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=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 14CAAECE58C for ; Tue, 15 Oct 2019 02:20:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DBF8021927 for ; Tue, 15 Oct 2019 02:20:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="dltxS1i1" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727069AbfJOCUk (ORCPT ); Mon, 14 Oct 2019 22:20:40 -0400 Received: from mail-pf1-f194.google.com ([209.85.210.194]:35523 "EHLO mail-pf1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726430AbfJOCUj (ORCPT ); Mon, 14 Oct 2019 22:20:39 -0400 Received: by mail-pf1-f194.google.com with SMTP id 205so11454747pfw.2; Mon, 14 Oct 2019 19:20:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=8H4x/0PzSc+cFgDx1YZ5+BsoHRjAf/XAcn/2vvNKiII=; b=dltxS1i19yhHH709eXXysC7QrJFjh2Ra7frwS53c0XKyRv95OMf9qIQd+7bqlNHGoJ x+DF9gvatAOdsY6Vz414vk54AyAU2eQ0TD5eNQ4hWJYvBwo9Mal8FUWnXkoie8e2JxVb MIkOVxxE9jhdAGZsbUXCIqnloynfoEuSOeWr43Rr2qE4TeaxWVrkYYCcySX5x058AC/C BIdgJnOJ/plwzzw4OBia4mLfcA6oZt+B5FtinPCw5tkXEBb3P8xBVQwmkrEfuvioc5P4 paqo9h8erqF+ZMX5z2IUJpVCEVkmlQFC2VXoZHAP71gIvejmGAE1+SGFpX0i9Hlfd24d RvJg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=8H4x/0PzSc+cFgDx1YZ5+BsoHRjAf/XAcn/2vvNKiII=; b=MW1r49OXPwZivgC3ozns9xAW1rsUhjkKVgPp1wPrOfPQ3wZ3kyAkhobQes/mounXjf pdFp6uF6OEAw4P1SZNNul3O7paRKySlAY2JkAO880LMRjfYsw5p8i9c7c/CufPR7PcLi 3eYrJhHve23TkrKOGD0OlY8qJx1f7pU6X1KdskowToRz+st0xfpnAVtInG+OqhnMeZDr QHi7NlfyztBENpD328hyozDfUBnOuYgH2/E4/w9XthI4uLXZeLiDPBAEwjjXQL15A6lI 88iYrkJ8V5YhihwJXhTqjrksZEKk+zsItooH7j3k1IwEg6L0+1UQ3wMw6oLGuEE8wee6 2JlQ== X-Gm-Message-State: APjAAAWd5vfxRrRLSrsRxhq48J0FC4cVPH3Txh1p9bunPfEyDyCmTHl2 yLwvsMmpgeje0cQfH+ekxsbwuUw= X-Google-Smtp-Source: APXvYqzOXpShh56uDCVPgANcyM3B+A2AAhIkbDujovTmxMJALaZxxy0iXsrKcX4LEPjKigJevZPUYw== X-Received: by 2002:a17:90a:c094:: with SMTP id o20mr39731453pjs.37.1571106037499; Mon, 14 Oct 2019 19:20:37 -0700 (PDT) Received: from mypc ([209.132.188.80]) by smtp.gmail.com with ESMTPSA id m5sm18914736pgt.15.2019.10.14.19.20.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 14 Oct 2019 19:20:36 -0700 (PDT) Date: Tue, 15 Oct 2019 10:20:26 +0800 From: Pingfan Liu To: Jan Kara Cc: Eric Sandeen , "Darrick J. Wong" , Hari Bathini , linuxppc-dev@lists.ozlabs.org, Dave Chinner , Eric Sandeen , Jan Kara , linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org Subject: Re: [PATCH] xfs: introduce "metasync" api to sync metadata to fsblock Message-ID: <20191015022026.GC14327@mypc> References: <1570977420-3944-1-git-send-email-kernelfans@gmail.com> <20191013163417.GQ13108@magnolia> <20191014083315.GA10091@mypc> <20191014094311.GD5939@quack2.suse.cz> <20191014200303.GF5939@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191014200303.GF5939@quack2.suse.cz> User-Agent: Mutt/1.11.3 (2019-02-01) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, Oct 14, 2019 at 10:03:03PM +0200, Jan Kara wrote: > On Mon 14-10-19 08:23:39, Eric Sandeen wrote: > > On 10/14/19 4:43 AM, Jan Kara wrote: > > > On Mon 14-10-19 16:33:15, Pingfan Liu wrote: > > > > On Sun, Oct 13, 2019 at 09:34:17AM -0700, Darrick J. Wong wrote: > > > > > On Sun, Oct 13, 2019 at 10:37:00PM +0800, Pingfan Liu wrote: > > > > > > When using fadump (fireware assist dump) mode on powerpc, a mismatch > > > > > > between grub xfs driver and kernel xfs driver has been obsevered. Note: > > > > > > fadump boots up in the following sequence: fireware -> grub reads kernel > > > > > > and initramfs -> kernel boots. > > > > > > > > > > > > The process to reproduce this mismatch: > > > > > > - On powerpc, boot kernel with fadump=on and edit /etc/kdump.conf. > > > > > > - Replacing "path /var/crash" with "path /var/crashnew", then, "kdumpctl > > > > > > restart" to rebuild the initramfs. Detail about the rebuilding looks > > > > > > like: mkdumprd /boot/initramfs-`uname -r`.img.tmp; > > > > > > mv /boot/initramfs-`uname -r`.img.tmp /boot/initramfs-`uname -r`.img > > > > > > sync > > > > > > - "echo c >/proc/sysrq-trigger". > > > > > > > > > > > > The result: > > > > > > The dump image will not be saved under /var/crashnew/* as expected, but > > > > > > still saved under /var/crash. > > > > > > > > > > > > The root cause: > > > > > > As Eric pointed out that on xfs, 'sync' ensures the consistency by writing > > > > > > back metadata to xlog, but not necessary to fsblock. This raises issue if > > > > > > grub can not replay the xlog before accessing the xfs files. Since the > > > > > > above dir entry of initramfs should be saved as inline data with xfs_inode, > > > > > > so xfs_fs_sync_fs() does not guarantee it written to fsblock. > > > > > > > > > > > > umount can be used to write metadata fsblock, but the filesystem can not be > > > > > > umounted if still in use. > > > > > > > > > > > > There are two ways to fix this mismatch, either grub or xfs. It may be > > > > > > easier to do this in xfs side by introducing an interface to flush metadata > > > > > > to fsblock explicitly. > > > > > > > > > > > > With this patch, metadata can be written to fsblock by: > > > > > > # update AIL > > > > > > sync > > > > > > # new introduced interface to flush metadata to fsblock > > > > > > mount -o remount,metasync mountpoint > > > > > > > > > > I think this ought to be an ioctl or some sort of generic call since the > > > > > jbd2 filesystems (ext3, ext4, ocfs2) suffer from the same "$BOOTLOADER > > > > > is too dumb to recover logs but still wants to write to the fs" > > > > > checkpointing problem. > > > > Yes, a syscall sounds more reasonable. > > > > > > > > > > (Or maybe we should just put all that stuff in a vfat filesystem, I > > > > > don't know...) > > > > I think it is unavoidable to involve in each fs' implementation. What > > > > about introducing an interface sync_to_fsblock(struct super_block *sb) in > > > > the struct super_operations, then let each fs manage its own case? > > > > > > Well, we already have a way to achieve what you need: fsfreeze. > > > Traditionally, that is guaranteed to put fs into a "clean" state very much > > > equivalent to the fs being unmounted and that seems to be what the > > > bootloader wants so that it can access the filesystem without worrying > > > about some recovery details. So do you see any problem with replacing > > > 'sync' in your example above with 'fsfreeze /boot && fsfreeze -u /boot'? > > > > > > Honza > > > > The problem with fsfreeze is that if the device you want to quiesce is, say, > > the root fs, freeze isn't really a good option. > > I agree you need to be really careful not to deadlock against yourself in > that case. But this particular use actually has a chance to work. > Yeah, normally there is a /boot partition in system, and if so, fsfreeze can work. > > But the other thing I want to highlight about this approach is that it does not > > solve the root problem: something is trying to read the block device without > > first replaying the log. > > > > A call such as the proposal here is only going to leave consistent metadata at > > the time the call returns; at any time after that, all guarantees are off again, > > so the problem hasn't been solved. > > Oh, absolutely agreed. I was also thinking about this before sending my > reply. Once you unfreeze, the log can start filling with changes and > there's no guarantee that e.g. inode does not move as part of these But just as fsync, we only guarantee the consistency before a sync. If the involved files change again, we need another sync. > changes. But to be fair, replaying the log isn't easy either, even more so > from a bootloader. You cannot write the changes from the log back into the > filesystem as e.g. in case of suspend-to-disk the resumed kernel gets > surprised and corrupts the fs under its hands (been there, tried that). So > you must keep changes only in memory and that's not really easy in the > constrained bootloader environment. Sigh, this is more complicated than I had thought. I guess it will be a long time to go with this bug, and use fsfreeze as a work around. Thanks and regards, Pingfan > > So I guess we are left with hacks that kind of mostly work and fsfreeze is > one of those. If you don't mess with the files after fsfreeze, you're > likely to find what you need even without replaying the log. > > Honza > -- > Jan Kara > SUSE Labs, CR