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

From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Pavel Machek <pavel@ucw.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	Nigel Cunningham <nigel@nigel.suspend2.net>,
	Uli Luckas <u.luckas@road.de>, Oleg Nesterov <oleg@tv-sign.ru>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH -mm] PM: Prevent frozen user mode helpers from failing the freezing of tasks (rev. 2)
Date: Tue, 03 Jul 2007 15:30:46 +1000	[thread overview]
Message-ID: <1183440646.10386.66.camel@localhost.localdomain> (raw)
In-Reply-To: <200706260027.02396.rjw@sisk.pl>

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.