[libvirt] libvirt 2.3.0 and later versions hanging

[Michal Privoznik]

On 03/30/2017 01:40 PM, Paul Gildea wrote:
> Hi, I am starting a libvritd process when booting up an embedded networking
> system via python, like so:
> subprocess.Popen(["libvirtd","-d"],stdout=subprocess.PIPE,stderr=subprocess.PIPE)
>
> This runs and works fine for version 1.2.20. However after I upgraded to
> 2.3.0 I started noticing an intermittent bug. Sometimes my CLI will hang
> when libvirtd is starting (most of the time it starts fine).
>
> I ssh'd in and had a look around.  libvirtd had a second process entry:
> [root at trx-r2 log]# ps ax | grep libvirt
>   826 ?        Sl     0:00 libvirtd -d
>   843 ?        S      0:00 libvirtd -d
>   869 pts/0    S+     0:00 grep libvirt
>
> Using strace I could see the second entry was blocking (FUTEX). Kill
> libvirtd processes and the boot continues as normal.  I updated libvirt to
> the latest version and this still happens. To confirm I downgraded to
> 1.2.20 again and everything works smoothly. Any idea of what may have
> changed to cause this, pointers for me as to where to have a look?

The best would be to see the process tree (ps axf) and also get a 
stacktrace of both daemons - what are they doing. From there we can make 
an educated guess where to look next.

Michal