From 23e575debfd9e3e0c64b8d348226e43fcfe6564e Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 3 Jul 2009 08:44:31 -0500
Subject: [PATCH] hrtimer: fixup hrtimer callback changes for preempt-rt

commit 305d0a1ab668ee560de7fe5eed0b62cf419a50f9 in tip.

In preempt-rt we can not call the callbacks which take sleeping locks
from the timer interrupt context.

Bring back the softirq split for now, until we fixed the signal
delivery problem for real.

[PG: restore cb_entry field; it is gone in 33+]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 67945c3..1cc4577 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -107,6 +107,8 @@ struct hrtimer {
 	enum hrtimer_restart		(*function)(struct hrtimer *);
 	struct hrtimer_clock_base	*base;
 	unsigned long			state;
+	struct list_head		cb_entry;
+	int				irqsafe;
 #ifdef CONFIG_TIMER_STATS
 	int				start_pid;
 	void				*start_site;
@@ -142,6 +144,7 @@ struct hrtimer_clock_base {
 	struct hrtimer_cpu_base	*cpu_base;
 	clockid_t		index;
 	struct rb_root		active;
+	struct list_head	expired;
 	struct rb_node		*first;
 	ktime_t			resolution;
 	ktime_t			(*get_time)(void);
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 93b2df2..f22611d 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -563,15 +563,24 @@ static int hrtimer_reprogram(struct hrtimer *timer,
 
 	WARN_ON_ONCE(hrtimer_get_expires_tv64(timer) < 0);
 
+#ifndef CONFIG_PREEMPT_RT
 	/*
 	 * When the callback is running, we do not reprogram the clock event
 	 * device. The timer callback is either running on a different CPU or
 	 * the callback is executed in the hrtimer_interrupt context. The
-	 * reprogramming is handled either by the softirq, which called the
-	 * callback or at the end of the hrtimer_interrupt.
+	 * reprogramming is handled at the end of the hrtimer_interrupt.
 	 */
 	if (hrtimer_callback_running(timer))
 		return 0;
+#else
+	/*
+	 * preempt-rt changes the rules here as long as we have not
+	 * solved the callback problem. For softirq based timers we
+	 * need to allow reprogramming.
+	 */
+	if (hrtimer_callback_running(timer) && timer->irqsafe)
+		return 0;
+#endif
 
 	/*
 	 * CLOCK_REALTIME timer might be requested with an absolute
@@ -679,6 +688,8 @@ static inline void hrtimer_init_timer_hres(struct hrtimer *timer)
 {
 }
 
+static void __run_hrtimer(struct hrtimer *timer, ktime_t *now);
+static int hrtimer_rt_defer(struct hrtimer *timer);
 
 /*
  * When High resolution timers are active, try to reprogram. Note, that in case
@@ -691,6 +702,19 @@ static inline int hrtimer_enqueue_reprogram(struct hrtimer *timer,
 					    int wakeup)
 {
 	if (base->cpu_base->hres_active && hrtimer_reprogram(timer, base)) {
+#ifdef CONFIG_PREEMPT_RT
+		/*
+		 * Move softirq based timers away from the rbtree in
+		 * case it expired already. Otherwise we would have a
+		 * stale base->first entry until the softirq runs.
+		 */
+		if (!hrtimer_rt_defer(timer)) {
+			ktime_t now = ktime_get();
+
+			__run_hrtimer(timer, &now);
+			return 1;
+		}
+#endif
 		if (wakeup) {
 			raw_spin_unlock(&base->cpu_base->lock);
 			raise_softirq_irqoff(HRTIMER_SOFTIRQ);
@@ -934,6 +958,11 @@ static void __remove_hrtimer(struct hrtimer *timer,
 	if (!(timer->state & HRTIMER_STATE_ENQUEUED))
 		goto out;
 
+	if (unlikely(!list_empty(&timer->cb_entry))) {
+		list_del_init(&timer->cb_entry);
+		goto out;
+	}
+
 	/*
 	 * Remove the timer from the rbtree and replace the first
 	 * entry pointer if necessary.
@@ -1189,6 +1218,7 @@ static void __hrtimer_init(struct hrtimer *timer, clockid_t clock_id,
 		clock_id = CLOCK_MONOTONIC;
 
 	timer->base = &cpu_base->clock_base[clock_id];
+	INIT_LIST_HEAD(&timer->cb_entry);
 	hrtimer_init_timer_hres(timer);
 
 #ifdef CONFIG_TIMER_STATS
@@ -1268,6 +1298,77 @@ static void __run_hrtimer(struct hrtimer *timer, ktime_t *now)
 	timer->state &= ~HRTIMER_STATE_CALLBACK;
 }
 
+#ifdef CONFIG_PREEMPT_RT
+
+/*
+ * The changes in mainline which removed the callback modes from
+ * hrtimer are not yet working with -rt. The non wakeup_process()
+ * based callbacks which involve sleeping locks need to be treated
+ * seperately.
+ */
+static void hrtimer_rt_run_pending(void)
+{
+	enum hrtimer_restart (*fn)(struct hrtimer *);
+	struct hrtimer_cpu_base *cpu_base;
+	struct hrtimer_clock_base *base;
+	struct hrtimer *timer;
+	int index, restart;
+
+	local_irq_disable();
+	cpu_base = &per_cpu(hrtimer_bases, smp_processor_id());
+
+	raw_spin_lock(&cpu_base->lock);
+
+	for (index = 0; index < HRTIMER_MAX_CLOCK_BASES; index++) {
+		base = &cpu_base->clock_base[index];
+
+		while (!list_empty(&base->expired)) {
+			timer = list_first_entry(&base->expired,
+						 struct hrtimer, cb_entry);
+
+			/*
+			 * Same as the above __run_hrtimer function
+			 * just we run with interrupts enabled.
+			 */
+			debug_hrtimer_deactivate(timer);
+			__remove_hrtimer(timer, base, HRTIMER_STATE_CALLBACK, 0);
+			timer_stats_account_hrtimer(timer);
+			fn = timer->function;
+
+			raw_spin_unlock_irq(&cpu_base->lock);
+			restart = fn(timer);
+			raw_spin_lock_irq(&cpu_base->lock);
+
+			if (restart != HRTIMER_NORESTART) {
+				BUG_ON(timer->state != HRTIMER_STATE_CALLBACK);
+				enqueue_hrtimer(timer, base);
+			}
+			timer->state &= ~HRTIMER_STATE_CALLBACK;
+		}
+	}
+
+	raw_spin_unlock_irq(&cpu_base->lock);
+
+	wake_up_timer_waiters(cpu_base);
+}
+
+static int hrtimer_rt_defer(struct hrtimer *timer)
+{
+	if (timer->irqsafe)
+		return 0;
+
+	__remove_hrtimer(timer, timer->base, timer->state, 0);
+	list_add_tail(&timer->cb_entry, &timer->base->expired);
+	return 1;
+}
+
+#else
+
+static inline void hrtimer_rt_run_pending(void) { }
+static inline int hrtimer_rt_defer(struct hrtimer *timer) { return 0; }
+
+#endif
+
 #ifdef CONFIG_HIGH_RES_TIMERS
 
 /*
@@ -1279,7 +1380,7 @@ void hrtimer_interrupt(struct clock_event_device *dev)
 	struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);
 	struct hrtimer_clock_base *base;
 	ktime_t expires_next, now, entry_time, delta;
-	int i, retries = 0;
+	int i, retries = 0, raise = 0;
 
 	BUG_ON(!cpu_base->hres_active);
 	cpu_base->nr_events++;
@@ -1335,7 +1436,10 @@ retry:
 				break;
 			}
 
-			__run_hrtimer(timer, &basenow);
+			if (!hrtimer_rt_defer(timer))
+				__run_hrtimer(timer, &basenow);
+			else
+				raise = 1;
 		}
 		base++;
 	}
@@ -1351,6 +1455,10 @@ retry:
 	if (expires_next.tv64 == KTIME_MAX ||
 	    !tick_program_event(expires_next, 0)) {
 		cpu_base->hang_detected = 0;
+
+		if (raise)
+			raise_softirq_irqoff(HRTIMER_SOFTIRQ);
+
 		return;
 	}
 
@@ -1428,17 +1536,18 @@ void hrtimer_peek_ahead_timers(void)
 	local_irq_restore(flags);
 }
 
-static void run_hrtimer_softirq(struct softirq_action *h)
-{
-	hrtimer_peek_ahead_timers();
-}
-
 #else /* CONFIG_HIGH_RES_TIMERS */
 
 static inline void __hrtimer_peek_ahead_timers(void) { }
 
 #endif	/* !CONFIG_HIGH_RES_TIMERS */
 
+static void run_hrtimer_softirq(struct softirq_action *h)
+{
+	hrtimer_peek_ahead_timers();
+	hrtimer_rt_run_pending();
+}
+
 /*
  * Called from timer softirq every jiffy, expire hrtimers:
  *
@@ -1473,7 +1582,7 @@ void hrtimer_run_queues(void)
 	struct rb_node *node;
 	struct hrtimer_cpu_base *cpu_base;
 	struct hrtimer_clock_base *base;
-	int index, gettime = 1;
+	int index, gettime = 1, raise = 0;
 
 	cpu_base = &per_cpu(hrtimer_bases, raw_smp_processor_id());
 	if (hrtimer_hres_active(cpu_base))
@@ -1500,12 +1609,16 @@ void hrtimer_run_queues(void)
 					hrtimer_get_expires_tv64(timer))
 				break;
 
-			__run_hrtimer(timer, &base->softirq_time);
+			if (!hrtimer_rt_defer(timer))
+				__run_hrtimer(timer, &base->softirq_time);
+			else
+				raise = 1;
 		}
 		raw_spin_unlock(&cpu_base->lock);
 	}
 
-	wake_up_timer_waiters(cpu_base);
+	if (raise)
+		raise_softirq_irqoff(HRTIMER_SOFTIRQ);
 }
 
 /*
@@ -1527,6 +1640,7 @@ static enum hrtimer_restart hrtimer_wakeup(struct hrtimer *timer)
 void hrtimer_init_sleeper(struct hrtimer_sleeper *sl, struct task_struct *task)
 {
 	sl->timer.function = hrtimer_wakeup;
+	sl->timer.irqsafe = 1;
 	sl->task = task;
 }
 EXPORT_SYMBOL_GPL(hrtimer_init_sleeper);
@@ -1662,8 +1776,10 @@ static void __cpuinit init_hrtimers_cpu(int cpu)
 
 	raw_spin_lock_init(&cpu_base->lock);
 
-	for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++)
+	for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
 		cpu_base->clock_base[i].cpu_base = cpu_base;
+		INIT_LIST_HEAD(&cpu_base->clock_base[i].expired);
+	}
 
 	hrtimer_init_hres(cpu_base);
 #ifdef CONFIG_PREEMPT_SOFTIRQS
@@ -1781,9 +1897,7 @@ void __init hrtimers_init(void)
 	hrtimer_cpu_notify(&hrtimers_nb, (unsigned long)CPU_UP_PREPARE,
 			  (void *)(long)smp_processor_id());
 	register_cpu_notifier(&hrtimers_nb);
-#ifdef CONFIG_HIGH_RES_TIMERS
 	open_softirq(HRTIMER_SOFTIRQ, run_hrtimer_softirq);
-#endif
 }
 
 /**
diff --git a/kernel/sched.c b/kernel/sched.c
index bc8f328..83fafcf 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -202,6 +202,7 @@ void init_rt_bandwidth(struct rt_bandwidth *rt_b, u64 period, u64 runtime)
 
 	hrtimer_init(&rt_b->rt_period_timer,
 			CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	rt_b->rt_period_timer.irqsafe = 1;
 	rt_b->rt_period_timer.function = sched_rt_period_timer;
 }
 
@@ -1229,6 +1230,7 @@ static void init_rq_hrtick(struct rq *rq)
 
 	hrtimer_init(&rq->hrtick_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 	rq->hrtick_timer.function = hrtick;
+	rq->hrtick_timer.irqsafe = 1;
 }
 #else	/* CONFIG_SCHED_HRTICK */
 static inline void hrtick_clear(struct rq *rq)
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index bc625d9..a85776e 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -733,6 +733,7 @@ void tick_setup_sched_timer(void)
 	 * Emulate tick processing via per-CPU hrtimers:
 	 */
 	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+	ts->sched_timer.irqsafe = 1;
 	ts->sched_timer.function = tick_sched_timer;
 
 	/* Get the next period (per cpu) */
-- 
1.7.1.1