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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 F1B8AC4321A for ; Tue, 11 Jun 2019 17:01:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CC5FD2086A for ; Tue, 11 Jun 2019 17:01:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404472AbfFKRB0 (ORCPT ); Tue, 11 Jun 2019 13:01:26 -0400 Received: from mx2.suse.de ([195.135.220.15]:47948 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2387767AbfFKRBZ (ORCPT ); Tue, 11 Jun 2019 13:01:25 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 079A0AD8F; Tue, 11 Jun 2019 17:01:24 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id 403ECDA905; Tue, 11 Jun 2019 19:02:15 +0200 (CEST) Date: Tue, 11 Jun 2019 19:02:15 +0200 From: David Sterba To: fdmanana@kernel.org Cc: linux-btrfs@vger.kernel.org Subject: Re: [PATCH v3] Btrfs: fix data loss after inode eviction, renaming it, and fsync it Message-ID: <20190611170215.GF3563@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, fdmanana@kernel.org, linux-btrfs@vger.kernel.org References: <20190606110719.20855-1-fdmanana@kernel.org> <20190607102524.32655-1-fdmanana@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190607102524.32655-1-fdmanana@kernel.org> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Fri, Jun 07, 2019 at 11:25:24AM +0100, fdmanana@kernel.org wrote: > From: Filipe Manana > > When we log an inode, regardless of logging it completely or only that it > exists, we always update it as logged (logged_trans and last_log_commit > fields of the inode are updated). This is generally fine and avoids future > attempts to log it from having to do repeated work that brings no value. > > However, if we write data to a file, then evict its inode after all the > dealloc was flushed (and ordered extents completed), rename the file and > fsync it, we end up not logging the new extents, since the rename may > result in logging that the inode exists in case the parent directory was > logged before. The following reproducer shows and explains how this can > happen: > > $ mkfs.btrfs -f /dev/sdb > $ mount /dev/sdb /mnt > > $ mkdir /mnt/dir > $ touch /mnt/dir/foo > $ touch /mnt/dir/bar > > # Do a direct IO write instead of a buffered write because with a > # buffered write we would need to make sure dealloc gets flushed and > # complete before we do the inode eviction later, and we can not do that > # from user space with call to things such as sync(2) since that results > # in a transaction commit as well. > $ xfs_io -d -c "pwrite -S 0xd3 0 4K" /mnt/dir/bar > > # Keep the directory dir in use while we evict inodes. We want our file > # bar's inode to be evicted but we don't want our directory's inode to > # be evicted (if it were evicted too, we would not be able to reproduce > # the issue since the first fsync below, of file foo, would result in a > # transaction commit. > $ ( cd /mnt/dir; while true; do :; done ) & > $ pid=$! > > # Wait a bit to give time for the background process to chdir. > $ sleep 0.1 > > # Evict all inodes, except the inode for the directory dir because it is > # currently in use by our background process. > $ echo 2 > /proc/sys/vm/drop_caches > > # fsync file foo, which ends up persisting information about the parent > # directory because it is a new inode. > $ xfs_io -c fsync /mnt/dir/foo > > # Rename bar, this results in logging that this inode exists (inode item, > # names, xattrs) because the parent directory is in the log. > $ mv /mnt/dir/bar /mnt/dir/baz > > # Now fsync baz, which ends up doing absolutely nothing because of the > # rename operation which logged that the inode exists only. > $ xfs_io -c fsync /mnt/dir/baz > > > > $ mount /dev/sdb /mnt > $ od -t x1 -A d /mnt/dir/baz > 0000000 > > --> Empty file, data we wrote is missing. > > Fix this by not updating last_sub_trans of an inode when we are logging > only that it exists and the inode was not yet logged since it was loaded > from disk (full_sync bit set), this is enough to make btrfs_inode_in_log() > return false for this scenario and make us log the inode. The logged_trans > of the inode is still always setsince that alone is used to track if names > need to be deleted as part of unlink operations. > > Fixes: 257c62e1bce03e ("Btrfs: avoid tree log commit when there are no changes") > Signed-off-by: Filipe Manana Added to misc-next, thanks.