1 files changed, 141 insertions, 0 deletions
diff --git a/kernel/sched/stop_task.c b/kernel/sched/stop_task.c
new file mode 100644
index 000000000..85590599b
--- /dev/null
+++ b/kernel/sched/stop_task.c
@@ -0,0 +1,141 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * stop-task scheduling class.
+ *
+ * The stop task is the highest priority task in the system, it preempts
+ * everything and will be preempted by nothing.
+ *
+ * See kernel/stop_machine.c
+ */
+
+#ifdef CONFIG_SMP
+static int
+select_task_rq_stop(struct task_struct *p, int cpu, int flags)
+{
+	return task_cpu(p); /* stop tasks as never migrate */
+}
+
+static int
+balance_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
+{
+	return sched_stop_runnable(rq);
+}
+#endif /* CONFIG_SMP */
+
+static void
+check_preempt_curr_stop(struct rq *rq, struct task_struct *p, int flags)
+{
+	/* we're never preempted */
+}
+
+static void set_next_task_stop(struct rq *rq, struct task_struct *stop, bool first)
+{
+	stop->se.exec_start = rq_clock_task(rq);
+}
+
+static struct task_struct *pick_task_stop(struct rq *rq)
+{
+	if (!sched_stop_runnable(rq))
+		return NULL;
+
+	return rq->stop;
+}
+
+static struct task_struct *pick_next_task_stop(struct rq *rq)
+{
+	struct task_struct *p = pick_task_stop(rq);
+
+	if (p)
+		set_next_task_stop(rq, p, true);
+
+	return p;
+}
+
+static void
+enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
+{
+	add_nr_running(rq, 1);
+}
+
+static void
+dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
+{
+	sub_nr_running(rq, 1);
+}
+
+static void yield_task_stop(struct rq *rq)
+{
+	BUG(); /* the stop task should never yield, its pointless. */
+}
+
+static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
+{
+	struct task_struct *curr = rq->curr;
+	u64 now, delta_exec;
+
+	now = rq_clock_task(rq);
+	delta_exec = now - curr->se.exec_start;
+	if (unlikely((s64)delta_exec < 0))
+		delta_exec = 0;
+
+	schedstat_set(curr->stats.exec_max,
+		      max(curr->stats.exec_max, delta_exec));
+
+	update_current_exec_runtime(curr, now, delta_exec);
+}
+
+/*
+ * scheduler tick hitting a task of our scheduling class.
+ *
+ * NOTE: This function can be called remotely by the tick offload that
+ * goes along full dynticks. Therefore no local assumption can be made
+ * and everything must be accessed through the @rq and @curr passed in
+ * parameters.
+ */
+static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
+{
+}
+
+static void switched_to_stop(struct rq *rq, struct task_struct *p)
+{
+	BUG(); /* its impossible to change to this class */
+}
+
+static void
+prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
+{
+	BUG(); /* how!?, what priority? */
+}
+
+static void update_curr_stop(struct rq *rq)
+{
+}
+
+/*
+ * Simple, special scheduling class for the per-CPU stop tasks:
+ */
+DEFINE_SCHED_CLASS(stop) = {
+
+	.enqueue_task		= enqueue_task_stop,
+	.dequeue_task		= dequeue_task_stop,
+	.yield_task		= yield_task_stop,
+
+	.check_preempt_curr	= check_preempt_curr_stop,
+
+	.pick_next_task		= pick_next_task_stop,
+	.put_prev_task		= put_prev_task_stop,
+	.set_next_task          = set_next_task_stop,
+
+#ifdef CONFIG_SMP
+	.balance		= balance_stop,
+	.pick_task		= pick_task_stop,
+	.select_task_rq		= select_task_rq_stop,
+	.set_cpus_allowed	= set_cpus_allowed_common,
+#endif
+
+	.task_tick		= task_tick_stop,
+
+	.prio_changed		= prio_changed_stop,
+	.switched_to		= switched_to_stop,
+	.update_curr		= update_curr_stop,
+};