@@ -143,6 +143,7 @@ static int move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
spinlock_t *old_ptl, *new_ptl;
bool force_flush = false;
unsigned long len = old_end - old_addr;
+ pmd_t dummy_pmdval;
int err = 0;
/*
@@ -175,7 +176,15 @@ 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);
+ /*
+ * Now new_pte is none, so hpage_collapse_scan_file() path can not find
+ * this by traversing file->f_mapping, so there is no concurrency with
+ * retract_page_tables(). In addition, we already hold the exclusive
+ * mmap_lock, so this new_pte page is stable, so there is no need to get
+ * pmdval and do pmd_same() check.
+ */
+ new_pte = pte_offset_map_rw_nolock(mm, new_pmd, new_addr, &dummy_pmdval,
+ &new_ptl);
if (!new_pte) {
pte_unmap_unlock(old_pte, old_ptl);
err = -EAGAIN;