[PATCH] mm/madvise: fix potential pte_unmap_unlock pte error

[Miaohe Lin <linmiaohe@xxxxxxxxxx>]

We can't assume pte_offset_map_lock will return same orig_pte value. So
it's necessary to reacquire the orig_pte or pte_unmap_unlock will unmap
the stale pte.

Fixes: 9c276cc65a58 ("mm: introduce MADV_COLD")
Fixes: 854e9ed09ded ("mm: support madvise(MADV_FREE)")
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
---
 mm/madvise.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index ec03a76244b7..4d6592488b51 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -437,12 +437,12 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
 			if (split_huge_page(page)) {
 				unlock_page(page);
 				put_page(page);
-				pte_offset_map_lock(mm, pmd, addr, &ptl);
+				orig_pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
 				break;
 			}
 			unlock_page(page);
 			put_page(page);
-			pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
+			orig_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
 			pte--;
 			addr -= PAGE_SIZE;
 			continue;
@@ -653,12 +653,12 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
 			if (split_huge_page(page)) {
 				unlock_page(page);
 				put_page(page);
-				pte_offset_map_lock(mm, pmd, addr, &ptl);
+				orig_pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
 				goto out;
 			}
 			unlock_page(page);
 			put_page(page);
-			pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
+			orig_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
 			pte--;
 			addr -= PAGE_SIZE;
 			continue;
-- 
2.23.0