Re: 2.6.14-rc5-rt6 -- False NMI lockup detects

[Ingo Molnar <mingo@elte.hu>]

* Steven Rostedt <rostedt@goodmis.org> wrote:

> Hi Ingo and Thomas,
> 
> On some of my machines, I've been experiencing false NMI lockups.  
> This usually happens on slower machines, and taking a look into this, 
> it seems to be due to a short time where no processes are using 
> timers, and the ktimer interrupts aren't needed. So the APIC timer, 
> which now is used only for the ktimers, has a five second pause, and 
> causes the NMI to go off.  The NMI uses the apic timer to determine 
> lockups.
> 
> So, I added a more generic method. This only works for x86 for now, 
> but it has a #ifdef to keep other archs working until it implements 
> this as well.  I added a nmi_irq_incr which is called by __do_IRQ in 
> the generic code.  This is what is used in the NMI code to determine 
> if the CPU has locked up.  This way we don't have to worry about what 
> resource we are using for timers.

but e.g. the APIC timer doesnt go through do_IRQ(), it has its own 
special IRQ entry code. The simple solution would be to also include the 
IRQ#0 count in the NMI watchdog detection condition - i.e. something 
like the patch below. Hm?

	Ingo

Index: linux/arch/i386/kernel/nmi.c
===================================================================
--- linux.orig/arch/i386/kernel/nmi.c
+++ linux/arch/i386/kernel/nmi.c
@@ -521,7 +521,7 @@ void notrace nmi_watchdog_tick (struct p
 	 */
 	int sum, cpu = smp_processor_id();
 
-	sum = per_cpu(irq_stat, cpu).apic_timer_irqs;
+	sum = per_cpu(irq_stat, cpu).apic_timer_irqs + kstat_irqs(0);
 
 	profile_tick(CPU_PROFILING, regs);
 	if (nmi_show_regs[cpu]) {