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Message-ID: <AANLkTimC6MqioV=6Ry=xvL9m4NeAEmZbkoOGQZ+66Duc@mail.gmail.com>
Date: Wed, 23 Mar 2011 13:47:19 +0100
From: Stephane Eranian <eranian@...gle.com>
To: Ingo Molnar <mingo@...e.hu>
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()
On Wed, Mar 23, 2011 at 12:36 PM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * 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.
>
Argh, I forgot to test !CGROUP.
I tend to agree with you on making those fields unconditional. We
don't save that
much by not doing it.
> Thanks,
>
> Ingo
>
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