Comment 12 for bug 1849165

Reviewed: https://review.opendev.org/690099
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=91a2056d526dd07edecba46f93119697190f112e
Submitter: Zuul
Branch: stable/train

commit 91a2056d526dd07edecba46f93119697190f112e
Author: Eric Fried <email address hidden>
Date: Mon Oct 21 12:18:10 2019 -0500

    Func: bug 1849165: mig race with _populate_assigned_resources

    Add a functional regression test for the referenced bug:

    If a migration is initiated, and update_available_resource runs on the
    destination between when the migration record is associated with the
    destination and when the migration context is added to the instance, it
    will raise a TypeError attempting to _populate_assigned_resources for
    that instance, because that method attempts to access the
    (as-yet-nonexistent) migration context.

    Note that this doesn't fail the migration; it just leaves ugly logs. In
    real life it probably also leaves other pieces of
    update_available_resource unfinished on the destination.

    Related-Bug: #1849165
    Change-Id: I7e96cd24049c205f76a684a2e7425f85b4376f73
    (cherry picked from commit 761be5d0cb364333cde267b431b1ef87920f7400)