[PATCH] timers: introduce try_to_del_timer_sync()

This patch splits del_timer_sync() into 2 functions.  The new one,
try_to_del_timer_sync(), returns -1 when it hits executing timer.

It can be used in interrupt context, or when the caller hold locks which
can prevent completion of the timer's handler.

NOTE.  Currently it can't be used in interrupt context in UP case, because
->running_timer is used only with CONFIG_SMP.

Should the need arise, it is possible to kill #ifdef CONFIG_SMP in
set_running_timer(), it is cheap.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/include/linux/timer.h b/include/linux/timer.h
index 2e78fedfc06929bfeb7ed70c380e60f31dcf3cba..221f81ac2002b29a454855b918fd106f069413ad 100644 (file)
--- 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 8aadc62efd65379dff44fcc08cc57e3c0fd90bbf..1f986c16d89f22ecac011dd98de7edf932f55b00 100644 (file)
--- 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);