In move_ptes(), we may modify the new_pte after acquiring the new_ptl, so
convert it to using pte_offset_map_rw_nolock(). But since we already hold
the exclusive mmap_lock, there is no need to get pmdval to do pmd_same()
check, just pass a dummy variable to it.
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
mm/mremap.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/mm/mremap.c b/mm/mremap.c
index 24712f8dbb6b5..f96b025c09079 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -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 +176,13 @@ 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_rw_nolock(mm, new_pmd, new_addr, &dummy_pmdval,
+ &new_ptl);
if (!new_pte) {
pte_unmap_unlock(old_pte, old_ptl);
err = -EAGAIN;
--
2.20.1
