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 <l...@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
