SLUB Debug: fix check for super sized slabs (>512k 64bit, >256k 32bit)

The check for super sized slabs where we can no longer move the free
pointer behind the object for debugging purposes etc is accessing a
field that is not setup yet.  We must use objsize here since the size of
the slab has not been determined yet.

The effect of this is that a global slab shrink via "slabinfo -s" will
show errors about offsets being wrong if booted with slub_debug.
Potentially there are other troubles with huge slabs under slub_debug
because the calculated free pointer offset is truncated.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/slub.c

@@ -939,7 +939,7 @@ static void kmem_cache_open_debug_check(struct kmem_cache *s)
 	 * Debugging or ctor may create a need to move the free
 	 * pointer. Fail if this happens.
 	 */
-	if (s->size >= 65535 * sizeof(void *)) {
+	if (s->objsize >= 65535 * sizeof(void *)) {
 		BUG_ON(s->flags & (SLAB_RED_ZONE | SLAB_POISON |
 				SLAB_STORE_USER | SLAB_DESTROY_BY_RCU));
 		BUG_ON(s->ctor);