How to release backing device from bcache?

[Brendan Boerner <bboerner.biz@gmail.com>]

How do I get bcache to completely give up access to a backing device
so I can mount it using losetup?

My backing device is an lvm logical volume which I expanded in size.

I want to mount it using losetup to use xfs_growfs however I can't
access the backing device:

root@timber4:/var/log# umount /mnt/archives/ ; echo 1 >
/sys/block/bcache1/bcache/stop ; echo 1 > /sys/block/dm-1/bcache/stop
; losetup -o 8192 /dev/loop0 /dev/vg-bfd02/archives_bc
-bash: /sys/block/dm-1/bcache/stop: No such file or directory
losetup: /dev/vg-bfd02/archives_bc: failed to set up loop device:
Device or resource busy

I know in some cases udev is scurrying in and causing the cache to be
recreated but even immediately after the stop and before udev can get
in the backing device is still locked:

Jan 22 11:48:33 timber4 kernel: [370093.820204] XFS (bcache1):
Unmounting Filesystem
Jan 22 11:48:33 timber4 kernel: [370093.830609] bcache:
bcache_device_free() bcache1 stopped
Jan 22 11:48:33 timber4 systemd[1]: Stopped File System Check on
/dev/disk/by-uuid/cb9c1149-73b8-4929-bcc6-d1599d41da73.
Jan 22 11:48:33 timber4 kernel: [370093.904348] bcache:
register_bcache() error /dev/dm-1: device busy

I was able to do this in the past when I first started learning to use
bcache which is why this is especially perplexing.

Suggestions?

Thanks,
Brendan