Em Thu, 28 Jan 2016 10:04:24 -0700
Shuah Khan <shuahkh@xxxxxxxxxxxxxxx> escreveu:
> 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().
I guess the call to:
device_remove_file(&mdev->devnode.dev, &dev_attr_model);
IMO, This should be, instead, at media_devnode_unregister().
Then, we can change the logic at media_devnode_unregister() to:
void media_devnode_unregister(struct media_devnode *mdev)
{
mutex_lock(&media_devnode_lock);
/* Check if mdev was ever registered at all */
if (!media_devnode_is_registered(mdev)) {
mutex_unlock(&media_devnode_lock);
return;
}
clear_bit(MEDIA_FLAG_REGISTERED, &mdev->flags);
mutex_unlock(&media_devnode_lock);
device_remove_file(&mdev->devnode.dev, &dev_attr_model);
device_unregister(&mdev->dev);
}
This sounds enough to avoid device_unregister() or device_remove_file()
to be called twice.
>
>
> >>
> >> 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
>
>
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