Hi!
[ Upstream commit a0cf36546cc24ae1c95d72253c7795d4d2fc77aa ]If this can happen, it should not WARN().
The pointer parent may be NULLed by the function amdgpu_vm_pt_parent.
To make the code more robust, check the pointer parent.
If this can not happen, we don't need the patch in stable.
Best regards,
Pavel