linux-kernel - [tip: timers/urgent] tick/nohz: Use WARN_ON

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Date:   Sun, 10 Apr 2022 10:33:01 -0000
From:   "tip-bot2 for Paul Gortmaker" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Paul Gortmaker <paul.gortmaker@...driver.com>,
        Thomas Gleixner <tglx@...utronix.de>, stable@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: timers/urgent] tick/nohz: Use WARN_ON_ONCE() to prevent console
 saturation

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

Commit-ID:     40e97e42961f8c6cc7bd5fe67cc18417e02d78f1
Gitweb:        https://git.kernel.org/tip/40e97e42961f8c6cc7bd5fe67cc18417e02d78f1
Author:        Paul Gortmaker <paul.gortmaker@...driver.com>
AuthorDate:    Mon, 06 Dec 2021 09:59:50 -05:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Sun, 10 Apr 2022 12:23:34 +02:00

tick/nohz: Use WARN_ON_ONCE() to prevent console saturation

While running some testing on code that happened to allow the variable
tick_nohz_full_running to get set but with no "possible" NOHZ cores to
back up that setting, this warning triggered:

        if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
                WARN_ON(tick_nohz_full_running);

The console was overwhemled with an endless stream of one WARN per tick
per core and there was no way to even see what was going on w/o using a
serial console to capture it and then trace it back to this.

Change it to WARN_ON_ONCE().

Fixes: 08ae95f4fd3b ("nohz_full: Allow the boot CPU to be nohz_full")
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/r/20211206145950.10927-3-paul.gortmaker@windriver.com

---
 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 2d76c91..3506f6e 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -188,7 +188,7 @@ static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
 	 */
 	if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)) {
 #ifdef CONFIG_NO_HZ_FULL
-		WARN_ON(tick_nohz_full_running);
+		WARN_ON_ONCE(tick_nohz_full_running);
 #endif
 		tick_do_timer_cpu = cpu;
 	}