mm/hugetlb: fix potential race in __update_and_free_hugetlb_folio()

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
					 folio_test_hugetlb
					  -- It's still hugetlb folio.
  folio_clear_hugetlb_hwpoison
  					  spin_lock_irq(&hugetlb_lock);
					   __get_huge_page_for_hwpoison
					    folio_set_hugetlb_hwpoison
					  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 the above race occurs, raw error page info will be leaked.  Even
worse, raw error pages won't have hwpoisoned flag set and hit
pcplists/buddy.  Fix this issue by deferring
folio_clear_hugetlb_hwpoison() until __folio_clear_hugetlb() is done.  So
all raw error pages will have hwpoisoned flag set.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 32c8771 ("hugetlb: do not clear hugetlb dtor until allocating vmemmap")
Signed-off-by: Miaohe Lin <[email protected]>
Acked-by: Muchun Song <[email protected]>
Reviewed-by: Oscar Salvador <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

mm/hugetlb.c

@@ -1729,13 +1729,6 @@ static void __update_and_free_hugetlb_folio(struct hstate *h,
 	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.
-	 */
-	if (unlikely(folio_test_hwpoison(folio)))
-		folio_clear_hugetlb_hwpoison(folio);
-
 	/*
 	 * If vmemmap pages were allocated above, then we need to clear the
 	 * hugetlb flag under the hugetlb lock.
@@ -1746,6 +1739,13 @@ static void __update_and_free_hugetlb_folio(struct hstate *h,
 		spin_unlock_irq(&hugetlb_lock);
 	}
 
+	/*
+	 * Move PageHWPoison flag from head page to the raw error pages,
+	 * which makes any healthy subpages reusable.
+	 */
+	if (unlikely(folio_test_hwpoison(folio)))
+		folio_clear_hugetlb_hwpoison(folio);
+
 	folio_ref_unfreeze(folio, 1);
 
 	/*