Re: [PATCH] drm/buddy: Fix alloc_range() error handling code

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

Hi Daniel,

On 2/9/2024 11:34 PM, Daniel Vetter wrote:
> On Fri, Feb 09, 2024 at 08:56:24PM +0530, Arunpravin Paneer Selvam wrote:
>> Few users have observed display corruption when they boot
>> the machine to KDE Plasma or playing games. We have root
>> caused the problem that whenever alloc_range() couldn't
>> find the required memory blocks the function was returning
>> SUCCESS in some of the corner cases.
>>
>> The right approach would be if the total allocated size
>> is less than the required size, the function should
>> return -ENOSPC.
>>
>> Cc:  <stable@vger.kernel.org> # 6.7+
>> Fixes: 0a1844bf0b53 ("drm/buddy: Improve contiguous memory allocation")
>> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3097
>> Tested-by: Mario Limonciello <mario.limonciello@amd.com>
>> Link: https://patchwork.kernel.org/project/dri-devel/patch/20240207174456.341121-1-Arunpravin.PaneerSelvam@amd.com/
>> Acked-by: Christian König <christian.koenig@amd.com>
>> Reviewed-by: Matthew Auld <matthew.auld@intel.com>
>> Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
> New unit test for this would be most excellent - these kind of missed edge
> cases is exactly what kunit is for. Can you please follow up with, since
> we don't want to hold up the bugfix for longer?
Matthew Auld has added a new unit test for this case. Please let us know 
if this will suffice.
https://patchwork.freedesktop.org/patch/577497/?series=129671&rev=1

Thanks,
Arun.
> -Sima
>
>> ---
>>   drivers/gpu/drm/drm_buddy.c | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
>> index f57e6d74fb0e..c1a99bf4dffd 100644
>> --- a/drivers/gpu/drm/drm_buddy.c
>> +++ b/drivers/gpu/drm/drm_buddy.c
>> @@ -539,6 +539,12 @@ static int __alloc_range(struct drm_buddy *mm,
>>   	} while (1);
>>   
>>   	list_splice_tail(&allocated, blocks);
>> +
>> +	if (total_allocated < size) {
>> +		err = -ENOSPC;
>> +		goto err_free;
>> +	}
>> +
>>   	return 0;
>>   
>>   err_undo:
>> -- 
>> 2.25.1
>>