Comment 0 for bug 1827363

When doing a openstack port list that filters for a fixed-ip/subnet and at the same time limits the amount of results neutron returns a 500 internal server error. This was already addressed in https://bugs.launchpad.net/neutron/+bug/1826186 but this bug is also present in other places.

While running tempest against a Neutron Queens installation I came across another _get_ports_query() in neutron/plugins/ml2/plugin.py where filter is again called onto the result of an already limited query.

See https://github.com/openstack/neutron/blob/6f4962dcf89aebf2552ee8ec0993c6389a953024/neutron/plugins/ml2/plugin.py#L2206

InvalidRequestError: Query.filter() being called on a Query which already has LIMIT or OFFSET applied. To modify the row-limited results of a Query, call from_self() first. Otherwise, call filter() before limit() or offset() are applied.
  File "pecan/core.py", line 683, in __call__
    self.invoke_controller(controller, args, kwargs, state)
[...]
  File "neutron/db/db_base_plugin_v2.py", line 1417, in get_ports
    page_reverse=page_reverse)
  File "neutron/plugins/ml2/plugin.py", line 1941, in _get_ports_query
    query = query.filter(substr_filter)
  File "<string>", line 2, in filter
  File "sqlalchemy/orm/base.py", line 200, in generate
    assertion(self, fn.__name__)
  File "sqlalchemy/orm/query.py", line 435, in _no_limit_offset
    % (meth, meth)

I applied a patch similar to the one Gabriele Cerami proposed in https://review.opendev.org/#/c/656066/

When doing a grep for _get_ports_query() in the neutron codebase I find a function with this name being called in neutron/db/dvr_mac_db.py in get_ports_on_host_by_subnet(), I do not have a stacktrace or test for that though.

See https://github.com/openstack/neutron/blob/6f4962dcf89aebf2552ee8ec0993c6389a953024/neutron/db/dvr_mac_db.py#L162