linux-kernel - Re: [PATCH 4/7] sched: implement force_cpus

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Message-ID: <4B1CE1E8.2070803@kernel.org>
Date:	Mon, 07 Dec 2009 20:07:20 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	tglx@...utronix.de, mingo@...e.hu, avi@...hat.com, efault@....de,
	rusty@...tcorp.com.au, linux-kernel@...r.kernel.org,
	Gautham R Shenoy <ego@...ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 4/7] sched: implement force_cpus_allowed()

Hello,

On 12/07/2009 07:54 PM, Peter Zijlstra wrote:
> So we seem to do cleanup_workqueue_thread() from CPU_POST_DEAD, but at
> that time any thread that might still be around will most certainly not
> be running on the offlined cpu anymore.
> 
> If you really want to ensure you remain on the cpu, you have to complete
> from CPU_DOWN_PREPARE.
> 
> We're not running things from offline CPUs.

Oh, no, we're not doing that.  We can't do that.  What we're doing is
to continue to process works which were queued on the now offline cpu
unless it has been flushed/cancled from one of the cpu down
notifications and the reason why we need to be able to fork after
active is clear is to guarantee those flush/cancels don't deadlock.

Thanks.

-- 
tejun
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