linux-kernel - Re: better oopsing when frozen

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Message-Id: <201107271121.21348.rjw@sisk.pl>
Date:	Wed, 27 Jul 2011 11:21:21 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Oliver Neukum <oneukum@...e.de>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: better oopsing when frozen

On Wednesday, July 27, 2011, Andrew Morton wrote:
> On Wed, 27 Jul 2011 00:24:11 +0200
> "Rafael J. Wysocki" <rjw@...k.pl> wrote:
> 
> > > Hi Rafael,
> > > 
> > > I had a problem with the kernel stopping the machine forever because I got an
> > > oops while tasks were frozen. It seems to me that we should thaw when this
> > > happens. How about this approach?
> > 
> > Well, we do something like this already for the OOM killer (see
> > oom_killer_disable() and friends), so I think it would be better to
> > simply extend/modify that mechanism instead of adding a new one
> > doing almost exactly the same thing.
> > 
> > I have no complaints about adding thaw_in_oops(), though, so long as
> > Andrew thinks it makes sense.
> 
> mm...  The patch as proposed is very simple, direct, explicit.  I
> suspect that trying to embed this operation within some other one would
> end up producing a less clear result.  Sometimes we do exceptional and
> weird things, and leaving the code exceptional and weird-looking is
> better than hiding it in some framework, if you follow what I mean.

My point is that instead of using the oom_killer_disabled variable in
page_alloc.c, we could use a oom_killer_disabled() function returning
the value of the new tasks_are_frozen variable.  Then,
oom_killer_disable/enable() won't be necessary any more.

> It does need some code comments to explain to people what it's doing
> and more importantly why it's doing it.  Also, something which doesn't
> break the build when CONFIG_FREEZER=n would be nice.

Right.

Thanks,
Rafael
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