drm/kms: Catch mode_object lifetime errors

Only dynamic mode objects, i.e. those which are refcounted and have a free
callback, can be added while the overall drm_device is visible to
userspace. All others must be added before drm_dev_register and
removed after drm_dev_unregister.

Small issue around drivers still using the load/unload callbacks, we
need to make sure we set dev->registered so that load/unload code in
these callbacks doesn't trigger false warnings. Only a small
adjustement in drm_dev_register was needed.

Motivated by some irc discussions about object ids of dynamic objects
like blobs become invalid, and me going on a bit an audit spree.
Reviewed-by: Sean Paul <sean@poorly.run>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190614061723.1173-1-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_drv.c

@@ -990,14 +990,14 @@ int drm_dev_register(struct drm_device *dev, unsigned long flags)
 	if (ret)
 		goto err_minors;
 
-	dev->registered = true;
-
 	if (dev->driver->load) {
 		ret = dev->driver->load(dev, flags);
 		if (ret)
 			goto err_minors;
 	}
 
+	dev->registered = true;
+
 	if (drm_core_check_feature(dev, DRIVER_MODESET))
 		drm_modeset_register_all(dev);
 

drivers/gpu/drm/drm_mode_object.c

@@ -42,6 +42,8 @@ int __drm_mode_object_add(struct drm_device *dev, struct drm_mode_object *obj,
 {
 	int ret;
 
+	WARN_ON(dev->registered && !obj_free_cb);
+
 	mutex_lock(&dev->mode_config.idr_mutex);
 	ret = idr_alloc(&dev->mode_config.object_idr, register_obj ? obj : NULL,
 			1, 0, GFP_KERNEL);
@@ -102,6 +104,8 @@ void drm_mode_object_register(struct drm_device *dev,
 void drm_mode_object_unregister(struct drm_device *dev,
 				struct drm_mode_object *object)
 {
+	WARN_ON(dev->registered && !object->free_cb);
+
 	mutex_lock(&dev->mode_config.idr_mutex);
 	if (object->id) {
 		idr_remove(&dev->mode_config.object_idr, object->id);