Re: [PATCH 4/5] [media] media-device: use kref for media_device instance

[Shuah Khan <shuahkh@osg.samsung.com>]

On 03/16/2016 06:04 AM, Mauro Carvalho Chehab wrote:
> Now that the media_device can be used by multiple drivers,
> via devres, we need to be sure that it will be dropped only
> when all drivers stop using it.
> 
> Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

Tested bind_unbind au0828 loop 1000 times, followed by bind_unbind
snd_usb_audio loop 1000 times. Didn't see any lock warnings on a
KASAN enabled kernel (lock testing enabled). No use-after-free errors
during these runs.

Ran device removal test and rmmod and modprobe tests on both drivers.

Generated graph after the runs and the graph looks good.

Reviewed-by: Shuah Khan <shuahkh@osg.samsung.com>
Tested-by: Shuah Khan <shuahkh@osg.samsung.com>

thanks,
-- Shuah

> ---
>  drivers/media/media-device.c | 48 +++++++++++++++++++++++++++++++-------------
>  include/media/media-device.h |  3 +++
>  2 files changed, 37 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
> index c32fa15cc76e..38e6c319fe6e 100644
> --- a/drivers/media/media-device.c
> +++ b/drivers/media/media-device.c
> @@ -721,6 +721,15 @@ int __must_check __media_device_register(struct media_device *mdev,
>  {
>  	int ret;
>  
> +	/* Check if mdev was ever registered at all */
> +	mutex_lock(&mdev->graph_mutex);
> +	if (media_devnode_is_registered(&mdev->devnode)) {
> +		kref_get(&mdev->kref);
> +		mutex_unlock(&mdev->graph_mutex);
> +		return 0;
> +	}
> +	kref_init(&mdev->kref);
> +
>  	/* Register the device node. */
>  	mdev->devnode.fops = &media_device_fops;
>  	mdev->devnode.parent = mdev->dev;
> @@ -730,8 +739,10 @@ int __must_check __media_device_register(struct media_device *mdev,
>  	mdev->topology_version = 0;
>  
>  	ret = media_devnode_register(&mdev->devnode, owner);
> -	if (ret < 0)
> +	if (ret < 0) {
> +		media_devnode_unregister(&mdev->devnode);
>  		return ret;
> +	}
>  
>  	ret = device_create_file(&mdev->devnode.dev, &dev_attr_model);
>  	if (ret < 0) {
> @@ -739,6 +750,7 @@ int __must_check __media_device_register(struct media_device *mdev,
>  		return ret;
>  	}
>  
> +	mutex_unlock(&mdev->graph_mutex);
>  	dev_dbg(mdev->dev, "Media device registered\n");
>  
>  	return 0;
> @@ -773,23 +785,15 @@ void media_device_unregister_entity_notify(struct media_device *mdev,
>  }
>  EXPORT_SYMBOL_GPL(media_device_unregister_entity_notify);
>  
> -void media_device_unregister(struct media_device *mdev)
> +static void do_media_device_unregister(struct kref *kref)
>  {
> +	struct media_device *mdev;
>  	struct media_entity *entity;
>  	struct media_entity *next;
>  	struct media_interface *intf, *tmp_intf;
>  	struct media_entity_notify *notify, *nextp;
>  
> -	if (mdev == NULL)
> -		return;
> -
> -	mutex_lock(&mdev->graph_mutex);
> -
> -	/* Check if mdev was ever registered at all */
> -	if (!media_devnode_is_registered(&mdev->devnode)) {
> -		mutex_unlock(&mdev->graph_mutex);
> -		return;
> -	}
> +	mdev = container_of(kref, struct media_device, kref);
>  
>  	/* Remove all entities from the media device */
>  	list_for_each_entry_safe(entity, next, &mdev->entities, graph_obj.list)
> @@ -807,13 +811,26 @@ void media_device_unregister(struct media_device *mdev)
>  		kfree(intf);
>  	}
>  
> -	mutex_unlock(&mdev->graph_mutex);
> +	/* Check if mdev devnode was registered */
> +	if (!media_devnode_is_registered(&mdev->devnode))
> +		return;
>  
>  	device_remove_file(&mdev->devnode.dev, &dev_attr_model);
>  	media_devnode_unregister(&mdev->devnode);
>  
>  	dev_dbg(mdev->dev, "Media device unregistered\n");
>  }
> +
> +void media_device_unregister(struct media_device *mdev)
> +{
> +	if (mdev == NULL)
> +		return;
> +
> +	mutex_lock(&mdev->graph_mutex);
> +	kref_put(&mdev->kref, do_media_device_unregister);
> +	mutex_unlock(&mdev->graph_mutex);
> +
> +}
>  EXPORT_SYMBOL_GPL(media_device_unregister);
>  
>  static void media_device_release_devres(struct device *dev, void *res)
> @@ -825,13 +842,16 @@ struct media_device *media_device_get_devres(struct device *dev)
>  	struct media_device *mdev;
>  
>  	mdev = devres_find(dev, media_device_release_devres, NULL, NULL);
> -	if (mdev)
> +	if (mdev) {
> +		kref_get(&mdev->kref);
>  		return mdev;
> +	}
>  
>  	mdev = devres_alloc(media_device_release_devres,
>  				sizeof(struct media_device), GFP_KERNEL);
>  	if (!mdev)
>  		return NULL;
> +
>  	return devres_get(dev, mdev, NULL, NULL);
>  }
>  EXPORT_SYMBOL_GPL(media_device_get_devres);
> diff --git a/include/media/media-device.h b/include/media/media-device.h
> index ca3871b853ba..73c16e6e6b6b 100644
> --- a/include/media/media-device.h
> +++ b/include/media/media-device.h
> @@ -23,6 +23,7 @@
>  #ifndef _MEDIA_DEVICE_H
>  #define _MEDIA_DEVICE_H
>  
> +#include <linux/kref.h>
>  #include <linux/list.h>
>  #include <linux/mutex.h>
>  
> @@ -283,6 +284,7 @@ struct media_entity_notify {
>   * struct media_device - Media device
>   * @dev:	Parent device
>   * @devnode:	Media device node
> + * @kref:	Object refcount
>   * @driver_name: Optional device driver name. If not set, calls to
>   *		%MEDIA_IOC_DEVICE_INFO will return dev->driver->name.
>   *		This is needed for USB drivers for example, as otherwise
> @@ -347,6 +349,7 @@ struct media_device {
>  	/* dev->driver_data points to this struct. */
>  	struct device *dev;
>  	struct media_devnode devnode;
> +	struct kref kref;
>  
>  	char model[32];
>  	char driver_name[32];
> 


-- 
Shuah Khan
Sr. Linux Kernel Developer
Open Source Innovation Group
Samsung Research America (Silicon Valley)
shuahkh@osg.samsung.com | (970) 217-8978