linux-kernel - Re: [linux-pm] [PATCH 04/18] x86 idle: EXPORT_SYMBOL(default_idle, pm

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Message-ID: <4D9714E3.8010302@linux.vnet.ibm.com>
Date:	Sat, 02 Apr 2011 17:51:55 +0530
From:	Trinabh Gupta <trinabh@...ux.vnet.ibm.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Len Brown <lenb@...nel.org>, Len Brown <len.brown@...el.com>,
	linux-pm@...ts.linux-foundation.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, Jiri Kosina <jkosina@...e.cz>
Subject: Re: [linux-pm] [PATCH 04/18] x86 idle: EXPORT_SYMBOL(default_idle,
 pm_idle) only when APM demands it



On 04/02/2011 04:58 PM, Alan Cox wrote:
> On Sat, 02 Apr 2011 02:22:46 -0400
> Len Brown<lenb@...nel.org>  wrote:
>
>> From: Len Brown<len.brown@...el.com>
>>
>> In the long run, we don't want default_idle() or (pm_idle)() to
>> be exported outside of process.c.  Start by not exporting them
>> to modules, unless the APM build demands it.
>
> Pointless added complexity. Why are you so determined to minimise this -
> it makes no odds to anyone.

Hi Alan,

I am not sure if I have understood you correctly but
I think one problem is that modules such as APM
save the value of pm_idle pointer, set it and restore it back.

At module init:

original_pm_idle = pm_idle;
pm_idle  = apm_cpu_idle;

At module exit:

pm_idle = original_pm_idle;

There is no guarantee that the pointer stored
is still valid. I think people have problem with such
usage; see http://lkml.org/lkml/2009/8/28/50

Thanks,
-Trinabh
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