vhost: simplify work flushing

We used to implement the work flushing through tracking queued seq,
done seq, and the number of flushing. This patch simplify this by just
implement work flushing through another kind of vhost work with
completion. This will be used by lockless enqueuing patch.
Signed-off-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/vhost/vhost.c

@@ -131,6 +131,19 @@ static void vhost_reset_is_le(struct vhost_virtqueue *vq)
 	vq->is_le = virtio_legacy_is_little_endian();
 }
 
+struct vhost_flush_struct {
+	struct vhost_work work;
+	struct completion wait_event;
+};
+
+static void vhost_flush_work(struct vhost_work *work)
+{
+	struct vhost_flush_struct *s;
+
+	s = container_of(work, struct vhost_flush_struct, work);
+	complete(&s->wait_event);
+}
+
 static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh,
 			    poll_table *pt)
 {
@@ -158,8 +171,6 @@ void vhost_work_init(struct vhost_work *work, vhost_work_fn_t fn)
 	INIT_LIST_HEAD(&work->node);
 	work->fn = fn;
 	init_waitqueue_head(&work->done);
-	work->flushing = 0;
-	work->queue_seq = work->done_seq = 0;
 }
 EXPORT_SYMBOL_GPL(vhost_work_init);
 
@@ -211,31 +222,17 @@ void vhost_poll_stop(struct vhost_poll *poll)
 }
 EXPORT_SYMBOL_GPL(vhost_poll_stop);
 
-static bool vhost_work_seq_done(struct vhost_dev *dev, struct vhost_work *work,
-				unsigned seq)
-{
-	int left;
-
-	spin_lock_irq(&dev->work_lock);
-	left = seq - work->done_seq;
-	spin_unlock_irq(&dev->work_lock);
-	return left <= 0;
-}
-
 void vhost_work_flush(struct vhost_dev *dev, struct vhost_work *work)
 {
-	unsigned seq;
-	int flushing;
+	struct vhost_flush_struct flush;
+
+	if (dev->worker) {
+		init_completion(&flush.wait_event);
+		vhost_work_init(&flush.work, vhost_flush_work);
 
-	spin_lock_irq(&dev->work_lock);
-	seq = work->queue_seq;
-	work->flushing++;
-	spin_unlock_irq(&dev->work_lock);
-	wait_event(work->done, vhost_work_seq_done(dev, work, seq));
-	spin_lock_irq(&dev->work_lock);
-	flushing = --work->flushing;
-	spin_unlock_irq(&dev->work_lock);
-	BUG_ON(flushing < 0);
+		vhost_work_queue(dev, &flush.work);
+		wait_for_completion(&flush.wait_event);
+	}
 }
 EXPORT_SYMBOL_GPL(vhost_work_flush);
 
@@ -254,7 +251,6 @@ void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work)
 	spin_lock_irqsave(&dev->work_lock, flags);
 	if (list_empty(&work->node)) {
 		list_add_tail(&work->node, &dev->work_list);
-		work->queue_seq++;
 		spin_unlock_irqrestore(&dev->work_lock, flags);
 		wake_up_process(dev->worker);
 	} else {
@@ -310,7 +306,6 @@ static int vhost_worker(void *data)
 {
 	struct vhost_dev *dev = data;
 	struct vhost_work *work = NULL;
-	unsigned uninitialized_var(seq);
 	mm_segment_t oldfs = get_fs();
 
 	set_fs(USER_DS);
@@ -321,11 +316,6 @@ static int vhost_worker(void *data)
 		set_current_state(TASK_INTERRUPTIBLE);
 
 		spin_lock_irq(&dev->work_lock);
-		if (work) {
-			work->done_seq = seq;
-			if (work->flushing)
-				wake_up_all(&work->done);
-		}
 
 		if (kthread_should_stop()) {
 			spin_unlock_irq(&dev->work_lock);
@@ -336,7 +326,6 @@ static int vhost_worker(void *data)
 			work = list_first_entry(&dev->work_list,
 						struct vhost_work, node);
 			list_del_init(&work->node);
-			seq = work->queue_seq;
 		} else
 			work = NULL;
 		spin_unlock_irq(&dev->work_lock);