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

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Message-ID: <20080728195324.GE30344@one.firstfloor.org>
Date:	Mon, 28 Jul 2008 21:53:24 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Andi Kleen <andi@...stfloor.org>,
	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>,
	Venkatesch Pallipadi <venkatesh.pallipadi@...el.com>,
	Len Brown <lenb@...nel.org>
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. 

But yes mwait_idle could be set up later after the saving state.
I suggested default_idle because it is safe, but yes it is probably
not the optimal choice.

Perhaps to solve this cleanly we really need to go to a hierarchy
of idle functions registered with priority instead of this fragile
pointer saving/restoring. 

-Andi
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