From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932288Ab1JDOll (ORCPT ); Tue, 4 Oct 2011 10:41:41 -0400 Received: from casper.infradead.org ([85.118.1.10]:37968 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932147Ab1JDOll convert rfc822-to-8bit (ORCPT ); Tue, 4 Oct 2011 10:41:41 -0400 Subject: Re: lockdep recursive locking detected (rcu_kthread / __cache_free) From: Peter Zijlstra To: Christoph Lameter Cc: "Paul E. McKenney" , Sitsofe Wheeler , Ingo Molnar , linux-kernel@vger.kernel.org, penberg@kernel.org, mpm@selenic.com, linux-mm@kvack.org, David Rientjes Date: Tue, 04 Oct 2011 16:40:25 +0200 In-Reply-To: References: <20111003175322.GA26122@sucs.org> <20111003203139.GH2403@linux.vnet.ibm.com> <20111003214739.GK2403@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT X-Mailer: Evolution 3.0.3- Message-ID: <1317739225.32543.9.camel@twins> Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2011-10-04 at 09:28 -0500, Christoph Lameter wrote: > On Mon, 3 Oct 2011, Paul E. McKenney wrote: > > > On Mon, Oct 03, 2011 at 03:46:11PM -0500, Christoph Lameter wrote: > > > On Mon, 3 Oct 2011, Paul E. McKenney wrote: > > > > > > > The first lock was acquired here in an RCU callback. The later lock that > > > > lockdep complained about appears to have been acquired from a recursive > > > > call to __cache_free(), with no help from RCU. This looks to me like > > > > one of the issues that arise from the slab allocator using itself to > > > > allocate slab metadata. > > > > > > Right. However, this is a false positive since the slab cache with > > > the metadata is different from the slab caches with the slab data. The slab > > > cache with the metadata does not use itself any metadata slab caches. > > > > Wouldn't it be possible to pass a new flag to the metadata slab caches > > upon creation so that their locks could be placed in a separate lock > > class? Just allocate a separate lock_class_key structure for each such > > lock in that case, and then use lockdep_set_class_and_name to associate > > that structure with the corresponding lock. I do this in kernel/rcutree.c > > in order to allow the rcu_node tree's locks to nest properly. > > We could give the kmalloc array a different class from created slab > caches. That should have the desired effect. > > But that seems to be already the case (looking at init_node_lock_keys). > Non OFF_SLAB caches seem to be getting a different lock class? Why is this > not working? > > static void init_node_lock_keys(int q) > { > struct cache_sizes *s = malloc_sizes; > > if (g_cpucache_up != FULL) > return; > > for (s = malloc_sizes; s->cs_size != ULONG_MAX; s++) { > struct kmem_list3 *l3; > > l3 = s->cs_cachep->nodelists[q]; > if (!l3 || OFF_SLAB(s->cs_cachep)) > continue; > > slab_set_lock_classes(s->cs_cachep, &on_slab_l3_key, > &on_slab_alc_key, q); > } > } Right, so we recently poked at this to fix some other splats, see: 30765b92ada267c5395fc788623cb15233276f5c 83835b3d9aec8e9f666d8223d8a386814f756266 It could of course be I got confused and broke stuff instead, could someone who knows slab (I guess that's either Pekka, Christoph or David) stare at those patches?