[PATCH] drm: remove min_order BUG_ON check

[Christian König]

Am 07.03.22 um 15:37 schrieb Arunpravin:
> place BUG_ON(order < min_order) outside do..while
> loop as it fails Unigine Heaven benchmark.
>
> Unigine Heaven has buffer allocation requests for
> example required pages are 161 and alignment request
> is 128. To allocate the remaining 33 pages, continues
> the iteration to find the order value which is 5 and
> when it compares with min_order = 7, enables the
> BUG_ON(). To avoid this problem, placed the BUG_ON
> check outside of do..while loop.

Well using BUG_ON sounds like the wrong approach in the first place.

A BUG_ON() is only justified if you prevent further data corruption, 
e.g. when you detect for example a reference count overflow or similar.

In all other cases you should trigger a WARN_ON() and abort the 
operation with -EINVAL if possible.

Regards,
Christian.

>
> Signed-off-by: Arunpravin <Arunpravin.PaneerSelvam at amd.com>
> ---
>   drivers/gpu/drm/drm_buddy.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
> index 72f52f293249..ed94c56b720f 100644
> --- a/drivers/gpu/drm/drm_buddy.c
> +++ b/drivers/gpu/drm/drm_buddy.c
> @@ -669,10 +669,11 @@ int drm_buddy_alloc_blocks(struct drm_buddy *mm,
>   	order = fls(pages) - 1;
>   	min_order = ilog2(min_page_size) - ilog2(mm->chunk_size);
>   
> +	BUG_ON(order < min_order);
> +
>   	do {
>   		order = min(order, (unsigned int)fls(pages) - 1);
>   		BUG_ON(order > mm->max_order);
> -		BUG_ON(order < min_order);
>   
>   		do {
>   			if (flags & DRM_BUDDY_RANGE_ALLOCATION)
>
> base-commit: 8025c79350b90e5a8029234d433578f12abbae2b