drm: delay minor destruction to drm_dev_free()

Instead of freeing minors in drm_dev_unregister(), we only unplug them and
delay the free to drm_dev_free(). Note that if drm_dev_register() has
never been called, minors are NULL and this has no effect.

This change is needed to allow early device unregistration. If we want to
call drm_dev_unregister() on live devices, we need to guarantee that
minors are still valid (but unplugged). This way, any open file can still
access file_priv->minor->dev to get the DRM device. However, the minor is
unplugged so no new users can occur.
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_stub.c

@@ -487,6 +487,10 @@ EXPORT_SYMBOL(drm_dev_alloc);
  */
 void drm_dev_free(struct drm_device *dev)
 {
+	drm_put_minor(dev->control);
+	drm_put_minor(dev->render);
+	drm_put_minor(dev->primary);
+
 	if (dev->driver->driver_features & DRIVER_GEM)
 		drm_gem_destroy(dev);
 
@@ -601,9 +605,9 @@ void drm_dev_unregister(struct drm_device *dev)
 	list_for_each_entry_safe(r_list, list_temp, &dev->maplist, head)
 		drm_rmmap(dev, r_list->map);
 
-	drm_put_minor(dev->control);
-	drm_put_minor(dev->render);
-	drm_put_minor(dev->primary);
+	drm_unplug_minor(dev->control);
+	drm_unplug_minor(dev->render);
+	drm_unplug_minor(dev->primary);
 
 	list_del(&dev->driver_item);
 }