linux-kernel - Re: Getting rid of freezer for suspend [was Re: [fuse-devel] [PATCH] fuse: make fuse daemon frozen along with kernel threads]

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: <20130210185504.GA17268@amd.pavel.ucw.cz>
Date:	Sun, 10 Feb 2013 19:55:05 +0100
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Miklos Szeredi <miklos@...redi.hu>,
	Goswin von Brederlow <goswin-v-b@....de>,
	Li Fei <fei.li@...el.com>, len.brown@...el.com,
	mingo@...hat.com, peterz@...radead.org, biao.wang@...el.com,
	linux-pm@...r.kernel.org, fuse-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, chuansheng.liu@...el.com
Subject: Re: Getting rid of freezer for suspend [was Re: [fuse-devel]
 [PATCH] fuse: make fuse daemon frozen along with kernel threads]

Hi!

> > > > The whole memory shrinking we do for hibernation is now done by allocating
> > > > memory, so the freezer is not necessary for *that* and there's *zero*
> > > > difference between suspend and hibernation with respect to why the freezer is
> > > > used.
> > > 
> > > Funny. Freezer was put there so that hibernation image was safe to
> > > write out. You need disk subsystems in workable state for hibernation.
> > 
> > I'm not really sure what you're talking about.  Why do you think the freezer is
> > necessary for that?

Well, from freezer you need:

1) user process frozen.

2) essential locks _not_ held so that block devices are still functional.

> > > mmap... what is problem with mmap? For suspend, memory is powered, so
> > > you can permit people changing it.
> > 
> > Suppose mmap is used to make the registers of some device available to user
> > space.  Yes, that can happen.

"Don't do it, then". Yes, can happen, but hopefully is not too common
these days. [And... freezer doing 1) but not 2) would be enough to
handle that. Freezer doing 1) but not 2) would also be simpler...]

> > Again, I'm not sure what you're talking about.  Once the image has been
> > created, it can be saved while user space is running just fine.
> 
> Of course, we don't want random changes to be made to persistent storage after
> the image has been created, because those changes might not be consistent with
> the memory contents stored in the image, and that's why user space is still
> frozen when we're saving the image.

Yes. That's the reason 1) for freezer.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
--
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/