From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53187) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xh5Mo-00085J-1I for qemu-devel@nongnu.org; Wed, 22 Oct 2014 19:31:02 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Xh5Mj-0006Nx-6J for qemu-devel@nongnu.org; Wed, 22 Oct 2014 19:30:57 -0400 Received: from indium.canonical.com ([91.189.90.7]:42862) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xh5Mj-0006Nt-13 for qemu-devel@nongnu.org; Wed, 22 Oct 2014 19:30:53 -0400 Received: from loganberry.canonical.com ([91.189.90.37]) by indium.canonical.com with esmtp (Exim 4.76 #1 (Debian)) id 1Xh5Mi-0003hM-46 for ; Wed, 22 Oct 2014 23:30:52 +0000 Received: from loganberry.canonical.com (localhost [127.0.0.1]) by loganberry.canonical.com (Postfix) with ESMTP id 118FC2E80CA for ; Wed, 22 Oct 2014 23:30:52 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Date: Wed, 22 Oct 2014 23:21:02 -0000 From: Tony Breeds Sender: bounces@canonical.com References: <20140912145823.442.8812.malonedeb@gac.canonical.com> Message-Id: <20141022232102.2046.55224.malone@gac.canonical.com> Errors-To: bounces@canonical.com Subject: [Qemu-devel] [Bug 1368815] Re: qemu-img convert intermittently corrupts output images Reply-To: Bug 1368815 <1368815@bugs.launchpad.net> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org FWIW the following 2 commits in qemu master resolve the issue for qemu- img. http://git.qemu.org/?p=3Dqemu.git;a=3Dcommit;h=3D38c4d0aea3e1264c86e282d9= 9560330adf2b6e25 http://git.qemu.org/?p=3Dqemu.git;a=3Dcommit;h=3D7c15903789953ead14a41788= 2657d52dc0c19a24 If possible they should be back ported to trusty and utopic. You'll also need something like: http://git.qemu.org/?p=3Dqemu.git;a=3Dcommit;h=3D4f11aa8a40351b28c0e67c7276= e0003b38cc46ac before my 2 patches. -- = You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1368815 Title: qemu-img convert intermittently corrupts output images Status in OpenStack Compute (Nova): In Progress Status in QEMU: In Progress Status in =E2=80=9Cqemu=E2=80=9D package in Ubuntu: Triaged Status in =E2=80=9Cqemu=E2=80=9D source package in Trusty: Triaged Bug description: -- Found in releases qemu-2.0.0, qemu-2.0.2, qemu-2.1.0. Tested on Ubuntu 14.04 using Ext4 filesystems. The command qemu-img convert -O raw inputimage.qcow2 outputimage.raw intermittently creates corrupted output images, when the input image is not yet fully synchronized to disk. While the issue has actually been discovered in operation of of OpenStack nova, it can be reproduced "easily" on command line using cat $SRC_PATH > $TMP_PATH && $QEMU_IMG_PATH convert -O raw $TMP_PATH $DST_PATH && cksum $DST_PATH on filesystems exposing this behavior. (The difficult part of this exercise is to prepare a filesystem to reliably trigger this race. On my test machine some filesystems are affected while other aren't, and unfortunately I haven't found the relevant difference between them, yet. Possible it's timing issues completely out of userspace control ...) The root cause, however, is the same as in http://lists.gnu.org/archive/html/coreutils/2011-04/msg00069.html and it can be solved the same way as suggested in http://lists.gnu.org/archive/html/coreutils/2011-04/msg00102.html In qemu, file block/raw-posix.c use the FIEMAP_FLAG_SYNC, i.e change f.fm.fm_flags =3D 0; to f.fm.fm_flags =3D FIEMAP_FLAG_SYNC; As discussed in the thread mentioned above, retrieving a page cache coherent map of file extents is possible only after fsync on that file. See also https://bugs.launchpad.net/nova/+bug/1350766 In that bug report filed against nova, fsync had been suggested to be performed by the framework invoking qemu-img. However, as the choice of fiemap -- implying this otherwise unneeded fsync of a temporary file -- is not made by the caller but by qemu-img, I agree with the nova bug reviewer's objection to put it into nova. The fsync should instead be triggered by qemu-img utilizing the FIEMAP_FLAG_SYNC, specifically intended for that purpose. To manage notifications about this bug go to: https://bugs.launchpad.net/nova/+bug/1368815/+subscriptions