From 68c147023af2485ad55e27ce69ebe33d126941b8 Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Wed, 28 Jan 2015 14:10:02 +0100
Subject: [PATCH] Revert "timers: do not raise softirq unconditionally"
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.0/patches-4.0.8-rt6.tar.xz

The patch I revert here triggers the HRtimer switch from hardirq instead
of from softirq. As a result we get a periodic interrupt before the
switch is complete (that is a hrtimer has been programmed) and so the
tick still programms periodic mode. Since the timer has been shutdown,
dev->next_event is set to max and the next increment makes it negative.
And now we wait…

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/hrtimer.h |    3 ++-
 kernel/time/hrtimer.c   |   31 ++++++++++++++++++++++++-------
 kernel/time/timer.c     |   46 ++--------------------------------------------
 3 files changed, 28 insertions(+), 52 deletions(-)

--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -457,8 +457,9 @@ extern int schedule_hrtimeout_range_cloc
 		unsigned long delta, const enum hrtimer_mode mode, int clock);
 extern int schedule_hrtimeout(ktime_t *expires, const enum hrtimer_mode mode);
 
-/* Called from the periodic timer tick */
+/* Soft interrupt function to run the hrtimer queues: */
 extern void hrtimer_run_queues(void);
+extern void hrtimer_run_pending(void);
 
 /* Bootup initialization: */
 extern void __init hrtimers_init(void);
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1654,6 +1654,30 @@ static void run_hrtimer_softirq(struct s
 }
 
 /*
+ * Called from timer softirq every jiffy, expire hrtimers:
+ *
+ * For HRT its the fall back code to run the softirq in the timer
+ * softirq context in case the hrtimer initialization failed or has
+ * not been done yet.
+ */
+void hrtimer_run_pending(void)
+{
+	if (hrtimer_hres_active())
+		return;
+
+	/*
+	 * This _is_ ugly: We have to check in the softirq context,
+	 * whether we can switch to highres and / or nohz mode. The
+	 * clocksource switch happens in the timer interrupt with
+	 * xtime_lock held. Notification from there only sets the
+	 * check bit in the tick_oneshot code, otherwise we might
+	 * deadlock vs. xtime_lock.
+	 */
+	if (tick_check_oneshot_change(!hrtimer_is_hres_enabled()))
+		hrtimer_switch_to_hres();
+}
+
+/*
  * Called from hardirq context every jiffy
  */
 void hrtimer_run_queues(void)
@@ -1666,13 +1690,6 @@ void hrtimer_run_queues(void)
 	if (hrtimer_hres_active())
 		return;
 
-	/*
-	 * Check whether we can switch to highres mode.
-	 */
-	if (tick_check_oneshot_change(!hrtimer_is_hres_enabled())
-	    && hrtimer_switch_to_hres())
-		return;
-
 	for (index = 0; index < HRTIMER_MAX_CLOCK_BASES; index++) {
 		base = &cpu_base->clock_base[index];
 		if (!timerqueue_getnext(&base->active))
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1463,6 +1463,8 @@ static void run_timer_softirq(struct sof
 {
 	struct tvec_base *base = __this_cpu_read(tvec_bases);
 
+	hrtimer_run_pending();
+
 	if (time_after_eq(jiffies, base->timer_jiffies))
 		__run_timers(base);
 }
@@ -1472,52 +1474,8 @@ static void run_timer_softirq(struct sof
  */
 void run_local_timers(void)
 {
-	struct tvec_base *base = __this_cpu_read(tvec_bases);
-
 	hrtimer_run_queues();
-	/*
-	 * We can access this lockless as we are in the timer
-	 * interrupt. If there are no timers queued, nothing to do in
-	 * the timer softirq.
-	 */
-#ifdef CONFIG_PREEMPT_RT_FULL
-
-#ifndef CONFIG_SMP
-	/*
-	 * The spin_do_trylock() later may fail as the lock may be hold before
-	 * the interrupt arrived. The spin-lock debugging code will raise a
-	 * warning if the try_lock fails on UP. Since this is only an
-	 * optimization for the FULL_NO_HZ case (not to run the timer softirq on
-	 * an nohz_full CPU) we don't really care and shedule the softirq.
-	 */
 	raise_softirq(TIMER_SOFTIRQ);
-	return;
-#endif
-
-	/* On RT, irq work runs from softirq */
-	if (irq_work_needs_cpu()) {
-		raise_softirq(TIMER_SOFTIRQ);
-		return;
-	}
-
-	if (!spin_do_trylock(&base->lock)) {
-		raise_softirq(TIMER_SOFTIRQ);
-		return;
-	}
-#endif
-
-	if (!base->active_timers)
-		goto out;
-
-	/* Check whether the next pending timer has expired */
-	if (time_before_eq(base->next_timer, jiffies))
-		raise_softirq(TIMER_SOFTIRQ);
-out:
-#ifdef CONFIG_PREEMPT_RT_FULL
-	rt_spin_unlock_after_trylock_in_irq(&base->lock);
-#endif
-	/* The ; ensures that gcc won't complain in the !RT case */
-	;
 }
 
 #ifdef __ARCH_WANT_SYS_ALARM