A temporary volume is created when an attached volume is backed up. This temporary volume can be deleted by DELETE API because its status is 'available'.
Deleting a LUN while it is connected causes unexpected errors in a volume backend. Depending on a volume backend, this can cause a serious problem which may affect other users.
This problem actually happened once in our production system by misoperation. As a result, some processes handling iSCSI devices such as a scsi command[1] got stuck. In cinder-volume, a thread which called the process also got stuck with holding a lock[2]. This blocked any operations requiring this lock.
[1] https://github.com/openstack/os-brick/blob/master/os_brick/initiator/linuxscsi.py#L81
[2] https://github.com/openstack/os-brick/blob/master/os_brick/initiator/connectors/iscsi.py#L865
Steps to reproduce:
1. Create a volume:
$ openstack volume create --size=20 myvolume
2. Attach the volume to a server:
$ openstack server add volume myvolume myserver --device /dev/vdb
3. Backup the volume:
$ openstack volume backup create myvolume --force
4. List volumes during backing up and find a temporary volume:
$ openstack volume list
+--------------------------------------+-------------------------------------------------+------------+------+---------------------------------------------------------------+
| ID | Name | Status | Size | Attached to |
+--------------------------------------+-------------------------------------------------+------------+------+---------------------------------------------------------------+
| 287b0cee-4ca2-41d4-8e98-d6d705751851 | backup-vol-c146c1fc-864d-4269-b369-dc5bfffca42f | available | 20 | |
| c146c1fc-864d-4269-b369-dc5bfffca42f | myvolume | backing-up | 20 | Attached to 78ce3358-364d-4500-b122-4bbef72b99cd on /dev/vdb |
+--------------------------------------+-------------------------------------------------+------------+------+---------------------------------------------------------------+
5. Delete the temporary volume:
$ openstack volume delete backup-vol-c146c1fc-864d-4269-b369-dc5bfffca42f
Reviewed: https:/
Committed: https:/
Submitter: "Zuul (22348)"
Branch: master
commit 53c13891b313d58
Author: Hironori Shiina <email address hidden>
Date: Fri Jan 28 21:38:03 2022 -0500
Prevent temporary volume from being deleted accidentally
A temporary volume can be deleted while it is in use by DELETE API
accidentally because its status is `available`. To avoid this deletion,
this fix sets a value which doesn't accept deletion to volume status of
a temporary volume. When a temporary volume is used for backing up,
`backing-up` is set. When a temporary volume is used for reverting a
snapshot, `in-use` is set because the volume is attached by a host.
Closes-Bug: #1970768
Change-Id: Ib6a2e4d68e532b