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Date: Fri, 10 May 2013 11:37:29 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>, Jiri Kosina <jkosina@suse.cz>,
        Tony Luck <tony.luck@intel.com>, linux-kernel@vger.kernel.org,
        x86@kernel.org
Subject: Re: NOHZ: WARNING: at arch/x86/kernel/smp.c:123
 native_smp_send_reschedule
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* Frederic Weisbecker <fweisbec@gmail.com> wrote:

> 2013/5/10 Borislav Petkov <bp@alien8.de>:
> > On Fri, May 10, 2013 at 02:29:31AM +0200, Frederic Weisbecker wrote:
> >> @@ -616,8 +616,17 @@ static bool wake_up_full_nohz_cpu(int cpu)
> >>  {
> >>       if (tick_nohz_full_cpu(cpu)) {
> >>               if (cpu != smp_processor_id() ||
> >> -                 tick_nohz_tick_stopped())
> >> +                 tick_nohz_tick_stopped()) {
> >> +                     if (!cpu_online(cpu)) {
> >> +                             static int printed = 0;
> >> +                             if (!printed) {
> >> +                                     printk("%d %d\n", cpu, smp_processor_id());
> >> +                                     dump_stack();
> >> +                                     printed = 1;
> >
> > You know about printk_once, right? We even have all the pr_<level>_once
> > macros.
> >
> > :-)
> 
> But but that didn't fit as I also want the dump_stack(). May be we
> want dump_stack_once().

The pattern I use in such cases is:

	if (WARN_ONCE(!cpu_online(cpu))) {
		printk("%d %d\n", cpu, smp_processor_id());
		dump_stack();
	}

Thanks,

	Ingo
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