sched: enforce ref-counting on current task/thread pointers

sched/core.c

@@ -215,18 +215,19 @@ void schedule_thread_on_cpu(struct thread *thr)
 
 void start_charge_period(void)
 {
-	struct thread *self = current_thread();
+	struct thread *self = get_current_thread();
 	if (!self) {
 		return;
 	}
 
 	self->tr_charge_period_start = get_cycles();
+	put_current_thread(self);
 }
 
 void end_charge_period(void)
 {
 	preempt_disable();
-	struct thread *self = current_thread();
+	struct thread *self = get_current_thread();
 	if (!self) {
 		return;
 	}
@@ -244,6 +245,7 @@ void end_charge_period(void)
 	}
 
 	self->tr_charge_period_start = 0;
+	put_current_thread(self);
 
 	// printk("%llu cycles charged to %s/%u", charge,
 	// self->tr_parent->t_name, self->tr_parent->t_id);