Linux 6.7-rc7
[linux-modified.git] / kernel / sched / stop_task.c
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
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
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
26 wakeup_preempt_stop(struct rq *rq, struct task_struct *p, int flags)
27 {
28         /* we're never preempted */
29 }
30
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
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 struct task_struct *pick_next_task_stop(struct rq *rq)
45 {
46         struct task_struct *p = pick_task_stop(rq);
47
48         if (p)
49                 set_next_task_stop(rq, p, true);
50
51         return p;
52 }
53
54 static void
55 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
56 {
57         add_nr_running(rq, 1);
58 }
59
60 static void
61 dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags)
62 {
63         sub_nr_running(rq, 1);
64 }
65
66 static void yield_task_stop(struct rq *rq)
67 {
68         BUG(); /* the stop task should never yield, its pointless. */
69 }
70
71 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
72 {
73         struct task_struct *curr = rq->curr;
74         u64 now, delta_exec;
75
76         now = rq_clock_task(rq);
77         delta_exec = now - curr->se.exec_start;
78         if (unlikely((s64)delta_exec < 0))
79                 delta_exec = 0;
80
81         schedstat_set(curr->stats.exec_max,
82                       max(curr->stats.exec_max, delta_exec));
83
84         update_current_exec_runtime(curr, now, delta_exec);
85 }
86
87 /*
88  * scheduler tick hitting a task of our scheduling class.
89  *
90  * NOTE: This function can be called remotely by the tick offload that
91  * goes along full dynticks. Therefore no local assumption can be made
92  * and everything must be accessed through the @rq and @curr passed in
93  * parameters.
94  */
95 static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
96 {
97 }
98
99 static void switched_to_stop(struct rq *rq, struct task_struct *p)
100 {
101         BUG(); /* its impossible to change to this class */
102 }
103
104 static void
105 prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio)
106 {
107         BUG(); /* how!?, what priority? */
108 }
109
110 static void update_curr_stop(struct rq *rq)
111 {
112 }
113
114 /*
115  * Simple, special scheduling class for the per-CPU stop tasks:
116  */
117 DEFINE_SCHED_CLASS(stop) = {
118
119         .enqueue_task           = enqueue_task_stop,
120         .dequeue_task           = dequeue_task_stop,
121         .yield_task             = yield_task_stop,
122
123         .wakeup_preempt         = wakeup_preempt_stop,
124
125         .pick_next_task         = pick_next_task_stop,
126         .put_prev_task          = put_prev_task_stop,
127         .set_next_task          = set_next_task_stop,
128
129 #ifdef CONFIG_SMP
130         .balance                = balance_stop,
131         .pick_task              = pick_task_stop,
132         .select_task_rq         = select_task_rq_stop,
133         .set_cpus_allowed       = set_cpus_allowed_common,
134 #endif
135
136         .task_tick              = task_tick_stop,
137
138         .prio_changed           = prio_changed_stop,
139         .switched_to            = switched_to_stop,
140         .update_curr            = update_curr_stop,
141 };