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sched: fix hrtick_start_fair and CPU-Hotplug

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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: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: stable@kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2008-04-29 10:02:46 +02:00 committed by Ingo Molnar
parent 104f64549c
commit b328ca182f
1 changed files with 65 additions and 1 deletions
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66
kernel/sched.c
View file

@ -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)