[Mesa-dev] [PATCH] util/ralloc: set prev-pointers correctly in ralloc_adopt

[Eric Engestrom]

On Monday, 2017-09-04 14:06:30 +0200, Nicolai Hähnle wrote:
> From: Nicolai Hähnle <nicolai.haehnle at amd.com>
> 
> Found by inspection.
> 
> I'm not aware of any actual failures caused by this, but a precise
> sequence of ralloc_adopt and ralloc_free should be able to cause
> problems.
> ---
>  src/util/ralloc.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/src/util/ralloc.c b/src/util/ralloc.c
> index bf46439df4e..50e629fe450 100644
> --- a/src/util/ralloc.c
> +++ b/src/util/ralloc.c
> @@ -304,24 +304,26 @@ ralloc_adopt(const void *new_ctx, void *old_ctx)
>     new_info = get_header(new_ctx);
>  
>     /* If there are no children, bail. */
>     if (unlikely(old_info->child == NULL))
>        return;
>  
>     /* Set all the children's parent to new_ctx; get a pointer to the last child. */
>     for (child = old_info->child; child->next != NULL; child = child->next) {
>        child->parent = new_info;
>     }
> +   child->parent = new_info;
>  
>     /* Connect the two lists together; parent them to new_ctx; make old_ctx empty. */
>     child->next = new_info->child;
> -   child->parent = new_info;

> +   if (new_info->child)
> +      new_info->child->prev = child;

I would've written it like this as I find it clearer:

   if (child->next)
      child->next->prev = child;

Doesn't change much though, so either way:
Reviewed-by: Eric Engestrom <eric.engestrom at imgtec.com>

>     new_info->child = old_info->child;
>     old_info->child = NULL;
>  }
>  
>  void *
>  ralloc_parent(const void *ptr)
>  {
>     ralloc_header *info;
>  
>     if (unlikely(ptr == NULL))
> -- 
> 2.11.0
>