Updates for the time/timer core code:

- Rework the initialization of the posix-timer kmem_cache and move the
     cache pointer into the timer_data structure to prevent false sharing.
 
   - Switch the alarmtimer code to lock guards.
 
   - Improve the CPU selection criteria in the per CPU validation of the
     clocksource watchdog to avoid arbitrary selections (or omissions) on
     systems with a small number of CPUs.
 
   - The usual cleanups and improvements
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Merge tag 'timers-core-2025-05-25' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull timer core updates from Thomas Gleixner:
 "Updates for the time/timer core code:

   - Rework the initialization of the posix-timer kmem_cache and move
     the cache pointer into the timer_data structure to prevent false
     sharing

   - Switch the alarmtimer code to lock guards

   - Improve the CPU selection criteria in the per CPU validation of the
     clocksource watchdog to avoid arbitrary selections (or omissions)
     on systems with a small number of CPUs

   - The usual cleanups and improvements"

* tag 'timers-core-2025-05-25' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  tick/nohz: Remove unused tick_nohz_full_add_cpus_to()
  clocksource: Fix the CPUs' choice in the watchdog per CPU verification
  alarmtimer: Switch spin_{lock,unlock}_irqsave() to guards
  alarmtimer: Remove dead return value in clock2alarm()
  time/jiffies: Change register_refined_jiffies() to void __init
  timers: Remove unused __round_jiffies(_up)
  posix-timers: Initialize cache early and move pointer into __timer_data

include/linux/jiffies.h

@@ -59,7 +59,7 @@
 /* LATCH is used in the interval timer and ftape setup. */
 #define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ)	/* For divider */
 
-extern int register_refined_jiffies(long clock_tick_rate);
+extern void register_refined_jiffies(long clock_tick_rate);
 
 /* TICK_USEC is the time between ticks in usec assuming SHIFTED_HZ */
 #define TICK_USEC ((USEC_PER_SEC + HZ/2) / HZ)

include/linux/tick.h

@@ -195,12 +195,6 @@ static inline bool tick_nohz_full_enabled(void)
 	__ret;								\
 })
 
-static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask)
-{
-	if (tick_nohz_full_enabled())
-		cpumask_or(mask, mask, tick_nohz_full_mask);
-}
-
 extern void tick_nohz_dep_set(enum tick_dep_bits bit);
 extern void tick_nohz_dep_clear(enum tick_dep_bits bit);
 extern void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit);
@@ -281,7 +275,6 @@ extern void __init tick_nohz_full_setup(cpumask_var_t cpumask);
 #else
 static inline bool tick_nohz_full_enabled(void) { return false; }
 static inline bool tick_nohz_full_cpu(int cpu) { return false; }
-static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask) { }
 
 static inline void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit) { }
 static inline void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit) { }

include/linux/timer.h

@@ -172,12 +172,10 @@ extern void timers_init(void);
 struct hrtimer;
 extern enum hrtimer_restart it_real_fn(struct hrtimer *);
 
-unsigned long __round_jiffies(unsigned long j, int cpu);
 unsigned long __round_jiffies_relative(unsigned long j, int cpu);
 unsigned long round_jiffies(unsigned long j);
 unsigned long round_jiffies_relative(unsigned long j);
 
-unsigned long __round_jiffies_up(unsigned long j, int cpu);
 unsigned long __round_jiffies_up_relative(unsigned long j, int cpu);
 unsigned long round_jiffies_up(unsigned long j);
 unsigned long round_jiffies_up_relative(unsigned long j);

kernel/time/alarmtimer.c

@@ -70,12 +70,10 @@ static DEFINE_SPINLOCK(rtcdev_lock);
  */
 struct rtc_device *alarmtimer_get_rtcdev(void)
 {
-	unsigned long flags;
 	struct rtc_device *ret;
 
-	spin_lock_irqsave(&rtcdev_lock, flags);
+	guard(spinlock_irqsave)(&rtcdev_lock);
 	ret = rtcdev;
-	spin_unlock_irqrestore(&rtcdev_lock, flags);
 
 	return ret;
 }
@@ -83,7 +81,6 @@ EXPORT_SYMBOL_GPL(alarmtimer_get_rtcdev);
 
 static int alarmtimer_rtc_add_device(struct device *dev)
 {
-	unsigned long flags;
 	struct rtc_device *rtc = to_rtc_device(dev);
 	struct platform_device *pdev;
 	int ret = 0;
@@ -101,25 +98,18 @@ static int alarmtimer_rtc_add_device(struct device *dev)
 	if (!IS_ERR(pdev))
 		device_init_wakeup(&pdev->dev, true);
 
-	spin_lock_irqsave(&rtcdev_lock, flags);
-	if (!IS_ERR(pdev) && !rtcdev) {
-		if (!try_module_get(rtc->owner)) {
+	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;
-			goto unlock;
 		}
-
-		rtcdev = rtc;
-		/* hold a reference so it doesn't go away */
-		get_device(dev);
-		pdev = NULL;
-	} else {
-		ret = -1;
 	}
-unlock:
-	spin_unlock_irqrestore(&rtcdev_lock, flags);
 
 	platform_device_unregister(pdev);
-
 	return ret;
 }
 
@@ -198,7 +188,7 @@ static enum hrtimer_restart alarmtimer_fired(struct hrtimer *timer)
 	struct alarm *alarm = container_of(timer, struct alarm, timer);
 	struct alarm_base *base = &alarm_bases[alarm->type];
 
-	scoped_guard (spinlock_irqsave, &base->lock)
+	scoped_guard(spinlock_irqsave, &base->lock)
 		alarmtimer_dequeue(base, alarm);
 
 	if (alarm->function)
@@ -228,17 +218,16 @@ EXPORT_SYMBOL_GPL(alarm_expires_remaining);
 static int alarmtimer_suspend(struct device *dev)
 {
 	ktime_t min, now, expires;
-	int i, ret, type;
 	struct rtc_device *rtc;
-	unsigned long flags;
 	struct rtc_time tm;
+	int i, ret, type;
 
-	spin_lock_irqsave(&freezer_delta_lock, flags);
-	min = freezer_delta;
-	expires = freezer_expires;
-	type = freezer_alarmtype;
-	freezer_delta = 0;
-	spin_unlock_irqrestore(&freezer_delta_lock, flags);
+	scoped_guard(spinlock_irqsave, &freezer_delta_lock) {
+		min = freezer_delta;
+		expires = freezer_expires;
+		type = freezer_alarmtype;
+		freezer_delta = 0;
+	}
 
 	rtc = alarmtimer_get_rtcdev();
 	/* If we have no rtcdev, just return */
@@ -251,9 +240,8 @@ static int alarmtimer_suspend(struct device *dev)
 		struct timerqueue_node *next;
 		ktime_t delta;
 
-		spin_lock_irqsave(&base->lock, flags);
-		next = timerqueue_getnext(&base->timerqueue);
-		spin_unlock_irqrestore(&base->lock, flags);
+		scoped_guard(spinlock_irqsave, &base->lock)
+			next = timerqueue_getnext(&base->timerqueue);
 		if (!next)
 			continue;
 		delta = ktime_sub(next->expires, base->get_ktime());
@@ -352,13 +340,12 @@ EXPORT_SYMBOL_GPL(alarm_init);
 void alarm_start(struct alarm *alarm, ktime_t start)
 {
 	struct alarm_base *base = &alarm_bases[alarm->type];
-	unsigned long flags;
 
-	spin_lock_irqsave(&base->lock, flags);
-	alarm->node.expires = start;
-	alarmtimer_enqueue(base, alarm);
-	hrtimer_start(&alarm->timer, alarm->node.expires, HRTIMER_MODE_ABS);
-	spin_unlock_irqrestore(&base->lock, flags);
+	scoped_guard(spinlock_irqsave, &base->lock) {
+		alarm->node.expires = start;
+		alarmtimer_enqueue(base, alarm);
+		hrtimer_start(&alarm->timer, alarm->node.expires, HRTIMER_MODE_ABS);
+	}
 
 	trace_alarmtimer_start(alarm, base->get_ktime());
 }
@@ -381,13 +368,11 @@ EXPORT_SYMBOL_GPL(alarm_start_relative);
 void alarm_restart(struct alarm *alarm)
 {
 	struct alarm_base *base = &alarm_bases[alarm->type];
-	unsigned long flags;
 
-	spin_lock_irqsave(&base->lock, flags);
+	guard(spinlock_irqsave)(&base->lock);
 	hrtimer_set_expires(&alarm->timer, alarm->node.expires);
 	hrtimer_restart(&alarm->timer);
 	alarmtimer_enqueue(base, alarm);
-	spin_unlock_irqrestore(&base->lock, flags);
 }
 EXPORT_SYMBOL_GPL(alarm_restart);
 
@@ -401,14 +386,13 @@ EXPORT_SYMBOL_GPL(alarm_restart);
 int alarm_try_to_cancel(struct alarm *alarm)
 {
 	struct alarm_base *base = &alarm_bases[alarm->type];
-	unsigned long flags;
 	int ret;
 
-	spin_lock_irqsave(&base->lock, flags);
-	ret = hrtimer_try_to_cancel(&alarm->timer);
-	if (ret >= 0)
-		alarmtimer_dequeue(base, alarm);
-	spin_unlock_irqrestore(&base->lock, flags);
+	scoped_guard(spinlock_irqsave, &base->lock) {
+		ret = hrtimer_try_to_cancel(&alarm->timer);
+		if (ret >= 0)
+			alarmtimer_dequeue(base, alarm);
+	}
 
 	trace_alarmtimer_cancel(alarm, base->get_ktime());
 	return ret;
@@ -479,7 +463,6 @@ EXPORT_SYMBOL_GPL(alarm_forward_now);
 static void alarmtimer_freezerset(ktime_t absexp, enum alarmtimer_type type)
 {
 	struct alarm_base *base;
-	unsigned long flags;
 	ktime_t delta;
 
 	switch(type) {
@@ -498,13 +481,12 @@ static void alarmtimer_freezerset(ktime_t absexp, enum alarmtimer_type type)
 
 	delta = ktime_sub(absexp, base->get_ktime());
 
-	spin_lock_irqsave(&freezer_delta_lock, flags);
+	guard(spinlock_irqsave)(&freezer_delta_lock);
 	if (!freezer_delta || (delta < freezer_delta)) {
 		freezer_delta = delta;
 		freezer_expires = absexp;
 		freezer_alarmtype = type;
 	}
-	spin_unlock_irqrestore(&freezer_delta_lock, flags);
 }
 
 /**
@@ -515,9 +497,9 @@ static enum alarmtimer_type clock2alarm(clockid_t clockid)
 {
 	if (clockid == CLOCK_REALTIME_ALARM)
 		return ALARM_REALTIME;
-	if (clockid == CLOCK_BOOTTIME_ALARM)
-		return ALARM_BOOTTIME;
-	return -1;
+
+	WARN_ON_ONCE(clockid != CLOCK_BOOTTIME_ALARM);
+	return ALARM_BOOTTIME;
 }
 
 /**

kernel/time/clocksource.c

@@ -310,7 +310,7 @@ static void clocksource_verify_choose_cpus(void)
 {
 	int cpu, i, n = verify_n_cpus;
 
-	if (n < 0) {
+	if (n < 0 || n >= num_online_cpus()) {
 		/* Check all of the CPUs. */
 		cpumask_copy(&cpus_chosen, cpu_online_mask);
 		cpumask_clear_cpu(smp_processor_id(), &cpus_chosen);

kernel/time/jiffies.c

@@ -75,13 +75,11 @@ struct clocksource * __init __weak clocksource_default_clock(void)
 
 static struct clocksource refined_jiffies;
 
-int register_refined_jiffies(long cycles_per_second)
+void __init register_refined_jiffies(long cycles_per_second)
 {
 	u64 nsec_per_tick, shift_hz;
 	long cycles_per_tick;
 
-
-
 	refined_jiffies = clocksource_jiffies;
 	refined_jiffies.name = "refined-jiffies";
 	refined_jiffies.rating++;
@@ -100,5 +98,4 @@ int register_refined_jiffies(long cycles_per_second)
 	refined_jiffies.mult = ((u32)nsec_per_tick) << JIFFIES_SHIFT;
 
 	__clocksource_register(&refined_jiffies);
-	return 0;
 }

kernel/time/posix-timers.c

@@ -30,8 +30,6 @@
 #include "timekeeping.h"
 #include "posix-timers.h"
 
-static struct kmem_cache *posix_timers_cache;
-
 /*
  * Timers are managed in a hash table for lockless lookup. The hash key is
  * constructed from current::signal and the timer ID and the timer is
@@ -49,10 +47,12 @@ struct timer_hash_bucket {
 static struct {
 	struct timer_hash_bucket	*buckets;
 	unsigned long			mask;
-} __timer_data __ro_after_init __aligned(2*sizeof(long));
+	struct kmem_cache		*cache;
+} __timer_data __ro_after_init __aligned(4*sizeof(long));
 
-#define timer_buckets	(__timer_data.buckets)
-#define timer_hashmask	(__timer_data.mask)
+#define timer_buckets		(__timer_data.buckets)
+#define timer_hashmask		(__timer_data.mask)
+#define posix_timers_cache	(__timer_data.cache)
 
 static const struct k_clock * const posix_clocks[];
 static const struct k_clock *clockid_to_kclock(const clockid_t id);
@@ -283,14 +283,6 @@ static int posix_get_hrtimer_res(clockid_t which_clock, struct timespec64 *tp)
 	return 0;
 }
 
-static __init int init_posix_timers(void)
-{
-	posix_timers_cache = kmem_cache_create("posix_timers_cache", sizeof(struct k_itimer),
-					       __alignof__(struct k_itimer), SLAB_ACCOUNT, NULL);
-	return 0;
-}
-__initcall(init_posix_timers);
-
 /*
  * The siginfo si_overrun field and the return value of timer_getoverrun(2)
  * are of type int. Clamp the overrun value to INT_MAX
@@ -1556,6 +1548,11 @@ static int __init posixtimer_init(void)
 	unsigned long i, size;
 	unsigned int shift;
 
+	posix_timers_cache = kmem_cache_create("posix_timers_cache",
+					       sizeof(struct k_itimer),
+					       __alignof__(struct k_itimer),
+					       SLAB_ACCOUNT, NULL);
+
 	if (IS_ENABLED(CONFIG_BASE_SMALL))
 		size = 512;
 	else

kernel/time/timer.c

@@ -385,32 +385,6 @@ static unsigned long round_jiffies_common(unsigned long j, int cpu,
 	return time_is_after_jiffies(j) ? j : original;
 }
 
-/**
- * __round_jiffies - function to round jiffies to a full second
- * @j: the time in (absolute) jiffies that should be rounded
- * @cpu: the processor number on which the timeout will happen
- *
- * __round_jiffies() rounds an absolute time in the future (in jiffies)
- * up or down to (approximately) full seconds. This is useful for timers
- * for which the exact time they fire does not matter too much, as long as
- * they fire approximately every X seconds.
- *
- * By rounding these timers to whole seconds, all such timers will fire
- * at the same time, rather than at various times spread out. The goal
- * of this is to have the CPU wake up less, which saves power.
- *
- * The exact rounding is skewed for each processor to avoid all
- * processors firing at the exact same time, which could lead
- * to lock contention or spurious cache line bouncing.
- *
- * The return value is the rounded version of the @j parameter.
- */
-unsigned long __round_jiffies(unsigned long j, int cpu)
-{
-	return round_jiffies_common(j, cpu, false);
-}
-EXPORT_SYMBOL_GPL(__round_jiffies);
-
 /**
  * __round_jiffies_relative - function to round jiffies to a full second
  * @j: the time in (relative) jiffies that should be rounded
@@ -482,22 +456,6 @@ unsigned long round_jiffies_relative(unsigned long j)
 }
 EXPORT_SYMBOL_GPL(round_jiffies_relative);
 
-/**
- * __round_jiffies_up - function to round jiffies up to a full second
- * @j: the time in (absolute) jiffies that should be rounded
- * @cpu: the processor number on which the timeout will happen
- *
- * This is the same as __round_jiffies() except that it will never
- * round down.  This is useful for timeouts for which the exact time
- * of firing does not matter too much, as long as they don't fire too
- * early.
- */
-unsigned long __round_jiffies_up(unsigned long j, int cpu)
-{
-	return round_jiffies_common(j, cpu, true);
-}
-EXPORT_SYMBOL_GPL(__round_jiffies_up);
-
 /**
  * __round_jiffies_up_relative - function to round jiffies up to a full second
  * @j: the time in (relative) jiffies that should be rounded