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From:   Jiang Biao <benbjiang@gmail.com>
Date:   Fri, 24 Jul 2020 20:08:43 +0800
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Subject: Re: [RFC PATCH 09/16] sched/fair: core wide cfs task priority
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To:     Aaron Lu <aaron.lwe@gmail.com>
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On Fri, 24 Jul 2020 at 15:17, Aaron Lu <aaron.lwe@gmail.com> wrote:
>
> On Wed, Jul 22, 2020 at 12:23:44AM +0000, benbjiang(=E8=92=8B=E5=BD=AA) w=
rote:
> >
> >
> > > +/*
> > > + * This function takes care of adjusting the min_vruntime of sibling=
s of
> > > + * a core during coresched enable/disable.
> > > + * This is called in stop machine context so no need to take the rq =
lock.
> > Hi,
> >
> > IMHO, it seems that stop machine context cannot guarantee race free. Th=
e param *cpu* maybe not *this_cpu*, rq lock should be taken even in stop ma=
chine context, and irq should be disabled too, to avoid potential races wit=
h other contexts.
> >
>
> In stop machine context, all CPUs except the active ones are spinning
> with irq disabled and in this invocation of stop_machine(), only one
> CPU is active so I don't think race is possible.
You're right, stop_machine provides much more protection than stop_*_cpu.
Thanks for the explanation.

Regards,
Jiang