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

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Date:   Mon, 12 Jun 2017 18:03:33 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xen.org
Cc:     linux-kernel@...r.kernel.org, jgross@...e.com,
        Stefano Stabellini <stefano@...reto.com>
Subject: Re: [PATCH v3 06/18] xen/pvcalls: handle commands from the frontend


> +
>  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