+++ This bug was initially created as a clone of Bug #623903 +++
See Bug 623903 and Bug 626544 for details. Basically, if a guest CPU is somehow stopped (eg, click the "pause" button in virt-manager, or issue the "destroy" command from virsh), and the qemu process receives an "info monitor" command, it will hang forever waiting for the stats to become ready.
This is "very bad", since virt-manager is constantly polling the libvirt "dominfo" command, which is constantly calling the qemu monitor with "info balloon". Without fail, if a guest is paused while virt-manager is running, the info balloon command will hang, resulting in qemu, libvirtd, and virt-manager all being hung.
The only way I've found to get out of this situation is to kill the qemu process *and* kill -9 libvirtd.
I witnessed this behavior in F14-beta updated on 2010-10-15:
qemu-kvm-0.13.0-0.7.rc1.fc14.x86_64
(libvirt from git 2010-10-15, post 0.8.3)
virt-manager-0.8.5-1.fc14.noarch
Also note Bug 626544, which presents another example of bad behavior from the same cause. Pay particular attention to https://bugzilla.redhat.com/show_bug.cgi?id=626544#c4, which points out that the fix proposed for
Here is the upstream qemu-kvm "fix" for this problem.
commit 07b0403dfc2b2ac179ae5b48105096cc2d03375a
Author: Eduardo Habkost <ehabkost>
Date: Tue Sep 14 13:43:39 2010 -0300
disable guest-provided stats on "info balloon" command
The addition of memory stats reporting to the virtio balloon causes
the 'info balloon' command to become asynchronous. This is a regression
because in some cases it can hang the user monitor.