From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx157.postini.com [74.125.245.157]) by kanga.kvack.org (Postfix) with SMTP id 204DE6B0034 for ; Thu, 6 Jun 2013 10:19:55 -0400 (EDT) Date: Thu, 6 Jun 2013 10:19:52 -0400 From: Luiz Capitulino Subject: Re: [PATCH v2] virtio_balloon: leak_balloon(): only tell host if we got pages deflated Message-ID: <20130606101952.5f2c7988@redhat.com> In-Reply-To: <20130606141357.GD30387@optiplex.redhat.com> References: <20130605211837.1fc9b902@redhat.com> <20130606141357.GD30387@optiplex.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Rafael Aquini Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org On Thu, 6 Jun 2013 11:13:58 -0300 Rafael Aquini wrote: > On Wed, Jun 05, 2013 at 09:18:37PM -0400, Luiz Capitulino wrote: > > The balloon_page_dequeue() function can return NULL. If it does for > > the first page being freed, then leak_balloon() will create a > > scatter list with len=0. Which in turn seems to generate an invalid > > virtio request. > > > > I didn't get this in practice, I found it by code review. On the other > > hand, such an invalid virtio request will cause errors in QEMU and > > fill_balloon() also performs the same check implemented by this commit. > > > > Signed-off-by: Luiz Capitulino > > Acked-by: Rafael Aquini > > --- > > > > o v2 > > > > - Improve changelog > > > > drivers/virtio/virtio_balloon.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > > index bd3ae32..71af7b5 100644 > > --- a/drivers/virtio/virtio_balloon.c > > +++ b/drivers/virtio/virtio_balloon.c > > @@ -191,7 +191,8 @@ static void leak_balloon(struct virtio_balloon *vb, size_t num) > > * virtio_has_feature(vdev, VIRTIO_BALLOON_F_MUST_TELL_HOST); > > * is true, we *have* to do it in this order > > */ > > - tell_host(vb, vb->deflate_vq); > > Luiz, sorry for not being clearer before. I was referring to add a commentary on > code, to explain in short words why we should not get rid of this check point. Oh. > > + if (vb->num_pfns != 0) > > + tell_host(vb, vb->deflate_vq); > > mutex_unlock(&vb->balloon_lock); > > If the comment is regarded as unnecessary, then just ignore my suggestion. I'm > OK with your patch. :) IMHO, the code is clear enough. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org