[tip: timers/core] tick-sched: Warn when next tick seems to be in the past

[tip-bot2 for Anna-Maria Behnsen]

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     cbf04a22026100dceeceec67fcbf1973383eb32f
Gitweb:        https://git.kernel.org/tip/cbf04a22026100dceeceec67fcbf1973383eb32f
Author:        Anna-Maria Behnsen <anna-maria@xxxxxxxxxxxxx>
AuthorDate:    Fri, 01 Dec 2023 10:26:25 +01:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Wed, 20 Dec 2023 16:49:38 +01:00

tick-sched: Warn when next tick seems to be in the past

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. To prevent complete misbehaviour, also
reset next_tick to basemono in this case.

Signed-off-by: Anna-Maria Behnsen <anna-maria@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20231201092654.34614-4-anna-maria@xxxxxxxxxxxxx

---
 kernel/time/tick-sched.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index fce3c6f..a17d260 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -839,6 +839,10 @@ static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu)
 		ts->next_timer = next_tick;
 	}
 
+	/* Make sure next_tick is never before basemono! */
+	if (WARN_ON_ONCE(basemono > next_tick))
+		next_tick = basemono;
+
 	/*
 	 * If the tick is due in the next period, keep it ticking or
 	 * force prod the timer.