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Commit a6037b61 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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hrtimer: fix recursion deadlock by re-introducing the softirq 



Impact: fix rare runtime deadlock

There are a few sites that do:

  spin_lock_irq(&foo)
  hrtimer_start(&bar)
    __run_hrtimer(&bar)
      func()
        spin_lock(&foo)

which obviously deadlocks. In order to avoid this, never call __run_hrtimer()
from hrtimer_start*() context, but instead defer this to softirq context.

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 731a55ba

include/linux/interrupt.h

+2 −1
Original line number Original line Diff line number Diff line
@@ -253,6 +253,7 @@ enum 
	BLOCK_SOFTIRQ,

	BLOCK_SOFTIRQ,

	TASKLET_SOFTIRQ,

	TASKLET_SOFTIRQ,

	SCHED_SOFTIRQ,

	SCHED_SOFTIRQ,

	HRTIMER_SOFTIRQ,

	RCU_SOFTIRQ,	/* Preferable RCU should always be the last softirq */

	RCU_SOFTIRQ,	/* Preferable RCU should always be the last softirq */





	NR_SOFTIRQS

	NR_SOFTIRQS

kernel/hrtimer.c

+27 −33
Original line number Original line Diff line number Diff line
@@ -634,7 +634,6 @@ static inline void hrtimer_init_timer_hres(struct hrtimer *timer) 
{

{

}

}





static void __run_hrtimer(struct hrtimer *timer);





/*

/*

 * When High resolution timers are active, try to reprogram. Note, that in case

 * When High resolution timers are active, try to reprogram. Note, that in case
@@ -646,13 +645,9 @@ static inline int hrtimer_enqueue_reprogram(struct hrtimer *timer, 
					    struct hrtimer_clock_base *base)

					    struct hrtimer_clock_base *base)

{

{

	if (base->cpu_base->hres_active && hrtimer_reprogram(timer, base)) {

	if (base->cpu_base->hres_active && hrtimer_reprogram(timer, base)) {

		/*

		spin_unlock(&base->cpu_base->lock);

		 * XXX: recursion check?

		raise_softirq_irqoff(HRTIMER_SOFTIRQ);

		 * hrtimer_forward() should round up with timer granularity

		spin_lock(&base->cpu_base->lock);

		 * so that we never get into inf recursion here,

		 * it doesn't do that though

		 */

		__run_hrtimer(timer);

		return 1;

		return 1;

	}

	}

	return 0;

	return 0;
@@ -705,11 +700,6 @@ static inline int hrtimer_enqueue_reprogram(struct hrtimer *timer, 
}

}

static inline void hrtimer_init_hres(struct hrtimer_cpu_base *base) { }

static inline void hrtimer_init_hres(struct hrtimer_cpu_base *base) { }

static inline void hrtimer_init_timer_hres(struct hrtimer *timer) { }

static inline void hrtimer_init_timer_hres(struct hrtimer *timer) { }

static inline int hrtimer_reprogram(struct hrtimer *timer,

				    struct hrtimer_clock_base *base)

{

	return 0;

}





#endif /* CONFIG_HIGH_RES_TIMERS */

#endif /* CONFIG_HIGH_RES_TIMERS */
@@ -780,9 +770,11 @@ EXPORT_SYMBOL_GPL(hrtimer_forward); 
 *

 *

 * The timer is inserted in expiry order. Insertion into the

 * The timer is inserted in expiry order. Insertion into the

 * red black tree is O(log(n)). Must hold the base lock.

 * red black tree is O(log(n)). Must hold the base lock.

 *

 * Returns 1 when the new timer is the leftmost timer in the tree.

 */

 */

static void enqueue_hrtimer(struct hrtimer *timer,

static int enqueue_hrtimer(struct hrtimer *timer,

			    struct hrtimer_clock_base *base, int reprogram)

			   struct hrtimer_clock_base *base)

{

{

	struct rb_node **link = &base->active.rb_node;

	struct rb_node **link = &base->active.rb_node;

	struct rb_node *parent = NULL;

	struct rb_node *parent = NULL;
@@ -814,20 +806,8 @@ static void enqueue_hrtimer(struct hrtimer *timer, 
	 * Insert the timer to the rbtree and check whether it

	 * Insert the timer to the rbtree and check whether it

	 * replaces the first pending timer

	 * replaces the first pending timer

	 */

	 */

	if (leftmost) {

	if (leftmost)

		/*

		 * Reprogram the clock event device. When the timer is already

		 * expired hrtimer_enqueue_reprogram has either called the

		 * callback or added it to the pending list and raised the

		 * softirq.

		 *

		 * This is a NOP for !HIGHRES

		 */

		if (reprogram && hrtimer_enqueue_reprogram(timer, base))

			return;



		base->first = &timer->node;

		base->first = &timer->node;

	}





	rb_link_node(&timer->node, parent, link);

	rb_link_node(&timer->node, parent, link);

	rb_insert_color(&timer->node, &base->active);

	rb_insert_color(&timer->node, &base->active);
@@ -836,6 +816,8 @@ static void enqueue_hrtimer(struct hrtimer *timer, 
	 * state of a possibly running callback.

	 * state of a possibly running callback.

	 */

	 */

	timer->state |= HRTIMER_STATE_ENQUEUED;

	timer->state |= HRTIMER_STATE_ENQUEUED;



	return leftmost;

}

}





/*

/*
@@ -912,7 +894,7 @@ hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim, unsigned long delta_n 
{

{

	struct hrtimer_clock_base *base, *new_base;

	struct hrtimer_clock_base *base, *new_base;

	unsigned long flags;

	unsigned long flags;

	int ret;

	int ret, leftmost;





	base = lock_hrtimer_base(timer, &flags);

	base = lock_hrtimer_base(timer, &flags);
@@ -940,12 +922,16 @@ hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim, unsigned long delta_n 




	timer_stats_hrtimer_set_start_info(timer);

	timer_stats_hrtimer_set_start_info(timer);





	leftmost = enqueue_hrtimer(timer, new_base);



	/*

	/*

	 * Only allow reprogramming if the new base is on this CPU.

	 * Only allow reprogramming if the new base is on this CPU.

	 * (it might still be on another CPU if the timer was pending)

	 * (it might still be on another CPU if the timer was pending)

	 *

	 * XXX send_remote_softirq() ?

	 */

	 */

	enqueue_hrtimer(timer, new_base,

	if (leftmost && new_base->cpu_base == &__get_cpu_var(hrtimer_bases))

			new_base->cpu_base == &__get_cpu_var(hrtimer_bases));

		hrtimer_enqueue_reprogram(timer, new_base);





	unlock_hrtimer_base(timer, &flags);

	unlock_hrtimer_base(timer, &flags);
@@ -1163,7 +1149,7 @@ static void __run_hrtimer(struct hrtimer *timer) 
	 */

	 */

	if (restart != HRTIMER_NORESTART) {

	if (restart != HRTIMER_NORESTART) {

		BUG_ON(timer->state != HRTIMER_STATE_CALLBACK);

		BUG_ON(timer->state != HRTIMER_STATE_CALLBACK);

		enqueue_hrtimer(timer, base, 0);

		enqueue_hrtimer(timer, base);

	}

	}

	timer->state &= ~HRTIMER_STATE_CALLBACK;

	timer->state &= ~HRTIMER_STATE_CALLBACK;

}

}
@@ -1277,6 +1263,11 @@ void hrtimer_peek_ahead_timers(void) 
	local_irq_restore(flags);

	local_irq_restore(flags);

}

}





static void run_hrtimer_softirq(struct softirq_action *h)

{

	hrtimer_peek_ahead_timers();

}



#endif	/* CONFIG_HIGH_RES_TIMERS */

#endif	/* CONFIG_HIGH_RES_TIMERS */





/*

/*
@@ -1532,7 +1523,7 @@ static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base, 
		 * is done, which will run all expired timers and re-programm

		 * is done, which will run all expired timers and re-programm

		 * the timer device.

		 * the timer device.

		 */

		 */

		enqueue_hrtimer(timer, new_base, 0);

		enqueue_hrtimer(timer, new_base);





		/* Clear the migration state bit */

		/* Clear the migration state bit */

		timer->state &= ~HRTIMER_STATE_MIGRATE;

		timer->state &= ~HRTIMER_STATE_MIGRATE;
@@ -1610,6 +1601,9 @@ void __init hrtimers_init(void) 
	hrtimer_cpu_notify(&hrtimers_nb, (unsigned long)CPU_UP_PREPARE,

	hrtimer_cpu_notify(&hrtimers_nb, (unsigned long)CPU_UP_PREPARE,

			  (void *)(long)smp_processor_id());

			  (void *)(long)smp_processor_id());

	register_cpu_notifier(&hrtimers_nb);

	register_cpu_notifier(&hrtimers_nb);

#ifdef CONFIG_HIGH_RES_TIMERS

	open_softirq(HRTIMER_SOFTIRQ, run_hrtimer_softirq);

#endif

}

}





/**

/**