[PATCH V2] drm/amdgpu: fix dereference null return value for the function amdgpu_vm_pt_parent

[Jesse Zhang]

The pointer parent may be NULLed by the function amdgpu_vm_pt_parent.
To make the code more robust, check the pointer parent.

V2: When parent is NULL here we should
 probably call BUG() instead. (Christian)

Signed-off-by: Jesse Zhang <jesse.zh...@amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c 
b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
index 0763382d305a..6fac8440012e 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
@@ -706,11 +706,17 @@ int amdgpu_vm_pde_update(struct amdgpu_vm_update_params 
*params,
                         struct amdgpu_vm_bo_base *entry)
 {
        struct amdgpu_vm_bo_base *parent = amdgpu_vm_pt_parent(entry);
-       struct amdgpu_bo *bo = parent->bo, *pbo;
+       struct amdgpu_bo *bo, *pbo;
        struct amdgpu_vm *vm = params->vm;
        uint64_t pde, pt, flags;
        unsigned int level;
 
+       if (!parent) {
+               BUG();
+               return -EINVAL;
+       }
+       bo = parent->bo;
+
        for (level = 0, pbo = bo->parent; pbo; ++level)
                pbo = pbo->parent;
 
-- 
2.25.1