linux-kernel - Re: [bisected] perf: yet another fuzzer triggered crash

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Date:	Mon, 8 Jul 2013 18:40:02 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Vince Weaver <vincent.weaver@...ne.edu>,
	linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	trinity@...r.kernel.org
Subject: Re: [bisected] perf: yet another fuzzer triggered crash

On Mon, Jul 08, 2013 at 03:50:48PM +0200, Jiri Olsa wrote:
> patch below gets rid of the warning, and probably the
> crash as well
> 
> the reason seems to be when HW context is cloned based
> on SW event that happened to get there because of the
> HW leader, which got closed just before (fd[15] event
> in the reproducer)
> 
> and the consequence is that in HW context we access
> SW's cpuctx -> and thus overwriting its task_ctx variable
> any time there's *sched_in routine
> 
> need to check if that does not break anything else ;-)
> 
> jirka
> 
> ---
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 1833bc5..1d1f030 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7465,7 +7465,7 @@ inherit_task_group(struct perf_event *event, struct task_struct *parent,
>  		 * child.
>  		 */
>  
> -		child_ctx = alloc_perf_context(event->pmu, child);
> +		child_ctx = alloc_perf_context(parent_ctx->pmu, child);
>  		if (!child_ctx)
>  			return -ENOMEM;
>  

Ha! very good catch. Thanks!
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