Re: [PATCH] drm: remove min_order BUG_ON check

[Arunpravin <arunpravin.paneerselvam@amd.com>]

On 07/03/22 9:23 pm, Christian König wrote:
> 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.
> 
ok, in this case, I think it is acceptable to use WARN_ON and abort
using -EINVAL

Regards,
Arun
>>
>> Signed-off-by: Arunpravin <Arunpravin.PaneerSelvam@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
>