Re: [PATCH 5/7] xen: sched: get rid of the per domain vCPU list in Credit2

[Dario Faggioli <dario.faggioli@citrix.com>]

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On Thu, 2015-10-08 at 14:56 +0100, Andrew Cooper wrote:
> On 08/10/15 13:53, Dario Faggioli wrote:
> > @@ -1443,7 +1433,7 @@ csched2_dom_cntl(
> >  
> >          if ( op->u.credit2.weight != 0 )
> >          {
> > -            struct list_head *iter;
> > +            struct vcpu *vc;
> 
> Any chance of starting to align on the more common practice of just v
> for a vcpu?
> 
I see. I'm a bit split, though. It's v in schedule.c, but it's
**always** (with only 2 exceptions) vc in sched_*.c.

I know that, if we want to align, we need to start from somewhere, but
OTOH, consistency is rather helpful when reading this code.

I'll think about it...

> > @@ -1539,9 +1528,7 @@ csched2_free_domdata(const struct scheduler
> > *ops, void *data)
> >  static void
> >  csched2_dom_destroy(const struct scheduler *ops, struct domain
> > *dom)
> >  {
> > -    struct csched2_dom *sdom = CSCHED2_DOM(dom);
> > -
> > -    BUG_ON(!list_empty(&sdom->vcpu));
> > +    BUG_ON(CSCHED2_DOM(dom)->nr_vcpus != 0);
> 
> This is a latent bug (excuse the pun) which can be triggered by
> userspace.  There is no guarantee or requirement that a domain
> registered with a scheduler has vcpus.
> 
Mmm... I think the original check wanted to catch cases where a domain
(or, at least, its scheduling related bits) is being destroyed with
vcpus still on.

While trying to retain the BUG_ON, even with sdom->vcpu not being there
any longer, I probably went too far.

 BUG_ON(CSCHED2_DOM(dom)->nr_vcpus > 0);

should be fine, I think.

Thanks and Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)


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