[PATCH v6 1/7] drm/client: Do not acquire module reference

[Thomas Zimmermann]

Am 02.11.23 um 14:08 schrieb Thomas Zimmermann:
> Do not acquire a reference on the module that provides a client's
> callback functions in drm_client_init(). The additional reference
> prevents the user from unloading the callback functions' module and
> thus creating dangling pointers.
> 
> This is only necessary if there is no direct dependency between the
> caller of drm_client_init() and the provider of the callbacks in
> struct drm_client_funcs. If this case ever existed, it has been
> removed from the DRM code. Callers of drm_client_init() also provide
> the callback implementation. The lifetime of the clients is tied to
> the dependency chain's outer-most module, which is the hardware's
> DRM driver. Before client helpers could be unloaded, the driver module
> would have to be unloaded, which also unregisters all clients.
> 
> Driver modules that set up DRM clients can now be unloaded.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> Acked-by: Javier Martinez Canillas <javierm at redhat.com>

I've added this patch to drm-misc-next.

> ---
>   drivers/gpu/drm/drm_client.c | 12 +-----------
>   1 file changed, 1 insertion(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_client.c b/drivers/gpu/drm/drm_client.c
> index c3027115d0552..9403b3f576f7b 100644
> --- a/drivers/gpu/drm/drm_client.c
> +++ b/drivers/gpu/drm/drm_client.c
> @@ -5,7 +5,6 @@
>   
>   #include <linux/iosys-map.h>
>   #include <linux/list.h>
> -#include <linux/module.h>
>   #include <linux/mutex.h>
>   #include <linux/seq_file.h>
>   #include <linux/slab.h>
> @@ -84,16 +83,13 @@ int drm_client_init(struct drm_device *dev, struct drm_client_dev *client,
>   	if (!drm_core_check_feature(dev, DRIVER_MODESET) || !dev->driver->dumb_create)
>   		return -EOPNOTSUPP;
>   
> -	if (funcs && !try_module_get(funcs->owner))
> -		return -ENODEV;
> -
>   	client->dev = dev;
>   	client->name = name;
>   	client->funcs = funcs;
>   
>   	ret = drm_client_modeset_create(client);
>   	if (ret)
> -		goto err_put_module;
> +		return ret;
>   
>   	ret = drm_client_open(client);
>   	if (ret)
> @@ -105,10 +101,6 @@ int drm_client_init(struct drm_device *dev, struct drm_client_dev *client,
>   
>   err_free:
>   	drm_client_modeset_free(client);
> -err_put_module:
> -	if (funcs)
> -		module_put(funcs->owner);
> -
>   	return ret;
>   }
>   EXPORT_SYMBOL(drm_client_init);
> @@ -177,8 +169,6 @@ void drm_client_release(struct drm_client_dev *client)
>   	drm_client_modeset_free(client);
>   	drm_client_close(client);
>   	drm_dev_put(dev);
> -	if (client->funcs)
> -		module_put(client->funcs->owner);
>   }
>   EXPORT_SYMBOL(drm_client_release);
>   

-- 
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)
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