On Tue, 22 Nov 2022, Thomas Gleixner wrote: > @@ -1605,6 +1629,48 @@ int timer_delete_sync(struct timer_list > } > 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 requires that the timer is not required to be functional > + * for the rest of the shutdown operation. NIT... Maybe the first requires could be replaced by assumes/expects/presupposes to prevent double use of required? Thanks, Anna-Maria
