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Commit 24f73b99 authored by Richard Cochran's avatar Richard Cochran Committed by Ingo Molnar
Browse files

timers/core: Convert to hotplug state machine 



When tearing down, call timers_dead_cpu() before notify_dead().
There is a hidden dependency between:

 - timers
 - block multiqueue
 - rcutree

If timers_dead_cpu() comes later than blk_mq_queue_reinit_notify()
that latter function causes a RCU stall.

Signed-off-by: default avatarRichard Cochran <rcochran@linutronix.de>
Signed-off-by: default avatarAnna-Maria Gleixner <anna-maria@linutronix.de>
Reviewed-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20160713153337.566790058@linutronix.de


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 27590dc1

include/linux/cpuhotplug.h

+1 −0
Original line number Diff line number Diff line
@@ -16,6 +16,7 @@ enum cpuhp_state { 
	CPUHP_X86_APB_DEAD,

	CPUHP_WORKQUEUE_PREP,

	CPUHP_HRTIMERS_PREPARE,

	CPUHP_TIMERS_DEAD,

	CPUHP_NOTIFY_PREPARE,

	CPUHP_BRINGUP_CPU,

	CPUHP_AP_IDLE_DEAD,

include/linux/timer.h

+6 −0
Original line number Diff line number Diff line
@@ -273,4 +273,10 @@ unsigned long __round_jiffies_up_relative(unsigned long j, int cpu); 
unsigned long round_jiffies_up(unsigned long j);

unsigned long round_jiffies_up_relative(unsigned long j);



#ifdef CONFIG_HOTPLUG_CPU

int timers_dead_cpu(unsigned int cpu);

#else

#define timers_dead_cpu NULL

#endif



#endif

kernel/cpu.c

+5 −0
Original line number Diff line number Diff line
@@ -1195,6 +1195,11 @@ static struct cpuhp_step cpuhp_bp_states[] = { 
		.startup = hrtimers_prepare_cpu,

		.teardown = hrtimers_dead_cpu,

	},

	[CPUHP_TIMERS_DEAD] = {

		.name = "timers dead",

		.startup = NULL,

		.teardown = timers_dead_cpu,

	},

	/*

	 * Preparatory and dead notifiers. Will be replaced once the notifiers

	 * are converted to states.

kernel/time/timer.c

+2 −23
Original line number Diff line number Diff line
@@ -1804,7 +1804,7 @@ static void migrate_timer_list(struct timer_base *new_base, struct hlist_head *h 
	}

}



static void migrate_timers(int cpu)

int timers_dead_cpu(unsigned int cpu)

{

	struct timer_base *old_base;

	struct timer_base *new_base;
@@ -1831,29 +1831,9 @@ static void migrate_timers(int cpu) 
		spin_unlock_irq(&new_base->lock);

		put_cpu_ptr(&timer_bases);

	}

	return 0;

}



static int timer_cpu_notify(struct notifier_block *self,

				unsigned long action, void *hcpu)

{

	switch (action) {

	case CPU_DEAD:

	case CPU_DEAD_FROZEN:

		migrate_timers((long)hcpu);

		break;

	default:

		break;

	}



	return NOTIFY_OK;

}



static inline void timer_register_cpu_notifier(void)

{

	cpu_notifier(timer_cpu_notify, 0);

}

#else

static inline void timer_register_cpu_notifier(void) { }

#endif /* CONFIG_HOTPLUG_CPU */



static void __init init_timer_cpu(int cpu)
@@ -1881,7 +1861,6 @@ void __init init_timers(void) 
{

	init_timer_cpus();

	init_timer_stats();

	timer_register_cpu_notifier();

	open_softirq(TIMER_SOFTIRQ, run_timer_softirq);

}