[patch 07/12] alarmtimer: Provide alarmtimer_start()

Thomas Gleixner
2026-04-07T08:54:51Z

Alarm timers utilize hrtimers for normal operation and only switch to the
RTC on suspend. In order to catch already expired timers early and without
going through a timer interrupt cycle, provide a new start function which
internally uses hrtimer_start_range_ns_user().

If hrtimer_start_range_ns_user() detects an already expired timer, it does
not queue it. In that case remove the timer from the alarm base as well.

Return the status queued or not back to the caller to handle the early
expiry.

Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: John Stultz <jstultz@google.com>
Cc: Stephen Boyd <sboyd@kernel.org>
---
include/linux/alarmtimer.h | 6 ++++++
kernel/time/alarmtimer.c | 28 ++++++++++++++++++++++++++++
2 files changed, 34 insertions(+)

--- a/include/linux/alarmtimer.h
+++ b/include/linux/alarmtimer.h
@@ -42,8 +42,14 @@ struct alarm {
void *data;
};

+static __always_inline ktime_t alarm_get_expires(struct alarm *alarm)
+{
+ return alarm->node.expires;
+}
+
void alarm_init(struct alarm *alarm, enum alarmtimer_type type,
void (*function)(struct alarm *, ktime_t));
+bool alarmtimer_start(struct alarm *alarm, ktime_t expires, bool relative);
void alarm_start(struct alarm *alarm, ktime_t start);
void alarm_start_relative(struct alarm *alarm, ktime_t start);
void alarm_restart(struct alarm *alarm);
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -365,6 +365,34 @@ void alarm_start_relative(struct alarm *
}
EXPORT_SYMBOL_GPL(alarm_start_relative);

+/**
+ * alarmtimer_start - Sets an alarm to fire
+ * @alarm: Pointer to alarm to set
+ * @expires: Expiry time
+ * @relative: True if @expires is relative
+ *
+ * Returns: True if the alarm was queued. False if it already expired
+ */
+bool alarmtimer_start(struct alarm *alarm, ktime_t expires, bool relative)
+{
+ struct alarm_base *base = &alarm_bases[alarm->type];
+
+ if (relative)
+ expires = ktime_add_safe(expires, base->get_ktime());
+
+ trace_alarmtimer_start(alarm, base->get_ktime());
+
+ guard(spinlock_irqsave)(&base->lock);
+ alarm->node.expires = expires;
+ alarmtimer_enqueue(base, alarm);
+ if (!hrtimer_start_range_ns_user(&alarm->timer, expires, 0, HRTIMER_MODE_ABS)) {
+ alarmtimer_dequeue(base, alarm);
+ return false;
+ }
+ return true;
+}
+EXPORT_SYMBOL_GPL(alarmtimer_start);
+
void alarm_restart(struct alarm *alarm)
{
struct alarm_base *base = &alarm_bases[alarm->type];