slab: fix init_lock_keys

Some architectures (e.g. powerpc built with CONFIG_PPC_256K_PAGES=y
CONFIG_FORCE_MAX_ZONEORDER=11) get PAGE_SHIFT + MAX_ORDER > 26.

In 3.10 kernels, CONFIG_LOCKDEP=y with PAGE_SHIFT + MAX_ORDER > 26 makes
init_lock_keys() dereference beyond kmalloc_caches[26].
This leads to an unbootable system (kernel panic at initializing SLAB)
if one of kmalloc_caches[26...PAGE_SHIFT+MAX_ORDER-1] is not NULL.

Fix this by making sure that init_lock_keys() does not dereference beyond
kmalloc_caches[26] arrays.

Signed-off-by: Christoph Lameter <[email protected]>
Reported-by: Tetsuo Handa <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: <[email protected]>	[3.10.x]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Pekka Enberg <[email protected]>

mm/slab.c

@@ -565,7 +565,7 @@ static void init_node_lock_keys(int q)
 	if (slab_state < UP)
 		return;
 
-	for (i = 1; i < PAGE_SHIFT + MAX_ORDER; i++) {
+	for (i = 1; i <= KMALLOC_SHIFT_HIGH; i++) {
 		struct kmem_cache_node *n;
 		struct kmem_cache *cache = kmalloc_caches[i];