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=-4.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY 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 9F946C4363A for ; Tue, 6 Oct 2020 02:51:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4CE5C206F4 for ; Tue, 6 Oct 2020 02:51:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="o/d8baE3" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726729AbgJFCva (ORCPT ); Mon, 5 Oct 2020 22:51:30 -0400 Received: from userp2120.oracle.com ([156.151.31.85]:52858 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725909AbgJFCva (ORCPT ); Mon, 5 Oct 2020 22:51:30 -0400 Received: from pps.filterd (userp2120.oracle.com [127.0.0.1]) by userp2120.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 0962nwax106626; Tue, 6 Oct 2020 02:51:15 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=date : from : to : cc : subject : message-id : references : mime-version : content-type : in-reply-to; s=corp-2020-01-29; bh=YosbUU7kIPdnSwmp8WXDorI0qaN8IkFGsOrxOmisByQ=; b=o/d8baE3rfitjkiEc+2W8xFn1pTeh35tEcBNdJsaGAm65xK2fy/zRSFUdjG8XQG3VWyh ETj1XOSUFr638HpqF6JG77zeXqNhXYoTMMwnOXVEIdoevGL5abYpkm83Hudr8vV2UOYH VZ1TEKEIaLx7ocsoXX4ZCCbeV/Bet7EN3MNZqIQi8zh65wbRpa+wX1TF3yUxhZaOleCJ 4UkotrK1jzRqizjEJN+yprguqLZihtiWH1JMJnoNt+P+EMBp1SNgwW5wkyDaKbLvnR7+ XXjkkve8Vs1La5Q3ZjU3Zp4j/gdhStg7anLGszJD2bCG7aXtbz7B/kJ3mUpX8th0cj/O 2w== Received: from aserp3020.oracle.com (aserp3020.oracle.com [141.146.126.70]) by userp2120.oracle.com with ESMTP id 33xhxmshps-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Tue, 06 Oct 2020 02:51:15 +0000 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 0962omMm058934; Tue, 6 Oct 2020 02:51:14 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by aserp3020.oracle.com with ESMTP id 33y36xc7s8-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 06 Oct 2020 02:51:14 +0000 Received: from abhmp0020.oracle.com (abhmp0020.oracle.com [141.146.116.26]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 0962pBIn029775; Tue, 6 Oct 2020 02:51:11 GMT Received: from localhost (/10.159.149.142) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 05 Oct 2020 19:51:11 -0700 Date: Mon, 5 Oct 2020 19:51:10 -0700 From: "Darrick J. Wong" To: Josh Triplett Cc: Linus Torvalds , "Theodore Ts'o" , Andreas Dilger , Jan Kara , Linux Kernel Mailing List , linux-ext4@vger.kernel.org Subject: Re: ext4 regression in v5.9-rc2 from e7bfb5c9bb3d on ro fs with overlapped bitmaps Message-ID: <20201006025110.GJ49559@magnolia> References: <20201005081454.GA493107@localhost> <20201005173639.GA2311765@magnolia> <20201006003216.GB6553@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201006003216.GB6553@localhost> X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9765 signatures=668680 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 adultscore=0 bulkscore=0 spamscore=0 malwarescore=0 suspectscore=0 phishscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2010060016 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9765 signatures=668680 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 malwarescore=0 bulkscore=0 impostorscore=0 lowpriorityscore=0 suspectscore=0 phishscore=0 mlxlogscore=999 adultscore=0 clxscore=1015 spamscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2010060016 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 05, 2020 at 05:32:16PM -0700, Josh Triplett wrote: > On Mon, Oct 05, 2020 at 10:36:39AM -0700, Darrick J. Wong wrote: > > On Mon, Oct 05, 2020 at 01:14:54AM -0700, Josh Triplett wrote: > > > Ran into an ext4 regression when testing upgrades to 5.9-rc kernels: > > > > > > Commit e7bfb5c9bb3d ("ext4: handle add_system_zone() failure in > > > ext4_setup_system_zone()") breaks mounting of read-only ext4 filesystems > > > with intentionally overlapping bitmap blocks. > > > > > > On an always-read-only filesystem explicitly marked with > > > EXT4_FEATURE_RO_COMPAT_SHARED_BLOCKS, prior to that commit, it's safe to > > > point all the block and inode bitmaps to a single block > > > > LOL, WHAT? > > > > I didn't know shared blocks applied to fs metadata. I thought that > > "shared" only applied to file extent maps being able to share physical > > blocks. > > The flag isn't documented very well yet, but since it specifically > forces the filesystem to always be mounted read-only, the bitmaps really > shouldn't matter at all. (In an ideal world, a permanently read-only > filesystem should be able to omit all the bitmaps entirely. Pointing > them all to a single disk block is the next best thing.) I disagree; creating undocumented forks of an existing ondisk format (especially one that presents as inconsistent metadata to regular tools) is creating a ton of pain for future users and maintainers when the incompat forks collide with the canonical implementation(s). (Granted, I don't know if you /created/ this new interpretation of the feature flag or if you've merely been stuck with it...) I don't say that as a theoretical argument -- you've just crashed right into this, because nobody knew that the in-kernel block validity doesn't know how to deal with this other than to error out. > > Could /somebody/ please document the ondisk format changes that are > > associated with this feature? > > I pretty much had to sort it out by looking at a combination of > e2fsprogs and the kernel, and a lot of experimentation, until I ended up > with something that the kernel was completely happy with without a > single complaint. > > I'd be happy to write up a summary of the format. Seems like a good idea, particularly since you're asking for a format change that requires kernel support and the ondisk format documentation lives under Documentation/. That said... > I'd still really like to see this patch applied for 5.9, to avoid having > filesystems that an old kernel can mount but a new one can't. This still > seems like a regression to me. > > > > of all 1s, > > > because a read-only filesystem will never allocate or free any blocks or > > > inodes. > > > > All 1s? So the inode bitmap says that every inode table slot is in use, > > even if the inode record itself says it isn't? > > Yes. > > > What does e2fsck -n > > think about that kind of metadata inconsistency? > > If you set up the rest of the metadata consistently with it (for > instance, 0 free blocks and 0 free inodes), you'll only get a single > complaint, from the e2fsck equivalent of block_validity. See > https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=956509 for details on > that; ...Ted shot down this whole thing six months ago. The Debian bug database is /not/ the designated forum to discuss changes to the ondisk format; linux-ext4 is. --D > with that fixed, e2fsck wouldn't complain at all. The kernel, > prior to 5.9-rc2, doesn't have a single complaint, whether at mount, > unmount, or read of every file and directory on the filesystem. > > The errors you got in your e2fsck run came because you just overrode the > bitmaps, but didn't make the rest of the metadata consistent with that. > I can provide a sample filesystem if that would help. > > - Josh