From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C0FE2C3A5A1 for ; Thu, 22 Aug 2019 15:41:25 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9610E233FD for ; Thu, 22 Aug 2019 15:41:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9610E233FD Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:44550 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i0pDI-0002IY-PL for qemu-devel@archiver.kernel.org; Thu, 22 Aug 2019 11:41:24 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:52875) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i0pCO-0001mU-F5 for qemu-devel@nongnu.org; Thu, 22 Aug 2019 11:40:29 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i0pCN-000312-Aw for qemu-devel@nongnu.org; Thu, 22 Aug 2019 11:40:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53066) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i0pCK-0002z3-CS; Thu, 22 Aug 2019 11:40:24 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 85F09796E7; Thu, 22 Aug 2019 15:40:23 +0000 (UTC) Received: from dresden.str.redhat.com (unknown [10.40.205.206]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 662471001B17; Thu, 22 Aug 2019 15:40:18 +0000 (UTC) From: Max Reitz To: =?UTF-8?B?THVrw6HFoSBEb2t0b3I=?= , QEMU Developers , qemu-block@nongnu.org, Anton Nefedov , Andrew Jones , Paolo Bonzini , Stefan Hajnoczi References: <84dd318a-28d4-b2f3-b03b-d870a5f618d5@redhat.com> <80341376-ecbd-cbf4-8800-022fdd65c04d@redhat.com> <8e42ea8e-0629-2645-d14d-785722df6466@redhat.com> Openpgp: preference=signencrypt Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: <9b09731a-1769-2cbe-4b6f-3d7787f74ebc@redhat.com> Date: Thu, 22 Aug 2019 17:40:17 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <8e42ea8e-0629-2645-d14d-785722df6466@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Thu, 22 Aug 2019 15:40:23 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] Broken aarch64 by qcow2: skip writing zero buffers to empty COW areas [v2] X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 22.08.19 17:25, Max Reitz wrote: > On 22.08.19 14:09, Max Reitz wrote: >> (CC-ing Paolo because of the XFS connection, and Stefan because why no= t.) >> >> On 22.08.19 13:27, Luk=C3=A1=C5=A1 Doktor wrote: >>> Dne 21. 08. 19 v 19:51 Max Reitz napsal(a): >>>> On 21.08.19 16:14, Luk=C3=A1=C5=A1 Doktor wrote: >>>>> Hello guys, >>>>> >>>>> First attempt was rejected due to zip attachment, let's try it agai= n with just Avocado-vt debug.log and serial console log files attached. >>>>> >>>>> I bisected a regression on aarch64 all the way to this commit: "qco= w2: skip writing zero buffers to empty COW areas" c8bb23cbdbe32f5c326365e= 0a82e1b0e68cdcd8a. Would you please have a look at it? >>>> >>>> I think I can see the issue on my x64 system (I don=E2=80=99t see th= e XFS >>>> corruption, but the installation fails because of some segfaults). >>>> >>>> I haven=E2=80=99t found a simpler way to reproduce the problem yet, = though, >>>> which is a pain... :-/ >>>> >>>> It looks like the problem disappears when I configure qemu with >>>> =E2=80=9C--disable-xfsctl=E2=80=9D. Can you try that? >>>> >>>> Max >>>> >>> >>> Hello Max, >>> >>> yes, I'm getting the same behavior. With "--disable-xfsctl" it works = well. Also looking at the option I understand why it only failed on aarch= 64 for me, I don't have libs installed on the other machines, therefor it= was disabled by "./configure" there. Anyway I guess disabling it in my b= uilds won't really fix the issue, right? :-) >> >> Thanks! >> >> No, it won=E2=80=99t, but it means the actual root of the problem is p= robably >> rather in some XFS-related code (be it because qemu uses it the wrong >> way or because of XFS kernel code) than in the pure qcow2 commit that >> made the problem surface by exercising it heavily. (Or in an >> interaction between the two.) >=20 > OK, I got a simpler reproducer now: >=20 > $ ./qemu-img create -f qcow2 test.qcow2 1M > $ (for i in $(seq 15 -1 0); do \ > echo "aio_write -P 42 $((i * 64 + 1))k 62k"; \ > done) \ > | ./qemu-io test.qcow2 > $ for i in $(seq 0 15); do \ > echo $i; \ > ofs=3D$((i * 64)); \ > ./qemu-io -c "read -P 0 ${ofs}k 1k" \ > -c "read -P 42 $((ofs + 1))k 62k" \ > -c "read -P 0 $((ofs + 63))k 1k" \ > test.qcow2 \ > | grep 'verification'; \ > done >=20 > On XFS with --enable-xfsctl, this basically always gives me some > verification failure somewhere. (On tmpfs or with --disable-xfsctl, it > never fails.) >=20 > So it seems to be related to I/O from back to front. >=20 > (You can also reproduce it with a plain =E2=80=9Cqemu-img bench=E2=80=9D= invocation, > like =E2=80=9C./qemu-img bench -w --pattern=3D42 -o 1k -S 64k -s 62k te= st.qcow2=E2=80=9D > (on, say, a 4 GB image), but then the failure appears much later in the > image, because you have to wait from some requests to come in reverse > (by chance) first.) The problem is the ftruncate() in xfs_write_zeroes(). It is possible for it to yield, then other requests come in, and the data they write may get discarded once the ftruncate() settles. Max