Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755491AbYHSBKk (ORCPT ); Mon, 18 Aug 2008 21:10:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751772AbYHSBKc (ORCPT ); Mon, 18 Aug 2008 21:10:32 -0400 Received: from e4.ny.us.ibm.com ([32.97.182.144]:53795 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751049AbYHSBKb (ORCPT ); Mon, 18 Aug 2008 21:10:31 -0400 Message-ID: <48AA1D5E.5050405@us.ibm.com> Date: Mon, 18 Aug 2008 20:09:50 -0500 From: Anthony Liguori User-Agent: Thunderbird 2.0.0.16 (X11/20080723) MIME-Version: 1.0 To: Linus Torvalds CC: linux-kernel@vger.kernel.org, Rusty Russell , Avi Kivity , virtualization@lists.linux-foundation.org, Chris Wright Subject: Re: [PATCH] virtio_balloon: fix towards_target when deflating balloon References: <1219097731-1224-1-git-send-email-aliguori@us.ibm.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2022 Lines: 59 Linus Torvalds wrote: > What's wrong with just doing > > return (s64)v - vb->num_pages; > > instead? > Nothing. It works just fine. However, I implemented it more verbosely because this is the second time we've "fixed" this problem. See commit bdc1681cdf1ab6a65fa935a2b3f8fc63b20c54ea Author: Rusty Russell Date: Mon Mar 17 22:58:15 2008 -0500 virtio: handle > 2 billion page balloon targets So I thought I'd rely a little less on the subtleties of promotion and make things a bit more clear. However, I don't feel that strongly about it so here you go. Both v and vb->num_pages are u32 and unsigned int respectively. If v is less than vb->num_pages (and it is, when deflating the balloon), the result is a very large 32-bit number. Since we're returning a s64, instead of getting the small negative number we desire, we get a very large positive number. This patch explicitly casts v to a s64 in which will cause the whole expression to be promoted resulting in the proper results. Rusty: please push this for 2.6.27-rc4. It's probably appropriate for the stable tree too as it will cause an unexpected OOM when ballooning. Signed-off-by: Anthony Liguori diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index bfef604..62eab43 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -158,7 +158,7 @@ static inline s64 towards_target(struct virtio_balloon *vb) vb->vdev->config->get(vb->vdev, offsetof(struct virtio_balloon_config, num_pages), &v, sizeof(v)); - return v - vb->num_pages; + return (s64)v - vb->num_pages; } static void update_balloon_size(struct virtio_balloon *vb) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/