[PATCH] Revert "drm/amdgpu: Use dma_buf from GEM object instance"

[Christian König]

On 12.08.25 11:12, Thomas Zimmermann wrote:
> Hi
> 
> Am 15.07.25 um 16:01 schrieb Alex Deucher:
>> On Tue, Jul 15, 2025 at 4:38 AM Thomas Zimmermann <tzimmermann at suse.de> wrote:
>>> This reverts commit 515986100d176663d0a03219a3056e4252f729e6.
>>>
>>> The dma_buf field in struct drm_gem_object is not stable over the
>>> object instance's lifetime. The field becomes NULL when user space
>>> releases the final GEM handle on the buffer object. This resulted
>>> in a NULL-pointer deref.
>>>
>>> Workarounds in commit 5307dce878d4 ("drm/gem: Acquire references on
>>> GEM handles for framebuffers") and commit f6bfc9afc751 ("drm/framebuffer:
>>> Acquire internal references on GEM handles") only solved the problem
>>> partially. They especially don't work for buffer objects without a DRM
>>> framebuffer associated.
>>>
>>> Hence, this revert to going back to using .import_attach->dmabuf.
>>>
>>> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
>> Acked-by: Alex Deucher <alexander.deucher at amd.com>
> 
> Can I take this patch into drm-misc-fixes?

Yeah, sure. Go ahead.

Thanks,
Christian.

> 
> Best regards
> Thomas
> 
>>
>>> ---
>>>   drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c | 2 +-
>>>   drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c     | 3 ++-
>>>   drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c      | 2 +-
>>>   3 files changed, 4 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
>>> index ff98c87b2e0b..5743ebb2f1b7 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
>>> @@ -514,7 +514,7 @@ bool amdgpu_dmabuf_is_xgmi_accessible(struct amdgpu_device *adev,
>>>                  return false;
>>>
>>>          if (drm_gem_is_imported(obj)) {
>>> -               struct dma_buf *dma_buf = obj->dma_buf;
>>> +               struct dma_buf *dma_buf = obj->import_attach->dmabuf;
>>>
>>>                  if (dma_buf->ops != &amdgpu_dmabuf_ops)
>>>                          /* No XGMI with non AMD GPUs */
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>> index 6626a6e64ff5..d1ccbfcf21fa 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
>>> @@ -317,7 +317,8 @@ static int amdgpu_gem_object_open(struct drm_gem_object *obj,
>>>           */
>>>          if (!vm->is_compute_context || !vm->process_info)
>>>                  return 0;
>>> -       if (!drm_gem_is_imported(obj) || !dma_buf_is_dynamic(obj->dma_buf))
>>> +       if (!drm_gem_is_imported(obj) ||
>>> +           !dma_buf_is_dynamic(obj->import_attach->dmabuf))
>>>                  return 0;
>>>          mutex_lock_nested(&vm->process_info->lock, 1);
>>>          if (!WARN_ON(!vm->process_info->eviction_fence)) {
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>> index af0f655dfd5b..b9b4f7d9186e 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>>> @@ -1272,7 +1272,7 @@ int amdgpu_vm_bo_update(struct amdgpu_device *adev, struct amdgpu_bo_va *bo_va,
>>>                  struct drm_gem_object *obj = &bo->tbo.base;
>>>
>>>                  if (drm_gem_is_imported(obj) && bo_va->is_xgmi) {
>>> -                       struct dma_buf *dma_buf = obj->dma_buf;
>>> +                       struct dma_buf *dma_buf = obj->import_attach->dmabuf;
>>>                          struct drm_gem_object *gobj = dma_buf->priv;
>>>                          struct amdgpu_bo *abo = gem_to_amdgpu_bo(gobj);
>>>
>>> -- 
>>> 2.50.0
>>>
>