linux-kernel - Re: [tip: timers/core] tick: Mark sched_timer to expire in hard interrupt context

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Date:   Wed, 28 Aug 2019 15:48:36 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     linux-tip-commits@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>
Subject: Re: [tip: timers/core] tick: Mark sched_timer to expire in hard
 interrupt context

On Wed, Aug 28, 2019 at 11:03:33AM -0000, tip-bot2 for Sebastian Andrzej Siewior wrote:
> The following commit has been merged into the timers/core branch of tip:
> 
> Commit-ID:     71fed982d63cb2bb88db6f36059e3b14a7913846
> Gitweb:        https://git.kernel.org/tip/71fed982d63cb2bb88db6f36059e3b14a7913846
> Author:        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> AuthorDate:    Fri, 23 Aug 2019 13:38:45 +02:00
> Committer:     Thomas Gleixner <tglx@...utronix.de>
> CommitterDate: Wed, 28 Aug 2019 13:01:26 +02:00
> 
> tick: Mark sched_timer to expire in hard interrupt context
> 
> sched_timer must be initialized with the _HARD mode suffix to ensure expiry
> in hard interrupt context on RT.
> 
> The previous conversion to HARD expiry mode missed on one instance in
> tick_nohz_switch_to_nohz(). Fix it up.
> 
> Fixes: 902a9f9c50905 ("tick: Mark tick related hrtimers to expiry in hard interrupt context")
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Link: https://lkml.kernel.org/r/20190823113845.12125-3-bigeasy@linutronix.de
> 
> ---
>  kernel/time/tick-sched.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index 01ff32a..9558517 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -1233,7 +1233,7 @@ static void tick_nohz_switch_to_nohz(void)
>  	 * Recycle the hrtimer in ts, so we can share the
>  	 * hrtimer_forward with the highres code.
>  	 */
> -	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
> +	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);

That said, this instance only uses hrtimer for time computing. The backend is
clockevent directly.

>  	/* Get the next period */
>  	next = tick_init_jiffy_update();
>