From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753507AbXDKSKS (ORCPT ); Wed, 11 Apr 2007 14:10:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753508AbXDKSKR (ORCPT ); Wed, 11 Apr 2007 14:10:17 -0400 Received: from out4.smtp.messagingengine.com ([66.111.4.28]:36730 "EHLO out4.smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753507AbXDKSKP (ORCPT ); Wed, 11 Apr 2007 14:10:15 -0400 X-Sasl-enc: DnQquBKrwx+gAy5Z/Ddgni1xxfbz6EWSYzyPyvKwURVJ 1176315015 Subject: Re: [PATCH] autofs4: fix race in unhashed dentry code From: Ian Kent To: Jeff Mahoney Cc: Linux Kernel Mailing List , Andrew Morton In-Reply-To: <1176314412.3377.29.camel@raven.themaw.net> References: <461CF939.9030104@suse.com> <1176313777.3377.21.camel@raven.themaw.net> <1176314412.3377.29.camel@raven.themaw.net> Content-Type: text/plain Date: Thu, 12 Apr 2007 02:08:14 +0800 Message-Id: <1176314894.3377.34.camel@raven.themaw.net> Mime-Version: 1.0 X-Mailer: Evolution 2.8.0 (2.8.0-32.el5) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2007-04-12 at 02:00 +0800, Ian Kent wrote: > On Thu, 2007-04-12 at 01:49 +0800, Ian Kent wrote: > > On Wed, 2007-04-11 at 11:05 -0400, Jeff Mahoney wrote: > > > Commit f50b6f8691cae2e0064c499dd3ef3f31142987f0 introduced a > > > race in autofs4 between autofs_lookup_unhashed() and > > > autofs_dentry_release(). > > > > > > autofs_dentry_release() ends up clearing the ->dentry and ->inode > > > members of autofs_info before removing it from the rehash list. The > > > list is protected by the rehash lock in both functions, but > > > since autofs_dentry_release() starts tearing the autofs_info struct > > > down before removing it from the list, autofs_lookup_unhashed() can > > > get a autofs_info with a NULL dentry. > > > > > > This patch moves the clearing of ->dentry and ->inode after the removal > > > from the rehash list. > > > > Oh .. excellent, I had a bug report but I just couldn't see it for > > looking. > > Maybe I've been a bit hasty with the celebration. > It looks like I've got a bigger locking problem here. > If autofs4_dentry_release waits on the rehash lock and > autofs4_lookup_unhashed reclaims it then the info struct and the dentry > go away unconditionally as the release is called just prior to freeing > the dentry memory, right?. No I'm wrong, dentry_iput holds the dcache locks till it sets d_inode to NULL, the point of the d_inode check in autofs4_lookup_unhashed. My day is still made. > > > > You've made my day. > > Thanks heaps > > Ian > > > > > > > > Signed-off-by: Jeff Mahoney > > Acked-by: Ian Kent > > > > > > > > --- > > > > > > fs/autofs4/root.c | 6 +++--- > > > 1 file changed, 3 insertions(+), 3 deletions(-) > > > > > > --- a/fs/autofs4/root.c 2007-04-11 09:41:44.000000000 -0400 > > > +++ b/fs/autofs4/root.c 2007-04-11 10:54:37.000000000 -0400 > > > @@ -470,9 +470,6 @@ void autofs4_dentry_release(struct dentr > > > if (inf) { > > > struct autofs_sb_info *sbi = autofs4_sbi(de->d_sb); > > > > > > - inf->dentry = NULL; > > > - inf->inode = NULL; > > > - > > > if (sbi) { > > > spin_lock(&sbi->rehash_lock); > > > if (!list_empty(&inf->rehash)) > > > @@ -480,6 +477,9 @@ void autofs4_dentry_release(struct dentr > > > spin_unlock(&sbi->rehash_lock); > > > } > > > > > > + inf->dentry = NULL; > > > + inf->inode = NULL; > > > + > > > autofs4_free_ino(inf); > > > } > > > } > > >