Comment 6 for bug 1838392

Reviewed: https://review.opendev.org/696151
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=939cd9b177db8f12952e72145a5c00a0574959eb
Submitter: Zuul
Branch: stable/train

commit 939cd9b177db8f12952e72145a5c00a0574959eb
Author: Lee Yarwood <email address hidden>
Date: Mon Jul 29 16:25:45 2019 +0100

    compute: Take an instance.uuid lock when rebooting

    Previously simultaneous requests to reboot and delete an instance could
    race as only the latter took a lock against the uuid of the instance.

    With the Libvirt driver this race could potentially result in attempts
    being made to reconnect previously disconnected volumes on the host.
    Depending on the volume backend being used this could then result in
    stale block devices point to unmapped volumes being left on the host
    that in turn could cause failures later on when connecting newly mapped
    volumes.

    This change avoids this race by ensuring any request to reboot an
    instance takes an instance.uuid lock within the compute manager,
    serialising requests to reboot and then delete the instance.

    Closes-Bug: #1838392
    Change-Id: Ieb59de10c63bb067f92ec054535766cdd722dae2
    (cherry picked from commit 9ad54f3dacbd372271f441baea5380f913072dde)