linux-kernel - Re: [4.9-rc1+] intel_uncore builtin + CONFIG_DEBUG_TEST_DRIVER

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Date:   Thu, 20 Oct 2016 11:04:16 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     CAI Qian <caiqian@...hat.com>, Rob Herring <robh@...nel.org>,
        Kan Liang <kan.liang@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [4.9-rc1+] intel_uncore builtin +
 CONFIG_DEBUG_TEST_DRIVER_REMOVE kernel panic

On Thu, Oct 20, 2016 at 10:58:03AM +0200, Jiri Olsa wrote:

> @@ -8869,11 +8869,15 @@ void perf_pmu_unregister(struct pmu *pmu)
>  	free_percpu(pmu->pmu_disable_count);
>  	if (pmu->type >= PERF_TYPE_MAX)
>  		idr_remove(&pmu_idr, pmu->type);
> -	if (pmu->nr_addr_filters)
> -		device_remove_file(pmu->dev, &dev_attr_nr_addr_filters);
> -	device_del(pmu->dev);
> -	put_device(pmu->dev);
> +	mutex_lock(&pmus_lock);
> +	if (pmu_bus_running) {
> +		if (pmu->nr_addr_filters)
> +			device_remove_file(pmu->dev, &dev_attr_nr_addr_filters);
> +		device_del(pmu->dev);
> +		put_device(pmu->dev);
> +	}
>  	free_pmu_context(pmu);
> +	mutex_unlock(&pmus_lock);
>  }
>  EXPORT_SYMBOL_GPL(perf_pmu_unregister);

I think that is still racy..


unregister:		sysfs_init:

mutex_lock(&pmus_lock);
list_del_rcu(&pmu->entry);
mutex_unlock(&pmus_lock);

synchronize_*rcu();

			mutex_lock(&pmus_lock);
			list_for_each_entry(pmu, &pmus, entry) {
				/* add device muck */
				/* will _NOT_ see our PMU */
			}
			pmus_bus_running = 1;
			mutex_unlock(&pmus_lock);

mutex_lock(&pmus_lock);
if (pmu_bus_running) {
	device_del() /* OOPS */


What you want is to read pmu_bus_running in the same pmus_lock section
as we do the list_del, and then use that local copy later.