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

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Message-ID: <07cd8e16-6967-410a-4006-6c82b0263397@huawei.com>
Date:   Thu, 16 Jul 2020 11:21:25 +0100
From:   John Garry <john.garry@...wei.com>
To:     Will Deacon <will@...nel.org>, Qi Liu <liuqi115@...wei.com>
CC:     <zhangshaokun@...ilicon.com>, <mark.rutland@....com>,
        <wang.wanghaifeng@...wei.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linuxarm@...wei.com>
Subject: Re: [PATCH] drivers/perf: Fix kernel panic when rmmod PMU modules
 during perf sampling

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