[PATCH v6] drm: Provide a driver hook for drm_dev_release()

[Daniel Vetter]

On Thu, Feb 02, 2017 at 09:36:32AM +0000, Chris Wilson wrote:
> Some state is coupled into the device lifetime outside of the
> load/unload timeframe and requires teardown during final unreference
> from drm_dev_release(). For example, dmabufs hold both a device and
> module reference and may live longer than expected (i.e. the current
> pattern of the driver tearing down its state and then releasing a
> reference to the drm device) and yet touch driver private state when
> destroyed.
> 
> v2: Export drm_dev_fini() and move the responsibility for finalizing the
> drm_device and freeing it to the release callback. (If no callback is
> provided, the core will call drm_dev_fini() and kfree(dev) as before.)
> v3: Remember to add drm_dev_fini() to drm_drv.h
> v4: Tidy language for kerneldoc
> v5: Cross reference from drm_dev_init() to note that driver->release()
> allows for arbitrary embedding.
> v6: Refer to driver data rather than driver state, as state is now
> becoming associated with the struct drm_atomic_state and friends.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  drivers/gpu/drm/drm_drv.c | 65 ++++++++++++++++++++++++++++++++---------------
>  include/drm/drm_drv.h     | 13 ++++++++++
>  2 files changed, 58 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index a8ce3179c07c..e122e4d022f8 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -465,7 +465,10 @@ static void drm_fs_inode_free(struct inode *inode)
>   * that do embed &struct drm_device it must be placed first in the overall
>   * structure, and the overall structure must be allocated using kmalloc(): The
>   * drm core's release function unconditionally calls kfree() on the @dev pointer
> - * when the final reference is released.
> + * when the final reference is released. To override this behaviour, and so
> + * allow embedding of the drm_device inside the driver's device struct at an
> + * arbitrary offset, you must supply a driver->release() callback and control

The new official way to reference a struct member is &foo.bar. I've
applied this polish to both places and applied your patch, thanks a lot.
-Daniel

> + * the finalization explicitly.
>   *
>   * RETURNS:
>   * 0 on success, or error code on failure.
> @@ -553,6 +556,41 @@ int drm_dev_init(struct drm_device *dev,
>  EXPORT_SYMBOL(drm_dev_init);
>  
>  /**
> + * drm_dev_fini - Finalize a dead DRM device
> + * @dev: DRM device
> + *
> + * Finalize a dead DRM device. This is the converse to drm_dev_init() and
> + * frees up all data allocated by it. All driver private data should be
> + * finalized first. Note that this function does not free the @dev, that is
> + * left to the caller.
> + *
> + * The ref-count of @dev must be zero, and drm_dev_fini() should only be called
> + * from a drm_driver->release() callback.
> + */
> +void drm_dev_fini(struct drm_device *dev)
> +{
> +	drm_vblank_cleanup(dev);
> +
> +	if (drm_core_check_feature(dev, DRIVER_GEM))
> +		drm_gem_destroy(dev);
> +
> +	drm_legacy_ctxbitmap_cleanup(dev);
> +	drm_ht_remove(&dev->map_hash);
> +	drm_fs_inode_free(dev->anon_inode);
> +
> +	drm_minor_free(dev, DRM_MINOR_PRIMARY);
> +	drm_minor_free(dev, DRM_MINOR_RENDER);
> +	drm_minor_free(dev, DRM_MINOR_CONTROL);
> +
> +	mutex_destroy(&dev->master_mutex);
> +	mutex_destroy(&dev->ctxlist_mutex);
> +	mutex_destroy(&dev->filelist_mutex);
> +	mutex_destroy(&dev->struct_mutex);
> +	kfree(dev->unique);
> +}
> +EXPORT_SYMBOL(drm_dev_fini);
> +
> +/**
>   * drm_dev_alloc - Allocate new DRM device
>   * @driver: DRM driver to allocate device for
>   * @parent: Parent device object
> @@ -598,25 +636,12 @@ static void drm_dev_release(struct kref *ref)
>  {
>  	struct drm_device *dev = container_of(ref, struct drm_device, ref);
>  
> -	drm_vblank_cleanup(dev);
> -
> -	if (drm_core_check_feature(dev, DRIVER_GEM))
> -		drm_gem_destroy(dev);
> -
> -	drm_legacy_ctxbitmap_cleanup(dev);
> -	drm_ht_remove(&dev->map_hash);
> -	drm_fs_inode_free(dev->anon_inode);
> -
> -	drm_minor_free(dev, DRM_MINOR_PRIMARY);
> -	drm_minor_free(dev, DRM_MINOR_RENDER);
> -	drm_minor_free(dev, DRM_MINOR_CONTROL);
> -
> -	mutex_destroy(&dev->master_mutex);
> -	mutex_destroy(&dev->ctxlist_mutex);
> -	mutex_destroy(&dev->filelist_mutex);
> -	mutex_destroy(&dev->struct_mutex);
> -	kfree(dev->unique);
> -	kfree(dev);
> +	if (dev->driver->release) {
> +		dev->driver->release(dev);
> +	} else {
> +		drm_dev_fini(dev);
> +		kfree(dev);
> +	}
>  }
>  
>  /**
> diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
> index 732e85652d1e..5699f42195fe 100644
> --- a/include/drm/drm_drv.h
> +++ b/include/drm/drm_drv.h
> @@ -102,6 +102,17 @@ struct drm_driver {
>  	 *
>  	 */
>  	void (*unload) (struct drm_device *);
> +
> +	/**
> +	 * @release:
> +	 *
> +	 * Optional callback for destroying device data after the final
> +	 * reference is released, i.e. the device is being destroyed. Drivers
> +	 * using this callback are responsible for calling drm_dev_fini()
> +	 * to finalize the device and then freeing the struct themselves.
> +	 */
> +	void (*release) (struct drm_device *);
> +
>  	int (*set_busid)(struct drm_device *dev, struct drm_master *master);
>  
>  	/**
> @@ -437,6 +448,8 @@ extern unsigned int drm_debug;
>  int drm_dev_init(struct drm_device *dev,
>  		 struct drm_driver *driver,
>  		 struct device *parent);
> +void drm_dev_fini(struct drm_device *dev);
> +
>  struct drm_device *drm_dev_alloc(struct drm_driver *driver,
>  				 struct device *parent);
>  int drm_dev_register(struct drm_device *dev, unsigned long flags);
> -- 
> 2.11.0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch