drm/amdgpu: add list empty check to avoid null pointer issue

Add list empty check to avoid null pointer issues in some corner cases.
- list_for_each_entry_safe()
Signed-off-by: Yang Wang <kevinyang.wang@amd.com>
Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -80,6 +80,9 @@ static void aca_banks_release(struct aca_banks *banks)
 {
 	struct aca_bank_node *node, *tmp;
 
+	if (list_empty(&banks->list))
+		return;
+
 	list_for_each_entry_safe(node, tmp, &banks->list, node) {
 		list_del(&node->node);
 		kvfree(node);
@@ -562,9 +565,13 @@ static void aca_error_fini(struct aca_error *aerr)
 	struct aca_bank_error *bank_error, *tmp;
 
 	mutex_lock(&aerr->lock);
+	if (list_empty(&aerr->list))
+		goto out_unlock;
+
 	list_for_each_entry_safe(bank_error, tmp, &aerr->list, node)
 		aca_bank_error_remove(aerr, bank_error);
 
+out_unlock:
 	mutex_destroy(&aerr->lock);
 }
 
@@ -680,6 +687,9 @@ static void aca_manager_fini(struct aca_handle_manager *mgr)
 {
 	struct aca_handle *handle, *tmp;
 
+	if (list_empty(&mgr->list))
+		return;
+
 	list_for_each_entry_safe(handle, tmp, &mgr->list, node)
 		amdgpu_aca_remove_handle(handle);
 }