From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753609Ab0DAHJE (ORCPT ); Thu, 1 Apr 2010 03:09:04 -0400 Received: from exprod5og111.obsmtp.com ([64.18.0.22]:56142 "EHLO exprod5og111.obsmtp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752131Ab0DAHI5 convert rfc822-to-8bit (ORCPT ); Thu, 1 Apr 2010 03:08:57 -0400 MIME-Version: 1.0 In-Reply-To: <4BB43D58.5030801@cs.helsinki.fi> References: <4BB43D58.5030801@cs.helsinki.fi> Date: Thu, 1 Apr 2010 15:08:50 +0800 Message-ID: Subject: Re: [PATCH] Fix missing of last user info while getting DEBUG_SLAB config enabled 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 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 Thanks for your feedback. The subject and comments are kind of misleading. Sorry about that. It intends to make both Red-Zone and LastUser are available even the alignment is larger than sizeof(long long). The idea is to reserve certain room ("align") to let the obj's offset is aligned to cache-line-size to address requirement of kmalloc(). Regarding align is less than sizeof(unsigned long long), I thin it is handled in previous code. Or you still expect to explicitly let align is no less than sizeof(unsigned long long)? if (flags & SLAB_RED_ZONE) { ralign = REDZONE_ALIGN; ... ... } -- Best Regards Hu Tao On Thu, Apr 1, 2010 at 2:29 PM, Pekka Enberg wrote: > ShiYong LI kirjoitti: >> >> Hi all, >>  For OMAP3430 chip, while getting DEBUG_SLAB config enabled, found a bug >> that last user information is missed in slab corruption log dumped by >> kernel. Actually, It's caused by ignorance of redzone and last user tag >> while calling kmem_cache_create() function if cache alignment > 16 bytes >> (unsigned long long).  Here is a patch to fix this problem. Already verified >> it on kernel 2.6.29. > > The patch is badly whitespace damaged. > >>  From 26a5a8ad2a1d7612929a91f6866cea9d1bea6077 Mon Sep 17 00:00:00 2001 >> From: Shiyong Li > > >> Date: Wed, 31 Mar 2010 10:09:35 +0800 >> Subject: [PATCH] Fix missing of last user info while getting DEBUG_SLAB >> config enabled. >> As OMAP3 cache line is 64 byte long, while calling kmem_cache_create() >> funtion, some cases need 64 byte alignment of requested memory space. >> But, if cache line > 16 bytes, current kernel ignore redzone >> and last user debug head/trail tag to make sure this alignment is not >> broken. >> This fix removes codes that ignorance of redzone and last user tag. >> Instead, use "align" argument value as object offset to guarantee the >> alignment. >> 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); >>  } > > I don't understand what you're trying to do here. What if align is less han > sizeof(unsigned long long)? What if SLAB_RED_ZONE is not enabled but >  SLAB_STORE_USER is? > >                        Pekka > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org.  For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org >