linux-kernel - Re: perf/x86/amd/power missing pmu::module initialisation

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Message-ID: <20171120155525.xqxfk4vrfkpxx6yc@lakrids.cambridge.arm.com>
Date:   Mon, 20 Nov 2017 15:55:25 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Huang Rui <ray.huang@....com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: perf/x86/amd/power missing pmu::module initialisation

Hi,

Sorry for the late reply.

On Tue, Nov 07, 2017 at 08:50:53PM +0800, Huang Rui wrote:
> On Fri, Nov 03, 2017 at 11:33:56AM +0000, Mark Rutland wrote:
> > As a heads-up, I believe that arch/x86/events/amd/power.c is currently
> > missing initialisation of pmu::module, which could result in problems
> > when the module is unloaded.
> > 
> > We've just spotted a similar problem in a couple of ARM PMUs, and AFAICT
> > the AMD power PMU is the only other PMU affected.
> > 
> > Other modular PMUs all initialise this to THIS_MODULE prior to calling
> > perf_pmu_register().
> 
> Thanks to let me know. I have dived into pmu for quite a while. Could you
> please share more information or forward related mail thread, so that I can
> repro this issue in my side. :-)

Unfortunately, in the other thread, we only noticed that this was
missing, and weren't entirely sure of the issue.

IIUC, without pmu::module initialised, the module can be freed
immediately after an event is created by perf_init_event(), while the
event is still around, with dangling pointers to the PMU (and other data
structures owned by the module that have been freed).

Thanks,
Mark.