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Commit 01548f4d authored by Martin Schwidefsky's avatar Martin Schwidefsky Committed by Thomas Gleixner
Browse files

clocksource: Avoid clocksource watchdog circular locking dependency 



stop_machine from a multithreaded workqueue is not allowed because
of a circular locking dependency between cpu_down and the workqueue
execution. Use a kernel thread to do the clocksource downgrade.

Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: john stultz <johnstul@us.ibm.com>
LKML-Reference: <20090818170942.3ab80c91@skybase>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent d0981a1b

kernel/time/clocksource.c

+16 −3
Original line number Diff line number Diff line
@@ -29,6 +29,7 @@ 
#include <linux/module.h>

#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */

#include <linux/tick.h>

#include <linux/kthread.h>



void timecounter_init(struct timecounter *tc,

		      const struct cyclecounter *cc,
@@ -130,7 +131,7 @@ static DEFINE_SPINLOCK(watchdog_lock); 
static cycle_t watchdog_last;

static int watchdog_running;



static void clocksource_watchdog_work(struct work_struct *work);

static int clocksource_watchdog_kthread(void *data);

static void __clocksource_change_rating(struct clocksource *cs, int rating);



/*
@@ -139,6 +140,15 @@ static void __clocksource_change_rating(struct clocksource *cs, int rating); 
#define WATCHDOG_INTERVAL (HZ >> 1)

#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)



static void clocksource_watchdog_work(struct work_struct *work)

{

	/*

	 * If kthread_run fails the next watchdog scan over the

	 * watchdog_list will find the unstable clock again.

	 */

	kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");

}



static void clocksource_unstable(struct clocksource *cs, int64_t delta)

{

	printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
@@ -167,8 +177,10 @@ static void clocksource_watchdog(unsigned long data) 
	list_for_each_entry(cs, &watchdog_list, wd_list) {



		/* Clocksource already marked unstable? */

		if (cs->flags & CLOCK_SOURCE_UNSTABLE)

		if (cs->flags & CLOCK_SOURCE_UNSTABLE) {

			schedule_work(&watchdog_work);

			continue;

		}



		csnow = cs->read(cs);
@@ -304,7 +316,7 @@ static void clocksource_dequeue_watchdog(struct clocksource *cs) 
	spin_unlock_irqrestore(&watchdog_lock, flags);

}



static void clocksource_watchdog_work(struct work_struct *work)

static int clocksource_watchdog_kthread(void *data)

{

	struct clocksource *cs, *tmp;

	unsigned long flags;
@@ -327,6 +339,7 @@ static void clocksource_watchdog_work(struct work_struct *work) 
		__clocksource_change_rating(cs, 0);

	}

	mutex_unlock(&clocksource_mutex);

	return 0;

}



#else /* CONFIG_CLOCKSOURCE_WATCHDOG */