[Bug 2103413] Re: [SRU] Python3.13: Garbage collection due to attribute cache inlining

[Guillaume Boutry]

Hello @juliank, tempest is the upstream OpenStack integration test
suite. It is a set of tests that will validate functionality of an
OpenStack cloud across services:
https://docs.openstack.org/tempest/latest/overview.html

It is the result the OpenStack team usually provides for SRUs. In this
specific instance, since the bug was simply failing to spawn VMs, just
creating a VM would prove that the bug is fixed.

In the tempest output, you will see the following tests:
- tempest.scenario.test_server_basic_ops.TestServerBasicOps.test_server_basic_ops
- tempest.api.compute.servers.test_create_server.ServersTestManualDisk.test_verify_server_details
- tempest.api.compute.servers.test_create_server.ServersTestManualDisk.test_list_servers
- tempest.api.compute.servers.test_attach_interfaces.AttachInterfacesUnderV243Test.test_add_remove_fixed_ip
- tempest.api.compute.servers.test_server_actions.ServerActionsTestJSON.test_reboot_server_hard
- tempest.api.compute.servers.test_server_addresses.ServerAddressesTestJSON.test_list_server_addresses
- ...

Which are tests that will test basic functionality, but all require
actually to spawn a VM. (You need a VM to be able to test reboot the vm,
get attached ips, testing attaching interfaces and so on...)

** Tags removed: open-3026 verification-needed verification-needed-plucky
** Tags added: verification-done verification-done-pluckyopen-3026

** Tags removed: verification-done-pluckyopen-3026
** Tags added: open-3026 verification-done-plucky

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https://bugs.launchpad.net/bugs/2103413

Title:
  [SRU] Python3.13: Garbage collection due to attribute cache inlining

Status in OpenStack Compute (nova):
  Fix Released
Status in Release Notes for Ubuntu:
  Fix Released
Status in nova package in Ubuntu:
  Fix Released
Status in nova source package in Plucky:
  Fix Committed

Bug description:
  [ Impact ]

   * Nova's neutron client wrapper fails under Python 3.13 due to a
  garbage collection bug in CPython that causes dictionary references to
  be prematurely cleared when one object's __dict__ is assigned to
  another object's __dict__. This completely prevents users from being
  able to spawn virtual VMs (or do other communication to Neutron that
  span multiple cpu cycles), which is the main purpose of Nova.

   * This bug fix stops ClientWrapper from inheriting clientv20.Client
  and directly referencing the base_client's __dict__. This allows
  ClientWrapper to act as a true proxy for clientv20.Client while
  preventing the cache inlining bug that leads to garbage collection.

  [ Test Plan ]

   * With a configured Nova, spawn a VM.
  To simplify testing, I've written a configuration script to help create a single node OpenStack cloud as VM: https://pastebin.ubuntu.com/p/JkHXBmKBbm/

  [ Where problems could occur ]

   * The change modifies how the ClientWrapper class accesses attributes
  from the underlying neutron client. If the __getattr__ implementation
  doesn't properly handle all attribute types or edge cases, it could
  result in AttributeError exceptions or unexpected behavior when
  accessing client methods or properties.

   * Since this changes the inheritance model (from inheritance to
  composition), any code that relies on isinstance() checks against
  clientv20.Client for the wrapper would fail.

  [ Other Info ]

   * This patch comes directly from upstream Nova and has been back-
  ported upstream to stable/2025.1, commit
  bdf62d0653c2e31ae291fc51e7016407b19f6ff4.

   * The fix specifically addresses Python 3.13 compatibility. The
  behavior is correct on Python 3.12 and earlier versions, but Python
  3.13 exhibits the dictionary clearing issue.

  Previous comment:
  https://bugs.launchpad.net/ubuntu/+source/nova/+bug/2103413/comments/0

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