Re: perf/x86/amd/power missing pmu::module initialisation

From: Mark Rutland
Date: Mon Nov 20 2017 - 10:55:32 EST


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).