Revert "Revert "Don't take the proxy mutex in the traffic path""

pkg/proxy/userspace/proxier_test.go

@@ -429,6 +429,9 @@ func TestTCPProxyStop(t *testing.T) {
 	if err != nil {
 		t.Fatalf("error adding new service: %#v", err)
 	}
+	if !svcInfo.isAlive() {
+		t.Fatalf("wrong value for isAlive(): expected true")
+	}
 	conn, err := net.Dial("tcp", joinHostPort("", svcInfo.proxyPort))
 	if err != nil {
 		t.Fatalf("error connecting to proxy: %v", err)
@@ -437,6 +440,9 @@ func TestTCPProxyStop(t *testing.T) {
 	waitForNumProxyLoops(t, p, 1)
 
 	stopProxyByName(p, service)
+	if svcInfo.isAlive() {
+		t.Fatalf("wrong value for isAlive(): expected false")
+	}
 	// Wait for the port to really close.
 	if err := waitForClosedPortTCP(p, svcInfo.proxyPort); err != nil {
 		t.Fatalf(err.Error())