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From:   Anna-Maria Behnsen <anna-maria@linutronix.de>
To:     linux-kernel@vger.kernel.org
Cc:     Peter Zijlstra <peterz@infradead.org>,
        John Stultz <john.stultz@linaro.org>,
        Eric Dumazet <edumazet@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        linux-pm@vger.kernel.org, Arjan van de Ven <arjan@infradead.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Rik van Riel <riel@redhat.com>,
        Anna-Maria Behnsen <anna-maria@linutronix.de>
Subject: [PATCH v3 02/17] tick-sched: Warn when next tick seems to be in the past
Date:   Tue, 25 Oct 2022 15:58:35 +0200
Message-Id: <20221025135850.51044-3-anna-maria@linutronix.de>
In-Reply-To: <20221025135850.51044-1-anna-maria@linutronix.de>
References: <20221025135850.51044-1-anna-maria@linutronix.de>
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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(+)

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