--- x/kernel/fork.c
+++ y/kernel/fork.c
@@ -692,6 +692,8 @@ static __latent_entropy int dup_mmap(str
 	for_each_vma(old_vmi, mpnt) {
 		struct file *file;
 
+		vma_start_write(mpnt);
+
 		if (mpnt->vm_flags & VM_DONTCOPY) {
 			vm_stat_account(mm, mpnt->vm_flags, -vma_pages(mpnt));
 			continue;