linux-kernel - Re: [RC][PATCH -mm] PM: Prevent frozen user mode helpers from failing the freezing of tasks

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Message-ID: <20070624170514.GA21757@elf.ucw.cz>
Date:	Sun, 24 Jun 2007 19:05:14 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Uli Luckas <u.luckas@...d.de>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [RC][PATCH -mm] PM: Prevent frozen user mode helpers from failing the freezing of tasks

Hi!

> > > Special thanks to Uli Luckas <u.luckas@...d.de> for reviewing the previous
> > > versions of this patch and for very useful comments.
> > ...
> > > Reviewed-by: Pavel Machek <pavel@....cz>
> > 
> > Eh, not sure this header is worth anything. Sometimes I'm lazy and
> > stop when I see first problem.
> > 
> > >  	switch (action) {
> > >  	case PM_HIBERNATION_PREPARE:
> > >  	case PM_SUSPEND_PREPARE:
> > >  		usermodehelper_disabled = 1;
> > > -		return NOTIFY_OK;
> > > +		retval = wait_event_timeout(running_helpers_waitq,
> > > +					atomic_read(&running_helpers) == 0,
> > 
> > Are you sure here? What happens when atomic variable changes between
> > the atomic_read and the function call?
> 
> Er, this is a macro. :-)
> 
> In fact we rely only on atomic_read(&running_helpers) being still zero after
> helper_finished() has woken us up, but I think that's acceptable.
> 
> IOW, if the wait_event_timeout() returns with retval different from zero, this
> means that atomic_read(&running_helpers) returned zero at one point after
> we'd set usermodehelper_disabled, which is enough.  OTOH, if it doesn't

Ok, can you write short comment explaining that? /* We have set
usermodehelper_disabled, so any new usermode helpers are not a problem
*/.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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