From mboxrd@z Thu Jan  1 00:00:00 1970
From: Cyrill Gorcunov <gorcunov@gmail.com>
Subject: Re: [patch 0/3] A few patches for dcache
Date: Fri, 29 Jul 2011 11:50:39 +0400
Message-ID: <20110729075039.GD15883@sun>
References: <20110728131219.146414619@openvz.org>
 <20110729032503.GD5404@dastard>
 <20110729055918.GB15883@sun>
 <20110729065951.GE5404@dastard>
 <20110729072441.GA2203@ZenIV.linux.org.uk>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Dave Chinner <david@fromorbit.com>,
	LINUXFS-ML <linux-fsdevel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Christoph Hellwig <hch@infradead.org>,
	James Bottomley <jbottomley@parallels.com>, xemul@openvz.org
To: Al Viro <viro@ZenIV.linux.org.uk>
Return-path: <linux-fsdevel-owner@vger.kernel.org>
Received: from mail-fx0-f46.google.com ([209.85.161.46]:63368 "EHLO
	mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1755040Ab1G2Huo (ORCPT
	<rfc822;linux-fsdevel@vger.kernel.org>);
	Fri, 29 Jul 2011 03:50:44 -0400
Received: by fxh19 with SMTP id 19so2034660fxh.19
        for <linux-fsdevel@vger.kernel.org>; Fri, 29 Jul 2011 00:50:43 -0700 (PDT)
Content-Disposition: inline
In-Reply-To: <20110729072441.GA2203@ZenIV.linux.org.uk>
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>

On Fri, Jul 29, 2011 at 08:24:41AM +0100, Al Viro wrote:
...
> > > 
> > > Thanks for comments, Dave! Still the read only lock without
> > > increasing sequence number might be useful, no? (patch 1)
> > 
> > I'll defer to Al on that one - the intricacies of the rename locking
> > are way over my head.
> 
> I'm not sure that's safe.  Note that one use of rename_lock is that
> we allow hash lookup to race with d_move().  Which can move object
> from one hash chain to another, so hash lookup may end up jumping
> from one chain to another and getting a false negative.  That's
> why __d_lookup() is not safe without read_seqretry loop (or seq_writelock,
> of course).
> 
...

Thanks a lot for explanations, Al!

	Cyrill