Messages in this thread Patch in this message | | | Date | Wed, 26 Jul 2006 10:50:28 +0200 | From | Heiko Carstens <> | Subject | [patch 1/2] slab: always consider caller mandated alignment |
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From: Heiko Carstens <heiko.carstens@de.ibm.com>
In case of CONFIG_DEBUG_SLAB kmem_cache_create() creates caches with an alignment lesser than ARCH_KMALLOC_MINALIGN. This breaks s390 (32bit), since it needs an eight byte alignment. Also it doesn't behave like it's decribed in mm/slab.c :
* Enforce a minimum alignment for the kmalloc caches. * Usually, the kmalloc caches are cache_line_size() aligned, except when * DEBUG and FORCED_DEBUG are enabled, then they are BYTES_PER_WORD aligned. * Some archs want to perform DMA into kmalloc caches and need a guaranteed * alignment larger than BYTES_PER_WORD. ARCH_KMALLOC_MINALIGN allows that. * Note that this flag disables some debug features.
For example the following might happen if kmem_cache_create() gets called with -- size: 64; align: 8; flags with SLAB_HWCACHE_ALIGN, SLAB_RED_ZONE and SLAB_STORE_USER set. These are the steps as numbered in kmem_cache_create() where 5) is after the "if (flags & SLAB_RED_ZONE)" statement.
1) align: 8 ralign 64 2) align: 8 ralign 64 3) align: 8 ralign 64 4) align: 64 ralign 64 5) align: 4 ralign 64
Note that in this case in step 3) 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 breaks s390.
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 2006-07-24 09:41:36.000000000 +0200 +++ linux-2.6/mm/slab.c 2006-07-26 09:55:54.000000000 +0200 @@ -2109,6 +2109,9 @@ if (ralign > BYTES_PER_WORD) flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER); } + if (align > BYTES_PER_WORD) + flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER); + /* * 4) Store it. Note that the debug code below can reduce * the alignment to BYTES_PER_WORD. - 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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