/dev/nullb0: Can't open blockdev
================================================
WARNING: lock held when returning to user space!
6.5.0-rc1-syzkaller #0 Not tainted
------------------------------------------------
syz-executor.2/4779 is leaving the kernel with locks still held!
1 lock held by syz-executor.2/4779:
 #0: ffff8880187ac0e0 (&type->s_umount_key#54){....}-{3:3}, at: get_tree_bdev+0x30d/0x600 fs/super.c:1343