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

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Message-Id: <200706260027.02396.rjw@sisk.pl>
Date:	Tue, 26 Jun 2007 00:27:01 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	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 Monday, 25 June 2007 23:55, Pavel Machek wrote:
> Hi!
> 
> > [I hope the ACKs still apply.]
> 
> Uhuh, not 100% sure.
> 
> > +static int usermodehelper_disabled;
> > +
> 
> 
> ...
> 
> >  	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.

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
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