[libvirt-users] Finding cause when "virsh list" hangs

[Eric Blake]

On 08/19/2012 12:19 PM, Whit Blauvelt wrote:
> Hi,
> 
> Did something dumb - had two VM hosts with DRBD mirroring of VMs on the same
> UPS, which failed and crashed them both. While I've got VMs running now on
> both, "virsh list" and "virsh start" and so on are just hanging. I'm not
> seeing it log anything in these instances - just hanging.
> 
> Both systems are Ubuntu 10.10, one with the stock libvirtd 0.8.3 and one
> with 0.9.12 compiled from source. They each brought up their autostart VMs
> okay. But I've got no working virsh shell on either now. The 0.9.12 host
> was, to complicate this report, okay with virsh initially, or "virsh list"
> anyway. But it hung with a "virsh start," and now "virsh list" fails too.

Libvirt 0.8.3 didn't have any priority commands - hang in one (such as
failure to communicate with the qemu monitor due to confusion on running
a domain twice) could starve all other commands.  But we fixed that in
the meantime, and libvirt 0.9.12 is supposed to be able to 'virsh list'
without any delay due to a hung low-priority command.

> 
> So ... what should I look for to have been left where by the crash that's
> making virsh hang? 

Do you have debugging symbols handy?  At this point, a gdb backtgrace
would be the best place to look for clues.

> 
> Is there any way to get virsh to provide debugging info in a
> coffee-addled-friendly way? I've of course Googled "virsh list" hanging, but
> without finding anything that seems to directly apply to my case, although
> it's been seen before.

I'm not sure I have the best suggestions today, but maybe someone else
can also chime in.  Good luck.

-- 
Eric Blake   eblake at redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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