Re: [libvirt] [PATCH v2] processSerialChangedEvent: Close agent monitor early

On Thu, May 07, 2015 at 11:33:58AM +0200, Michal Privoznik wrote: > https://bugzilla.redhat.com/show_bug.cgi?id=890648 > > So, imagine you've issued an API that involves guest agent. For > instance, you want to query guest's IP addresses. So the API acquires > QUERY_JOB, locks the guest agent and issues the agent command. > However, for some reason, guest agent replies to initial ping > correctly, but then crashes tragically while executing real command > (in this case guest-network-get-interfaces). Since initial ping went > well, libvirt thinks guest agent is accessible and awaits reply to the > real command. But it will never come. What will is a monitor event. > Our handler (processSerialChangedEvent) will try to acquire > MODIFY_JOB, which will fail obviously because the other thread that's > executing the API already holds a job. So the event handler exits > early, and the QUERY_JOB is never released nor ended. > > The way how to solve this is to put flag somewhere in the monitor > internals. The flag is called @running and agent commands are issued > iff the flag is set. The flag itself is set when we connect to the > agent socket. And unset whenever we see DISCONNECT event from the > agent. Moreover, we must wake up all the threads waiting for the > agent. This is done by signalizing the condition they're waiting on. > > Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; > --- > ACK, all of that is necessary and it also complies with the error message flag request from v1.