libvirt users - Mar 2012 - [LXC] Attempt to start X in guest makes host X die

I have attempted to start X in a rawhide LXC guest on a Fedora 16 host, using

   echo a > /sys/fs/cgroup/devices/libvirt/lxc/Rawhide/devices.allow

to allow me to create all the necessary devices in /dev in the guest
(dangerous, I know, but I only ran that command after the guest systemd 
finished booting).

This is with the nouveau open source driver. 

I ran X using

   /usr/bin/startx -- :7 vt7

Immediately the host X server dies, even though it's on a different virtual 
terminal (VT1).

It seems to be something to do with DRM. The /var/log/Xorg.0.log in the host 
says something about drmSetMaster failing.

What's strange is that according to the guest Xorg.7.log, DRM opening fails 
there too: "drmOpenDevice: open result is -1, (No such device)". If
there is
no such device (even though I created it), how can the guest be affecting the 
host?

I think it might possibly be related to 
https://bugzilla.redhat.com/show_bug.cgi?id=680677

Maybe the guest X immediately fails to start but for some reason does not 
release the DRM master (at all, or quickly enough), and the host X tries to 
regain the DRM master but fails and dies. I looked at some other drivers to 
see if any other X drivers have better handling of the latter condition, but I 
couldn't find any which do a retry in this case.

I would report a bug, but I'm not sure which Fedora component to report this
against.

> What's strange is that according to the guest Xorg.7.log, DRM opening
fails
> there too: "drmOpenDevice: open result is -1, (No such device)".
Indeed if I just 

# cat </dev/dri/card0 
-bash: /dev/dri/card0: No such device

I don't get that in the host. So this does look like a kernel issue.