[PATCH v2 8/8] mm: memory-failure: fix race window when trying to get hugetlb folio

[Miaohe Lin]

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.

Fixes: 25182f05ffed ("mm,hwpoison: fix race with hugetlb page allocation")
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Acked-by: Naoya Horiguchi <naoya.horiguchi@xxxxxxx>
---
 mm/memory-failure.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index af34fd4669d3..9ab97016877e 100644
--- a/mm/memory-failure.c
+++ b/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,
-- 
2.33.0