Do not spawn a goroutine when calling stack.NDPDispatcher's methods

Do not start a new goroutine when calling
stack.NDPDispatcher.OnDuplicateAddressDetectionStatus.

PiperOrigin-RevId: 292268574

pkg/tcpip/stack/ndp.go

@@ -167,8 +167,8 @@ type NDPDispatcher interface {
 	// reason, such as the address being removed). If an error occured
 	// during DAD, err will be set and resolved must be ignored.
 	//
-	// This function is permitted to block indefinitely without interfering
-	// with the stack's operation.
+	// This function is not permitted to block indefinitely. This function
+	// is also not permitted to call into the stack.
 	OnDuplicateAddressDetectionStatus(nicID tcpip.NICID, addr tcpip.Address, resolved bool, err *tcpip.Error)
 
 	// OnDefaultRouterDiscovered will be called when a new default router is
@@ -607,8 +607,8 @@ func (ndp *ndpState) stopDuplicateAddressDetection(addr tcpip.Address) {
 	delete(ndp.dad, addr)
 
 	// Let the integrator know DAD did not resolve.
-	if ndp.nic.stack.ndpDisp != nil {
-		go ndp.nic.stack.ndpDisp.OnDuplicateAddressDetectionStatus(ndp.nic.ID(), addr, false, nil)
+	if ndpDisp := ndp.nic.stack.ndpDisp; ndpDisp != nil {
+		ndpDisp.OnDuplicateAddressDetectionStatus(ndp.nic.ID(), addr, false, nil)
 	}
 }
 

pkg/tcpip/stack/ndp_test.go

@@ -497,7 +497,7 @@ func TestDADFail(t *testing.T) {
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
 			ndpDisp := ndpDispatcher{
-				dadC: make(chan ndpDADEvent),
+				dadC: make(chan ndpDADEvent, 1),
 			}
 			ndpConfigs := stack.DefaultNDPConfigurations()
 			opts := stack.Options{
@@ -576,7 +576,7 @@ func TestDADFail(t *testing.T) {
 // removed.
 func TestDADStop(t *testing.T) {
 	ndpDisp := ndpDispatcher{
-		dadC: make(chan ndpDADEvent),
+		dadC: make(chan ndpDADEvent, 1),
 	}
 	ndpConfigs := stack.NDPConfigurations{
 		RetransmitTimer:        time.Second,