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

[Mauro Carvalho Chehab <mchehab@osg.samsung.com>]

Em Wed, 16 Mar 2016 08:05:15 -0600
Shuah Khan <shuahkh@osg.samsung.com> escreveu:

> 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>
> > ---
> >  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 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);  
> 
> Patch looks good.
> 
> Reviewed-by: Shuah Khan <shuahkh@osg.samsung.com>
> 
> Please see a few comments below that aren't related to this patch.
> 
> The above is unprotected and could be done twice when two drivers
> call media_device_unregister(). I think we still mark the media
> device unregistered in media_devnode_unregister(). We have to
> protect these two steps still.
> 
> I attempted to do this with a unregister in progress flag which
> gets set at the beginning in media_device_unregister(). That
> does ensure media_device_unregister() runs only once. If that
> approach isn't desirable, we have to find another way.

Do you mean do_media_device_unregister()? This is protected, as
this function is only called via media_device_unregister(),
with the mutex hold. I opted to take the mutex there, as
it makes the return code simpler.

> 
> -- Shuah
> >  
> >  	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];
> >   
> 
> 


-- 
Thanks,
Mauro