[libvirt] serial console runs out of buffer and console messages soft lock the CPU

[Bryan McLellan]

I recently started configuring guests to use both a serial console and
a graphics element. One of the nodes with this configuration kept
locking up after running for some time. Trying to access the guest
through virt-manager would leave virt-viewer hung at the connecting to
screen. The guest would not respond to any network traffic including
icmp. The user would destroy the domain and restart it to recover.
Eventually the problem came to me and I found that immediately upon
running 'virsh console domain' the guest would recover. The console
contained:

BUG: soft lockup - CPU#0 stuck for 94393s! [postgresql-8.3:4975]

I discovered a bug in a puppet recipe caused postgres to reload
regularly, printing a message to the console each time. Running puppet
in a loop to continue producing these messages to the console caused
another lockup that was recoverable by accessing the serial console in
the same manner. I have since fixed that recipe, but I'm uncomfortable
about the possibility of this happening again.

Is there a way to configure libvirt to cache the serial console on the
host so the buffer on the guest does not fill up when you aren't
connected to the console, or should I disable the serial console?

Bryan

https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/301897