[PATCH 09/14] mm: mremap: move_ptes() use pte_offset_map_maywrite_nolock()

[Qi Zheng]

In move_ptes(), we may modify the new_pte after acquiring the new_ptl, so
convert it to using pte_offset_map_maywrite_nolock(). But since we already
hold the exclusive mmap_lock, there is no need to get pmdval to do
pmd_same() check, just pass NULL to pmdvalp parameter.

Signed-off-by: Qi Zheng <zhengqi.a...@bytedance.com>
---
 mm/mremap.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/mremap.c b/mm/mremap.c
index e7ae140fc6409..33a0ccf79c32d 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -175,7 +175,12 @@ static int move_ptes(struct vm_area_struct *vma, pmd_t 
*old_pmd,
                err = -EAGAIN;
                goto out;
        }
-       new_pte = pte_offset_map_nolock(mm, new_pmd, new_addr, &new_ptl);
+       /*
+        * Use the maywrite version to indicate that new_pte will be modified,
+        * but since we hold the exclusive mmap_lock, there is no need to
+        * recheck pmd_same() after acquiring the new_ptl.
+        */
+       new_pte = pte_offset_map_maywrite_nolock(mm, new_pmd, new_addr, NULL, 
&new_ptl);
        if (!new_pte) {
                pte_unmap_unlock(old_pte, old_ptl);
                err = -EAGAIN;
-- 
2.20.1