linux-kernel - Re: [PATCH/RFC 0/4] Add stop_machine_get/put_threads to stop

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Message-Id: <200810081127.05311.rusty@rustcorp.com.au>
Date:	Wed, 8 Oct 2008 10:27:04 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	jens.axboe@...cle.com, schwidefsky@...ibm.com,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH/RFC 0/4] Add stop_machine_get/put_threads to stop_machine infrastructrue.

On Wednesday 08 October 2008 02:38:54 Heiko Carstens wrote:
> On Tue, Oct 07, 2008 at 11:39:58AM +1000, Rusty Russell wrote:
> > That's exactly my idea.  We kmalloc already because NR_CPUS might be too
> > big for the stack.  This version would just kmalloc a struct containing
> > everything we need.
>
> Ok, I did that but the resulting code is astonishingly ugly, so I thought I
> should share it :)

Yeah, the diffstat tells the story.

> Another thing that comes to mind is cpu hotplug: if somebody issued
> stop_machine_prepare() and then a cpu hotplug operation gets started we
> need to create or kill a kstop thread. For that we need the "sm" so we can
> save/find the task_struct pointer of the thread.

Erk, good point.  Suckage.

OK, idea #2.  Let's just always have a kstopmachine thread running on every 
online cpu.  Is there a sane way to reuse the workqueue threads for this?

Thanks,
Rusty.

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