race condition with resize causing old resources not to be free

[Moshe Levi]

While I was working on fixing the resize for pci passthrough [1] I have notice the following issue in resize.

If you are using small image and you resize-confirm it very fast the old resources are not getting freed.

After debug this issue I found out the root cause of it.

A Good run of resize is as detailed below:

When doing resize the _update_usage_from_migration in the resource trucker called twice.

1. The first call we return the instance type of the new flavor and will enter this case

                     https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L718

2. Then it will put in the tracked_migrations the migration and the new instance_type

                    https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L763

3. The second call we return the old instance_type and will enter this case

                     https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L725

4. Then in the tracked_migrations it will overwrite the old value with migration and the old instance type

5. https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L763

6. When doing resize-confirm the drop_move_claim called with the old instance type

https://github.com/openstack/nova/blob/9a05d38f48ef0f630c5e49e332075b273cee38b9/nova/compute/manager.py#L3369

7. The drop_move_claim will compare the instance_type[id] from the tracked_migrations to the instance_type.id (which is the old one)

8. And because they are equals it will remove the old resource usage

                    https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L315-L328

But with small image like CirrOS and doing the revert-confirm fast the second call of _update_usage_from_migration will not get executing.

The result is that when we enter the drop_move_claim it compares it with the new instance_type and this expression is false https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L314

This mean that this code block is not executed https://github.com/openstack/nova/blob/master/nova/compute/resource_tracker.py#L315-L326 and therefore old resources are not getting freed.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/327356

[OpenStack Infra (hudson-openstack)]

Change abandoned by Moshe Levi (<email address hidden>) on branch: master
Review: https://review.openstack.org/327356

[Sean Dague (sdague)]

There are no currently open reviews on this bug, changing
the status back to the previous state and unassigning. If
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[Sean Dague (sdague)]

I saw you abandoned the patch, is this still a known bug?

[Launchpad Janitor (janitor)]

[Expired for OpenStack Compute (nova) because there has been no activity for 60 days.]