linux-kernel - Re: [PATCH V2] cpufreq: Disallow ->resolve_freq() for drivers providing ->target

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Message-ID: <20160721234558.GX27987@graphite.smuckle.net>
Date:	Thu, 21 Jul 2016 16:45:58 -0700
From:	Steve Muckle <steve.muckle@...aro.org>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	Steve Muckle <steve.muckle@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Linux PM <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Juri Lelli <Juri.Lelli@....com>,
	Patrick Bellasi <patrick.bellasi@....com>
Subject: Re: [PATCH V2] cpufreq: Disallow ->resolve_freq() for drivers
 providing ->target_index()

On Fri, Jul 22, 2016 at 01:32:00AM +0200, Rafael J. Wysocki wrote:
> On Fri, Jul 22, 2016 at 1:22 AM, Steve Muckle <steve.muckle@...aro.org> wrote:
> > On Fri, Jul 22, 2016 at 01:22:22AM +0200, Rafael J. Wysocki wrote:
> >> OK, applied.
> >
> > FWIW I do have a concern on this patch, I think it adds unnecessary
> > overhead.
> 
> It isn't unnecessary.  It prevents an otherwise possible kernel crash
> from happening.

The logic may not be unecessary, but the overhead is. The crash could be
prevented in a way that doesn't require repeatedly checking a pointer
that doesn't change.