linux-kernel - RE: [PATCH] ACPI/CPUIDLE: prevent setting pm

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Message-ID: <7E82351C108FA840AB1866AC776AEC4608E237D5@orsmsx505.amr.corp.intel.com>
Date:	Mon, 28 Jul 2008 15:05:09 -0700
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	Andi Kleen <andi@...stfloor.org>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Len Brown <lenb@...nel.org>
Subject: RE: [PATCH] ACPI/CPUIDLE: prevent setting pm_idle to NULL



>-----Original Message-----
>From: Andi Kleen [mailto:andi@...stfloor.org]
>Sent: Monday, July 28, 2008 12:53 PM
>To: Thomas Gleixner
>Cc: Andi Kleen; Linus Torvalds; Andrew Morton; LKML; Ingo
>Molnar; Dhaval Giani; Pallipadi, Venkatesh; Len Brown
>Subject: Re: [PATCH] ACPI/CPUIDLE: prevent setting pm_idle to NULL
>
>> The problem here is that the acpi/cpuidle code can be in a
>state where
>> the _save/old variables _ARE_ NULL because they had not been
>> initialized with the original pm_idle before the module is removed or
>> the cst state changes. So all we have to do is to prevent pm_idle to
>> be set to NULL.
>
>It still seems wrong to me to fall back to the cpuidle idle function
>instead of the earlier idle function just because cpuidle was loaded
>in a weird way.
>

CPUIDLE code does not have any problem here, as it always saves the
pm_idle from initcall, which should be set to right idle, default or mwait.
It is just a safety check getting added.

Real problem reported here is in acpi processor_idle without CPUIDLE, and
in a case where there are no real ACPI C-states on the platform,
it was ending up marking pm_idle = NULL at run time (cpu offline/online path),
as there is no saved idle pointer.

Thanks,
Venki
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