[PATCH] drm: drm_auth: Convert mutex usage to guard(mutex)

[Thomas Zimmermann]

Hi

Am 09.05.25 um 16:26 schrieb André Almeida:
> Replace open-coded mutex handling with cleanup.h guard(mutex). This
> simplifies the code and removes the "goto unlock" pattern.
>
> Tested with igt tests core_auth and core_setmaster.
>
> Signed-off-by: André Almeida <andrealmeid at igalia.com>

Reviewed-by: Thomas Zimmermann <tzimmermann at suse.de>

but with questions below

> ---
>
> For more information about guard(mutex):
> https://www.kernel.org/doc/html/latest/core-api/cleanup.html

This page lists issues with guards, so conversion from manual locking 
should be decided on a case-by-case base IMHO.

> ---
>   drivers/gpu/drm/drm_auth.c | 64 ++++++++++++++------------------------
>   1 file changed, 23 insertions(+), 41 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
> index 22aa015df387..d6bf605b4b90 100644
> --- a/drivers/gpu/drm/drm_auth.c
> +++ b/drivers/gpu/drm/drm_auth.c
> @@ -95,7 +95,7 @@ int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv)
>   	struct drm_auth *auth = data;
>   	int ret = 0;
>   
> -	mutex_lock(&dev->master_mutex);
> +	guard(mutex)(&dev->master_mutex);

These guard statements are hidden variable declarations. Shouldn't they 
rather go to the function top with the other declarations? This would 
also help to prevent the problem listed in cleanup.html to some extend.

Best regards
Thomas

>   	if (!file_priv->magic) {
>   		ret = idr_alloc(&file_priv->master->magic_map, file_priv,
>   				1, 0, GFP_KERNEL);
> @@ -103,7 +103,6 @@ int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv)
>   			file_priv->magic = ret;
>   	}
>   	auth->magic = file_priv->magic;
> -	mutex_unlock(&dev->master_mutex);
>   
>   	drm_dbg_core(dev, "%u\n", auth->magic);
>   
> @@ -118,13 +117,12 @@ int drm_authmagic(struct drm_device *dev, void *data,
>   
>   	drm_dbg_core(dev, "%u\n", auth->magic);
>   
> -	mutex_lock(&dev->master_mutex);
> +	guard(mutex)(&dev->master_mutex);
>   	file = idr_find(&file_priv->master->magic_map, auth->magic);
>   	if (file) {
>   		file->authenticated = 1;
>   		idr_replace(&file_priv->master->magic_map, NULL, auth->magic);
>   	}
> -	mutex_unlock(&dev->master_mutex);
>   
>   	return file ? 0 : -EINVAL;
>   }
> @@ -248,41 +246,33 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data,
>   {
>   	int ret;
>   
> -	mutex_lock(&dev->master_mutex);
> +	guard(mutex)(&dev->master_mutex);
>   
>   	ret = drm_master_check_perm(dev, file_priv);
>   	if (ret)
> -		goto out_unlock;
> +		return ret;
>   
>   	if (drm_is_current_master_locked(file_priv))
> -		goto out_unlock;
> +		return ret;
>   
> -	if (dev->master) {
> -		ret = -EBUSY;
> -		goto out_unlock;
> -	}
> +	if (dev->master)
> +		return -EBUSY;
>   
> -	if (!file_priv->master) {
> -		ret = -EINVAL;
> -		goto out_unlock;
> -	}
> +	if (!file_priv->master)
> +		return -EINVAL;
>   
> -	if (!file_priv->is_master) {
> -		ret = drm_new_set_master(dev, file_priv);
> -		goto out_unlock;
> -	}
> +	if (!file_priv->is_master)
> +		return drm_new_set_master(dev, file_priv);
>   
>   	if (file_priv->master->lessor != NULL) {
>   		drm_dbg_lease(dev,
>   			      "Attempt to set lessee %d as master\n",
>   			      file_priv->master->lessee_id);
> -		ret = -EINVAL;
> -		goto out_unlock;
> +		return -EINVAL;
>   	}
>   
>   	drm_set_master(dev, file_priv, false);
> -out_unlock:
> -	mutex_unlock(&dev->master_mutex);
> +
>   	return ret;
>   }
>   
> @@ -299,33 +289,27 @@ int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
>   {
>   	int ret;
>   
> -	mutex_lock(&dev->master_mutex);
> +	guard(mutex)(&dev->master_mutex);
>   
>   	ret = drm_master_check_perm(dev, file_priv);
>   	if (ret)
> -		goto out_unlock;
> +		return ret;
>   
> -	if (!drm_is_current_master_locked(file_priv)) {
> -		ret = -EINVAL;
> -		goto out_unlock;
> -	}
> +	if (!drm_is_current_master_locked(file_priv))
> +		return -EINVAL;
>   
> -	if (!dev->master) {
> -		ret = -EINVAL;
> -		goto out_unlock;
> -	}
> +	if (!dev->master)
> +		return -EINVAL;
>   
>   	if (file_priv->master->lessor != NULL) {
>   		drm_dbg_lease(dev,
>   			      "Attempt to drop lessee %d as master\n",
>   			      file_priv->master->lessee_id);
> -		ret = -EINVAL;
> -		goto out_unlock;
> +		return -EINVAL;
>   	}
>   
>   	drm_drop_master(dev, file_priv);
> -out_unlock:
> -	mutex_unlock(&dev->master_mutex);
> +
>   	return ret;
>   }
>   
> @@ -337,7 +321,7 @@ 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);
> +	guard(mutex)(&dev->master_mutex);
>   	if (!dev->master) {
>   		ret = drm_new_set_master(dev, file_priv);
>   	} else {
> @@ -345,7 +329,6 @@ int drm_master_open(struct drm_file *file_priv)
>   		file_priv->master = drm_master_get(dev->master);
>   		spin_unlock(&file_priv->master_lookup_lock);
>   	}
> -	mutex_unlock(&dev->master_mutex);
>   
>   	return ret;
>   }
> @@ -355,7 +338,7 @@ void drm_master_release(struct drm_file *file_priv)
>   	struct drm_device *dev = file_priv->minor->dev;
>   	struct drm_master *master;
>   
> -	mutex_lock(&dev->master_mutex);
> +	guard(mutex)(&dev->master_mutex);
>   	master = file_priv->master;
>   	if (file_priv->magic)
>   		idr_remove(&file_priv->master->magic_map, file_priv->magic);
> @@ -376,7 +359,6 @@ void drm_master_release(struct drm_file *file_priv)
>   	/* drop the master reference held by the file priv */
>   	if (file_priv->master)
>   		drm_master_put(&file_priv->master);
> -	mutex_unlock(&dev->master_mutex);
>   }
>   
>   /**

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)