[tip: timers/core] posix-timers: Handle the timer_[re]arm() return value

[tip-bot2 for Thomas Gleixner]

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

Commit-ID:     cfb7fe3fdd4ca1d37da1ed15a1897d4a27c47a8a
Gitweb:        https://git.kernel.org/tip/cfb7fe3fdd4ca1d37da1ed15a1897d4a27c47a8a
Author:        Thomas Gleixner <tglx@xxxxxxxxxx>
AuthorDate:    Wed, 08 Apr 2026 13:54:01 +02:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxx>
CommitterDate: Fri, 01 May 2026 21:36:12 +02:00

posix-timers: Handle the timer_[re]arm() return value

The [re]arm callbacks will return true when the timer was queued and false
if it was already expired at enqueue time.

In both cases the call sites can trivially queue the signal right there,
when the timer was already expired. That avoids a full round trip through
the hrtimer interrupt.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxx>
Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://patch.msgid.link/20260408114952.198028466@xxxxxxxxxx
---
 kernel/time/posix-timers.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index da04ed4..db62cfa 100644
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -299,6 +299,8 @@ static bool common_hrtimer_rearm(struct k_itimer *timr)
 
 static bool __posixtimer_deliver_signal(struct kernel_siginfo *info, struct k_itimer *timr)
 {
+	bool queued;
+
 	guard(spinlock)(&timr->it_lock);
 
 	/*
@@ -312,12 +314,18 @@ static bool __posixtimer_deliver_signal(struct kernel_siginfo *info, struct k_it
 	if (!timr->it_interval || WARN_ON_ONCE(timr->it_status != POSIX_TIMER_REQUEUE_PENDING))
 		return true;
 
-	timr->kclock->timer_rearm(timr);
-	timr->it_status = POSIX_TIMER_ARMED;
+	/* timer_rearm() updates timr::it_overrun */
+	queued = timr->kclock->timer_rearm(timr);
+
 	timr->it_overrun_last = timr->it_overrun;
 	timr->it_overrun = -1LL;
 	++timr->it_signal_seq;
 	info->si_overrun = timer_overrun_to_int(timr);
+
+	if (queued)
+		timr->it_status = POSIX_TIMER_ARMED;
+	else
+		posix_timer_queue_signal(timr);
 	return true;
 }
 
@@ -905,9 +913,13 @@ int common_timer_set(struct k_itimer *timr, int flags,
 		expires = timens_ktime_to_host(timr->it_clock, expires);
 	sigev_none = timr->it_sigev_notify == SIGEV_NONE;
 
-	kc->timer_arm(timr, expires, flags & TIMER_ABSTIME, sigev_none);
-	if (!sigev_none)
-		timr->it_status = POSIX_TIMER_ARMED;
+	if (kc->timer_arm(timr, expires, flags & TIMER_ABSTIME, sigev_none)) {
+		if (!sigev_none)
+			timr->it_status = POSIX_TIMER_ARMED;
+	} else {
+		/* Timer was already expired, queue the signal */
+		posix_timer_queue_signal(timr);
+	}
 	return 0;
 }