linux-kernel - Re: [patch 128/197] freezer: add try_to

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Message-ID: <20070509104949.GA8164@elf.ucw.cz>
Date:	Wed, 9 May 2007 12:49:49 +0200
From:	Pavel Machek <pavel@....cz>
To:	Stefan Richter <stefanr@...6.in-berlin.de>
Cc:	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	rjw@...k.pl, James.Bottomley@...elEye.com, aneesh.kumar@...il.com,
	drzeus@...eus.cx, dwmw2@...radead.org, ego@...ibm.com,
	greg@...ah.com, mingo@...e.hu, neilb@...e.de, oleg@...sign.ru,
	paulmck@...ux.vnet.ibm.com, vatsa@...ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 128/197] freezer: add try_to_freeze calls to all kernel threads

Hi!

> > Add try_to_freeze() calls to the remaining kernel threads that do not call
> > try_to_freeze() already, although they set PF_NOFREEZE.
> > 
> > In the future we are going to replace PF_NOFREEZE with a set of flags that
> > will be set to indicate in which situations the task should not be frozen (for
> > example, there can be a task that should be frozen for the CPU hotplugging and
> > should not be frozen for the system suspend).  For this reason every kernel
> > thread should be able to freeze itself (ie.  call try_to_freeze()), so that it
> > can be frozen whenever necessary.
> 
> A few questions:
> 
> Does try_to_freeze()'s kerneldoc document that try_to_freeze() is a
> no-op sometimes but should nevertheless be called for this and that
> reason?  (I don't know the entire patch series.)
> 
> Why add no-op-try_to_freeze() everywhere now, instead of adding it later
> when it will actually be needed?  (I.e. "in the future".)

It is needed later in the patch series... for kprobes, etc.

> Can we please have a future where no device driver has to care if and
> when and how to freeze its threads?

No. Freezing is useful for kprobes/cpu hotplug as well as suspend.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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