From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756908Ab3KMMjz (ORCPT ); Wed, 13 Nov 2013 07:39:55 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:45640 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751530Ab3KMMjv (ORCPT ); Wed, 13 Nov 2013 07:39:51 -0500 Date: Wed, 13 Nov 2013 12:39:47 +0000 From: Al Viro To: Michael Marineau Cc: Waiman Long , linux-kernel@vger.kernel.org Subject: Re: 3.12 Regression: dcache: Translating dentry into pathname without taking rename_lock 232d2d60 Message-ID: <20131113123947.GB13318@ZenIV.linux.org.uk> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 13, 2013 at 03:34:13AM -0800, Michael Marineau wrote: > Greetings, > > Commit 232d2d60aa5469bb097f55728f65146bd49c1d25 causes intermittent > errors in /proc/*/fd/* where readlink returns "/" instead of the > correct path. This can be reproduced by the script below which copies > the kernel source directory structure while obsessively looking up > directory fds in proc from another process. Reverting > 232d2d60aa5469bb097f55728f65146bd49c1d25 after two related commits > 48f5ec21d9c67e881ff35343988e290ef5cf933f > 1812997720ab90d029548778c55d7315555e1fef fixes the issue. Looking into it... It seems that we are getting to the end of prepend_path() with non-negative error and bptr == *buffer. What the... OK, I see what's going on. We never reinitialize dentry, vfsmount and mnt if we decide to restart. See if the following helps: diff --git a/fs/dcache.c b/fs/dcache.c index ae6ebb8..89f9671 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2881,9 +2881,9 @@ static int prepend_path(const struct path *path, const struct path *root, char **buffer, int *buflen) { - struct dentry *dentry = path->dentry; - struct vfsmount *vfsmnt = path->mnt; - struct mount *mnt = real_mount(vfsmnt); + struct dentry *dentry; + struct vfsmount *vfsmnt; + struct mount *mnt; int error = 0; unsigned seq = 0; char *bptr; @@ -2893,6 +2893,9 @@ static int prepend_path(const struct path *path, restart: bptr = *buffer; blen = *buflen; + dentry = path->dentry; + vfsmnt = path->mnt; + mnt = real_mount(vfsmnt); read_seqbegin_or_lock(&rename_lock, &seq); while (dentry != root->dentry || vfsmnt != root->mnt) { struct dentry * parent;