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

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Date:	Thu, 19 Jun 2014 09:52:47 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...two.org>
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	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, Jun 19, 2014 at 10:03:04AM -0500, Christoph Lameter wrote:
> On Thu, 19 Jun 2014, Sasha Levin wrote:
> 
> > [  690.770137] ? __this_cpu_preempt_check (lib/smp_processor_id.c:63)
> > [  690.770137] __slab_alloc (mm/slub.c:1732 mm/slub.c:2205 mm/slub.c:2369)
> > [  690.770137] ? __lock_acquire (kernel/locking/lockdep.c:3189)
> > [  690.770137] ? __debug_object_init (lib/debugobjects.c:100 lib/debugobjects.c:312)
> > [  690.770137] kmem_cache_alloc (mm/slub.c:2442 mm/slub.c:2484 mm/slub.c:2489)
> > [  690.770137] ? __debug_object_init (lib/debugobjects.c:100 lib/debugobjects.c:312)
> > [  690.770137] ? debug_object_activate (lib/debugobjects.c:439)
> > [  690.770137] __debug_object_init (lib/debugobjects.c:100 lib/debugobjects.c:312)
> > [  690.770137] debug_object_init (lib/debugobjects.c:365)
> > [  690.770137] rcuhead_fixup_activate (kernel/rcu/update.c:231)
> > [  690.770137] debug_object_activate (lib/debugobjects.c:280 lib/debugobjects.c:439)
> > [  690.770137] ? discard_slab (mm/slub.c:1486)
> > [  690.770137] __call_rcu (kernel/rcu/rcu.h:76 (discriminator 2) kernel/rcu/tree.c:2585 (discriminator 2))
> 
> __call_rcu does a slab allocation? This means __call_rcu can no longer be
> used in slab allocators? What happened?

My guess is that the root cause is a double call_rcu(), call_rcu_sched(),
call_rcu_bh(), or call_srcu().

Perhaps the DEBUG_OBJECTS code now allocates memory to report errors?
That would be unfortunate...

							Thanx, Paul

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