Comment 6 for bug 1818914

Reviewed: https://review.opendev.org/641806
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=ad9f37350ad1f4e598a9a5df559b9160db1a11c1
Submitter: Zuul
Branch: master

commit ad9f37350ad1f4e598a9a5df559b9160db1a11c1
Author: Matt Riedemann <email address hidden>
Date: Thu Mar 7 16:07:18 2019 -0500

    Update usage in RT.drop_move_claim during confirm resize

    The confirm resize flow in the compute manager
    runs on the source host. It calls RT.drop_move_claim
    to drop resource usage from the source host for the
    old flavor. The problem with drop_move_claim is it
    only decrements the old flavor from the reported usage
    if the instance is in RT.tracked_migrations, which will
    only be there on the source host if the update_available_resource
    periodic task runs before the resize is confirmed, otherwise
    the instance is still just tracked in RT.tracked_instances on
    the source host. This leaves the source compute incorrectly
    reporting resource usage for the old flavor until the next
    periodic runs, which could be a large window if resizes are
    configured to automatically confirm, e.g. resize_confirm_window=1,
    and the periodic interval is big, e.g. update_resources_interval=600.

    This fixes the issue by also updating usage in drop_move_claim
    when the instance is not in tracked_migrations but is in
    tracked_instances.

    Because of the tight coupling with the instance.migration_context
    we need to ensure the migration_context still exists before
    drop_move_claim is called during confirm_resize, so a test wrinkle
    is added to enforce that.

    test_drop_move_claim_on_revert also needed some updating for
    reality because of how drop_move_claim is called during
    revert_resize.

    And finally, the functional recreate test is updated to show the
    bug is fixed.

    Change-Id: Ia6d8a7909081b0b856bd7e290e234af7e42a2b38
    Closes-Bug: #1818914
    Related-Bug: #1641750
    Related-Bug: #1498126