[PATCH 12/14] mm: multi-gen LRU: walk_pte_range() use pte_offset_map_maywrite_nolock()
From: Qi Zheng <hidden>
Date: 2024-08-21 08:20:48
Also in:
linux-arm-kernel, linux-mm, lkml
Subsystem:
memory management, memory management - mglru (multi-gen lru), memory management - reclaim, the rest · Maintainers:
Andrew Morton, Johannes Weiner, Linus Torvalds
In walk_pte_range(), we may modify the pte entry after holding the ptl, so convert it to using pte_offset_map_maywrite_nolock(). At this time, the write lock of mmap_lock is not held, and 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 <redacted> --- mm/vmscan.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5dc96a843466a..a6620211f138a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c@@ -3396,8 +3396,10 @@ 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_maywrite_nolock(args->mm, pmd, start & PMD_MASK, + &pmdval, &ptl); if (!pte) return false; if (!spin_trylock(ptl)) {
@@ -3405,6 +3407,11 @@ 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