linux-kernel - Re: [PATCH 1/2] [CPUFREQ] powernow-k8: Don't notify of successful transition if we failed.

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Message-ID: <20110615222608.GA14031@dumpdata.com>
Date:	Wed, 15 Jun 2011 18:26:08 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
	davej@...hat.com, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, x86@...nel.org, cpufreq@...r.kernel.org,
	andre.przywara@....com, Mark.Langsdorf@....com
Subject: Re: [PATCH 1/2] [CPUFREQ] powernow-k8: Don't notify of successful
 transition if we failed.

> > @@ -1112,6 +1114,9 @@ static int transition_frequency_pstate(struct powernow_k8_data *data,
> >  	}
> >  
> >  	res = transition_pstate(data, pstate);
> > +	if (res)
> > +		return res;
> 
> That's wrong because transition_pstate() returns 0 unconditionally
> (at least it does so on 3.0-rc3). But this change accidentally fixes
> a different bug because res is used uninitialized, containing stack
> garbage otherwise.
> 
> A proper fix should be to check against data->max_hw_pstate and
> check whether the entry is not CPUFREQ_ENTRY_INVALID (look at
> fill_powernow_table_pstate() for example).

Aha! I can respin a patch for that tomorrow.
> 
> I'm guessing this oops happens when powernow-k8 is loaded in the guest
> and that the actual power management is done in the hypervisor?

Yes.
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