asterisk users - Jan 2012 - Deadlock detected in asterisk-1.8.9.0 x86_64

I am having problems with a deadlock in Asterisk 1.8.9.0.

The system is a x86_64 machine that is being used as a callcenter. The agents
log in via the AgentLogin application, and each Agent/XXXX channel is assigned
to one or more queues. A custom separate process generates calls into the queues
for the agents to
answer. The calls all go out through a SIP trunk, and all of the agent
extensions are SIP. After an hour or so, asterisk deadlocks. Any attempt to run
"agent show" or "agent show online" through the console
hangs. Also, AMI events seem to stop. However,
the users seem to be still connected, only they do not receive calls anymore
(the custom process waits forever for the Originate response). The deadlock is
apparently spontaneous - there is no explicit action taken by the administrator
that seems to induce
the issue. I will try to make sense of the attached traces, but I hope someone
on the list could provide a clue on what to look for.

Backtraces attached to https://issues.asterisk.org/jira/browse/ASTERISK-19285
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