[PATCH 7/8] drm/vmwgfx: Add comments about drm_file.object_idr issues

[Simona Vetter]

On Wed, May 28, 2025 at 11:13:05AM +0200, Simona Vetter wrote:
> idr_for_each_entry() is fine, but will prematurely terminate on
> transient NULL entries. It should be switched over to idr_for_each,
> which allows you to handle this explicitly.
> 
> Note that transient NULL pointers in drm_file.object_idr have been a
> thing since f6cd7daecff5 ("drm: Release driver references to handle
> before making it available again"), this is a really old issue.
> 
> Since it's just a premature loop terminate the impact should be fairly
> benign, at least for any debugfs or fdinfo code.

Rereading idr_get_next I now think it's all fine, please disregard this
patch.
-Sima

> 
> Signed-off-by: Simona Vetter <simona.vetter at intel.com>
> Signed-off-by: Simona Vetter <simona.vetter at ffwll.ch>
> Cc: Zack Rusin <zack.rusin at broadcom.com>
> Cc: Broadcom internal kernel review list <bcm-kernel-feedback-list at broadcom.com>
> ---
>  drivers/gpu/drm/vmwgfx/vmwgfx_gem.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c b/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c
> index c55382167c1b..438e40b92281 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_gem.c
> @@ -323,6 +323,7 @@ static int vmw_debugfs_gem_info_show(struct seq_file *m, void *unused)
>  		rcu_read_unlock();
>  
>  		spin_lock(&file->table_lock);
> +		/* FIXME: Use idr_for_each to handle transient NULL pointers */
>  		idr_for_each_entry(&file->object_idr, gobj, id) {
>  			struct vmw_bo *bo = to_vmw_bo(gobj);
>  
> -- 
> 2.49.0
> 

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