Re: [Patch v1] drm/amdgpu: null check for hmm_pfns ptr before freeing it

["Kuehling, Felix" <felix.kuehling@amd.com>]

On 2025-10-23 03:48, Arunpravin Paneer Selvam wrote:
> Acked-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
>
> Regards,
> Arun.
> On 10/23/2025 12:28 PM, Sunil Khatri wrote:
>> Due to low memory or when num of pages is too big to be
>> accomodated, allocation could fail for pfn's.
>>
>> Chekc hmm_pfns for NULL before calling the kvfree for the it.
>>
>> Signed-off-by: Sunil Khatri <sunil.khatri@amd.com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_hmm.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_hmm.c 
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_hmm.c
>> index d6f903a2d573..6ac206e2bc46 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_hmm.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_hmm.c
>> @@ -286,7 +286,11 @@ void amdgpu_hmm_range_free(struct 
>> amdgpu_hmm_range *range)
>>       if (!range)
>>           return;
>>   -    kvfree(range->hmm_range.hmm_pfns);
>> +    if (range->hmm_range.hmm_pfns) {
>> +        kvfree(range->hmm_range.hmm_pfns);
>> +        range->hmm_range.hmm_pfns = NULL;
>> +    }

NULL-checks before kfree and friends are unnecessary. There are actually 
static checkers that complain about such unnecessary NULL-checks. For 
example, see https://lkml.org/lkml/2024/8/11/168.

The same is also true for the standard libc free in usermode: 
https://stackoverflow.com/questions/1912325/checking-for-null-before-calling-free.

Finally, setting range->hmm_range.hmm_pfns = NULL is also unnecessary 
because you're about to free the whole range structure anyway.

Regards,
   Felix


>> +
>>       amdgpu_bo_unref(&range->bo);
>>       kfree(range);
>>   }
>