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=BAYES_00, 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 CE5D1C4361B for ; Tue, 15 Dec 2020 18:03:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 93236223D6 for ; Tue, 15 Dec 2020 18:03:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730109AbgLOSDd (ORCPT ); Tue, 15 Dec 2020 13:03:33 -0500 Received: from mx2.suse.de ([195.135.220.15]:55796 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725973AbgLOSDa (ORCPT ); Tue, 15 Dec 2020 13:03:30 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id D2AC0AC7F; Tue, 15 Dec 2020 18:02:48 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id C71BEDA7C3; Tue, 15 Dec 2020 19:01:09 +0100 (CET) Date: Tue, 15 Dec 2020 19:01:09 +0100 From: David Sterba To: Boris Burkov Cc: dsterba@suse.cz, linux-btrfs@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH v7 01/12] btrfs: lift rw mount setup from mount and remount Message-ID: <20201215180109.GB6430@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Boris Burkov , linux-btrfs@vger.kernel.org, kernel-team@fb.com References: <20201123165040.GF8669@twin.jikos.cz> <20201130233142.GA3661143@devbig008.ftw2.facebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201130233142.GA3661143@devbig008.ftw2.facebook.com> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Mon, Nov 30, 2020 at 03:31:42PM -0800, Boris Burkov wrote: > On Mon, Nov 23, 2020 at 05:50:40PM +0100, David Sterba wrote: > > On Wed, Nov 18, 2020 at 03:06:16PM -0800, Boris Burkov wrote: > > > Mounting rw and remounting from ro to rw naturally share invariants and > > > functionality which result in a correctly setup rw filesystem. Luckily, > > > there is even a strong unity in the code which implements them. In > > > mount's open_ctree, these operations mostly happen after an early return > > > for ro file systems, and in remount, they happen in a section devoted to > > > remounting ro->rw, after some remount specific validation passes. > > > > > > However, there are unfortunately a few differences. There are small > > > deviations in the order of some of the operations, remount does not > > > cleanup orphan inodes in root_tree or fs_tree, remount does not create > > > the free space tree, and remount does not handle "one-shot" mount > > > options like clear_cache and uuid tree rescan. > > > > > > Since we want to add building the free space tree to remount, and since > > > it is possible to leak orphans on a filesystem mounted as ro then > > > remounted rw > > > > The statement is not specific if the orphans are files or roots. But I > > don't agree that a leak is possible, or need a proof of the claim above. > > > > The mount-time orphan cleanup will start early, but otherwise orphan > > cleanup is checked and started on dentry lookups (btrfs_lookup_dentry). > > Deleted but not clened tree roorts are all found and removed, regardless > > of rw or ro->rw mount. > > > > So I wonder if you claim there's a leak just by lack of an explicit call > > on the remount path. > > For what it's worth, the example I had in mind is the free space inode > orphans after a block_group delete or the new "clear v1 space cache" > code in this stack. > > I hadn't considered btrfs_lookup_dentry because I was focused on those > specific inodes, but it's possible that gets called in a way that would > clean them too. > > However, another thing I think I overlooked is that it doesn't look > like remount would affect the set of delayed_iputs, so that mechanism for > removing the orphans should still work. Further, the new function only > runs when going from ro->rw, but any ro mount would run delayed iputs > before completing as part of btrfs_commit_super. > > So with all that, I agree with you that there isn't a leak. Going > forward with this, I can certainly fix the commit messages, or even get > rid of the patch that does the orphan cleanup in remount. I can't think > of a reason that the cleanup would be bad, but on the other hand, just > "unity" is a flimsy justification for adding it. Let me know what you > prefer. Thanks for checking, the committed changelog does not contain 'leak' and I slighthly rephrased only that sentence.