Reviewed:  https://review.openstack.org/488510
Committed: 
https://git.openstack.org/cgit/openstack/nova/commit/?id=5390210a4fa46e2af6b6aec9b41c03147b52760c
Submitter: Jenkins
Branch:    master

commit 5390210a4fa46e2af6b6aec9b41c03147b52760c
Author: Jay Pipes <jaypi...@gmail.com>
Date:   Wed Aug 2 17:48:38 2017 -0400

    Remove provider allocs in confirm/revert resize
    
    Now that the scheduler creates a doubled-up allocation for the duration
    of a move operation (with part of the allocation referring to the
    source and part referring to the destination host), we need to remove
    the source provider when confirming the resize and remove the
    destination provider from the allocation when reverting a resize. This
    patch adds this logic in the RT's drop_move_claim() method.
    
    Change-Id: I6f8afe6680f83125da9381c812016b3623503825
    Co-Authored-By: Dan Smith <d...@danplanet.com>
    Fixes-bug: #1707071


** Changed in: nova
       Status: In Progress => Fix Released

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https://bugs.launchpad.net/bugs/1707071

Title:
  Compute nodes will fight over allocations during migration

Status in OpenStack Compute (nova):
  Fix Released
Status in OpenStack Compute (nova) ocata series:
  Confirmed

Bug description:
  As far back as Ocata, compute nodes that manage allocations will end
  up overwriting allocations from other compute nodes when doing a
  migration. This stems from the fact that the Resource Tracker was
  designed to manage a per-compute-node set of accounting, but placement
  is per-instance accounting. When we try to create/update/delete
  allocations for instances on compute nodes from the existing resource
  tracker code paths, we end up deleting allocations that apply to other
  compute nodes in the process.

  For example, when an instance A is running against compute1, there is
  an allocation for its resources against that node. When migrating that
  instance to compute2, the target compute (or scheduler) may create
  allocations for instance A against compute2, which overwrite those for
  compute1. Then, compute1's periodic healing task runs, and deletes the
  allocation for instance A against compute2, replacing it with one for
  compute1. When migration completes, compute2 heals again and
  overwrites the allocation with one for the new home of the instance.
  Then, compute1 may delete the allocation it thinks it owns, followed
  finally by another heal on compute2. While this is going on, the
  scheduler (via placement) does not have a consistent view of resources
  to make proper decisions.

  In order to fix this, we need a combination of changes:

  1. There should be allocations against both compute nodes for an instance 
during a migration
  2. Compute nodes should respect the double claim, and not delete allocations 
for instances it used to own, if the allocation has no resources for its 
resource provider
  3. Compute nodes should not delete allocations for instances unless they own 
the instance _and_ the instance is in DELETED/SHELVED_OFFLOADED state

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