ipn/ipnlocal: use lockAndGetUnlock in Start

This removes one of the Lock,Unlock,Lock,Unlock at least in
the Start function. Still has 3 more of these.

Updates #11649

Signed-off-by: Maisem Ali <maisem@tailscale.com>

ipn/ipnlocal/local.go

@@ -402,7 +402,6 @@ func NewLocalBackend(logf logger.Logf, logID logid.PublicID, sys *tsd.System, lo
 	osshare.SetFileSharingEnabled(false, logf)
 
 	ctx, cancel := context.WithCancel(context.Background())
-	portpoll := new(portlist.Poller)
 	clock := tstime.StdClock{}
 
 	b := &LocalBackend{
@@ -420,7 +419,7 @@ func NewLocalBackend(logf logger.Logf, logID logid.PublicID, sys *tsd.System, lo
 		pm:                  pm,
 		backendLogID:        logID,
 		state:               ipn.NoState,
-		portpoll:            portpoll,
+		portpoll:            new(portlist.Poller),
 		em:                  newExpiryManager(logf),
 		gotPortPollRes:      make(chan struct{}),
 		loginFlags:          loginFlags,
@@ -1593,6 +1592,14 @@ func (b *LocalBackend) NodeViewByIDForTest(id tailcfg.NodeID) (_ tailcfg.NodeVie
 	return n, ok
 }
 
+// DisablePortMapperForTest disables the portmapper for tests.
+// It must be called before Start.
+func (b *LocalBackend) DisablePortMapperForTest() {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	b.portpoll = nil
+}
+
 // PeersForTest returns all the current peers, sorted by Node.ID,
 // for integration tests in another repo.
 func (b *LocalBackend) PeersForTest() []tailcfg.NodeView {
@@ -1605,9 +1612,7 @@ func (b *LocalBackend) PeersForTest() []tailcfg.NodeView {
 	return ret
 }
 
-func (b *LocalBackend) getNewControlClientFunc() clientGen {
-	b.mu.Lock()
-	defer b.mu.Unlock()
+func (b *LocalBackend) getNewControlClientFuncLocked() clientGen {
 	if b.ccGen == nil {
 		// Initialize it rather than just returning the
 		// default to make any future call to
@@ -1632,11 +1637,17 @@ func (b *LocalBackend) getNewControlClientFunc() clientGen {
 func (b *LocalBackend) Start(opts ipn.Options) error {
 	b.logf("Start")
 
-	b.mu.Lock()
+	var clientToShutdown controlclient.Client
+	defer func() {
+		if clientToShutdown != nil {
+			clientToShutdown.Shutdown()
+		}
+	}()
+	unlock := b.lockAndGetUnlock()
+	defer unlock()
 
 	if opts.UpdatePrefs != nil {
 		if err := b.checkPrefsLocked(opts.UpdatePrefs); err != nil {
-			b.mu.Unlock()
 			return err
 		}
 	}
@@ -1668,7 +1679,7 @@ func (b *LocalBackend) Start(opts ipn.Options) error {
 	// into sync with the minimal changes. But that's not how it
 	// is right now, which is a sign that the code is still too
 	// complicated.
-	prevCC := b.resetControlClientLocked()
+	clientToShutdown = b.resetControlClientLocked()
 	httpTestClient := b.httpTestClient
 
 	if b.hostinfo != nil {
@@ -1697,7 +1708,6 @@ func (b *LocalBackend) Start(opts ipn.Options) error {
 	wantRunning := prefs.WantRunning()
 	if wantRunning {
 		if err := b.initMachineKeyLocked(); err != nil {
-			b.mu.Unlock()
 			return fmt.Errorf("initMachineKeyLocked: %w", err)
 		}
 	}
@@ -1716,7 +1726,6 @@ func (b *LocalBackend) Start(opts ipn.Options) error {
 		persistv = new(persist.Persist)
 	}
 	b.updateFilterLocked(nil, ipn.PrefsView{})
-	b.mu.Unlock()
 
 	if b.portpoll != nil {
 		b.portpollOnce.Do(func() {
@@ -1748,15 +1757,11 @@ func (b *LocalBackend) Start(opts ipn.Options) error {
 		debugFlags = append([]string{"netstack"}, debugFlags...)
 	}
 
-	if prevCC != nil {
-		prevCC.Shutdown()
-	}
-
 	// TODO(apenwarr): The only way to change the ServerURL is to
 	// re-run b.Start, because this is the only place we create a
 	// new controlclient. EditPrefs allows you to overwrite ServerURL,
 	// but it won't take effect until the next Start.
-	cc, err := b.getNewControlClientFunc()(controlclient.Options{
+	cc, err := b.getNewControlClientFuncLocked()(controlclient.Options{
 		GetMachinePrivateKey:       b.createGetMachinePrivateKeyFunc(),
 		Logf:                       logger.WithPrefix(b.logf, "control: "),
 		Persist:                    *persistv,
@@ -1786,14 +1791,6 @@ func (b *LocalBackend) Start(opts ipn.Options) error {
 		return err
 	}
 
-	b.mu.Lock()
-	// Even though we reset b.cc above, we might have raced with
-	// another Start() call. If so, shut down the previous one again
-	// as we do not know if it was created with the same options.
-	prevCC = b.resetControlClientLocked()
-	if prevCC != nil {
-		defer prevCC.Shutdown() // must be called after b.mu is unlocked
-	}
 	b.setControlClientLocked(cc)
 	endpoints := b.endpoints
 
@@ -1804,13 +1801,12 @@ func (b *LocalBackend) Start(opts ipn.Options) error {
 	if b.tka != nil {
 		head, err := b.tka.authority.Head().MarshalText()
 		if err != nil {
-			b.mu.Unlock()
 			return fmt.Errorf("marshalling tka head: %w", err)
 		}
 		tkaHead = string(head)
 	}
 	confWantRunning := b.conf != nil && wantRunning
-	b.mu.Unlock()
+	unlock.UnlockEarly()
 
 	if endpoints != nil {
 		cc.UpdateEndpoints(endpoints)

ipn/ipnlocal/state_test.go

@@ -316,6 +316,7 @@ func TestStateMachine(t *testing.T) {
 	if err != nil {
 		t.Fatalf("NewLocalBackend: %v", err)
 	}
+	b.DisablePortMapperForTest()
 
 	var cc, previousCC *mockControl
 	b.SetControlClientGetterForTesting(func(opts controlclient.Options) (controlclient.Client, error) {