diff --git a/mm/vma.c b/mm/vma.c
index 88ef92ab24ec..0325b3979313 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -538,6 +538,7 @@ __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
 			return err;
 	}
 
+	vma_start_write(vma);
 	new = vm_area_dup(vma);
 	if (!new)
 		return -ENOMEM;
@@ -568,7 +569,6 @@ __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	if (new->vm_ops && new->vm_ops->open)
 		new->vm_ops->open(new);
 
-	vma_start_write(vma);
 	vma_start_write(new);
 
 	init_vma_prep(&vp, vma);
diff --git a/mm/vma_init.c b/mm/vma_init.c
index baa7e82f47e3..d661f229a734 100644
--- a/mm/vma_init.c
+++ b/mm/vma_init.c
@@ -127,6 +127,9 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
 {
 	struct vm_area_struct *new = kmem_cache_alloc(vm_area_cachep, GFP_KERNEL);
 
+	/* Must hold a write lock to stabilise atomic VMA flags. */
+	vma_assert_write_locked(orig);
+
 	if (!new)
 		return NULL;