diff --git a/fs/super.c b/fs/super.c
index e848649..8a06881 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -71,6 +71,7 @@
 #else
 		INIT_LIST_HEAD(&s->s_files);
 #endif
+		s->s_bdi = &default_backing_dev_info;
 		INIT_LIST_HEAD(&s->s_instances);
 		INIT_HLIST_BL_HEAD(&s->s_anon);
 		INIT_LIST_HEAD(&s->s_inodes);
@@ -936,6 +937,7 @@
 	sb = root->d_sb;
 	BUG_ON(!sb);
 	WARN_ON(!sb->s_bdi);
+	WARN_ON(sb->s_bdi == &default_backing_dev_info);
 	sb->s_flags |= MS_BORN;
 
 	error = security_sb_kern_mount(sb, flags, secdata);