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Commit ca5f9703 authored by Pekka Enberg's avatar Pekka Enberg Committed by Linus Torvalds
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[PATCH] slab: respect architecture and caller mandated alignment 



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 <heiko.carstens@de.ibm.com>
Cc: Christoph Lameter <clameter@sgi.com>
Signed-off-by: default avatarManfred Spraul <manfred@colorfullife.com>
Signed-off-by: default avatarPekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent db37648c

mm/slab.c

+16 −9
Original line number Diff line number Diff line
@@ -2096,6 +2096,15 @@ kmem_cache_create (const char *name, size_t size, size_t align, 
	} 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;
@@ -2109,8 +2118,7 @@ kmem_cache_create (const char *name, size_t size, size_t align, 
			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;
@@ -2122,20 +2130,19 @@ kmem_cache_create (const char *name, size_t size, size_t align, 
#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)