Don't need reentry guard here.

src/Avalonia.SceneGraph/Rendering/Renderer.cs

@@ -13,7 +13,6 @@ namespace Avalonia.Rendering
         private IRenderRoot _root;
         private IRenderTarget _renderTarget;
         private bool _dirty;
-        private bool _rendering;
 
         public void Attach(IRenderRoot root, IRenderLoop renderLoop)
         {
@@ -36,11 +35,6 @@ namespace Avalonia.Rendering
 
         public void Render(Rect rect)
         {
-            if (_rendering)
-            {
-                return;
-            }
-
             if (_renderTarget == null)
             {
                 _renderTarget = _root.CreateRenderTarget();
@@ -48,7 +42,6 @@ namespace Avalonia.Rendering
 
             try
             {
-                _rendering = true;
                 _renderTarget.Render(_root);
             }
             catch (RenderTargetCorruptedException ex)
@@ -59,7 +52,6 @@ namespace Avalonia.Rendering
             }
             finally
             {
-                _rendering = false;
                 _dirty = false;
             }
         }