linux-kernel - Re: [PATCH 1/3] PM: Introduce new top level suspend and hibernation callbacks (rev. 8)

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Message-Id: <200804140259.20962.rjw@sisk.pl>
Date:	Mon, 14 Apr 2008 02:59:19 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	benh@...nel.crashing.org
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Nigel Cunningham <ncunningham@...a.org.au>,
	Greg KH <greg@...ah.com>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Len Brown <lenb@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexey Starikovskiy <astarikovskiy@...e.de>,
	David Brownell <david-b@...bell.net>,
	Pavel Machek <pavel@....cz>, Oliver Neukum <oliver@...kum.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/3] PM: Introduce new top level suspend and hibernation callbacks (rev. 8)

On Monday, 14 of April 2008, Benjamin Herrenschmidt wrote:
> 
> > Please have a look at this thread:
> > http://lkml.org/lkml/2008/3/21/322
> > (in short, the reporter sees APM suspend breakage under stress, occuring
> > because APM uses our suspending of devices without the freezer).
> > 
> > It mostly appears to work without the freezer, but that's bacuse no one
> > actually does things that might break it.  I don't think we can rely on users
> > being so kind to us forever. :-)
> 
> As far as I'm concerned, it's yet another case of the freezer papering
> over a problem rather than fixing it properly.

Well, this is not a user's point of view.

> If we're going to introduce new callbacks, we should have the right
> semantic from day 1 -and- fix those problems, rather than going to the
> same old recursive nonsensical arguments and do things to paper over
> problems.

Still, we're not supposed to break things, as far as the functionality is
concerned, and that's important, because it means we _have_ _to_ make changes
in steps.

To be more precise, what you suggest (move ->prepare() before the freezer
right now) means a patch with _functional_ changes (it's impossible to register
new children of dev after ->prepare(dev) has run which can affect the user
space in the window before ->prepare() and the freezer), whereas what I'd like
to do is the (present) patch without functional changes.

Thanks,
Rafael
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