linux-kernel - Re: [RFC v2 5/7] perf: add a pmu capability for "exclusive" events

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Date:	Tue, 24 Jun 2014 19:18:19 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Robert Richter <rric@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [RFC v2 5/7] perf: add a pmu capability for "exclusive" events

On Wed, Jun 11, 2014 at 06:41:48PM +0300, Alexander Shishkin wrote:
> +static bool exclusive_event_ok(struct perf_event *event,
> +			      struct perf_event_context *ctx)
> +{
> +	struct perf_event *iter_event;
> +
> +	if (!(event->pmu->capabilities & PERF_PMU_CAP_EXCLUSIVE))
> +		return true;
> +
> +	list_for_each_entry(iter_event, &ctx->event_list, event_entry) {
> +		if (exclusive_event_match(iter_event, event))
> +			return false;
> +	}

This list iteration needs either rcu or ctx->lock or ctx->mutex, and the
two callsites below don't have either afaict.

> +
> +	return true;
> +}
> +
>  /**
>   * sys_perf_event_open - open a performance event, associate it to a task/cpu
>   *
> @@ -7261,6 +7287,11 @@ SYSCALL_DEFINE5(perf_event_open,
>  		goto err_alloc;
>  	}
>  
> +	if (!exclusive_event_ok(event, ctx)) {
> +		err = -EBUSY;
> +		goto err_context;
> +	}
> +
>  	if (task) {
>  		put_task_struct(task);
>  		task = NULL;
> @@ -7427,6 +7458,13 @@ perf_event_create_kernel_counter(struct perf_event_attr *attr, int cpu,
>  		goto err_free;
>  	}
>  
> +	if (!exclusive_event_ok(event, ctx)) {
> +		perf_unpin_context(ctx);
> +		put_ctx(ctx);
> +		err = -EBUSY;
> +		goto err_free;
> +	}
> +
>  	WARN_ON_ONCE(ctx->parent_ctx);
>  	mutex_lock(&ctx->mutex);
>  	perf_install_in_context(ctx, event, cpu);
> -- 
> 2.0.0
> 

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