hrtimer: Cleanup coding style and comments

As this code has some major surgery ahead, clean up coding style and bring comments up to date. No functional change intended. Signed-off-by: Thomas Gleixner <tglx@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://patch.msgid.link/20260224163430.342740952@kernel.org
2026-05-16 04:21:09 -04:00 · 2026-02-24 17:37:09 +01:00
parent 6abfc2bd5b
commit 0c6af0ea51
1 changed files with 143 additions and 221 deletions
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -77,43 +77,22 @@ static ktime_t __hrtimer_cb_get_time(clockid_t clock_id);
 * to reach a base using a clockid, hrtimer_clockid_to_base()
 * is used to convert from clockid to the proper hrtimer_base_type.
 */
+
+#define BASE_INIT(idx, cid)			\
+	[idx] = { .index = idx, .clockid = cid }
+
 DEFINE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases) =
 {
 	.lock = __RAW_SPIN_LOCK_UNLOCKED(hrtimer_bases.lock),
-	.clock_base =
-	{
-		{
-			.index = HRTIMER_BASE_MONOTONIC,
-			.clockid = CLOCK_MONOTONIC,
-		},
-		{
-			.index = HRTIMER_BASE_REALTIME,
-			.clockid = CLOCK_REALTIME,
-		},
-		{
-			.index = HRTIMER_BASE_BOOTTIME,
-			.clockid = CLOCK_BOOTTIME,
-		},
-		{
-			.index = HRTIMER_BASE_TAI,
-			.clockid = CLOCK_TAI,
-		},
-		{
-			.index = HRTIMER_BASE_MONOTONIC_SOFT,
-			.clockid = CLOCK_MONOTONIC,
-		},
-		{
-			.index = HRTIMER_BASE_REALTIME_SOFT,
-			.clockid = CLOCK_REALTIME,
-		},
-		{
-			.index = HRTIMER_BASE_BOOTTIME_SOFT,
-			.clockid = CLOCK_BOOTTIME,
-		},
-		{
-			.index = HRTIMER_BASE_TAI_SOFT,
-			.clockid = CLOCK_TAI,
-		},
+	.clock_base = {
+		BASE_INIT(HRTIMER_BASE_MONOTONIC,	CLOCK_MONOTONIC),
+		BASE_INIT(HRTIMER_BASE_REALTIME,	CLOCK_REALTIME),
+		BASE_INIT(HRTIMER_BASE_BOOTTIME,	CLOCK_BOOTTIME),
+		BASE_INIT(HRTIMER_BASE_TAI,		CLOCK_TAI),
+		BASE_INIT(HRTIMER_BASE_MONOTONIC_SOFT,	CLOCK_MONOTONIC),
+		BASE_INIT(HRTIMER_BASE_REALTIME_SOFT,	CLOCK_REALTIME),
+		BASE_INIT(HRTIMER_BASE_BOOTTIME_SOFT,	CLOCK_BOOTTIME),
+		BASE_INIT(HRTIMER_BASE_TAI_SOFT,	CLOCK_TAI),
 	},
 	.csd = CSD_INIT(retrigger_next_event, NULL)
 };
@@ -150,18 +129,19 @@ static inline void hrtimer_schedule_hres_work(void) { }
 * single place
 */
 #ifdef CONFIG_SMP
-
 /*
 * We require the migration_base for lock_hrtimer_base()/switch_hrtimer_base()
 * such that hrtimer_callback_running() can unconditionally dereference
 * timer->base->cpu_base
 */
 static struct hrtimer_cpu_base migration_cpu_base = {
-	.clock_base = { {
-		.cpu_base = &migration_cpu_base,
-		.seq      = SEQCNT_RAW_SPINLOCK_ZERO(migration_cpu_base.seq,
-						     &migration_cpu_base.lock),
-	}, },
+	.clock_base = {
+		[0] = {
+			.cpu_base = &migration_cpu_base,
+			.seq      = SEQCNT_RAW_SPINLOCK_ZERO(migration_cpu_base.seq,
+							     &migration_cpu_base.lock),
+		},
+	},
 };

 #define migration_base	migration_cpu_base.clock_base[0]
@@ -178,15 +158,13 @@ static struct hrtimer_cpu_base migration_cpu_base = {
 * possible to set timer->base = &migration_base and drop the lock: the timer
 * remains locked.
 */
-static
-struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer,
-					     unsigned long *flags)
+static struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer,
+						    unsigned long *flags)
 	__acquires(&timer->base->lock)
 {
-	struct hrtimer_clock_base *base;
-
 	for (;;) {
-		base = READ_ONCE(timer->base);
+		struct hrtimer_clock_base *base = READ_ONCE(timer->base);
+
 		if (likely(base != &migration_base)) {
 			raw_spin_lock_irqsave(&base->cpu_base->lock, *flags);
 			if (likely(base == timer->base))
@@ -239,7 +217,7 @@ static bool hrtimer_suitable_target(struct hrtimer *timer, struct hrtimer_clock_
 	return expires >= new_base->cpu_base->expires_next;
 }

-static inline struct hrtimer_cpu_base *get_target_base(struct hrtimer_cpu_base *base, int pinned)
+static inline struct hrtimer_cpu_base *get_target_base(struct hrtimer_cpu_base *base, bool pinned)
 {
 	if (!hrtimer_base_is_online(base)) {
 		int cpu = cpumask_any_and(cpu_online_mask, housekeeping_cpumask(HK_TYPE_TIMER));
@@ -267,8 +245,7 @@ static inline struct hrtimer_cpu_base *get_target_base(struct hrtimer_cpu_base *
 * the timer callback is currently running.
 */
 static inline struct hrtimer_clock_base *
-switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base,
-		    int pinned)
+switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base, bool pinned)
 {
 	struct hrtimer_cpu_base *new_cpu_base, *this_cpu_base;
 	struct hrtimer_clock_base *new_base;
@@ -281,13 +258,12 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base,

 	if (base != new_base) {
 		/*
-		 * We are trying to move timer to new_base.
-		 * However we can't change timer's base while it is running,
-		 * so we keep it on the same CPU. No hassle vs. reprogramming
-		 * the event source in the high resolution case. The softirq
-		 * code will take care of this when the timer function has
-		 * completed. There is no conflict as we hold the lock until
-		 * the timer is enqueued.
+		 * We are trying to move timer to new_base. However we can't
+		 * change timer's base while it is running, so we keep it on
+		 * the same CPU. No hassle vs. reprogramming the event source
+		 * in the high resolution case. The remote CPU will take care
+		 * of this when the timer function has completed. There is no
+		 * conflict as we hold the lock until the timer is enqueued.
 		 */
 		if (unlikely(hrtimer_callback_running(timer)))
 			return base;
@@ -297,8 +273,7 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base,
 		raw_spin_unlock(&base->cpu_base->lock);
 		raw_spin_lock(&new_base->cpu_base->lock);

-		if (!hrtimer_suitable_target(timer, new_base, new_cpu_base,
-					     this_cpu_base)) {
+		if (!hrtimer_suitable_target(timer, new_base, new_cpu_base, this_cpu_base)) {
 			raw_spin_unlock(&new_base->cpu_base->lock);
 			raw_spin_lock(&base->cpu_base->lock);
 			new_cpu_base = this_cpu_base;
@@ -317,14 +292,13 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base,

 #else /* CONFIG_SMP */

-static inline struct hrtimer_clock_base *
-lock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags)
+static inline struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer,
+							   unsigned long *flags)
 	__acquires(&timer->base->cpu_base->lock)
 {
 	struct hrtimer_clock_base *base = timer->base;

 	raw_spin_lock_irqsave(&base->cpu_base->lock, *flags);
-
 	return base;
 }

@@ -484,8 +458,7 @@ static inline void debug_hrtimer_init_on_stack(struct hrtimer *timer)
 	debug_object_init_on_stack(timer, &hrtimer_debug_descr);
 }

-static inline void debug_hrtimer_activate(struct hrtimer *timer,
-					  enum hrtimer_mode mode)
+static inline void debug_hrtimer_activate(struct hrtimer *timer, enum hrtimer_mode mode)
 {
 	debug_object_activate(timer, &hrtimer_debug_descr);
 }
@@ -510,8 +483,7 @@ EXPORT_SYMBOL_GPL(destroy_hrtimer_on_stack);

 static inline void debug_hrtimer_init(struct hrtimer *timer) { }
 static inline void debug_hrtimer_init_on_stack(struct hrtimer *timer) { }
-static inline void debug_hrtimer_activate(struct hrtimer *timer,
-					  enum hrtimer_mode mode) { }
+static inline void debug_hrtimer_activate(struct hrtimer *timer, enum hrtimer_mode mode) { }
 static inline void debug_hrtimer_deactivate(struct hrtimer *timer) { }
 static inline void debug_hrtimer_assert_init(struct hrtimer *timer) { }
 #endif
@@ -549,13 +521,12 @@ __next_base(struct hrtimer_cpu_base *cpu_base, unsigned int *active)
 	return &cpu_base->clock_base[idx];
 }

-#define for_each_active_base(base, cpu_base, active)	\
+#define for_each_active_base(base, cpu_base, active)		\
 	while ((base = __next_base((cpu_base), &(active))))

 static ktime_t __hrtimer_next_event_base(struct hrtimer_cpu_base *cpu_base,
 					 const struct hrtimer *exclude,
-					 unsigned int active,
-					 ktime_t expires_next)
+					 unsigned int active, ktime_t expires_next)
 {
 	struct hrtimer_clock_base *base;
 	ktime_t expires;
@@ -618,29 +589,24 @@ static ktime_t __hrtimer_next_event_base(struct hrtimer_cpu_base *cpu_base,
 *  - HRTIMER_ACTIVE_SOFT, or
 *  - HRTIMER_ACTIVE_HARD.
 */
-static ktime_t
-__hrtimer_get_next_event(struct hrtimer_cpu_base *cpu_base, unsigned int active_mask)
+static ktime_t __hrtimer_get_next_event(struct hrtimer_cpu_base *cpu_base, unsigned int active_mask)
 {
-	unsigned int active;
 	struct hrtimer *next_timer = NULL;
 	ktime_t expires_next = KTIME_MAX;
+	unsigned int active;

 	if (!cpu_base->softirq_activated && (active_mask & HRTIMER_ACTIVE_SOFT)) {
 		active = cpu_base->active_bases & HRTIMER_ACTIVE_SOFT;
 		cpu_base->softirq_next_timer = NULL;
-		expires_next = __hrtimer_next_event_base(cpu_base, NULL,
-							 active, KTIME_MAX);
-
+		expires_next = __hrtimer_next_event_base(cpu_base, NULL, active, KTIME_MAX);
 		next_timer = cpu_base->softirq_next_timer;
 	}

 	if (active_mask & HRTIMER_ACTIVE_HARD) {
 		active = cpu_base->active_bases & HRTIMER_ACTIVE_HARD;
 		cpu_base->next_timer = next_timer;
-		expires_next = __hrtimer_next_event_base(cpu_base, NULL, active,
-							 expires_next);
+		expires_next = __hrtimer_next_event_base(cpu_base, NULL, active, expires_next);
 	}
-
 	return expires_next;
 }

@@ -681,8 +647,8 @@ static inline ktime_t hrtimer_update_base(struct hrtimer_cpu_base *base)
 	ktime_t *offs_boot = &base->clock_base[HRTIMER_BASE_BOOTTIME].offset;
 	ktime_t *offs_tai = &base->clock_base[HRTIMER_BASE_TAI].offset;

-	ktime_t now = ktime_get_update_offsets_now(&base->clock_was_set_seq,
-					    offs_real, offs_boot, offs_tai);
+	ktime_t now = ktime_get_update_offsets_now(&base->clock_was_set_seq, offs_real,
+						   offs_boot, offs_tai);

 	base->clock_base[HRTIMER_BASE_REALTIME_SOFT].offset = *offs_real;
 	base->clock_base[HRTIMER_BASE_BOOTTIME_SOFT].offset = *offs_boot;
@@ -702,8 +668,7 @@ static inline int hrtimer_hres_active(struct hrtimer_cpu_base *cpu_base)
 		cpu_base->hres_active : 0;
 }

-static void __hrtimer_reprogram(struct hrtimer_cpu_base *cpu_base,
-				struct hrtimer *next_timer,
+static void __hrtimer_reprogram(struct hrtimer_cpu_base *cpu_base, struct hrtimer *next_timer,
 				ktime_t expires_next)
 {
 	cpu_base->expires_next = expires_next;
@@ -736,12 +701,9 @@ static void __hrtimer_reprogram(struct hrtimer_cpu_base *cpu_base,
 * next event
 * Called with interrupts disabled and base->lock held
 */
-static void
-hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal)
+static void hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, bool skip_equal)
 {
-	ktime_t expires_next;
-
-	expires_next = hrtimer_update_next_event(cpu_base);
+	ktime_t expires_next = hrtimer_update_next_event(cpu_base);

 	if (skip_equal && expires_next == cpu_base->expires_next)
 		return;
@@ -752,41 +714,31 @@ hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal)
 /* High resolution timer related functions */
 #ifdef CONFIG_HIGH_RES_TIMERS

-/*
- * High resolution timer enabled ?
- */
+/* High resolution timer enabled ? */
 static bool hrtimer_hres_enabled __read_mostly  = true;
 unsigned int hrtimer_resolution __read_mostly = LOW_RES_NSEC;
 EXPORT_SYMBOL_GPL(hrtimer_resolution);

-/*
- * Enable / Disable high resolution mode
- */
+/* Enable / Disable high resolution mode */
 static int __init setup_hrtimer_hres(char *str)
 {
 	return (kstrtobool(str, &hrtimer_hres_enabled) == 0);
 }
-
 __setup("highres=", setup_hrtimer_hres);

-/*
- * hrtimer_high_res_enabled - query, if the highres mode is enabled
- */
-static inline int hrtimer_is_hres_enabled(void)
+/* hrtimer_high_res_enabled - query, if the highres mode is enabled */
+static inline bool hrtimer_is_hres_enabled(void)
 {
 	return hrtimer_hres_enabled;
 }

-/*
- * Switch to high resolution mode
- */
+/* Switch to high resolution mode */
 static void hrtimer_switch_to_hres(void)
 {
 	struct hrtimer_cpu_base *base = this_cpu_ptr(&hrtimer_bases);

 	if (tick_init_highres()) {
-		pr_warn("Could not switch to high resolution mode on CPU %u\n",
-			base->cpu);
+		pr_warn("Could not switch to high resolution mode on CPU %u\n",	base->cpu);
 		return;
 	}
 	base->hres_active = 1;
@@ -800,10 +752,11 @@ static void hrtimer_switch_to_hres(void)

 #else

-static inline int hrtimer_is_hres_enabled(void) { return 0; }
+static inline bool hrtimer_is_hres_enabled(void) { return 0; }
 static inline void hrtimer_switch_to_hres(void) { }

 #endif /* CONFIG_HIGH_RES_TIMERS */
+
 /*
 * Retrigger next event is called after clock was set with interrupts
 * disabled through an SMP function call or directly from low level
@@ -841,7 +794,7 @@ static void retrigger_next_event(void *arg)
 	guard(raw_spinlock)(&base->lock);
 	hrtimer_update_base(base);
 	if (hrtimer_hres_active(base))
-		hrtimer_force_reprogram(base, 0);
+		hrtimer_force_reprogram(base, /* skip_equal */ false);
 	else
 		hrtimer_update_next_event(base);
 }
@@ -887,8 +840,7 @@ static void hrtimer_reprogram(struct hrtimer *timer, bool reprogram)
 		timer_cpu_base->softirq_next_timer = timer;
 		timer_cpu_base->softirq_expires_next = expires;

-		if (!ktime_before(expires, timer_cpu_base->expires_next) ||
-		    !reprogram)
+		if (!ktime_before(expires, timer_cpu_base->expires_next) || !reprogram)
 			return;
 	}

@@ -914,8 +866,7 @@ static void hrtimer_reprogram(struct hrtimer *timer, bool reprogram)
 	__hrtimer_reprogram(cpu_base, timer, expires);
 }

-static bool update_needs_ipi(struct hrtimer_cpu_base *cpu_base,
-			     unsigned int active)
+static bool update_needs_ipi(struct hrtimer_cpu_base *cpu_base, unsigned int active)
 {
 	struct hrtimer_clock_base *base;
 	unsigned int seq;
@@ -1050,11 +1001,8 @@ void hrtimers_resume_local(void)
 	retrigger_next_event(NULL);
 }

-/*
- * Counterpart to lock_hrtimer_base above:
- */
-static inline
-void unlock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags)
+/* Counterpart to lock_hrtimer_base above */
+static inline void unlock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags)
 	__releases(&timer->base->cpu_base->lock)
 {
 	raw_spin_unlock_irqrestore(&timer->base->cpu_base->lock, *flags);
@@ -1071,7 +1019,7 @@ void unlock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags)
 * .. note::
 *  This only updates the timer expiry value and does not requeue the timer.
 *
- * There is also a variant of the function hrtimer_forward_now().
+ * There is also a variant of this function: hrtimer_forward_now().
 *
 * Context: Can be safely called from the callback function of @timer. If called
 *          from other contexts @timer must neither be enqueued nor running the
@@ -1081,8 +1029,8 @@ void unlock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags)
 */
 u64 hrtimer_forward(struct hrtimer *timer, ktime_t now, ktime_t interval)
 {
-	u64 orun = 1;
 	ktime_t delta;
+	u64 orun = 1;

 	delta = ktime_sub(now, hrtimer_get_expires(timer));

@@ -1118,13 +1066,15 @@ EXPORT_SYMBOL_GPL(hrtimer_forward);
 * enqueue_hrtimer - internal function to (re)start a timer
 *
 * The timer is inserted in expiry order. Insertion into the
- * red black tree is O(log(n)). Must hold the base lock.
+ * red black tree is O(log(n)).
 *
 * Returns true when the new timer is the leftmost timer in the tree.
 */
 static bool enqueue_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base,
 			    enum hrtimer_mode mode, bool was_armed)
 {
+	lockdep_assert_held(&base->cpu_base->lock);
+
 	debug_activate(timer, mode, was_armed);
 	WARN_ON_ONCE(!base->cpu_base->online);

@@ -1139,20 +1089,19 @@ static bool enqueue_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *ba
 /*
 * __remove_hrtimer - internal function to remove a timer
 *
- * Caller must hold the base lock.
- *
 * High resolution timer mode reprograms the clock event device when the
 * timer is the one which expires next. The caller can disable this by setting
 * reprogram to zero. This is useful, when the context does a reprogramming
 * anyway (e.g. timer interrupt)
 */
-static void __remove_hrtimer(struct hrtimer *timer,
-			     struct hrtimer_clock_base *base,
-			     u8 newstate, int reprogram)
+static void __remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base,
+			     u8 newstate, bool reprogram)
 {
 	struct hrtimer_cpu_base *cpu_base = base->cpu_base;
 	u8 state = timer->state;

+	lockdep_assert_held(&cpu_base->lock);
+
 	/* Pairs with the lockless read in hrtimer_is_queued() */
 	WRITE_ONCE(timer->state, newstate);
 	if (!(state & HRTIMER_STATE_ENQUEUED))
@@ -1162,26 +1111,25 @@ static void __remove_hrtimer(struct hrtimer *timer,
 		cpu_base->active_bases &= ~(1 << base->index);

 	/*
-	 * Note: If reprogram is false we do not update
-	 * cpu_base->next_timer. This happens when we remove the first
-	 * timer on a remote cpu. No harm as we never dereference
-	 * cpu_base->next_timer. So the worst thing what can happen is
-	 * an superfluous call to hrtimer_force_reprogram() on the
-	 * remote cpu later on if the same timer gets enqueued again.
+	 * If reprogram is false don't update cpu_base->next_timer and do not
+	 * touch the clock event device.
+	 *
+	 * This happens when removing the first timer on a remote CPU, which
+	 * will be handled by the remote CPU's interrupt. It also happens when
+	 * a local timer is removed to be immediately restarted. That's handled
+	 * at the call site.
 	 */
 	if (reprogram && timer == cpu_base->next_timer && !timer->is_lazy)
-		hrtimer_force_reprogram(cpu_base, 1);
+		hrtimer_force_reprogram(cpu_base, /* skip_equal */ true);
 }

-/*
- * remove hrtimer, called with base lock held
- */
-static inline int
-remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base,
-	       bool restart, bool keep_local)
+static inline bool remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base,
+				 bool restart, bool keep_local)
 {
 	u8 state = timer->state;

+	lockdep_assert_held(&base->cpu_base->lock);
+
 	if (state & HRTIMER_STATE_ENQUEUED) {
 		bool reprogram;

@@ -1209,9 +1157,9 @@ remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base,
 			reprogram &= !keep_local;

 		__remove_hrtimer(timer, base, state, reprogram);
-		return 1;
+		return true;
 	}
-	return 0;
+	return false;
 }

 static inline ktime_t hrtimer_update_lowres(struct hrtimer *timer, ktime_t tim,
@@ -1230,34 +1178,27 @@ static inline ktime_t hrtimer_update_lowres(struct hrtimer *timer, ktime_t tim,
 	return tim;
 }

-static void
-hrtimer_update_softirq_timer(struct hrtimer_cpu_base *cpu_base, bool reprogram)
+static void hrtimer_update_softirq_timer(struct hrtimer_cpu_base *cpu_base, bool reprogram)
 {
-	ktime_t expires;
+	ktime_t expires = __hrtimer_get_next_event(cpu_base, HRTIMER_ACTIVE_SOFT);

 	/*
-	 * Find the next SOFT expiration.
-	 */
-	expires = __hrtimer_get_next_event(cpu_base, HRTIMER_ACTIVE_SOFT);
-
-	/*
-	 * reprogramming needs to be triggered, even if the next soft
-	 * hrtimer expires at the same time than the next hard
+	 * Reprogramming needs to be triggered, even if the next soft
+	 * hrtimer expires at the same time as the next hard
 	 * hrtimer. cpu_base->softirq_expires_next needs to be updated!
 	 */
 	if (expires == KTIME_MAX)
 		return;

 	/*
-	 * cpu_base->*next_timer is recomputed by __hrtimer_get_next_event()
-	 * cpu_base->*expires_next is only set by hrtimer_reprogram()
+	 * cpu_base->next_timer is recomputed by __hrtimer_get_next_event()
+	 * cpu_base->expires_next is only set by hrtimer_reprogram()
 	 */
 	hrtimer_reprogram(cpu_base->softirq_next_timer, reprogram);
 }

-static int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
-				    u64 delta_ns, const enum hrtimer_mode mode,
-				    struct hrtimer_clock_base *base)
+static bool __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim, u64 delta_ns,
+				     const enum hrtimer_mode mode, struct hrtimer_clock_base *base)
 {
 	struct hrtimer_cpu_base *this_cpu_base = this_cpu_ptr(&hrtimer_bases);
 	struct hrtimer_clock_base *new_base;
@@ -1301,12 +1242,10 @@ static int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
 	hrtimer_set_expires_range_ns(timer, tim, delta_ns);

 	/* Switch the timer base, if necessary: */
-	if (!force_local) {
-		new_base = switch_hrtimer_base(timer, base,
-					       mode & HRTIMER_MODE_PINNED);
-	} else {
+	if (!force_local)
+		new_base = switch_hrtimer_base(timer, base, mode & HRTIMER_MODE_PINNED);
+	else
 		new_base = base;
-	}

 	first = enqueue_hrtimer(timer, new_base, mode, was_armed);

@@ -1319,9 +1258,12 @@ static int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,

 	if (!force_local) {
 		/*
-		 * If the current CPU base is online, then the timer is
-		 * never queued on a remote CPU if it would be the first
-		 * expiring timer there.
+		 * If the current CPU base is online, then the timer is never
+		 * queued on a remote CPU if it would be the first expiring
+		 * timer there unless the timer callback is currently executed
+		 * on the remote CPU. In the latter case the remote CPU will
+		 * re-evaluate the first expiring timer after completing the
+		 * callbacks.
 		 */
 		if (hrtimer_base_is_online(this_cpu_base))
 			return first;
@@ -1336,7 +1278,7 @@ static int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,

 			smp_call_function_single_async(new_cpu_base->cpu, &new_cpu_base->csd);
 		}
-		return 0;
+		return false;
 	}

 	/*
@@ -1350,7 +1292,7 @@ static int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
 	 */
 	if (timer->is_lazy) {
 		if (new_base->cpu_base->expires_next <= hrtimer_get_expires(timer))
-			return 0;
+			return false;
 	}

 	/*
@@ -1358,8 +1300,8 @@ static int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
 	 * reprogramming on removal and enqueue. Force reprogram the
 	 * hardware by evaluating the new first expiring timer.
 	 */
-	hrtimer_force_reprogram(new_base->cpu_base, 1);
-	return 0;
+	hrtimer_force_reprogram(new_base->cpu_base, /* skip_equal */ true);
+	return false;
 }

 /**
@@ -1371,8 +1313,8 @@ static int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
 *		relative (HRTIMER_MODE_REL), and pinned (HRTIMER_MODE_PINNED);
 *		softirq based mode is considered for debug purpose only!
 */
-void hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim,
-			    u64 delta_ns, const enum hrtimer_mode mode)
+void hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim, u64 delta_ns,
+			    const enum hrtimer_mode mode)
 {
 	struct hrtimer_clock_base *base;
 	unsigned long flags;
@@ -1464,8 +1406,7 @@ static void hrtimer_cpu_base_unlock_expiry(struct hrtimer_cpu_base *base)
 * the timer callback to finish. Drop expiry_lock and reacquire it. That
 * allows the waiter to acquire the lock and make progress.
 */
-static void hrtimer_sync_wait_running(struct hrtimer_cpu_base *cpu_base,
-				      unsigned long flags)
+static void hrtimer_sync_wait_running(struct hrtimer_cpu_base *cpu_base, unsigned long flags)
 {
 	if (atomic_read(&cpu_base->timer_waiters)) {
 		raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
@@ -1530,14 +1471,10 @@ void hrtimer_cancel_wait_running(const struct hrtimer *timer)
 	spin_unlock_bh(&base->cpu_base->softirq_expiry_lock);
 }
 #else
-static inline void
-hrtimer_cpu_base_init_expiry_lock(struct hrtimer_cpu_base *base) { }
-static inline void
-hrtimer_cpu_base_lock_expiry(struct hrtimer_cpu_base *base) { }
-static inline void
-hrtimer_cpu_base_unlock_expiry(struct hrtimer_cpu_base *base) { }
-static inline void hrtimer_sync_wait_running(struct hrtimer_cpu_base *base,
-					     unsigned long flags) { }
+static inline void hrtimer_cpu_base_init_expiry_lock(struct hrtimer_cpu_base *base) { }
+static inline void hrtimer_cpu_base_lock_expiry(struct hrtimer_cpu_base *base) { }
+static inline void hrtimer_cpu_base_unlock_expiry(struct hrtimer_cpu_base *base) { }
+static inline void hrtimer_sync_wait_running(struct hrtimer_cpu_base *base, unsigned long fl) { }
 #endif

 /**
@@ -1668,8 +1605,7 @@ ktime_t hrtimer_cb_get_time(const struct hrtimer *timer)
 }
 EXPORT_SYMBOL_GPL(hrtimer_cb_get_time);

-static void __hrtimer_setup(struct hrtimer *timer,
-			    enum hrtimer_restart (*function)(struct hrtimer *),
+static void __hrtimer_setup(struct hrtimer *timer, enum hrtimer_restart (*fn)(struct hrtimer *),
 			    clockid_t clock_id, enum hrtimer_mode mode)
 {
 	bool softtimer = !!(mode & HRTIMER_MODE_SOFT);
@@ -1705,10 +1641,10 @@ static void __hrtimer_setup(struct hrtimer *timer,
 	timer->base = &cpu_base->clock_base[base];
 	timerqueue_init(&timer->node);

-	if (WARN_ON_ONCE(!function))
+	if (WARN_ON_ONCE(!fn))
 		ACCESS_PRIVATE(timer, function) = hrtimer_dummy_timeout;
 	else
-		ACCESS_PRIVATE(timer, function) = function;
+		ACCESS_PRIVATE(timer, function) = fn;
 }

 /**
@@ -1767,12 +1703,10 @@ bool hrtimer_active(const struct hrtimer *timer)
 		base = READ_ONCE(timer->base);
 		seq = raw_read_seqcount_begin(&base->seq);

-		if (timer->state != HRTIMER_STATE_INACTIVE ||
-		    base->running == timer)
+		if (timer->state != HRTIMER_STATE_INACTIVE || base->running == timer)
 			return true;

-	} while (read_seqcount_retry(&base->seq, seq) ||
-		 base != READ_ONCE(timer->base));
+	} while (read_seqcount_retry(&base->seq, seq) || base != READ_ONCE(timer->base));

 	return false;
 }
@@ -1795,11 +1729,9 @@ EXPORT_SYMBOL_GPL(hrtimer_active);
 * a false negative if the read side got smeared over multiple consecutive
 * __run_hrtimer() invocations.
 */
-
-static void __run_hrtimer(struct hrtimer_cpu_base *cpu_base,
-			  struct hrtimer_clock_base *base,
-			  struct hrtimer *timer, ktime_t *now,
-			  unsigned long flags) __must_hold(&cpu_base->lock)
+static void __run_hrtimer(struct hrtimer_cpu_base *cpu_base, struct hrtimer_clock_base *base,
+			  struct hrtimer *timer, ktime_t *now, unsigned long flags)
+	__must_hold(&cpu_base->lock)
 {
 	enum hrtimer_restart (*fn)(struct hrtimer *);
 	bool expires_in_hardirq;
@@ -1819,7 +1751,7 @@ static void __run_hrtimer(struct hrtimer_cpu_base *cpu_base,
 	 */
 	raw_write_seqcount_barrier(&base->seq);

-	__remove_hrtimer(timer, base, HRTIMER_STATE_INACTIVE, 0);
+	__remove_hrtimer(timer, base, HRTIMER_STATE_INACTIVE, false);
 	fn = ACCESS_PRIVATE(timer, function);

 	/*
@@ -1854,8 +1786,7 @@ static void __run_hrtimer(struct hrtimer_cpu_base *cpu_base,
 	 * hrtimer_start_range_ns() can have popped in and enqueued the timer
 	 * for us already.
 	 */
-	if (restart != HRTIMER_NORESTART &&
-	    !(timer->state & HRTIMER_STATE_ENQUEUED))
+	if (restart != HRTIMER_NORESTART && !(timer->state & HRTIMER_STATE_ENQUEUED))
 		enqueue_hrtimer(timer, base, HRTIMER_MODE_ABS, false);

 	/*
@@ -1874,8 +1805,8 @@ static void __run_hrtimer(struct hrtimer_cpu_base *cpu_base,
 static void __hrtimer_run_queues(struct hrtimer_cpu_base *cpu_base, ktime_t now,
 				 unsigned long flags, unsigned int active_mask)
 {
-	struct hrtimer_clock_base *base;
 	unsigned int active = cpu_base->active_bases & active_mask;
+	struct hrtimer_clock_base *base;

 	for_each_active_base(base, cpu_base, active) {
 		struct timerqueue_node *node;
@@ -1951,11 +1882,10 @@ void hrtimer_interrupt(struct clock_event_device *dev)
 retry:
 	cpu_base->in_hrtirq = 1;
 	/*
-	 * We set expires_next to KTIME_MAX here with cpu_base->lock
-	 * held to prevent that a timer is enqueued in our queue via
-	 * the migration code. This does not affect enqueueing of
-	 * timers which run their callback and need to be requeued on
-	 * this CPU.
+	 * Set expires_next to KTIME_MAX, which prevents that remote CPUs queue
+	 * timers while __hrtimer_run_queues() is expiring the clock bases.
+	 * Timers which are re/enqueued on the local CPU are not affected by
+	 * this.
 	 */
 	cpu_base->expires_next = KTIME_MAX;

@@ -2069,8 +1999,7 @@ void hrtimer_run_queues(void)
 */
 static enum hrtimer_restart hrtimer_wakeup(struct hrtimer *timer)
 {
-	struct hrtimer_sleeper *t =
-		container_of(timer, struct hrtimer_sleeper, timer);
+	struct hrtimer_sleeper *t = container_of(timer, struct hrtimer_sleeper, timer);
 	struct task_struct *task = t->task;

 	t->task = NULL;
@@ -2088,8 +2017,7 @@ static enum hrtimer_restart hrtimer_wakeup(struct hrtimer *timer)
 * Wrapper around hrtimer_start_expires() for hrtimer_sleeper based timers
 * to allow PREEMPT_RT to tweak the delivery mode (soft/hardirq context)
 */
-void hrtimer_sleeper_start_expires(struct hrtimer_sleeper *sl,
-				   enum hrtimer_mode mode)
+void hrtimer_sleeper_start_expires(struct hrtimer_sleeper *sl, enum hrtimer_mode mode)
 {
 	/*
 	 * Make the enqueue delivery mode check work on RT. If the sleeper
@@ -2105,8 +2033,8 @@ void hrtimer_sleeper_start_expires(struct hrtimer_sleeper *sl,
 }
 EXPORT_SYMBOL_GPL(hrtimer_sleeper_start_expires);

-static void __hrtimer_setup_sleeper(struct hrtimer_sleeper *sl,
-				    clockid_t clock_id, enum hrtimer_mode mode)
+static void __hrtimer_setup_sleeper(struct hrtimer_sleeper *sl, clockid_t clock_id,
+				    enum hrtimer_mode mode)
 {
 	/*
 	 * On PREEMPT_RT enabled kernels hrtimers which are not explicitly
@@ -2142,8 +2070,8 @@ static void __hrtimer_setup_sleeper(struct hrtimer_sleeper *sl,
 * @clock_id:	the clock to be used
 * @mode:	timer mode abs/rel
 */
-void hrtimer_setup_sleeper_on_stack(struct hrtimer_sleeper *sl,
-				    clockid_t clock_id, enum hrtimer_mode mode)
+void hrtimer_setup_sleeper_on_stack(struct hrtimer_sleeper *sl, clockid_t clock_id,
+				    enum hrtimer_mode mode)
 {
 	debug_setup_on_stack(&sl->timer, clock_id, mode);
 	__hrtimer_setup_sleeper(sl, clock_id, mode);
@@ -2216,8 +2144,7 @@ static long __sched hrtimer_nanosleep_restart(struct restart_block *restart)
 	return ret;
 }

-long hrtimer_nanosleep(ktime_t rqtp, const enum hrtimer_mode mode,
-		       const clockid_t clockid)
+long hrtimer_nanosleep(ktime_t rqtp, const enum hrtimer_mode mode, const clockid_t clockid)
 {
 	struct restart_block *restart;
 	struct hrtimer_sleeper t;
@@ -2260,8 +2187,7 @@ SYSCALL_DEFINE2(nanosleep, struct __kernel_timespec __user *, rqtp,
 	current->restart_block.fn = do_no_restart_syscall;
 	current->restart_block.nanosleep.type = rmtp ? TT_NATIVE : TT_NONE;
 	current->restart_block.nanosleep.rmtp = rmtp;
-	return hrtimer_nanosleep(timespec64_to_ktime(tu), HRTIMER_MODE_REL,
-				 CLOCK_MONOTONIC);
+	return hrtimer_nanosleep(timespec64_to_ktime(tu), HRTIMER_MODE_REL, CLOCK_MONOTONIC);
 }

 #endif
@@ -2269,7 +2195,7 @@ SYSCALL_DEFINE2(nanosleep, struct __kernel_timespec __user *, rqtp,
 #ifdef CONFIG_COMPAT_32BIT_TIME

 SYSCALL_DEFINE2(nanosleep_time32, struct old_timespec32 __user *, rqtp,
-		       struct old_timespec32 __user *, rmtp)
+		struct old_timespec32 __user *, rmtp)
 {
 	struct timespec64 tu;

@@ -2282,8 +2208,7 @@ SYSCALL_DEFINE2(nanosleep_time32, struct old_timespec32 __user *, rqtp,
 	current->restart_block.fn = do_no_restart_syscall;
 	current->restart_block.nanosleep.type = rmtp ? TT_COMPAT : TT_NONE;
 	current->restart_block.nanosleep.compat_rmtp = rmtp;
-	return hrtimer_nanosleep(timespec64_to_ktime(tu), HRTIMER_MODE_REL,
-				 CLOCK_MONOTONIC);
+	return hrtimer_nanosleep(timespec64_to_ktime(tu), HRTIMER_MODE_REL, CLOCK_MONOTONIC);
 }
 #endif

@@ -2293,9 +2218,8 @@ SYSCALL_DEFINE2(nanosleep_time32, struct old_timespec32 __user *, rqtp,
 int hrtimers_prepare_cpu(unsigned int cpu)
 {
 	struct hrtimer_cpu_base *cpu_base = &per_cpu(hrtimer_bases, cpu);
-	int i;

-	for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
+	for (int i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
 		struct hrtimer_clock_base *clock_b = &cpu_base->clock_base[i];

 		clock_b->cpu_base = cpu_base;
@@ -2329,8 +2253,8 @@ int hrtimers_cpu_starting(unsigned int cpu)
 static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
 				struct hrtimer_clock_base *new_base)
 {
-	struct hrtimer *timer;
 	struct timerqueue_node *node;
+	struct hrtimer *timer;

 	while ((node = timerqueue_getnext(&old_base->active))) {
 		timer = container_of(node, struct hrtimer, node);
@@ -2342,7 +2266,7 @@ static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
 		 * timer could be seen as !active and just vanish away
 		 * under us on another CPU
 		 */
-		__remove_hrtimer(timer, old_base, HRTIMER_STATE_ENQUEUED, 0);
+		__remove_hrtimer(timer, old_base, HRTIMER_STATE_ENQUEUED, false);
 		timer->base = new_base;
 		/*
 		 * Enqueue the timers on the new cpu. This does not
@@ -2358,7 +2282,7 @@ static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,

 int hrtimers_cpu_dying(unsigned int dying_cpu)
 {
-	int i, ncpu = cpumask_any_and(cpu_active_mask, housekeeping_cpumask(HK_TYPE_TIMER));
+	int ncpu = cpumask_any_and(cpu_active_mask, housekeeping_cpumask(HK_TYPE_TIMER));
 	struct hrtimer_cpu_base *old_base, *new_base;

 	old_base = this_cpu_ptr(&hrtimer_bases);
@@ -2371,10 +2295,8 @@ int hrtimers_cpu_dying(unsigned int dying_cpu)
 	raw_spin_lock(&old_base->lock);
 	raw_spin_lock_nested(&new_base->lock, SINGLE_DEPTH_NESTING);

-	for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
-		migrate_hrtimer_list(&old_base->clock_base[i],
-				     &new_base->clock_base[i]);
-	}
+	for (int i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++)
+		migrate_hrtimer_list(&old_base->clock_base[i], &new_base->clock_base[i]);

 	/* Tell the other CPU to retrigger the next event */
 	smp_call_function_single(ncpu, retrigger_next_event, NULL, 0);