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

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Message-ID: <20241120144603.GG19989@noisy.programming.kicks-ass.net>
Date: Wed, 20 Nov 2024 15:46:03 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Ravi Bangoria <ravi.bangoria@....com>
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
Subject: Re: [PATCH 06/19] perf: Simplify perf_pmu_register()

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?

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;
 }