On Mon, Jan 21, 2013 at 10:56 AM, Matthieu CASTET
<matthieu.cas...@parrot.com> wrote:
> The current slab code only allow to put redzone( and user store) info if
> "buffer
> alignment(ralign) <= __alignof__(unsigned long long)". This was done because
> we
> want to keep the buffer aligned for user even after adding redzone at the
> beginning of the buffer (the user store is stored after user buffer) [1]
>
> But instead of disabling this feature when "ralign > __alignof__(unsigned long
> long)", we can force the alignment by allocating ralign before user buffer.
>
> This is done by setting ralign in obj_offset when "ralign >
> __alignof__(unsigned
> long long)" and keeping the old behavior when "ralign <= __alignof__(unsigned
> long long)" (we set sizeof(unsigned long long)).
>
> The 5c5e3b33b7cb959a401f823707bee006caadd76e commit wasn't handling "ralign <=
> __alignof__(unsigned long long)", that's why it broked some configuration.
>
> This was tested on omap3 (ralign is 64 and __alignof__(unsigned long long) is
> 8)
>
> [1]
> /*
> * memory layout of objects:
> * 0 : objp
> * 0 .. cachep->obj_offset - BYTES_PER_WORD - 1: padding. This ensures that
> * the end of an object is aligned with the end of the real
> * allocation. Catches writes behind the end of the allocation.
> * cachep->obj_offset - BYTES_PER_WORD .. cachep->obj_offset - 1:
> * redzone word.
> * cachep->obj_offset: The real object.
> * cachep->buffer_size - 2* BYTES_PER_WORD: redzone word [BYTES_PER_WORD long]
> * cachep->buffer_size - 1* BYTES_PER_WORD: last caller address
> * [BYTES_PER_WORD long]
> */
Ping,
Thanks,
Matthieu
>
> Signed-off-by: Matthieu Castet <matthieu.cas...@parrot.com>
> CC: Russell King <r...@arm.linux.org.uk>
> CC: Pekka Enberg <penb...@cs.helsinki.fi>
> ---
> mm/slab.c | 8 +++-----
> 1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/mm/slab.c b/mm/slab.c
> index e7667a3..d2380d9 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -2392,9 +2392,6 @@ __kmem_cache_create (struct kmem_cache *cachep,
> unsigned long flags)
> if (ralign < cachep->align) {
> ralign = cachep->align;
> }
> - /* disable debug if necessary */
> - if (ralign > __alignof__(unsigned long long))
> - flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER);
> /*
> * 4) Store it.
> */
> @@ -2414,8 +2411,9 @@ __kmem_cache_create (struct kmem_cache *cachep,
> unsigned long flags)
> */
> if (flags & SLAB_RED_ZONE) {
> /* add space for red zone words */
> - cachep->obj_offset += sizeof(unsigned long long);
> - size += 2 * sizeof(unsigned long long);
> + int offset = max(ralign, sizeof(unsigned long long));
> + cachep->obj_offset += offset;
> + size += offset + sizeof(unsigned long long);
> }
> if (flags & SLAB_STORE_USER) {
> /* user store requires one word storage behind the end of
> --
> 1.7.10.4
>
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