Comment 7 for bug 1425402

Reviewed: https://review.openstack.org/236983
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=f76ef76f2516dad794818ce56fb15d16437f7314
Submitter: Jenkins
Branch: master

commit f76ef76f2516dad794818ce56fb15d16437f7314
Author: Eugene Nikanorov <email address hidden>
Date: Mon Oct 19 17:41:32 2015 +0400

    Avoid race condition for reserved DHCP ports

    This patch introduces mechanism similar to compare-and-swap
    for updating reserved DHCP port.

    This addresses a case when two DHCP agents that start nearly at
    the same time are assigned to one network and there is a reserved
    DHCP port in the network. Then each of agents will try to use it
    because agents don't check if reserved port is still available.
    Reserved DHCP port can be acquired by different agent between calls to
    get_active_networks and update_port, so this patch adds a check for
    this case.

    Change-Id: I0277ab537ff9d3a664c03ea291b9ec2b0e784dbb
    Closes-Bug: #1425402