diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index f8c0fd57e041..eba204b27785 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -66,7 +66,7 @@ struct nullb_page {
 #define NULLB_PAGE_FREE (MAP_SZ - 2)
 
 static LIST_HEAD(nullb_list);
-static struct mutex lock;
+static DEFINE_MUTEX(lock);
 static int null_major;
 static DEFINE_IDA(nullb_indexes);
 static struct blk_mq_tag_set tag_set;
@@ -2166,8 +2166,6 @@ static int __init null_init(void)
 	if (ret)
 		return ret;
 
-	mutex_init(&lock);
-
 	null_major = register_blkdev(0, "nullb");
 	if (null_major < 0) {
 		ret = null_major;