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

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Date:	Mon, 11 Feb 2013 00:31:03 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
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]

On Sunday, February 10, 2013 07:55:05 PM Pavel Machek wrote:
> 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 mean.

Are you trying to say that it would be OK to freeze user space tasks in
the D state?

Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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