linux-kernel - Re: freeze vs freezer

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Message-Id: <200801042154.08758.oliver@neukum.org>
Date:	Fri, 4 Jan 2008 21:54:06 +0100
From:	Oliver Neukum <oliver@...kum.org>
To:	nigel@...el.suspend2.net
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, Pavel Machek <pavel@....cz>,
	Kyle Moffett <mrmacman_g4@....com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	David Chinner <dgc@....com>,
	Jeremy Fitzhardinge <jeremy@...p.org>, xfs-masters@....sgi.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: freeze vs freezer

Am Donnerstag, 3. Januar 2008 23:06:07 schrieb Nigel Cunningham:
> Hi.
> 
> Oliver Neukum wrote:
> > Am Donnerstag, 3. Januar 2008 10:52:53 schrieb Nigel Cunningham:
> >> Hi.
> >>
> >> Oliver Neukum wrote:
> >>> Am Donnerstag 03 Januar 2008 schrieb Nigel Cunningham:
> >>>> On top of this, I made a (too simple at the moment) freeze_filesystems
> >>>> function which iterates through &super_blocks in reverse order, freezing
> >>>> fuse filesystems or ordinary ones. I say 'too simple' because it doesn't
> >>>> currently allow for the possibility of someone mounting (say) ext3 on
> >>>> fuse, but that would just be an extension of what's already done.
> >>> How do you deal with fuse server tasks using other fuse filesystems?
> >> Since they're frozen in reverse order, the dependant one would be frozen
> >> first.
> > 
> > Say I do:
> > 
> > a) mount fuse on /tmp/first
> > b) mount fuse on /tmp/second
> > 
> > Then the server task for (a) does "ls /tmp/second". So it will be frozen,
> > right? How do you then freeze (a)? And keep in mind that the server task
> > may have forked.
> 
> I guess I should first ask, is this a real life problem or a
> hypothetical twisted web? I don't see why you would want to make two
> filesystems interdependent - it sounds like the way to create livelock
> and deadlocks in normal use, before we even begin to think about
> hibernating.

Good questions. I personally don't use fuse, but I do care about power
management. The problem I see is that an unprivileged user could make
that dependency, even inadvertedly.

	Regards
		Oliver

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