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: 25182f05ffed ("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>

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 133737580a7ecd76d3da7a881d2c0c6a33078834..70f44180ef804057f92392be6ac2507bd74f6f9c 100644 (file)
--- 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,