linux-kernel - Re: mmotm 2010-03-09-19-15: Lot of scheduling while atomic warnings related to RCU

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Message-Id: <E1NpsRW-0006gl-Cm@smtp.tuxdriver.com>
Date:	Thu, 11 Mar 2010 19:09:35 -0500
From:	nhorman@...l.tuxdriver.com
To:	"Andi Kleen" <andi@...stfloor.org>,
	"Neil Horman" <nhorman@...driver.com>
Cc:	"Mel Gorman" <mel@....ul.ie>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, "Andi Kleen" <andi@...stfloor.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: mmotm 2010-03-09-19-15: Lot of scheduling while atomic warnings related to RCU


On Thu, 11 Mar 2010 17:30:48 -0500, Andi Kleen wrote:
> > a/lib/kobject_uevent.c~sysctl-fix-up-remaining-references-to-uevent_helper-fix
> > +++ a/lib/kobject_uevent.c
> > @@ -273,10 +273,11 @@ int kobject_uevent_env(struct kobject *k
> >  #endif
> > 
> >         /* call uevent_helper, usually only enabled during early boot */
> > +       rcu_read_lock();
> >         helper = rcu_dereference(uevent_helper);
> >         if (helper[0])
> >                 retval = uevent_call_helper(subsystem, env);
> > -
> > +       rcu_read_unlock();
> >  exit:
> 
> The data actually has to be copied, there's a helper for this in rcustring.
> I'll try to send a patch later.
> 
> > loads/unloads while changing uevent_helper.  Anywho, should be easy to fix,
> > Mel, can you modify the code to copy helper to a private variable, then unlock
> > the rcu read side prior to calling uevent_call_helper?  I imagine that would be
> 
> Yes, except rcustring already has a helper for that :)
> 
Yes but the rcustring bits all got reverted, trashing my series :), so its all got to be rediffed anyway

Neil
> -Andi
> 

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