diff mbox series

[v3,02/17] tick-sched: Warn when next tick seems to be in the past

Message ID 20221025135850.51044-3-anna-maria@linutronix.de
State New
Headers
Series timer: Move from a push remote at enqueue to a pull at expiry model |

Commit Message

Anna-Maria Behnsen Oct. 25, 2022, 1:58 p.m. UTC 
  When the next tick is in the past, the delta between basemono and the next
tick gets negativ. But the next tick should never be in the past. The
negative effect of a wrong next tick might be a stop of the tick and timers
might expire late.

To prevent expensive debugging when changing underlying code, add a
WARN_ON_ONCE into this code path.

Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/time/tick-sched.c | 2 ++
 1 file changed, 2 insertions(+)

Comments

Frederic Weisbecker Oct. 25, 2022, 10:11 p.m. UTC | #1 
On Tue, Oct 25, 2022 at 03:58:35PM +0200, Anna-Maria Behnsen wrote:
> When the next tick is in the past, the delta between basemono and the next
> tick gets negativ. But the next tick should never be in the past. The
> negative effect of a wrong next tick might be a stop of the tick and timers
> might expire late.
> 
> To prevent expensive debugging when changing underlying code, add a
> WARN_ON_ONCE into this code path.
> 
> Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
> Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

Reviewed-by: Frederic Weisbecker <frederic@kernel.org>

> ---
>  kernel/time/tick-sched.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index b0e3c9205946..7ffdc7ba19b4 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -826,6 +826,8 @@ static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu)
>  	 * If the tick is due in the next period, keep it ticking or
>  	 * force prod the timer.
>  	 */
> +	WARN_ON_ONCE(basemono > next_tick);
> +
>  	delta = next_tick - basemono;
>  	if (delta <= (u64)TICK_NSEC) {
>  		/*
> -- 
> 2.30.2
>
diff mbox series

Patch

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index b0e3c9205946..7ffdc7ba19b4 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -826,6 +826,8 @@  static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu)
 	 * If the tick is due in the next period, keep it ticking or
 	 * force prod the timer.
 	 */
+	WARN_ON_ONCE(basemono > next_tick);
+
 	delta = next_tick - basemono;
 	if (delta <= (u64)TICK_NSEC) {
 		/*