From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1758269AbeDXOUx (ORCPT <rfc822;w@1wt.eu>);
        Tue, 24 Apr 2018 10:20:53 -0400
Received: from mx2.suse.de ([195.135.220.15]:56796 "EHLO mx2.suse.de"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1758088AbeDXOUv (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 24 Apr 2018 10:20:51 -0400
Date: Tue, 24 Apr 2018 16:20:50 +0200
Message-ID: <s5ho9i8sn25.wl-tiwai@suse.de>
From: Takashi Iwai <tiwai@suse.de>
To: "Oleksandr Andrushchenko" <andr2000@gmail.com>
Cc: <alsa-devel@alsa-project.org>, <xen-devel@lists.xenproject.org>,
        <boris.ostrovsky@oracle.com>, <konrad.wilk@oracle.com>,
        <perex@perex.cz>, "Juergen Gross" <jgross@suse.com>,
        <linux-kernel@vger.kernel.org>,
        "Oleksandr Andrushchenko" <oleksandr_andrushchenko@epam.com>
Subject: Re: [PATCH v2 3/5] ALSA: xen-front: Implement Xen event channel handling
In-Reply-To: <20180416062453.24743-4-andr2000@gmail.com>
References: <20180416062453.24743-1-andr2000@gmail.com>
        <20180416062453.24743-4-andr2000@gmail.com>
User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI/1.14.6 (Maruoka)
 FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 Emacs/25.3
 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO)
MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka")
Content-Type: text/plain; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

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