[BUG] a bug in slub on 3.2 and 3.4

[Zefan Li <lizefan@huawei.com>]

I think 3.2 and 3.4 need to backport 43d77867a4f3 ("slub: refactoring unfreeze_partials()")

On 3.4 kernel, we found there are tens of thousands of free task_struct slabs
in the partial list of node 0 when they should have been discarded, which is
essentially a huge memory leak.

Looking into the code, seems the cause is, we check n->nr_partial but the page
might be in n2 where n != n2, and then the page is added to n2->partial though
n2->partial > s->min_partial.

static void unfreeze_partials(struct kmem_cache *s)
{
	...
	while ((page = c->partial)) {
			...
			c->partial = page->next;
			...
			if (!new.inuse && (!n || n->nr_partial > s->min_partial))
				m = M_FREE;
			else {
				struct kmem_cache_node *n2 = get_node(s,
							page_to_nid(page));
				m = M_PARTIAL;
				if (n != n2) {
					...
					n = n2;
					...
				}
		...
	}
	...
}