linux-kernel - Re: [PATCH v2 3/5] ALSA: xen-front: Implement Xen event channel handling

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Date:   Tue, 24 Apr 2018 16:20:50 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     "Oleksandr Andrushchenko" <andr2000@...il.com>
Cc:     <alsa-devel@...a-project.org>, <xen-devel@...ts.xenproject.org>,
        <boris.ostrovsky@...cle.com>, <konrad.wilk@...cle.com>,
        <perex@...ex.cz>, "Juergen Gross" <jgross@...e.com>,
        <linux-kernel@...r.kernel.org>,
        "Oleksandr Andrushchenko" <oleksandr_andrushchenko@...m.com>
Subject: Re: [PATCH v2 3/5] ALSA: xen-front: Implement Xen event channel handling

On Mon, 16 Apr 2018 08:24:51 +0200,
Oleksandr Andrushchenko wrote:
> +static irqreturn_t evtchnl_interrupt_req(int irq, void *dev_id)
> +{
> +	struct xen_snd_front_evtchnl *channel = dev_id;
> +	struct xen_snd_front_info *front_info = channel->front_info;
> +	struct xensnd_resp *resp;
> +	RING_IDX i, rp;
> +	unsigned long flags;
> +
> +	if (unlikely(channel->state != EVTCHNL_STATE_CONNECTED))
> +		return IRQ_HANDLED;
> +
> +	spin_lock_irqsave(&front_info->io_lock, flags);
> +
> +again:
> +	rp = channel->u.req.ring.sring->rsp_prod;
> +	/* ensure we see queued responses up to rp */
> +	rmb();
> +
> +	for (i = channel->u.req.ring.rsp_cons; i != rp; i++) {

I'm not familiar with Xen stuff in general, but through a quick
glance, this kind of code worries me a bit.

If channel->u.req.ring.rsp_cons has a bogus number, this may lead to a
very long loop, no?  Better to have a sanity check of the ring buffer
size.

> +static irqreturn_t evtchnl_interrupt_evt(int irq, void *dev_id)
> +{
> +	struct xen_snd_front_evtchnl *channel = dev_id;
> +	struct xen_snd_front_info *front_info = channel->front_info;
> +	struct xensnd_event_page *page = channel->u.evt.page;
> +	u32 cons, prod;
> +	unsigned long flags;
> +
> +	if (unlikely(channel->state != EVTCHNL_STATE_CONNECTED))
> +		return IRQ_HANDLED;
> +
> +	spin_lock_irqsave(&front_info->io_lock, flags);
> +
> +	prod = page->in_prod;
> +	/* ensure we see ring contents up to prod */
> +	virt_rmb();
> +	if (prod == page->in_cons)
> +		goto out;
> +
> +	for (cons = page->in_cons; cons != prod; cons++) {

Ditto.


thanks,

Takashi