diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 8ac4aad66ebc..cea5ee9be639 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -2045,8 +2045,7 @@ static struct blkg_policy_data *ioc_pd_alloc(gfp_t gfp, struct request_queue *q,
 	int levels = blkcg->css.cgroup->level + 1;
 	struct ioc_gq *iocg;
 
-	iocg = kzalloc_node(sizeof(*iocg) + levels * sizeof(iocg->ancestors[0]),
-			    gfp, q->node);
+	iocg = kzalloc_node(struct_size(iocg, ancestors, levels), gfp, q->node);
 	if (!iocg)
 		return NULL;