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clocksource: Avoid clocksource watchdog circular locking dependency

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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: Martin 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: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Martin Schwidefsky 2009-08-18 17:09:42 +02:00 • committed by Thomas Gleixner
parent d0981a1b21
commit 01548f4d3e
1 changed files with 16 additions and 3 deletions
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19
kernel/time/clocksource.c
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@ -29,6 +29,7 @@
#include <linux/module.h> #include <linux/module.h>
#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */ #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
#include <linux/tick.h> #include <linux/tick.h>
#include <linux/kthread.h>
void timecounter_init(struct timecounter *tc, void timecounter_init(struct timecounter *tc,
const struct cyclecounter *cc, const struct cyclecounter *cc,
@ -130,7 +131,7 @@ static DEFINE_SPINLOCK(watchdog_lock);
static cycle_t watchdog_last; static cycle_t watchdog_last;
static int watchdog_running; 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); 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_INTERVAL (HZ >> 1)
#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4) #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) static void clocksource_unstable(struct clocksource *cs, int64_t delta)
{ {
printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n", 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) { list_for_each_entry(cs, &watchdog_list, wd_list) {
/* Clocksource already marked unstable? */ /* Clocksource already marked unstable? */
if (cs->flags & CLOCK_SOURCE_UNSTABLE) if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
schedule_work(&watchdog_work);
continue; continue;
}
csnow = cs->read(cs); csnow = cs->read(cs);
@ -304,7 +316,7 @@ static void clocksource_dequeue_watchdog(struct clocksource *cs)
spin_unlock_irqrestore(&watchdog_lock, flags); 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; struct clocksource *cs, *tmp;
unsigned long flags; unsigned long flags;
@ -327,6 +339,7 @@ static void clocksource_watchdog_work(struct work_struct *work)
__clocksource_change_rating(cs, 0); __clocksource_change_rating(cs, 0);
} }
mutex_unlock(&clocksource_mutex); mutex_unlock(&clocksource_mutex);
return 0;
} }
#else /* CONFIG_CLOCKSOURCE_WATCHDOG */ #else /* CONFIG_CLOCKSOURCE_WATCHDOG */