@@ -184,6 +184,8 @@ extern void add_timer(struct timer_list *timer);
extern int try_to_del_timer_sync(struct timer_list *timer);
extern int timer_delete_sync(struct timer_list *timer);
extern int timer_delete(struct timer_list *timer);
+extern int timer_shutdown_sync(struct timer_list *timer);
+extern int timer_shutdown(struct timer_list *timer);
/**
* del_timer_sync - Delete a pending timer and wait for a running callback
@@ -1319,6 +1319,27 @@ 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
@@ -1552,6 +1573,9 @@ 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
@@ -1562,6 +1586,48 @@ 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)