linux-kernel - Re: perf: easily crash kernel with rapl event close

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Message-ID: <20150122101720.GA2896@worktop.programming.kicks-ass.net>
Date:	Thu, 22 Jan 2015 11:17:20 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	eranian@...il.com
Cc:	Vince Weaver <vincent.weaver@...ne.edu>,
	LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: perf: easily crash kernel with rapl event close

On Wed, Jan 21, 2015 at 09:13:11PM -0800, Stephane Eranian wrote:
> Vince,
> 
> On Wed, Jan 21, 2015 at 10:55 AM, Vince Weaver <vincent.weaver@...ne.edu> wrote:
> > Hello
> >
> > on my haswell system, running 3.19-rc5, and with
> >         echo "0" > /proc/sys/kernel/perf_event_paranoid
> >
> > I can easily crash my system with the attached test program that simply
> > opens a RAPL event and then closes it.
> >
> > This bug was found by the perf_fuzzer.
> >
> > It looks like somehow rapl_pmu gets freed to NULL but the
> > call in rapl_scale()
> >         __this_cpu_read(rapl_pmu->hw_unit)
> > still happens.
> >
> I don't see how this can happen.
> 
> I get some crashes but not with your program on my laptop.
> But I cannot catch the serial console from my laptop.
> Will try with another machine tomorrow.

I saw it today as well on an ivb-ep. I disabled rapl for now since I'm
chasing other things.
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