From mboxrd@z Thu Jan  1 00:00:00 1970
From: Samuel Thibault <samuel.thibault@eu.citrix.com>
Subject: Re: barriers before {req/rsp}_cons = cons?
Date: Mon, 21 Jul 2008 11:08:49 +0100
Message-ID: <20080721100849.GE4501@implementation.uk.xensource.com>
References: <20080718193304.GI4576@implementation>
	<C4AA0746.245DB%keir.fraser@eu.citrix.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Transfer-Encoding: quoted-printable
Return-path: <xen-devel-bounces@lists.xensource.com>
Content-Disposition: inline
In-Reply-To: <C4AA0746.245DB%keir.fraser@eu.citrix.com>
List-Unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xensource.com>
List-Help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-Subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
Sender: xen-devel-bounces@lists.xensource.com
Errors-To: xen-devel-bounces@lists.xensource.com
To: Keir Fraser <keir.fraser@eu.citrix.com>
Cc: xen-devel@lists.xensource.com
List-Id: xen-devel@lists.xenproject.org

Keir Fraser, le Mon 21 Jul 2008 09:28:38 +0100, a =E9crit :
> On 18/7/08 20:33, "Samuel Thibault" <samuel.thibault@eu.citrix.com> wro=
te:
>=20
> >> Could you describe the race you believe is made possible by the abse=
nce of
> >> the barrier?
> >=20
> > It is very unlikely, but the write into req_cons could happen before
> > actually doing the memcpy, and so another processor could try to reus=
e
> > the same request slot.
>=20
> req_cons is not shared with the frontend driver,

Aow, right, I had forgotten that on the frontend side we are using the
rsp index, so that there is no more in-flight requests than ring slots.

Samuel