
    Reviewed by:            tuexen, #transport
    MFC after:              2 weeks
    Sponsored by:           NetApp, Inc.
    Differential Revision:  https://reviews.freebsd.org/D36046
---
 sys/netinet/tcp_input.c | 39 ++++++++++++++++++++++-----------------
 1 file changed, 22 insertions(+), 17 deletions(-)

diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
index bf963840cd23..e8f2676f2aa8 100644
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -268,6 +268,20 @@ kmod_tcpstat_add(int statnum, int val)
 	counter_u64_add(VNET(tcpstat)[statnum], val);
 }
 
+/*
+ * Make sure that we only start a SACK loss recovery when
+ * receiving a duplicate ACK with a SACK block, and also
+ * complete SACK loss recovery in case the other end
+ * reneges.
+ */
+static bool inline
+tcp_is_sack_recovery(struct tcpcb *tp, struct tcpopt *to)
+{
+	return ((tp->t_flags & TF_SACK_PERMIT) &&
+		((to->to_flags & TOF_SACK) ||
+		(!TAILQ_EMPTY(&tp->snd_holes))));
+}
+
 #ifdef TCP_HHOOK
 /*
  * Wrapper for the TCP established input helper hook.
@@ -2491,9 +2505,7 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 			TCPSTAT_INC(tcps_rcvacktoomuch);
 			goto dropafterack;
 		}
-		if ((tp->t_flags & TF_SACK_PERMIT) &&
-		    ((to.to_flags & TOF_SACK) ||
-		     !TAILQ_EMPTY(&tp->snd_holes))) {
+		if (tcp_is_sack_recovery(tp, &to)) {
 			if (((sack_changed = tcp_sack_doack(tp, &to, th->th_ack)) != 0) &&
 			    (tp->t_flags & TF_LRD)) {
 				tcp_sack_lost_retransmission(tp, th);
@@ -2566,8 +2578,7 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 				 * duplicating packets or a possible DoS attack.
 				 */
 				if (th->th_ack != tp->snd_una ||
-				    ((tp->t_flags & TF_SACK_PERMIT) &&
-				    (to.to_flags & TOF_SACK) &&
+				    (tcp_is_sack_recovery(tp, &to) &&
 				    !sack_changed))
 					break;
 				else if (!tcp_timer_active(tp, TT_REXMT))
@@ -2579,8 +2590,7 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 					if (V_tcp_do_prr &&
 					    IN_FASTRECOVERY(tp->t_flags)) {
 						tcp_do_prr_ack(tp, th, &to);
-					} else if ((tp->t_flags & TF_SACK_PERMIT) &&
-					    (to.to_flags & TOF_SACK) &&
+					} else if (tcp_is_sack_recovery(tp, &to) &&
 					    IN_FASTRECOVERY(tp->t_flags)) {
 						int awnd;
 
@@ -2653,8 +2663,7 @@ enter_recovery:
 						 * snd_ssthresh is already updated by
 						 * cc_cong_signal.
 						 */
-						if ((tp->t_flags & TF_SACK_PERMIT) &&
-						    (to.to_flags & TOF_SACK)) {
+						if (tcp_is_sack_recovery(tp, &to)) {
 							tp->sackhint.prr_delivered =
 							    tp->sackhint.sacked_bytes;
 						} else {
@@ -2666,8 +2675,7 @@ enter_recovery:
 						tp->sackhint.recover_fs = max(1,
 						    tp->snd_nxt - tp->snd_una);
 					}
-					if ((tp->t_flags & TF_SACK_PERMIT) &&
-					    (to.to_flags & TOF_SACK)) {
+					if (tcp_is_sack_recovery(tp, &to)) {
 						TCPSTAT_INC(
 						    tcps_sack_recovery_episode);
 						tp->snd_recover = tp->snd_nxt;
@@ -2759,8 +2767,7 @@ enter_recovery:
 			 * from the left side. Such partial ACKs should not be
 			 * counted as dupacks here.
 			 */
-			if ((tp->t_flags & TF_SACK_PERMIT) &&
-			    (to.to_flags & TOF_SACK) &&
+			if (tcp_is_sack_recovery(tp, &to) &&
 			    sack_changed) {
 				tp->t_dupacks++;
 				/* limit overhead by setting maxseg last */
@@ -3942,8 +3949,7 @@ tcp_do_prr_ack(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
 	 * (del_data) and an estimate of how many bytes are in the
 	 * network.
 	 */
-	if (((tp->t_flags & TF_SACK_PERMIT) &&
-	    (to->to_flags & TOF_SACK)) ||
+	if (tcp_is_sack_recovery(tp, to) ||
 	    (IN_CONGRECOVERY(tp->t_flags) &&
 	     !IN_FASTRECOVERY(tp->t_flags))) {
 		del_data = tp->sackhint.delivered_data;
@@ -3987,8 +3993,7 @@ tcp_do_prr_ack(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
 	 * accordingly.
 	 */
 	if (IN_FASTRECOVERY(tp->t_flags)) {
-		if ((tp->t_flags & TF_SACK_PERMIT) &&
-		    (to->to_flags & TOF_SACK)) {
+		if (tcp_is_sack_recovery(tp, to)) {
 			tp->snd_cwnd = tp->snd_nxt - tp->snd_recover +
 					    tp->sackhint.sack_bytes_rexmit +
 					    (snd_cnt * maxseg);