From 489ac10c6983b9f2a383804a9de709723099202d Mon Sep 17 00:00:00 2001
From: Kevin Krakauer <krakauer@google.com>
Date: Wed, 17 Jul 2024 18:06:11 -0700
Subject: [PATCH] Automated rollback of changelist 634071568

PiperOrigin-RevId: 653421213
---
 pkg/tcpip/transport/tcp/rack.go              |  6 ++----
 pkg/tcpip/transport/tcp/snd.go               | 14 ++++----------
 pkg/tcpip/transport/tcp/test/e2e/tcp_test.go |  1 -
 3 files changed, 6 insertions(+), 15 deletions(-)

diff --git a/pkg/tcpip/transport/tcp/rack.go b/pkg/tcpip/transport/tcp/rack.go
index 35e6cc725..66ea6e5b0 100644
--- a/pkg/tcpip/transport/tcp/rack.go
+++ b/pkg/tcpip/transport/tcp/rack.go
@@ -357,13 +357,11 @@ func (rc *rackControl) detectLoss(rcvTime tcpip.MonotonicTime) int {
 	var timeout time.Duration
 	numLost := 0
 	for seg := rc.snd.writeList.Front(); seg != nil && seg.xmitCount != 0; seg = seg.Next() {
-		// xmitCount can be 0 for packets that are broken up for PMTUD.
-		// The initial transmission "doesn't count" WRT loss detection.
-		if rc.snd.ep.scoreboard.IsSACKED(seg.sackBlock()) || seg.xmitCount == 0 {
+		if rc.snd.ep.scoreboard.IsSACKED(seg.sackBlock()) {
 			continue
 		}
 
-		if seg.lost && seg.xmitCount > 1 {
+		if seg.lost && seg.xmitCount == 1 {
 			numLost++
 			continue
 		}
diff --git a/pkg/tcpip/transport/tcp/snd.go b/pkg/tcpip/transport/tcp/snd.go
index 2301ae905..1e20ac2c3 100644
--- a/pkg/tcpip/transport/tcp/snd.go
+++ b/pkg/tcpip/transport/tcp/snd.go
@@ -342,16 +342,10 @@ func (s *sender) updateMaxPayloadSize(mtu, count int) {
 			break
 		}
 
-		if seg.payloadSize() > m {
-			// xmitCount is used for loss detection, but
-			// retransmission doesn't indicate congestion here,
-			// it's just PMTUD.
-			seg.xmitCount = 0
-			if nextSeg == s.writeNext {
-				// We found a segment exceeding the MTU. Rewind
-				// writeNext and try to retransmit it.
-				nextSeg = seg
-			}
+		if nextSeg == s.writeNext && seg.payloadSize() > m {
+			// We found a segment exceeding the MTU. Rewind
+			// writeNext and try to retransmit it.
+			nextSeg = seg
 		}
 
 		if s.ep.SACKPermitted && s.ep.scoreboard.IsSACKED(seg.sackBlock()) {
diff --git a/pkg/tcpip/transport/tcp/test/e2e/tcp_test.go b/pkg/tcpip/transport/tcp/test/e2e/tcp_test.go
index 5981be60f..9dcb8de85 100644
--- a/pkg/tcpip/transport/tcp/test/e2e/tcp_test.go
+++ b/pkg/tcpip/transport/tcp/test/e2e/tcp_test.go
@@ -5739,7 +5739,6 @@ func TestPathMTUDiscovery(t *testing.T) {
 			}
 			checker.IPv4(t, p,
 				checker.PayloadLen(size+header.TCPMinimumSize),
-				checker.FragmentFlags(header.IPv4FlagDontFragment),
 				checker.TCP(
 					checker.DstPort(context.TestPort),
 					checker.TCPSeqNum(seqNum),