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 12static int 13select_task_rq_stop(struct task_struct *p, int cpu, int flags) 14{ 15 return task_cpu(p); /* stop tasks as never migrate */ 16} 17 18static int 19balance_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 25static void 26wakeup_preempt_stop(struct rq *rq, struct task_struct *p, int flags) 27{ 28 /* we're never preempted */ 29} 30 31static 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 36static 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 44static 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 54static void 55enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags) 56{ 57 add_nr_running(rq, 1); 58} 59 60static void 61dequeue_task_stop(struct rq *rq, struct task_struct *p, int flags) 62{ 63 sub_nr_running(rq, 1); 64} 65 66static void yield_task_stop(struct rq *rq) 67{ 68 BUG(); /* the stop task should never yield, its pointless. */ 69} 70 71static void put_prev_task_stop(struct rq *rq, struct task_struct *prev) 72{ 73 update_curr_common(rq); 74} 75 76/* 77 * scheduler tick hitting a task of our scheduling class. 78 * 79 * NOTE: This function can be called remotely by the tick offload that 80 * goes along full dynticks. Therefore no local assumption can be made 81 * and everything must be accessed through the @rq and @curr passed in 82 * parameters. 83 */ 84static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued) 85{ 86} 87 88static void switched_to_stop(struct rq *rq, struct task_struct *p) 89{ 90 BUG(); /* its impossible to change to this class */ 91} 92 93static void 94prio_changed_stop(struct rq *rq, struct task_struct *p, int oldprio) 95{ 96 BUG(); /* how!?, what priority? */ 97} 98 99static void update_curr_stop(struct rq *rq) 100{ 101} 102 103/* 104 * Simple, special scheduling class for the per-CPU stop tasks: 105 */ 106DEFINE_SCHED_CLASS(stop) = { 107 108 .enqueue_task = enqueue_task_stop, 109 .dequeue_task = dequeue_task_stop, 110 .yield_task = yield_task_stop, 111 112 .wakeup_preempt = wakeup_preempt_stop, 113 114 .pick_next_task = pick_next_task_stop, 115 .put_prev_task = put_prev_task_stop, 116 .set_next_task = set_next_task_stop, 117 118#ifdef CONFIG_SMP 119 .balance = balance_stop, 120 .pick_task = pick_task_stop, 121 .select_task_rq = select_task_rq_stop, 122 .set_cpus_allowed = set_cpus_allowed_common, 123#endif 124 125 .task_tick = task_tick_stop, 126 127 .prio_changed = prio_changed_stop, 128 .switched_to = switched_to_stop, 129 .update_curr = update_curr_stop, 130}; 131