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

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

On 03/22/2016 01:56 PM, Shuah Khan wrote:
> 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>
> 

Acked the wrong patch. Sorry. Will ack the v2 which is the one I tested.

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