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 CFF6ACA9EA0 for ; Mon, 21 Oct 2019 01:38:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A5856218BA for ; Mon, 21 Oct 2019 01:38:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726827AbfJUBit (ORCPT ); Sun, 20 Oct 2019 21:38:49 -0400 Received: from outgoing-auth-1.mit.edu ([18.9.28.11]:43953 "EHLO outgoing.mit.edu" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726718AbfJUBis (ORCPT ); Sun, 20 Oct 2019 21:38:48 -0400 Received: from callcc.thunk.org (pool-72-93-95-157.bstnma.fios.verizon.net [72.93.95.157]) (authenticated bits=0) (User authenticated as tytso@ATHENA.MIT.EDU) by outgoing.mit.edu (8.14.7/8.12.4) with ESMTP id x9L1ch5h006028 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Sun, 20 Oct 2019 21:38:43 -0400 Received: by callcc.thunk.org (Postfix, from userid 15806) id 03063420458; Sun, 20 Oct 2019 21:38:42 -0400 (EDT) Date: Sun, 20 Oct 2019 21:38:42 -0400 From: "Theodore Y. Ts'o" To: Jan Kara Cc: linux-ext4@vger.kernel.org Subject: Re: [PATCH 05/22] ext4: Fix ext4_should_journal_data() for EA inodes Message-ID: <20191021013842.GF6799@mit.edu> References: <20191003215523.7313-1-jack@suse.cz> <20191003220613.10791-5-jack@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191003220613.10791-5-jack@suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Fri, Oct 04, 2019 at 12:05:51AM +0200, Jan Kara wrote: > Similarly to directories, EA inodes do only journalled modifications to > their data. Change ext4_should_journal_data() to return true for them so > that we don't have to special-case them during truncate. We are already special-casing EA inodes in ext4_clear_blocks() in fs/ext4/indirect.c, and get_default_free_blocks_flags() in fs/ext4/extents.c, and like S_ISDIR, we want to treat EA inode blocks as metadata. So I'm not sure I see the value of this change? As an aside, I was looking at fs/ext4/mballoc.c to see what the difference is for treating a block as a metadata block versus a journaled data block, and what I found made my hair rise on end: /* * We need to make sure we don't reuse the freed block until after the * transaction is committed. We make an exception if the inode is to be * written in writeback mode since writeback mode has weak data * consistency guarantees. */ So in data=writeback, if a file is deleted, its blocks are available for immediate reallocation, and if we are under heavy memory pressure, the deleted file's blocks could get overwritten --- even in the case where we crash and the transaction never committed. While it's true that date=writeback mode has weaker guarantees, my understanding is that it only applied to the exposure stale data, and not to a long-standing file's blocks getting corrupted if it is almost deleted, but not quite before a crash. Granted, the situation where this would happen is quite wrare, but it seems quite wrong.... - Ted