linux-kernel - Re: [PATCH - V2] Fix missing of last user while dumping slab corruption log

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Date:	Thu, 15 Apr 2010 11:04:38 +0800
From:	TAO HU <tghk48@...orola.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	ShiYong LI <shi-yong.li@...orola.com>,
	linux-kernel@...r.kernel.org, cl@...ux-foundation.org,
	mpm@...enic.com, linux-mm@...ck.org, dwmw2@...radead.org,
	TAO HU <taohu@...orola.com>
Subject: Re: [PATCH - V2] Fix missing of last user while dumping slab 
	corruption log

Hi, Pekka Enberg

Thanks!
If we hadn't seen the last user info, we would not have fixed a
difficult bug in our system.
So very glad to know.

-- 
Best Regards
Hu Tao

On Thu, Apr 15, 2010 at 1:56 AM, Pekka Enberg <penberg@...helsinki.fi> wrote:
> ShiYong LI wrote:
>>
>> Hi,
>>
>> Compared to previous version, add alignment checking to make sure
>> memory space storing redzone2 and last user tags is 8 byte alignment.
>>
>> From 949e8c29e8681a2359e23a8fbd8b9d4833f42344 Mon Sep 17 00:00:00 2001
>> From: Shiyong Li <shi-yong.li@...orola.com>
>> Date: Mon, 12 Apr 2010 13:48:21 +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 unless
>> the required alignment breaks redzone's.
>>
>> Signed-off-by: Shiyong Li <shi-yong.li@...orola.com>
>
> OK, I added this to linux-next for testing. Thanks!
>
>> ---
>>  mm/slab.c |    8 ++++----
>>  1 files changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/slab.c b/mm/slab.c
>> index a8a38ca..b97c57e 100644
>> --- a/mm/slab.c
>> +++ b/mm/slab.c
>> @@ -2267,8 +2267,8 @@ 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))
>> +       /* disable debug if not aligning with REDZONE_ALIGN */
>> +       if (ralign & (__alignof__(unsigned long long) - 1))
>>                flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER);
>>        /*
>>         * 4) Store it.
>> @@ -2289,8 +2289,8 @@ 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
>
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