linux-kernel - Re: Ext4 and the "30 second window of death"

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20090403134208.GB19774@srcf.ucam.org>
Date:	Fri, 3 Apr 2009 14:42:08 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	david@...g.hm
Cc:	Theodore Tso <tytso@....edu>, Sitsofe Wheeler <sitsofe@...oo.com>,
	"Andreas T.Auer" <andreas.t.auer_lkml_73537@...us.ath.cx>,
	Alberto Gonzalez <info@...bu.es>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Ext4 and the "30 second window of death"

On Thu, Apr 02, 2009 at 08:08:36PM -0700, david@...g.hm wrote:
> On Fri, 3 Apr 2009, Matthew Garrett wrote:
> >Well, yes, the administrator could hate the user. They could achieve the
> >same affect by just LD_PRELOADING something that stubbed out fsync() and
> >inserted random data into every other write(). We generally trust that
> >admins won't do that.
> 
> then trust the admins to make a reasonable decision for or with the user 
> on this as well.

What a reasonable decision is here depends on what software the user is 
running. There simply isn't a reasonable default other than to allow 
fsync() to work. Changing requires auditing every single piece of code 
the user may run.

> >There's various circumstances in which it's beneficial. The difference
> >between an optimal algorithm for typical use and an optimal algorithm
> >for typical use where there's an fsync() every 5 minutes isn't actually
> >that great.
> 
> mixing some sub-threads a bit to combine thoughts
> 
> you object to calling something like this 'laptop mode'
> 
> Ted's statements about laptop mode indicate that he believes that it 
> delays writes for a configurable time rather than accelerating writes.

As I said, the code is pretty easy to read.

(snip)

> thoughts?

I've certainly got no objection to the addition of a mode that changes 
the behaviour of fsync() - personally I think it would be an error for 
almost anyone to use it, but that's really up to the individual 
situation. But it would have a different goal to the existing 
laptop-mode and so should have a different name in order to avoid 
confusion.

-- 
Matthew Garrett | mjg59@...f.ucam.org
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/