Messages in this thread Patch in this message | | | Date | Wed, 26 Jul 2006 10:51:13 +0200 | From | Heiko Carstens <> | Subject | [patch 2/2] slab: always consider arch mandated alignment |
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From: Heiko Carstens <heiko.carstens@de.ibm.com>
Since ARCH_KMALLOC_MINALIGN didn't work on s390 I tried ARCH_SLAB_MINALIGN instead, just to find out that it didn't work too. In case of CONFIG_DEBUG_SLAB kmem_cache_create() creates caches with an alignment lesser than ARCH_SLAB_MINALIGN, which it shouldn't according to this comment in mm/slab.c :
* Enforce a minimum alignment for all caches. * Intended for archs that get misalignment faults even for BYTES_PER_WORD * aligned buffers. Includes ARCH_KMALLOC_MINALIGN. * If possible: Do not enable this flag for CONFIG_DEBUG_SLAB, it disables * some debug features.
For example the following might happen if kmem_cache_create() gets called with -- size: 64; align: 0; flags with SLAB_HWCACHE_ALIGN, SLAB_RED_ZONE and SLAB_STORE_USER set. ARCH_SLAB_MINALIGN is 8. These are the steps as numbered in kmem_cache_create() where 5) is after the "if (flags & SLAB_RED_ZONE)" statement.
1) align: 0 ralign 64 2) align: 0 ralign 64 3) align: 0 ralign 64 4) align: 64 ralign 64 5) align: 4 ralign 64
Note that in this case in step 2) the flags SLAB_RED_ZONE and SLAB_STORE_USER don't get masked out and that this causes an BYTES_PER_WORD alignment in step 5) which is lesser than ARCH_SLAB_MINALIGN.
Cc: Christoph Lameter <clameter@sgi.com> Cc: Pekka Enberg <penberg@cs.helsinki.fi> Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> ---
mm/slab.c | 3 +++ 1 files changed, 3 insertions(+)
Index: linux-2.6/mm/slab.c =================================================================== --- linux-2.6.orig/mm/slab.c 2006-07-26 09:55:54.000000000 +0200 +++ linux-2.6/mm/slab.c 2006-07-26 09:57:07.000000000 +0200 @@ -2103,6 +2103,9 @@ if (ralign > BYTES_PER_WORD) flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER); } + if (BYTES_PER_WORD < ARCH_SLAB_MINALIGN) + flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER); + /* 3) caller mandated alignment: disables debug if necessary */ if (ralign < align) { ralign = align; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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