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: Fri, 18 Jul 2008 20:34:45 +0100
Message-ID: <20080718193445.GJ4576@implementation>
References: <20080718185240.GH4576@implementation>
	<C4A6AE11.1B457%keir.fraser@eu.citrix.com>
	<20080718193304.GI4576@implementation>
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Samuel Thibault, le Fri 18 Jul 2008 20:33:04 +0100, a =E9crit :
> Keir Fraser, le Fri 18 Jul 2008 20:31:13 +0100, a =E9crit :
> > > cons =3D netif->tx.req_cons;
> > > rmb(); /* Ensure that we see the request before we copy it. */
> > > memcpy(&txreq, RING_GET_REQUEST(&netif->tx, i), sizeof(txreq));
> > > some checks
> > > netif->tx.req_cons =3D ++cons;
> >=20
> > Could you describe the race you believe is made possible by the absen=
ce of
> > the barrier?
>=20
> It is very unlikely, but the write into req_cons could happen before
> actually doing the memcpy,

(more precisely, the read, of course).

> and so another processor could try to reuse
> the same request slot.

Samuel