linux-kernel - Re: [RFC V1 10/13] vdpa_sim: flush workers on suspend

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Date: Tue, 16 Jan 2024 19:57:56 +0100
From: Eugenio Perez Martin <eperezma@...hat.com>
To: Steve Sistare <steven.sistare@...cle.com>
Cc: virtualization@...ts.linux-foundation.org, linux-kernel@...r.kernel.org, 
	"Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>, Si-Wei Liu <si-wei.liu@...cle.com>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Dragos Tatulea <dtatulea@...dia.com>, 
	Eli Cohen <elic@...dia.com>, Xie Yongji <xieyongji@...edance.com>
Subject: Re: [RFC V1 10/13] vdpa_sim: flush workers on suspend

On Wed, Jan 10, 2024 at 9:40 PM Steve Sistare <steven.sistare@...cle.com> wrote:
>
> To pass ownership of a live vdpa device to a new process, the user
> suspends the device, calls VHOST_NEW_OWNER to change the mm, and calls
> VHOST_IOTLB_REMAP to change the user virtual addresses to match the new
> mm.  Flush workers in suspend to guarantee that no worker sees the new
> mm and old VA in between.
>

The worker should already be stopped by the end of the suspend ioctl,
so maybe we can consider this a fix?

> Signed-off-by: Steve Sistare <steven.sistare@...cle.com>
> ---
>  drivers/vdpa/vdpa_sim/vdpa_sim.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> index 6304cb0b4770..8734834983cb 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> @@ -74,6 +74,17 @@ static void vdpasim_worker_change_mm_sync(struct vdpasim *vdpasim,
>         kthread_flush_work(work);
>  }
>
> +static void flush_work_fn(struct kthread_work *work) {}
> +
> +static void vdpasim_flush_work(struct vdpasim *vdpasim)
> +{
> +       struct kthread_work work;
> +
> +       kthread_init_work(&work, flush_work_fn);
> +       kthread_queue_work(vdpasim->worker, &work);
> +       kthread_flush_work(&work);

Wouldn't it be better to cancel the work with kthread_cancel_work_sync here?

> +}
> +
>  static struct vdpasim *vdpa_to_sim(struct vdpa_device *vdpa)
>  {
>         return container_of(vdpa, struct vdpasim, vdpa);
> @@ -512,6 +523,8 @@ static int vdpasim_suspend(struct vdpa_device *vdpa)
>         vdpasim->running = false;
>         mutex_unlock(&vdpasim->mutex);
>
> +       vdpasim_flush_work(vdpasim);
> +
>         return 0;
>  }
>
> --
> 2.39.3
>