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Commit f833bab8 authored by Suresh Siddha's avatar Suresh Siddha Committed by Thomas Gleixner
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clockevent: Prevent dead lock on clockevents_lock 



Currently clockevents_notify() is called with interrupts enabled at
some places and interrupts disabled at some other places.

This results in a deadlock in this scenario.

cpu A holds clockevents_lock in clockevents_notify() with irqs enabled
cpu B waits for clockevents_lock in clockevents_notify() with irqs disabled
cpu C doing set_mtrr() which will try to rendezvous of all the cpus.

This will result in C and A come to the rendezvous point and waiting
for B. B is stuck forever waiting for the spinlock and thus not
reaching the rendezvous point.

Fix the clockevents code so that clockevents_lock is taken with
interrupts disabled and thus avoid the above deadlock.

Also call lapic_timer_propagate_broadcast() on the destination cpu so
that we avoid calling smp_call_function() in the clockevents notifier
chain.

This issue left us wondering if we need to change the MTRR rendezvous
logic to use stop machine logic (instead of smp_call_function) or add
a check in spinlock debug code to see if there are other spinlocks
which gets taken under both interrupts enabled/disabled conditions.

Signed-off-by: default avatarSuresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: default avatarVenkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Cc: "Pallipadi Venkatesh" <venkatesh.pallipadi@intel.com>
Cc: "Brown Len" <len.brown@intel.com>
LKML-Reference: <1250544899.2709.210.camel@sbs-t61.sc.intel.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent de809347

arch/x86/kernel/process.c

+1 −5
Original line number Diff line number Diff line
@@ -519,16 +519,12 @@ static void c1e_idle(void) 
		if (!cpumask_test_cpu(cpu, c1e_mask)) {

			cpumask_set_cpu(cpu, c1e_mask);

			/*

			 * Force broadcast so ACPI can not interfere. Needs

			 * to run with interrupts enabled as it uses

			 * smp_function_call.

			 * Force broadcast so ACPI can not interfere.

			 */

			local_irq_enable();

			clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_FORCE,

					   &cpu);

			printk(KERN_INFO "Switch to broadcast mode on CPU%d\n",

			       cpu);

			local_irq_disable();

		}

		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);

drivers/acpi/processor_idle.c

+4 −2
Original line number Diff line number Diff line
@@ -162,8 +162,9 @@ static void lapic_timer_check_state(int state, struct acpi_processor *pr, 
		pr->power.timer_broadcast_on_state = state;

}



static void lapic_timer_propagate_broadcast(struct acpi_processor *pr)

static void lapic_timer_propagate_broadcast(void *arg)

{

	struct acpi_processor *pr = (struct acpi_processor *) arg;

	unsigned long reason;



	reason = pr->power.timer_broadcast_on_state < INT_MAX ?
@@ -635,7 +636,8 @@ static int acpi_processor_power_verify(struct acpi_processor *pr) 
		working++;

	}



	lapic_timer_propagate_broadcast(pr);

	smp_call_function_single(pr->id, lapic_timer_propagate_broadcast,

				 pr, 1);



	return (working);

}

kernel/time/clockevents.c

+10 −6
Original line number Diff line number Diff line
@@ -137,11 +137,12 @@ int clockevents_program_event(struct clock_event_device *dev, ktime_t expires, 
 */

int clockevents_register_notifier(struct notifier_block *nb)

{

	unsigned long flags;

	int ret;



	spin_lock(&clockevents_lock);

	spin_lock_irqsave(&clockevents_lock, flags);

	ret = raw_notifier_chain_register(&clockevents_chain, nb);

	spin_unlock(&clockevents_lock);

	spin_unlock_irqrestore(&clockevents_lock, flags);



	return ret;

}
@@ -178,16 +179,18 @@ static void clockevents_notify_released(void) 
 */

void clockevents_register_device(struct clock_event_device *dev)

{

	unsigned long flags;



	BUG_ON(dev->mode != CLOCK_EVT_MODE_UNUSED);

	BUG_ON(!dev->cpumask);



	spin_lock(&clockevents_lock);

	spin_lock_irqsave(&clockevents_lock, flags);



	list_add(&dev->list, &clockevent_devices);

	clockevents_do_notify(CLOCK_EVT_NOTIFY_ADD, dev);

	clockevents_notify_released();



	spin_unlock(&clockevents_lock);

	spin_unlock_irqrestore(&clockevents_lock, flags);

}

EXPORT_SYMBOL_GPL(clockevents_register_device);
@@ -235,8 +238,9 @@ void clockevents_exchange_device(struct clock_event_device *old, 
void clockevents_notify(unsigned long reason, void *arg)

{

	struct list_head *node, *tmp;

	unsigned long flags;



	spin_lock(&clockevents_lock);

	spin_lock_irqsave(&clockevents_lock, flags);

	clockevents_do_notify(reason, arg);



	switch (reason) {
@@ -251,7 +255,7 @@ void clockevents_notify(unsigned long reason, void *arg) 
	default:

		break;

	}

	spin_unlock(&clockevents_lock);

	spin_unlock_irqrestore(&clockevents_lock, flags);

}

EXPORT_SYMBOL_GPL(clockevents_notify);

#endif

kernel/time/tick-broadcast.c

+3 −4
Original line number Diff line number Diff line
@@ -205,11 +205,11 @@ static void tick_handle_periodic_broadcast(struct clock_event_device *dev) 
 * Powerstate information: The system enters/leaves a state, where

 * affected devices might stop

 */

static void tick_do_broadcast_on_off(void *why)

static void tick_do_broadcast_on_off(unsigned long *reason)

{

	struct clock_event_device *bc, *dev;

	struct tick_device *td;

	unsigned long flags, *reason = why;

	unsigned long flags;

	int cpu, bc_stopped;



	spin_lock_irqsave(&tick_broadcast_lock, flags);
@@ -276,8 +276,7 @@ void tick_broadcast_on_off(unsigned long reason, int *oncpu) 
		printk(KERN_ERR "tick-broadcast: ignoring broadcast for "

		       "offline CPU #%d\n", *oncpu);

	else

		smp_call_function_single(*oncpu, tick_do_broadcast_on_off,

					 &reason, 1);

		tick_do_broadcast_on_off(&reason);

}



/*