[PATCH] mm: Fix list corruption in put_pages_list

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

My recent change to put_pages_list() dereferences folio->lru.next after
returning the folio to the page allocator.  Usually this is now on the
pcp list with other free folios, so we try to free an already-free
folio.  This only happens with lists that have more than 15 entries, so
it wasn't immediately discovered.  Revert to using list_for_each_safe()
so we dereference lru.next before disposing of the folio.

Reported-by: "Borah, Chaitanya Kumar" <chaitanya.kumar.borah@intel.com>
Fixes: 24835f899c01 (mm: use free_unref_folios() in put_pages_list())
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 mm/swap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/swap.c b/mm/swap.c
index a910af21ba68..1d4b7713605d 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -139,10 +139,10 @@ EXPORT_SYMBOL(__folio_put);
 void put_pages_list(struct list_head *pages)
 {
 	struct folio_batch fbatch;
-	struct folio *folio;
+	struct folio *folio, *next;
 
 	folio_batch_init(&fbatch);
-	list_for_each_entry(folio, pages, lru) {
+	list_for_each_entry_safe(folio, next, pages, lru) {
 		if (!folio_put_testzero(folio))
 			continue;
 		if (folio_test_hugetlb(folio)) {
-- 
2.43.0