linux-kernel - Re: linux-next-20110923: warning kernel/rcutree.c:1833

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Message-ID: <20111001163533.GA2539@linux.vnet.ibm.com>
Date:	Sat, 1 Oct 2011 09:35:33 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	linux-kernel@...r.kernel.org, Dipankar Sarma <dipankar@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Lai Jiangshan <laijs@...fujitsu.com>
Subject: Re: linux-next-20110923: warning kernel/rcutree.c:1833

On Sat, Oct 01, 2011 at 02:28:10PM +0200, Frederic Weisbecker wrote:
> 2011/10/1 Frederic Weisbecker <fweisbec@...il.com>:
> > Yeah something like this (untested):
> >
> > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> > index d5097c4..ad3ecad 100644
> > --- a/kernel/time/tick-sched.c
> > +++ b/kernel/time/tick-sched.c
> > @@ -273,9 +273,12 @@ void tick_nohz_stop_sched_tick(int inidle)
> >         * updated. Thus, it must not be called in the event we are called from
> >         * irq_exit() with the prior state different than idle.
> >         */
> > -       if (!inidle && !ts->inidle)
> > +       if (inidle)
> > +               rcu_idle_enter();
> > +       else if (!ts->inidle)
> >                goto end;
> >
> > +
> >        /*
> >         * Set ts->inidle unconditionally. Even if the system did not
> >         * switch to NOHZ mode the cpu frequency governers rely on the
> > @@ -409,7 +412,6 @@ void tick_nohz_stop_sched_tick(int inidle)
> >                        ts->idle_tick = hrtimer_get_expires(&ts->sched_timer);
> >                        ts->tick_stopped = 1;
> >                        ts->idle_jiffies = last_jiffies;
> > -                       rcu_enter_nohz();
> >                }
> >
> >                ts->idle_sleeps++;
> > @@ -505,6 +507,9 @@ void tick_nohz_restart_sched_tick(void)
> >        ktime_t now;
> >
> >        local_irq_disable();
> > +
> > +       rcu_idle_exit();
> > +
> >        if (ts->idle_active || (ts->inidle && ts->tick_stopped))
> >                now = ktime_get();
> >
> > @@ -519,8 +524,6 @@ void tick_nohz_restart_sched_tick(void)
> >
> >        ts->inidle = 0;
> >
> > -       rcu_exit_nohz();
> > -
> >        /* Update jiffies first */
> >        select_nohz_load_balancer(0);
> >        tick_do_update_jiffies64(now);
> >
> 
> Ah I see you fixed it in the delta. Ok :)

But rcutorture still hates it.  Possibly because of this boneheaded bug:

int rcu_is_cpu_rrupt_from_idle(void)
{
	return (__get_cpu_var(rcu_dynticks).dynticks_nesting & 0x1) <= 1;
}

Do you think that it might work better if I drop off the "& 0x1" that
I copy-pasted from rcu_is_cpu_idle()?  ;-)

Sigh!!!  Giving it a try now.

							Thanx, Paul
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