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=-16.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 A819AC433E6 for ; Mon, 11 Jan 2021 17:18:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 779C122ADF for ; Mon, 11 Jan 2021 17:18:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388263AbhAKRSY (ORCPT ); Mon, 11 Jan 2021 12:18:24 -0500 Received: from mail.kernel.org ([198.145.29.99]:54720 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728844AbhAKRSX (ORCPT ); Mon, 11 Jan 2021 12:18:23 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 43730221F9; Mon, 11 Jan 2021 17:17:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1610385462; bh=gSvoVCwtO+qWBoAHQgLqtcSt+6qzHKCjYsRPBsxmUhI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ShLdD4h73LUQQUOGMFfajZmhwPfUOCDaGVi6n/KxqDvfPvQrBpLVrM0nY6jtGlR7/ nQ7sJkrtUnunGY1TvGfWTdmx0NbJ/4kXGGCi3MbEeVghgM+He9WNd3lphzzTf4ZK9y Ra9oODkLKov+W8HpUZCQGFKoG8WPlu2wDHaQTt8GuIspnEGI+UbnLzfqma6iojtPjJ qGkuVxRUbfqB3IGVn7OkefeRA2CyxV8/Zcngzjq5JaJY3C/a2XAVgiHBLF3i8vcNw9 DOZiKK9XEX2OcFiRF1BAMNtjUsdCsD4ofNce7PLjE2xWJALHpaJWw+D3Dir6lKnBOn MJzOlDYy/UqIg== Date: Mon, 11 Jan 2021 09:17:42 -0800 From: "Darrick J. Wong" To: Brian Foster Cc: "Darrick J. Wong" , wenli xie , xfs , chiluk@ubuntu.com, Dave Chinner Subject: Re: [PATCH v2] xfs: fix an ABBA deadlock in xfs_rename Message-ID: <20210111171742.GA1164246@magnolia> References: <20210108015648.GP6918@magnolia> <20210108151858.GB893097@bfoster> <20210109013948.GT6918@magnolia> <20210111140541.GA1091932@bfoster> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210111140541.GA1091932@bfoster> Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Mon, Jan 11, 2021 at 09:05:41AM -0500, Brian Foster wrote: > On Fri, Jan 08, 2021 at 05:39:48PM -0800, Darrick J. Wong wrote: > > On Fri, Jan 08, 2021 at 10:18:58AM -0500, Brian Foster wrote: > > > On Thu, Jan 07, 2021 at 05:56:48PM -0800, Darrick J. Wong wrote: > > > > From: Darrick J. Wong > > > > > > > > When overlayfs is running on top of xfs and the user unlinks a file in > > > > the overlay, overlayfs will create a whiteout inode and ask xfs to > > > > "rename" the whiteout file atop the one being unlinked. If the file > > > > being unlinked loses its one nlink, we then have to put the inode on the > > > > unlinked list. > > > > > > > > This requires us to grab the AGI buffer of the whiteout inode to take it > > > > off the unlinked list (which is where whiteouts are created) and to grab > > > > the AGI buffer of the file being deleted. If the whiteout was created > > > > in a higher numbered AG than the file being deleted, we'll lock the AGIs > > > > in the wrong order and deadlock. > > > > > > > > Therefore, grab all the AGI locks we think we'll need ahead of time, and > > > > in order of increasing AG number per the locking rules. Set > > > > t_firstblock so that a subsequent directory block allocation never tries > > > > to grab a lower-numbered AGF than the AGIs we grabbed. > > > > > > > > > > I don't see this patch do anything with t_firstblock... Even so, is that > > > necessary? I thought we had to lock AGIs before AGFs and always in agno > > > order, but not necessarily lock an AGF >= previously locked AGIs. Hm? > > > > Oops, heh. Yeah, I'd added chunks to prevent block allocation, but on > > further analysis I don't think that was necessary. > > > > > > Reduce the likelihood that a directory expansion will ENOSPC by starting > > > > with AG 0 when allocating whiteout files. > > > > > > > > Reported-by: wenli xie > > > > Fixes: 93597ae8dac0 ("xfs: Fix deadlock between AGI and AGF when target_ip exists in xfs_rename()") > > > > Signed-off-by: Darrick J. Wong > > > > --- > > > > v2: Make it more obvious that we're grabbing all the AGI locks ahead of > > > > the AGFs, and hide functions that we don't need to export anymore. > > > > --- > > > > fs/xfs/libxfs/xfs_dir2.h | 2 -- > > > > fs/xfs/libxfs/xfs_dir2_sf.c | 2 +- > > > > fs/xfs/xfs_inode.c | 57 ++++++++++++++++++++++++++++++------------- > > > > 3 files changed, 41 insertions(+), 20 deletions(-) > > > > > > > > diff --git a/fs/xfs/libxfs/xfs_dir2.h b/fs/xfs/libxfs/xfs_dir2.h > > > > index e55378640b05..d03e6098ded9 100644 > > > > --- a/fs/xfs/libxfs/xfs_dir2.h > > > > +++ b/fs/xfs/libxfs/xfs_dir2.h > > > > @@ -47,8 +47,6 @@ extern int xfs_dir_lookup(struct xfs_trans *tp, struct xfs_inode *dp, > > > > extern int xfs_dir_removename(struct xfs_trans *tp, struct xfs_inode *dp, > > > > struct xfs_name *name, xfs_ino_t ino, > > > > xfs_extlen_t tot); > > > > -extern bool xfs_dir2_sf_replace_needblock(struct xfs_inode *dp, > > > > - xfs_ino_t inum); > > > > extern int xfs_dir_replace(struct xfs_trans *tp, struct xfs_inode *dp, > > > > struct xfs_name *name, xfs_ino_t inum, > > > > xfs_extlen_t tot); > > > > diff --git a/fs/xfs/libxfs/xfs_dir2_sf.c b/fs/xfs/libxfs/xfs_dir2_sf.c > > > > index 2463b5d73447..8c4f76bba88b 100644 > > > > --- a/fs/xfs/libxfs/xfs_dir2_sf.c > > > > +++ b/fs/xfs/libxfs/xfs_dir2_sf.c > > > > @@ -1018,7 +1018,7 @@ xfs_dir2_sf_removename( > > > > /* > > > > * Check whether the sf dir replace operation need more blocks. > > > > */ > > > > -bool > > > > +static bool > > > > xfs_dir2_sf_replace_needblock( > > > > struct xfs_inode *dp, > > > > xfs_ino_t inum) > > > > diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c > > > > index b7352bc4c815..528152770dc9 100644 > > > > --- a/fs/xfs/xfs_inode.c > > > > +++ b/fs/xfs/xfs_inode.c > > > > @@ -3000,6 +3000,24 @@ xfs_rename_alloc_whiteout( > > > > return 0; > > > > } > > > > > > > > +/* Decide if we need to lock the target IP's AGI as part of a rename. */ > > > > +static inline bool > > > > +xfs_rename_lock_target_ip( > > > > + struct xfs_inode *src_ip, > > > > + struct xfs_inode *target_ip) > > > > +{ > > > > + unsigned int tgt_nlink = VFS_I(target_ip)->i_nlink; > > > > + bool src_is_dir = S_ISDIR(VFS_I(src_ip)->i_mode); > > > > + > > > > + /* > > > > + * We only need to lock the AGI if the target ip will end up on the > > > > + * unlinked list. > > > > + */ > > > > + if (src_is_dir) > > > > + return tgt_nlink == 2; > > > > > > IIUC, we can't rename dirs over nondirs and vice versa. I.e.: > > > > > > # mv dir file > > > mv: overwrite 'file'? y > > > mv: cannot overwrite non-directory 'file' with directory 'dir' > > > # mv -T file dir > > > mv: overwrite 'dir'? y > > > mv: cannot overwrite directory 'dir' with non-directory > > > > > > That means that if src_is_dir is true, target must either be NULL or an > > > empty directory for the rename to succeed, right? If so, have we already > > > enforced that by this point? I'm wondering if we need to check the link > > > count == 2 in this case or could possibly just reduce the logic to > > > (tgt_nlink == 1 || src_is_dir) And if so, whether that still warrants an > > > inline helper (where I suppose we could still assert that nlink == 2). Yes, I /think/ we could get away with that conditional. It leaves a (probably negligible) logic bomb in that we're assuming that the vfs has checked that target_ip is an empty dir if src is a directory. That said, I think the existing rename code also makes that assumption, so I think I can just simplify the patch and not leave more ASSERTs. > > Hm. I /think/ it's true that we can't ever rename atop an existing > > directory, so I think this cna go away: > > > > $ mkdir /tmp/xx > > $ touch /tmp/yy > > $ strace -s99 -e renameat ./src/renameat2 /tmp/yy /tmp/xx > > renameat(AT_FDCWD, "/tmp/yy", AT_FDCWD, "/tmp/xx") = -1 EISDIR (Is a directory) > > > > Not sure if you mean to qualify that as "with another nondir" or not, > but fwiw we can rename over an empty dir if the source is a dir: > > # mkdir d1 > # mkdir d2 > # ~/xfstests-dev/src/renameat2 d1 d2 Oops, yes, that is correct. --D > > Brian > > > --D > > > > > Brian > > > > > > > + return tgt_nlink == 1; > > > > +} > > > > + > > > > /* > > > > * xfs_rename > > > > */ > > > > @@ -3017,7 +3035,7 @@ xfs_rename( > > > > struct xfs_trans *tp; > > > > struct xfs_inode *wip = NULL; /* whiteout inode */ > > > > struct xfs_inode *inodes[__XFS_SORT_INODES]; > > > > - struct xfs_buf *agibp; > > > > + int i; > > > > int num_inodes = __XFS_SORT_INODES; > > > > bool new_parent = (src_dp != target_dp); > > > > bool src_is_directory = S_ISDIR(VFS_I(src_ip)->i_mode); > > > > @@ -3130,6 +3148,27 @@ xfs_rename( > > > > } > > > > } > > > > > > > > + /* > > > > + * Lock the AGI buffers we need to handle bumping the nlink of the > > > > + * whiteout inode off the unlinked list and to handle dropping the > > > > + * nlink of the target inode. We have to do this in increasing AG > > > > + * order to avoid deadlocks, and before directory block allocation > > > > + * tries to grab AGFs. > > > > + */ > > > > + for (i = 0; i < num_inodes && inodes[i] != NULL; i++) { > > > > + if (inodes[i] == wip || > > > > + (inodes[i] == target_ip && > > > > + xfs_rename_lock_target_ip(src_ip, target_ip))) { > > > > + struct xfs_buf *bp; > > > > + xfs_agnumber_t agno; > > > > + > > > > + agno = XFS_INO_TO_AGNO(mp, inodes[i]->i_ino); > > > > + error = xfs_read_agi(mp, tp, agno, &bp); > > > > + if (error) > > > > + goto out_trans_cancel; > > > > + } > > > > + } > > > > + > > > > /* > > > > * Directory entry creation below may acquire the AGF. Remove > > > > * the whiteout from the unlinked list first to preserve correct > > > > @@ -3182,22 +3221,6 @@ xfs_rename( > > > > * In case there is already an entry with the same > > > > * name at the destination directory, remove it first. > > > > */ > > > > - > > > > - /* > > > > - * Check whether the replace operation will need to allocate > > > > - * blocks. This happens when the shortform directory lacks > > > > - * space and we have to convert it to a block format directory. > > > > - * When more blocks are necessary, we must lock the AGI first > > > > - * to preserve locking order (AGI -> AGF). > > > > - */ > > > > - if (xfs_dir2_sf_replace_needblock(target_dp, src_ip->i_ino)) { > > > > - error = xfs_read_agi(mp, tp, > > > > - XFS_INO_TO_AGNO(mp, target_ip->i_ino), > > > > - &agibp); > > > > - if (error) > > > > - goto out_trans_cancel; > > > > - } > > > > - > > > > error = xfs_dir_replace(tp, target_dp, target_name, > > > > src_ip->i_ino, spaceres); > > > > if (error) > > > > > > > > > >