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=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 1EB71C63777 for ; Mon, 30 Nov 2020 23:33:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A5B0A20725 for ; Mon, 30 Nov 2020 23:33:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=bur.io header.i=@bur.io header.b="ThULZl3J"; dkim=temperror (0-bit key) header.d=messagingengine.com header.i=@messagingengine.com header.b="Vi1Y66mK" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388710AbgK3Xc4 (ORCPT ); Mon, 30 Nov 2020 18:32:56 -0500 Received: from out3-smtp.messagingengine.com ([66.111.4.27]:43605 "EHLO out3-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388510AbgK3Xc4 (ORCPT ); Mon, 30 Nov 2020 18:32:56 -0500 Received: from compute2.internal (compute2.nyi.internal [10.202.2.42]) by mailout.nyi.internal (Postfix) with ESMTP id 221475C0036; Mon, 30 Nov 2020 18:31:50 -0500 (EST) Received: from mailfrontend2 ([10.202.2.163]) by compute2.internal (MEProxy); Mon, 30 Nov 2020 18:31:50 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bur.io; h=date :from:to:subject:message-id:references:mime-version:content-type :in-reply-to; s=fm2; bh=YwpqwQBtzNTbCvuUB6knReZ71mkva0wtAQBDz73B iT0=; b=ThULZl3JvyB5nV74+5CrJYNKSM3gRmWA3E85k9OnWyH3Uh67sSfzFx5A j8rue7+JhE34QBxpA5i1QAvhoMA1pUcCe7Qj/H11MbcDA8COkMcxiUMA3DFxi9+6 lQO7QEQGJmURS9JNSaaCwm4XgulccPIEfF/3ZOzTtXXyVrWr5XD7VI+K2R/hMXk0 HBZqxiteDAZoenjFAcUoDcKKAfwtdoPosM8+6wW8x1pTCGUM1RiBj0XVF9+5R1f7 jYdzZumsDgOqZjMMe+5yRaaDjUFlqbDwP+pyuCqunmaPKhWNRbm3ADIBrtgS8HKf CMj/4wVBEoAF/vYe0e9gD3XFWFv8Rg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to:x-me-proxy :x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s=fm1; bh=YwpqwQ BtzNTbCvuUB6knReZ71mkva0wtAQBDz73BiT0=; b=Vi1Y66mKEfK9r+VxuICgGR xO0f6fHJ46q34vlalumcqKofrwi0WMOh38txLsv3fY6uaKrqm/QyjIGzQD2GopZS /2QFxJnuBW1g5/jJaGnk+WQpKPebGtCUXSf3e0EbRJVrW7kH8qTv+55REUeIyrdA v4D1y7NvdFcgcZ/YwoYE2bZxtAxHu9IsBvMUl/8rBVY9w55KPnt/Eajzzq4czRv/ p/yFqNj8mX+zToE90H2vOl7R3HFjoB1Ry4oomg2I49WP8kkAD/vCA3T5A8IR7wYc y3GlE40ieZYB2RpHRam1eyP0UZXIjlXrxYZMo8hp4WOZ1PaNGLVyOB6Nc19Y5znA == X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedujedrudeiuddgudduucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucenucfjughrpeffhffvuffkfhggtggujggfsehttd ertddtredvnecuhfhrohhmpeeuohhrihhsuceuuhhrkhhovhcuoegsohhrihhssegsuhhr rdhioheqnecuggftrfgrthhtvghrnhepvdfhgffhteeugefgtdegudevudegkeeguedvvd fhudegudfhteekvedtiedtgeeunecukfhppeduieefrdduudegrddufedvrdefnecuvehl uhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrhhomhepsghorhhishessg hurhdrihho X-ME-Proxy: Received: from localhost (unknown [163.114.132.3]) by mail.messagingengine.com (Postfix) with ESMTPA id 3AD063064AAA; Mon, 30 Nov 2020 18:31:49 -0500 (EST) Date: Mon, 30 Nov 2020 15:31:42 -0800 From: Boris Burkov To: 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: <20201130233142.GA3661143@devbig008.ftw2.facebook.com> References: <20201123165040.GF8669@twin.jikos.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201123165040.GF8669@twin.jikos.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org 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 the review, Boris