From: Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 3 Jul 2009 08:44:31 -0500
Subject: hrtimer: Fixup hrtimer callback changes for preempt-rt
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.6/older/patches-4.6.2-rt5.tar.xz

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.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

---
 include/linux/hrtimer.h  |    7 ++
 kernel/sched/core.c      |    1 
 kernel/sched/rt.c        |    1 
 kernel/time/hrtimer.c    |  137 +++++++++++++++++++++++++++++++++++++++++++----
 kernel/time/tick-sched.c |    1 
 kernel/watchdog.c        |    1 
 6 files changed, 139 insertions(+), 9 deletions(-)

--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -87,6 +87,8 @@ enum hrtimer_restart {
  * @function:	timer expiry callback function
  * @base:	pointer to the timer base (per cpu and per clock)
  * @state:	state information (See bit values above)
+ * @cb_entry:	list entry to defer timers from hardirq context
+ * @irqsafe:	timer can run in hardirq context
  * @praecox:	timer expiry time if expired at the time of programming
  * @is_rel:	Set if the timer was armed relative
  * @start_pid:  timer statistics field to store the pid of the task which
@@ -104,6 +106,8 @@ struct hrtimer {
 	enum hrtimer_restart		(*function)(struct hrtimer *);
 	struct hrtimer_clock_base	*base;
 	u8				state;
+	struct list_head		cb_entry;
+	int				irqsafe;
 #ifdef CONFIG_MISSED_TIMER_OFFSETS_HIST
 	ktime_t				praecox;
 #endif
@@ -136,6 +140,7 @@ struct hrtimer_sleeper {
  *			timer to a base on another cpu.
  * @clockid:		clock id for per_cpu support
  * @active:		red black tree root node for the active timers
+ * @expired:		list head for deferred timers.
  * @get_time:		function to retrieve the current time of the clock
  * @offset:		offset of this clock to the monotonic base
  */
@@ -144,6 +149,7 @@ struct hrtimer_clock_base {
 	int			index;
 	clockid_t		clockid;
 	struct timerqueue_head	active;
+	struct list_head	expired;
 	ktime_t			(*get_time)(void);
 	ktime_t			offset;
 } __attribute__((__aligned__(HRTIMER_CLOCK_BASE_ALIGN)));
@@ -187,6 +193,7 @@ struct hrtimer_cpu_base {
 	raw_spinlock_t			lock;
 	seqcount_t			seq;
 	struct hrtimer			*running;
+	struct hrtimer			*running_soft;
 	unsigned int			cpu;
 	unsigned int			active_bases;
 	unsigned int			clock_was_set_seq;
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -306,6 +306,7 @@ 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)
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -47,6 +47,7 @@ void init_rt_bandwidth(struct rt_bandwid
 
 	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;
 }
 
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -724,11 +724,8 @@ static inline int hrtimer_is_hres_enable
 static inline void hrtimer_switch_to_hres(void) { }
 static inline void
 hrtimer_force_reprogram(struct hrtimer_cpu_base *base, int skip_equal) { }
-static inline int hrtimer_reprogram(struct hrtimer *timer,
-				    struct hrtimer_clock_base *base)
-{
-	return 0;
-}
+static inline void hrtimer_reprogram(struct hrtimer *timer,
+				     struct hrtimer_clock_base *base) { }
 static inline void hrtimer_init_hres(struct hrtimer_cpu_base *base) { }
 static inline void retrigger_next_event(void *arg) { }
 
@@ -877,7 +874,7 @@ void hrtimer_wait_for_timer(const struct
 {
 	struct hrtimer_clock_base *base = timer->base;
 
-	if (base && base->cpu_base && !hrtimer_hres_active())
+	if (base && base->cpu_base && !timer->irqsafe)
 		wait_event(base->cpu_base->wait,
 				!(hrtimer_callback_running(timer)));
 }
@@ -927,6 +924,11 @@ static void __remove_hrtimer(struct hrti
 	if (!(state & HRTIMER_STATE_ENQUEUED))
 		return;
 
+	if (unlikely(!list_empty(&timer->cb_entry))) {
+		list_del_init(&timer->cb_entry);
+		return;
+	}
+
 	if (!timerqueue_del(&base->active, &timer->node))
 		cpu_base->active_bases &= ~(1 << base->index);
 
@@ -1167,6 +1169,7 @@ static void __hrtimer_init(struct hrtime
 
 	base = hrtimer_clockid_to_base(clock_id);
 	timer->base = &cpu_base->clock_base[base];
+	INIT_LIST_HEAD(&timer->cb_entry);
 	timerqueue_init(&timer->node);
 
 #ifdef CONFIG_TIMER_STATS
@@ -1207,6 +1210,7 @@ bool hrtimer_active(const struct hrtimer
 		seq = raw_read_seqcount_begin(&cpu_base->seq);
 
 		if (timer->state != HRTIMER_STATE_INACTIVE ||
+		    cpu_base->running_soft == timer ||
 		    cpu_base->running == timer)
 			return true;
 
@@ -1305,12 +1309,112 @@ static void __run_hrtimer(struct hrtimer
 	cpu_base->running = NULL;
 }
 
+#ifdef CONFIG_PREEMPT_RT_BASE
+static void hrtimer_rt_reprogram(int restart, struct hrtimer *timer,
+				 struct hrtimer_clock_base *base)
+{
+	int leftmost;
+
+	if (restart != HRTIMER_NORESTART &&
+	    !(timer->state & HRTIMER_STATE_ENQUEUED)) {
+
+		leftmost = enqueue_hrtimer(timer, base);
+		if (!leftmost)
+			return;
+#ifdef CONFIG_HIGH_RES_TIMERS
+		if (!hrtimer_is_hres_active(timer)) {
+			/*
+			 * Kick to reschedule the next tick to handle the new timer
+			 * on dynticks target.
+			 */
+			if (base->cpu_base->nohz_active)
+				wake_up_nohz_cpu(base->cpu_base->cpu);
+		} else {
+
+			hrtimer_reprogram(timer, base);
+		}
+#endif
+	}
+}
+
+/*
+ * 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_deactivate(timer);
+			cpu_base->running_soft = timer;
+			raw_write_seqcount_barrier(&cpu_base->seq);
+
+			__remove_hrtimer(timer, base, HRTIMER_STATE_INACTIVE, 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);
+
+			hrtimer_rt_reprogram(restart, timer, base);
+			raw_write_seqcount_barrier(&cpu_base->seq);
+
+			WARN_ON_ONCE(cpu_base->running_soft != timer);
+			cpu_base->running_soft = NULL;
+		}
+	}
+
+	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 int hrtimer_rt_defer(struct hrtimer *timer) { return 0; }
+
+#endif
+
 static enum hrtimer_restart hrtimer_wakeup(struct hrtimer *timer);
 
 static void __hrtimer_run_queues(struct hrtimer_cpu_base *cpu_base, ktime_t now)
 {
 	struct hrtimer_clock_base *base = cpu_base->clock_base;
 	unsigned int active = cpu_base->active_bases;
+	int raise = 0;
 
 	for (; active; base++, active >>= 1) {
 		struct timerqueue_node *node;
@@ -1350,9 +1454,14 @@ static void __hrtimer_run_queues(struct
 			if (basenow.tv64 < hrtimer_get_softexpires_tv64(timer))
 				break;
 
-			__run_hrtimer(cpu_base, base, timer, &basenow);
+			if (!hrtimer_rt_defer(timer))
+				__run_hrtimer(cpu_base, base, timer, &basenow);
+			else
+				raise = 1;
 		}
 	}
+	if (raise)
+		raise_softirq_irqoff(HRTIMER_SOFTIRQ);
 }
 
 #ifdef CONFIG_HIGH_RES_TIMERS
@@ -1494,8 +1603,6 @@ void hrtimer_run_queues(void)
 	now = hrtimer_update_base(cpu_base);
 	__hrtimer_run_queues(cpu_base, now);
 	raw_spin_unlock(&cpu_base->lock);
-
-	wake_up_timer_waiters(cpu_base);
 }
 
 /*
@@ -1517,6 +1624,7 @@ static enum hrtimer_restart hrtimer_wake
 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);
@@ -1651,6 +1759,7 @@ static void init_hrtimers_cpu(int cpu)
 	for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
 		cpu_base->clock_base[i].cpu_base = cpu_base;
 		timerqueue_init_head(&cpu_base->clock_base[i].active);
+		INIT_LIST_HEAD(&cpu_base->clock_base[i].expired);
 	}
 
 	cpu_base->cpu = cpu;
@@ -1755,11 +1864,21 @@ static struct notifier_block hrtimers_nb
 	.notifier_call = hrtimer_cpu_notify,
 };
 
+#ifdef CONFIG_PREEMPT_RT_BASE
+static void run_hrtimer_softirq(struct softirq_action *h)
+{
+	hrtimer_rt_run_pending();
+}
+#endif
+
 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_PREEMPT_RT_BASE
+	open_softirq(HRTIMER_SOFTIRQ, run_hrtimer_softirq);
+#endif
 }
 
 /**
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -1213,6 +1213,7 @@ 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) */
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -523,6 +523,7 @@ static void watchdog_enable(unsigned int
 	/* kick off the timer for the hardlockup detector */
 	hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 	hrtimer->function = watchdog_timer_fn;
+	hrtimer->irqsafe = 1;
 
 	/* Enable the perf event */
 	watchdog_nmi_enable(cpu);
