Re: Possible regression due to "hrtimer: Get rid of hrtimer softirq"

From: Simon Horman
Date: Thu May 07 2015 - 09:25:53 EST


Hi Thomas,

On Thu, May 07, 2015 at 02:35:59PM +0200, Thomas Gleixner wrote:
> On Thu, 7 May 2015, Simon Horman wrote:
> > ------------[ cut here ]------------
> > kernel BUG at kernel/irq_work.c:135!
>
> BUG_ON(!irqs_disabled());
>
> So something enables interrupts in the periodic tick handling
> machinery. Seems you have high resolution timers disabled, but nohz
> enabled. And that code path has a local_irq_disable/enable pair which
> causes havoc. Patch below.

Thanks for your quick response. I have been able to confirm that
when applied on top of next-20150507 the problem I observed no longer
manifests. I have successfully tested it on all the boards
where I previously observed a problem.

If you are planning to formally submit the patch below feel free to add:

Tested-by: Simon Horman <horms+renesas@xxxxxxxxxxxx>

> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index 753c211f6195..812f7a3b9898 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -967,11 +967,9 @@ static void tick_nohz_switch_to_nohz(void)
> if (!tick_nohz_enabled)
> return;
>
> - local_irq_disable();
> - if (tick_switch_to_oneshot(tick_nohz_handler)) {
> - local_irq_enable();
> + if (tick_switch_to_oneshot(tick_nohz_handler))
> return;
> - }
> +
> tick_nohz_active = 1;
> ts->nohz_mode = NOHZ_MODE_LOWRES;
>
> @@ -986,7 +984,6 @@ static void tick_nohz_switch_to_nohz(void)
> hrtimer_forward_now(&ts->sched_timer, tick_period);
> hrtimer_set_expires(&ts->sched_timer, next);
> tick_program_event(next, 1);
> - local_irq_enable();
> }
>
> /*
> @@ -1171,7 +1168,7 @@ void tick_oneshot_notify(void)
> * Called cyclic from the hrtimer softirq (driven by the timer
> * softirq) allow_nohz signals, that we can switch into low-res nohz
> * mode, because high resolution timers are disabled (either compile
> - * or runtime).
> + * or runtime). Called with interrupts disabled.
> */
> int tick_check_oneshot_change(int allow_nohz)
> {
>
>
>
>
>
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