Re: [Xen-devel] [PATCH 2/7] xen: sched: fix locking for insert_vcpu() in credit1 and RTDS

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Thu, 2015-10-08 at 17:49 +0200, Dario Faggioli wrote:
> On Thu, 2015-10-08 at 16:16 +0100, George Dunlap wrote:

> > It seems to me that the locking here wasn't to protect insert_vcpu,
> > but
> > to prevent any scheduling events from happening on cpu until all
> > the
> > expected infrastructure (ticks, idle vcpu, &c) were ready.  I can't
> > immediately convince myself that removing these is safe in that
> > regard.
> >  Can you address this?
> > 
> Scheduling can't happen on the cpu, until later than the end of this
> function, when, in cpupool_assign_cpu_locked(), we set to 1 its
> corresponding bit in the target cpupool's cpu_valid mask.

> We've been discussing, basically about the same issue, with Jan in
> here:
> https://www.choon.net/forum/read.php?22,3817262,3817489
> 
> And I'll add the promised ASSERT() and comment, when sending v2 of
> that
> patch. :-)
> 
Or, of course, I can put them down when doing v2 of _this_ patch, if
that makes it easier to understand why what I'm doing here is safe.

Yes, I think I'll do it here, I like it better that way.

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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