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

[Arunpravin Paneer Selvam <arunpravin.paneerselvam@xxxxxxx>]

On 16/03/22 5:01 pm, Matthew Auld wrote:
> 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@xxxxxxx>
>> ---
>>   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?

I sent a patch adding a check to reject any size not aligned to the
min_page_size. Please review
> 
> [1] https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatchwork.freedesktop.org%2Fpatch%2F477414%2F%3Fseries%3D101108%26rev%3D1&amp;data=04%7C01%7CArunpravin.PaneerSelvam%40amd.com%7C51e60632b18847b73da808da074085d6%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637830270945242954%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=wVVqKzjUoL6jL00uxXiXZz7%2FzJQeuC%2BuBdB8hPKqQao%3D&amp;reserved=0
> 
>>   				err = -ENOSPC;
>>   				goto err_free;
>>   			}
>>
>> base-commit: 3bd60c0259406c5ca3ce5cdc958fb910ad4b8175