diff --git a/mm/mmap.c b/mm/mmap.c
index 8ba51e73f626..83adf86fd62b 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2270,6 +2270,7 @@ int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
 static inline int munmap_sidetree(struct vm_area_struct *vma,
 				   struct ma_state *mas_detach)
 {
+	vma_start_write(vma);
 	mas_set_range(mas_detach, vma->vm_start, vma->vm_end - 1);
 	if (mas_store_gfp(mas_detach, vma, GFP_KERNEL))
 		return -ENOMEM;