Subject: Re: [PATCH v2 6/8] vdpa_sim: use kthread worker

From: Simon Horman <[email-masked]>
Date: Thu, 2 Mar 2023 16:30:04 +0100

On Thu, Mar 02, 2023 at 12:34:19PM +0100, Stefano Garzarella wrote:
> Let's use our own kthread to run device jobs.
> This allows us more flexibility, especially we can attach the kthread
> to the user address space when vDPA uses user's VA.
> 
> Signed-off-by: Stefano Garzarella <[email-masked]>
> ---
>  drivers/vdpa/vdpa_sim/vdpa_sim.h |  3 ++-
>  drivers/vdpa/vdpa_sim/vdpa_sim.c | 17 ++++++++++++-----
>  2 files changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.h b/drivers/vdpa/vdpa_sim/vdpa_sim.h
> index acee20faaf6a..ce83f9130a5d 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.h
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.h
> @@ -57,7 +57,8 @@ struct vdpasim_dev_attr {
>  struct vdpasim {
>  	struct vdpa_device vdpa;
>  	struct vdpasim_virtqueue *vqs;
> -	struct work_struct work;
> +	struct kthread_worker *worker;
> +	struct kthread_work work;
>  	struct vdpasim_dev_attr dev_attr;
>  	/* spinlock to synchronize virtqueue state */
>  	spinlock_t lock;
> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> index a6ee830efc38..6feb29726c2a 100644
> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
> @@ -11,8 +11,8 @@
>  #include <linux/module.h>
>  #include <linux/device.h>
>  #include <linux/kernel.h>
> +#include <linux/kthread.h>
>  #include <linux/slab.h>
> -#include <linux/sched.h>
>  #include <linux/dma-map-ops.h>
>  #include <linux/vringh.h>
>  #include <linux/vdpa.h>
> @@ -116,7 +116,7 @@ static void vdpasim_do_reset(struct vdpasim *vdpasim)
>  static const struct vdpa_config_ops vdpasim_config_ops;
>  static const struct vdpa_config_ops vdpasim_batch_config_ops;
>  
> -static void vdpasim_work_fn(struct work_struct *work)
> +static void vdpasim_work_fn(struct kthread_work *work)
>  {
>  	struct vdpasim *vdpasim = container_of(work, struct vdpasim, work);
>  
> @@ -159,7 +159,13 @@ struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr,
>  
>  	vdpasim = vdpa_to_sim(vdpa);
>  	vdpasim->dev_attr = *dev_attr;
> -	INIT_WORK(&vdpasim->work, vdpasim_work_fn);
> +
> +	kthread_init_work(&vdpasim->work, vdpasim_work_fn);
> +	vdpasim->worker = kthread_create_worker(0, "vDPA sim worker: %s",
> +						dev_attr->name);
> +	if (IS_ERR(vdpasim->worker))
> +		goto err_iommu;

Branching to err_iommu will result in a call to put_device(dev)...

> +
>  	spin_lock_init(&vdpasim->lock);
>  	spin_lock_init(&vdpasim->iommu_lock);

... but dev is not initialised until the line following this hunk,
which is:

	dev = &vdpasim->vdpa.dev;

In order to avoid leaking dev I _think_ the correct approach
is to move the initialisation of dev above the branch to
err_iommu, perhaps above the call to kthread_init_work()
is a good place.

This does move the assignment outside the locks above.
But I _think_ that is ok.

> @@ -212,7 +218,7 @@ EXPORT_SYMBOL_GPL(vdpasim_create);
>  
>  void vdpasim_schedule_work(struct vdpasim *vdpasim)
>  {
> -	schedule_work(&vdpasim->work);
> +	kthread_queue_work(vdpasim->worker, &vdpasim->work);
>  }
>  EXPORT_SYMBOL_GPL(vdpasim_schedule_work);
>  
> @@ -612,7 +618,8 @@ static void vdpasim_free(struct vdpa_device *vdpa)
>  	struct vdpasim *vdpasim = vdpa_to_sim(vdpa);
>  	int i;
>  
> -	cancel_work_sync(&vdpasim->work);
> +	kthread_cancel_work_sync(&vdpasim->work);
> +	kthread_destroy_worker(vdpasim->worker);
>  
>  	for (i = 0; i < vdpasim->dev_attr.nvqs; i++) {
>  		vringh_kiov_cleanup(&vdpasim->vqs[i].out_iov);
> -- 
> 2.39.2
>