slub: ksize() abuse checks

Add a WARN_ON for pages that don't have PageSlab nor PageCompound set to catch
the worst abusers of ksize() in the kernel.

Acked-by: Christoph Lameter <clameter@sgi.com>
Cc: Matt Mackall <mpm@selenic.com>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

mm/slub.c

@@ -2726,9 +2726,10 @@ size_t ksize(const void *object)
 
 	page = virt_to_head_page(object);
 
-	if (unlikely(!PageSlab(page)))
+	if (unlikely(!PageSlab(page))) {
+		WARN_ON(!PageCompound(page));
 		return PAGE_SIZE << compound_order(page);
-
+	}
 	s = page->slab;
 
 #ifdef CONFIG_SLUB_DEBUG