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

[Kuehling, Felix]

On 2025-10-23 03:48, Arunpravin Paneer Selvam wrote:
Acked-by: Arunpravin Paneer Selvam <arunpravin.paneersel...@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.kha...@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);
  }