From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751982Ab2AVLqN (ORCPT ); Sun, 22 Jan 2012 06:46:13 -0500 Received: from mx1.redhat.com ([209.132.183.28]:29508 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751926Ab2AVLpq (ORCPT ); Sun, 22 Jan 2012 06:45:46 -0500 Date: Sun, 22 Jan 2012 13:47:57 +0200 From: "Michael S. Tsirkin" To: Jason Wang Cc: rusty@rustcorp.com.au, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH 2/2] virtio: correct the memory barrier in virtqueue_kick_prepare() Message-ID: <20120122114757.GD27222@redhat.com> References: <20120120081658.50747.10625.stgit@amd-6168-8-1.englab.nay.redhat.com> <20120120081708.50747.60241.stgit@amd-6168-8-1.englab.nay.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120120081708.50747.60241.stgit@amd-6168-8-1.englab.nay.redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 20, 2012 at 04:17:08PM +0800, Jason Wang wrote: > Use virtio_mb() to make sure the available index to be exposed before > checking the the avail event. Otherwise we may get stale value of > avail event in guest and never kick the host after. > > Signed-off-by: Jason Wang Good catch. Note: this fixes a bug introduced by ee7cd8981e15bcb365fc762afe3fc47b8242f630. Acked-by: Michael S. Tsirkin > --- > drivers/virtio/virtio_ring.c | 6 +++--- > 1 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index 78428a8..07d9360 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -308,9 +308,9 @@ bool virtqueue_kick_prepare(struct virtqueue *_vq) > bool needs_kick; > > START_USE(vq); > - /* Descriptors and available array need to be set before we expose the > - * new available array entries. */ > - virtio_wmb(vq); > + /* We need expose available array entries before checking avail Nit: We need expose -> Need to expose > + * event. */ > + virtio_mb(vq); > > old = vq->vring.avail->idx - vq->num_added; > new = vq->vring.avail->idx;