Remove sndQueue as its pointless now.

sndQueue made sense when the worker goroutine and the syscall context held
different locks. Now both lock the endpoint lock before doing anything which
means adding to sndQueue is pointless as we move it to writeList immediately
after that in endpoint.Write() by calling e.drainSendQueue.

PiperOrigin-RevId: 381523177

pkg/tcpip/stack/tcp.go

@@ -380,9 +380,6 @@ type TCPSndBufState struct {
 	// SndClosed indicates that the endpoint has been closed for sends.
 	SndClosed bool
 
-	// SndBufInQueue is the number of bytes in the send queue.
-	SndBufInQueue seqnum.Size
-
 	// PacketTooBigCount is used to notify the main protocol routine how
 	// many times a "packet too big" control packet is received.
 	PacketTooBigCount int

pkg/tcpip/transport/tcp/connect.go

@@ -909,30 +909,13 @@ func (e *endpoint) sendRaw(data buffer.VectorisedView, flags header.TCPFlags, se
 	return err
 }
 
-func (e *endpoint) handleWrite() {
-	e.sndQueueInfo.sndQueueMu.Lock()
-	next := e.drainSendQueueLocked()
-	e.sndQueueInfo.sndQueueMu.Unlock()
-
-	e.sendData(next)
-}
-
-// Move packets from send queue to send list.
-//
-// Precondition: e.sndBufMu must be locked.
-func (e *endpoint) drainSendQueueLocked() *segment {
-	first := e.sndQueueInfo.sndQueue.Front()
-	if first != nil {
-		e.snd.writeList.PushBackList(&e.sndQueueInfo.sndQueue)
-		e.sndQueueInfo.SndBufInQueue = 0
-	}
-	return first
-}
-
 // Precondition: e.mu must be locked.
 func (e *endpoint) sendData(next *segment) {
 	// Initialize the next segment to write if it's currently nil.
 	if e.snd.writeNext == nil {
+		if next == nil {
+			return
+		}
 		e.snd.writeNext = next
 	}
 
@@ -940,17 +923,6 @@ func (e *endpoint) sendData(next *segment) {
 	e.snd.sendData()
 }
 
-func (e *endpoint) handleClose() {
-	if !e.EndpointState().connected() {
-		return
-	}
-	// Drain the send queue.
-	e.handleWrite()
-
-	// Mark send side as closed.
-	e.snd.Closed = true
-}
-
 // resetConnectionLocked puts the endpoint in an error state with the given
 // error code and sends a RST if and only if the error is not ErrConnectionReset
 // indicating that the connection is being reset due to receiving a RST. This
@@ -1402,14 +1374,7 @@ func (e *endpoint) protocolMainLoop(handshake bool, wakerInitDone chan<- struct{
 		{
 			w: &e.sndQueueInfo.sndWaker,
 			f: func() tcpip.Error {
-				e.handleWrite()
-				return nil
-			},
-		},
-		{
-			w: &e.sndQueueInfo.sndCloseWaker,
-			f: func() tcpip.Error {
-				e.handleClose()
+				e.sendData(nil /* next */)
 				return nil
 			},
 		},

pkg/tcpip/transport/tcp/endpoint.go

@@ -293,16 +293,9 @@ type sndQueueInfo struct {
 	sndQueueMu sync.Mutex `state:"nosave"`
 	stack.TCPSndBufState
 
-	// sndQueue holds segments that are ready to be sent.
-	sndQueue segmentList `state:"wait"`
-
-	// sndWaker is used to signal the protocol goroutine when segments are
-	// added to the `sndQueue`.
+	// sndWaker is used to signal the protocol goroutine when there may be
+	// segments that need to be sent.
 	sndWaker sleep.Waker `state:"manual"`
-
-	// sndCloseWaker is used to notify the protocol goroutine when the send
-	// side is closed.
-	sndCloseWaker sleep.Waker `state:"manual"`
 }
 
 // rcvQueueInfo contains the endpoint's rcvQueue and associated metadata.
@@ -1558,10 +1551,9 @@ func (e *endpoint) Write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, tcp
 		// Add data to the send queue.
 		s := newOutgoingSegment(e.TransportEndpointInfo.ID, e.stack.Clock(), v)
 		e.sndQueueInfo.SndBufUsed += len(v)
-		e.sndQueueInfo.SndBufInQueue += seqnum.Size(len(v))
-		e.sndQueueInfo.sndQueue.PushBack(s)
+		e.snd.writeList.PushBack(s)
 
-		return e.drainSendQueueLocked(), len(v), nil
+		return s, len(v), nil
 	}()
 	// Return if either we didn't queue anything or if an error occurred while
 	// attempting to queue data.
@@ -2314,7 +2306,7 @@ func (e *endpoint) connect(addr tcpip.FullAddress, handshake bool, run bool) tcp
 	// connection setting here.
 	if !handshake {
 		e.segmentQueue.mu.Lock()
-		for _, l := range []segmentList{e.segmentQueue.list, e.sndQueueInfo.sndQueue, e.snd.writeList} {
+		for _, l := range []segmentList{e.segmentQueue.list, e.snd.writeList} {
 			for s := l.Front(); s != nil; s = s.Next() {
 				s.id = e.TransportEndpointInfo.ID
 				e.sndQueueInfo.sndWaker.Assert()
@@ -2391,12 +2383,17 @@ func (e *endpoint) shutdownLocked(flags tcpip.ShutdownFlags) tcpip.Error {
 
 			// Queue fin segment.
 			s := newOutgoingSegment(e.TransportEndpointInfo.ID, e.stack.Clock(), nil)
-			e.sndQueueInfo.sndQueue.PushBack(s)
-			e.sndQueueInfo.SndBufInQueue++
+			e.snd.writeList.PushBack(s)
 			// Mark endpoint as closed.
 			e.sndQueueInfo.SndClosed = true
 			e.sndQueueInfo.sndQueueMu.Unlock()
-			e.handleClose()
+
+			// Drain the send queue.
+			e.sendData(s)
+
+			// Mark send side as closed.
+			e.snd.Closed = true
+
 			// Wake up any writers that maybe waiting for the stream to become
 			// writable.
 			e.waiterQueue.Notify(waiter.WritableEvents)