From: Heiko Carstens <[email protected]>
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 <[email protected]>
Cc: Pekka Enberg <[email protected]>
Signed-off-by: Heiko Carstens <[email protected]>
---
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.
-
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