Merge tag 'timers-core-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull timers and timekeeping updates from Thomas Gleixner:
 "Core:

   - Robustness improvements for the NOHZ tick management

   - Fixes and consolidation of the NTP/RTC synchronization code

   - Small fixes and improvements in various places

   - A set of function documentation udpates and fixes

   Drivers:

   - Cleanups and improvements in various clocksoure/event drivers

   - Removal of the EZChip NPS clocksource driver as the platfrom
     support was removed from ARC

   - The usual set of new device tree binding and json conversions

   - The RTC driver which have been acked by the RTC maintainer:

       * fix a long standing bug in the MC146818 library code which can
         cause reading garbage during the RTC internal update.

       * changes related to the NTP/RTC consolidation work"

* tag 'timers-core-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (46 commits)
  ntp: Fix prototype in the !CONFIG_GENERIC_CMOS_UPDATE case
  tick/sched: Make jiffies update quick check more robust
  ntp: Consolidate the RTC update implementation
  ntp: Make the RTC sync offset less obscure
  ntp, rtc: Move rtc_set_ntp_time() to ntp code
  ntp: Make the RTC synchronization more reliable
  rtc: core: Make the sync offset default more realistic
  rtc: cmos: Make rtc_cmos sync offset correct
  rtc: mc146818: Reduce spinlock section in mc146818_set_time()
  rtc: mc146818: Prevent reading garbage
  clocksource/drivers/sh_cmt: Fix potential deadlock when calling runtime PM
  clocksource/drivers/arm_arch_timer: Correct fault programming of CNTKCTL_EL1.EVNTI
  clocksource/drivers/arm_arch_timer: Use stable count reader in erratum sne
  clocksource/drivers/dw_apb_timer_of: Add error handling if no clock available
  clocksource/drivers/riscv: Make RISCV_TIMER depends on RISCV_SBI
  clocksource/drivers/ingenic: Fix section mismatch
  clocksource/drivers/cadence_ttc: Fix memory leak in ttc_setup_clockevent()
  dt-bindings: timer: renesas: tmu: Convert to json-schema
  dt-bindings: timer: renesas: tmu: Document r8a774e1 bindings
  clocksource/drivers/orion: Add missing clk_disable_unprepare() on error path
  ...

13 files changed, 366 insertions, 251 deletions

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 387b4bef7dd1..743c852e10f2 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1284,7 +1284,7 @@ int hrtimer_cancel(struct hrtimer *timer)
 EXPORT_SYMBOL_GPL(hrtimer_cancel);
 
 /**
- * hrtimer_get_remaining - get remaining time for the timer
+ * __hrtimer_get_remaining - get remaining time for the timer
  * @timer:	the timer to read
  * @adjust:	adjust relative timers when CONFIG_TIME_LOW_RES=y
  */
diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
index eddcf4970444..a5cffe2a1770 100644
--- a/kernel/time/jiffies.c
+++ b/kernel/time/jiffies.c
@@ -59,7 +59,8 @@ static struct clocksource clocksource_jiffies = {
 };
 
 __cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(jiffies_lock);
-__cacheline_aligned_in_smp seqcount_t jiffies_seq;
+__cacheline_aligned_in_smp seqcount_raw_spinlock_t jiffies_seq =
+	SEQCNT_RAW_SPINLOCK_ZERO(jiffies_seq, &jiffies_lock);
 
 #if (BITS_PER_LONG < 64)
 u64 get_jiffies_64(void)
diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index 069ca78fb0bf..7404d3831527 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -494,65 +494,74 @@ out:
 	return leap;
 }
 
+#if defined(CONFIG_GENERIC_CMOS_UPDATE) || defined(CONFIG_RTC_SYSTOHC)
 static void sync_hw_clock(struct work_struct *work);
-static DECLARE_DELAYED_WORK(sync_work, sync_hw_clock);
-
-static void sched_sync_hw_clock(struct timespec64 now,
-				unsigned long target_nsec, bool fail)
+static DECLARE_WORK(sync_work, sync_hw_clock);
+static struct hrtimer sync_hrtimer;
+#define SYNC_PERIOD_NS (11UL * 60 * NSEC_PER_SEC)
 
+static enum hrtimer_restart sync_timer_callback(struct hrtimer *timer)
 {
-	struct timespec64 next;
-
-	ktime_get_real_ts64(&next);
-	if (!fail)
-		next.tv_sec = 659;
-	else {
-		/*
-		 * Try again as soon as possible. Delaying long periods
-		 * decreases the accuracy of the work queue timer. Due to this
-		 * the algorithm is very likely to require a short-sleep retry
-		 * after the above long sleep to synchronize ts_nsec.
-		 */
-		next.tv_sec = 0;
-	}
-
-	/* Compute the needed delay that will get to tv_nsec == target_nsec */
-	next.tv_nsec = target_nsec - next.tv_nsec;
-	if (next.tv_nsec <= 0)
-		next.tv_nsec += NSEC_PER_SEC;
-	if (next.tv_nsec >= NSEC_PER_SEC) {
-		next.tv_sec++;
-		next.tv_nsec -= NSEC_PER_SEC;
-	}
+	queue_work(system_power_efficient_wq, &sync_work);
 
-	queue_delayed_work(system_power_efficient_wq, &sync_work,
-			   timespec64_to_jiffies(&next));
+	return HRTIMER_NORESTART;
 }
 
-static void sync_rtc_clock(void)
+static void sched_sync_hw_clock(unsigned long offset_nsec, bool retry)
 {
-	unsigned long target_nsec;
-	struct timespec64 adjust, now;
-	int rc;
+	ktime_t exp = ktime_set(ktime_get_real_seconds(), 0);
 
-	if (!IS_ENABLED(CONFIG_RTC_SYSTOHC))
-		return;
+	if (retry)
+		exp = ktime_add_ns(exp, 2 * NSEC_PER_SEC - offset_nsec);
+	else
+		exp = ktime_add_ns(exp, SYNC_PERIOD_NS - offset_nsec);
 
-	ktime_get_real_ts64(&now);
+	hrtimer_start(&sync_hrtimer, exp, HRTIMER_MODE_ABS);
+}
 
-	adjust = now;
-	if (persistent_clock_is_local)
-		adjust.tv_sec -= (sys_tz.tz_minuteswest * 60);
+/*
+ * Check whether @now is correct versus the required time to update the RTC
+ * and calculate the value which needs to be written to the RTC so that the
+ * next seconds increment of the RTC after the write is aligned with the next
+ * seconds increment of clock REALTIME.
+ *
+ * tsched     t1 write(t2.tv_sec - 1sec))	t2 RTC increments seconds
+ *
+ * t2.tv_nsec == 0
+ * tsched = t2 - set_offset_nsec
+ * newval = t2 - NSEC_PER_SEC
+ *
+ * ==> neval = tsched + set_offset_nsec - NSEC_PER_SEC
+ *
+ * As the execution of this code is not guaranteed to happen exactly at
+ * tsched this allows it to happen within a fuzzy region:
+ *
+ *	abs(now - tsched) < FUZZ
+ *
+ * If @now is not inside the allowed window the function returns false.
+ */
+static inline bool rtc_tv_nsec_ok(unsigned long set_offset_nsec,
+				  struct timespec64 *to_set,
+				  const struct timespec64 *now)
+{
+	/* Allowed error in tv_nsec, arbitarily set to 5 jiffies in ns. */
+	const unsigned long TIME_SET_NSEC_FUZZ = TICK_NSEC * 5;
+	struct timespec64 delay = {.tv_sec = -1,
+				   .tv_nsec = set_offset_nsec};
 
-	/*
-	 * The current RTC in use will provide the target_nsec it wants to be
-	 * called at, and does rtc_tv_nsec_ok internally.
-	 */
-	rc = rtc_set_ntp_time(adjust, &target_nsec);
-	if (rc == -ENODEV)
-		return;
+	*to_set = timespec64_add(*now, delay);
+
+	if (to_set->tv_nsec < TIME_SET_NSEC_FUZZ) {
+		to_set->tv_nsec = 0;
+		return true;
+	}
 
-	sched_sync_hw_clock(now, target_nsec, rc);
+	if (to_set->tv_nsec > NSEC_PER_SEC - TIME_SET_NSEC_FUZZ) {
+		to_set->tv_sec++;
+		to_set->tv_nsec = 0;
+		return true;
+	}
+	return false;
 }
 
 #ifdef CONFIG_GENERIC_CMOS_UPDATE
@@ -560,48 +569,47 @@ int __weak update_persistent_clock64(struct timespec64 now64)
 {
 	return -ENODEV;
 }
+#else
+static inline int update_persistent_clock64(struct timespec64 now64)
+{
+	return -ENODEV;
+}
 #endif
 
-static bool sync_cmos_clock(void)
+#ifdef CONFIG_RTC_SYSTOHC
+/* Save NTP synchronized time to the RTC */
+static int update_rtc(struct timespec64 *to_set, unsigned long *offset_nsec)
 {
-	static bool no_cmos;
-	struct timespec64 now;
-	struct timespec64 adjust;
-	int rc = -EPROTO;
-	long target_nsec = NSEC_PER_SEC / 2;
+	struct rtc_device *rtc;
+	struct rtc_time tm;
+	int err = -ENODEV;
 
-	if (!IS_ENABLED(CONFIG_GENERIC_CMOS_UPDATE))
-		return false;
+	rtc = rtc_class_open(CONFIG_RTC_SYSTOHC_DEVICE);
+	if (!rtc)
+		return -ENODEV;
 
-	if (no_cmos)
-		return false;
+	if (!rtc->ops || !rtc->ops->set_time)
+		goto out_close;
 
-	/*
-	 * Historically update_persistent_clock64() has followed x86
-	 * semantics, which match the MC146818A/etc RTC. This RTC will store
-	 * 'adjust' and then in .5s it will advance once second.
-	 *
-	 * Architectures are strongly encouraged to use rtclib and not
-	 * implement this legacy API.
-	 */
-	ktime_get_real_ts64(&now);
-	if (rtc_tv_nsec_ok(-1 * target_nsec, &adjust, &now)) {
-		if (persistent_clock_is_local)
-			adjust.tv_sec -= (sys_tz.tz_minuteswest * 60);
-		rc = update_persistent_clock64(adjust);
-		/*
-		 * The machine does not support update_persistent_clock64 even
-		 * though it defines CONFIG_GENERIC_CMOS_UPDATE.
-		 */
-		if (rc == -ENODEV) {
-			no_cmos = true;
-			return false;
-		}
+	/* First call might not have the correct offset */
+	if (*offset_nsec == rtc->set_offset_nsec) {
+		rtc_time64_to_tm(to_set->tv_sec, &tm);
+		err = rtc_set_time(rtc, &tm);
+	} else {
+		/* Store the update offset and let the caller try again */
+		*offset_nsec = rtc->set_offset_nsec;
+		err = -EAGAIN;
 	}
-
-	sched_sync_hw_clock(now, target_nsec, rc);
-	return true;
+out_close:
+	rtc_class_close(rtc);
+	return err;
+}
+#else
+static inline int update_rtc(struct timespec64 *to_set, unsigned long *offset_nsec)
+{
+	return -ENODEV;
 }
+#endif
 
 /*
  * If we have an externally synchronized Linux clock, then update RTC clock
@@ -613,24 +621,64 @@ static bool sync_cmos_clock(void)
  */
 static void sync_hw_clock(struct work_struct *work)
 {
-	if (!ntp_synced())
-		return;
+	/*
+	 * The default synchronization offset is 500ms for the deprecated
+	 * update_persistent_clock64() under the assumption that it uses
+	 * the infamous CMOS clock (MC146818).
+	 */
+	static unsigned long offset_nsec = NSEC_PER_SEC / 2;
+	struct timespec64 now, to_set;
+	int res = -EAGAIN;
 
-	if (sync_cmos_clock())
+	/*
+	 * Don't update if STA_UNSYNC is set and if ntp_notify_cmos_timer()
+	 * managed to schedule the work between the timer firing and the
+	 * work being able to rearm the timer. Wait for the timer to expire.
+	 */
+	if (!ntp_synced() || hrtimer_is_queued(&sync_hrtimer))
 		return;
 
-	sync_rtc_clock();
+	ktime_get_real_ts64(&now);
+	/* If @now is not in the allowed window, try again */
+	if (!rtc_tv_nsec_ok(offset_nsec, &to_set, &now))
+		goto rearm;
+
+	/* Take timezone adjusted RTCs into account */
+	if (persistent_clock_is_local)
+		to_set.tv_sec -= (sys_tz.tz_minuteswest * 60);
+
+	/* Try the legacy RTC first. */
+	res = update_persistent_clock64(to_set);
+	if (res != -ENODEV)
+		goto rearm;
+
+	/* Try the RTC class */
+	res = update_rtc(&to_set, &offset_nsec);
+	if (res == -ENODEV)
+		return;
+rearm:
+	sched_sync_hw_clock(offset_nsec, res != 0);
 }
 
 void ntp_notify_cmos_timer(void)
 {
-	if (!ntp_synced())
-		return;
+	/*
+	 * When the work is currently executed but has not yet the timer
+	 * rearmed this queues the work immediately again. No big issue,
+	 * just a pointless work scheduled.
+	 */
+	if (ntp_synced() && !hrtimer_is_queued(&sync_hrtimer))
+		queue_work(system_power_efficient_wq, &sync_work);
+}
 
-	if (IS_ENABLED(CONFIG_GENERIC_CMOS_UPDATE) ||
-	    IS_ENABLED(CONFIG_RTC_SYSTOHC))
-		queue_delayed_work(system_power_efficient_wq, &sync_work, 0);
+static void __init ntp_init_cmos_sync(void)
+{
+	hrtimer_init(&sync_hrtimer, CLOCK_REALTIME, HRTIMER_MODE_ABS);
+	sync_hrtimer.function = sync_timer_callback;
 }
+#else /* CONFIG_GENERIC_CMOS_UPDATE) || defined(CONFIG_RTC_SYSTOHC) */
+static inline void __init ntp_init_cmos_sync(void) { }
+#endif /* !CONFIG_GENERIC_CMOS_UPDATE) || defined(CONFIG_RTC_SYSTOHC) */
 
 /*
  * Propagate a new txc->status value into the NTP state:
@@ -1044,4 +1092,5 @@ __setup("ntp_tick_adj=", ntp_tick_adj_setup);
 void __init ntp_init(void)
 {
 	ntp_clear();
+	ntp_init_cmos_sync();
 }
diff --git a/kernel/time/ntp_internal.h b/kernel/time/ntp_internal.h
index 908ecaa65fc3..23d1b74c3065 100644
--- a/kernel/time/ntp_internal.h
+++ b/kernel/time/ntp_internal.h
@@ -12,4 +12,11 @@ extern int __do_adjtimex(struct __kernel_timex *txc,
 			 const struct timespec64 *ts,
 			 s32 *time_tai, struct audit_ntp_data *ad);
 extern void __hardpps(const struct timespec64 *phase_ts, const struct timespec64 *raw_ts);
+
+#if defined(CONFIG_GENERIC_CMOS_UPDATE) || defined(CONFIG_RTC_SYSTOHC)
+extern void ntp_notify_cmos_timer(void);
+#else
+static inline void ntp_notify_cmos_timer(void) { }
+#endif
+
 #endif /* _LINUX_NTP_INTERNAL_H */
diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index 36d7464c8962..5a23829372c7 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -331,7 +331,7 @@ static void tick_handle_periodic_broadcast(struct clock_event_device *dev)
 	bc_local = tick_do_periodic_broadcast();
 
 	if (clockevent_state_oneshot(dev)) {
-		ktime_t next = ktime_add(dev->next_event, tick_period);
+		ktime_t next = ktime_add_ns(dev->next_event, TICK_NSEC);
 
 		clockevents_program_event(dev, next, true);
 	}
@@ -877,6 +877,22 @@ static void tick_broadcast_init_next_event(struct cpumask *mask,
 	}
 }
 
+static inline ktime_t tick_get_next_period(void)
+{
+	ktime_t next;
+
+	/*
+	 * Protect against concurrent updates (store /load tearing on
+	 * 32bit). It does not matter if the time is already in the
+	 * past. The broadcast device which is about to be programmed will
+	 * fire in any case.
+	 */
+	raw_spin_lock(&jiffies_lock);
+	next = tick_next_period;
+	raw_spin_unlock(&jiffies_lock);
+	return next;
+}
+
 /**
  * tick_broadcast_setup_oneshot - setup the broadcast device
  */
@@ -905,10 +921,11 @@ static void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
 			   tick_broadcast_oneshot_mask, tmpmask);
 
 		if (was_periodic && !cpumask_empty(tmpmask)) {
+			ktime_t nextevt = tick_get_next_period();
+
 			clockevents_switch_state(bc, CLOCK_EVT_STATE_ONESHOT);
-			tick_broadcast_init_next_event(tmpmask,
-						       tick_next_period);
-			tick_broadcast_set_event(bc, cpu, tick_next_period);
+			tick_broadcast_init_next_event(tmpmask, nextevt);
+			tick_broadcast_set_event(bc, cpu, nextevt);
 		} else
 			bc->next_event = KTIME_MAX;
 	} else {
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 6c9c342dd0e5..a03764df5366 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -27,10 +27,11 @@
  */
 DEFINE_PER_CPU(struct tick_device, tick_cpu_device);
 /*
- * Tick next event: keeps track of the tick time
+ * Tick next event: keeps track of the tick time. It's updated by the
+ * CPU which handles the tick and protected by jiffies_lock. There is
+ * no requirement to write hold the jiffies seqcount for it.
  */
 ktime_t tick_next_period;
-ktime_t tick_period;
 
 /*
  * tick_do_timer_cpu is a timer core internal variable which holds the CPU NR
@@ -88,7 +89,7 @@ static void tick_periodic(int cpu)
 		write_seqcount_begin(&jiffies_seq);
 
 		/* Keep track of the next tick event */
-		tick_next_period = ktime_add(tick_next_period, tick_period);
+		tick_next_period = ktime_add_ns(tick_next_period, TICK_NSEC);
 
 		do_timer(1);
 		write_seqcount_end(&jiffies_seq);
@@ -127,7 +128,7 @@ void tick_handle_periodic(struct clock_event_device *dev)
 		 * Setup the next period for devices, which do not have
 		 * periodic mode:
 		 */
-		next = ktime_add(next, tick_period);
+		next = ktime_add_ns(next, TICK_NSEC);
 
 		if (!clockevents_program_event(dev, next, false))
 			return;
@@ -173,7 +174,7 @@ void tick_setup_periodic(struct clock_event_device *dev, int broadcast)
 		for (;;) {
 			if (!clockevents_program_event(dev, next, false))
 				return;
-			next = ktime_add(next, tick_period);
+			next = ktime_add_ns(next, TICK_NSEC);
 		}
 	}
 }
@@ -220,7 +221,6 @@ static void tick_setup_device(struct tick_device *td,
 			tick_do_timer_cpu = cpu;
 
 			tick_next_period = ktime_get();
-			tick_period = NSEC_PER_SEC / HZ;
 #ifdef CONFIG_NO_HZ_FULL
 			/*
 			 * The boot CPU may be nohz_full, in which case set
diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index 7b2496136729..7a981c9e87a4 100644
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -15,7 +15,6 @@
 
 DECLARE_PER_CPU(struct tick_device, tick_cpu_device);
 extern ktime_t tick_next_period;
-extern ktime_t tick_period;
 extern int tick_do_timer_cpu __read_mostly;
 
 extern void tick_setup_periodic(struct clock_event_device *dev, int broadcast);
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 81632cd5e3b7..a9e68936822d 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -20,6 +20,7 @@
 #include <linux/sched/clock.h>
 #include <linux/sched/stat.h>
 #include <linux/sched/nohz.h>
+#include <linux/sched/loadavg.h>
 #include <linux/module.h>
 #include <linux/irq_work.h>
 #include <linux/posix-timers.h>
@@ -44,7 +45,9 @@ struct tick_sched *tick_get_tick_sched(int cpu)
 
 #if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)
 /*
- * The time, when the last jiffy update happened. Protected by jiffies_lock.
+ * The time, when the last jiffy update happened. Write access must hold
+ * jiffies_lock and jiffies_seq. tick_nohz_next_event() needs to get a
+ * consistent view of jiffies and last_jiffies_update.
  */
 static ktime_t last_jiffies_update;
 
@@ -53,50 +56,97 @@ static ktime_t last_jiffies_update;
  */
 static void tick_do_update_jiffies64(ktime_t now)
 {
-	unsigned long ticks = 0;
-	ktime_t delta;
+	unsigned long ticks = 1;
+	ktime_t delta, nextp;
 
 	/*
-	 * Do a quick check without holding jiffies_lock:
-	 * The READ_ONCE() pairs with two updates done later in this function.
+	 * 64bit can do a quick check without holding jiffies lock and
+	 * without looking at the sequence count. The smp_load_acquire()
+	 * pairs with the update done later in this function.
+	 *
+	 * 32bit cannot do that because the store of tick_next_period
+	 * consists of two 32bit stores and the first store could move it
+	 * to a random point in the future.
 	 */
-	delta = ktime_sub(now, READ_ONCE(last_jiffies_update));
-	if (delta < tick_period)
-		return;
+	if (IS_ENABLED(CONFIG_64BIT)) {
+		if (ktime_before(now, smp_load_acquire(&tick_next_period)))
+			return;
+	} else {
+		unsigned int seq;
 
-	/* Reevaluate with jiffies_lock held */
+		/*
+		 * Avoid contention on jiffies_lock and protect the quick
+		 * check with the sequence count.
+		 */
+		do {
+			seq = read_seqcount_begin(&jiffies_seq);
+			nextp = tick_next_period;
+		} while (read_seqcount_retry(&jiffies_seq, seq));
+
+		if (ktime_before(now, nextp))
+			return;
+	}
+
+	/* Quick check failed, i.e. update is required. */
 	raw_spin_lock(&jiffies_lock);
+	/*
+	 * Reevaluate with the lock held. Another CPU might have done the
+	 * update already.
+	 */
+	if (ktime_before(now, tick_next_period)) {
+		raw_spin_unlock(&jiffies_lock);
+		return;
+	}
+
 	write_seqcount_begin(&jiffies_seq);
 
-	delta = ktime_sub(now, last_jiffies_update);
-	if (delta >= tick_period) {
+	delta = ktime_sub(now, tick_next_period);
+	if (unlikely(delta >= TICK_NSEC)) {
+		/* Slow path for long idle sleep times */
+		s64 incr = TICK_NSEC;
 
-		delta = ktime_sub(delta, tick_period);
-		/* Pairs with the lockless read in this function. */
-		WRITE_ONCE(last_jiffies_update,
-			   ktime_add(last_jiffies_update, tick_period));
+		ticks += ktime_divns(delta, incr);
 
-		/* Slow path for long timeouts */
-		if (unlikely(delta >= tick_period)) {
-			s64 incr = ktime_to_ns(tick_period);
+		last_jiffies_update = ktime_add_ns(last_jiffies_update,
+						   incr * ticks);
+	} else {
+		last_jiffies_update = ktime_add_ns(last_jiffies_update,
+						   TICK_NSEC);
+	}
 
-			ticks = ktime_divns(delta, incr);
+	/* Advance jiffies to complete the jiffies_seq protected job */
+	jiffies_64 += ticks;
 
-			/* Pairs with the lockless read in this function. */
-			WRITE_ONCE(last_jiffies_update,
-				   ktime_add_ns(last_jiffies_update,
-						incr * ticks));
-		}
-		do_timer(++ticks);
+	/*
+	 * Keep the tick_next_period variable up to date.
+	 */
+	nextp = ktime_add_ns(last_jiffies_update, TICK_NSEC);
 
-		/* Keep the tick_next_period variable up to date */
-		tick_next_period = ktime_add(last_jiffies_update, tick_period);
+	if (IS_ENABLED(CONFIG_64BIT)) {
+		/*
+		 * Pairs with smp_load_acquire() in the lockless quick
+		 * check above and ensures that the update to jiffies_64 is
+		 * not reordered vs. the store to tick_next_period, neither
+		 * by the compiler nor by the CPU.
+		 */
+		smp_store_release(&tick_next_period, nextp);
 	} else {
-		write_seqcount_end(&jiffies_seq);
-		raw_spin_unlock(&jiffies_lock);
-		return;
+		/*
+		 * A plain store is good enough on 32bit as the quick check
+		 * above is protected by the sequence count.
+		 */
+		tick_next_period = nextp;
 	}
+
+	/*
+	 * Release the sequence count. calc_global_load() below is not
+	 * protected by it, but jiffies_lock needs to be held to prevent
+	 * concurrent invocations.
+	 */
 	write_seqcount_end(&jiffies_seq);
+
+	calc_global_load();
+
 	raw_spin_unlock(&jiffies_lock);
 	update_wall_time();
 }
@@ -661,7 +711,7 @@ static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
 	hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
 
 	/* Forward the time to expire in the future */
-	hrtimer_forward(&ts->sched_timer, now, tick_period);
+	hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
 
 	if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
 		hrtimer_start_expires(&ts->sched_timer,
@@ -1230,7 +1280,7 @@ static void tick_nohz_handler(struct clock_event_device *dev)
 	if (unlikely(ts->tick_stopped))
 		return;
 
-	hrtimer_forward(&ts->sched_timer, now, tick_period);
+	hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
 	tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
 }
 
@@ -1267,7 +1317,7 @@ static void tick_nohz_switch_to_nohz(void)
 	next = tick_init_jiffy_update();
 
 	hrtimer_set_expires(&ts->sched_timer, next);
-	hrtimer_forward_now(&ts->sched_timer, tick_period);
+	hrtimer_forward_now(&ts->sched_timer, TICK_NSEC);
 	tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
 	tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
 }
@@ -1333,7 +1383,7 @@ static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
 	if (unlikely(ts->tick_stopped))
 		return HRTIMER_NORESTART;
 
-	hrtimer_forward(timer, now, tick_period);
+	hrtimer_forward(timer, now, TICK_NSEC);
 
 	return HRTIMER_RESTART;
 }
@@ -1367,13 +1417,13 @@ void tick_setup_sched_timer(void)
 
 	/* Offset the tick to avert jiffies_lock contention. */
 	if (sched_skew_tick) {
-		u64 offset = ktime_to_ns(tick_period) >> 1;
+		u64 offset = TICK_NSEC >> 1;
 		do_div(offset, num_possible_cpus());
 		offset *= smp_processor_id();
 		hrtimer_add_expires_ns(&ts->sched_timer, offset);
 	}
 
-	hrtimer_forward(&ts->sched_timer, now, tick_period);
+	hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
 	hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED_HARD);
 	tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
 }
diff --git a/kernel/time/timeconv.c b/kernel/time/timeconv.c
index 589e0a552129..62e3b46717a6 100644
--- a/kernel/time/timeconv.c
+++ b/kernel/time/timeconv.c
@@ -70,10 +70,10 @@ static const unsigned short __mon_yday[2][13] = {
 /**
  * time64_to_tm - converts the calendar time to local broken-down time
  *
- * @totalsecs	the number of seconds elapsed since 00:00:00 on January 1, 1970,
+ * @totalsecs:	the number of seconds elapsed since 00:00:00 on January 1, 1970,
  *		Coordinated Universal Time (UTC).
- * @offset	offset seconds adding to totalsecs.
- * @result	pointer to struct tm variable to receive broken-down time
+ * @offset:	offset seconds adding to totalsecs.
+ * @result:	pointer to struct tm variable to receive broken-down time
  */
 void time64_to_tm(time64_t totalsecs, int offset, struct tm *result)
 {
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 6858a31364b6..74503c0151e5 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -407,6 +407,7 @@ static inline u64 timekeeping_cycles_to_ns(const struct tk_read_base *tkr, u64 c
 /**
  * update_fast_timekeeper - Update the fast and NMI safe monotonic timekeeper.
  * @tkr: Timekeeping readout base from which we take the update
+ * @tkf: Pointer to NMI safe timekeeper
  *
  * We want to use this from any context including NMI and tracing /
  * instrumenting the timekeeping code itself.
@@ -436,6 +437,27 @@ static void update_fast_timekeeper(const struct tk_read_base *tkr,
 	memcpy(base + 1, base, sizeof(*base));
 }
 
+static __always_inline u64 __ktime_get_fast_ns(struct tk_fast *tkf)
+{
+	struct tk_read_base *tkr;
+	unsigned int seq;
+	u64 now;
+
+	do {
+		seq = raw_read_seqcount_latch(&tkf->seq);
+		tkr = tkf->base + (seq & 0x01);
+		now = ktime_to_ns(tkr->base);
+
+		now += timekeeping_delta_to_ns(tkr,
+				clocksource_delta(
+					tk_clock_read(tkr),
+					tkr->cycle_last,
+					tkr->mask));
+	} while (read_seqcount_latch_retry(&tkf->seq, seq));
+
+	return now;
+}
+
 /**
  * ktime_get_mono_fast_ns - Fast NMI safe access to clock monotonic
  *
@@ -462,39 +484,24 @@ static void update_fast_timekeeper(const struct tk_read_base *tkr,
  *
  * So reader 6 will observe time going backwards versus reader 5.
  *
- * While other CPUs are likely to be able observe that, the only way
+ * While other CPUs are likely to be able to observe that, the only way
  * for a CPU local observation is when an NMI hits in the middle of
  * the update. Timestamps taken from that NMI context might be ahead
  * of the following timestamps. Callers need to be aware of that and
  * deal with it.
  */
-static __always_inline u64 __ktime_get_fast_ns(struct tk_fast *tkf)
-{
-	struct tk_read_base *tkr;
-	unsigned int seq;
-	u64 now;
-
-	do {
-		seq = raw_read_seqcount_latch(&tkf->seq);
-		tkr = tkf->base + (seq & 0x01);
-		now = ktime_to_ns(tkr->base);
-
-		now += timekeeping_delta_to_ns(tkr,
-				clocksource_delta(
-					tk_clock_read(tkr),
-					tkr->cycle_last,
-					tkr->mask));
-	} while (read_seqcount_latch_retry(&tkf->seq, seq));
-
-	return now;
-}
-
 u64 ktime_get_mono_fast_ns(void)
 {
 	return __ktime_get_fast_ns(&tk_fast_mono);
 }
 EXPORT_SYMBOL_GPL(ktime_get_mono_fast_ns);
 
+/**
+ * ktime_get_raw_fast_ns - Fast NMI safe access to clock monotonic raw
+ *
+ * Contrary to ktime_get_mono_fast_ns() this is always correct because the
+ * conversion factor is not affected by NTP/PTP correction.
+ */
 u64 ktime_get_raw_fast_ns(void)
 {
 	return __ktime_get_fast_ns(&tk_fast_raw);
@@ -521,6 +528,9 @@ EXPORT_SYMBOL_GPL(ktime_get_raw_fast_ns);
  * (2) On 32-bit systems, the 64-bit boot offset (tk->offs_boot) may be
  * partially updated.  Since the tk->offs_boot update is a rare event, this
  * should be a rare occurrence which postprocessing should be able to handle.
+ *
+ * The caveats vs. timestamp ordering as documented for ktime_get_fast_ns()
+ * apply as well.
  */
 u64 notrace ktime_get_boot_fast_ns(void)
 {
@@ -530,9 +540,6 @@ u64 notrace ktime_get_boot_fast_ns(void)
 }
 EXPORT_SYMBOL_GPL(ktime_get_boot_fast_ns);
 
-/*
- * See comment for __ktime_get_fast_ns() vs. timestamp ordering
- */
 static __always_inline u64 __ktime_get_real_fast(struct tk_fast *tkf, u64 *mono)
 {
 	struct tk_read_base *tkr;
@@ -557,6 +564,8 @@ static __always_inline u64 __ktime_get_real_fast(struct tk_fast *tkf, u64 *mono)
 
 /**
  * ktime_get_real_fast_ns: - NMI safe and fast access to clock realtime.
+ *
+ * See ktime_get_fast_ns() for documentation of the time stamp ordering.
  */
 u64 ktime_get_real_fast_ns(void)
 {
@@ -654,6 +663,7 @@ static void update_pvclock_gtod(struct timekeeper *tk, bool was_set)
 
 /**
  * pvclock_gtod_register_notifier - register a pvclock timedata update listener
+ * @nb: Pointer to the notifier block to register
  */
 int pvclock_gtod_register_notifier(struct notifier_block *nb)
 {
@@ -673,6 +683,7 @@ EXPORT_SYMBOL_GPL(pvclock_gtod_register_notifier);
 /**
  * pvclock_gtod_unregister_notifier - unregister a pvclock
  * timedata update listener
+ * @nb: Pointer to the notifier block to unregister
  */
 int pvclock_gtod_unregister_notifier(struct notifier_block *nb)
 {
@@ -763,6 +774,7 @@ static void timekeeping_update(struct timekeeper *tk, unsigned int action)
 
 /**
  * timekeeping_forward_now - update clock to the current time
+ * @tk:		Pointer to the timekeeper to update
  *
  * Forward the current clock to update its state since the last call to
  * update_wall_time(). This is useful before significant clock changes,
@@ -1339,7 +1351,7 @@ EXPORT_SYMBOL(do_settimeofday64);
 
 /**
  * timekeeping_inject_offset - Adds or subtracts from the current time.
- * @tv:		pointer to the timespec variable containing the offset
+ * @ts:		Pointer to the timespec variable containing the offset
  *
  * Adds or subtracts an offset value from the current time.
  */
@@ -1415,9 +1427,8 @@ void timekeeping_warp_clock(void)
 	}
 }
 
-/**
+/*
  * __timekeeping_set_tai_offset - Sets the TAI offset from UTC and monotonic
- *
  */
 static void __timekeeping_set_tai_offset(struct timekeeper *tk, s32 tai_offset)
 {
@@ -1425,7 +1436,7 @@ static void __timekeeping_set_tai_offset(struct timekeeper *tk, s32 tai_offset)
 	tk->offs_tai = ktime_add(tk->offs_real, ktime_set(tai_offset, 0));
 }
 
-/**
+/*
  * change_clocksource - Swaps clocksources if a new one is available
  *
  * Accumulates current time interval and initializes new clocksource
@@ -1548,6 +1559,7 @@ u64 timekeeping_max_deferment(void)
 
 /**
  * read_persistent_clock64 -  Return time from the persistent clock.
+ * @ts: Pointer to the storage for the readout value
  *
  * Weak dummy function for arches that do not yet support it.
  * Reads the time from the battery backed persistent clock.
@@ -1566,8 +1578,9 @@ void __weak read_persistent_clock64(struct timespec64 *ts)
  *                                        from the boot.
  *
  * Weak dummy function for arches that do not yet support it.
- * wall_time	- current time as returned by persistent clock
- * boot_offset	- offset that is defined as wall_time - boot_time
+ * @wall_time:	- current time as returned by persistent clock
+ * @boot_offset: - offset that is defined as wall_time - boot_time
+ *
  * The default function calculates offset based on the current value of
  * local_clock(). This way architectures that support sched_clock() but don't
  * support dedicated boot time clock will provide the best estimate of the
@@ -1652,7 +1665,8 @@ static struct timespec64 timekeeping_suspend_time;
 
 /**
  * __timekeeping_inject_sleeptime - Internal function to add sleep interval
- * @delta: pointer to a timespec delta value
+ * @tk:		Pointer to the timekeeper to be updated
+ * @delta:	Pointer to the delta value in timespec64 format
  *
  * Takes a timespec offset measuring a suspend interval and properly
  * adds the sleep offset to the timekeeping variables.
@@ -2023,13 +2037,12 @@ static void timekeeping_adjust(struct timekeeper *tk, s64 offset)
 	}
 }
 
-/**
+/*
  * accumulate_nsecs_to_secs - Accumulates nsecs into secs
  *
  * Helper function that accumulates the nsecs greater than a second
  * from the xtime_nsec field to the xtime_secs field.
  * It also calls into the NTP code to handle leapsecond processing.
- *
  */
 static inline unsigned int accumulate_nsecs_to_secs(struct timekeeper *tk)
 {
@@ -2071,7 +2084,7 @@ static inline unsigned int accumulate_nsecs_to_secs(struct timekeeper *tk)
 	return clock_set;
 }
 
-/**
+/*
  * logarithmic_accumulation - shifted accumulation of cycles
  *
  * This functions accumulates a shifted interval of cycles into
@@ -2314,7 +2327,7 @@ ktime_t ktime_get_update_offsets_now(unsigned int *cwsseq, ktime_t *offs_real,
 	return base;
 }
 
-/**
+/*
  * timekeeping_validate_timex - Ensures the timex is ok for use in do_adjtimex
  */
 static int timekeeping_validate_timex(const struct __kernel_timex *txc)
diff --git a/kernel/time/timekeeping.h b/kernel/time/timekeeping.h
index 099737f6f10c..6c2cbd9ef999 100644
--- a/kernel/time/timekeeping.h
+++ b/kernel/time/timekeeping.h
@@ -26,7 +26,7 @@ extern void do_timer(unsigned long ticks);
 extern void update_wall_time(void);
 
 extern raw_spinlock_t jiffies_lock;
-extern seqcount_t jiffies_seq;
+extern seqcount_raw_spinlock_t jiffies_seq;
 
 #define CS_NAME_LEN	32