I just experienced this on https://review.openstack.org/#/c/55492/. It looks to me like the detach volume fails because libvirt has become unavailable:
2013-11-15 00:49:45.034 29876 DEBUG nova.openstack.common.rpc.amqp [-] received {u'_context_roles': [u'_member_'], u'_context_request_id': u'req-0fdc657c-fdb3-4aef-96c6-c7d3c
6f18b33', u'_context_quota_class': None, u'_context_user_name': u'tempest.scenario.manager-tempest-1652099598-user', u'_context_project_name': u'tempest.scenario.manager-temp
est-1652099598-tenant', u'_context_service_catalog': [{u'endpoints_links': [], u'endpoints': [{u'adminURL': u'http://127.0.0.1:8776/v1/49a55ed418d44af8b8104157045e8347', u're
gion': u'RegionOne', u'internalURL': u'http://127.0.0.1:8776/v1/49a55ed418d44af8b8104157045e8347', u'serviceName': u'cinder', u'id': u'1a7219a8e4e543909f4b2a497810fa7c', u'pu
blicURL': u'http://127.0.0.1:8776/v1/49a55ed418d44af8b8104157045e8347'}], u'type': u'volume', u'name': u'cinder'}], u'_context_tenant': u'49a55ed418d44af8b8104157045e8347', u
'_context_auth_token': '<SANITIZED>', u'args': {u'instance': {u'vm_state': u'active', u'availability_zone': None, u'terminated_at': None, u'ephemeral_gb': 0, u'instance_type_
id': 6, u'user_data': None, u'cleaned': False, u'vm_mode': None, u'deleted_at': None, u'reservation_id': u'r-2ivdfgiz', u'id': 101, u'security_groups': [{u'deleted_at': None,
u'user_id': u'2a86d0c9e67a4aa4b6e7b84ce2dd4776', u'description': u'default', u'deleted': False, u'created_at': u'2013-11-15T00:48:31.000000', u'updated_at': None, u'project_
id': u'49a55ed418d44af8b8104157045e8347', u'id': 90, u'name': u'default'}], u'disable_terminate': False, u'root_device_name': u'/dev/vda', u'display_name': u'scenario-server-
-tempest-1998782633', u'uuid': u'9dbd99d4-09d7-43df-b8de-c6e65043e012', u'default_swap_device': None, u'info_cache': {u'instance_uuid': u'9dbd99d4-09d7-43df-b8de-c6e65043e012
', u'deleted': False, u'created_at': u'2013-11-15T00:48:31.000000', u'updated_at': u'2013-11-15T00:49:18.000000', u'network_info': [{u'ovs_interfaceid': None, u'network': {u'
bridge': u'br100', u'label': u'private', u'meta': {u'tenant_id': None, u'should_create_bridge': True, u'bridge_interface': u'eth0'}, u'id': u'd00c22d4-05b0-4c71-86ba-1c5d60b4
45bd', u'subnets': [{u'ips': [{u'meta': {}, u'type': u'fixed', u'floating_ips': [{u'meta': {}, u'type': u'floating', u'version': 4, u'address': u'172.24.4.225'}], u'version':
4, u'address': u'10.1.0.4'}], u'version': 4, u'meta': {u'dhcp_server': u'10.1.0.1'}, u'dns': [{u'meta': {}, u'type': u'dns', u'version': 4, u'address': u'8.8.4.4'}], u'route
s': [], u'cidr': u'10.1.0.0/24', u'gateway': {u'meta': {}, u'type': u'gateway', u'version': 4, u'address': u'10.1.0.1'}}, {u'ips': [], u'version': None, u'meta': {u'dhcp_serv
er': None}, u'dns': [], u'routes': [], u'cidr': None, u'gateway': {u'meta': {}, u'type': u'gateway', u'version': None, u'address': None}}]}, u'devname': None, u'qbh_params':
None, u'meta': {}, u'address': u'fa:16:3e:57:00:d4', u'type': u'bridge', u'id': u'c7cdc48e-2ef3-43b8-9d8f-88c644afac78', u'qbg_params': None}], u'deleted_at': None}, u'hostna
me': u'scenario-server--tempest-1998782633', u'launched_on': u'devstack-precise-check-rax-ord-658168.slave.openstack.org', u'display_description': u'scenario-server--tempest-
1998782633', u'key_data': u'ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDWN4HLjQWmJu2prhyp8mSkcVOx3W4dhK6GB1L4upm83DU7Ogj3Tg2cTuMqmO4bIt3gJv+BZB16auiyq5w+SEK8VVSuTresc7dD5qW7dej+bD
aF6w/gLsEbP8s0rOvMo93esqF0Cwt7WyqpBXsRr8DEjdPDkJL9fRjFuuGz6sjpM9qAiKd7e1v37y+z39T2y7PoJA5241b0QDG5H6uHNdrCwxIaWxtX5+ac2kUJSxS7FjjtACPgsoBD0tltcpaEQaxmQANdAm4hkhe1rTpP7vfSrmEN
I0ZrwSjre2ZbWLA0IcM3JJwmsXWzXdPvjNC+GVqWmltugTNH77vOfwTbec+x Generated by Nova\n', u'deleted': False, u'config_drive': u'', u'power_state': 1, u'default_ephemeral_device': No
ne, u'progress': 0, u'project_id': u'49a55ed418d44af8b8104157045e8347', u'launched_at': u'2013-11-15T00:48:50.000000', u'scheduled_at': u'2013-11-15T00:48:31.000000', u'node'
: u'devstack-precise-check-rax-ord-658168.slave.openstack.org', u'ramdisk_id': u'258c4266-6e2b-4aca-ae56-b495ea8d8b5f', u'access_ip_v6': None, u'access_ip_v4': None, u'kernel
_id': u'47643b93-2bc5-49b3-8c2d-83791ee8a0e2', u'key_name': u'scenario-keypair--tempest-1179721946', u'updated_at': u'2013-11-15T00:49:16.000000', u'host': u'devstack-precise
-check-rax-ord-658168.slave.openstack.org', u'user_id': u'2a86d0c9e67a4aa4b6e7b84ce2dd4776', u'system_metadata': {u'image_kernel_id': u'47643b93-2bc5-49b3-8c2d-83791ee8a0e2',
u'instance_type_memory_mb': u'64', u'instance_type_swap': u'0', u'instance_type_vcpu_weight': None, u'instance_type_root_gb': u'0', u'instance_type_id': u'6', u'image_ramdis
k_id': u'258c4266-6e2b-4aca-ae56-b495ea8d8b5f', u'instance_type_name': u'm1.nano', u'instance_type_ephemeral_gb': u'0', u'instance_type_rxtx_factor': u'1.0', u'image_disk_for
mat': u'ami', u'instance_type_flavorid': u'42', u'image_container_format': u'ami', u'instance_type_vcpus': u'1', u'image_min_ram': u'0', u'image_min_disk': u'0', u'image_base
_image_ref': u'c9676f02-4f3e-4014-b79e-1252e37faa45'}, u'task_state': None, u'shutdown_terminate': False, u'cell_name': None, u'root_gb': 0, u'locked': False, u'name': u'inst
ance-00000065', u'created_at': u'2013-11-15T00:48:31.000000', u'locked_by': None, u'launch_index': 0, u'memory_mb': 64, u'vcpus': 1, u'image_ref': u'c9676f02-4f3e-4014-b79e-1
252e37faa45', u'architecture': None, u'auto_disk_config': False, u'os_type': None, u'metadata': {}}, u'volume_id': u'7caf0141-ec38-40a9-9860-f3275989d2c5'}, u'namespace': Non
e, u'_context_instance_lock_checked': False, u'_context_timestamp': u'2013-11-15T00:49:44.545660', u'_context_is_admin': False, u'version': u'2.0', u'_context_project_id': u'
49a55ed418d44af8b8104157045e8347', u'_context_user': u'2a86d0c9e67a4aa4b6e7b84ce2dd4776', u'_unique_id': u'a906d8ed501b44b4a1324c846ae48c8d', u'_context_read_deleted': u'no',
u'_context_user_id': u'2a86d0c9e67a4aa4b6e7b84ce2dd4776', u'method': u'detach_volume', u'_context_remote_address': u'127.0.0.1'} _safe_log /opt/stack/new/nova/nova/openstack
/common/rpc/common.py:277
2013-11-15 00:49:45.035 29876 DEBUG nova.openstack.common.rpc.amqp [-] unpacked context: {'read_deleted': u'no', 'project_name': u'tempest.scenario.manager-tempest-1652099598-tenant', 'user_id': u'2a86d0c9e67a4aa4b6e7b84ce2dd4776', 'roles': [u'_member_'], 'timestamp': u'2013-11-15T00:49:44.545660', 'auth_token': '<SANITIZED>', 'remote_address': u'127.0.0.1', 'quota_class': None, 'is_admin': False, 'user': u'2a86d0c9e67a4aa4b6e7b84ce2dd4776', 'service_catalog': [{u'endpoints': [{u'adminURL': u'http://127.0.0.1:8776/v1/49a55ed418d44af8b8104157045e8347', u'region': u'RegionOne', u'id': u'1a7219a8e4e543909f4b2a497810fa7c', u'serviceName': u'cinder', u'internalURL': u'http://127.0.0.1:8776/v1/49a55ed418d44af8b8104157045e8347', u'publicURL': u'http://127.0.0.1:8776/v1/49a55ed418d44af8b8104157045e8347'}], u'endpoints_links': [], u'type': u'volume', u'name': u'cinder'}], 'request_id': u'req-0fdc657c-fdb3-4aef-96c6-c7d3c6f18b33', 'instance_lock_checked': False, 'project_id': u'49a55ed418d44af8b8104157045e8347', 'user_name': u'tempest.scenario.manager-tempest-1652099598-user', 'tenant': u'49a55ed418d44af8b8104157045e8347'} _safe_log /opt/stack/new/nova/nova/openstack/common/rpc/common.py:277
2013-11-15 00:49:45.036 DEBUG nova.openstack.common.rpc.amqp [req-0fdc657c-fdb3-4aef-96c6-c7d3c6f18b33 tempest.scenario.manager-tempest-1652099598-user tempest.scenario.manager-tempest-1652099598-tenant] Making synchronous call on conductor ... multicall /opt/stack/new/nova/nova/openstack/common/rpc/amqp.py:553
2013-11-15 00:49:45.037 DEBUG nova.openstack.common.rpc.amqp [req-0fdc657c-fdb3-4aef-96c6-c7d3c6f18b33 tempest.scenario.manager-tempest-1652099598-user tempest.scenario.manager-tempest-1652099598-tenant] MSG_ID is 4e48fe5fc3844f18903fc60cdac9545a multicall /opt/stack/new/nova/nova/openstack/common/rpc/amqp.py:556
2013-11-15 00:49:45.037 DEBUG nova.openstack.common.rpc.amqp [req-0fdc657c-fdb3-4aef-96c6-c7d3c6f18b33 tempest.scenario.manager-tempest-1652099598-user tempest.scenario.manager-tempest-1652099598-tenant] UNIQUE_ID is 9fe3d2e29e364a1dbde5c4fba5185bae. _add_unique_id /opt/stack/new/nova/nova/openstack/common/rpc/amqp.py:341
2013-11-15 00:49:45.047 29876 DEBUG amqp [-] Closed channel #1 _do_close /usr/local/lib/python2.7/dist-packages/amqp/channel.py:95
2013-11-15 00:49:45.048 29876 DEBUG amqp [-] using channel_id: 1 __init__ /usr/local/lib/python2.7/dist-packages/amqp/channel.py:71
2013-11-15 00:49:45.050 29876 DEBUG amqp [-] Channel open _open_ok /usr/local/lib/python2.7/dist-packages/amqp/channel.py:429
2013-11-15 00:49:45.071 AUDIT nova.compute.manager [req-0fdc657c-fdb3-4aef-96c6-c7d3c6f18b33 tempest.scenario.manager-tempest-1652099598-user tempest.scenario.manager-tempest-1652099598-tenant] [instance: 9dbd99d4-09d7-43df-b8de-c6e65043e012] Detach volume 7caf0141-ec38-40a9-9860-f3275989d2c5 from mountpoint /dev/vdb
2013-11-15 00:49:46.513 DEBUG nova.openstack.common.lockutils [req-0fdc657c-fdb3-4aef-96c6-c7d3c6f18b33 tempest.scenario.manager-tempest-1652099598-user tempest.scenario.manager-tempest-1652099598-tenant] Got semaphore "connect_volume" lock /opt/stack/new/nova/nova/openstack/common/lockutils.py:167
2013-11-15 00:49:46.513 DEBUG nova.openstack.common.lockutils [req-0fdc657c-fdb3-4aef-96c6-c7d3c6f18b33 tempest.scenario.manager-tempest-1652099598-user tempest.scenario.manager-tempest-1652099598-tenant] Got semaphore / lock "disconnect_volume" inner /opt/stack/new/nova/nova/openstack/common/lockutils.py:247
2013-11-15 00:49:48.640 DEBUG nova.virt.libvirt.driver [req-0fdc657c-fdb3-4aef-96c6-c7d3c6f18b33 tempest.scenario.manager-tempest-1652099598-user tempest.scenario.manager-tempest-1652099598-tenant] Connection to libvirt broke _test_connection /opt/stack/new/nova/nova/virt/libvirt/driver.py:699
2013-11-15 00:49:48.640 DEBUG nova.virt.libvirt.driver [req-0fdc657c-fdb3-4aef-96c6-c7d3c6f18b33 tempest.scenario.manager-tempest-1652099598-user tempest.scenario.manager-tempest-1652099598-tenant] Connecting to libvirt: qemu:///system _get_new_connection /opt/stack/new/nova/nova/virt/libvirt/driver.py:625
2013-11-15 00:49:48.641 29876 ERROR nova.virt.libvirt.driver [-] Connection to libvirt failed: Failed to connect socket to '/var/run/libvirt/libvirt-sock': Connection refused
2013-11-15 00:49:48.641 29876 TRACE nova.virt.libvirt.driver Traceback (most recent call last):
2013-11-15 00:49:48.641 29876 TRACE nova.virt.libvirt.driver File "/opt/stack/new/nova/nova/virt/libvirt/driver.py", line 740, in _connect
2013-11-15 00:49:48.641 29876 TRACE nova.virt.libvirt.driver return libvirt.openAuth(uri, auth, flags)
2013-11-15 00:49:48.641 29876 TRACE nova.virt.libvirt.driver File "/usr/lib/python2.7/dist-packages/libvirt.py", line 102, in openAuth
2013-11-15 00:49:48.641 29876 TRACE nova.virt.libvirt.driver if ret is None:raise libvirtError('virConnectOpenAuth() failed')
2013-11-15 00:49:48.641 29876 TRACE nova.virt.libvirt.driver libvirtError: Failed to connect socket to '/var/run/libvirt/libvirt-sock': Connection refused
2013-11-15 00:49:48.641 29876 TRACE nova.virt.libvirt.driver
Logstash query that finds this. It turns out there's only one occurrence in the last week:
http://