Date: Wed, 21 Dec 2016 14:38:54 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Alexander Stein <alexander.stein@systec-electronic.com>
Cc: Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Will Deacon <will.deacon@arm.com>, Mark Rutland <mark.rutland@arm.com>,
        Russell King <linux@armlinux.org.uk>, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 2/3] drivers/perf: arm_pmu: add arm_pmu_device_remove
Message-ID: <20161221133854.GU3124@twins.programming.kicks-ass.net>
References: <20161221101935.17178-1-alexander.stein@systec-electronic.com>
 <20161221101935.17178-3-alexander.stein@systec-electronic.com>
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On Wed, Dec 21, 2016 at 11:19:34AM +0100, Alexander Stein wrote:
> Add ARM PMU removal function. This will be required by perf event drivers
> when option DEBUG_TEST_DRIVER_REMOVE is enabled.
> 
> Signed-off-by: Alexander Stein <alexander.stein@systec-electronic.com>
> ---
>  drivers/perf/arm_pmu.c       | 14 ++++++++++++++
>  include/linux/perf/arm_pmu.h |  2 ++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
> index a9bbdbf..b7ddc4c 100644
> --- a/drivers/perf/arm_pmu.c
> +++ b/drivers/perf/arm_pmu.c
> @@ -1022,6 +1022,7 @@ int arm_pmu_device_probe(struct platform_device *pdev,
>  	armpmu_init(pmu);
>  
>  	pmu->plat_device = pdev;
> +	platform_set_drvdata(pdev, pmu);
>  
>  	if (node && (of_id = of_match_node(of_table, pdev->dev.of_node))) {
>  		init_fn = of_id->data;
> @@ -1073,6 +1074,19 @@ int arm_pmu_device_probe(struct platform_device *pdev,
>  	return ret;
>  }
>  
> +int arm_pmu_device_remove(struct platform_device *pdev)
> +{
> +	struct arm_pmu *pmu = platform_get_drvdata(pdev);
> +
> +	__oprofile_cpu_pmu = NULL;
> +
> +	perf_pmu_unregister(&pmu->pmu);
> +
> +	cpu_pmu_destroy(pmu);
> +
> +	return 0;
> +}

So normally, if there are events that use this pmu, we hold a reference
on its module, which avoids removal from happening.

How is that guarantee made by DEBUG_TEST_DRIVER_REMOVE ? Or will it
simply kill everything even though there's active events for the PMU?