Comment 17 for bug 1774249

Reviewed: https://review.opendev.org/685391
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=6198f317be549e6d2bd324a48f226b379556e945
Submitter: Zuul
Branch: master

commit 6198f317be549e6d2bd324a48f226b379556e945
Author: Matthew Booth <email address hidden>
Date: Fri Sep 27 16:51:02 2019 +0100

    libvirt: Ignore DiskNotFound during update_available_resource

    There was a previous attempt to fix this in
    change Id687e11e235fd6c2f99bb647184310dfdce9a08d. However, there were 2
    problems with the previous fix:

    1. The handling of missing volumes and disks, while typically having the
       same cause, was inconsistent.

    2. It failed to consider the very wide race opportunity in
       _get_disk_over_committed_size_total between initially fetching the
       instance list from the DB and later getting disk sizes.

    Because _get_disk_over_committed_size_total() can be a very long
    operation, we found that we were reliably hitting this race in CI.
    It might be possible to fix the race, but this would add unnecessary
    complication to code which isn't critical. It's far more robust just to
    log it and ignore it, which is also consistent with the handling of
    missing volumes.

    Closes-Bug: #1774249

    Change-Id: I48719c02713113a41176b8f5cc3c5831f1284a39