From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752419AbZHYIbr (ORCPT ); Tue, 25 Aug 2009 04:31:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751917AbZHYIbp (ORCPT ); Tue, 25 Aug 2009 04:31:45 -0400 Received: from courier.cs.helsinki.fi ([128.214.9.1]:53771 "EHLO mail.cs.helsinki.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751771AbZHYIbo (ORCPT ); Tue, 25 Aug 2009 04:31:44 -0400 Subject: Re: WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (f6f6e1a4), by kmemleak's scan_block() From: Pekka Enberg To: Catalin Marinas Cc: Vegard Nossum , Ingo Molnar , linux-kernel@vger.kernel.org In-Reply-To: <1251188859.15678.6.camel@pc1117.cambridge.arm.com> References: <20090825071959.GA25877@elte.hu> <19f34abd0908250104y6e877545y485a2104c2b97cfd@mail.gmail.com> <1251187716.7261.2.camel@penberg-laptop> <1251188859.15678.6.camel@pc1117.cambridge.arm.com> Date: Tue, 25 Aug 2009 11:31:45 +0300 Message-Id: <1251189105.7261.4.camel@penberg-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 7bit X-Mailer: Evolution 2.24.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2009-08-25 at 09:27 +0100, Catalin Marinas wrote: > On Tue, 2009-08-25 at 11:08 +0300, Pekka Enberg wrote: > > On Tue, 2009-08-25 at 10:04 +0200, Vegard Nossum wrote: > > > 2009/8/25 Ingo Molnar : > > > > FYI, -tip testing triggered the following kmemcheck warning in > > > > kmemleak: > > > > > > > > PM: Adding info for No Bus:vcsa7 > > > > WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (f6f6e1a4) > > > > d873f9f600000000c42ae4c1005c87f70000000070665f666978656400000000 > > > > i i i i u u u u i i i i i i i i i i i i i i i i i i i i i u u u > [...] > > > Already the patch to make kmemcheck and kmemleak mutually exclusive is > > > underway. It is not surprising that kmemleak is scanning uninitialized > > > memory. But if you say that you have tried it before, it is strange > > > that it didn't appear until now. > > > > Why isn't it surprising? Yes, it's non-fatal for kmemleak to scan > > uninitialized memory but we could be looking at non-initialized struct > > member that's a bug waiting to happen elsewhere in the code (that > > doesn't trigger often). > > It isn't surprising to me either. Kmemleak scans the memory periodically > but it cannot know whether such memory was initialised or not to avoid > scanning it. So I would expect such warnings if both kmemleak and > kmemcheck are enabled. Scanning uninitialised memory is fine with > kmemleak, it just increases the number of false negatives (with > SLAB_DEBUG enabled, however, the allocated blocks are pre-initialised). > > So kmemleak and kmemcheck should be exclusive, unless there is a way for > kmemleak to validate an address with kmemcheck before deciding whether > to scan a memory block. It's possible. Look at the kmemcheck_shadow_lookup() and kmemcheck_shadow_test() calls in kmemcheck_read_strict(), for example. Vegard, what do you think? I think making kmemcheck and kmemleak play nice with each other is useful for people like Ingo who do automated testing. Pekka