linux-kernel - [tip: timers/core] timers/nohz: Switch to ONESHOT_STOPPED in the low-res handler when the tick is stopped

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Date:   Mon, 25 Apr 2022 12:50:56 -0000
From:   "tip-bot2 for Nicholas Piggin" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Nicholas Piggin <npiggin@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: timers/core] timers/nohz: Switch to ONESHOT_STOPPED in the
 low-res handler when the tick is stopped

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

Commit-ID:     62c1256d544747b38e77ca9b5bfe3a26f9592576
Gitweb:        https://git.kernel.org/tip/62c1256d544747b38e77ca9b5bfe3a26f9592576
Author:        Nicholas Piggin <npiggin@...il.com>
AuthorDate:    Sat, 23 Apr 2022 00:14:46 +10:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Mon, 25 Apr 2022 14:45:22 +02:00

timers/nohz: Switch to ONESHOT_STOPPED in the low-res handler when the tick is stopped

When tick_nohz_stop_tick() stops the tick and high resolution timers are
disabled, then the clock event device is not put into ONESHOT_STOPPED
mode. This can lead to spurious timer interrupts with some clock event
device drivers that don't shut down entirely after firing.

Eliminate these by putting the device into ONESHOT_STOPPED mode at points
where it is not being reprogrammed. When there are no timers active, then
tick_program_event() with KTIME_MAX can be used to stop the device. When
there is a timer active, the device can be stopped at the next tick (any
new timer added by timers will reprogram the tick).

Signed-off-by: Nicholas Piggin <npiggin@...il.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lore.kernel.org/r/20220422141446.915024-1-npiggin@gmail.com
---
 kernel/time/tick-sched.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 2d76c91..b1b105d 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -928,6 +928,8 @@ static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu)
 	if (unlikely(expires == KTIME_MAX)) {
 		if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
 			hrtimer_cancel(&ts->sched_timer);
+		else
+			tick_program_event(KTIME_MAX, 1);
 		return;
 	}
 
@@ -1364,9 +1366,15 @@ static void tick_nohz_handler(struct clock_event_device *dev)
 	tick_sched_do_timer(ts, now);
 	tick_sched_handle(ts, regs);
 
-	/* No need to reprogram if we are running tickless  */
-	if (unlikely(ts->tick_stopped))
+	if (unlikely(ts->tick_stopped)) {
+		/*
+		 * The clockevent device is not reprogrammed, so change the
+		 * clock event device to ONESHOT_STOPPED to avoid spurious
+		 * interrupts on devices which might not be truly one shot.
+		 */
+		tick_program_event(KTIME_MAX, 1);
 		return;
+	}
 
 	hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
 	tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);