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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_MUTT autolearn=unavailable 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 A0F1DC43381 for ; Fri, 15 Feb 2019 15:57:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 663B32190C for ; Fri, 15 Feb 2019 15:57:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="TdxYLF2/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389873AbfBOP5A (ORCPT ); Fri, 15 Feb 2019 10:57:00 -0500 Received: from userp2130.oracle.com ([156.151.31.86]:52550 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726597AbfBOP5A (ORCPT ); Fri, 15 Feb 2019 10:57:00 -0500 Received: from pps.filterd (userp2130.oracle.com [127.0.0.1]) by userp2130.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x1FFskfS012978; Fri, 15 Feb 2019 15:56:11 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=date : from : to : cc : subject : message-id : references : mime-version : content-type : in-reply-to; s=corp-2018-07-02; bh=H/p/uq6cj+GvpAsur9UGOGjTXxChi2YnrN/BPDly/rc=; b=TdxYLF2/O4gQakE7ACJ4NA+Y1Iheezehzn0io67FMGYJLAR2YY+3paZCVCKZ5vpe1B6r z0JMzvi5iw8COHJ5AwoJ30GEUMyLt0iB5Tj3QAzdTv4JIyE9iIN21vckRnmKp+AHrfH0 g8nSvpK18iihz1bf9Aj4otmpbSET1Yjt+r6/ZB0c1X35usKeC1BqLKZ9VSibIIZ/IdVq Ad/bKDzbQGbMAkdBM1zjSa3rbsl/TFiJLoTac5cUXf/jVjtPwjC9JiZYFW5A8xFqOa8T wqkxfMwzvybBV9apPU6ZLUpjiQo0WaRKxqIq5mcvwAaKaCiNad8kSN3KQdxe2xm0lM5o Vw== Received: from aserv0022.oracle.com (aserv0022.oracle.com [141.146.126.234]) by userp2130.oracle.com with ESMTP id 2qhrekxm1m-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 15 Feb 2019 15:56:10 +0000 Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by aserv0022.oracle.com (8.14.4/8.14.4) with ESMTP id x1FFu916002203 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 15 Feb 2019 15:56:09 GMT Received: from abhmp0019.oracle.com (abhmp0019.oracle.com [141.146.116.25]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id x1FFu6iw026202; Fri, 15 Feb 2019 15:56:07 GMT Received: from localhost (/67.169.218.210) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Fri, 15 Feb 2019 15:56:06 +0000 Date: Fri, 15 Feb 2019 07:56:04 -0800 From: "Darrick J. Wong" To: Amir Goldstein Cc: Chris Mason , Josef Bacik , dsterba@suse.com, Al Viro , Jan Kara , Theodore Tso , Andreas Dilger , Jaegeuk Kim , yuchao0@huawei.com, Hugh Dickins , Christoph Hellwig , Richard Weinberger , Artem Bityutskiy , Adrian Hunter , linux-xfs , Linux Btrfs , linux-fsdevel , Ext4 , linux-f2fs-devel@lists.sourceforge.net, linux-mtd@lists.infradead.org, Linux MM Subject: Re: [PATCH] vfs: don't decrement i_nlink in d_tmpfile Message-ID: <20190215155604.GL32253@magnolia> References: <20190214234908.GA6474@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9168 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1902150109 Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Fri, Feb 15, 2019 at 10:04:12AM +0200, Amir Goldstein wrote: > On Fri, Feb 15, 2019 at 4:23 AM Darrick J. Wong wrote: > > > > From: Darrick J. Wong > > > > d_tmpfile was introduced to instantiate an inode in the dentry cache as > > a temporary file. This helper decrements the inode's nlink count and > > dirties the inode, presumably so that filesystems could call new_inode > > to create a new inode with nlink == 1 and then call d_tmpfile which will > > decrement nlink. > > > > However, this doesn't play well with XFS, which needs to allocate, > > initialize, and insert a tempfile inode on its unlinked list in a single > > transaction. In order to maintain referential integrity of the XFS > > metadata, we cannot have an inode on the unlinked list with nlink >= 1. > > > > XFS and btrfs hack around d_tmpfile's behavior by creating the inode > > with nlink == 0 and then incrementing it just prior to calling > > d_tmpfile, anticipating that it will be reset to 0. > > > > Everywhere else outside of d_tmpfile, it appears that nlink updates and > > persistence is the responsibility of individual filesystems. Therefore, > > move the nlink decrement out of d_tmpfile into the callers, and require > > that callers only pass in inodes with nlink already set to 0. > > > > Signed-off-by: Darrick J. Wong > > --- > > fs/btrfs/inode.c | 8 -------- > > fs/dcache.c | 8 ++++++-- > > fs/ext2/namei.c | 2 +- > > fs/ext4/namei.c | 1 + > > fs/f2fs/namei.c | 1 + > > fs/minix/namei.c | 2 +- > > fs/ubifs/dir.c | 1 + > > fs/udf/namei.c | 2 +- > > fs/xfs/xfs_iops.c | 13 ++----------- > > mm/shmem.c | 1 + > > 10 files changed, 15 insertions(+), 24 deletions(-) > > > > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c > > index 5c349667c761..bd189fc50f83 100644 > > --- a/fs/btrfs/inode.c > > +++ b/fs/btrfs/inode.c > > @@ -10382,14 +10382,6 @@ static int btrfs_tmpfile(struct inode *dir, struct dentry *dentry, umode_t mode) > > if (ret) > > goto out; > > > > - /* > > - * We set number of links to 0 in btrfs_new_inode(), and here we set > > - * it to 1 because d_tmpfile() will issue a warning if the count is 0, > > - * through: > > - * > > - * d_tmpfile() -> inode_dec_link_count() -> drop_nlink() > > - */ > > - set_nlink(inode, 1); > > d_tmpfile(dentry, inode); > > unlock_new_inode(inode); > > mark_inode_dirty(inode); > > diff --git a/fs/dcache.c b/fs/dcache.c > > index aac41adf4743..5fb4ecce2589 100644 > > --- a/fs/dcache.c > > +++ b/fs/dcache.c > > @@ -3042,12 +3042,16 @@ void d_genocide(struct dentry *parent) > > > > EXPORT_SYMBOL(d_genocide); > > > > +/* > > + * Instantiate an inode in the dentry cache as a temporary file. Callers must > > + * ensure that @inode has a zero link count. > > + */ > > void d_tmpfile(struct dentry *dentry, struct inode *inode) > > { > > - inode_dec_link_count(inode); > > BUG_ON(dentry->d_name.name != dentry->d_iname || > > !hlist_unhashed(&dentry->d_u.d_alias) || > > - !d_unlinked(dentry)); > > + !d_unlinked(dentry) || > > + inode->i_nlink != 0); > > You've just promoted i_nlink filesystem accounting error (which > are not that rare) from WARN_ON() to BUG_ON(), not to mention > Linus' objection to any use of BUG_ON() at all. > > !hlist_unhashed is anyway checked again in d_instantiate(). > !d_unlinked is not a reason to break the machine. > The name check is really not a reason to break the machine. > Can probably make tmp name code conditional to WARN_ON(). Fair enough, I'll remove the redundant checks and downgrade that to a WARN_ON, if nobody else objects.... --D > Thanks, > Amir.