media: v4l2-subdev: handle module refcounting here

The module ownership refcounting was done in media_entity_get/put,
but that was very confusing and it did not work either in case an
application had a v4l-subdevX device open and the module was
unbound. When the v4l-subdevX device was closed the media_entity_put
was never called and the module refcount was left one too high, making
it impossible to unload it.

Since v4l2-subdev.c was the only place where media_entity_get/put was
called, just move the functionality to v4l2-subdev.c and drop those
confusing entity functions.

Store the module in subdev_fh so module_put no longer depends on
the media_entity struct.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/media-entity.c

@@ -17,7 +17,6 @@
  */
 
 #include <linux/bitmap.h>
-#include <linux/module.h>
 #include <linux/property.h>
 #include <linux/slab.h>
 #include <media/media-entity.h>
@@ -587,33 +586,6 @@ void media_pipeline_stop(struct media_entity *entity)
 }
 EXPORT_SYMBOL_GPL(media_pipeline_stop);
 
-/* -----------------------------------------------------------------------------
- * Module use count
- */
-
-struct media_entity *media_entity_get(struct media_entity *entity)
-{
-	if (entity == NULL)
-		return NULL;
-
-	if (entity->graph_obj.mdev->dev &&
-	    !try_module_get(entity->graph_obj.mdev->dev->driver->owner))
-		return NULL;
-
-	return entity;
-}
-EXPORT_SYMBOL_GPL(media_entity_get);
-
-void media_entity_put(struct media_entity *entity)
-{
-	if (entity == NULL)
-		return;
-
-	if (entity->graph_obj.mdev->dev)
-		module_put(entity->graph_obj.mdev->dev->driver->owner);
-}
-EXPORT_SYMBOL_GPL(media_entity_put);
-
 /* -----------------------------------------------------------------------------
  * Links management
  */

drivers/media/v4l2-core/v4l2-subdev.c

@@ -18,6 +18,7 @@
 
 #include <linux/ioctl.h>
 #include <linux/mm.h>
+#include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/videodev2.h>
@@ -54,9 +55,6 @@ static int subdev_open(struct file *file)
 	struct video_device *vdev = video_devdata(file);
 	struct v4l2_subdev *sd = vdev_to_v4l2_subdev(vdev);
 	struct v4l2_subdev_fh *subdev_fh;
-#if defined(CONFIG_MEDIA_CONTROLLER)
-	struct media_entity *entity = NULL;
-#endif
 	int ret;
 
 	subdev_fh = kzalloc(sizeof(*subdev_fh), GFP_KERNEL);
@@ -73,12 +71,15 @@ static int subdev_open(struct file *file)
 	v4l2_fh_add(&subdev_fh->vfh);
 	file->private_data = &subdev_fh->vfh;
 #if defined(CONFIG_MEDIA_CONTROLLER)
-	if (sd->v4l2_dev->mdev) {
-		entity = media_entity_get(&sd->entity);
-		if (!entity) {
+	if (sd->v4l2_dev->mdev && sd->entity.graph_obj.mdev->dev) {
+		struct module *owner;
+
+		owner = sd->entity.graph_obj.mdev->dev->driver->owner;
+		if (!try_module_get(owner)) {
 			ret = -EBUSY;
 			goto err;
 		}
+		subdev_fh->owner = owner;
 	}
 #endif
 
@@ -91,9 +92,7 @@ static int subdev_open(struct file *file)
 	return 0;
 
 err:
-#if defined(CONFIG_MEDIA_CONTROLLER)
-	media_entity_put(entity);
-#endif
+	module_put(subdev_fh->owner);
 	v4l2_fh_del(&subdev_fh->vfh);
 	v4l2_fh_exit(&subdev_fh->vfh);
 	subdev_fh_free(subdev_fh);
@@ -111,10 +110,7 @@ static int subdev_close(struct file *file)
 
 	if (sd->internal_ops && sd->internal_ops->close)
 		sd->internal_ops->close(sd, subdev_fh);
-#if defined(CONFIG_MEDIA_CONTROLLER)
-	if (sd->v4l2_dev->mdev)
-		media_entity_put(&sd->entity);
-#endif
+	module_put(subdev_fh->owner);
 	v4l2_fh_del(vfh);
 	v4l2_fh_exit(vfh);
 	subdev_fh_free(subdev_fh);

include/media/media-entity.h

@@ -864,19 +864,6 @@ struct media_link *media_entity_find_link(struct media_pad *source,
  */
 struct media_pad *media_entity_remote_pad(const struct media_pad *pad);
 
-/**
- * media_entity_get - Get a reference to the parent module
- *
- * @entity: The entity
- *
- * Get a reference to the parent media device module.
- *
- * The function will return immediately if @entity is %NULL.
- *
- * Return: returns a pointer to the entity on success or %NULL on failure.
- */
-struct media_entity *media_entity_get(struct media_entity *entity);
-
 /**
  * media_entity_get_fwnode_pad - Get pad number from fwnode
  *
@@ -916,17 +903,6 @@ __must_check int media_graph_walk_init(
  */
 void media_graph_walk_cleanup(struct media_graph *graph);
 
-/**
- * media_entity_put - Release the reference to the parent module
- *
- * @entity: The entity
- *
- * Release the reference count acquired by media_entity_get().
- *
- * The function will return immediately if @entity is %NULL.
- */
-void media_entity_put(struct media_entity *entity);
-
 /**
  * media_graph_walk_start - Start walking the media graph at a
  *	given entity

include/media/v4l2-subdev.h

@@ -910,9 +910,11 @@ struct v4l2_subdev {
  *
  * @vfh: pointer to &struct v4l2_fh
  * @pad: pointer to &struct v4l2_subdev_pad_config
+ * @owner: module pointer to the owner of this file handle
  */
 struct v4l2_subdev_fh {
 	struct v4l2_fh vfh;
+	struct module *owner;
 #if defined(CONFIG_VIDEO_V4L2_SUBDEV_API)
 	struct v4l2_subdev_pad_config *pad;
 #endif