linux-kernel - Re: [PATCH 06/19] perf: Simplify perf_pmu

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Message-ID: <197f9c0e-e057-41d4-8492-8e49adc45d18@amd.com>
Date: Wed, 20 Nov 2024 21:23:56 +0530
From: Ravi Bangoria <ravi.bangoria@....com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mingo@...nel.org, lucas.demarchi@...el.com, linux-kernel@...r.kernel.org,
 willy@...radead.org, acme@...nel.org, namhyung@...nel.org,
 mark.rutland@....com, alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
 irogers@...gle.com, adrian.hunter@...el.com, kan.liang@...ux.intel.com,
 Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH 06/19] perf: Simplify perf_pmu_register()

On 20-Nov-24 8:16 PM, Peter Zijlstra wrote:
> On Wed, Nov 20, 2024 at 06:36:55PM +0530, Ravi Bangoria wrote:
>> Hi Peter,
>>
>>> --- a/kernel/events/core.c
>>> +++ b/kernel/events/core.c
>>> @@ -11778,52 +11778,49 @@ static void perf_pmu_free(struct pmu *pm
>>>  	free_percpu(pmu->cpu_pmu_context);
>>>  }
>>>  
>>> -int perf_pmu_register(struct pmu *pmu, const char *name, int type)
>>> +DEFINE_FREE(pmu_unregister, struct pmu *, if (_T) perf_pmu_free(_T))
>>> +
>>> +int perf_pmu_register(struct pmu *_pmu, const char *name, int type)
>>>  {
>>> -	int cpu, ret, max = PERF_TYPE_MAX;
>>> +	int cpu, max = PERF_TYPE_MAX;
>>>  
>>> -	pmu->type = -1;
>>> +	struct pmu *pmu __free(pmu_unregister) = _pmu;
>>> +	guard(mutex)(&pmus_lock);
>>>  
>>> -	mutex_lock(&pmus_lock);
>>> -	ret = -ENOMEM;
>>>  	pmu->pmu_disable_count = alloc_percpu(int);
>>>  	if (!pmu->pmu_disable_count)
>>> -		goto unlock;
>>> +		return -ENOMEM;
>>>  
>>> -	if (WARN_ONCE(!name, "Can not register anonymous pmu.\n")) {
>>> -		ret = -EINVAL;
>>> -		goto free;
>>> -	}
>>> +	if (WARN_ONCE(!name, "Can not register anonymous pmu.\n"))
>>> +		return -EINVAL;
>>>  
>>> -	if (WARN_ONCE(pmu->scope >= PERF_PMU_MAX_SCOPE, "Can not register a pmu with an invalid scope.\n")) {
>>> -		ret = -EINVAL;
>>> -		goto free;
>>> -	}
>>> +	if (WARN_ONCE(pmu->scope >= PERF_PMU_MAX_SCOPE,
>>> +		      "Can not register a pmu with an invalid scope.\n"))
>>> +		return -EINVAL;
>>>  
>>>  	pmu->name = name;
>>>  
>>>  	if (type >= 0)
>>>  		max = type;
>>>  
>>> -	ret = idr_alloc(&pmu_idr, NULL, max, 0, GFP_KERNEL);
>>> -	if (ret < 0)
>>> -		goto free;
>>> +	CLASS(idr_alloc, pmu_type)(&pmu_idr, NULL, max, 0, GFP_KERNEL);
>>> +	if (pmu_type.id < 0)
>>> +		return pmu_type.id;
>>>  
>>> -	WARN_ON(type >= 0 && ret != type);
>>> +	WARN_ON(type >= 0 && pmu_type.id != type);
>>>  
>>> -	pmu->type = ret;
>>> +	pmu->type = pmu_type.id;
>>>  	atomic_set(&pmu->exclusive_cnt, 0);
>>>  
>>>  	if (pmu_bus_running && !pmu->dev) {
>>> -		ret = pmu_dev_alloc(pmu);
>>> +		int ret = pmu_dev_alloc(pmu);
>>>  		if (ret)
>>> -			goto free;
>>> +			return ret;
>>
>> pmu_dev_alloc() can fail before or in device_add(). perf_pmu_free() should
>> not call device_del() for such cases. No?
> 
> Right you are -- but is this not introduced in the previous patch?

I didn't notice that.

> Also, this should cure things, no?
> 
> ---
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -11810,6 +11810,7 @@ static int pmu_dev_alloc(struct pmu *pmu
>  
>  free_dev:
>  	put_device(pmu->dev);
> +	pmu->dev = NULL;
>  	goto out;
>  }
>  

Yes, this should fix it.

Thanks,
Ravi