Created attachment 1151143 [details]
Neutron server runs into deadlock when syslog config is enabled

Description of problem:

I was trying to turn on the syslog and corresponding configuration (see attached statement) for Neutron server but it doesn't create any consumer for the QPLUGIN queue. This causes all the Neutron agents stop functioning as it cannot communicate with the Neutron server.

Digging it deeper and looks like Neutron server fork the RPC worker when they create the QPLUGIN consumer. But since we use SyslogHandler which create lock in the critical section and this will cause deadlock when the child (Forked) process is trying to log message. Simialar explanation can be found here: http://bugs.python.org/issue6721

Even this issue above is opened against for Python 3, I can reproduce it by running the attached script (lock_fork_thread_deadlock_demo.py) in the issue in RH with Python 2.7.5 .


Version-Release number of selected component (if applicable):


How reproducible:

1. Save the attached logging.conf and in the neutron.conf, set the following under the DEFAULT section:

log_config=/etc/neutron/logging.conf
logging_context_format_string="1 %(asctime)sZ mcp1.paslab013000.mc.metacloud.in neutron-server %(process)d - [MetaCloud@40521 levelname="%(levelname)s" component="neutron-server" funcname="%(name)s" request_id="%(request_id)s" user="%(user)s" tenant="%(tenant)s" instance="%(instance)s" lineno="%(pathname)s:%(lineno)d"] %(name)s %(message)s"
logging_default_format_string="1 %(asctime)sZ mcp1.paslab013000.mc.metacloud.in neutron-server %(process)d - [MetaCloud@40521 levelname="%(levelname)s" component="neutron-server" funcname="%(name)s" instance="%(instance)s" lineno="%(pathname)s:%(lineno)d"] %(name)s %(message)s"
logging_exception_prefix="!!!NL!!! %(process)d TRACE %(name)s %(instance)s"

2. Run neutron-server command like:
/usr/bin/python2 /usr/bin/neutron-server --config-file /usr/share/neutron/neutron-dist.conf --config-dir /usr/share/neutron/server --config-file /etc/neutron/neutron.conf --config-file /etc/neutron/plugin.ini --config-dir /etc/neutron/conf.d/common --config-dir /etc/neutron/conf.d/neutron-server 

3. Check qplugin queue in rabbitmq:
sudo rabbitmqctl list_queues name messages messages_ready messages_unacknowledged consumers

You will notice that qplugin has 0 consumers

Also, check neutron agent-list, you will see all agents are reports as dead.


Steps to Reproduce:
1.
2.
3.

Actual results:


Expected results:


Additional info: