From: Taehee Yoo <ap420073@gmail.com>
Date: Mon, 31 Dec 2018 01:31:43 +0900

+void exit_umh(struct task_struct *tsk)
+{
+	struct umh_info *info;
+	pid_t pid = tsk->pid;
+
+	mutex_lock(&umh_list_lock);
+	list_for_each_entry(info, &umh_list, list) {

So this is probably too expensive of a cost for every process exit.
The problem is that the cost will be taken even if the process is
not a UMH.

I've taken my time to respond in hopes that I could come up with a
good alternative to suggest, but so far I don't have any better ideas.

I'll keep thinking about this some more, please let me know if you
have any ideas.