linux-kernel - Re: [PATCH] adjust root-domain->online span in response to hotplug event

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Date:	Sat, 8 Mar 2008 18:35:15 -0800
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Gregory Haskins <ghaskins@...ell.com>
Cc:	suresh.b.siddha@...el.com, rjw@...k.pl, akpm@...ux-foundation.org,
	dmitry.adamushko@...il.com, ego@...ibm.com, mingo@...e.hu,
	oleg@...sign.ru, yi.y.yang@...el.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de
Subject: Re: [PATCH] adjust root-domain->online span in response to hotplug event

On Sat, Mar 08, 2008 at 12:10:15AM -0500, Gregory Haskins wrote:
> Suresh Siddha wrote:
>  >
>  > -	cpus_and(*lowest_mask, task_rq(task)->rd->online, task->cpus_allowed);
>  > +	cpus_and(*lowest_mask, task->cpus_allowed, cpu_online_map);
> 
> Hi Suresh,
>    Unfortunately, this patch will introduce its own set of bugs. 

Is that because of the missing get/put_online_cpus() ?

> However, your analysis was spot-on.  I think I see the problem now.  It 
> was introduced when I put a hack in to "fix" s2ram problems in -mm as a 
> result of the new root-domain logic.  I think the following patch will 
> fix both issues:

BTW, what is use of per root domains online map, when we have global
cpu_online_map() ? Each domains span & cpu_online_map should give
domain_online_map anyhow.

And is n't it buggy if someone accesses rd->online with out get/put_online_map()

thanks,
suresh
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