Re: [Outreachy kernel] [PATCH 1/2] drm: introduce drm_dev_{get/put} functions

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On Fri, Sep 22, 2017 at 01:17:06AM +0530, Aishwarya Pant wrote:
> Reference counting functions in the kernel typically use get/put suffixes. For
> maintaining coding style consistency, introduce drm_dev_{get/put} functions
> and let the old APIs (with ref/unref suffixes) remain for compatibility.
> 
> Signed-off-by: Aishwarya Pant <aishpant@xxxxxxxxx>

Excellent idea to fill this gap, we totally overlooked this in the initial
work!

> ---
>  drivers/gpu/drm/drm_drv.c | 64 +++++++++++++++++++++++++++++++++--------------
>  include/drm/drm_drv.h     |  4 ++-

Please also update scripts/coccinelle/api/drm-get-put.cocci with this new
transformation.

>  2 files changed, 48 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index be38ac7..4592314 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -286,13 +286,13 @@ struct drm_minor *drm_minor_acquire(unsigned int minor_id)
>  	spin_lock_irqsave(&drm_minor_lock, flags);
>  	minor = idr_find(&drm_minors_idr, minor_id);
>  	if (minor)
> -		drm_dev_ref(minor->dev);
> +		drm_dev_get(minor->dev);
>  	spin_unlock_irqrestore(&drm_minor_lock, flags);
>  
>  	if (!minor) {
>  		return ERR_PTR(-ENODEV);
>  	} else if (drm_dev_is_unplugged(minor->dev)) {
> -		drm_dev_unref(minor->dev);
> +		drm_dev_put(minor->dev);
>  		return ERR_PTR(-ENODEV);
>  	}
>  
> @@ -301,7 +301,7 @@ struct drm_minor *drm_minor_acquire(unsigned int minor_id)
>  
>  void drm_minor_release(struct drm_minor *minor)
>  {
> -	drm_dev_unref(minor->dev);
> +	drm_dev_put(minor->dev);
>  }
>  
>  /**
> @@ -326,11 +326,11 @@ void drm_minor_release(struct drm_minor *minor)
>   * When cleaning up a device instance everything needs to be done in reverse:
>   * First unpublish the device instance with drm_dev_unregister(). Then clean up
>   * any other resources allocated at device initialization and drop the driver's
> - * reference to &drm_device using drm_dev_unref().
> + * reference to &drm_device using drm_dev_put().
>   *
>   * Note that the lifetime rules for &drm_device instance has still a lot of
>   * historical baggage. Hence use the reference counting provided by
> - * drm_dev_ref() and drm_dev_unref() only carefully.
> + * drm_dev_get() and drm_dev_put() only carefully.
>   *
>   * It is recommended that drivers embed &struct drm_device into their own device
>   * structure, which is supported through drm_dev_init().
> @@ -345,7 +345,7 @@ void drm_minor_release(struct drm_minor *minor)
>   * Cleans up all DRM device, calling drm_lastclose().
>   *
>   * Note: Use of this function is deprecated. It will eventually go away
> - * completely.  Please use drm_dev_unregister() and drm_dev_unref() explicitly
> + * completely.  Please use drm_dev_unregister() and drm_dev_put() explicitly
>   * instead to make sure that the device isn't userspace accessible any more
>   * while teardown is in progress, ensuring that userspace can't access an
>   * inconsistent state.
> @@ -360,7 +360,7 @@ void drm_put_dev(struct drm_device *dev)
>  	}
>  
>  	drm_dev_unregister(dev);
> -	drm_dev_unref(dev);
> +	drm_dev_put(dev);
>  }
>  EXPORT_SYMBOL(drm_put_dev);
>  
> @@ -386,7 +386,7 @@ void drm_dev_unplug(struct drm_device *dev)
>  	mutex_lock(&drm_global_mutex);
>  	drm_device_set_unplugged(dev);
>  	if (dev->open_count == 0)
> -		drm_dev_unref(dev);
> +		drm_dev_put(dev);
>  	mutex_unlock(&drm_global_mutex);
>  }
>  EXPORT_SYMBOL(drm_dev_unplug);
> @@ -475,8 +475,8 @@ static void drm_fs_inode_free(struct inode *inode)
>   * initialization sequence to make sure userspace can't access an inconsistent
>   * state.
>   *
> - * The initial ref-count of the object is 1. Use drm_dev_ref() and
> - * drm_dev_unref() to take and drop further ref-counts.
> + * The initial ref-count of the object is 1. Use drm_dev_get() and
> + * drm_dev_put() to take and drop further ref-counts.
>   *
>   * Note that for purely virtual devices @parent can be NULL.
>   *
> @@ -626,8 +626,8 @@ EXPORT_SYMBOL(drm_dev_fini);
>   * initialization sequence to make sure userspace can't access an inconsistent
>   * state.
>   *
> - * The initial ref-count of the object is 1. Use drm_dev_ref() and
> - * drm_dev_unref() to take and drop further ref-counts.
> + * The initial ref-count of the object is 1. Use drm_dev_get() and
> + * drm_dev_put() to take and drop further ref-counts.
>   *
>   * Note that for purely virtual devices @parent can be NULL.
>   *
> @@ -670,36 +670,62 @@ static void drm_dev_release(struct kref *ref)
>  }
>  
>  /**
> - * drm_dev_ref - Take reference of a DRM device
> + * drm_dev_get - Take reference of a DRM device
>   * @dev: device to take reference of or NULL
>   *
>   * This increases the ref-count of @dev by one. You *must* already own a
> - * reference when calling this. Use drm_dev_unref() to drop this reference
> + * reference when calling this. Use drm_dev_put() to drop this reference
>   * again.
>   *
>   * This function never fails. However, this function does not provide *any*
>   * guarantee whether the device is alive or running. It only provides a
>   * reference to the object and the memory associated with it.
>   */
> -void drm_dev_ref(struct drm_device *dev)
> +void drm_dev_get(struct drm_device *dev)
>  {
>  	if (dev)
>  		kref_get(&dev->ref);
>  }
> -EXPORT_SYMBOL(drm_dev_ref);
> +EXPORT_SYMBOL(drm_dev_get);
>  
>  /**
> - * drm_dev_unref - Drop reference of a DRM device
> + * drm_dev_put - Drop reference of a DRM device
>   * @dev: device to drop reference of or NULL
>   *
>   * This decreases the ref-count of @dev by one. The device is destroyed if the
>   * ref-count drops to zero.
>   */
> -void drm_dev_unref(struct drm_device *dev)
> +void drm_dev_put(struct drm_device *dev)
>  {
>  	if (dev)
>  		kref_put(&dev->ref, drm_dev_release);
>  }
> +EXPORT_SYMBOL(drm_dev_put);
> +
> +/**
> + * drm_dev_ref - Take reference of a DRM device
> + * @dev: device to take reference of or NULL
> + *
> + * This is a compatibility alias for drm_dev_get() and should not be used by new
> + * code.
> + */
> +void drm_dev_ref(struct drm_device *dev)
> +{
> +	drm_dev_get(dev);
> +}
> +EXPORT_SYMBOL(drm_dev_ref);

I think you've already converted all callers for drm_dev_ref() with this
patch here, so no need to add the compat function and risk getting new
callers. Once a conversion is done in upstream we should remove these.

Please remove.

With those 2 nits addressed I think your patch is ready for merging,
please resend with those changes.

Thanks, Daniel

> +
> +/**
> + * drm_dev_unref - Drop reference of a DRM device
> + * @dev: device to drop reference of or NULL
> + *
> + * This is a compatibility alias for drm_dev_put() and should not be used by new
> + * code.
> + */
> +void drm_dev_unref(struct drm_device *dev)
> +{
> +	drm_dev_put(dev);
> +}
>  EXPORT_SYMBOL(drm_dev_unref);
>  
>  static int create_compat_control_link(struct drm_device *dev)
> @@ -839,7 +865,7 @@ EXPORT_SYMBOL(drm_dev_register);
>   *
>   * Unregister the DRM device from the system. This does the reverse of
>   * drm_dev_register() but does not deallocate the device. The caller must call
> - * drm_dev_unref() to drop their final reference.
> + * drm_dev_put() to drop their final reference.
>   *
>   * A special form of unregistering for hotpluggable devices is drm_dev_unplug(),
>   * which can be called while there are still open users of @dev.
> diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
> index 71bbaae..e574fa0 100644
> --- a/include/drm/drm_drv.h
> +++ b/include/drm/drm_drv.h
> @@ -155,7 +155,7 @@ struct drm_driver {
>  	 * reverse order of the initialization.  Similarly to the load
>  	 * hook, this handler is deprecated and its usage should be
>  	 * dropped in favor of an open-coded teardown function at the
> -	 * driver layer.  See drm_dev_unregister() and drm_dev_unref()
> +	 * driver layer.  See drm_dev_unregister() and drm_dev_put()
>  	 * for the proper way to remove a &struct drm_device.
>  	 *
>  	 * The unload() hook is called right after unregistering
> @@ -611,6 +611,8 @@ struct drm_device *drm_dev_alloc(struct drm_driver *driver,
>  int drm_dev_register(struct drm_device *dev, unsigned long flags);
>  void drm_dev_unregister(struct drm_device *dev);
>  
> +void drm_dev_get(struct drm_device *dev);
> +void drm_dev_put(struct drm_device *dev);
>  void drm_dev_ref(struct drm_device *dev);
>  void drm_dev_unref(struct drm_device *dev);
>  void drm_put_dev(struct drm_device *dev);
> -- 
> 2.7.4
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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