1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * stop-task scheduling class.
4 *
5 * The stop task is the highest priority task in the system, it preempts
6 * everything and will be preempted by nothing.
7 *
8 * See kernel/stop_machine.c
9 */
10
11 #ifdef CONFIG_SMP
12 static int
select_task_rq_stop(struct task_struct * p,int cpu,int flags)13 select_task_rq_stop(struct task_struct *p, int cpu, int flags)
14 {
15 return task_cpu(p); /* stop tasks as never migrate */
16 }
17
18 static int
balance_stop(struct rq * rq,struct task_struct * prev,struct rq_flags * rf)19 balance_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
20 {
21 return sched_stop_runnable(rq);
22 }
23 #endif /* CONFIG_SMP */
24
25 static void
wakeup_preempt_stop(struct rq * rq,struct task_struct * p,int flags)26 wakeup_preempt_stop(struct rq *rq, struct task_struct *p, int flags)
27 {
28 /* we're never preempted */
29 }
30
set_next_task_stop(struct rq * rq,struct task_struct * stop,bool first)31 static void set_next_task_stop(struct rq *rq, struct task_struct *stop, bool first)
32 {
33 stop->se.exec_start = rq_clock_task(rq);
34 }
35
pick_task_stop(struct rq * rq)36 static struct task_struct *pick_task_stop(struct rq *rq)
37 {
38 if (!sched_stop_runnable(rq))
39 return NULL;
40
41 return rq->stop;
42 }
43
44 static void
enqueue_task_stop(struct rq * rq,struct task_struct * p,int flags)45 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
46 {
47 add_nr_running(rq, 1);
48 }
49
50 static bool
dequeue_task_stop(struct rq * rq,struct task_struct * p,int flags)51 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
52 {
53 sub_nr_running(rq, 1);
54 return true;
55 }
56
yield_task_stop(struct rq * rq)57 static void yield_task_stop(struct rq *rq)
58 {
59 BUG(); /* the stop task should never yield, its pointless. */
60 }
61
put_prev_task_stop(struct rq * rq,struct task_struct * prev,struct task_struct * next)62 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev, struct task_struct *next)
63 {
64 update_curr_common(rq);
65 }
66
67 /*
68 * scheduler tick hitting a task of our scheduling class.
69 *
70 * NOTE: This function can be called remotely by the tick offload that
71 * goes along full dynticks. Therefore no local assumption can be made
72 * and everything must be accessed through the @rq and @curr passed in
73 * parameters.
74 */
task_tick_stop(struct rq * rq,struct task_struct * curr,int queued)75 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
76 {
77 }
78
switched_to_stop(struct rq * rq,struct task_struct * p)79 static void switched_to_stop(struct rq *rq, struct task_struct *p)
80 {
81 BUG(); /* its impossible to change to this class */
82 }
83
84 static void
prio_changed_stop(struct rq * rq,struct task_struct * p,int oldprio)85 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
86 {
87 BUG(); /* how!?, what priority? */
88 }
89
update_curr_stop(struct rq * rq)90 static void update_curr_stop(struct rq *rq)
91 {
92 }
93
94 /*
95 * Simple, special scheduling class for the per-CPU stop tasks:
96 */
97 DEFINE_SCHED_CLASS(stop) = {
98
99 .enqueue_task = enqueue_task_stop,
100 .dequeue_task = dequeue_task_stop,
101 .yield_task = yield_task_stop,
102
103 .wakeup_preempt = wakeup_preempt_stop,
104
105 .pick_task = pick_task_stop,
106 .put_prev_task = put_prev_task_stop,
107 .set_next_task = set_next_task_stop,
108
109 #ifdef CONFIG_SMP
110 .balance = balance_stop,
111 .select_task_rq = select_task_rq_stop,
112 .set_cpus_allowed = set_cpus_allowed_common,
113 #endif
114
115 .task_tick = task_tick_stop,
116
117 .prio_changed = prio_changed_stop,
118 .switched_to = switched_to_stop,
119 .update_curr = update_curr_stop,
120 };
121