On Thu, Jan 24, 2019 at 01:15:18PM -0800, Suren Baghdasaryan wrote:

 static void psi_update_work(struct work_struct *work)
 {
 	struct delayed_work *dwork;
 	struct psi_group *group;
+	bool first_pass = true;
+	u64 next_update;
+	u32 change_mask;
+	int polling;
 	bool nonidle;
+	u64 now;
 
 	dwork = to_delayed_work(work);
 	group = container_of(dwork, struct psi_group, clock_work);
 
+	now = sched_clock();
+
+	mutex_lock(&group->update_lock);

actually acquiring a mutex can take a fairly long while; would it not
make more sense to take the @now timestanp _after_ it, instead of
before?