linux-kernel - Re: [PATCH 2/3] work_on_cpu: Use our own workqueue.

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Date:	Mon, 26 Jan 2009 15:01:24 -0800
From:	Mike Travis <travis@....com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	a.p.zijlstra@...llo.nl, rusty@...tcorp.com.au, mingo@...hat.com,
	davej@...hat.com, cpufreq@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] work_on_cpu: Use our own workqueue.

Ingo Molnar wrote:
> * Oleg Nesterov <oleg@...hat.com> wrote:
> 
>> But "[PATCH 1/3] work_on_cpu: dont try to get_online_cpus() in 
>> work_on_cpu." removes get_online_cpus/put_online_cpus, this means the 
>> work can run on the wrong CPU anyway. Or work_on_cpu() can hang forever 
>> if CPU has already gone away before queue_work_on().
>>
>> Confused.
> 
> The idea was to require work_on_cpu() users to be CPU hotplug-safe. But 
> ... Rusty pointed it out in the past that this might be fragile, and we 
> could put back the get_online_cpus()/put_online_cpus() calls.
> 
> Rusty, what do you think?
> 
> 	Ingo


I believe that is the intention, in that the caller should insure that
the cpu does not go offline.  But also as Rusty stated, the previous usages
of set_cpus_allowed did not always insure this, so it's at least not a
regression.

I'll put it on my todo list to check the references in tip/cpus4096 to see
where they stand on the get_online_cpus() issue.

Thanks,
Mike
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