linux-kernel - Re: [RFC PATCH v3 7/9] yield_to(), cpu-hotplug: Prevent offlining of other CPUs properly

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Message-ID: <20121209204053.GA6593@redhat.com>
Date:	Sun, 9 Dec 2012 21:40:53 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Cc:	tglx@...utronix.de, peterz@...radead.org,
	paulmck@...ux.vnet.ibm.com, rusty@...tcorp.com.au,
	mingo@...nel.org, akpm@...ux-foundation.org, namhyung@...nel.org,
	vincent.guittot@...aro.org, tj@...nel.org, sbw@....edu,
	amit.kucheria@...aro.org, rostedt@...dmis.org, rjw@...k.pl,
	wangyun@...ux.vnet.ibm.com, xiaoguangrong@...ux.vnet.ibm.com,
	nikunj@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v3 7/9] yield_to(), cpu-hotplug: Prevent offlining
	of other CPUs properly

On 12/10, Srivatsa S. Bhat wrote:
>
> On 12/10/2012 01:18 AM, Oleg Nesterov wrote:
> >> -		if (preempt && rq != p_rq)
> >> +		if (preempt && rq != p_rq && cpu_online(task_cpu(p)))
> >
> > Why do we need this change?
> >
> > Afaics, you could add BUG_ON(!cpu_online(...)) instead?
> >
> > I am just curious.
> >
>
> Oh, I think that's a remnant of v1 (which needed readers to use
> cpu_online_stable()). You're right, we don't need it.

Ah OK, thanks.

> Or we could put a
> BUG_ON instead, like you suggested.

IMHO it would be better to simply drop this chunk.

Oleg.

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