Re: [Xen-devel] [PATCH 1/2] xen: fix a (latent) cpupool-related race during domain destroy

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Thu, 2016-07-14 at 10:37 +0100, Andrew Cooper wrote:
> On 14/07/16 07:41, Dario Faggioli wrote:
> > 
> > So, during domain destruction, we do:
> >  cpupool_rm_domain()    [ in domain_destroy() ]
> >  sched_destroy_domain() [ in complete_domain_destroy() ]
> > 
> > Therefore, there's a window during which, from the
> > scheduler's point of view, a domain is still there, but
> > without it being part of any cpupool.
> > 
> > [...]
> >
> > On the other hand, cpupool_rm_domain() "only" does
> > cpupool related bookkeeping, and there's no harm
> > postponing it a little bit.
> > 
> > Finally, considering that, during domain initialization,
> > we do:
> >  cpupool_add_domain()
> >  sched_init_domain()
> > 
> > It looks like it makes much more sense for the domain
> > destroy path to look like the opposite of it, i.e.:
> >  sched_destroy_domain()
> >  cpupool_rm_domain()
> > 
> > This patch does that, and it's considered worth, as it
> > fixes a bug, even if only a latent one.
> > 
> > Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
> As the cpupool bookkeeping is very closely related to the scheduler
> bookkeeping, how about having the sched_*_domain() functions involve
> the
> cpupool_*_domain() functions?
> 
That's certainly a good point.

At minimum, I certainly can (and probably should have :-P) put a couple
of ASSERT()-s in place.

However, both cpupool_add_domain() and cpupool_rm_domain() are called
only once, and I guess I can make them go into sched_init_domain() and
sched_destroy_domain(), respectively.

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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