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Subject: Re: [PATCH] drivers/perf: Fix kernel panic when rmmod PMU modules
 during perf sampling
To:     Will Deacon <will@kernel.org>, Qi Liu <liuqi115@huawei.com>
Cc:     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
References: <1594891165-8228-1-git-send-email-liuqi115@huawei.com>
 <20200716094144.GC6771@willie-the-truck>
From:   Robin Murphy <robin.murphy@arm.com>
Message-ID: <a0f3d0c2-6a08-16a5-f7e9-42ac1d96ea11@arm.com>
Date:   Thu, 16 Jul 2020 11:26:25 +0100
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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.

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.

Robin.