In walk_pte_range(), we may modify the pte entry after holding the ptl, so
convert it to using pte_offset_map_rw_nolock(). At this time, the
pte_same() check is not performed after the ptl held, so we should get
pmdval and do pmd_same() check to ensure the stability of pmd entry.
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Reviewed-by: Muchun Song <muchun.song@xxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
---
mm/vmscan.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 749cdc110c745..bdca94e663bc5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3375,8 +3375,10 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
struct pglist_data *pgdat = lruvec_pgdat(walk->lruvec);
DEFINE_MAX_SEQ(walk->lruvec);
int old_gen, new_gen = lru_gen_from_seq(max_seq);
+ pmd_t pmdval;
- pte = pte_offset_map_nolock(args->mm, pmd, start & PMD_MASK, &ptl);
+ pte = pte_offset_map_rw_nolock(args->mm, pmd, start & PMD_MASK, &pmdval,
+ &ptl);
if (!pte)
return false;
if (!spin_trylock(ptl)) {
@@ -3384,6 +3386,11 @@ static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
return false;
}
+ if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(pmd)))) {
+ pte_unmap_unlock(pte, ptl);
+ return false;
+ }
+
arch_enter_lazy_mmu_mode();
restart:
for (i = pte_index(start), addr = start; addr != end; i++, addr += PAGE_SIZE) {
--
2.20.1
