From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756749AbYDBQIU (ORCPT ); Wed, 2 Apr 2008 12:08:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755456AbYDBQIO (ORCPT ); Wed, 2 Apr 2008 12:08:14 -0400 Received: from e34.co.us.ibm.com ([32.97.110.152]:34017 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754865AbYDBQIN (ORCPT ); Wed, 2 Apr 2008 12:08:13 -0400 Date: Wed, 2 Apr 2008 09:08:09 -0700 From: "Paul E. McKenney" To: Pekka Enberg Cc: Ingo Molnar , Jens Axboe , Peter Zijlstra , Vegard Nossum , Linux Kernel Mailing List Subject: Re: kmemcheck caught read from freed memory (cfq_free_io_context) Message-ID: <20080402160809.GA4123@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <19f34abd0804011408v19e13b6cje1ca89a2a471484c@mail.gmail.com> <1207085788.29991.6.camel@lappy> <20080402071709.GC12774@kernel.dk> <20080402072456.GI12774@kernel.dk> <20080402072846.GA16454@elte.hu> <20080402105539.GA5610@linux.vnet.ibm.com> <84144f020804020401j4e5863dcofd16662baa54574@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <84144f020804020401j4e5863dcofd16662baa54574@mail.gmail.com> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 02, 2008 at 02:01:13PM +0300, Pekka Enberg wrote: > Hi Paul, > > On Wed, Apr 2, 2008 at 1:55 PM, Paul E. McKenney > wrote: > > I will check this when I get back to some bandwidth -- but in the meantime, > > does kmemcheck special-case SLAB_DESTROY_BY_RCU? It is legal to access > > newly-freed items in that case, as long as you did rcu_read_lock() > > before gaining a reference to them and don't hold the reference past > > the matching rcu_read_unlock(). > > No, kmemcheck is work in progress and does not know about > SLAB_DESTROY_BY_RCU yet. The reason I asked Vegard to post the warning > was because Peter, Vegard, and myself identified this particular > warning as a real problem. But yeah, kmemcheck can cause false > positives for RCU for now. Would the following be an appropriate fix? It seems to me to be in the same spirit as the existing check for s->ctor. Signed-off-by: Paul E. McKenney --- slub_kmemcheck.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/slub_kmemcheck.c b/mm/slub_kmemcheck.c index 8620a8b..e07f62a 100644 --- a/mm/slub_kmemcheck.c +++ b/mm/slub_kmemcheck.c @@ -93,6 +93,6 @@ kmemcheck_slab_alloc(struct kmem_cache *s, gfp_t gfpflags, void *object) void kmemcheck_slab_free(struct kmem_cache *s, void *object) { - if (!s->ctor) + if (!s->ctor && !(s->flags & SLAB_DESTROY_BY_RCU)) kmemcheck_mark_freed(object, s->objsize); }