clocksource: Move watchdog downgrade to a work queue thread

Move the downgrade of an unstable clocksource from the timer interrupt
context into the process context of a work queue thread. This is
needed to be able to do the clocksource switch with stop_machine.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: John Stultz <johnstul@us.ibm.com>
Cc: Daniel Walker <dwalker@fifo99.com>
LKML-Reference: <20090814134809.354926067@de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 39 insertions, 17 deletions

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 56aaa749645..f1508019bfb 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -143,10 +143,13 @@ fs_initcall(clocksource_done_booting);
 static LIST_HEAD(watchdog_list);
 static struct clocksource *watchdog;
 static struct timer_list watchdog_timer;
+static struct work_struct watchdog_work;
 static DEFINE_SPINLOCK(watchdog_lock);
 static cycle_t watchdog_last;
 static int watchdog_running;
 
+static void clocksource_watchdog_work(struct work_struct *work);
+
 /*
  * Interval: 0.5sec Threshold: 0.0625s
  */
@@ -158,15 +161,16 @@ static void clocksource_unstable(struct clocksource *cs, int64_t delta)
         printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
                cs->name, delta);
         cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
-        clocksource_change_rating(cs, 0);
-        list_del(&cs->wd_list);
+        cs->flags |= CLOCK_SOURCE_UNSTABLE;
+        schedule_work(&watchdog_work);
 }
 
 static void clocksource_watchdog(unsigned long data)
 {
-        struct clocksource *cs, *tmp;
+        struct clocksource *cs;
         cycle_t csnow, wdnow;
         int64_t wd_nsec, cs_nsec;
+        int next_cpu;
 
         spin_lock(&watchdog_lock);
         if (!watchdog_running)
@@ -176,7 +180,12 @@ static void clocksource_watchdog(unsigned long data)
         wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask);
         watchdog_last = wdnow;
 
-        list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
+        list_for_each_entry(cs, &watchdog_list, wd_list) {
+
+                /* Clocksource already marked unstable? */
+                if (cs->flags & CLOCK_SOURCE_UNSTABLE)
+                        continue;
+
                 csnow = cs->read(cs);
 
                 /* Clocksource initialized ? */
@@ -207,19 +216,15 @@ static void clocksource_watchdog(unsigned long data)
                 }
         }
 
-        if (!list_empty(&watchdog_list)) {
-                /*
-                 * Cycle through CPUs to check if the CPUs stay
-                 * synchronized to each other.
-                 */
-                int next_cpu = cpumask_next(raw_smp_processor_id(),
-                                            cpu_online_mask);
-
-                if (next_cpu >= nr_cpu_ids)
-                        next_cpu = cpumask_first(cpu_online_mask);
-                watchdog_timer.expires += WATCHDOG_INTERVAL;
-                add_timer_on(&watchdog_timer, next_cpu);
-        }
+        /*
+         * Cycle through CPUs to check if the CPUs stay synchronized
+         * to each other.
+         */
+        next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
+        if (next_cpu >= nr_cpu_ids)
+                next_cpu = cpumask_first(cpu_online_mask);
+        watchdog_timer.expires += WATCHDOG_INTERVAL;
+        add_timer_on(&watchdog_timer, next_cpu);
 out:
         spin_unlock(&watchdog_lock);
 }
@@ -228,6 +233,7 @@ static inline void clocksource_start_watchdog(void)
 {
         if (watchdog_running || !watchdog || list_empty(&watchdog_list))
                 return;
+        INIT_WORK(&watchdog_work, clocksource_watchdog_work);
         init_timer(&watchdog_timer);
         watchdog_timer.function = clocksource_watchdog;
         watchdog_last = watchdog->read(watchdog);
@@ -313,6 +319,22 @@ static void clocksource_dequeue_watchdog(struct clocksource *cs)
         spin_unlock_irqrestore(&watchdog_lock, flags);
 }
 
+static void clocksource_watchdog_work(struct work_struct *work)
+{
+        struct clocksource *cs, *tmp;
+        unsigned long flags;
+
+        spin_lock_irqsave(&watchdog_lock, flags);
+        list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list)
+                if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
+                        list_del_init(&cs->wd_list);
+                        clocksource_change_rating(cs, 0);
+                }
+        /* Check if the watchdog timer needs to be stopped. */
+        clocksource_stop_watchdog();
+        spin_unlock(&watchdog_lock);
+}
+
 #else /* CONFIG_CLOCKSOURCE_WATCHDOG */
 
 static void clocksource_enqueue_watchdog(struct clocksource *cs)