Race condition exists for mac uniqueness

[Maru Newby]

The mac uniqueness check is being done in code (https://github.com/openstack/quantum/blob/master/quantum/db/db_base_plugin_v2.py#L289) without explicit locking, which opens the door to a race condition if multiple requests try to secure the same mac.

It probably makes sense to move the check into a uniqueness constraint on the model.

[yong sheng gong (gongysh)]

I have registered a BP: https://blueprints.launchpad.net/quantum/+spec/distributed-lock-resource-allocation for such kind of bugs.

[yong sheng gong (gongysh)]

https://review.openstack.org/#/c/34695/

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/34823

[Eugene Nikanorov (enikanorov)]

The code of _generate_mac was fixed in order to account for possible duplication.
 Meanwhile it's still not 100% race-condition safe.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/146404

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/146404
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=09fe057cd475fe9068339f9805fa855476e248bf
Submitter: Jenkins
Branch: master

commit 09fe057cd475fe9068339f9805fa855476e248bf
Author: Cedric Brandily <email address hidden>
Date: Sat Jan 10 14:25:04 2015 +0000

    Use db constraint to ensure mac address uniqueness

    Currently port mac address uniqueness per network is checked before Port
    db object create but without locking. It implies 2 port create requests
    can allocate the same mac address on a network if each request performs
    mac address uniqueness check before the other creates the Port db object.

    This change replaces the check by a db unique constraint on Port
    (network_id, mac_address).

    Change-Id: Iad7460356ceb74d963cddf5ec33268d77792f1fe
    Closes-Bug: #1194565