Re: [PATCH v8 2/8] vhost: Reintroduce vhost_worker to support kthread

[Stefano Garzarella]

On Fri, Mar 28, 2025 at 06:02:46PM +0800, Cindy Lu wrote:
> Add the previously removed function vhost_worker() back
> to support the kthread and rename it to vhost_run_work_kthread_list.
>
> The old function vhost_worker was change to support task in

nit: s/change/changed

> commit 6e890c5d5021 ("vhost: use vhost_tasks for worker threads")
> change to xarray in
> commit 1cdaafa1b8b4 ("vhost: replace single worker pointer with xarray")
>
> Signed-off-by: Cindy Lu <lulu@xxxxxxxxxx>
> ---
> drivers/vhost/vhost.c | 38 ++++++++++++++++++++++++++++++++++++++
> 1 file changed, 38 insertions(+)

I tried to build commit by commit (mainly to check bisection), and I
discovered that nowdays unused functions produce an error (yes, we can 
mute it for example by setting CONFIG_WERROR to N), but I wanted to 
point it out:

../drivers/vhost/vhost.c:391:12: error: ‘vhost_run_work_kthread_list’ defined but not used [-Werror=unused-function]
  391 | static int vhost_run_work_kthread_list(void *data)

So not sure if we need to squash this where we use it.

Same issue also for the next 2 patches.

Thanks,
Stefano

> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 250dc43f1786..9500e85b42ce 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -388,6 +388,44 @@ 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;
> --
> 2.45.0