RACK: Create a new list for segments.

RACK requires the segments to be in the order of their transmission
or retransmission times. This cl creates a new list and moves the
retransmitted segments to the end of the list.

PiperOrigin-RevId: 327325153

1 files changed, 26 insertions, 15 deletions

diff --git a/pkg/tcpip/transport/tcp/snd.go b/pkg/tcpip/transport/tcp/snd.go
index c55589c45..31151f23d 100644
--- a/pkg/tcpip/transport/tcp/snd.go
+++ b/pkg/tcpip/transport/tcp/snd.go
@@ -154,6 +154,7 @@ type sender struct {
 	closed      bool
 	writeNext   *segment
 	writeList   segmentList
+	rcList      rackSegmentList
 	resendTimer timer       `state:"nosave"`
 	resendWaker sleep.Waker `state:"nosave"`
 
@@ -367,7 +368,7 @@ func (s *sender) updateMaxPayloadSize(mtu, count int) {
 
 	// Rewind writeNext to the first segment exceeding the MTU. Do nothing
 	// if it is already before such a packet.
-	for seg := s.writeList.Front(); seg != nil; seg = seg.Next() {
+	for seg := s.writeList.Front(); seg != nil; seg = seg.segEntry.Next() {
 		if seg == s.writeNext {
 			// We got to writeNext before we could find a segment
 			// exceeding the MTU.
@@ -622,6 +623,7 @@ func (s *sender) splitSeg(seg *segment, size int) {
 	nSeg.data.TrimFront(size)
 	nSeg.sequenceNumber.UpdateForward(seqnum.Size(size))
 	s.writeList.InsertAfter(seg, nSeg)
+	s.rcList.InsertAfter(seg, nSeg)
 
 	// The segment being split does not carry PUSH flag because it is
 	// followed by the newly split segment.
@@ -653,7 +655,7 @@ func (s *sender) NextSeg(nextSegHint *segment) (nextSeg, hint *segment, rescueRt
 	var s3 *segment
 	var s4 *segment
 	// Step 1.
-	for seg := nextSegHint; seg != nil; seg = seg.Next() {
+	for seg := nextSegHint; seg != nil; seg = seg.segEntry.Next() {
 		// Stop iteration if we hit a segment that has never been
 		// transmitted (i.e. either it has no assigned sequence number
 		// or if it does have one, it's >= the next sequence number
@@ -683,7 +685,7 @@ func (s *sender) NextSeg(nextSegHint *segment) (nextSeg, hint *segment, rescueRt
 				// NextSeg():
 				//     (1.c) IsLost(S2) returns true.
 				if s.ep.scoreboard.IsLost(segSeq) {
-					return seg, seg.Next(), false
+					return seg, seg.segEntry.Next(), false
 				}
 
 				// NextSeg():
@@ -697,7 +699,7 @@ func (s *sender) NextSeg(nextSegHint *segment) (nextSeg, hint *segment, rescueRt
 				// SHOULD be returned.
 				if s3 == nil {
 					s3 = seg
-					hint = seg.Next()
+					hint = seg.segEntry.Next()
 				}
 			}
 			// NextSeg():
@@ -731,7 +733,7 @@ func (s *sender) NextSeg(nextSegHint *segment) (nextSeg, hint *segment, rescueRt
 	// range of one segment of up to SMSS octets of
 	// previously unsent data starting with sequence number
 	// HighData+1 MUST be returned."
-	for seg := s.writeNext; seg != nil; seg = seg.Next() {
+	for seg := s.writeNext; seg != nil; seg = seg.segEntry.Next() {
 		if s.isAssignedSequenceNumber(seg) && seg.sequenceNumber.LessThan(s.sndNxt) {
 			continue
 		}
@@ -773,15 +775,16 @@ func (s *sender) maybeSendSegment(seg *segment, limit int, end seqnum.Value) (se
 			// triggering bugs in poorly written DNS
 			// implementations.
 			var nextTooBig bool
-			for seg.Next() != nil && seg.Next().data.Size() != 0 {
-				if seg.data.Size()+seg.Next().data.Size() > available {
+			for seg.segEntry.Next() != nil && seg.segEntry.Next().data.Size() != 0 {
+				if seg.data.Size()+seg.segEntry.Next().data.Size() > available {
 					nextTooBig = true
 					break
 				}
-				seg.data.Append(seg.Next().data)
+				seg.data.Append(seg.segEntry.Next().data)
 
 				// Consume the segment that we just merged in.
-				s.writeList.Remove(seg.Next())
+				s.writeList.Remove(seg.segEntry.Next())
+				s.rcList.Remove(seg.rackSegEntry.Next())
 			}
 			if !nextTooBig && seg.data.Size() < available {
 				// Segment is not full.
@@ -948,7 +951,7 @@ func (s *sender) handleSACKRecovery(limit int, end seqnum.Value) (dataSent bool)
 			}
 			dataSent = true
 			s.outstanding++
-			s.writeNext = nextSeg.Next()
+			s.writeNext = nextSeg.segEntry.Next()
 			continue
 		}
 
@@ -961,6 +964,7 @@ func (s *sender) handleSACKRecovery(limit int, end seqnum.Value) (dataSent bool)
 		// transmitted in (C.1)."
 		s.outstanding++
 		dataSent = true
+
 		s.sendSegment(nextSeg)
 
 		segEnd := nextSeg.sequenceNumber.Add(nextSeg.logicalLen())
@@ -1035,7 +1039,7 @@ func (s *sender) sendData() {
 	if s.fr.active && s.ep.sackPermitted {
 		dataSent = s.handleSACKRecovery(s.maxPayloadSize, end)
 	} else {
-		for seg := s.writeNext; seg != nil && s.outstanding < s.sndCwnd; seg = seg.Next() {
+		for seg := s.writeNext; seg != nil && s.outstanding < s.sndCwnd; seg = seg.segEntry.Next() {
 			cwndLimit := (s.sndCwnd - s.outstanding) * s.maxPayloadSize
 			if cwndLimit < limit {
 				limit = cwndLimit
@@ -1043,7 +1047,7 @@ func (s *sender) sendData() {
 			if s.isAssignedSequenceNumber(seg) && s.ep.sackPermitted && s.ep.scoreboard.IsSACKED(seg.sackBlock()) {
 				// Move writeNext along so that we don't try and scan data that
 				// has already been SACKED.
-				s.writeNext = seg.Next()
+				s.writeNext = seg.segEntry.Next()
 				continue
 			}
 			if sent := s.maybeSendSegment(seg, limit, end); !sent {
@@ -1051,7 +1055,7 @@ func (s *sender) sendData() {
 			}
 			dataSent = true
 			s.outstanding += s.pCount(seg)
-			s.writeNext = seg.Next()
+			s.writeNext = seg.segEntry.Next()
 		}
 	}
 
@@ -1182,7 +1186,7 @@ func (s *sender) SetPipe() {
 	}
 	pipe := 0
 	smss := seqnum.Size(s.ep.scoreboard.SMSS())
-	for s1 := s.writeList.Front(); s1 != nil && s1.data.Size() != 0 && s.isAssignedSequenceNumber(s1); s1 = s1.Next() {
+	for s1 := s.writeList.Front(); s1 != nil && s1.data.Size() != 0 && s.isAssignedSequenceNumber(s1); s1 = s1.segEntry.Next() {
 		// With GSO each segment can be much larger than SMSS. So check the segment
 		// in SMSS sized ranges.
 		segEnd := s1.sequenceNumber.Add(seqnum.Size(s1.data.Size()))
@@ -1384,7 +1388,7 @@ func (s *sender) handleRcvdSegment(rcvdSeg *segment) {
 			}
 
 			if s.writeNext == seg {
-				s.writeNext = seg.Next()
+				s.writeNext = seg.segEntry.Next()
 			}
 
 			// Update the RACK fields if SACK is enabled.
@@ -1393,6 +1397,7 @@ func (s *sender) handleRcvdSegment(rcvdSeg *segment) {
 			}
 
 			s.writeList.Remove(seg)
+			s.rcList.Remove(seg)
 
 			// if SACK is enabled then Only reduce outstanding if
 			// the segment was not previously SACKED as these have
@@ -1460,6 +1465,12 @@ func (s *sender) sendSegment(seg *segment) *tcpip.Error {
 		if s.sndCwnd < s.sndSsthresh {
 			s.ep.stack.Stats().TCP.SlowStartRetransmits.Increment()
 		}
+
+		// Move the segment which has to be retransmitted to the end of the list, as
+		// RACK requires the segments in the order of their transmission times.
+		// See: https://tools.ietf.org/html/draft-ietf-tcpm-rack-09#section-6.2
+		// Step 5
+		s.rcList.PushBack(seg)
 	}
 	seg.xmitTime = time.Now()
 	seg.xmitCount++