[tip: timers/core] tick/broadcast: Allow late registered device to enter oneshot mode

[tip-bot2 for Jindong Yue]

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

Commit-ID:     9c336c9935cff267470bb3aaa85c66fac194b650
Gitweb:        https://git.kernel.org/tip/9c336c9935cff267470bb3aaa85c66fac194b650
Author:        Jindong Yue <jindong.yue@xxxxxxx>
AuthorDate:    Wed, 31 Mar 2021 16:33:18 +08:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Fri, 16 Apr 2021 21:03:50 +02:00

tick/broadcast: Allow late registered device to enter oneshot mode

The broadcast device is switched to oneshot mode when the system switches
to oneshot mode. If a broadcast clock event device is registered after the
system switched to oneshot mode, it will stay in periodic mode forever.

Ensure that a late registered device which is selected as broadcast device
is initialized in oneshot mode when the system already uses oneshot mode.

[ tglx: Massage changelog ]

Signed-off-by: Jindong Yue <jindong.yue@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210331083318.21794-1-jindong.yue@xxxxxxx

---
 kernel/time/tick-broadcast.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index 6ec7855..a440552 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -107,6 +107,19 @@ void tick_install_broadcast_device(struct clock_event_device *dev)
 	tick_broadcast_device.evtdev = dev;
 	if (!cpumask_empty(tick_broadcast_mask))
 		tick_broadcast_start_periodic(dev);
+
+	if (!(dev->features & CLOCK_EVT_FEAT_ONESHOT))
+		return;
+
+	/*
+	 * If the system already runs in oneshot mode, switch the newly
+	 * registered broadcast device to oneshot mode explicitly.
+	 */
+	if (tick_broadcast_oneshot_active()) {
+		tick_broadcast_switch_to_oneshot();
+		return;
+	}
+
 	/*
 	 * Inform all cpus about this. We might be in a situation
 	 * where we did not switch to oneshot mode because the per cpu
@@ -115,8 +128,7 @@ void tick_install_broadcast_device(struct clock_event_device *dev)
 	 * notification the systems stays stuck in periodic mode
 	 * forever.
 	 */
-	if (dev->features & CLOCK_EVT_FEAT_ONESHOT)
-		tick_clock_notify();
+	tick_clock_notify();
 }
 
 /*