[OVN] AgentCache.agents can change during an iteration operation

[Rodolfo Alonso]

Reference bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2089420

During the ``neutron.plugins.ml2.drivers.ovn.agent.neutron_agent.AgentCache.__iter__`` iteration, an event to add or deleted an OVN agent can happen. The dictionary ``AgentCache.agents`` can change and trigger the error reported in the snippet.

Snippet: https://paste.opendev.org/show/bWn8eKHKIjsWb4MM6pd2/

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/neutron/+/843933

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/neutron/+/843933
Committed: https://opendev.org/openstack/neutron/commit/a71fe45d9628f0dc67ccd12d94a51a7b801ec9d0
Submitter: "Zuul (22348)"
Branch: master

commit a71fe45d9628f0dc67ccd12d94a51a7b801ec9d0
Author: Rodolfo Alonso Hernandez <email address hidden>
Date: Sun May 15 22:48:46 2022 +0000

    [OVN] Protect the AgentCache iteration by copying the local cache

    During the execution of ``AgentCache.__iter__``, the content of
    "self.agents" can change; the Neutron server can attend to an event
    to add or delete an OVN agent. If that happens, the iteration will
    fail with the error:
      "RuntimeError: dictionary changed size during iteration"

    To avoid this, before iterating the list of agents, the cache
    singleton creates a copy of the local cache. The aim of making this
    copy is to avoid using locks between threads.

    Closes-Bug: #1976292
    Change-Id: Icf92685579409282bad0a80ba42531c93738e0b1

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/yoga
Review: https://review.opendev.org/c/openstack/neutron/+/844493

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/xena
Review: https://review.opendev.org/c/openstack/neutron/+/844549

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/wallaby
Review: https://review.opendev.org/c/openstack/neutron/+/844552

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/neutron/+/844549
Committed: https://opendev.org/openstack/neutron/commit/eb562b60a3f128fc45c9a90e1a849efbd6a62c57
Submitter: "Zuul (22348)"
Branch: stable/xena

commit eb562b60a3f128fc45c9a90e1a849efbd6a62c57
Author: Rodolfo Alonso Hernandez <email address hidden>
Date: Sun May 15 22:48:46 2022 +0000

    [OVN] Protect the AgentCache iteration by copying the local cache

    During the execution of ``AgentCache.__iter__``, the content of
    "self.agents" can change; the Neutron server can attend to an event
    to add or delete an OVN agent. If that happens, the iteration will
    fail with the error:
      "RuntimeError: dictionary changed size during iteration"

    To avoid this, before iterating the list of agents, the cache
    singleton creates a copy of the local cache. The aim of making this
    copy is to avoid using locks between threads.

    Conflicts:
        neutron/plugins/ml2/drivers/ovn/agent/neutron_agent.py

    Closes-Bug: #1976292
    Change-Id: Icf92685579409282bad0a80ba42531c93738e0b1
    (cherry picked from commit a71fe45d9628f0dc67ccd12d94a51a7b801ec9d0)

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/neutron/+/844493
Committed: https://opendev.org/openstack/neutron/commit/fbacaf7becd8c25824cadcd7c1f4080d8daf50b7
Submitter: "Zuul (22348)"
Branch: stable/yoga

commit fbacaf7becd8c25824cadcd7c1f4080d8daf50b7
Author: Rodolfo Alonso Hernandez <email address hidden>
Date: Sun May 15 22:48:46 2022 +0000

    [OVN] Protect the AgentCache iteration by copying the local cache

    During the execution of ``AgentCache.__iter__``, the content of
    "self.agents" can change; the Neutron server can attend to an event
    to add or delete an OVN agent. If that happens, the iteration will
    fail with the error:
      "RuntimeError: dictionary changed size during iteration"

    To avoid this, before iterating the list of agents, the cache
    singleton creates a copy of the local cache. The aim of making this
    copy is to avoid using locks between threads.

    Conflicts:
        neutron/plugins/ml2/drivers/ovn/agent/neutron_agent.py

    Closes-Bug: #1976292
    Change-Id: Icf92685579409282bad0a80ba42531c93738e0b1
    (cherry picked from commit a71fe45d9628f0dc67ccd12d94a51a7b801ec9d0)

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/neutron/+/844552
Committed: https://opendev.org/openstack/neutron/commit/9182712672f05d1b2849957c7632d703180c5e0f
Submitter: "Zuul (22348)"
Branch: stable/wallaby

commit 9182712672f05d1b2849957c7632d703180c5e0f
Author: Rodolfo Alonso Hernandez <email address hidden>
Date: Sun May 15 22:48:46 2022 +0000

    [OVN] Protect the AgentCache iteration by copying the local cache

    During the execution of ``AgentCache.__iter__``, the content of
    "self.agents" can change; the Neutron server can attend to an event
    to add or delete an OVN agent. If that happens, the iteration will
    fail with the error:
      "RuntimeError: dictionary changed size during iteration"

    To avoid this, before iterating the list of agents, the cache
    singleton creates a copy of the local cache. The aim of making this
    copy is to avoid using locks between threads.

    Conflicts:
        neutron/plugins/ml2/drivers/ovn/agent/neutron_agent.py

    Closes-Bug: #1976292
    Change-Id: Icf92685579409282bad0a80ba42531c93738e0b1
    (cherry picked from commit a71fe45d9628f0dc67ccd12d94a51a7b801ec9d0)
    (cherry picked from commit eb562b60a3f128fc45c9a90e1a849efbd6a62c57)

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/neutron 18.5.0 release.

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/neutron 19.4.0 release.

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/neutron 20.2.0 release.

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/neutron 21.0.0.0rc1 release candidate.