slub: Add frozen check in __slab_alloc

Verify that objects returned from __slab_alloc come from slab pages
in the correct state.
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

mm/slub.c

@@ -2245,6 +2245,12 @@ static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 	stat(s, ALLOC_REFILL);
 
 load_freelist:
+	/*
+	 * freelist is pointing to the list of objects to be used.
+	 * page is pointing to the page from which the objects are obtained.
+	 * That page must be frozen for per cpu allocations to work.
+	 */
+	VM_BUG_ON(!c->page->frozen);
 	c->freelist = get_freepointer(s, freelist);
 	c->tid = next_tid(c->tid);
 	local_irq_restore(flags);