+++ This bug was initially created as a clone of Bug #1725012 +++

Description of problem:
While verifying backport of Cinder multi attach support to OSP13 detach of isnt1 from a mulitattach volume succeeded, however detaching second instance (isnt2) from same volume fails, volume remains in "detaching" status.

Version-Release number of selected component (if applicable):


How reproducible:
Unsure

Steps to Reproduce:
1. Create a multi attached volume

cinder type-create multiattach
cinder type-key multiattach set volume_backend_name=3pariscsi_1
cinder type-key multiattach set multiattach="<is> True"
openstack volume create --size 1 --type multiattach vol1 
vol id - >  c5d00d17-5eaa-49d1-aac6-5ecc2c429f2d 

2. Boot two instances
nova list
+--------------------------------------+-------+--------+------------+-------------+--------------------+
| ID                                   | Name  | Status | Task State | Power State | Networks           |
+--------------------------------------+-------+--------+------------+-------------+--------------------+
| 438c5fcd-bd81-44c8-ad88-1f8ef0e1b50d | inst1 | ACTIVE | -          | Running     | sneha=10.50.9.122  |
| fd2acc67-25ab-4a56-bc6b-d8bdf5732f6b | inst2 | ACTIVE | -          | Running     | default=172.20.1.6 |
+--------------------------------------+-------+--------+------------+-------------+--------------------+           |


3. Attach volume to both instances

cinder list
+--------------------------------------+-----------+------------------------+------+-------------+----------+---------------------------------------------------------------------------+
| ID                                   | Status    | Name                   | Size | Volume Type | Bootable | Attached to                                                               |
+--------------------------------------+-----------+------------------------+------+-------------+----------+---------------------------------------------------------------------------+
| c5d00d17-5eaa-49d1-aac6-5ecc2c429f2d | in-use| vol1                   | 1    | multiattach | false    | 438c5fcd-bd81-44c8-ad88-1f8ef0e1b50d, fd2acc67-25ab-4a56-bc6b-d8bdf5732f6b |
+--------------------------------------+-----------+------------------------+------+-------------+----------+---------------------------------------------------------------------------+





4. Detach inst2 instance

openstack server remove volume inst2 vol1

cinder list
+--------------------------------------+-----------+------------------------+------+-------------+----------+---------------------------------------------------------------------------+
| ID                                   | Status    | Name                   | Size | Volume Type | Bootable | Attached to                                                               |
+--------------------------------------+-----------+------------------------+------+-------------+----------+---------------------------------------------------------------------------+
| c5d00d17-5eaa-49d1-aac6-5ecc2c429f2d | in-use| vol1                   | 1    | multiattach | false    | 438c5fcd-bd81-44c8-ad88-1f8ef0e1b50d |
+--------------------------------------+-----------+------------------------+------+-------------+----------+---------------------------------------------------------------------------+

Volume detached successfully from inst2, as we see above it only remains attached to isnt1 (status in-use).  


5. Detach inst1 instance 
openstack server remove volume inst1 vol1

cinder list
+--------------------------------------+-----------+------------------------+------+-------------+----------+---------------------------------------------------------------------------+
| ID                                   | Status    | Name                   | Size | Volume Type | Bootable | Attached to                                                               |
+--------------------------------------+-----------+------------------------+------+-------------+----------+---------------------------------------------------------------------------+
| c5d00d17-5eaa-49d1-aac6-5ecc2c429f2d | detaching | vol1                   | 1    | multiattach | false    | 438c5fcd-bd81-44c8-ad88-1f8ef0e1b50d                                      |
+--------------------------------------+-----------+------------------------+------+-------------+----------+---------------------------------------------------------------------------+

Even after a few minutes volume status remains in detaching state. 

what I noticed in the cinder-volume.log is, when user sends a detach instance call for the first time it removes the host entry from 3PAR. Now since there is no LUN connectivity with 3PAR, further detach of instances fails. For detailed logs please check attached log file.

Actual results:
Nova volume detach fails to complete due to no host found error in cinder-volume.log
Volume remains in detaching state. 

Expected results:
Volume should successfully detach from second instance as it did from the first one. 

Additional info: