On 2024/9/4 16:40, Qi Zheng wrote:
In copy_pte_range(), we may modify the src_pte entry after holding the
src_ptl, so convert it to using pte_offset_map_rw_nolock(). Since we may
free the PTE page in retract_page_tables() without holding the read lock
of mmap_lock, so we still need to get pmdval and do pmd_same() check after
the ptl is held.
See commit 3db82b9374ca92, copy_pte_range and retract_page_tables
are using vma->anon_vma to be exclusive.
retract_page_tables() copy_page_range()
vma_interval_tree_foreach() if (!vma_needs_copy())
if (READ_ONCE(vma->anon_vma)) return 0;
continue; copy_pte_range()
So I think mmap write lock here is also used for keeping ->anon_vma stable.
And we do not need pmd_same().
Muchun,
Thanks.
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
Hi Muchun, since the code has changed, I dropped your Reviewed-by tag here.
mm/memory.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/mm/memory.c b/mm/memory.c
index 06674f94b7a4e..47974cc4bd7f2 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1082,6 +1082,7 @@ copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
struct mm_struct *src_mm = src_vma->vm_mm;
pte_t *orig_src_pte, *orig_dst_pte;
pte_t *src_pte, *dst_pte;
+ pmd_t pmdval;
pte_t ptent;
spinlock_t *src_ptl, *dst_ptl;
int progress, max_nr, ret = 0;
@@ -1107,13 +1108,28 @@ copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
ret = -ENOMEM;
goto out;
}
- src_pte = pte_offset_map_nolock(src_mm, src_pmd, addr, &src_ptl);
+
+ /*
+ * Since we may free the PTE page in retract_page_tables() without
+ * holding the read lock of mmap_lock, so we still need to do a
+ * pmd_same() check after holding the PTL.
+ */
+ src_pte = pte_offset_map_rw_nolock(src_mm, src_pmd, addr, &pmdval,
+ &src_ptl);
if (!src_pte) {
pte_unmap_unlock(dst_pte, dst_ptl);
/* ret == 0 */
goto out;
}
spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
+
+ if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(src_pmd)))) {
+ pte_unmap_unlock(src_pte, src_ptl);
+ pte_unmap_unlock(dst_pte, dst_ptl);
+ /* ret == 0 */
+ goto out;
+ }
+
orig_src_pte = src_pte;
orig_dst_pte = dst_pte;
arch_enter_lazy_mmu_mode();
