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    SubjectRe: 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@gmail.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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