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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 27-10-2025 07:58 pm, Christian König wrote: > > On 10/23/25 17:30, Kuehling, Felix wrote: >> On 2025-10-23 03:48, Arunpravin Paneer Selvam wrote: >>> Acked-by: Arunpravin Paneer Selvam >>> >>> 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 >>>> --- >>>>   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, seehttps://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. > Agree completely with Felix. > > Sunil why do you think that this is necessary and blocking KFD for some reason? > > Regards, > Christian. KFD side reported the error of NULL dereference pfns = kvmalloc_array(npages, sizeof(*pfns), GFP_KERNEL); //fails if the size is too big. Now when we free the memory in function amdgpu_hmm_range_free and try to do a kvfree of the range->hmm_range.hmm_pfns which is NULL and we were seeing the NULL dereference. So i added a check to check for the memory to be valid ptr first before calling kvfree. This actually fixed the issue but i do agree that *"setting range->hmm_range.hmm_pfns = NULL could be avoided and that why i did not added that check in the final patch that i merged" This is the final code after this merge.* voidamdgpu_hmm_range_free(structamdgpu_hmm_range*range) { if(!range) return; if(range->hmm_range.hmm_pfns) kvfree(range->hmm_range.hmm_pfns); amdgpu_bo_unref(&range->bo); kfree(range); } Regards Sunil Khatri >> Regards, >>   Felix >> >> >>>> + >>>>       amdgpu_bo_unref(&range->bo); >>>>       kfree(range); >>>>   } --------------nQPZQY0UIZzqQ0q4F7T40007 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: 8bit


On 27-10-2025 07:58 pm, Christian König wrote:

On 10/23/25 17:30, Kuehling, Felix wrote:

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.

Agree completely with Felix.

Sunil why do you think that this is necessary and blocking KFD for some reason?

Regards,
Christian.

KFD side reported the error of NULL dereference

pfns = kvmalloc_array(npages, sizeof(*pfns), GFP_KERNEL); //fails if the size is too big.

Now when we free the memory in function amdgpu_hmm_range_free and try to do a kvfree of the range->hmm_range.hmm_pfns which is NULL and we were seeing the NULL dereference.
So i added a check to check for the memory to be valid ptr first before calling kvfree. 

This actually fixed the issue but i do agree that "setting range->hmm_range.hmm_pfns = NULL could be avoided and that why i did not added that check in the final patch that i merged" This is the final code after this merge.

void amdgpu_hmm_range_free(struct amdgpu_hmm_range *range)
{
        if (!range)
                return;
        if (range->hmm_range.hmm_pfns)
                kvfree(range->hmm_range.hmm_pfns);
        amdgpu_bo_unref(&range->bo);
        kfree(range);
}


Regards Sunil Khatri


      

        
Regards,
  Felix




        

          

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


          

          

        

      

      

    

  


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