[tip: timers/core] alarmtimer: Drop the spinlock around the rtcdev variable

[tip-bot2 for Thomas Weißschuh]

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

Commit-ID:     6d771f75f3761d7c8aaf57b06a2b4ddcb25b4ce8
Gitweb:        https://git.kernel.org/tip/6d771f75f3761d7c8aaf57b06a2b4ddcb25b4ce8
Author:        Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
AuthorDate:    Mon, 02 Nov 2026 06:11:54 
Committer:     Thomas Gleixner <tglx@xxxxxxxxxx>
CommitterDate: Mon, 09 Nov 2026 20:50:03 +01:00

alarmtimer: Drop the spinlock around the rtcdev variable

The spinlock serializes calls to alarmtimer_rtc_add_device(), making sure
the 'rtcdev' variable is written only once. It also protects the read of
the 'rtcdev' variable in alarmtimer_get_rtcdev().

But alarmtimer_rtc_add_device() is already synchronized externally through
the driver core's subsystem lock. So the additional spinlock can be dropped
and replaced with WRITE_ONCE()/READ_ONCE() for consistent access.

This removes lock/unlock operations from the alarmtimer's clock callbacks.

[ tglx: Massage change log ]

Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxx>
Link: https://patch.msgid.link/20261102-alarmtimer-locking-v1-1-3c79a698aeae@xxxxxxxxxxxxxx
---
 kernel/time/alarmtimer.c | 24 ++++++++----------------
 1 file changed, 8 insertions(+), 16 deletions(-)

diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index d6dc6e8..601ebdc 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -61,7 +61,6 @@ static DEFINE_SPINLOCK(freezer_delta_lock);
 /* rtc timer and device for setting alarm wakeups at suspend */
 static struct rtc_timer		rtctimer;
 static struct rtc_device	*rtcdev;
-static DEFINE_SPINLOCK(rtcdev_lock);
 
 /**
  * alarmtimer_get_rtcdev - Return selected rtcdevice
@@ -70,12 +69,7 @@ static DEFINE_SPINLOCK(rtcdev_lock);
  */
 struct rtc_device *alarmtimer_get_rtcdev(void)
 {
-	struct rtc_device *ret;
-
-	guard(spinlock_irqsave)(&rtcdev_lock);
-	ret = rtcdev;
-
-	return ret;
+	return READ_ONCE(rtcdev);
 }
 EXPORT_SYMBOL_GPL(alarmtimer_get_rtcdev);
 
@@ -98,15 +92,13 @@ static int alarmtimer_rtc_add_device(struct device *dev)
 	if (!IS_ERR(pdev))
 		device_init_wakeup(&pdev->dev, true);
 
-	scoped_guard(spinlock_irqsave, &rtcdev_lock) {
-		if (!IS_ERR(pdev) && !rtcdev && try_module_get(rtc->owner)) {
-			rtcdev = rtc;
-			/* hold a reference so it doesn't go away */
-			get_device(dev);
-			pdev = NULL;
-		} else {
-			ret = -1;
-		}
+	if (!IS_ERR(pdev) && try_module_get(rtc->owner)) {
+		WRITE_ONCE(rtcdev, rtc);
+		/* hold a reference so it doesn't go away */
+		get_device(dev);
+		pdev = NULL;
+	} else {
+		ret = -1;
 	}
 
 	platform_device_unregister(pdev);