Re: [PATCH] drivers/perf: Fix kernel panic when rmmod PMU modules during perf sampling

[John Garry]

On 16/07/2020 10:41, Will Deacon wrote:
> On Thu, Jul 16, 2020 at 05:19:25PM +0800, Qi Liu wrote:
> > Kernel panic will also happen when users try to unbind PMU drivers with
> > device. This unbind issue could be solved by another patch latter.
> >
> >   drivers/perf/arm_smmuv3_pmu.c                 | 1 +
> >   drivers/perf/fsl_imx8_ddr_perf.c              | 1 +
> >   drivers/perf/hisilicon/hisi_uncore_ddrc_pmu.c | 1 +
> >   drivers/perf/hisilicon/hisi_uncore_hha_pmu.c  | 1 +
> >   drivers/perf/hisilicon/hisi_uncore_l3c_pmu.c  | 1 +
> >   5 files changed, 5 insertions(+)
> >
> > diff --git a/drivers/perf/arm_smmuv3_pmu.c b/drivers/perf/arm_smmuv3_pmu.c
> > index 48e28ef..90caba56 100644
> > --- a/drivers/perf/arm_smmuv3_pmu.c
> > +++ b/drivers/perf/arm_smmuv3_pmu.c
> > @@ -742,6 +742,7 @@ static int smmu_pmu_probe(struct platform_device *pdev)
> >   	platform_set_drvdata(pdev, smmu_pmu);
> >
> >   	smmu_pmu->pmu = (struct pmu) {
> > +		.module		= THIS_MODULE,
>
> I thought platform_driver_register() did this automatically?

Isn't that something different? The perf framework knows nothing of the 
platform_device/driver really, and just knows the event_source device 
which it creates. And so we also need to tell the perf framework about 
the module backing this pmu.

I think some relevant code is perf_try_init_event() -> 
try_module_get(pmu->module).

Thanks,
John