linux-kernel - Re: [PATCH] cpuidle: Make cpuidle_enable_device() call poll_idle

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Message-Id: <201101112152.19642.rjw@sisk.pl>
Date:	Tue, 11 Jan 2011 21:52:19 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Thomas Renninger <trenn@...e.de>
Cc:	Len Brown <lenb@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	"Linux-pm mailing list" <linux-pm@...ts.linux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] cpuidle: Make cpuidle_enable_device() call poll_idle_init()

On Tuesday, January 11, 2011, Thomas Renninger wrote:
> On Tuesday 11 January 2011 01:05:53 Rafael J. Wysocki wrote:
> > On Tuesday, January 11, 2011, Rafael J. Wysocki wrote:
> > > On Tuesday, January 11, 2011, Len Brown wrote:
> > > > >  /**
> > > > >   * cpuidle_enable_device - enables idle PM for a CPU
> > > > >   * @dev: the CPU
> > > > > @@ -176,6 +215,8 @@ int cpuidle_enable_device(struct cpuidle
> > > > >  		ret = __cpuidle_register_device(dev);
> > > > >  		if (ret)
> > > > >  			return ret;
> > > > > +	} else {
> > > > > +		poll_idle_init(dev);
> > > > >  	}
> > > > 
> > > > how about calling poll_idle_init() unconditionally here
> > > > and deleting the call to it from within __cpuidle_register_device()?
> > > 
> > > Fine by me, as long as poll_idle_init() is called before the conditional. :-)
> > 
> > In fact, it even doesn't need to be called before the conditional.
> > 
> > So fine by me anyway.
> What exactly was broken?
> Is it only sysfs values?

Not only that, the entire state[0] was busted.

> Looks like an uninitialized "poll" state can cause cpuidle
> to not enter "poll" state when it should or enter "poll" when
> it should not.
> Hm, if cpuidle would try to call state[0]->enter,
> it might even segfault?

Yes, in theory.

> Even not that many machines might be affected because most won't
> implement runtime C-state changes, shouldn't this still be
> submitted for stable@ kernels?

I think it should.

Thanks,
Rafael
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