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Commit b328ca18 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched: fix hrtick_start_fair and CPU-Hotplug 



Gautham R Shenoy reported:

 > While running the usual CPU-Hotplug stress tests on linux-2.6.25,
 > I noticed the following in the console logs.
 >
 > This is a wee bit difficult to reproduce. In the past 10 runs I hit this
 > only once.
 >
 > ------------[ cut here ]------------
 >
 > WARNING: at kernel/sched.c:962 hrtick+0x2e/0x65()
 >
 > Just wondering if we are doing a good job at handling the cancellation
 > of any per-cpu scheduler timers during CPU-Hotplug.

This looks like its indeed not cancelled at all and migrates the it to
another cpu. Fix it via a proper hotplug notifier mechanism.

Reported-by: default avatarGautham R Shenoy <ego@in.ibm.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: stable@kernel.org
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 104f6454

kernel/sched.c

+65 −1
Original line number Diff line number Diff line
@@ -1191,6 +1191,7 @@ static inline void resched_rq(struct rq *rq) 
enum {

	HRTICK_SET,		/* re-programm hrtick_timer */

	HRTICK_RESET,		/* not a new slice */

	HRTICK_BLOCK,		/* stop hrtick operations */

};



/*
@@ -1202,6 +1203,8 @@ static inline int hrtick_enabled(struct rq *rq) 
{

	if (!sched_feat(HRTICK))

		return 0;

	if (unlikely(test_bit(HRTICK_BLOCK, &rq->hrtick_flags)))

		return 0;

	return hrtimer_is_hres_active(&rq->hrtick_timer);

}
@@ -1284,7 +1287,63 @@ static enum hrtimer_restart hrtick(struct hrtimer *timer) 
	return HRTIMER_NORESTART;

}



static inline void init_rq_hrtick(struct rq *rq)

static void hotplug_hrtick_disable(int cpu)

{

	struct rq *rq = cpu_rq(cpu);

	unsigned long flags;



	spin_lock_irqsave(&rq->lock, flags);

	rq->hrtick_flags = 0;

	__set_bit(HRTICK_BLOCK, &rq->hrtick_flags);

	spin_unlock_irqrestore(&rq->lock, flags);



	hrtick_clear(rq);

}



static void hotplug_hrtick_enable(int cpu)

{

	struct rq *rq = cpu_rq(cpu);

	unsigned long flags;



	spin_lock_irqsave(&rq->lock, flags);

	__clear_bit(HRTICK_BLOCK, &rq->hrtick_flags);

	spin_unlock_irqrestore(&rq->lock, flags);

}



static int

hotplug_hrtick(struct notifier_block *nfb, unsigned long action, void *hcpu)

{

	int cpu = (int)(long)hcpu;



	switch (action) {

	case CPU_UP_CANCELED:

	case CPU_UP_CANCELED_FROZEN:

	case CPU_DOWN_PREPARE:

	case CPU_DOWN_PREPARE_FROZEN:

	case CPU_DEAD:

	case CPU_DEAD_FROZEN:

		hotplug_hrtick_disable(cpu);

		return NOTIFY_OK;



	case CPU_UP_PREPARE:

	case CPU_UP_PREPARE_FROZEN:

	case CPU_DOWN_FAILED:

	case CPU_DOWN_FAILED_FROZEN:

	case CPU_ONLINE:

	case CPU_ONLINE_FROZEN:

		hotplug_hrtick_enable(cpu);

		return NOTIFY_OK;

	}



	return NOTIFY_DONE;

}



static void init_hrtick(void)

{

	hotcpu_notifier(hotplug_hrtick, 0);

}



static void init_rq_hrtick(struct rq *rq)

{

	rq->hrtick_flags = 0;

	hrtimer_init(&rq->hrtick_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
@@ -1321,6 +1380,10 @@ static inline void init_rq_hrtick(struct rq *rq) 
void hrtick_resched(void)

{

}



static inline void init_hrtick(void)

{

}

#endif



/*
@@ -7943,6 +8006,7 @@ void __init sched_init_smp(void) 
	put_online_cpus();

	/* XXX: Theoretical race here - CPU may be hotplugged now */

	hotcpu_notifier(update_sched_domains, 0);

	init_hrtick();



	/* Move init over to a non-isolated CPU */

	if (set_cpus_allowed_ptr(current, &non_isolated_cpus) < 0)