linux-kernel - Re: [PATCH] perf_events: fix cgrp stale pointer in update_cgrp_time_from

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Date:	Wed, 23 Mar 2011 12:36:01 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.org,
	perfmon2-devel@...ts.sf.net, paulus@...ba.org, davem@...emloft.net
Subject: Re: [PATCH] perf_events: fix cgrp stale pointer in
 update_cgrp_time_from_cpuctx()


* Stephane Eranian <eranian@...gle.com> wrote:

> -	if (is_cgroup_event(event))
> +	if (is_cgroup_event(event)) {
>  		ctx->nr_cgroups--;
> +		cpuctx = __get_cpu_context(ctx);
> +		/*
> +		 * if there are no more cgroup events
> +		 * then clear cgrp to avoid stale pointer
> +		 * in update_cgrp_time_from_cpuctx()
> +		 */
> +		if (!ctx->nr_cgroups)
> +			cpuctx->cgrp = NULL;
> +	}

The ->cgrp pointer does not exist on !CGROUPS kernels. I suspect the cleanest 
approach would be to make those two cgrp fields available unconditionally in 
struct perf_event.

Thanks,

	Ingo
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