Re: [Xen-devel] [PATCH v3 06/18] xen/pvcalls: handle commands from the frontend

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

> +
>  static void pvcalls_back_work(struct work_struct *work)
>  {
> +     struct pvcalls_fedata *priv = container_of(work,
> +             struct pvcalls_fedata, register_work);
> +     int notify, notify_all = 0, more = 1;
> +     struct xen_pvcalls_request req;
> +     struct xenbus_device *dev = priv->dev;
> +
> +     while (more) {
> +             while (RING_HAS_UNCONSUMED_REQUESTS(&priv->ring)) {
> +                     RING_COPY_REQUEST(&priv->ring,
> +                                       priv->ring.req_cons++,
> +                                       &req);
> +
> +                     if (!pvcalls_back_handle_cmd(dev, &req)) {
> +                             RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(
> +                                     &priv->ring, notify);
> +                             notify_all += notify;
> +                     }
> +             }
> +
> +             if (notify_all)
> +                     notify_remote_via_irq(priv->irq);
> +
> +             RING_FINAL_CHECK_FOR_REQUESTS(&priv->ring, more);
> +     }
>  }
>  
>  static irqreturn_t pvcalls_back_event(int irq, void *dev_id)
>  {
> +     struct xenbus_device *dev = dev_id;
> +     struct pvcalls_fedata *priv = NULL;
> +
> +     if (dev == NULL)
> +             return IRQ_HANDLED;
> +
> +     priv = dev_get_drvdata(&dev->dev);
> +     if (priv == NULL)
> +             return IRQ_HANDLED;
> +
> +     /*
> +      * TODO: a small theoretical race exists if we try to queue work
> +      * after pvcalls_back_work checked for final requests and before
> +      * it returns. The queuing will fail, and pvcalls_back_work
> +      * won't do the work because it is about to return. In that
> +      * case, we lose the notification.
> +      */
> +     queue_work(priv->wq, &priv->register_work);

Would queuing delayed work (if queue_work() failed) help? And canceling
it on next invocation of pvcalls_back_event()?

-boris

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