Return-Path: linux-nfs-owner@vger.kernel.org Received: from fieldses.org ([174.143.236.118]:55393 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752141AbaAPQKT (ORCPT ); Thu, 16 Jan 2014 11:10:19 -0500 Date: Thu, 16 Jan 2014 11:10:16 -0500 From: "J. Bruce Fields" To: Al Viro Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org, Miklos Szeredi , Steven Whitehouse Subject: Re: [PATCH] dcache: fix d_splice_alias handling of aliases Message-ID: <20140116161015.GC16829@fieldses.org> References: <20140115151749.GF23999@fieldses.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20140115151749.GF23999@fieldses.org> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Wed, Jan 15, 2014 at 10:17:49AM -0500, bfields wrote: > From: "J. Bruce Fields" > > d_splice_alias can create duplicate directory aliases (in the !new > case), or (in the new case) d_move without holding appropriate locks. > > d_materialise_unique deals with both of these problems. (The latter > seems to be dealt by trylocks (see __d_unalias), which look like they > could cause spurious lookup failures--but that's at least better than > corrupting the dcache.) > > Signed-off-by: J. Bruce Fields > --- > fs/dcache.c | 25 +------------------------ > 1 file changed, 1 insertion(+), 24 deletions(-) > > Only lightly tested.... If this is right, then we can also just ditch > d_splice_alias completely, and clean up the various d_find_alias's. > > I think the only reason we have both d_splice_alias and > d_materialise_unique is that the former was written for exportable > filesystems and the latter for distributed filesystems. > > But we have at least one exportable filesystem (fuse) using > d_materialise_unique. And I doubt d_splice_alias was ever completely > correct even for on-disk filesystems. > > Am I missing some subtlety? Hm, I just noticed: commit 0d0d110720d7960b77c03c9f2597faaff4b484ae Author: Miklos Szeredi Date: Mon Sep 16 14:52:00 2013 +0200 GFS2: d_splice_alias() can't return error unless it was given an IS_ERR(inode), which isn't the case here. So clean up the unnecessary error handling in gfs2_create_inode(). This paves the way for real fixes (hence the stable Cc). Signed-off-by: Miklos Szeredi Signed-off-by: Steven Whitehouse Cc: stable@vger.kernel.org While the statement is true for the current implementation of d_splice_alias, I don't think it's actually true for any correct implementation of d_splice_alias, which must be able to return at least -ELOOP in the directory case. Does gfs2 need fixing? --b.