linux-kernel - Re: [PATCH 01/40] sched: consult online mask instead of active in select_fallback

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Message-ID: <4B544571.7020609@kernel.org>
Date:	Mon, 18 Jan 2010 20:26:41 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	torvalds@...ux-foundation.org, mingo@...e.hu, awalls@...ix.net,
	linux-kernel@...r.kernel.org, jeff@...zik.org,
	akpm@...ux-foundation.org, jens.axboe@...cle.com,
	rusty@...tcorp.com.au, cl@...ux-foundation.org,
	dhowells@...hat.com, arjan@...ux.intel.com, avi@...hat.com,
	johannes@...solutions.net, andi@...stfloor.org
Subject: Re: [PATCH 01/40] sched: consult online mask instead of active in
 select_fallback_rq()

Hello,

On 01/18/2010 07:13 PM, Peter Zijlstra wrote:
> On Mon, 2010-01-18 at 09:57 +0900, Tejun Heo wrote:
>> If called after sched_class chooses a CPU which isn't in a task's
>> cpus_allowed mask,
> 
> I can only see this happening when you're changing cpus_allowed after
> starting to take down the cpu. IOW you're moving a thread to a dying
> cpu.
> 
> This is because you're spawning workqueue threads while we're going
> down?

It got triggered by the hotplug callback creating the trustee kthread
and kthread_bind()ing it to the target cpu during CPU_DOWN_PREPARE.

Thanks.

-- 
tejun
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