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SubjectRe: [PATCH] Fix missing of last user info while getting DEBUG_SLAB config enabled
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 <shi-yong.li@motorola.com
> <mailto:shi-yong.li@motorola.com>>
> 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 <shi-yong.li@motorola.com
> <mailto:shi-yong.li@motorola.com>>
> ---
> 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


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