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Date:   Thu, 16 Jul 2020 11:30:59 +0100
From:   Will Deacon <will@kernel.org>
To:     Robin Murphy <robin.murphy@arm.com>
Cc:     Qi Liu <liuqi115@huawei.com>, mark.rutland@arm.com,
        john.garry@huawei.com, linux-kernel@vger.kernel.org,
        linuxarm@huawei.com, zhangshaokun@hisilicon.com,
        wang.wanghaifeng@huawei.com, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] drivers/perf: Fix kernel panic when rmmod PMU modules
 during perf sampling
Message-ID: <20200716103058.GE7036@willie-the-truck>
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 <20200716094144.GC6771@willie-the-truck>
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On Thu, Jul 16, 2020 at 11:26:25AM +0100, Robin Murphy wrote:
> On 2020-07-16 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?
> 
> For the platform device itself, yes, but this is for the PMU device - perf
> needs to take a reference to the module, otherwise the platform device can
> still be pulled out from under its feet.

Urgh, gross.

> I can't remember if we ever discussed making perf_pmu_register() do the same
> trick as platform_device_register() and friends, but obviously it's a
> possibility.

Yeah, but I suppose this patch is the right thing to do for now. I'll queue
it as a fix.

Will