This patch reintroduces kthread mode support in vhost,
It also introduces struct vhost_worker_ops to abstract
worker create/stop/wakeup operations.

* Bring back the original vhost_worker() implementation,
  and renamed to vhost_run_work_kthread_list().

* Add cgroup support for the kthread

* Introduce struct vhost_worker_ops:
  - Encapsulates create / stop / wake‑up callbacks.
  - vhost_worker_create() selects the proper ops according to
    inherit_owner.

This partially reverts or improves upon:
commit 6e890c5d5021 ("vhost: use vhost_tasks for worker threads")
commit 1cdaafa1b8b4 ("vhost: replace single worker pointer with xarray")

Signed-off-by: Cindy Lu <lulu@redhat.com>
---
 drivers/vhost/vhost.c | 188 ++++++++++++++++++++++++++++++++++++++----
 drivers/vhost/vhost.h |  12 +++
 2 files changed, 182 insertions(+), 18 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 250dc43f1786..be97028a8baf 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -22,6 +22,7 @@
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 #include <linux/kthread.h>
+#include <linux/cgroup.h>
 #include <linux/module.h>
 #include <linux/sort.h>
 #include <linux/sched/mm.h>
@@ -242,7 +243,7 @@ static void vhost_worker_queue(struct vhost_worker *worker,
 		 * test_and_set_bit() implies a memory barrier.
 		 */
 		llist_add(&work->node, &worker->work_list);
-		vhost_task_wake(worker->vtsk);
+		worker->ops->wakeup(worker);
 	}
 }
 
@@ -388,6 +389,44 @@ static void vhost_vq_reset(struct vhost_dev *dev,
 	__vhost_vq_meta_reset(vq);
 }
 
+static int vhost_run_work_kthread_list(void *data)
+{
+	struct vhost_worker *worker = data;
+	struct vhost_work *work, *work_next;
+	struct vhost_dev *dev = worker->dev;
+	struct llist_node *node;
+
+	kthread_use_mm(dev->mm);
+
+	for (;;) {
+		/* mb paired w/ kthread_stop */
+		set_current_state(TASK_INTERRUPTIBLE);
+
+		if (kthread_should_stop()) {
+			__set_current_state(TASK_RUNNING);
+			break;
+		}
+		node = llist_del_all(&worker->work_list);
+		if (!node)
+			schedule();
+
+		node = llist_reverse_order(node);
+		/* make sure flag is seen after deletion */
+		smp_wmb();
+		llist_for_each_entry_safe(work, work_next, node, node) {
+			clear_bit(VHOST_WORK_QUEUED, &work->flags);
+			__set_current_state(TASK_RUNNING);
+			kcov_remote_start_common(worker->kcov_handle);
+			work->fn(work);
+			kcov_remote_stop();
+			cond_resched();
+		}
+	}
+	kthread_unuse_mm(dev->mm);
+
+	return 0;
+}
+
 static bool vhost_run_work_list(void *data)
 {
 	struct vhost_worker *worker = data;
@@ -582,6 +621,46 @@ long vhost_dev_check_owner(struct vhost_dev *dev)
 }
 EXPORT_SYMBOL_GPL(vhost_dev_check_owner);
 
+struct vhost_attach_cgroups_struct {
+	struct vhost_work work;
+	struct task_struct *owner;
+	int ret;
+};
+
+static void vhost_attach_cgroups_work(struct vhost_work *work)
+{
+	struct vhost_attach_cgroups_struct *s;
+
+	s = container_of(work, struct vhost_attach_cgroups_struct, work);
+	s->ret = cgroup_attach_task_all(s->owner, current);
+}
+
+static int vhost_attach_task_to_cgroups(struct vhost_worker *worker)
+{
+	struct vhost_attach_cgroups_struct attach;
+	int saved_cnt;
+
+	attach.owner = current;
+
+	vhost_work_init(&attach.work, vhost_attach_cgroups_work);
+	vhost_worker_queue(worker, &attach.work);
+
+	mutex_lock(&worker->mutex);
+
+	/*
+	 * Bypass attachment_cnt check in __vhost_worker_flush:
+	 * Temporarily change it to INT_MAX to bypass the check
+	 */
+	saved_cnt = worker->attachment_cnt;
+	worker->attachment_cnt = INT_MAX;
+	__vhost_worker_flush(worker);
+	worker->attachment_cnt = saved_cnt;
+
+	mutex_unlock(&worker->mutex);
+
+	return attach.ret;
+}
+
 /* Caller should have device mutex */
 bool vhost_dev_has_owner(struct vhost_dev *dev)
 {
@@ -627,7 +706,7 @@ static void vhost_worker_destroy(struct vhost_dev *dev,
 
 	WARN_ON(!llist_empty(&worker->work_list));
 	xa_erase(&dev->worker_xa, worker->id);
-	vhost_task_stop(worker->vtsk);
+	worker->ops->stop(worker);
 	kfree(worker);
 }
 
@@ -650,42 +729,115 @@ static void vhost_workers_free(struct vhost_dev *dev)
 	xa_destroy(&dev->worker_xa);
 }
 
+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)
+{
+	struct vhost_task *vtsk;
+	u32 id;
+	int ret;
+
+	vtsk = vhost_task_create(vhost_run_work_list, vhost_worker_killed,
+				 worker, name);
+	if (IS_ERR(vtsk))
+		return PTR_ERR(vtsk);
+
+	worker->vtsk = vtsk;
+	vhost_task_start(vtsk);
+	ret = xa_alloc(&dev->worker_xa, &id, worker, xa_limit_32b, GFP_KERNEL);
+	if (ret < 0) {
+		vhost_task_do_stop(worker);
+		return ret;
+	}
+	worker->id = id;
+	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,
+	.wakeup = vhost_task_wakeup,
+};
+
 static struct vhost_worker *vhost_worker_create(struct vhost_dev *dev)
 {
 	struct vhost_worker *worker;
-	struct vhost_task *vtsk;
 	char name[TASK_COMM_LEN];
 	int ret;
-	u32 id;
+	const struct vhost_worker_ops *ops =
+		dev->inherit_owner ? &vhost_task_ops : &kthread_ops;
 
 	worker = kzalloc(sizeof(*worker), GFP_KERNEL_ACCOUNT);
 	if (!worker)
 		return NULL;
 
 	worker->dev = dev;
+	worker->ops = ops;
 	snprintf(name, sizeof(name), "vhost-%d", current->pid);
 
-	vtsk = vhost_task_create(vhost_run_work_list, vhost_worker_killed,
-				 worker, name);
-	if (IS_ERR(vtsk))
-		goto free_worker;
-
 	mutex_init(&worker->mutex);
 	init_llist_head(&worker->work_list);
 	worker->kcov_handle = kcov_common_handle();
-	worker->vtsk = vtsk;
-
-	vhost_task_start(vtsk);
-
-	ret = xa_alloc(&dev->worker_xa, &id, worker, xa_limit_32b, GFP_KERNEL);
+	ret = ops->create(worker, dev, name);
 	if (ret < 0)
-		goto stop_worker;
-	worker->id = id;
+		goto free_worker;
 
 	return worker;
 
-stop_worker:
-	vhost_task_stop(vtsk);
 free_worker:
 	kfree(worker);
 	return NULL;
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 19bb94922a0e..af4b2f7d3b91 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -26,7 +26,18 @@ struct vhost_work {
 	unsigned long		flags;
 };
 
+struct vhost_worker;
+struct vhost_dev;
+
+struct vhost_worker_ops {
+	int (*create)(struct vhost_worker *worker, struct vhost_dev *dev,
+		      const char *name);
+	void (*stop)(struct vhost_worker *worker);
+	void (*wakeup)(struct vhost_worker *worker);
+};
+
 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. */
@@ -36,6 +47,7 @@ struct vhost_worker {
 	u32			id;
 	int			attachment_cnt;
 	bool			killed;
+	const struct vhost_worker_ops *ops;
 };
 
 /* Poll a file (eventfd or socket) */
-- 
2.45.0

On Mon, Apr 21, 2025 at 10:44:08AM +0800, Cindy Lu wrote:
> This patch reintroduces kthread mode support in vhost,
> It also introduces struct vhost_worker_ops to abstract
> worker create/stop/wakeup operations.
> 
> * Bring back the original vhost_worker() implementation,
>   and renamed to vhost_run_work_kthread_list().
> 
> * Add cgroup support for the kthread
> 
> * Introduce struct vhost_worker_ops:
>   - Encapsulates create / stop / wake‑up callbacks.
>   - vhost_worker_create() selects the proper ops according to
>     inherit_owner.
> 
> This partially reverts or improves upon:
> commit 6e890c5d5021 ("vhost: use vhost_tasks for worker threads")
> commit 1cdaafa1b8b4 ("vhost: replace single worker pointer with xarray")
> 
> Signed-off-by: Cindy Lu <lulu@redhat.com>
> ---
>  drivers/vhost/vhost.c | 188 ++++++++++++++++++++++++++++++++++++++----
>  drivers/vhost/vhost.h |  12 +++
>  2 files changed, 182 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 250dc43f1786..be97028a8baf 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -22,6 +22,7 @@
>  #include <linux/slab.h>
>  #include <linux/vmalloc.h>
>  #include <linux/kthread.h>
> +#include <linux/cgroup.h>
>  #include <linux/module.h>
>  #include <linux/sort.h>
>  #include <linux/sched/mm.h>
> @@ -242,7 +243,7 @@ static void vhost_worker_queue(struct vhost_worker *worker,
>  		 * test_and_set_bit() implies a memory barrier.
>  		 */
>  		llist_add(&work->node, &worker->work_list);
> -		vhost_task_wake(worker->vtsk);
> +		worker->ops->wakeup(worker);
>  	}
>  }
>  
> @@ -388,6 +389,44 @@ static void vhost_vq_reset(struct vhost_dev *dev,
>  	__vhost_vq_meta_reset(vq);
>  }
>  
> +static int vhost_run_work_kthread_list(void *data)
> +{
> +	struct vhost_worker *worker = data;
> +	struct vhost_work *work, *work_next;
> +	struct vhost_dev *dev = worker->dev;
> +	struct llist_node *node;
> +
> +	kthread_use_mm(dev->mm);
> +
> +	for (;;) {
> +		/* mb paired w/ kthread_stop */
> +		set_current_state(TASK_INTERRUPTIBLE);
> +
> +		if (kthread_should_stop()) {
> +			__set_current_state(TASK_RUNNING);
> +			break;
> +		}
> +		node = llist_del_all(&worker->work_list);
> +		if (!node)
> +			schedule();
> +
> +		node = llist_reverse_order(node);
> +		/* make sure flag is seen after deletion */
> +		smp_wmb();
> +		llist_for_each_entry_safe(work, work_next, node, node) {
> +			clear_bit(VHOST_WORK_QUEUED, &work->flags);
> +			__set_current_state(TASK_RUNNING);
> +			kcov_remote_start_common(worker->kcov_handle);
> +			work->fn(work);
> +			kcov_remote_stop();
> +			cond_resched();
> +		}
> +	}
> +	kthread_unuse_mm(dev->mm);
> +
> +	return 0;
> +}
> +
>  static bool vhost_run_work_list(void *data)
>  {
>  	struct vhost_worker *worker = data;
> @@ -582,6 +621,46 @@ long vhost_dev_check_owner(struct vhost_dev *dev)
>  }
>  EXPORT_SYMBOL_GPL(vhost_dev_check_owner);
>  
> +struct vhost_attach_cgroups_struct {
> +	struct vhost_work work;
> +	struct task_struct *owner;
> +	int ret;
> +};
> +
> +static void vhost_attach_cgroups_work(struct vhost_work *work)
> +{
> +	struct vhost_attach_cgroups_struct *s;
> +
> +	s = container_of(work, struct vhost_attach_cgroups_struct, work);
> +	s->ret = cgroup_attach_task_all(s->owner, current);
> +}
> +
> +static int vhost_attach_task_to_cgroups(struct vhost_worker *worker)
> +{
> +	struct vhost_attach_cgroups_struct attach;
> +	int saved_cnt;
> +
> +	attach.owner = current;
> +
> +	vhost_work_init(&attach.work, vhost_attach_cgroups_work);
> +	vhost_worker_queue(worker, &attach.work);
> +
> +	mutex_lock(&worker->mutex);
> +
> +	/*
> +	 * Bypass attachment_cnt check in __vhost_worker_flush:
> +	 * Temporarily change it to INT_MAX to bypass the check
> +	 */
> +	saved_cnt = worker->attachment_cnt;
> +	worker->attachment_cnt = INT_MAX;
> +	__vhost_worker_flush(worker);
> +	worker->attachment_cnt = saved_cnt;


You mean this one?
        if (!worker->attachment_cnt || worker->killed)
                return;


Just introduce a variant of __vhost_worker_flush that
skips this check.

E.g.

Rename __vhost_worker_flush -> _vhost_worker_flush.

then rework:

static void _vhost_worker_flush(struct vhost_worker *worker)
{
        struct vhost_flush_struct flush; 
                                  
        if (!worker->attachment_cnt || worker->killed)
                return;

	__vhost_worker_flush(worker);
}





> +
> +	mutex_unlock(&worker->mutex);
> +
> +	return attach.ret;
> +}
> +
>  /* Caller should have device mutex */
>  bool vhost_dev_has_owner(struct vhost_dev *dev)
>  {
> @@ -627,7 +706,7 @@ static void vhost_worker_destroy(struct vhost_dev *dev,
>  
>  	WARN_ON(!llist_empty(&worker->work_list));
>  	xa_erase(&dev->worker_xa, worker->id);
> -	vhost_task_stop(worker->vtsk);
> +	worker->ops->stop(worker);
>  	kfree(worker);
>  }
>  
> @@ -650,42 +729,115 @@ static void vhost_workers_free(struct vhost_dev *dev)
>  	xa_destroy(&dev->worker_xa);
>  }
>  
> +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)
> +{
> +	struct vhost_task *vtsk;
> +	u32 id;
> +	int ret;
> +
> +	vtsk = vhost_task_create(vhost_run_work_list, vhost_worker_killed,
> +				 worker, name);
> +	if (IS_ERR(vtsk))
> +		return PTR_ERR(vtsk);
> +
> +	worker->vtsk = vtsk;
> +	vhost_task_start(vtsk);
> +	ret = xa_alloc(&dev->worker_xa, &id, worker, xa_limit_32b, GFP_KERNEL);
> +	if (ret < 0) {
> +		vhost_task_do_stop(worker);
> +		return ret;
> +	}
> +	worker->id = id;
> +	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,
> +	.wakeup = vhost_task_wakeup,
> +};
> +
>  static struct vhost_worker *vhost_worker_create(struct vhost_dev *dev)
>  {
>  	struct vhost_worker *worker;
> -	struct vhost_task *vtsk;
>  	char name[TASK_COMM_LEN];
>  	int ret;
> -	u32 id;
> +	const struct vhost_worker_ops *ops =
> +		dev->inherit_owner ? &vhost_task_ops : &kthread_ops;
>  
>  	worker = kzalloc(sizeof(*worker), GFP_KERNEL_ACCOUNT);
>  	if (!worker)
>  		return NULL;
>  
>  	worker->dev = dev;
> +	worker->ops = ops;
>  	snprintf(name, sizeof(name), "vhost-%d", current->pid);
>  
> -	vtsk = vhost_task_create(vhost_run_work_list, vhost_worker_killed,
> -				 worker, name);
> -	if (IS_ERR(vtsk))
> -		goto free_worker;
> -
>  	mutex_init(&worker->mutex);
>  	init_llist_head(&worker->work_list);
>  	worker->kcov_handle = kcov_common_handle();
> -	worker->vtsk = vtsk;
> -
> -	vhost_task_start(vtsk);
> -
> -	ret = xa_alloc(&dev->worker_xa, &id, worker, xa_limit_32b, GFP_KERNEL);
> +	ret = ops->create(worker, dev, name);
>  	if (ret < 0)
> -		goto stop_worker;
> -	worker->id = id;
> +		goto free_worker;
>  
>  	return worker;
>  
> -stop_worker:
> -	vhost_task_stop(vtsk);
>  free_worker:
>  	kfree(worker);
>  	return NULL;
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index 19bb94922a0e..af4b2f7d3b91 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -26,7 +26,18 @@ struct vhost_work {
>  	unsigned long		flags;
>  };
>  
> +struct vhost_worker;
> +struct vhost_dev;
> +
> +struct vhost_worker_ops {
> +	int (*create)(struct vhost_worker *worker, struct vhost_dev *dev,
> +		      const char *name);
> +	void (*stop)(struct vhost_worker *worker);
> +	void (*wakeup)(struct vhost_worker *worker);
> +};
> +
>  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. */
> @@ -36,6 +47,7 @@ struct vhost_worker {
>  	u32			id;
>  	int			attachment_cnt;
>  	bool			killed;
> +	const struct vhost_worker_ops *ops;
>  };
>  
>  /* Poll a file (eventfd or socket) */
> -- 
> 2.45.0

On Mon, Apr 21, 2025 at 10:45 AM Cindy Lu <lulu@redhat.com> wrote:
>
> This patch reintroduces kthread mode support in vhost,
> It also introduces struct vhost_worker_ops to abstract
> worker create/stop/wakeup operations.
>
> * Bring back the original vhost_worker() implementation,
>   and renamed to vhost_run_work_kthread_list().
>
> * Add cgroup support for the kthread
>
> * Introduce struct vhost_worker_ops:
>   - Encapsulates create / stop / wake‑up callbacks.
>   - vhost_worker_create() selects the proper ops according to
>     inherit_owner.
>
> This partially reverts or improves upon:
> commit 6e890c5d5021 ("vhost: use vhost_tasks for worker threads")
> commit 1cdaafa1b8b4 ("vhost: replace single worker pointer with xarray")
>
> Signed-off-by: Cindy Lu <lulu@redhat.com>
> ---
>  drivers/vhost/vhost.c | 188 ++++++++++++++++++++++++++++++++++++++----
>  drivers/vhost/vhost.h |  12 +++
>  2 files changed, 182 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 250dc43f1786..be97028a8baf 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -22,6 +22,7 @@
>  #include <linux/slab.h>
>  #include <linux/vmalloc.h>
>  #include <linux/kthread.h>
> +#include <linux/cgroup.h>
>  #include <linux/module.h>
>  #include <linux/sort.h>
>  #include <linux/sched/mm.h>
> @@ -242,7 +243,7 @@ static void vhost_worker_queue(struct vhost_worker *worker,
>                  * test_and_set_bit() implies a memory barrier.
>                  */
>                 llist_add(&work->node, &worker->work_list);
> -               vhost_task_wake(worker->vtsk);
> +               worker->ops->wakeup(worker);
>         }
>  }
>
> @@ -388,6 +389,44 @@ static void vhost_vq_reset(struct vhost_dev *dev,
>         __vhost_vq_meta_reset(vq);
>  }
>
> +static int vhost_run_work_kthread_list(void *data)
> +{
> +       struct vhost_worker *worker = data;
> +       struct vhost_work *work, *work_next;
> +       struct vhost_dev *dev = worker->dev;
> +       struct llist_node *node;
> +
> +       kthread_use_mm(dev->mm);
> +
> +       for (;;) {
> +               /* mb paired w/ kthread_stop */
> +               set_current_state(TASK_INTERRUPTIBLE);
> +
> +               if (kthread_should_stop()) {
> +                       __set_current_state(TASK_RUNNING);
> +                       break;
> +               }
> +               node = llist_del_all(&worker->work_list);
> +               if (!node)
> +                       schedule();
> +
> +               node = llist_reverse_order(node);
> +               /* make sure flag is seen after deletion */
> +               smp_wmb();
> +               llist_for_each_entry_safe(work, work_next, node, node) {
> +                       clear_bit(VHOST_WORK_QUEUED, &work->flags);
> +                       __set_current_state(TASK_RUNNING);
> +                       kcov_remote_start_common(worker->kcov_handle);
> +                       work->fn(work);
> +                       kcov_remote_stop();
> +                       cond_resched();
> +               }
> +       }
> +       kthread_unuse_mm(dev->mm);
> +
> +       return 0;
> +}
> +
>  static bool vhost_run_work_list(void *data)
>  {
>         struct vhost_worker *worker = data;
> @@ -582,6 +621,46 @@ long vhost_dev_check_owner(struct vhost_dev *dev)
>  }
>  EXPORT_SYMBOL_GPL(vhost_dev_check_owner);
>
> +struct vhost_attach_cgroups_struct {
> +       struct vhost_work work;
> +       struct task_struct *owner;
> +       int ret;
> +};
> +
> +static void vhost_attach_cgroups_work(struct vhost_work *work)
> +{
> +       struct vhost_attach_cgroups_struct *s;
> +
> +       s = container_of(work, struct vhost_attach_cgroups_struct, work);
> +       s->ret = cgroup_attach_task_all(s->owner, current);
> +}
> +
> +static int vhost_attach_task_to_cgroups(struct vhost_worker *worker)
> +{
> +       struct vhost_attach_cgroups_struct attach;
> +       int saved_cnt;
> +
> +       attach.owner = current;
> +
> +       vhost_work_init(&attach.work, vhost_attach_cgroups_work);
> +       vhost_worker_queue(worker, &attach.work);
> +
> +       mutex_lock(&worker->mutex);
> +
> +       /*
> +        * Bypass attachment_cnt check in __vhost_worker_flush:
> +        * Temporarily change it to INT_MAX to bypass the check
> +        */
> +       saved_cnt = worker->attachment_cnt;
> +       worker->attachment_cnt = INT_MAX;
> +       __vhost_worker_flush(worker);
> +       worker->attachment_cnt = saved_cnt;

I wonder if it's easier to re-introduce the flush that was used before
vhost kthread to avoid the tricks here. We can have flush ops for
example.

Thanks

On Mon, Apr 21, 2025 at 11:39:14AM +0800, Jason Wang wrote:
> On Mon, Apr 21, 2025 at 10:45 AM Cindy Lu <lulu@redhat.com> wrote:
> >
> > This patch reintroduces kthread mode support in vhost,
> > It also introduces struct vhost_worker_ops to abstract
> > worker create/stop/wakeup operations.
> >
> > * Bring back the original vhost_worker() implementation,
> >   and renamed to vhost_run_work_kthread_list().
> >
> > * Add cgroup support for the kthread
> >
> > * Introduce struct vhost_worker_ops:
> >   - Encapsulates create / stop / wake‑up callbacks.
> >   - vhost_worker_create() selects the proper ops according to
> >     inherit_owner.
> >
> > This partially reverts or improves upon:
> > commit 6e890c5d5021 ("vhost: use vhost_tasks for worker threads")
> > commit 1cdaafa1b8b4 ("vhost: replace single worker pointer with xarray")
> >
> > Signed-off-by: Cindy Lu <lulu@redhat.com>
> > ---
> >  drivers/vhost/vhost.c | 188 ++++++++++++++++++++++++++++++++++++++----
> >  drivers/vhost/vhost.h |  12 +++
> >  2 files changed, 182 insertions(+), 18 deletions(-)
> >
> > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > index 250dc43f1786..be97028a8baf 100644
> > --- a/drivers/vhost/vhost.c
> > +++ b/drivers/vhost/vhost.c
> > @@ -22,6 +22,7 @@
> >  #include <linux/slab.h>
> >  #include <linux/vmalloc.h>
> >  #include <linux/kthread.h>
> > +#include <linux/cgroup.h>
> >  #include <linux/module.h>
> >  #include <linux/sort.h>
> >  #include <linux/sched/mm.h>
> > @@ -242,7 +243,7 @@ static void vhost_worker_queue(struct vhost_worker *worker,
> >                  * test_and_set_bit() implies a memory barrier.
> >                  */
> >                 llist_add(&work->node, &worker->work_list);
> > -               vhost_task_wake(worker->vtsk);
> > +               worker->ops->wakeup(worker);
> >         }
> >  }
> >
> > @@ -388,6 +389,44 @@ static void vhost_vq_reset(struct vhost_dev *dev,
> >         __vhost_vq_meta_reset(vq);
> >  }
> >
> > +static int vhost_run_work_kthread_list(void *data)
> > +{
> > +       struct vhost_worker *worker = data;
> > +       struct vhost_work *work, *work_next;
> > +       struct vhost_dev *dev = worker->dev;
> > +       struct llist_node *node;
> > +
> > +       kthread_use_mm(dev->mm);
> > +
> > +       for (;;) {
> > +               /* mb paired w/ kthread_stop */
> > +               set_current_state(TASK_INTERRUPTIBLE);
> > +
> > +               if (kthread_should_stop()) {
> > +                       __set_current_state(TASK_RUNNING);
> > +                       break;
> > +               }
> > +               node = llist_del_all(&worker->work_list);
> > +               if (!node)
> > +                       schedule();
> > +
> > +               node = llist_reverse_order(node);
> > +               /* make sure flag is seen after deletion */
> > +               smp_wmb();
> > +               llist_for_each_entry_safe(work, work_next, node, node) {
> > +                       clear_bit(VHOST_WORK_QUEUED, &work->flags);
> > +                       __set_current_state(TASK_RUNNING);
> > +                       kcov_remote_start_common(worker->kcov_handle);
> > +                       work->fn(work);
> > +                       kcov_remote_stop();
> > +                       cond_resched();
> > +               }
> > +       }
> > +       kthread_unuse_mm(dev->mm);
> > +
> > +       return 0;
> > +}
> > +
> >  static bool vhost_run_work_list(void *data)
> >  {
> >         struct vhost_worker *worker = data;
> > @@ -582,6 +621,46 @@ long vhost_dev_check_owner(struct vhost_dev *dev)
> >  }
> >  EXPORT_SYMBOL_GPL(vhost_dev_check_owner);
> >
> > +struct vhost_attach_cgroups_struct {
> > +       struct vhost_work work;
> > +       struct task_struct *owner;
> > +       int ret;
> > +};
> > +
> > +static void vhost_attach_cgroups_work(struct vhost_work *work)
> > +{
> > +       struct vhost_attach_cgroups_struct *s;
> > +
> > +       s = container_of(work, struct vhost_attach_cgroups_struct, work);
> > +       s->ret = cgroup_attach_task_all(s->owner, current);
> > +}
> > +
> > +static int vhost_attach_task_to_cgroups(struct vhost_worker *worker)
> > +{
> > +       struct vhost_attach_cgroups_struct attach;
> > +       int saved_cnt;
> > +
> > +       attach.owner = current;
> > +
> > +       vhost_work_init(&attach.work, vhost_attach_cgroups_work);
> > +       vhost_worker_queue(worker, &attach.work);
> > +
> > +       mutex_lock(&worker->mutex);
> > +
> > +       /*
> > +        * Bypass attachment_cnt check in __vhost_worker_flush:
> > +        * Temporarily change it to INT_MAX to bypass the check
> > +        */
> > +       saved_cnt = worker->attachment_cnt;
> > +       worker->attachment_cnt = INT_MAX;
> > +       __vhost_worker_flush(worker);
> > +       worker->attachment_cnt = saved_cnt;
> 
> I wonder if it's easier to re-introduce the flush that was used before
> vhost kthread to avoid the tricks here. We can have flush ops for
> example.
> 
> Thanks

Nah we do not need ops, __vhost_worker_flush is just an internal
function. Refactor it so we can call the part without the check.

-- 
MST