From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta7.messagelabs.com (mail6.bemta7.messagelabs.com [216.82.255.55]) by kanga.kvack.org (Postfix) with ESMTP id 4CD49900149 for ; Tue, 4 Oct 2011 10:29:00 -0400 (EDT) Date: Tue, 4 Oct 2011 09:28:54 -0500 (CDT) From: Christoph Lameter Subject: Re: lockdep recursive locking detected (rcu_kthread / __cache_free) In-Reply-To: <20111003214739.GK2403@linux.vnet.ibm.com> Message-ID: References: <20111003175322.GA26122@sucs.org> <20111003203139.GH2403@linux.vnet.ibm.com> <20111003214739.GK2403@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: "Paul E. McKenney" Cc: Sitsofe Wheeler , Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, penberg@kernel.org, mpm@selenic.com, linux-mm@kvack.org 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); } } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org