From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756174Ab0DHDNu (ORCPT ); Wed, 7 Apr 2010 23:13:50 -0400 Received: from exprod5og104.obsmtp.com ([64.18.0.178]:60064 "EHLO exprod5og104.obsmtp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753545Ab0DHDNr convert rfc822-to-8bit (ORCPT ); Wed, 7 Apr 2010 23:13:47 -0400 MIME-Version: 1.0 In-Reply-To: References: Date: Thu, 8 Apr 2010 11:13:40 +0800 Message-ID: Subject: Re: [PATCH] Fix missing of last user while dumping slab corruption log From: TAO HU To: Pekka Enberg Cc: ShiYong LI , linux-kernel@vger.kernel.org, cl@linux-foundation.org, mpm@selenic.com, linux-mm@kvack.org, TAO HU , dwmw2@infradead.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Pekka Enberg We verified on OMAP3 (ARM V7). 1 thing we're sure a) cachep->obj_offset will be aligned with "align" passed to kmem_cache_create () Are you concerned about alignment for red-zone obj? We'll double check. -- Best Regards Hu Tao On Wed, Apr 7, 2010 at 11:25 PM, Pekka Enberg wrote: > Hi, > > (I'm cc'ing David who did some fixes in this area previously.) > > On Fri, Apr 2, 2010 at 10:21 AM, ShiYong LI wrote: >> Even with SLAB_RED_ZONE and SLAB_STORE_USER enabled, kernel would NOT >> store redzone and last user data around allocated memory space if arch >> cache line > sizeof(unsigned long long). As a result, last user information >> is unexpectedly MISSED while dumping slab corruption log. >> >> This patch makes sure that redzone and last user tags get stored whatever >> arch cache line. >> >> Compared to original codes, the change surely affects head redzone (redzone1). >> Actually, with SLAB_RED_ZONE and SLAB_STORE_USER enabled, >> allocated memory layout is as below: >> >> [ redzone1 ]   <--------- Affected area. >> [ real object space ] >> [ redzone2 ] >> [ last user ] >> [ ... ] >> >> Let's do some analysis: (whatever SLAB_STORE_USER is). >> >> 1) With SLAB_RED_ZONE on, "align" >= sizeof(unsigned long long) according to >>    the following codes: >>        /* 2) arch mandated alignment */ >>        if (ralign < ARCH_SLAB_MINALIGN) { >>                ralign = ARCH_SLAB_MINALIGN; >>        } >>        /* 3) caller mandated alignment */ >>        if (ralign < align) { >>                ralign = align; >>        } >>        ... >>        /* >>         * 4) Store it. >>         */ >>        align = ralign; >> >>    That's to say, could guarantee that redzone1 does NOT get broken >> at all. Meanwhile, >>    Real object space could meet the need of cache line size by using >> "align"  argument. >> >> 2) With SLAB_RED_ZONE off, the change has no impact. >> >> >> From 03b28964311090533643acd267abe0cbc3c9b0a5 Mon Sep 17 00:00:00 2001 >> From: Shiyong Li >> Date: Fri, 2 Apr 2010 14:50:30 +0800 >> Subject: [PATCH] Fix missing of last user info while getting >> DEBUG_SLAB config enabled. >> >> Even with SLAB_RED_ZONE and SLAB_STORE_USER enabled, kernel would NOT >> store redzone and last user data around allocated memory space if arch >> cache line > sizeof(unsigned long long). As a result, last user information >> is unexpectedly MISSED while dumping slab corruption log. >> >> This fix makes sure that redzone and last user tags get stored whatever >> cache line. >> >> Signed-off-by: Shiyong Li >> --- >>  mm/slab.c |    7 ++----- >>  1 files changed, 2 insertions(+), 5 deletions(-) >> >> diff --git a/mm/slab.c b/mm/slab.c >> index a8a38ca..84af997 100644 >> --- a/mm/slab.c >> +++ b/mm/slab.c >> @@ -2267,9 +2267,6 @@ kmem_cache_create (const char *name, size_t >> size, size_t align, >>        if (ralign < align) { >>                ralign = align; >>        } >> -       /* disable debug if necessary */ >> -       if (ralign > __alignof__(unsigned long long)) >> -               flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER); >>        /* >>         * 4) Store it. >>         */ >> @@ -2289,8 +2286,8 @@ kmem_cache_create (const char *name, size_t >> size, size_t align, >>         */ >>        if (flags & SLAB_RED_ZONE) { >>                /* add space for red zone words */ >> -               cachep->obj_offset += sizeof(unsigned long long); >> -               size += 2 * sizeof(unsigned long long); >> +               cachep->obj_offset += align; >> +               size += align + sizeof(unsigned long long); >>        } >>        if (flags & SLAB_STORE_USER) { >>                /* user store requires one word storage behind the end of > > The problem I have with this patch is that I am unable to convince > myself that it's correct. > > The code in question is pretty hard to follow and it can break on > architectures with strict alignment requirements. I'm not sure I fully > understand why we've been disabling debugging in the first place. > > On which architectures have you verified this fix? > >                        Pekka >