Return-Path: <linux-kernel-owner+willy=40w.ods.org@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id <S265108AbTAPPxt>; Thu, 16 Jan 2003 10:53:49 -0500
Received: (majordomo@vger.kernel.org) by vger.kernel.org
	id <S266278AbTAPPxt>; Thu, 16 Jan 2003 10:53:49 -0500
Received: from 216-42-72-144.ppp.netsville.net ([216.42.72.144]:45800 "EHLO
	tiny.suse.com") by vger.kernel.org with ESMTP id <S265108AbTAPPxs>;
	Thu, 16 Jan 2003 10:53:48 -0500
Subject: Re: [2.4] VFS locking problem during concurrent link/unlink
From: Chris Mason <mason@suse.com>
To: Oleg Drokin <green@namesys.com>
Cc: linux-kernel@vger.kernel.org, eazgwmir@umail.furryterror.org,
       viro@math.psu.edu, nikita@namesys.com
In-Reply-To: <20030116184352.A32192@namesys.com>
References: <20030116140015.A17612@namesys.com>
	 <1042731580.31099.2195.camel@tiny.suse.com>
	 <20030116184352.A32192@namesys.com>
Content-Type: text/plain
Organization: 
Message-Id: <1042732927.31100.2205.camel@tiny.suse.com>
Mime-Version: 1.0
X-Mailer: Ximian Evolution 1.2.1 
Date: 16 Jan 2003 11:02:08 -0500
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, 2003-01-16 at 10:43, Oleg Drokin wrote:
> Hello!
> 
> On Thu, Jan 16, 2003 at 10:39:41AM -0500, Chris Mason wrote:
> > >    Debugging reiserfs problem that can be demonstrated with script created by
> > >    Zygo Blaxell, I started to wonder if the problem presented is indeed reiserfs
> > >    fault and not VFS.
> > >    Though the Zygo claims script only produces problems on reiserfs, I am trying
> > >    it now myself on ext2 (which will take some time).
> > > 
> > >    Debugging shows that reiserfs_link is sometimes called for inodes whose
> > >    i_nlink is zero (and all corresponding data is deleted already).
> > >    So my current guess of what's going on is this:
> > No, this is a reiserfs bug, since we schedule after doing link checks in
> > reiserfs_link and reiserfs_unlink.  I sent a patch to reiserfs dev a
> > while ago, I'll pull it out of the suse kernel and rediff against
> > 2.4.20.
> 
> Yes we do.
> But on the other hand I've put a check at the beginning of reiserfs_link
> and I am still seeing these links on inodes with i_nlink == 0.

That's because we don't inc the link count in reiserfs_link before we
schedule.  The bug works a little like this:

link count at 1
reiserfs_link: make new directory entry for link, schedule()
reiserfs_unlink: dec link count to zero, remove file stat data
reiserfs_link: inc link count, return thinking the stat data is still
there

All of which leads to expanding chaos as we process this link pointing
to nowhere but still have a valid in ram inode pointing to it.

-chris


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/