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Date: Sat, 26 Mar 2011 18:09:22 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Jiri Olsa <jolsa@redhat.com>, Paul Mackerras <paulus@samba.org>,
        Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH,RFC] perf: panic due to inclied cpu context task_ctx
	value
Message-ID: <20110326170922.GA20329@redhat.com>
References: <20110324164436.GC1930@jolsa.brq.redhat.com> <1301153868.2250.359.camel@laptop> <20110326161346.GA18272@redhat.com> <1301157483.2250.366.camel@laptop>
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On 03/26, Peter Zijlstra wrote:
>
> diff --git a/kernel/perf_event.c b/kernel/perf_event.c
> index c75925c..e9e4e35 100644
> --- a/kernel/perf_event.c
> +++ b/kernel/perf_event.c
> @@ -1073,6 +1073,8 @@ event_sched_out(struct perf_event *event,
>  	if (!is_software_event(event))
>  		cpuctx->active_oncpu--;
>  	ctx->nr_active--;
> +	if (!ctx->nr_active && cpuctx->task_ctx == ctx)
> +		cpuctx->task_ctx = NULL;

If we clear cpuctx->task_ctx, we should also clear ctx->is_active.

Otherwise I can't see any problem, but I do not understand this code
enough.

Oleg.