Merge tag 'vmwgfx-fixes-4.3-151014' of git://people.freedesktop.org/~thomash/linux into drm-fixes

Pull request of 2015-10-14

* tag 'vmwgfx-fixes-4.3-151014' of git://people.freedesktop.org/~thomash/linux:
  drm/vmwgfx: Fix kernel NULL pointer dereference on older hardware

drivers/gpu/drm/vmwgfx/vmwgfx_surface.c

@@ -657,7 +657,8 @@ static void vmw_user_surface_base_release(struct ttm_base_object **p_base)
 	struct vmw_resource *res = &user_srf->srf.res;
 
 	*p_base = NULL;
-	ttm_base_object_unref(&user_srf->backup_base);
+	if (user_srf->backup_base)
+		ttm_base_object_unref(&user_srf->backup_base);
 	vmw_resource_unreference(&res);
 }