From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46884) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XrfnH-0006qL-Pc for qemu-devel@nongnu.org; Thu, 20 Nov 2014 23:26:09 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XrfnC-0006t6-HC for qemu-devel@nongnu.org; Thu, 20 Nov 2014 23:26:03 -0500 Received: from indium.canonical.com ([91.189.90.7]:51312) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XrfnC-0006rJ-8h for qemu-devel@nongnu.org; Thu, 20 Nov 2014 23:25:58 -0500 Received: from loganberry.canonical.com ([91.189.90.37]) by indium.canonical.com with esmtp (Exim 4.76 #1 (Debian)) id 1XrfnB-0001cz-FS for ; Fri, 21 Nov 2014 04:25:57 +0000 Received: from loganberry.canonical.com (localhost [127.0.0.1]) by loganberry.canonical.com (Postfix) with ESMTP id 737102E808D for ; Fri, 21 Nov 2014 04:25:57 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Date: Fri, 21 Nov 2014 04:17:48 -0000 From: Serge Hallyn <1368815@bugs.launchpad.net> Sender: bounces@canonical.com References: <20140912145823.442.8812.malonedeb@gac.canonical.com> Message-Id: <20141121041748.28347.27599.malone@wampee.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 Hi Tony, yes, I've uploaded a proposed fix for trusty-proposed earlier today. It should be available for testing as soon as it is accepted. -- = 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: Fix Released Status in =E2=80=9Cqemu=E2=80=9D source package in Trusty: Triaged Status in =E2=80=9Cqemu=E2=80=9D source package in Utopic: Triaged Status in =E2=80=9Cqemu=E2=80=9D source package in Vivid: Fix Released Bug description: =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D Impact: occasional qcow2 corruption Test case: see the qemu-img command below Regression potential: this cherrypicks a patch from upstream to a not-ins= ignificantly older qemu source tree. While the cherrypick seems sane, it's= possible that there are subtle interactions with the other delta. I'd rea= lly like for a full qa-regression-test qemu testcase to be run against this= package. =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D -- 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