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

[Thomas Zimmermann]

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?

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
>>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)