Re: [Xen-devel] [PATCH 1/6] xen/sched: call cpu_disable_scheduler() via cpu notifier

[Dario Faggioli <dfaggioli@xxxxxxxx>]

On Wed, 2019-03-27 at 18:06 +0100, Juergen Gross wrote:
> On 27/03/2019 17:58, Jan Beulich wrote:
> > > > > 
> > Well, of course nothing's going to run on that CPU anymore.
> > But vCPU-s may still have associations with it, so what I'm
> > worried about is e.g. something finding v->processor pointing
> > at an offline CPU and getting confused. Another, more exotic
> 
> v->processor is allowed to have a stale value as long as the vcpu
> isn't running.
> 
I was also concerned about things being done no longer in stop-machine, 
like Jan, and in fact, I asked for similar reassurances.

Thinking more about this, I agree with Juergen that it should work. In
fact, it's important for v->processor to point to a CPU that has its
scheduling data structure allocated and valid.

In current approach, right before suspend, that is only true for the
BSP, and that's why we move every vcpu there. But after this series,
since we don't deallocate such structs any longer, it should be ok that
v->processor retains its value.

Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Software Engineer @ SUSE https://www.suse.com/

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