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Date:	Thu, 19 Jun 2014 13:53:36 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Lameter <cl@...two.org>,
	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, Jun 19, 2014 at 04:42:11PM -0400, Sasha Levin wrote:
> On 06/19/2014 04:29 PM, Paul E. McKenney wrote:
> > rcu: Provide call_rcu_alloc() and call_rcu_sched_alloc() to avoid recursion
> > 
> > The sl*b allocators use call_rcu() to manage object lifetimes, but
> > call_rcu() can use debug-objects, which in turn invokes the sl*b
> > allocators.  These allocators are not prepared for this sort of
> > recursion, which can result in failures.
> > 
> > This commit therefore creates call_rcu_alloc() and call_rcu_sched_alloc(),
> > which act as their call_rcu() and call_rcu_sched() counterparts, but
> > which avoid invoking debug-objects.  These new API members are intended
> > only for use by the sl*b allocators, and this commit makes the sl*b
> > allocators use call_rcu_alloc().  Why call_rcu_sched_alloc()?  Because
> > in CONFIG_PREEMPT=n kernels, call_rcu() maps to call_rcu_sched(), so
> > therefore call_rcu_alloc() must map to call_rcu_sched_alloc().
> > 
> > Reported-by: Sasha Levin <sasha.levin@...cle.com>
> > Set-straight-by: Thomas Gleixner <tglx@...utronix.de>
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 
> Paul, what is this patch based on? It won't apply cleanly on -next
> or Linus's tree.

On my -rcu tree, but I think that Thomas's approach is better.

							Thanx, Paul

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