Message-ID: <4140311D.4080405@yahoo.com.au>
Date: Thu, 09 Sep 2004 20:31:57 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Rusty Russell <rusty@rustcorp.com.au>
CC: Nick Piggin <piggin@cyberone.com.au>,
       Nathan Lynch <nathanl@austin.ibm.com>,
       lkml - Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@osdl.org>, Ingo Molnar <mingo@elte.hu>
Subject: Re: [patch 2/2] cpu hotplug notifier for updating sched domains
References: <200409071849.i87Inw3f143238@austin.ibm.com>	 <413E55D8.8030608@cyberone.com.au> <1094608996.8015.5.camel@booger>	 <413E6C49.5080106@cyberone.com.au> <1094725124.25639.18.camel@bach>
In-Reply-To: <1094725124.25639.18.camel@bach>
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Rusty Russell wrote:
> On Wed, 2004-09-08 at 12:19, Nick Piggin wrote:

>>Do you have a theoretical race here? Can we hotplug a CPU before the notifier
>>is registered? (I know we *can't* because it is still earlyish boot).
> 
> 
> No, init has so many serial assumptions that this is the least of our
> worries.
> 

No. But the point is, you cannot (easily) set something up like this:

"do some setup with this specific, valid cpu_online_map";
"register notifier so we can keep everything valid";

without a race between them. Protecting the notifier chain under a
different lock is the trivial fix. I'll send the patch if you'd
like?
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