timers: Split [try_to_]del_timer[_sync]() to prepare for shutdown mode

mainline inclusion
from mainline-v6.2-rc1
commit 8553b5f2
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I7R8WG

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8553b5f2774a66b1f293b7d783934210afb8f23c

--------------------------------

Tearing down timers which have circular dependencies to other
functionality, e.g. workqueues, where the timer can schedule work and work
can arm timers, is not trivial.

In those cases it is desired to shutdown the timer in a way which prevents
rearming of the timer. The mechanism to do so is to set timer->function to
NULL and use this as an indicator for the timer arming functions to ignore
the (re)arm request.

Split the inner workings of try_do_del_timer_sync(), del_timer_sync() and
del_timer() into helper functions to prepare for implementing the shutdown
functionality.

No functional change.
Co-developed-by: NSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Tested-by: NGuenter Roeck <linux@roeck-us.net>
Reviewed-by: NJacob Keller <jacob.e.keller@intel.com>
Reviewed-by: NAnna-Maria Behnsen <anna-maria@linutronix.de>
Link: https://lore.kernel.org/all/20220407161745.7d6754b3@gandalf.local.home
Link: https://lore.kernel.org/all/20221110064101.429013735@goodmis.org
Link: https://lore.kernel.org/r/20221123201625.195147423@linutronix.deSigned-off-by: NYu Liao <liaoyu15@huawei.com>

kernel/time/timer.c

@@ -1245,20 +1245,14 @@ void add_timer_on(struct timer_list *timer, int cpu)
 EXPORT_SYMBOL_GPL(add_timer_on);
 
 /**
- * timer_delete - Deactivate a timer
+ * __timer_delete - Internal function: Deactivate a timer
  * @timer:	The timer to be deactivated
  *
- * The function only deactivates a pending timer, but contrary to
- * timer_delete_sync() it does not take into account whether the timer's
- * callback function is concurrently executed on a different CPU or not.
- * It neither prevents rearming of the timer. If @timer can be rearmed
- * concurrently then the return value of this function is meaningless.
- *
  * Return:
  * * %0 - The timer was not pending
  * * %1 - The timer was pending and deactivated
  */
-int timer_delete(struct timer_list *timer)
+static int __timer_delete(struct timer_list *timer)
 {
 	struct timer_base *base;
 	unsigned long flags;
@@ -1274,25 +1268,37 @@ int timer_delete(struct timer_list *timer)
 
 	return ret;
 }
-EXPORT_SYMBOL(timer_delete);
 
 /**
- * try_to_del_timer_sync - Try to deactivate a timer
- * @timer:	Timer to deactivate
+ * timer_delete - Deactivate a timer
+ * @timer:	The timer to be deactivated
  *
- * This function tries to deactivate a timer. On success the timer is not
- * queued and the timer callback function is not running on any CPU.
+ * The function only deactivates a pending timer, but contrary to
+ * timer_delete_sync() it does not take into account whether the timer's
+ * callback function is concurrently executed on a different CPU or not.
+ * It neither prevents rearming of the timer.  If @timer can be rearmed
+ * concurrently then the return value of this function is meaningless.
  *
- * This function does not guarantee that the timer cannot be rearmed right
- * after dropping the base lock. That needs to be prevented by the calling
- * code if necessary.
+ * Return:
+ * * %0 - The timer was not pending
+ * * %1 - The timer was pending and deactivated
+ */
+int timer_delete(struct timer_list *timer)
+{
+	return __timer_delete(timer);
+}
+EXPORT_SYMBOL(timer_delete);
+
+/**
+ * __try_to_del_timer_sync - Internal function: Try to deactivate a timer
+ * @timer:	Timer to deactivate
  *
  * Return:
  * * %0  - The timer was not pending
  * * %1  - The timer was pending and deactivated
  * * %-1 - The timer callback function is running on a different CPU
  */
-int try_to_del_timer_sync(struct timer_list *timer)
+static int __try_to_del_timer_sync(struct timer_list *timer)
 {
 	struct timer_base *base;
 	unsigned long flags;
@@ -1309,6 +1315,27 @@ int try_to_del_timer_sync(struct timer_list *timer)
 
 	return ret;
 }
+
+/**
+ * try_to_del_timer_sync - Try to deactivate a timer
+ * @timer:	Timer to deactivate
+ *
+ * This function tries to deactivate a timer. On success the timer is not
+ * queued and the timer callback function is not running on any CPU.
+ *
+ * This function does not guarantee that the timer cannot be rearmed right
+ * after dropping the base lock. That needs to be prevented by the calling
+ * code if necessary.
+ *
+ * Return:
+ * * %0  - The timer was not pending
+ * * %1  - The timer was pending and deactivated
+ * * %-1 - The timer callback function is running on a different CPU
+ */
+int try_to_del_timer_sync(struct timer_list *timer)
+{
+	return __try_to_del_timer_sync(timer);
+}
 EXPORT_SYMBOL(try_to_del_timer_sync);
 
 #ifdef CONFIG_PREEMPT_RT
@@ -1384,6 +1411,49 @@ static inline void timer_sync_wait_running(struct timer_base *base) { }
 static inline void del_timer_wait_running(struct timer_list *timer) { }
 #endif
 
+/**
+ * __timer_delete_sync - Internal function: Deactivate a timer and wait
+ *			 for the handler to finish.
+ * @timer:	The timer to be deactivated
+ *
+ * Return:
+ * * %0	- The timer was not pending
+ * * %1	- The timer was pending and deactivated
+ */
+static int __timer_delete_sync(struct timer_list *timer)
+{
+	int ret;
+
+#ifdef CONFIG_LOCKDEP
+	unsigned long flags;
+
+	/*
+	 * If lockdep gives a backtrace here, please reference
+	 * the synchronization rules above.
+	 */
+	local_irq_save(flags);
+	lock_map_acquire(&timer->lockdep_map);
+	lock_map_release(&timer->lockdep_map);
+	local_irq_restore(flags);
+#endif
+	/*
+	 * don't use it in hardirq context, because it
+	 * could lead to deadlock.
+	 */
+	WARN_ON(in_irq() && !(timer->flags & TIMER_IRQSAFE));
+
+	do {
+		ret = __try_to_del_timer_sync(timer);
+
+		if (unlikely(ret < 0)) {
+			del_timer_wait_running(timer);
+			cpu_relax();
+		}
+	} while (ret < 0);
+
+	return ret;
+}
+
 /**
  * timer_delete_sync - Deactivate a timer and wait for the handler to finish.
  * @timer:	The timer to be deactivated
@@ -1425,36 +1495,7 @@ static inline void del_timer_wait_running(struct timer_list *timer) { }
  */
 int timer_delete_sync(struct timer_list *timer)
 {
-	int ret;
-
-#ifdef CONFIG_LOCKDEP
-	unsigned long flags;
-
-	/*
-	 * If lockdep gives a backtrace here, please reference
-	 * the synchronization rules above.
-	 */
-	local_irq_save(flags);
-	lock_map_acquire(&timer->lockdep_map);
-	lock_map_release(&timer->lockdep_map);
-	local_irq_restore(flags);
-#endif
-	/*
-	 * don't use it in hardirq context, because it
-	 * could lead to deadlock.
-	 */
-	WARN_ON(in_irq() && !(timer->flags & TIMER_IRQSAFE));
-
-	do {
-		ret = try_to_del_timer_sync(timer);
-
-		if (unlikely(ret < 0)) {
-			del_timer_wait_running(timer);
-			cpu_relax();
-		}
-	} while (ret < 0);
-
-	return ret;
+	return __timer_delete_sync(timer);
 }
 EXPORT_SYMBOL(timer_delete_sync);