[PATCH v2] drm: Fix a infinite loop condition when order becomes 0

[Matthew Auld]

On 16/03/2022 06:34, Arunpravin Paneer Selvam wrote:
> handle a situation in the condition order-- == min_order,
> when order = 0 and min_order = 0, leading to order = -1,
> it now won't exit the loop. To avoid this problem,
> added a order check in the same condition, (i.e)
> when order is 0, we return -ENOSPC
> 
> v2: use full name in email program and in Signed-off tag
> 
> Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam at amd.com>
> ---
>   drivers/gpu/drm/drm_buddy.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
> index 72f52f293249..5ab66aaf2bbd 100644
> --- a/drivers/gpu/drm/drm_buddy.c
> +++ b/drivers/gpu/drm/drm_buddy.c
> @@ -685,7 +685,7 @@ int drm_buddy_alloc_blocks(struct drm_buddy *mm,
>   			if (!IS_ERR(block))
>   				break;
>   
> -			if (order-- == min_order) {
> +			if (!order || order-- == min_order) {

It shouldn't be possible to enter an infinite loop here, without first 
tripping up the BUG_ON(order < min_order) further up, and for that, as 
we discussed here[1], it sounded like the conclusion was to rather add a 
simple check somewhere in drm_buddy_alloc_blocks() to reject any size 
not aligned to the min_page_size?

[1] https://patchwork.freedesktop.org/patch/477414/?series=101108&rev=1

>   				err = -ENOSPC;
>   				goto err_free;
>   			}
> 
> base-commit: 3bd60c0259406c5ca3ce5cdc958fb910ad4b8175