Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934861AbaFTIR5 (ORCPT ); Fri, 20 Jun 2014 04:17:57 -0400 Received: from www.linutronix.de ([62.245.132.108]:57404 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934721AbaFTIRx (ORCPT ); Fri, 20 Jun 2014 04:17:53 -0400 Date: Fri, 20 Jun 2014 10:17:32 +0200 (CEST) From: Thomas Gleixner To: "Paul E. McKenney" cc: Christoph Lameter , Sasha Levin , Pekka Enberg , Matt Mackall , Andrew Morton , Dave Jones , "linux-mm@kvack.org" , LKML Subject: Re: slub/debugobjects: lockup when freeing memory In-Reply-To: <20140619220449.GT4904@linux.vnet.ibm.com> Message-ID: References: <53A2F406.4010109@oracle.com> <20140619165247.GA4904@linux.vnet.ibm.com> <20140619202928.GG4904@linux.vnet.ibm.com> <20140619205307.GL4904@linux.vnet.ibm.com> <20140619220449.GT4904@linux.vnet.ibm.com> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 19 Jun 2014, Paul E. McKenney wrote: > On Thu, Jun 19, 2014 at 11:32:41PM +0200, Thomas Gleixner wrote: > > > > > > On Thu, 19 Jun 2014, Paul E. McKenney wrote: > > > > > On Thu, Jun 19, 2014 at 10:37:17PM +0200, Thomas Gleixner wrote: > > > > On Thu, 19 Jun 2014, Paul E. McKenney wrote: > > > > > On Thu, Jun 19, 2014 at 09:29:08PM +0200, Thomas Gleixner wrote: > > > > > > On Thu, 19 Jun 2014, Paul E. McKenney 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 .... > > > > > > > > > > OK, got it. And you are right, call_rcu() has done this for a very > > > > > long time, so not sure what changed. But it seems like the right > > > > > approach is to provide a debug-object-free call_rcu_alloc() for use > > > > > by the memory allocators. > > > > > > > > > > Seem reasonable? If so, please see the following patch. > > > > > > > > Not really, you're torpedoing the whole purpose of debugobjects :) > > > > > > > > So, why can't we just init the rcu head when the stuff is created? > > > > > > That would allow me to keep my code unchanged, so I am in favor. ;-) > > > > Almost unchanged. You need to provide a function to do so, i.e. make > > use of > > > > debug_init_rcu_head() > > You mean like this? I'd rather name it init_rcu_head() and free_rcu_head() w/o the debug_ prefix, so it's consistent with init_rcu_head_on_stack / destroy_rcu_head_on_stack. But either way works for me. Acked-by: Thomas Gleixner -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/