mm: multi-gen LRU: walk_pte_range() use pte_offset_map_rw_nolock()

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.

Link: https://lkml.kernel.org/r/7e9c194a5efacc9609cfd31abb9c7df88b53b530.1727332572.git.zhengqi.arch@bytedance.com
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 20dd72c98813d20f3f268140bc173a0c7b42eb7d..8f25dd6cec54b5d0cb67c41e84b40207c66f6aaf 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3386,8 +3386,10 @@ 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)) {
@@ -3395,6 +3397,11 @@ 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) {