netstack: use defer in segmentQueue

The lack of defer is leftover from the days when using one would actually push
functions onto a stack in dead-simple cases.

PiperOrigin-RevId: 537477095

pkg/tcpip/transport/tcp/segment_queue.go

@@ -37,10 +37,8 @@ func (q *segmentQueue) emptyLocked() bool {
 // empty determines if the queue is empty.
 func (q *segmentQueue) empty() bool {
 	q.mu.Lock()
-	r := q.emptyLocked()
-	q.mu.Unlock()
-
-	return r
+	defer q.mu.Unlock()
+	return q.emptyLocked()
 }
 
 // enqueue adds the given segment to the queue.
@@ -54,7 +52,10 @@ func (q *segmentQueue) enqueue(s *segment) bool {
 	// avoid lock order inversion.
 	bufSz := q.ep.ops.GetReceiveBufferSize()
 	used := q.ep.receiveMemUsed()
+
 	q.mu.Lock()
+	defer q.mu.Unlock()
+
 	// Allow zero sized segments (ACK/FIN/RSTs etc even if the segment queue
 	// is currently full).
 	allow := (used <= int(bufSz) || s.payloadSize() == 0) && !q.frozen
@@ -65,7 +66,6 @@ func (q *segmentQueue) enqueue(s *segment) bool {
 		// Set the owner now that the endpoint owns the segment.
 		s.setOwner(q.ep, recvQ)
 	}
-	q.mu.Unlock()
 
 	return allow
 }
@@ -75,11 +75,12 @@ func (q *segmentQueue) enqueue(s *segment) bool {
 // the ref count when done.
 func (q *segmentQueue) dequeue() *segment {
 	q.mu.Lock()
+	defer q.mu.Unlock()
+
 	s := q.list.Front()
 	if s != nil {
 		q.list.Remove(s)
 	}
-	q.mu.Unlock()
 
 	return s
 }
@@ -89,14 +90,14 @@ func (q *segmentQueue) dequeue() *segment {
 // queue till the queue is unfroze with a corresponding segmentQueue.thaw call.
 func (q *segmentQueue) freeze() {
 	q.mu.Lock()
+	defer q.mu.Unlock()
 	q.frozen = true
-	q.mu.Unlock()
 }
 
 // thaw unfreezes a previously frozen queue using segmentQueue.freeze() and
 // allows new segments to be queued again.
 func (q *segmentQueue) thaw() {
 	q.mu.Lock()
+	defer q.mu.Unlock()
 	q.frozen = false
-	q.mu.Unlock()
 }