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=-12.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 08F33C433B4 for ; Tue, 18 May 2021 18:40:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D8511610CD for ; Tue, 18 May 2021 18:40:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351611AbhERSlU (ORCPT ); Tue, 18 May 2021 14:41:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55942 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343747AbhERSlT (ORCPT ); Tue, 18 May 2021 14:41:19 -0400 Received: from fieldses.org (fieldses.org [IPv6:2600:3c00:e000:2f7::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C7166C061573 for ; Tue, 18 May 2021 11:40:00 -0700 (PDT) Received: by fieldses.org (Postfix, from userid 2815) id C35054F7D; Tue, 18 May 2021 14:39:59 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.11.0 fieldses.org C35054F7D DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fieldses.org; s=default; t=1621363199; bh=pcz8UXo9//gxbL3GlspfgdEbVFVh6hDUCWykYhuttcw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=s9bpohjW/0j5QYiJyrhWDVirY3lPd+OyNbO/17tu1nBnqQOrW34/2u26gwxbOwr6/ a8THasDie4ieMaBlY970ADPHuYEcKxk18mgMh/vlWQIStAlv6UYKkrpCi6r3OzHp8e o4crlVE4WesxNsfGrt+p2FgrYrW0q42QfbBauC10= Date: Tue, 18 May 2021 14:39:59 -0400 From: "bfields@fieldses.org" To: Trond Myklebust Cc: "robbieko@synology.com" , "bingjingc@synology.com" , "linux-nfs@vger.kernel.org" , "hch@infradead.org" , "nickhuang@synology.com" , "chuck.lever@oracle.com" Subject: Re: [PATCH] nfsd: Prevent truncation of an unlinked inode from blocking access to its directory Message-ID: <20210518183959.GC26957@fieldses.org> References: <20210514035829.5230-1-nickhuang@synology.com> <00195ec8bf1752306f549540eed74c3938c5e312.camel@hammerspace.com> <4387867bd64c5d3d8c67830a633b90e4a7e1ba38.camel@hammerspace.com> <20210518182115.GB26957@fieldses.org> <924d92d52116cff9c0203b84a02d45352bfad361.camel@hammerspace.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <924d92d52116cff9c0203b84a02d45352bfad361.camel@hammerspace.com> User-Agent: Mutt/1.5.21 (2010-09-15) Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org On Tue, May 18, 2021 at 06:36:23PM +0000, Trond Myklebust wrote: > On Tue, 2021-05-18 at 14:21 -0400, bfields@fieldses.org wrote: > > On Tue, May 18, 2021 at 05:53:47PM +0000, Trond Myklebust wrote: > > > On Sat, 2021-05-15 at 08:02 +0100, Christoph Hellwig wrote: > > > > On Fri, May 14, 2021 at 03:46:57PM +0000, Trond Myklebust wrote: > > > > > Why leave the commit_metadata() call under the lock? If you're > > > > > concerned about latency, then it makes more sense to call > > > > > fh_unlock() > > > > > before flushing those metadata updates to disk. > > > > > > > > Also I'm not sure why the extra inode reference is needed.  What > > > > speaks > > > > against just moving the dput out of the locked section? > > > > > > Isn't the inode reference taken just in order to ensure that the > > > call > > > to iput_final() (and in particular the call to > > > truncate_inode_pages_final()) is performed outside the lock? > > > > > > The dput() is presumably usually not particularly expensive, since > > > the > > > dentry is just a completely ordinary negative dentry at this point. > > > > Right, but why bother with the extra ihold/iput instead of just > > postponing the dput? > > As I said above, the dentry is negative at this point. It doesn't carry > a reference to the inode any more, so that wouldn't defer the inode > truncation. Oh, of course, thanks! --b. > > > > > diff --git a/fs/namei.c b/fs/namei.c > > index 79b0ff9b151e..aeed93c9874c 100644 > > --- a/fs/namei.c > > +++ b/fs/namei.c > > @@ -4084,7 +4084,6 @@ long do_unlinkat(int dfd, struct filename > > *name) > >                 inode = dentry->d_inode; > >                 if (d_is_negative(dentry)) > >                         goto slashes; > > -               ihold(inode); > >                 error = security_path_unlink(&path, dentry); > >                 if (error) > >                         goto exit2; > > @@ -4092,11 +4091,10 @@ long do_unlinkat(int dfd, struct filename > > *name) > >                 error = vfs_unlink(mnt_userns, path.dentry->d_inode, > > dentry, > >                                    &delegated_inode); > >  exit2: > > -               dput(dentry); > >         } > >         inode_unlock(path.dentry->d_inode); > > -       if (inode) > > -               iput(inode);    /* truncate the inode here */ > > +       if (!IS_ERR(dentry)) > > +               dput(dentry);   /* truncate the inode here */ > >         inode = NULL; > >         if (delegated_inode) { > >                 error = break_deleg_wait(&delegated_inode); > > > > ? > > > > --b. > > -- > Trond Myklebust > Linux NFS client maintainer, Hammerspace > trond.myklebust@hammerspace.com > >