mm: memory-failure: fix race window when trying to get hugetlb folio

page_folio() is fetched before calling get_hwpoison_hugetlb_folio()
without hugetlb_lock being held.  So hugetlb page could be demoted before
get_hwpoison_hugetlb_folio() holding hugetlb_lock but after page_folio()
is fetched.  So get_hwpoison_hugetlb_folio() will hold unexpected extra
refcnt of hugetlb folio while leaving demoted page un-refcnted.

Link: https://lkml.kernel.org/r/20230711055016.2286677-9-linmiaohe@huawei.com
Fixes: 25182f0 ("mm,hwpoison: fix race with hugetlb page allocation")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Acked-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memory-failure.c

@@ -1383,8 +1383,15 @@ static int __get_hwpoison_page(struct page *page, unsigned long flags)
 	bool hugetlb = false;
 
 	ret = get_hwpoison_hugetlb_folio(folio, &hugetlb, false);
-	if (hugetlb)
-		return ret;
+	if (hugetlb) {
+		/* Make sure hugetlb demotion did not happen from under us. */
+		if (folio == page_folio(page))
+			return ret;
+		if (ret > 0) {
+			folio_put(folio);
+			folio = page_folio(page);
+		}
+	}
 
 	/*
 	 * This check prevents from calling folio_try_get() for any
@@ -1473,8 +1480,13 @@ static int __get_unpoison_page(struct page *page)
 	bool hugetlb = false;
 
 	ret = get_hwpoison_hugetlb_folio(folio, &hugetlb, true);
-	if (hugetlb)
-		return ret;
+	if (hugetlb) {
+		/* Make sure hugetlb demotion did not happen from under us. */
+		if (folio == page_folio(page))
+			return ret;
+		if (ret > 0)
+			folio_put(folio);
+	}
 
 	/*
 	 * PageHWPoisonTakenOff pages are not only marked as PG_hwpoison,