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 BE7DCC433B4 for ; Tue, 18 May 2021 18:21:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8DB97600D4 for ; Tue, 18 May 2021 18:21:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344389AbhERSWf (ORCPT ); Tue, 18 May 2021 14:22:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51634 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245506AbhERSWe (ORCPT ); Tue, 18 May 2021 14:22:34 -0400 Received: from fieldses.org (fieldses.org [IPv6:2600:3c00:e000:2f7::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4041EC061573 for ; Tue, 18 May 2021 11:21:16 -0700 (PDT) Received: by fieldses.org (Postfix, from userid 2815) id 1688C64B9; Tue, 18 May 2021 14:21:15 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.11.0 fieldses.org 1688C64B9 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fieldses.org; s=default; t=1621362075; bh=eDZ5wijqSsSeETdzDqG2bQWmCJjMFwhiJ2aNURILkjE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=RSnQ6lCQDcVnjwpekBKIKvlfhoTLk513jTU4K4vAL6hZKsPYTkk+cbrzYUz4hDXqU Ja8XX9ZvZbvB/fD/2n1bL/ZOpjuHE/aqgsmQoI9ZeDnX7EX+SykYAF4oqj2asr8ZlT S037iWBEbNPvPf5jSFWXY5KaSSGt15IRgNppjW4A= Date: Tue, 18 May 2021 14:21:15 -0400 From: "bfields@fieldses.org" To: Trond Myklebust Cc: "hch@infradead.org" , "robbieko@synology.com" , "bingjingc@synology.com" , "linux-nfs@vger.kernel.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: <20210518182115.GB26957@fieldses.org> References: <20210514035829.5230-1-nickhuang@synology.com> <00195ec8bf1752306f549540eed74c3938c5e312.camel@hammerspace.com> <4387867bd64c5d3d8c67830a633b90e4a7e1ba38.camel@hammerspace.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <4387867bd64c5d3d8c67830a633b90e4a7e1ba38.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 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? 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.