linux-kernel - Re: [PATCH -mm] PM: Prevent frozen user mode helpers from failing the freezing of tasks (rev. 2)

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Date:	Tue, 03 Jul 2007 15:30:46 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Pavel Machek <pavel@....cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Uli Luckas <u.luckas@...d.de>, Oleg Nesterov <oleg@...sign.ru>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm] PM: Prevent frozen user mode helpers from failing
	the freezing of tasks (rev. 2)

On Tue, 2007-06-26 at 00:27 +0200, Rafael J. Wysocki wrote:
> > >     case PM_HIBERNATION_PREPARE:
> > >     case PM_SUSPEND_PREPARE:
> > >             usermodehelper_disabled = 1;
> > > -           return NOTIFY_OK;
> > > +           smp_mb();
> > 
> > usermodehelper_disabled should be atomic variable, too, so we don't
> > have to play these ugly tricks by hand? This should not be
> > performance-critical, right?
> 
> Well, I think we'd need to add the barriers anyway.
> 
> The problem, as far as I understand it, is that the instructions can
> get
> reordered if there are no barriers in there.

That seems dodgy either way to me :-)

Just use a spinlock.

Ben.

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