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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DBC56C433EF for ; Thu, 16 Dec 2021 19:25:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240902AbhLPTZv (ORCPT ); Thu, 16 Dec 2021 14:25:51 -0500 Received: from dfw.source.kernel.org ([139.178.84.217]:52140 "EHLO dfw.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231376AbhLPTZu (ORCPT ); Thu, 16 Dec 2021 14:25:50 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id A419861F2A for ; Thu, 16 Dec 2021 19:25:50 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 024C4C36AE3; Thu, 16 Dec 2021 19:25:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1639682750; bh=bqkoxqojgixNXaZ4wDoQ/5873zRznHIbizGsVw1N1C8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=VrKBqSBr/YDdAbON4MT90Iq60FT90mxR00gRUtbjR7AbEz5NH3UlF/82qSIto/EQW BLao6lPwg2EBjX/W3EzgAV4yrDzQ8L20iBr4zts+IRFpdYb7cCELtjX0dlbCo9Ijqr A+VM7h72hrObn4W3pqftyg8dk200MYi71Bi2zz3CIWr7Zh0K3PpMxO0daVjJU4EIab sSIrW4XVXPqvOCJRbttfyfyz2VVgWQlV//FN/ZJH5hucTI6zb3RC9tiPOgRSv0VY9H wcUo0TYrm2VkV5TXoWzd2/T5zd1EseRAw2y8ZZPHk2xhVVvGffHhamQlYv9DCmGRZo v+Pv2RL/NP54Q== Date: Thu, 16 Dec 2021 11:25:49 -0800 From: "Darrick J. Wong" To: Dave Chinner Cc: linux-xfs@vger.kernel.org Subject: Re: [PATCH 3/7] xfs: fix a bug in the online fsck directory leaf1 bestcount check Message-ID: <20211216192549.GC27664@magnolia> References: <163961695502.3129691.3496134437073533141.stgit@magnolia> <163961697197.3129691.1911552605195534271.stgit@magnolia> <20211216050537.GA449541@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211216050537.GA449541@dread.disaster.area> Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Thu, Dec 16, 2021 at 04:05:37PM +1100, Dave Chinner wrote: > On Wed, Dec 15, 2021 at 05:09:32PM -0800, Darrick J. Wong wrote: > > From: Darrick J. Wong > > > > When xfs_scrub encounters a directory with a leaf1 block, it tries to > > validate that the leaf1 block's bestcount (aka the best free count of > > each directory data block) is the correct size. Previously, this author > > believed that comparing bestcount to the directory isize (since > > directory data blocks are under isize, and leaf/bestfree blocks are > > above it) was sufficient. > > > > Unfortunately during testing of online repair, it was discovered that it > > is possible to create a directory with a hole between the last directory > > block and isize. > > We have xfs_da3_swap_lastblock() that can leave an -empty- da block > between the last referenced block and isize, but that's not a "hole" > in the file. If you don't mean xfs_da3_swap_lastblock(), then can > you clarify what you mean by a "hole" here and explain to me how the > situation it occurs in comes about? I don't actually know how it comes about. I wrote a test that sets up fsstress to expand and contract directories and races xfs_scrub -n, and noticed that I'd periodically get complaints about directories (usually $SCRATCH_MNT/p$CPU) where the last block(s) before i_size were actually holes. I began reading the dir2 code to try to figure out how this came about (clearly we're not updating i_size somewhere) but then took the shortcut of seeing if xfs_repair or xfs_check complained about this situation. Neither of them did, and I found a couple more directories in a similar situation on my crash test dummy machine, and concluded "Wellllp, I guess this is part of the ondisk format!" and committed the patch. Also, I thought xfs_da3_swap_lastblock only operates on leaf and da btree blocks, not the blocks containing directory entries? I /think/ the actual explanation is that something goes wrong in xfs_dir2_shrink_inode (maybe?) such that the mapping goes away but i_disk_size doesn't get updated? Not sure how /that/ can happen, though... --D > > Cheers, > > Dave. > -- > Dave Chinner > david@fromorbit.com