linux-kernel - Re: [PATCH] arm: kernel/perf_event_cpu.c: fix error null pointer dereference check

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Message-ID: <20130114174020.GH31341@mudshark.cambridge.arm.com>
Date:	Mon, 14 Jan 2013 17:40:20 +0000
From:	Will Deacon <will.deacon@....com>
To:	Cong Ding <dinggnu@...il.com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm: kernel/perf_event_cpu.c: fix error null pointer
 dereference check

On Mon, Jan 14, 2013 at 05:38:26PM +0000, Cong Ding wrote:
> On Mon, Jan 14, 2013 at 05:23:46PM +0000, Russell King - ARM Linux wrote:
> > On Mon, Jan 14, 2013 at 05:18:53PM +0000, Cong Ding wrote:
> > > the pointer cpu_pmu is used without null pointer dereference check, and is
> > > checked after the using of it, so we move the null pointer check to before the
> > > first use.
> > 
> > The NULL pointer check is not necessary.  cpu_pmu_init() is called
> > after cpu_pmu has already been dereferenced by its caller:
> > 
> >         cpu_pmu = pmu;
> >         cpu_pmu->plat_device = pdev;
> >         cpu_pmu_init(cpu_pmu);
> > 
> > So...
> > 
> > > -	/* Ensure the PMU has sane values out of reset. */
> > > -	if (cpu_pmu && cpu_pmu->reset)
> > 
> > Just replace this with:
> > 	if (cpu_pmu->reset)
> Thanks Russell, I will send version 2.

No need, I've taken this into my perf/updates branch.

Thanks,

Will
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