linux-kernel - Re: No freezing of kernel threads (was: Re: [GIT PULL] libata fixes for v3.13-rc5)

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Date:	Sat, 11 Jan 2014 22:15:21 +0100
From:	Pavel Machek <pavel@....cz>
To:	Tejun Heo <tj@...nel.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Alan Stern <stern@...land.harvard.edu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	linux-ide@...r.kernel.org,
	Linux-pm mailing list <linux-pm@...r.kernel.org>
Subject: Re: No freezing of kernel threads (was: Re: [GIT PULL] libata
 fixes for v3.13-rc5)

Hi!

> > Well, it looks like we don't really know why things are done the way they
> > are done at least in some cases, so in my personal view it would be good to
> > go through all of the kernel freezer users just for this reason alone.  We
> > can't really say which of them are legitimate without that and how difficult
> > it would be for them to switch over to using something more fine grained than
> > the freezer.
> 
> I'm a bit worried about things which may not be explicit.
> ie. something which is broken but sorta working because things like
> writeback and jbd are frozen.  I think I worry about that because I
> remember one argument for kernel freezer from way way back, that it's
> too hard to implement proper suspend/resume for all drivers and by
> freezing most kthreads things should mostly work, which sounded pretty
> crazy to me even back then.  Hopefully, we don't have much left
> depending on such magic.

Careful there. Hibernation depends on data on disk not changing after
freeze.

So you definitely do _not_ want writeback/jbd running while uswsusp
does its image writing.

(I wonder what happens if uswsusp needs to trigger writeback to free
memory. But I'm too scared to check :-).
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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