clocksource: Let clocksource_unregister() return success/error

The unregister call can fail, if the clocksource is the current one
and there is no replacement clocksource available. It can also fail,
if the clocksource is the watchdog clocksource and I'm not going to
provide support for this.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Magnus Damm <magnus.damm@gmail.com>
Link: http://lkml.kernel.org/r/20130425143436.029915527@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 32a895b114d88cb38dd401a5c37146aa4ae3a91f..2f39a4911668e13385e2d91d32685e53cdb0ddd5 100644 (file)
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -282,7 +282,7 @@ static inline s64 clocksource_cyc2ns(cycle_t cycles, u32 mult, u32 shift)
 
 
 extern int clocksource_register(struct clocksource*);
-extern void clocksource_unregister(struct clocksource*);
+extern int clocksource_unregister(struct clocksource*);
 extern void clocksource_touch_watchdog(void);
 extern struct clocksource* clocksource_get_next(void);
 extern void clocksource_change_rating(struct clocksource *cs, int rating);

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 791d1aeb17acd7a47dd0f89840e9a4318dff1495..31b90332f47b362742162fae8ca5e110d06e5d20 100644 (file)
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -389,28 +389,17 @@ static void clocksource_enqueue_watchdog(struct clocksource *cs)
 
 static void clocksource_dequeue_watchdog(struct clocksource *cs)
 {
-       struct clocksource *tmp;
        unsigned long flags;
 
        spin_lock_irqsave(&watchdog_lock, flags);
-       if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
-               /* cs is a watched clocksource. */
-               list_del_init(&cs->wd_list);
-       } else if (cs == watchdog) {
-               /* Reset watchdog cycles */
-               clocksource_reset_watchdog();
-               /* Current watchdog is removed. Find an alternative. */
-               watchdog = NULL;
-               list_for_each_entry(tmp, &clocksource_list, list) {
-                       if (tmp == cs || tmp->flags & CLOCK_SOURCE_MUST_VERIFY)
-                               continue;
-                       if (!watchdog || tmp->rating > watchdog->rating)
-                               watchdog = tmp;
+       if (cs != watchdog) {
+               if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
+                       /* cs is a watched clocksource. */
+                       list_del_init(&cs->wd_list);
+                       /* Check if the watchdog timer needs to be stopped. */
+                       clocksource_stop_watchdog();
                }
        }
-       cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
-       /* Check if the watchdog timer needs to be stopped. */
-       clocksource_stop_watchdog();
        spin_unlock_irqrestore(&watchdog_lock, flags);
 }
 
@@ -841,13 +830,15 @@ static int clocksource_unbind(struct clocksource *cs)
  * clocksource_unregister - remove a registered clocksource
  * @cs:        clocksource to be unregistered
  */
-void clocksource_unregister(struct clocksource *cs)
+int clocksource_unregister(struct clocksource *cs)
 {
+       int ret = 0;
+
        mutex_lock(&clocksource_mutex);
-       clocksource_dequeue_watchdog(cs);
-       list_del(&cs->list);
-       clocksource_select();
+       if (!list_empty(&cs->list))
+               ret = clocksource_unbind(cs);
        mutex_unlock(&clocksource_mutex);
+       return ret;
 }
 EXPORT_SYMBOL(clocksource_unregister);