timer: Make try_to_del_timer_sync() the same on SMP and UP

On UP try_to_del_timer_sync() is mapped to del_timer() which does not
take the running timer callback into account, so it has different
semantics.

Remove the SMP dependency of try_to_del_timer_sync() by using
base->running_timer in the UP case as well.

[ tglx: Removed set_running_timer() inline and tweaked the changelog ]

Signed-off-by: Yong Zhang <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Acked-by: Oleg Nesterov <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>

include/linux/timer.h

···
 
 extern void add_timer(struct timer_list *timer);
 
+extern int try_to_del_timer_sync(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 try_to_del_timer_sync(t)	del_timer(t)
 # define del_timer_sync(t)		del_timer(t)
 #endif
 

kernel/timer.c

···
 }
 EXPORT_SYMBOL_GPL(set_timer_slack);
 
-
-static inline void set_running_timer(struct tvec_base *base,
-					struct timer_list *timer)
-{
-#ifdef CONFIG_SMP
-	base->running_timer = timer;
-#endif
-}
-
 static void internal_add_timer(struct tvec_base *base, struct timer_list *timer)
 {
 	unsigned long expires = timer->expires;
···
 }
 EXPORT_SYMBOL(del_timer);
 
-#ifdef CONFIG_SMP
 /**
  * try_to_del_timer_sync - Try to deactivate a timer
  * @timer: timer do del
  *
  * 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)
 {
···
 }
 EXPORT_SYMBOL(try_to_del_timer_sync);
 
+#ifdef CONFIG_SMP
 /**
  * del_timer_sync - deactivate a timer and wait for the handler to finish.
  * @timer: the timer to be deactivated
···
 
 			timer_stats_account_timer(timer);
 
-			set_running_timer(base, timer);
+			base->running_timer = timer;
 			detach_timer(timer, 1);
 
 			spin_unlock_irq(&base->lock);
···
 			spin_lock_irq(&base->lock);
 		}
 	}
-	set_running_timer(base, NULL);
+	base->running_timer = NULL;
 	spin_unlock_irq(&base->lock);
 }