maximum recursion depth exceeded while getting the str of an object

[yoctozepto]

SUMMARY

On Ansible 2.10.0rc1 (Ansible base version 2.10.1) we get: "maximum recursion depth exceeded while getting the str of an object" on CentOS 8 (running Python 3.6).
We don't have this error on Ansible before 2.10 and with Ansible 2.10 but on Debian Buster (Python 3.7) or Ubuntu Focal (Python 3.8).

The full error is attached because it includes the variable expansion that failed and that's quite lengthy (but still finite and the dictionary is not that deep).

ISSUE TYPE

• Bug Report

COMPONENT NAME

ANSIBLE VERSION

ansible 2.10.1

CONFIGURATION

OS / ENVIRONMENT

CentOS 8 stream

STEPS TO REPRODUCE

Sorry, I haven't had a chance to distill a minimal test-case yet.

EXPECTED RESULTS

Variable expands just fine (like it did and can do but on other platforms).

ACTUAL RESULTS

I got it attached.

expansion_error.txt

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[samdoran]

Please create a simple reproducer so we can investigate this further.

needs_info

[yoctozepto]

Unfortunately it belongs to the 'easier said than done' category.

I did not succeed in isolating the failure.

However, I noticed that different scenarios fail at different tasks, and hence different vars.
One is even very simple. Consider the vars:

network_interface: "eth0"
tunnel_interface: "{{ network_interface }}"
neutron_sriov_physnet_mappings:
  sriovnet1: "{{ tunnel_interface }}"

And the error is:

An unhandled exception occurred while templating '{{ neutron_sriov_physnet_mappings.items() | map('join', ':') | join(',') }}'. Error was a <class 'RecursionError'>, original message: maximum recursion depth exceeded while calling a Python object

It looks as if something destroys some internal state during the execution and it will fail on sufficiently long scenarios.

Please tell me how I can show stack trace of that failure to let us see some details. I could not find a way.

[yoctozepto]

Cross-ref links: https://bugs.launchpad.net/kolla-ansible/+bug/1896594 & https://review.opendev.org/752420

I managed to scope it to our Neutron role. Other tested do not exhibit this behaviour.
Still unable to reproduce in a simple case.

[mdavis-xyz]

This is likely a duplicate of #71920.

(Well, that one is a duplicate of this because this is older, but that one has a MWE and is closer to a solution.)

[mdavis-xyz]

#71920 has just been closed with a PR, so I think this ticket should be closed too.

[mkrizek]

Closing per above.