Re: [PATCH 21/51] drm: Use drmm_ for drm_dev_init cleanup

[Sam Ravnborg <sam@ravnborg.org>]

Hi Daniel.

On Mon, Mar 23, 2020 at 03:49:20PM +0100, Daniel Vetter wrote:
> Well for the simple stuff at least, vblank, gem and minor cleanup I
> want to further split up as a demonstration.
> 
> v2: We need to clear drm_device->dev otherwise the debug drm printing
> after our cleanup hook (e.g. in drm_manged_release) will chase
> released memory and result in a use-after-free. Not really pretty, but
> oh well.
> 
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  drivers/gpu/drm/drm_drv.c | 48 ++++++++++++++++++++-------------------
>  1 file changed, 25 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index c80ebc6811b1..a710c53d13a8 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -580,6 +580,23 @@ static void drm_fs_inode_free(struct inode *inode)
>   *    used.
>   */
>  
> +static void drm_dev_init_release(struct drm_device *dev, void *res)
> +{
> +	drm_legacy_ctxbitmap_cleanup(dev);
> +	drm_legacy_remove_map_hash(dev);
> +	drm_fs_inode_free(dev->anon_inode);
> +
> +	put_device(dev->dev);
> +	/* Prevent use-after-free in drm_managed_release when debugging is
> +	 * enabled. Slightly awkward, but can't really be helped. */
> +	dev->dev = NULL;
> +	mutex_destroy(&dev->master_mutex);
> +	mutex_destroy(&dev->clientlist_mutex);
> +	mutex_destroy(&dev->filelist_mutex);
> +	mutex_destroy(&dev->struct_mutex);
> +	drm_legacy_destroy_members(dev);
> +}
> +
>  /**
>   * drm_dev_init - Initialise new DRM device
>   * @dev: DRM device
> @@ -647,11 +664,15 @@ int drm_dev_init(struct drm_device *dev,
>  	mutex_init(&dev->clientlist_mutex);
>  	mutex_init(&dev->master_mutex);
>  
> +	ret = drmm_add_action(dev, drm_dev_init_release, NULL);
> +	if (ret)
> +		return ret;
> +
>  	dev->anon_inode = drm_fs_inode_new();
>  	if (IS_ERR(dev->anon_inode)) {
>  		ret = PTR_ERR(dev->anon_inode);
>  		DRM_ERROR("Cannot allocate anonymous inode: %d\n", ret);
> -		goto err_free;
> +		goto err;
>  	}
>  
>  	if (drm_core_check_feature(dev, DRIVER_RENDER)) {
> @@ -688,19 +709,12 @@ int drm_dev_init(struct drm_device *dev,
>  	if (drm_core_check_feature(dev, DRIVER_GEM))
>  		drm_gem_destroy(dev);
>  err_ctxbitmap:
> -	drm_legacy_ctxbitmap_cleanup(dev);
> -	drm_legacy_remove_map_hash(dev);
>  err_minors:
>  	drm_minor_free(dev, DRM_MINOR_PRIMARY);
>  	drm_minor_free(dev, DRM_MINOR_RENDER);
> -	drm_fs_inode_free(dev->anon_inode);
> -err_free:
> -	put_device(dev->dev);
> -	mutex_destroy(&dev->master_mutex);
> -	mutex_destroy(&dev->clientlist_mutex);
> -	mutex_destroy(&dev->filelist_mutex);
> -	mutex_destroy(&dev->struct_mutex);
> -	drm_legacy_destroy_members(dev);
> +err:
> +	drm_managed_release(dev);
If for example drmm_add_action() fails this will call the following
functions without their init parts called:

    drm_legacy_ctxbitmap_cleanup(dev);

        This function do:
	    mutex_lock(&dev->struct_mutex);
            idr_destroy(&dev->ctx_idr);
            mutex_unlock(&dev->struct_mutex);
        Use of struct_mutex - OK
	Call to idr_destroy() - I could not convince myself this was OK.
	But I did not look too deep into idr_destroy() - thsi is unknown
	land for me.

    drm_legacy_remove_map_hash(dev);

        This function do:
	    drm_ht_remove(&dev->map_hash); =>
	        if ((&dev->map_hash)->table) {

        ->table is NULL is init fucntion is not called - OK


    drm_fs_inode_free(dev->anon_inode);

      NOP if anon_inode is NULL - OK

So if idr_destroy() call is OK then error handling looks OK
and the patch is:
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>

The error handling is even nicer later in this series.
But I looked only at this patch for now.

	Sam



> +
>  	return ret;
>  }
>  EXPORT_SYMBOL(drm_dev_init);
> @@ -763,20 +777,8 @@ void drm_dev_fini(struct drm_device *dev)
>  	if (drm_core_check_feature(dev, DRIVER_GEM))
>  		drm_gem_destroy(dev);
>  
> -	drm_legacy_ctxbitmap_cleanup(dev);
> -	drm_legacy_remove_map_hash(dev);
> -	drm_fs_inode_free(dev->anon_inode);
> -
>  	drm_minor_free(dev, DRM_MINOR_PRIMARY);
>  	drm_minor_free(dev, DRM_MINOR_RENDER);
> -
> -	put_device(dev->dev);
> -
> -	mutex_destroy(&dev->master_mutex);
> -	mutex_destroy(&dev->clientlist_mutex);
> -	mutex_destroy(&dev->filelist_mutex);
> -	mutex_destroy(&dev->struct_mutex);
> -	drm_legacy_destroy_members(dev);
>  }
>  EXPORT_SYMBOL(drm_dev_fini);
>  
> -- 
> 2.25.1
> 
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