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

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Message-ID: <50C55F6A.4040909@linux.vnet.ibm.com>
Date:	Mon, 10 Dec 2012 09:34:58 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.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 12/10/2012 02:10 AM, Oleg Nesterov wrote:
> 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.
> 

Sure, will drop it. Its distracting, if nothing else ;-)

Regards,
Srivatsa S. Bhat

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