linux-kernel - Re: [PULL] module, param and stop

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Message-ID: <20081026124239.GA4787@osiris.boeblingen.de.ibm.com>
Date:	Sun, 26 Oct 2008 13:42:39 +0100
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andi Kleen <ak@...e.de>, Greg Kroah-Hartman <gregkh@...e.de>,
	Arjan van de Ven <arjan@...radead.org>,
	Hugh Dickins <hugh@...itas.com>, walt <w41ter@...il.com>
Subject: Re: [PULL] module, param and stop_machine patches

On Sun, Oct 26, 2008 at 07:16:16PM +1100, Rusty Russell wrote:
> On Sunday 26 October 2008 09:33:43 Linus Torvalds wrote:
> > On Sun, 26 Oct 2008, Rusty Russell wrote:
> > > Thanks, Heiko tracked this down; he's probably sleeping now but Hugh and
> > > Walt reported this fixes it for them and it makes sense.
> > I'm not seeing any "tracked it down".
> He tracked it down to moving init_workqueues() too early, so he moved that
> back.
> 
> > And it then mixes things up with 'stop_machine_init()' mess. Why does that
> > need to run so early?
> 
> The S/390 guys want to run it stop_machine v. early, so when Heiko introduced
> stop_machine_init() he made it an early_initcall().
> 
> > IOW, I don't think that patch is anything but a "hey, test if it works
> > with this". None of the changes or the problems are explained.
> 
> Indeed.
> 
> Turns out it's the cpu_online_map difference.  If init_workqueues() is called
> too early, only the boot cpu is set.  We then only create_workqueue_thread()
> for the boot cpu.
> 
> If CONFIG_HOTPLUG_CPU=y, it's fine since the hotplug callback will create the
> workqueue threads for the other cpus as they come up.  Without it, the kevent
> workqueues on non-boot cpus don't get processed.
> 
> Still boots for me, but was a bit sick (varying, but no keyboard was one
> symptom).

Yes, it's all my fault. I always think in terms of CONFIG_HOTPLUG_CPU=y, so
I couldn't make any sense of the bug reports and just reverted the
init_workqueues() call move and added an explicit stop_machine_init() call,
so that we don't depend on linkage order.
Thanks for tracking it down, Rusty!

> > Nor do I see a sign-off from Heiko on it.

Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>

But I guess you don't need that anymore since you already committed a
fix for this.

Thanks,
Heiko
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