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SubjectRe: kerneloops.org report for the week of June 14 2009
On Tue, 23 Jun 2009 13:55:10 +0200
Ingo Molnar <mingo@elte.hu> wrote:

>
> * Thomas Gleixner <tglx@linutronix.de> wrote:
>
> > On Sun, 14 Jun 2009, Arjan van de Ven wrote:
> > > Rank 3: getnstimeofday (warning)
> > > Reported 309 times (2446 total reports)
> > > [suspend resume] getnstimeofday() is called before
> > > timekeeping is
> > resumed
> >
> > > Rank 6: hres_timers_resume (warning)
> > > Reported 188 times (1024 total reports)
> > > [suspend resume] hres_timers_resume() is incorrectly
> > > called with interrupts on
> >
> > Both have the same root cause. Something enables interrupts in the
> > early resume path. IIRC, there was a culprit identified recently.
> > Rafael ?
>
> This can be debugged automatically today, using lockdep, by using a
> 'helper lock':
>
> static DEFINE_PER_CPU(struct lockdep_map, helper_lock);
>
> Then mark the lock irq-safe by doing something like:
>
> static void mark_lock_irqsafe(void)
> {
> unsigned long flags;
> int cpu;
>
> local_irq_save(flags);
> irq_enter(0);
>
> for_each_online_cpu(cpu) {
> lock_acquire(&per_cpu(helper_lock, cpu), 0, 0, 0, 0,
> NULL, 0); lock_release(&per_cpu(helper_lock, cpu), 0, 0, 0, 0, NULL,
> 0); }
>
> irq_exit(0);
> local_irq_restore(flags);
> }
>
> Then, the resume path, when it disables irqs, you can disallow
> irq-enable via:
>
> local_irq_disable();
> lock_acquire(&__get_cpu_var(helper_lock), 0, 0, 0, 0, NULL,
> 0); ...
> <extensive suspend or resume codepaths, callbacks>
> ...
> lock_release(&__get_cpu_var(helper_lock), 0, 0, 0, 0, NULL,
> 0); local_irq_enable();
>
> And lockdep will warn if any function inbetween enables IRQs, by
> emitting a splat about incorrectly enabled hardirqs. It will warn
> about the specific place and will emit a relevant backtrace, - not
> just the handler in general.

looks like an interesting approach; it'll pinpoint the bad guy exactly
where he's enabling interrupts.. (assuming he's using kernel facilities
of course)



--
Arjan van de Ven Intel Open Source Technology Centre
For development, discussion and tips for power savings,
visit http://www.lesswatts.org


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