From 46f3d976213452350f9d10b0c2780c2681f7075b Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Thu, 19 Jul 2012 13:52:53 -0700 Subject: kthread_worker: reimplement flush_kthread_work() to allow freeing the work item being executed kthread_worker provides minimalistic workqueue-like interface for users which need a dedicated worker thread (e.g. for realtime priority). It has basic queue, flush_work, flush_worker operations which mostly match the workqueue counterparts; however, due to the way flush_work() is implemented, it has a noticeable difference of not allowing work items to be freed while being executed. While the current users of kthread_worker are okay with the current behavior, the restriction does impede some valid use cases. Also, removing this difference isn't difficult and actually makes the code easier to understand. This patch reimplements flush_kthread_work() such that it uses a flush_work item instead of queue/done sequence numbers. Signed-off-by: Tejun Heo --- kernel/kthread.c | 48 +++++++++++++++++++++++++++--------------------- 1 file changed, 27 insertions(+), 21 deletions(-) (limited to 'kernel/kthread.c') diff --git a/kernel/kthread.c b/kernel/kthread.c index 4bfbff36d447..b579af57ea10 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -360,16 +360,12 @@ repeat: struct kthread_work, node); list_del_init(&work->node); } + worker->current_work = work; spin_unlock_irq(&worker->lock); if (work) { __set_current_state(TASK_RUNNING); work->func(work); - smp_wmb(); /* wmb worker-b0 paired with flush-b1 */ - work->done_seq = work->queue_seq; - smp_mb(); /* mb worker-b1 paired with flush-b0 */ - if (atomic_read(&work->flushing)) - wake_up_all(&work->done); } else if (!freezing(current)) schedule(); @@ -386,7 +382,7 @@ static void insert_kthread_work(struct kthread_worker *worker, lockdep_assert_held(&worker->lock); list_add_tail(&work->node, pos); - work->queue_seq++; + work->worker = worker; if (likely(worker->task)) wake_up_process(worker->task); } @@ -436,25 +432,35 @@ static void kthread_flush_work_fn(struct kthread_work *work) */ void flush_kthread_work(struct kthread_work *work) { - int seq = work->queue_seq; + struct kthread_flush_work fwork = { + KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn), + COMPLETION_INITIALIZER_ONSTACK(fwork.done), + }; + struct kthread_worker *worker; + bool noop = false; + +retry: + worker = work->worker; + if (!worker) + return; - atomic_inc(&work->flushing); + spin_lock_irq(&worker->lock); + if (work->worker != worker) { + spin_unlock_irq(&worker->lock); + goto retry; + } - /* - * mb flush-b0 paired with worker-b1, to make sure either - * worker sees the above increment or we see done_seq update. - */ - smp_mb__after_atomic_inc(); + if (!list_empty(&work->node)) + insert_kthread_work(worker, &fwork.work, work->node.next); + else if (worker->current_work == work) + insert_kthread_work(worker, &fwork.work, worker->work_list.next); + else + noop = true; - /* A - B <= 0 tests whether B is in front of A regardless of overflow */ - wait_event(work->done, seq - work->done_seq <= 0); - atomic_dec(&work->flushing); + spin_unlock_irq(&worker->lock); - /* - * rmb flush-b1 paired with worker-b0, to make sure our caller - * sees every change made by work->func(). - */ - smp_mb__after_atomic_dec(); + if (!noop) + wait_for_completion(&fwork.done); } EXPORT_SYMBOL_GPL(flush_kthread_work); -- cgit