Ceph » rbd

When I removing a cache tier,some errors occurs.
Steps are as follows
1. ceph osd tier cache-mode cache forward --yes-i-really-mean-it
2. rados -p cache cache-flush-evict-all
when I perform step 2，error follows:

```
    failed to evict /rbd_header.dcdf36b8b4567: (16) Device or resource busy
        rbd_header.2d1e256b8b4567
    failed to evict /rbd_header.2d1e256b8b4567: (16) Device or resource busy
        rbd_header.dcad46f615160
    failed to evict /rbd_header.dcad46f615160: (16) Device or resource busy
        rbd_header.ea8166b8b4567
    failed to evict /rbd_header.ea8166b8b4567: (16) Device or resource busy
        rbd_header.67c3d6b8b4567
    failed to evict /rbd_header.67c3d6b8b4567: (16) Device or resource busy
        rbd_header.2dbc366b8b4567
     failed to evict /rbd_header.2dbc366b8b4567: (16) Device or resource busy
   ```

If I enforce to perform step: ceph osd tier remove-overlay {pool},All the vms changed to read-only and can't reboot. I cann't find a good solution .Any ideas?
My ceph version is 12.2.10。