[PATCH v7 01/21] tick-sched: Warn when next tick seems to be in the past

From: Anna-Maria Behnsen
Date: Wed May 24 2023 - 03:07:07 EST

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@xxxxxxxxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
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 52254679ec48..62836490ba4d 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -831,6 +831,8 @@ 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) {