[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>

[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>
Oleg Nesterov · Linus Torvalds
1 parent 55c888d6d0
Showing 2 changed files with 36 additions and 21 deletions Side-by-side Diff
include/linux/timer.h
kernel/timer.c
@@ -76,9 +76,11 @@
 }
  
 #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)
@@ -365,6 +365,34 @@
 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 @@
  */
 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);
...	...	@@ -76,9 +76,11 @@
76	76	}
77	77
78	78	#ifdef CONFIG_SMP
	79	+ extern int try_to_del_timer_sync(struct timer_list *timer);
79	80	extern int del_timer_sync(struct timer_list *timer);
80	81	#else
81		-# define del_timer_sync(t) del_timer(t)
	82	+# define try_to_del_timer_sync(t) del_timer(t)
	83	+# define del_timer_sync(t) del_timer(t)
82	84	#endif
83	85
84	86	#define del_singleshot_timer_sync(t) del_timer_sync(t)
...	...	@@ -365,6 +365,34 @@
365	365	EXPORT_SYMBOL(del_timer);
366	366
367	367	#ifdef CONFIG_SMP
	368	+/*
	369	+ * This function tries to deactivate a timer. Upon successful (ret >= 0)
	370	+ * exit the timer is not queued and the handler is not running on any CPU.
	371	+ *
	372	+ * It must not be called from interrupt contexts.
	373	+ */
	374	+int try_to_del_timer_sync(struct timer_list *timer)
	375	+{
	376	+ timer_base_t *base;
	377	+ unsigned long flags;
	378	+ int ret = -1;
	379	+
	380	+ base = lock_timer_base(timer, &flags);
	381	+
	382	+ if (base->running_timer == timer)
	383	+ goto out;
	384	+
	385	+ ret = 0;
	386	+ if (timer_pending(timer)) {
	387	+ detach_timer(timer, 1);
	388	+ ret = 1;
	389	+ }
	390	+out:
	391	+ spin_unlock_irqrestore(&base->lock, flags);
	392	+
	393	+ return ret;
	394	+}
	395	+
368	396	/***
369	397	* del_timer_sync - deactivate a timer and wait for the handler to finish.
370	398	* @timer: the timer to be deactivated
371	399
...	...	@@ -384,28 +412,13 @@
384	412	*/
385	413	int del_timer_sync(struct timer_list *timer)
386	414	{
387		- timer_base_t *base;
388		- unsigned long flags;
389		- int ret = -1;
390		-
391	415	check_timer(timer);
392	416
393		- do {
394		- base = lock_timer_base(timer, &flags);
395		-
396		- if (base->running_timer == timer)
397		- goto unlock;
398		-
399		- ret = 0;
400		- if (timer_pending(timer)) {
401		- detach_timer(timer, 1);
402		- ret = 1;
403		- }
404		-unlock:
405		- spin_unlock_irqrestore(&base->lock, flags);
406		- } while (ret < 0);
407		-
408		- return ret;
	417	+ for (;;) {
	418	+ int ret = try_to_del_timer_sync(timer);
	419	+ if (ret >= 0)
	420	+ return ret;
	421	+ }
409	422	}
410	423
411	424	EXPORT_SYMBOL(del_timer_sync);