linux-kernel - Re: slub/debugobjects: lockup when freeing memory

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Date:	Thu, 19 Jun 2014 22:28:14 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Christoph Lameter <cl@...two.org>
cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Jones <davej@...hat.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: slub/debugobjects: lockup when freeing memory

On Thu, 19 Jun 2014, Christoph Lameter wrote:
> On Thu, 19 Jun 2014, Thomas Gleixner wrote:
> 
> > Well, no. Look at the callchain:
> >
> > __call_rcu
> >     debug_object_activate
> >        rcuhead_fixup_activate
> >           debug_object_init
> >               kmem_cache_alloc
> >
> > So call rcu activates the object, but the object has no reference in
> > the debug objects code so the fixup code is called which inits the
> > object and allocates a reference ....
> 
> So we need to init the object in the page struct before the __call_rcu?
 
Looks like RCU is lazily relying on the state callback to initialize
the objects.

There is an unused debug_init_rcu_head() inline in kernel/rcu/update.c

Paul????


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