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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: 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>
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1 changed files with 65 additions and 1 deletions
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@ -1191,6 +1191,7 @@ static inline void resched_rq(struct rq *rq)
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enum {
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HRTICK_SET, /* re-programm hrtick_timer */
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HRTICK_RESET, /* not a new slice */
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HRTICK_BLOCK, /* stop hrtick operations */
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};
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/*
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@ -1202,6 +1203,8 @@ static inline int hrtick_enabled(struct rq *rq)
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{
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if (!sched_feat(HRTICK))
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return 0;
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if (unlikely(test_bit(HRTICK_BLOCK, &rq->hrtick_flags)))
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return 0;
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return hrtimer_is_hres_active(&rq->hrtick_timer);
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}
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@ -1284,7 +1287,63 @@ static enum hrtimer_restart hrtick(struct hrtimer *timer)
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return HRTIMER_NORESTART;
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}
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static inline void init_rq_hrtick(struct rq *rq)
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static void hotplug_hrtick_disable(int cpu)
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{
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struct rq *rq = cpu_rq(cpu);
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unsigned long flags;
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spin_lock_irqsave(&rq->lock, flags);
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rq->hrtick_flags = 0;
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__set_bit(HRTICK_BLOCK, &rq->hrtick_flags);
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spin_unlock_irqrestore(&rq->lock, flags);
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hrtick_clear(rq);
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}
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static void hotplug_hrtick_enable(int cpu)
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{
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struct rq *rq = cpu_rq(cpu);
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unsigned long flags;
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spin_lock_irqsave(&rq->lock, flags);
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__clear_bit(HRTICK_BLOCK, &rq->hrtick_flags);
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spin_unlock_irqrestore(&rq->lock, flags);
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}
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static int
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hotplug_hrtick(struct notifier_block *nfb, unsigned long action, void *hcpu)
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{
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int cpu = (int)(long)hcpu;
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switch (action) {
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case CPU_UP_CANCELED:
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case CPU_UP_CANCELED_FROZEN:
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case CPU_DOWN_PREPARE:
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case CPU_DOWN_PREPARE_FROZEN:
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case CPU_DEAD:
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case CPU_DEAD_FROZEN:
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hotplug_hrtick_disable(cpu);
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return NOTIFY_OK;
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case CPU_UP_PREPARE:
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case CPU_UP_PREPARE_FROZEN:
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case CPU_DOWN_FAILED:
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case CPU_DOWN_FAILED_FROZEN:
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case CPU_ONLINE:
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case CPU_ONLINE_FROZEN:
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hotplug_hrtick_enable(cpu);
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return NOTIFY_OK;
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}
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return NOTIFY_DONE;
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}
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static void init_hrtick(void)
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{
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hotcpu_notifier(hotplug_hrtick, 0);
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}
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static void init_rq_hrtick(struct rq *rq)
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{
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rq->hrtick_flags = 0;
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hrtimer_init(&rq->hrtick_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
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@ -1321,6 +1380,10 @@ static inline void init_rq_hrtick(struct rq *rq)
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void hrtick_resched(void)
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{
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}
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static inline void init_hrtick(void)
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{
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}
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#endif
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/*
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@ -7943,6 +8006,7 @@ void __init sched_init_smp(void)
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put_online_cpus();
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/* XXX: Theoretical race here - CPU may be hotplugged now */
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hotcpu_notifier(update_sched_domains, 0);
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init_hrtick();
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/* Move init over to a non-isolated CPU */
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if (set_cpus_allowed_ptr(current, &non_isolated_cpus) < 0)
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