timers and timekeeping updates:

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.
 
     - The changes related to the NTP/RTC consolidation work.
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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
  ...

kernel/time/timer.c

@@ -1283,7 +1283,7 @@ static void del_timer_wait_running(struct timer_list *timer)
 	u32 tf;
 
 	tf = READ_ONCE(timer->flags);
-	if (!(tf & TIMER_MIGRATING)) {
+	if (!(tf & (TIMER_MIGRATING | TIMER_IRQSAFE))) {
 		struct timer_base *base = get_timer_base(tf);
 
 		/*
@@ -1367,6 +1367,13 @@ int del_timer_sync(struct timer_list *timer)
 	 */
 	WARN_ON(in_irq() && !(timer->flags & TIMER_IRQSAFE));
 
+	/*
+	 * Must be able to sleep on PREEMPT_RT because of the slowpath in
+	 * del_timer_wait_running().
+	 */
+	if (IS_ENABLED(CONFIG_PREEMPT_RT) && !(timer->flags & TIMER_IRQSAFE))
+		lockdep_assert_preemption_enabled();
+
 	do {
 		ret = try_to_del_timer_sync(timer);
 
@@ -1693,29 +1700,6 @@ void timer_clear_idle(void)
 }
 #endif
 
-/*
- * Called from the timer interrupt handler to charge one tick to the current
- * process.  user_tick is 1 if the tick is user time, 0 for system.
- */
-void update_process_times(int user_tick)
-{
-	struct task_struct *p = current;
-
-	PRANDOM_ADD_NOISE(jiffies, user_tick, p, 0);
-
-	/* Note: this timer irq context must be accounted for as well. */
-	account_process_tick(p, user_tick);
-	run_local_timers();
-	rcu_sched_clock_irq(user_tick);
-#ifdef CONFIG_IRQ_WORK
-	if (in_irq())
-		irq_work_tick();
-#endif
-	scheduler_tick();
-	if (IS_ENABLED(CONFIG_POSIX_TIMERS))
-		run_posix_cpu_timers();
-}
-
 /**
  * __run_timers - run all expired timers (if any) on this CPU.
  * @base: the timer vector to be processed.
@@ -1765,7 +1749,7 @@ static __latent_entropy void run_timer_softirq(struct softirq_action *h)
 /*
  * Called by the local, per-CPU timer interrupt on SMP.
  */
-void run_local_timers(void)
+static void run_local_timers(void)
 {
 	struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
 
@@ -1782,6 +1766,29 @@ void run_local_timers(void)
 	raise_softirq(TIMER_SOFTIRQ);
 }
 
+/*
+ * Called from the timer interrupt handler to charge one tick to the current
+ * process.  user_tick is 1 if the tick is user time, 0 for system.
+ */
+void update_process_times(int user_tick)
+{
+	struct task_struct *p = current;
+
+	PRANDOM_ADD_NOISE(jiffies, user_tick, p, 0);
+
+	/* Note: this timer irq context must be accounted for as well. */
+	account_process_tick(p, user_tick);
+	run_local_timers();
+	rcu_sched_clock_irq(user_tick);
+#ifdef CONFIG_IRQ_WORK
+	if (in_irq())
+		irq_work_tick();
+#endif
+	scheduler_tick();
+	if (IS_ENABLED(CONFIG_POSIX_TIMERS))
+		run_posix_cpu_timers();
+}
+
 /*
  * Since schedule_timeout()'s timer is defined on the stack, it must store
  * the target task on the stack as well.