1 files changed, 66 insertions, 0 deletions

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 167e43c9451c..63a8ce7177dd 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1363,6 +1363,27 @@ int timer_delete(struct timer_list *timer)
 EXPORT_SYMBOL(timer_delete);
 
 /**
+ * timer_shutdown - Deactivate a timer and prevent rearming
+ * @timer:	The timer to be deactivated
+ *
+ * The function does not wait for an eventually running timer callback on a
+ * different CPU but it prevents rearming of the timer. Any attempt to arm
+ * @timer after this function returns will be silently ignored.
+ *
+ * This function is useful for teardown code and should only be used when
+ * timer_shutdown_sync() cannot be invoked due to locking or context constraints.
+ *
+ * Return:
+ * * %0 - The timer was not pending
+ * * %1 - The timer was pending
+ */
+int timer_shutdown(struct timer_list *timer)
+{
+	return __timer_delete(timer, true);
+}
+EXPORT_SYMBOL_GPL(timer_shutdown);
+
+/**
  * __try_to_del_timer_sync - Internal function: Try to deactivate a timer
  * @timer:	Timer to deactivate
  * @shutdown:	If true, this indicates that the timer is about to be
@@ -1595,6 +1616,9 @@ static int __timer_delete_sync(struct timer_list *timer, bool shutdown)
  * lock. If there is the possibility of a concurrent rearm then the return
  * value of the function is meaningless.
  *
+ * If such a guarantee is needed, e.g. for teardown situations then use
+ * timer_shutdown_sync() instead.
+ *
  * Return:
  * * %0	- The timer was not pending
  * * %1	- The timer was pending and deactivated
@@ -1605,6 +1629,48 @@ int timer_delete_sync(struct timer_list *timer)
 }
 EXPORT_SYMBOL(timer_delete_sync);
 
+/**
+ * timer_shutdown_sync - Shutdown a timer and prevent rearming
+ * @timer: The timer to be shutdown
+ *
+ * When the function returns it is guaranteed that:
+ *   - @timer is not queued
+ *   - The callback function of @timer is not running
+ *   - @timer cannot be enqueued again. Any attempt to rearm
+ *     @timer is silently ignored.
+ *
+ * See timer_delete_sync() for synchronization rules.
+ *
+ * This function is useful for final teardown of an infrastructure where
+ * the timer is subject to a circular dependency problem.
+ *
+ * A common pattern for this is a timer and a workqueue where the timer can
+ * schedule work and work can arm the timer. On shutdown the workqueue must
+ * be destroyed and the timer must be prevented from rearming. Unless the
+ * code has conditionals like 'if (mything->in_shutdown)' to prevent that
+ * there is no way to get this correct with timer_delete_sync().
+ *
+ * timer_shutdown_sync() is solving the problem. The correct ordering of
+ * calls in this case is:
+ *
+ *	timer_shutdown_sync(&mything->timer);
+ *	workqueue_destroy(&mything->workqueue);
+ *
+ * After this 'mything' can be safely freed.
+ *
+ * This obviously implies that the timer is not required to be functional
+ * for the rest of the shutdown operation.
+ *
+ * Return:
+ * * %0 - The timer was not pending
+ * * %1 - The timer was pending
+ */
+int timer_shutdown_sync(struct timer_list *timer)
+{
+	return __timer_delete_sync(timer, true);
+}
+EXPORT_SYMBOL_GPL(timer_shutdown_sync);
+
 static void call_timer_fn(struct timer_list *timer,
 			  void (*fn)(struct timer_list *),
 			  unsigned long baseclk)