From owner-freebsd-fs@FreeBSD.ORG  Fri Jan 13 00:24:55 2012
Return-Path: <owner-freebsd-fs@FreeBSD.ORG>
Delivered-To: freebsd-fs@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 711CB106564A;
	Fri, 13 Jan 2012 00:24:55 +0000 (UTC)
	(envelope-from mckusick@mckusick.com)
Received: from chez.mckusick.com (unknown
	[IPv6:2001:5a8:4:7e72:4a5b:39ff:fe12:452])
	by mx1.freebsd.org (Postfix) with ESMTP id 52D478FC0A;
	Fri, 13 Jan 2012 00:24:55 +0000 (UTC)
Received: from chez.mckusick.com (localhost [127.0.0.1])
	by chez.mckusick.com (8.14.3/8.14.3) with ESMTP id q0D0OflU055874;
	Thu, 12 Jan 2012 16:24:41 -0800 (PST)
	(envelope-from mckusick@chez.mckusick.com)
Message-Id: <201201130024.q0D0OflU055874@chez.mckusick.com>
To: freebsd-fs@freebsd.org
In-reply-to: <20120111103039.d342aef4.lists@yamagi.org> 
Date: Thu, 12 Jan 2012 16:24:41 -0800
From: Kirk McKusick <mckusick@mckusick.com>
X-Spam-Status: No, score=0.0 required=5.0 tests=MISSING_MID, UNPARSEABLE_RELAY
	autolearn=failed version=3.2.5
X-Spam-Checker-Version: SpamAssassin 3.2.5 (2008-06-10) on chez.mckusick.com
Cc: bryce@bryce.net, Gautam Mani <gautam@execve.net>
Subject: Re: FS hang when creating snapshots on a UFS SU+J setup 
X-BeenThere: freebsd-fs@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Filesystems <freebsd-fs.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-fs>,
	<mailto:freebsd-fs-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-fs>
List-Post: <mailto:freebsd-fs@freebsd.org>
List-Help: <mailto:freebsd-fs-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-fs>,
	<mailto:freebsd-fs-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 13 Jan 2012 00:24:55 -0000

Hi all,

With a gentle reminder from Peter Holm that he has a test that
demonstrates this problem and the additional examples provided
by several of you, I can now reliably reproduce the problem.

Having spent a day trying to get to the bottom of it, I have
decided that it is a `hard problem' which is going to require
some time to figure out. I am hopeful that Jeff will come up
with some time to help out here, but know that he is rather
busy on other projects at the moment.

My conclusion is that as an interim solution, we disable the
ability to request snapshots on filesystems that are using SU+J.
Notably, if a snapshot is attempted, the request fail with a
message that reports that snapshots are currently supported
only on systems running with SU. I think that this would be
far preferable to the current situation. Does this seem like
a reasonable approach?

	Kirk McKusick