[tip: timers/urgent] tick/nohz: Use WARN_ON_ONCE() to prevent console saturation

tip-bot2 for Paul Gortmaker
2022-04-10T10:33:25Z

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@windriver.com>
AuthorDate: Mon, 06 Dec 2021 09:59:50 -05:00
Committer: Thomas Gleixner <tglx@linutronix.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@windriver.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.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;
}