From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754614AbZHYJL1 (ORCPT ); Tue, 25 Aug 2009 05:11:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752776AbZHYJLZ (ORCPT ); Tue, 25 Aug 2009 05:11:25 -0400 Received: from cam-admin0.cambridge.arm.com ([193.131.176.58]:47384 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752636AbZHYJLY (ORCPT ); Tue, 25 Aug 2009 05:11:24 -0400 Subject: Re: WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (f6f6e1a4), by kmemleak's scan_block() From: Catalin Marinas To: Vegard Nossum Cc: Pekka Enberg , Ingo Molnar , linux-kernel@vger.kernel.org In-Reply-To: <19f34abd0908250203h52257f52v306545a3d8890577@mail.gmail.com> References: <20090825071959.GA25877@elte.hu> <19f34abd0908250104y6e877545y485a2104c2b97cfd@mail.gmail.com> <20090825083222.GC17692@elte.hu> <1251189914.7261.11.camel@penberg-laptop> <20090825084808.GA14003@elte.hu> <1251190466.7261.12.camel@penberg-laptop> <19f34abd0908250203h52257f52v306545a3d8890577@mail.gmail.com> Content-Type: text/plain Organization: ARM Ltd Date: Tue, 25 Aug 2009 10:11:18 +0100 Message-Id: <1251191478.15678.14.camel@pc1117.cambridge.arm.com> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 25 Aug 2009 09:11:19.0308 (UTC) FILETIME=[01F214C0:01CA2564] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2009-08-25 at 11:03 +0200, Vegard Nossum wrote: > 2009/8/25 Pekka Enberg : > > diff --git a/arch/x86/mm/kmemcheck/kmemcheck.c b/arch/x86/mm/kmemcheck/kmemcheck.c > > index 2c55ed0..528bf95 100644 > > --- a/arch/x86/mm/kmemcheck/kmemcheck.c > > +++ b/arch/x86/mm/kmemcheck/kmemcheck.c > > @@ -331,6 +331,20 @@ static void kmemcheck_read_strict(struct pt_regs *regs, > > kmemcheck_shadow_set(shadow, size); > > } > > > > +bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size) > > +{ > > + enum kmemcheck_shadow status; > > + void *shadow; > > + > > + shadow = kmemcheck_shadow_lookup(addr); > > + if (!shadow) > > + return true; > > + > > + status = kmemcheck_shadow_test(shadow, size); > > + > > + return status == KMEMCHECK_SHADOW_INITIALIZED; > > +} [...] > I don't know so much about the kmemleak internals, but this I can say > about the kmemcheck part: According to your definition, an object is > initialized if all the bytes of an object are initialized. > > Is it possible that because of this, if we have a partially > uninitialized object, kmemleak will not record the pointers found in > that object? If so, it might skip valid pointers, and deem an object > unreferenced. Which could make kmemleak give false-positives. Yes, that's possible. Does kmemcheck work on a page-range basis. If an object doesn't cross page boundaries, would it be considered fully initialised after writing a single location? > I think it would be better to ask kmemcheck on a per-pointer basis > (i.e. for each pointer-sized word in the object), whether it is > initialized or not. This should work but how expensive is this check? -- Catalin