+ int ret = 1;
+
+ /*
+ * We rely page->lru.next never has bit 0 set, unless the page
+ * is PageTail(). Let's make sure that's true even for poisoned ->lru.
+ */
+ BUILD_BUG_ON((unsigned long)LIST_POISON1 & 1);
+
+ if (!IS_ENABLED(CONFIG_DEBUG_VM)) {
+ ret = 0;
+ goto out;
+ }
+ switch (page - head_page) {
+ case 1:
+ /* the first tail page: ->mapping is compound_mapcount() */
+ if (unlikely(compound_mapcount(page))) {
+ bad_page(page, "nonzero compound_mapcount", 0);
+ goto out;
+ }
+ break;
+ case 2:
+ /*
+ * the second tail page: ->mapping is
+ * page_deferred_list().next -- ignore value.
+ */
+ break;
+ default:
+ if (page->mapping != TAIL_MAPPING) {
+ bad_page(page, "corrupted mapping in tail page", 0);
+ goto out;
+ }
+ break;
+ }