[Intel-gfx] [PATCH 12/14] drm: Move master pointer from drm_minor to drm_device

[Chris Wilson]

On Tue, Jun 14, 2016 at 08:51:07PM +0200, Daniel Vetter wrote:
> There can only be one current master, and it's for the overall device.
> Render/control minors don't support master-based auth at all.
> 
> This simplifies the master logic a lot, at least in my eyes: All these
> additional pointer chases are just confusing.

One master for the device, on the struct drm_device, as opposed to hidden
behind the first of three minors, makes sense.

> @@ -128,13 +128,13 @@ static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv)
>  	lockdep_assert_held_once(&dev->master_mutex);
>  
>  	/* create a new master */
> -	fpriv->minor->master = drm_master_create(fpriv->minor->dev);
> -	if (!fpriv->minor->master)
> +	dev->master = drm_master_create(dev);
> +	if (!dev->master)
>  		return -ENOMEM;
>  
>  	/* take another reference for the copy in the local file priv */
>  	old_master = fpriv->master;
> -	fpriv->master = drm_master_get(fpriv->minor->master);
> +	fpriv->master = drm_master_get(dev->master);
>  
>  	if (dev->driver->master_create) {
>  		ret = dev->driver->master_create(dev, fpriv->master);

> @@ -234,10 +234,10 @@ int drm_master_open(struct drm_file *file_priv)
>  	/* if there is no current master make this fd it, but do not create
>  	 * any master object for render clients */
>  	mutex_lock(&dev->master_mutex);
> -	if (!file_priv->minor->master)
> +	if (!dev->master)
>  		ret = drm_new_set_master(dev, file_priv);
>  	else
> -		file_priv->master = drm_master_get(file_priv->minor->master);
> +		file_priv->master = drm_master_get(dev->master);
>  	mutex_unlock(&dev->master_mutex);

You could take the opportunity to make this a bit simpler:

	if (!READ_ONCE(dev->master)) {
		int ret;

		ret = 0;
		mutex_lock(&dev->master_mutex);
		if (!dev->master)
			ret = drm_new_master(dev);
		mutex_unlock(&dev->master_mutex);
		if (ret)
			return ret;
	}

	file_priv->master = drm_master_get(dev->master);
	return 0;

Just to straighten out the kref dance.

>  
>  	return ret;
> @@ -271,11 +271,11 @@ void drm_master_release(struct drm_file *file_priv)
>  		mutex_unlock(&dev->struct_mutex);
>  	}
>  
> -	if (file_priv->minor->master == file_priv->master) {
> +	if (dev->master == file_priv->master) {
>  		/* drop the reference held my the minor */
>  		if (dev->driver->master_drop)
>  			dev->driver->master_drop(dev, file_priv, true);
> -		drm_master_put(&file_priv->minor->master);
> +		drm_master_put(&dev->master);

This still makes me uneasy. This is not equivalent to dropmaster_ioctl
and subsequent setmaster_ioctl will fail as dev->master is still
assigned (but the owner has gone).
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre