drm/amdgpu: bo could be null when access in vm bo update

Signed-off-by: Junwei Zhang <Jerry.Zhang@amd.com>
Reviewed-by: David Zhou <david1.zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c

@@ -1509,7 +1509,6 @@ int amdgpu_vm_bo_update(struct amdgpu_device *adev,
 	struct drm_mm_node *nodes;
 	struct dma_fence *exclusive, **last_update;
 	uint64_t flags;
-	uint32_t mem_type;
 	int r;
 
 	if (clear || !bo_va->base.bo) {
@@ -1568,9 +1567,9 @@ int amdgpu_vm_bo_update(struct amdgpu_device *adev,
 	 * the evicted list so that it gets validated again on the
 	 * next command submission.
 	 */
-	mem_type = bo->tbo.mem.mem_type;
 	if (bo && bo->tbo.resv == vm->root.base.bo->tbo.resv &&
-	    !(bo->preferred_domains & amdgpu_mem_type_to_domain(mem_type)))
+	    !(bo->preferred_domains &
+	    amdgpu_mem_type_to_domain(bo->tbo.mem.mem_type)))
 		list_add_tail(&bo_va->base.vm_status, &vm->evicted);
 	spin_unlock(&vm->status_lock);