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

[Julian Andres Klode]

Hello Guillaume, or anyone else affected,

Accepted nova into plucky-proposed. The package will build now and be
available at
https://launchpad.net/ubuntu/+source/nova/3:31.0.0-0ubuntu1.1 in a few
hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
plucky to verification-done-plucky. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-plucky. In either case, without details of your testing we will
not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

** Changed in: nova (Ubuntu Plucky)
       Status: Confirmed => Fix Committed

** Tags added: verification-needed verification-needed-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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