[PATCH] mm/hugetlb: fix potential race with try_memory_failure_hugetlb()

[Miaohe Lin]

There is a potential race between __update_and_free_hugetlb_folio() and
try_memory_failure_hugetlb():

 CPU1					CPU2
 __update_and_free_hugetlb_folio	try_memory_failure_hugetlb
  					 spin_lock_irq(&hugetlb_lock);
					 __get_huge_page_for_hwpoison
					  folio_test_hugetlb
					  -- It's still hugetlb folio.
  folio_test_hugetlb_raw_hwp_unreliable
  -- raw_hwp_unreliable flag is not set yet.
					  folio_set_hugetlb_hwpoison
					  -- raw_hwp_unreliable flag might
					     be set.
					 spin_unlock_irq(&hugetlb_lock);
  spin_lock_irq(&hugetlb_lock);
  __folio_clear_hugetlb(folio);
   -- Hugetlb flag is cleared but too late!
  spin_unlock_irq(&hugetlb_lock);

When above race occurs, raw error pages will hit pcplists/buddy. Fix
this issue by deferring folio_test_hugetlb_raw_hwp_unreliable() until
__folio_clear_hugetlb() is done. The raw_hwp_unreliable flag cannot be
set after hugetlb folio flag is cleared.

Fixes: 32c877191e02 ("hugetlb: do not clear hugetlb dtor until allocating vmemmap")
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
 mm/hugetlb.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 9155144a654c..3d65b68cf78f 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1705,13 +1705,6 @@ static void __update_and_free_hugetlb_folio(struct hstate *h,
 	if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
 		return;
 
-	/*
-	 * If we don't know which subpages are hwpoisoned, we can't free
-	 * the hugepage, so it's leaked intentionally.
-	 */
-	if (folio_test_hugetlb_raw_hwp_unreliable(folio))
-		return;
-
 	/*
 	 * If folio is not vmemmap optimized (!clear_flag), then the folio
 	 * is no longer identified as a hugetlb page.  hugetlb_vmemmap_restore_folio
@@ -1739,6 +1732,13 @@ static void __update_and_free_hugetlb_folio(struct hstate *h,
 		spin_unlock_irq(&hugetlb_lock);
 	}
 
+	/*
+	 * If we don't know which subpages are hwpoisoned, we can't free
+	 * the hugepage, so it's leaked intentionally.
+	 */
+	if (folio_test_hugetlb_raw_hwp_unreliable(folio))
+		return;
+
 	/*
 	 * Move PageHWPoison flag from head page to the raw error pages,
 	 * which makes any healthy subpages reusable.
-- 
2.33.0