Re: [PATCH 29/31] media: track media device unregister in progress

[Shuah Khan]

On 01/28/2016 10:01 AM, Mauro Carvalho Chehab wrote:
> Em Wed,  6 Jan 2016 13:27:18 -0700
> Shuah Khan <shuahkh@xxxxxxxxxxxxxxx> escreveu:
> 
>> Add support to track media device unregister in progress
>> state to prevent more than one driver entering unregister.
>> This enables fixing the general protection faults while
>> snd-usb-audio was cleaning up media resources for pcm
>> streams and mixers. In this patch a new interface is added
>> to return the unregister in progress state. Subsequent
>> patches to snd-usb-audio and au0828-core use this interface
>> to avoid entering unregister and attempting to unregister
>> entities and remove devnodes while unregister is in progress.
>> Media device unregister removes entities and interface nodes.
> 
> Hmm... isn't the spinlock enough to serialize it? It seems weird the
> need of an extra bool here to warrant that this is really serialized.
> 

The spinlock and check for media_devnode_is_registered(&mdev->devnode)
aren't enough to ensure only one driver enters the unregister. Please
note that the devnode isn't marked unregistered until the end in
media_device_unregister().


>>
>> Signed-off-by: Shuah Khan <shuahkh@xxxxxxxxxxxxxxx>
>> ---
>>  drivers/media/media-device.c |  5 ++++-
>>  include/media/media-device.h | 17 +++++++++++++++++
>>  2 files changed, 21 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
>> index 20c85a9..1bb9a5f 100644
>> --- a/drivers/media/media-device.c
>> +++ b/drivers/media/media-device.c
>> @@ -749,10 +749,13 @@ void media_device_unregister(struct media_device *mdev)
>>  	spin_lock(&mdev->lock);
>>  
>>  	/* Check if mdev was ever registered at all */
>> -	if (!media_devnode_is_registered(&mdev->devnode)) {
>> +	/* check if unregister is in progress */
>> +	if (!media_devnode_is_registered(&mdev->devnode) ||
>> +	    mdev->unregister_in_progress) {
>>  		spin_unlock(&mdev->lock);
>>  		return;
>>  	}
>> +	mdev->unregister_in_progress = true;
>>  
>>  	/* Remove all entities from the media device */
>>  	list_for_each_entry_safe(entity, next, &mdev->entities, graph_obj.list)
>> diff --git a/include/media/media-device.h b/include/media/media-device.h
>> index 04b6c2e..0807292 100644
>> --- a/include/media/media-device.h
>> +++ b/include/media/media-device.h
>> @@ -332,6 +332,10 @@ struct media_device {
>>  	spinlock_t lock;
>>  	/* Serializes graph operations. */
>>  	struct mutex graph_mutex;
>> +	/* Tracks unregister in progress state to prevent
>> +	 * more than one driver entering unregister
>> +	*/
>> +	bool unregister_in_progress;
>>  
>>  	/* Handlers to find source entity for the sink entity and
>>  	 * check if it is available, and activate the link using
>> @@ -365,6 +369,7 @@ struct media_device {
>>  /* media_devnode to media_device */
>>  #define to_media_device(node) container_of(node, struct media_device, devnode)
>>  
>> +
>>  /**
>>   * media_entity_enum_init - Initialise an entity enumeration
>>   *
>> @@ -553,6 +558,12 @@ struct media_device *media_device_get_devres(struct device *dev);
>>   * @dev: pointer to struct &device.
>>   */
>>  struct media_device *media_device_find_devres(struct device *dev);
>> +/* return unregister in progress state */
>> +static inline bool media_device_is_unregister_in_progress(
>> +					struct media_device *mdev)
>> +{
>> +	return mdev->unregister_in_progress;
>> +}
>>  
>>  /* Iterate over all entities. */
>>  #define media_device_for_each_entity(entity, mdev)			\
>> @@ -569,6 +580,7 @@ struct media_device *media_device_find_devres(struct device *dev);
>>  /* Iterate over all links. */
>>  #define media_device_for_each_link(link, mdev)			\
>>  	list_for_each_entry(link, &(mdev)->links, graph_obj.list)
>> +
>>  #else
>>  static inline int media_device_register(struct media_device *mdev)
>>  {
>> @@ -604,5 +616,10 @@ static inline struct media_device *media_device_find_devres(struct device *dev)
>>  {
>>  	return NULL;
>>  }
>> +static inline bool media_device_is_unregister_in_progress(
>> +					struct media_device *mdev)
>> +{
>> +	return false;
>> +}
>>  #endif /* CONFIG_MEDIA_CONTROLLER */
>>  #endif


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