From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758837AbYLLNqA (ORCPT ); Fri, 12 Dec 2008 08:46:00 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758131AbYLLNpw (ORCPT ); Fri, 12 Dec 2008 08:45:52 -0500 Received: from cam-admin0.cambridge.arm.com ([193.131.176.58]:62700 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757040AbYLLNpv (ORCPT ); Fri, 12 Dec 2008 08:45:51 -0500 Subject: Re: [PATCH 05/15] kmemleak: Add the slub memory allocation/freeing hooks From: Catalin Marinas To: Pekka Enberg Cc: linux-kernel@vger.kernel.org, Christoph Lameter In-Reply-To: <4941866D.5040005@cs.helsinki.fi> References: <20081210182652.30323.4594.stgit@pc1117.cambridge.arm.com> <20081210182721.30323.55530.stgit@pc1117.cambridge.arm.com> <4941866D.5040005@cs.helsinki.fi> Content-Type: text/plain Organization: ARM Ltd Date: Fri, 12 Dec 2008 13:45:43 +0000 Message-Id: <1229089544.15045.24.camel@pc1117.cambridge.arm.com> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 12 Dec 2008 13:45:44.0945 (UTC) FILETIME=[EE7AE610:01C95C5F] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2008-12-11 at 23:30 +0200, Pekka Enberg wrote: > Catalin Marinas wrote: > > This patch adds the callbacks to memleak_(alloc|free) functions from the > > slub allocator. > > > > Signed-off-by: Catalin Marinas > > Cc: Christoph Lameter > > Cc: Pekka Enberg > > Hmm, I'm not sure I understand why struct kmem_cache_cpu ->freelist is > never scanned. Did you get any false positives? Or were you expecting false negatives because of freelist scanning which never occurred? > For SMP, I suppose kmemleak doesn't scan the per-CPU > areas? It should scan the per-CPU areas in the memleak_scan() function: #ifdef CONFIG_SMP /* per-cpu sections scanning */ for_each_possible_cpu(i) scan_block(__per_cpu_start + per_cpu_offset(i), __per_cpu_end + per_cpu_offset(i), NULL); #endif > But for UP, struct kmem_cache is allocated with kmalloc() and > that contains struct kmem_cache_cpu as well. They should be scanned as well. > And I suppose we never scan struct pages either. Otherwise ->freelist > there would be a problem as well. It was scanning the mem_map arrays in the past but removed this part and haven't seen any problems (on ARM). Why would the ->freelist be a problem? I don't fully understand the slub allocator. Aren't objects added to the freelist only after they were freed? In __slab_alloc there seems to be a line: c->page->freelist = NULL; so the freelist won't count as a reference anymore. After freeing an object, kmemleak no longer cares about references to it. -- Catalin