2 files changed, 36 insertions, 21 deletions

diff --git a/include/linux/timer.h b/include/linux/timer.h
index 2e78fedfc069..221f81ac2002 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -76,9 +76,11 @@ static inline void add_timer(struct timer_list * timer)
 }
 
 #ifdef CONFIG_SMP
+  extern int try_to_del_timer_sync(struct timer_list *timer);
   extern int del_timer_sync(struct timer_list *timer);
 #else
-# define del_timer_sync(t) del_timer(t)
+# define try_to_del_timer_sync(t)       del_timer(t)
+# define del_timer_sync(t)              del_timer(t)
 #endif
 
 #define del_singleshot_timer_sync(t) del_timer_sync(t)
diff --git a/kernel/timer.c b/kernel/timer.c
index 8aadc62efd65..1f986c16d89f 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -365,6 +365,34 @@ int del_timer(struct timer_list *timer)
 EXPORT_SYMBOL(del_timer);
 
 #ifdef CONFIG_SMP
+/*
+ * This function tries to deactivate a timer. Upon successful (ret >= 0)
+ * exit the timer is not queued and the handler is not running on any CPU.
+ *
+ * It must not be called from interrupt contexts.
+ */
+int try_to_del_timer_sync(struct timer_list *timer)
+{
+        timer_base_t *base;
+        unsigned long flags;
+        int ret = -1;
+
+        base = lock_timer_base(timer, &flags);
+
+        if (base->running_timer == timer)
+                goto out;
+
+        ret = 0;
+        if (timer_pending(timer)) {
+                detach_timer(timer, 1);
+                ret = 1;
+        }
+out:
+        spin_unlock_irqrestore(&base->lock, flags);
+
+        return ret;
+}
+
 /***
  * del_timer_sync - deactivate a timer and wait for the handler to finish.
  * @timer: the timer to be deactivated
@@ -384,28 +412,13 @@ EXPORT_SYMBOL(del_timer);
  */
 int del_timer_sync(struct timer_list *timer)
 {
-        timer_base_t *base;
-        unsigned long flags;
-        int ret = -1;
-
         check_timer(timer);
 
-        do {
-                base = lock_timer_base(timer, &flags);
-
-                if (base->running_timer == timer)
-                        goto unlock;
-
-                ret = 0;
-                if (timer_pending(timer)) {
-                        detach_timer(timer, 1);
-                        ret = 1;
-                }
-unlock:
-                spin_unlock_irqrestore(&base->lock, flags);
-        } while (ret < 0);
-
-        return ret;
+        for (;;) {
+                int ret = try_to_del_timer_sync(timer);
+                if (ret >= 0)
+                        return ret;
+        }
 }
 
 EXPORT_SYMBOL(del_timer_sync);