[PATCH v3 08/14] mm: copy_pte_range() use pte_offset_map_rw_nolock()

[Qi Zheng]

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.

Signed-off-by: Qi Zheng <zhengqi.a...@bytedance.com>
---
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();
-- 
2.20.1