From: Pekka Enberg <[email protected]>
As explained by Heiko, on s390 (32-bit) ARCH_KMALLOC_MINALIGN is set to eight
because their common I/O layer allocates data structures that need to have an
eight byte alignment. This does not work when CONFIG_SLAB_DEBUG is enabled
because kmem_cache_create will override alignment to BYTES_PER_WORD which is
four.
So change kmem_cache_create to ensure cache alignment is always at minimum
what the architecture or caller mandates even if slab debugging is enabled.
Cc: Heiko Carstens <[email protected]>
Cc: Christoph Lameter <[email protected]>
Signed-off-by: Manfred Spraul <[email protected]>
Signed-off-by: Pekka Enberg <[email protected]>
---
mm/slab.c | 25 ++++++++++++++++---------
1 file changed, 16 insertions(+), 9 deletions(-)
Index: 2.6/mm/slab.c
===================================================================
--- 2.6.orig/mm/slab.c
+++ 2.6/mm/slab.c
@@ -2097,6 +2097,15 @@ kmem_cache_create (const char *name, siz
} else {
ralign = BYTES_PER_WORD;
}
+
+ /*
+ * Redzoning and user store require word alignment. Note this will be
+ * overridden by architecture or caller mandated alignment if either
+ * is greater than BYTES_PER_WORD.
+ */
+ if (flags & SLAB_RED_ZONE || flags & SLAB_STORE_USER)
+ ralign = BYTES_PER_WORD;
+
/* 2) arch mandated alignment: disables debug if necessary */
if (ralign < ARCH_SLAB_MINALIGN) {
ralign = ARCH_SLAB_MINALIGN;
@@ -2110,8 +2119,7 @@ kmem_cache_create (const char *name, siz
flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER);
}
/*
- * 4) Store it. Note that the debug code below can reduce
- * the alignment to BYTES_PER_WORD.
+ * 4) Store it.
*/
align = ralign;
@@ -2123,20 +2131,19 @@ kmem_cache_create (const char *name, siz
#if DEBUG
cachep->obj_size = size;
+ /*
+ * Both debugging options require word-alignment which is calculated
+ * into align above.
+ */
if (flags & SLAB_RED_ZONE) {
- /* redzoning only works with word aligned caches */
- align = BYTES_PER_WORD;
-
/* add space for red zone words */
cachep->obj_offset += BYTES_PER_WORD;
size += 2 * BYTES_PER_WORD;
}
if (flags & SLAB_STORE_USER) {
- /* user store requires word alignment and
- * one word storage behind the end of the real
- * object.
+ /* user store requires one word storage behind the end of
+ * the real object.
*/
- align = BYTES_PER_WORD;
size += BYTES_PER_WORD;
}
#if FORCED_DEBUG && defined(CONFIG_DEBUG_PAGEALLOC)
-
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