Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755142AbZICNmZ (ORCPT ); Thu, 3 Sep 2009 09:42:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752920AbZICNmZ (ORCPT ); Thu, 3 Sep 2009 09:42:25 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:39609 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752829AbZICNmX (ORCPT ); Thu, 3 Sep 2009 09:42:23 -0400 Date: Thu, 3 Sep 2009 06:42:25 -0700 From: "Paul E. McKenney" To: Pekka Enberg Cc: Eric Dumazet , Zdenek Kabelac , Patrick McHardy , Christoph Lameter , Robin Holt , Linux Kernel Mailing List , Jesper Dangaard Brouer , Linux Netdev List , Netfilter Developers Subject: Re: [PATCH] slub: fix slab_pad_check() and SLAB_DESTROY_BY_RCU Message-ID: <20090903134224.GI7138@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <4A87CE60.4020506@gmail.com> <4A896324.3040104@trash.net> <4A9EEF07.5070800@gmail.com> <4A9F1620.2080105@gmail.com> <84144f020909022331x2b275aa5n428f88670e0ae8bc@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <84144f020909022331x2b275aa5n428f88670e0ae8bc@mail.gmail.com> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3221 Lines: 82 On Thu, Sep 03, 2009 at 09:31:01AM +0300, Pekka Enberg wrote: > On Thu, Sep 3, 2009 at 4:04 AM, Eric Dumazet wrote: > > Zdenek Kabelac a ?crit : > >> > >> Well I'm not noticing any ill behavior - also note - rcu_barrier() is > >> there before the cache is destroyed. > >> But as I said - it's just my shot into the dark - which seems to work for me... > >> > > > > Reading again your traces, I do believe there are two bugs in slub > > > > Maybe not explaining your problem, but worth to fix ! > > > > Thank you > > > > [PATCH] slub: fix slab_pad_check() and SLAB_DESTROY_BY_RCU > > > > When SLAB_POISON is used and slab_pad_check() finds an overwrite of the > > slab padding, we call restore_bytes() on the whole slab, not only > > on the padding. > > > > kmem_cache_destroy() should call rcu_barrier() *after* kmem_cache_close() > > and *before* sysfs_slab_remove() or risk rcu_free_slab() > > being called after kmem_cache is deleted (kfreed). > > > > rmmod nf_conntrack can crash the machine because it has to > > kmem_cache_destroy() a SLAB_DESTROY_BY_RCU enabled cache. > > > > Reported-by: Zdenek Kabelac > > Signed-off-by: Eric Dumazet > > --- > > diff --git a/mm/slub.c b/mm/slub.c > > index b9f1491..0ac839f 100644 > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -646,7 +646,7 @@ static int slab_pad_check(struct kmem_cache *s, struct page *page) > > ? ? ? ?slab_err(s, page, "Padding overwritten. 0x%p-0x%p", fault, end - 1); > > ? ? ? ?print_section("Padding", end - remainder, remainder); > > > > - ? ? ? restore_bytes(s, "slab padding", POISON_INUSE, start, end); > > + ? ? ? restore_bytes(s, "slab padding", POISON_INUSE, end - remainder, end); > > OK, makes sense. > > > ? ? ? ?return 0; > > ?} > > > > @@ -2594,8 +2594,6 @@ static inline int kmem_cache_close(struct kmem_cache *s) > > ?*/ > > ?void kmem_cache_destroy(struct kmem_cache *s) > > ?{ > > - ? ? ? if (s->flags & SLAB_DESTROY_BY_RCU) > > - ? ? ? ? ? ? ? rcu_barrier(); > > ? ? ? ?down_write(&slub_lock); > > ? ? ? ?s->refcount--; > > ? ? ? ?if (!s->refcount) { > > @@ -2606,6 +2604,8 @@ void kmem_cache_destroy(struct kmem_cache *s) > > ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?"still has objects.\n", s->name, __func__); > > ? ? ? ? ? ? ? ? ? ? ? ?dump_stack(); > > ? ? ? ? ? ? ? ?} > > + ? ? ? ? ? ? ? if (s->flags & SLAB_DESTROY_BY_RCU) > > + ? ? ? ? ? ? ? ? ? ? ? rcu_barrier(); > > ? ? ? ? ? ? ? ?sysfs_slab_remove(s); > > ? ? ? ?} else > > ? ? ? ? ? ? ? ?up_write(&slub_lock); > > The rcu_barrier() call was added by this commit: > > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=7ed9f7e5db58c6e8c2b4b738a75d5dcd8e17aad5 > > I guess we should CC Paul as well. I agree that moving the rcu_barrier() as you have done is the right thing to do -- no point in doing the rcu_barrier() unless you actually are destroying the kmem_cache! Acked-by: Paul E. McKenney -- 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/