[PATCH v8 5/8] vhost: Reintroduce kthread mode support in vhost

[Cindy Lu <lulu@redhat.com>]

This commit restores the previously removed functions kthread
wake/stop/create, and use ops structure vhost_worker_ops to
manage worker wakeup, stop and creation. The function
vhost_worker_create initializes these ops pointers based on
the value of inherit_owner

The old function was remove in
commit 6e890c5d5021 ("vhost: use vhost_tasks for worker threads")

Signed-off-by: Cindy Lu <lulu@redhat.com>
---
 drivers/vhost/vhost.c | 48 ++++++++++++++++++++++++++++++++++++++++++-
 drivers/vhost/vhost.h |  1 +
 2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index c162ad772f8f..be97028a8baf 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -734,11 +734,21 @@ static void vhost_task_wakeup(struct vhost_worker *worker)
 	return vhost_task_wake(worker->vtsk);
 }
 
+static void vhost_kthread_wakeup(struct vhost_worker *worker)
+{
+	wake_up_process(worker->kthread_task);
+}
+
 static void vhost_task_do_stop(struct vhost_worker *worker)
 {
 	return vhost_task_stop(worker->vtsk);
 }
 
+static void vhost_kthread_do_stop(struct vhost_worker *worker)
+{
+	kthread_stop(worker->kthread_task);
+}
+
 static int vhost_task_worker_create(struct vhost_worker *worker,
 				    struct vhost_dev *dev, const char *name)
 {
@@ -762,6 +772,41 @@ static int vhost_task_worker_create(struct vhost_worker *worker,
 	return 0;
 }
 
+static int vhost_kthread_worker_create(struct vhost_worker *worker,
+				       struct vhost_dev *dev, const char *name)
+{
+	struct task_struct *task;
+	u32 id;
+	int ret;
+
+	task = kthread_create(vhost_run_work_kthread_list, worker, "%s", name);
+	if (IS_ERR(task))
+		return PTR_ERR(task);
+
+	worker->kthread_task = task;
+	wake_up_process(task);
+	ret = xa_alloc(&dev->worker_xa, &id, worker, xa_limit_32b, GFP_KERNEL);
+	if (ret < 0)
+		goto stop_worker;
+
+	ret = vhost_attach_task_to_cgroups(worker);
+	if (ret)
+		goto stop_worker;
+
+	worker->id = id;
+	return 0;
+
+stop_worker:
+	vhost_kthread_do_stop(worker);
+	return ret;
+}
+
+static const struct vhost_worker_ops kthread_ops = {
+	.create = vhost_kthread_worker_create,
+	.stop = vhost_kthread_do_stop,
+	.wakeup = vhost_kthread_wakeup,
+};
+
 static const struct vhost_worker_ops vhost_task_ops = {
 	.create = vhost_task_worker_create,
 	.stop = vhost_task_do_stop,
@@ -773,7 +818,8 @@ static struct vhost_worker *vhost_worker_create(struct vhost_dev *dev)
 	struct vhost_worker *worker;
 	char name[TASK_COMM_LEN];
 	int ret;
-	const struct vhost_worker_ops *ops = &vhost_task_ops;
+	const struct vhost_worker_ops *ops =
+		dev->inherit_owner ? &vhost_task_ops : &kthread_ops;
 
 	worker = kzalloc(sizeof(*worker), GFP_KERNEL_ACCOUNT);
 	if (!worker)
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 98895e299efa..af4b2f7d3b91 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -37,6 +37,7 @@ struct vhost_worker_ops {
 };
 
 struct vhost_worker {
+	struct task_struct *kthread_task;
 	struct vhost_task	*vtsk;
 	struct vhost_dev	*dev;
 	/* Used to serialize device wide flushing with worker swapping. */
-- 
2.45.0