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
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