slab: fix to calm down kmemleak warning

After using struct page as slab management, we should not call
kmemleak_scan_area(), since struct page isn't the tracking object of
kmemleak. Without this patch and if CONFIG_DEBUG_KMEMLEAK is enabled,
so many kmemleak warnings are printed.
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NPekka Enberg <penberg@iki.fi>

mm/slab.c

@@ -2531,14 +2531,6 @@ static struct freelist *alloc_slabmgmt(struct kmem_cache *cachep,
 		/* Slab management obj is off-slab. */
 		freelist = kmem_cache_alloc_node(cachep->freelist_cache,
 					      local_flags, nodeid);
-		/*
-		 * If the first object in the slab is leaked (it's allocated
-		 * but no one has a reference to it), we want to make sure
-		 * kmemleak does not treat the ->s_mem pointer as a reference
-		 * to the object. Otherwise we will not report the leak.
-		 */
-		kmemleak_scan_area(&page->lru, sizeof(struct list_head),
-				   local_flags);
 		if (!freelist)
 			return NULL;
 	} else {