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Date: Mon, 28 Mar 2016 15:28:41 -0300
From: Mauro Carvalho Chehab <mchehab@....samsung.com>
To: Shuah Khan <shuahkh@....samsung.com>
Cc: <laurent.pinchart@...asonboard.com>, <perex@...ex.cz>,
<tiwai@...e.com>, <hans.verkuil@...co.com>,
<chehabrafael@...il.com>, <javier@....samsung.com>,
<jh1009.sung@...sung.com>, <linux-kernel@...r.kernel.org>,
<linux-media@...r.kernel.org>, <alsa-devel@...a-project.org>
Subject: Re: [RFC PATCH 3/4] media: Add refcount to keep track of media
device registrations
Em Fri, 25 Mar 2016 22:38:44 -0600
Shuah Khan <shuahkh@....samsung.com> escreveu:
> Add refcount to keep track of media device registrations to avoid release
> of media device when one of the drivers does unregister when media device
> belongs to more than one driver. Also add a new interfaces to unregister
> a media device allocated using Media Device Allocator and a hold register
> refcount. Change media_open() to get media device reference and put the
> reference in media_release().
>
> Signed-off-by: Shuah Khan <shuahkh@....samsung.com>
> ---
> drivers/media/media-device.c | 53 +++++++++++++++++++++++++++++++++++++++++++
> drivers/media/media-devnode.c | 3 +++
> include/media/media-device.h | 32 ++++++++++++++++++++++++++
> 3 files changed, 88 insertions(+)
>
> diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
> index 93aff4e..3359235 100644
> --- a/drivers/media/media-device.c
> +++ b/drivers/media/media-device.c
> @@ -36,6 +36,7 @@
> #include <media/media-device.h>
> #include <media/media-devnode.h>
> #include <media/media-entity.h>
> +#include <media/media-dev-allocator.h>
>
> #ifdef CONFIG_MEDIA_CONTROLLER
>
> @@ -702,6 +703,7 @@ void media_device_init(struct media_device *mdev)
> INIT_LIST_HEAD(&mdev->entity_notify);
> mutex_init(&mdev->graph_mutex);
> ida_init(&mdev->entity_internal_idx);
> + kref_init(&mdev->refcount);
>
> dev_dbg(mdev->dev, "Media device initialized\n");
> }
> @@ -730,6 +732,13 @@ printk("%s: mdev %p\n", __func__, mdev);
> /* Check if mdev was ever registered at all */
> mutex_lock(&mdev->graph_mutex);
>
> + /* if media device is already registered, bump the register refcount */
> + if (media_devnode_is_registered(&mdev->devnode)) {
> + kref_get(&mdev->refcount);
> + mutex_unlock(&mdev->graph_mutex);
> + return 0;
> + }
> +
> /* Register the device node. */
> mdev->devnode.fops = &media_device_fops;
> mdev->devnode.parent = mdev->dev;
> @@ -756,6 +765,22 @@ err:
> }
> EXPORT_SYMBOL_GPL(__media_device_register);
>
> +void media_device_register_ref(struct media_device *mdev)
> +{
> + if (!mdev)
> + return;
> +
> + pr_info("%s: mdev %p\n", __func__, mdev);
> + mutex_lock(&mdev->graph_mutex);
> +
> + /* Check if mdev is registered - bump registered refcount */
> + if (media_devnode_is_registered(&mdev->devnode))
> + kref_get(&mdev->refcount);
> +
> + mutex_unlock(&mdev->graph_mutex);
> +}
> +EXPORT_SYMBOL_GPL(media_device_register_ref);
> +
> int __must_check media_device_register_entity_notify(struct media_device *mdev,
> struct media_entity_notify *nptr)
> {
> @@ -829,6 +854,34 @@ printk("%s: mdev=%p\n", __func__, mdev);
> }
> EXPORT_SYMBOL_GPL(media_device_unregister);
>
> +static void __media_device_unregister_kref(struct kref *kref)
> +{
> + struct media_device *mdev;
> +
> + mdev = container_of(kref, struct media_device, refcount);
> + __media_device_unregister(mdev);
> +}
> +
> +void media_device_unregister_put(struct media_device *mdev)
> +{
> + int ret;
> +
> + if (mdev == NULL)
> + return;
> +
> + pr_info("%s: mdev=%p\n", __func__, mdev);
> + ret = kref_put_mutex(&mdev->refcount, __media_device_unregister_kref,
> + &mdev->graph_mutex);
> + if (ret) {
> + /* __media_device_unregister() ran */
> + __media_device_cleanup(mdev);
> + mutex_unlock(&mdev->graph_mutex);
> + mutex_destroy(&mdev->graph_mutex);
> + media_device_set_to_delete_state(mdev->dev);
Where you're freeing the media_dev (or its container struct)?
You need to be sure that it will be freed only here.
> + }
> +}
> +EXPORT_SYMBOL_GPL(media_device_unregister_put);
> +
> static void media_device_release_devres(struct device *dev, void *res)
> {
> }
> diff --git a/drivers/media/media-devnode.c b/drivers/media/media-devnode.c
> index 29409f4..d1d1263 100644
> --- a/drivers/media/media-devnode.c
> +++ b/drivers/media/media-devnode.c
> @@ -44,6 +44,7 @@
> #include <linux/uaccess.h>
>
> #include <media/media-devnode.h>
> +#include <media/media-dev-allocator.h>
>
> #define MEDIA_NUM_DEVICES 256
> #define MEDIA_NAME "media"
> @@ -186,6 +187,7 @@ static int media_open(struct inode *inode, struct file *filp)
> }
> }
>
> + media_device_get_ref(mdev->parent);
> return 0;
> }
>
> @@ -201,6 +203,7 @@ static int media_release(struct inode *inode, struct file *filp)
> return value is ignored. */
> put_device(&mdev->dev);
> filp->private_data = NULL;
> + media_device_put(mdev->parent);
> return 0;
> }
>
> diff --git a/include/media/media-device.h b/include/media/media-device.h
> index e59772e..64114ae 100644
> --- a/include/media/media-device.h
> +++ b/include/media/media-device.h
> @@ -284,6 +284,8 @@ struct media_entity_notify {
> * struct media_device - Media device
> * @dev: Parent device
> * @devnode: Media device node
> + * @refcount: Media device register reference count. Used when more
> + * than one driver owns the device.
> * @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
> @@ -348,6 +350,7 @@ struct media_device {
> /* dev->driver_data points to this struct. */
> struct device *dev;
> struct media_devnode devnode;
> + struct kref refcount;
You can't simply embed a kref at media_device. The problem is that
several conditions should be met for this approach to work:
1) The structs that have struct media_device should not have a kref
their own (I guess that's the current case, but it should be documented
somewhere);
2) the struct that embeds it can only be destroyed when kref refcount
reaches zero. That actually means that the core should either allocate
the struct itself or that a release callback for those structs should
do the kfree(). It means that all drivers should be changed for it to
happen.
Also, if you're adding a kref here, you likely should not have a kref
at struct media_device_instance(), as there's no need for two kref
destroy logic.
>
> char model[32];
> char driver_name[32];
> @@ -501,6 +504,17 @@ int __must_check __media_device_register(struct media_device *mdev,
> #define media_device_register(mdev) __media_device_register(mdev, THIS_MODULE)
>
> /**
> + * media_device_register_ref() - Increments media device register refcount
> + *
> + * @mdev: pointer to struct &media_device
> + *
> + * When more than one driver is associated with the media device, it is
> + * necessary to refcount the number of registrations to avoid unregister
> + * when it is still in use.
> + */
> +void media_device_register_ref(struct media_device *mdev);
> +
> +/**
> * media_device_unregister() - Unregisters a media device element
> *
> * @mdev: pointer to struct &media_device
> @@ -512,6 +526,18 @@ int __must_check __media_device_register(struct media_device *mdev,
> void media_device_unregister(struct media_device *mdev);
>
> /**
> + * media_device_unregister_put() - Unregisters a media device element
> + *
> + * @mdev: pointer to struct &media_device
> + *
> + * Should be called to unregister media device allocated with Media Device
> + * Allocator API media_device_get() interface.
> + * It is safe to call this function on an unregistered (but initialised)
> + * media device.
> + */
> +void media_device_unregister_put(struct media_device *mdev);
> +
> +/**
> * media_device_register_entity() - registers a media entity inside a
> * previously registered media device.
> *
> @@ -681,9 +707,15 @@ static inline int media_device_register(struct media_device *mdev)
> {
> return 0;
> }
> +static inline void media_device_register_ref(struct media_device *mdev)
> +{
> +}
> static inline void media_device_unregister(struct media_device *mdev)
> {
> }
> +static inline void media_device_unregister_put(struct media_device *mdev)
> +{
> +}
> static inline int media_device_register_entity(struct media_device *mdev,
> struct media_entity *entity)
> {
--
Thanks,
Mauro
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