From: Eric Sandeen Subject: Re: [PATCH 3/3] Add timeout feature Date: Mon, 29 Sep 2008 09:45:31 -0500 Message-ID: <48E0EA0B.7000701@sandeen.net> References: <20080908205337t-sato@mail.jp.nec.com> <20080908171119.GB22521@infradead.org> <48DBFD42.6030307@redhat.com> <20080929141326.GA31781@infradead.org> <48E0E7D4.1090409@sandeen.net> <20080929143749.GA13286@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Takashi Sato , Ric Wheeler , Andrew Morton , Oleg Nesterov , linux-fsdevel@vger.kernel.org, dm-devel@redhat.com, viro@ZenIV.linux.org.uk, linux-ext4@vger.kernel.org, xfs@oss.sgi.com, axboe@kernel.dk, mtk.manpages@googlemail.com, linux-kernel@vger.kernel.org To: Christoph Hellwig Return-path: Received: from sandeen.net ([209.173.210.139]:14066 "EHLO sandeen.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751482AbYI2Opd (ORCPT ); Mon, 29 Sep 2008 10:45:33 -0400 In-Reply-To: <20080929143749.GA13286@infradead.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: Christoph Hellwig wrote: > On Mon, Sep 29, 2008 at 09:36:04AM -0500, Eric Sandeen wrote: >> Christoph Hellwig wrote: >>> On Fri, Sep 26, 2008 at 05:52:35PM +0900, Takashi Sato wrote: >>>> I think that your concern is that the freezer cannot recognize the occurrence >>>> of a timeout and it continues the backup process and the backup data is >>>> corrupted finally. >>> What timeout should happen? the freeze ioctl must not return until the >>> filesystem is a clean state and all writes are blocked. >> The suggestion was that *UN*freeze would return ETIMEDOUT if the >> filesystem had already unfrozen itself, I think. That way you know that >> the snapshot you just took is worthless, at least. > > But why would the filesystem every unfreeze itself? That defeats the > whole point of freezing it. I agree. Was just trying to clarify the above point. But there have been what, 12 submissions now, with the unfreeze timeout in place so it's a persistent theme ;) Perhaps a demonstration of just how easy (or not easy) it is to deadlock a filesystem by freezing the root might be in order, at least. And even if it is relatively easy, I still maintain that it is the administrator's role to not inflict damage on the machine being administered. There are a lot of potentially dangerous tools at root's disposal; why this particular one needs a nanny I'm still not quite sure. -Eric