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Date: Thu, 28 May 2009 22:19:44 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Martin Schwidefsky <schwidefsky@de.ibm.com>
cc: linux-kernel@vger.kernel.org, Rob van der Heij <rvdheij@gmail.com>,
       Heiko Carstens <heiko.carstens@de.ibm.com>, Ingo Molnar <mingo@elte.hu>,
       john stultz <johnstul@us.ibm.com>
Subject: Re: [patch 1/2] idle profile hits with NOHZ
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On Thu, 28 May 2009, Martin Schwidefsky wrote:
> --- quilt-2.6.orig/kernel/time/tick-sched.c
> +++ quilt-2.6/kernel/time/tick-sched.c
> @@ -166,6 +166,7 @@ static void tick_nohz_stop_idle(int cpu)
>  		ts->idle_lastupdate = now;
>  		ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
>  		ts->idle_active = 0;
> +		ts->idle_pc = profile_pc(get_irq_regs());

  Hmm, tick_nohz_stop_idle() is called from
  tick_nohz_restart_sched_tick() as well in the context of the idle
  task.

  I think there is no guarantee that get_irq_regs() will return
  anything useful in thread context.

  So get_irq_regs() might return a NULL pointer which will explode
  some of the profile_pc() implementations. If not it can still feed
  total nonsense to the profile_hits() call.

Thanks,

	tglx