Re: [patch 1/2] idle profile hits with NOHZ

Thomas Gleixner
2009-05-29T13:15:56Z

On Fri, 29 May 2009, Martin Schwidefsky wrote:
> On Thu, 28 May 2009 22:19:44 +0200 (CEST)
> Thomas Gleixner <tglx@linutronix.de> wrote:
>
> > 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.
>
> Drat, but if it is called from idle we should be able to just skip the
> assignment to ts->idle_pc, no? Then a simple in_interrupt() test is
> missing.

That should do the trick.

Thanks,

tglx