Re: [PATCH 2/2] xen/netback: cleanup init and deinit code

[Paul Durrant]

On Mon, 14 Oct 2019 at 10:09, Juergen Gross <jgross@xxxxxxxx> wrote:
>
> Do some cleanup of the netback init and deinit code:
>
> - add an omnipotent queue deinit function usable from
>   xenvif_disconnect_data() and the error path of xenvif_connect_data()
> - only install the irq handlers after initializing all relevant items
>   (especially the kthreads related to the queue)
> - there is no need to use get_task_struct() after creating a kthread
>   and using put_task_struct() again after having stopped it.
> - use kthread_run() instead of kthread_create() to spare the call of
>   wake_up_process().

I guess the reason it was done that way was to ensure that queue->task
and queue->dealloc_task would be set before the relevant threads
executed, but I don't see anywhere relying on this so I guess change
is safe. The rest of it looks fine.

>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>

Reviewed-by: Paul Durrant <paul@xxxxxxx>

> ---
>  drivers/net/xen-netback/interface.c | 114 +++++++++++++++++-------------------
>  1 file changed, 54 insertions(+), 60 deletions(-)
>
> diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
> index 103ed00775eb..68dd7bb07ca6 100644
> --- a/drivers/net/xen-netback/interface.c
> +++ b/drivers/net/xen-netback/interface.c
> @@ -626,6 +626,38 @@ int xenvif_connect_ctrl(struct xenvif *vif, grant_ref_t ring_ref,
>         return err;
>  }
>
> +static void xenvif_disconnect_queue(struct xenvif_queue *queue)
> +{
> +       if (queue->tx_irq) {
> +               unbind_from_irqhandler(queue->tx_irq, queue);
> +               if (queue->tx_irq == queue->rx_irq)
> +                       queue->rx_irq = 0;
> +               queue->tx_irq = 0;
> +       }
> +
> +       if (queue->rx_irq) {
> +               unbind_from_irqhandler(queue->rx_irq, queue);
> +               queue->rx_irq = 0;
> +       }
> +
> +       if (queue->task) {
> +               kthread_stop(queue->task);
> +               queue->task = NULL;
> +       }
> +
> +       if (queue->dealloc_task) {
> +               kthread_stop(queue->dealloc_task);
> +               queue->dealloc_task = NULL;
> +       }
> +
> +       if (queue->napi.poll) {
> +               netif_napi_del(&queue->napi);
> +               queue->napi.poll = NULL;
> +       }
> +
> +       xenvif_unmap_frontend_data_rings(queue);
> +}
> +
>  int xenvif_connect_data(struct xenvif_queue *queue,
>                         unsigned long tx_ring_ref,
>                         unsigned long rx_ring_ref,
> @@ -651,13 +683,27 @@ int xenvif_connect_data(struct xenvif_queue *queue,
>         netif_napi_add(queue->vif->dev, &queue->napi, xenvif_poll,
>                         XENVIF_NAPI_WEIGHT);
>
> +       queue->stalled = true;
> +
> +       task = kthread_run(xenvif_kthread_guest_rx, queue,
> +                          "%s-guest-rx", queue->name);
> +       if (IS_ERR(task))
> +               goto kthread_err;
> +       queue->task = task;
> +
> +       task = kthread_run(xenvif_dealloc_kthread, queue,
> +                          "%s-dealloc", queue->name);
> +       if (IS_ERR(task))
> +               goto kthread_err;
> +       queue->dealloc_task = task;
> +
>         if (tx_evtchn == rx_evtchn) {
>                 /* feature-split-event-channels == 0 */
>                 err = bind_interdomain_evtchn_to_irqhandler(
>                         queue->vif->domid, tx_evtchn, xenvif_interrupt, 0,
>                         queue->name, queue);
>                 if (err < 0)
> -                       goto err_unmap;
> +                       goto err;
>                 queue->tx_irq = queue->rx_irq = err;
>                 disable_irq(queue->tx_irq);
>         } else {
> @@ -668,7 +714,7 @@ int xenvif_connect_data(struct xenvif_queue *queue,
>                         queue->vif->domid, tx_evtchn, xenvif_tx_interrupt, 0,
>                         queue->tx_irq_name, queue);
>                 if (err < 0)
> -                       goto err_unmap;
> +                       goto err;
>                 queue->tx_irq = err;
>                 disable_irq(queue->tx_irq);
>
> @@ -678,47 +724,18 @@ int xenvif_connect_data(struct xenvif_queue *queue,
>                         queue->vif->domid, rx_evtchn, xenvif_rx_interrupt, 0,
>                         queue->rx_irq_name, queue);
>                 if (err < 0)
> -                       goto err_tx_unbind;
> +                       goto err;
>                 queue->rx_irq = err;
>                 disable_irq(queue->rx_irq);
>         }
>
> -       queue->stalled = true;
> -
> -       task = kthread_create(xenvif_kthread_guest_rx,
> -                             (void *)queue, "%s-guest-rx", queue->name);
> -       if (IS_ERR(task)) {
> -               pr_warn("Could not allocate kthread for %s\n", queue->name);
> -               err = PTR_ERR(task);
> -               goto err_rx_unbind;
> -       }
> -       queue->task = task;
> -       get_task_struct(task);
> -
> -       task = kthread_create(xenvif_dealloc_kthread,
> -                             (void *)queue, "%s-dealloc", queue->name);
> -       if (IS_ERR(task)) {
> -               pr_warn("Could not allocate kthread for %s\n", queue->name);
> -               err = PTR_ERR(task);
> -               goto err_rx_unbind;
> -       }
> -       queue->dealloc_task = task;
> -
> -       wake_up_process(queue->task);
> -       wake_up_process(queue->dealloc_task);
> -
>         return 0;
>
> -err_rx_unbind:
> -       unbind_from_irqhandler(queue->rx_irq, queue);
> -       queue->rx_irq = 0;
> -err_tx_unbind:
> -       unbind_from_irqhandler(queue->tx_irq, queue);
> -       queue->tx_irq = 0;
> -err_unmap:
> -       xenvif_unmap_frontend_data_rings(queue);
> -       netif_napi_del(&queue->napi);
> +kthread_err:
> +       pr_warn("Could not allocate kthread for %s\n", queue->name);
> +       err = PTR_ERR(task);
>  err:
> +       xenvif_disconnect_queue(queue);
>         return err;
>  }
>
> @@ -746,30 +763,7 @@ void xenvif_disconnect_data(struct xenvif *vif)
>         for (queue_index = 0; queue_index < num_queues; ++queue_index) {
>                 queue = &vif->queues[queue_index];
>
> -               netif_napi_del(&queue->napi);
> -
> -               if (queue->task) {
> -                       kthread_stop(queue->task);
> -                       put_task_struct(queue->task);
> -                       queue->task = NULL;
> -               }
> -
> -               if (queue->dealloc_task) {
> -                       kthread_stop(queue->dealloc_task);
> -                       queue->dealloc_task = NULL;
> -               }
> -
> -               if (queue->tx_irq) {
> -                       if (queue->tx_irq == queue->rx_irq)
> -                               unbind_from_irqhandler(queue->tx_irq, queue);
> -                       else {
> -                               unbind_from_irqhandler(queue->tx_irq, queue);
> -                               unbind_from_irqhandler(queue->rx_irq, queue);
> -                       }
> -                       queue->tx_irq = 0;
> -               }
> -
> -               xenvif_unmap_frontend_data_rings(queue);
> +               xenvif_disconnect_queue(queue);
>         }
>
>         xenvif_mcast_addr_list_free(vif);
> --
> 2.16.4
>