如何释放安装到无法访问的地方的块设备？

Question

root@vi-notebook:~# cat /proc/mounts | grep raidy
/dev/md0 /root/e/i/wpc2/boot/mnt/raidy reiserfs ro,nosuid,nodev,noexec,noatime 0 0

root@vi-notebook:~# umount -n /root/e/i/wpc2/boot/mnt/raidy
umount: /root/e/i/wpc2/boot/mnt/raidy: Transport endpoint is not connected

root@vi-notebook:~# mount /dev/md/raidy /mnt/raidy/ -t reiserfs -o nodev,nosuid,noexec,acl,noatime
mount: /dev/md0 already mounted or /mnt/raidy/ busy

我发现的唯一解决方法是：

root@vi-notebook:~# losetup /dev/loop0 /dev/md/raidy 
root@vi-notebook:~# mount /dev/loop0 /mnt/raidy/ -t reiserfs -o nodev,nosuid,noexec,acl,noatime