mm/slab: fix unaligned access on sparc64

Commit bf0dea23 ("mm/slab: use percpu allocator for cpu cache")
changed the allocation method for cpu cache array from slab allocator to
percpu allocator.  Alignment should be provided for aligned memory in
percpu allocator case, but, that commit mistakenly set this alignment to
0.  So, percpu allocator returns unaligned memory address.  It doesn't
cause any problem on x86 which permits unaligned access, but, it causes
the problem on sparc64 which needs strong guarantee of alignment.

Following bug report is reported from David Miller.

  I'm getting tons of the following on sparc64:

  [603965.383447] Kernel unaligned access at TPC[546b58] free_block+0x98/0x1a0
  [603965.396987] Kernel unaligned access at TPC[546b60] free_block+0xa0/0x1a0
  ...
  [603970.554394] log_unaligned: 333 callbacks suppressed
  ...

This patch provides a proper alignment parameter when allocating cpu
cache to fix this unaligned memory access problem on sparc64.
Reported-by: David Miller <davem@davemloft.net>
Tested-by: David Miller <davem@davemloft.net>
Tested-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/slab.c

@@ -1992,7 +1992,7 @@ static struct array_cache __percpu *alloc_kmem_cache_cpus(
 	struct array_cache __percpu *cpu_cache;
 
 	size = sizeof(void *) * entries + sizeof(struct array_cache);
-	cpu_cache = __alloc_percpu(size, 0);
+	cpu_cache = __alloc_percpu(size, sizeof(void *));
 
 	if (!cpu_cache)
 		return NULL;