Re: [libvirt] [RFC PATCH] lxc: don't return error on GetInfo when cgroups not yet set up
On Thu, Sep 29, 2011 at 10:12:17PM -0500, Serge E. Hallyn wrote:
Quoting Daniel P. Berrange (berrange(a)redhat.com):
> On Wed, Sep 28, 2011 at 02:14:52PM -0500, Serge E. Hallyn wrote:
> > Nova (openstack) calls libvirt to create a container, then
> > periodically checks using GetInfo to see whether the container
> > is up. If it does this too quickly, then libvirt returns an
> > error, which in libvirt.py causes an exception to be raised,
> > the same type as if the container was bad.
> lxcDomainGetInfo(), holds a mutex on 'dom' for the duration of
> its execution. It checks for virDomainObjIsActive() before
> trying to use the cgroups.
Yes, it does, but
> lxcDomainStart(), holds the mutex on 'dom' for the duration of
> its execution, and does not return until the container is running
> and cgroups are present.
No. It calls the lxc_controller with --background. The controller
main task in turn exits before the cgroups have been set up. There
is the race.
The lxcDomainStart() method isn't actually waiting on the child
pid directly, so the --background flag ought not to matter. We
have a pipe that we pass into the controller, which we wait on
for a notification after running the process. The controller
does not notify the 'handshake' FD until after cgroups have
been setup, unless I'm mis-interpreting our code
Daniel
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