1/*
2 * Generic entry point for the idle threads
3 */
4#include <linux/sched.h>
5#include <linux/cpu.h>
6#include <linux/cpuidle.h>
7#include <linux/tick.h>
8#include <linux/mm.h>
9#include <linux/stackprotector.h>
10#include <linux/suspend.h>
11
12#include <asm/tlb.h>
13
14#include <trace/events/power.h>
15
16#include "sched.h"
17
18/**
19 * sched_idle_set_state - Record idle state for the current CPU.
20 * @idle_state: State to record.
21 */
22void sched_idle_set_state(struct cpuidle_state *idle_state)
23{
24	idle_set_state(this_rq(), idle_state);
25}
26
27static int __read_mostly cpu_idle_force_poll;
28
29void cpu_idle_poll_ctrl(bool enable)
30{
31	if (enable) {
32		cpu_idle_force_poll++;
33	} else {
34		cpu_idle_force_poll--;
35		WARN_ON_ONCE(cpu_idle_force_poll < 0);
36	}
37}
38
39#ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
40static int __init cpu_idle_poll_setup(char *__unused)
41{
42	cpu_idle_force_poll = 1;
43	return 1;
44}
45__setup("nohlt", cpu_idle_poll_setup);
46
47static int __init cpu_idle_nopoll_setup(char *__unused)
48{
49	cpu_idle_force_poll = 0;
50	return 1;
51}
52__setup("hlt", cpu_idle_nopoll_setup);
53#endif
54
55static inline int cpu_idle_poll(void)
56{
57	rcu_idle_enter();
58	trace_cpu_idle_rcuidle(0, smp_processor_id());
59	local_irq_enable();
60	stop_critical_timings();
61	while (!tif_need_resched() &&
62		(cpu_idle_force_poll || tick_check_broadcast_expired()))
63		cpu_relax();
64	start_critical_timings();
65	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
66	rcu_idle_exit();
67	return 1;
68}
69
70/* Weak implementations for optional arch specific functions */
71void __weak arch_cpu_idle_prepare(void) { }
72void __weak arch_cpu_idle_enter(void) { }
73void __weak arch_cpu_idle_exit(void) { }
74void __weak arch_cpu_idle_dead(void) { }
75void __weak arch_cpu_idle(void)
76{
77	cpu_idle_force_poll = 1;
78	local_irq_enable();
79}
80
81/**
82 * default_idle_call - Default CPU idle routine.
83 *
84 * To use when the cpuidle framework cannot be used.
85 */
86void default_idle_call(void)
87{
88	if (current_clr_polling_and_test()) {
89		local_irq_enable();
90	} else {
91		stop_critical_timings();
92		arch_cpu_idle();
93		start_critical_timings();
94	}
95}
96
97static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
98		      int next_state)
99{
100	/* Fall back to the default arch idle method on errors. */
101	if (next_state < 0) {
102		default_idle_call();
103		return next_state;
104	}
105
106	/*
107	 * The idle task must be scheduled, it is pointless to go to idle, just
108	 * update no idle residency and return.
109	 */
110	if (current_clr_polling_and_test()) {
111		dev->last_residency = 0;
112		local_irq_enable();
113		return -EBUSY;
114	}
115
116	/*
117	 * Enter the idle state previously returned by the governor decision.
118	 * This function will block until an interrupt occurs and will take
119	 * care of re-enabling the local interrupts
120	 */
121	return cpuidle_enter(drv, dev, next_state);
122}
123
124/**
125 * cpuidle_idle_call - the main idle function
126 *
127 * NOTE: no locks or semaphores should be used here
128 *
129 * On archs that support TIF_POLLING_NRFLAG, is called with polling
130 * set, and it returns with polling set.  If it ever stops polling, it
131 * must clear the polling bit.
132 */
133static void cpuidle_idle_call(void)
134{
135	struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
136	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
137	int next_state, entered_state;
138
139	/*
140	 * Check if the idle task must be rescheduled. If it is the
141	 * case, exit the function after re-enabling the local irq.
142	 */
143	if (need_resched()) {
144		local_irq_enable();
145		return;
146	}
147
148	/*
149	 * Tell the RCU framework we are entering an idle section,
150	 * so no more rcu read side critical sections and one more
151	 * step to the grace period
152	 */
153	rcu_idle_enter();
154
155	if (cpuidle_not_available(drv, dev)) {
156		default_idle_call();
157		goto exit_idle;
158	}
159
160	/*
161	 * Suspend-to-idle ("freeze") is a system state in which all user space
162	 * has been frozen, all I/O devices have been suspended and the only
163	 * activity happens here and in iterrupts (if any).  In that case bypass
164	 * the cpuidle governor and go stratight for the deepest idle state
165	 * available.  Possibly also suspend the local tick and the entire
166	 * timekeeping to prevent timer interrupts from kicking us out of idle
167	 * until a proper wakeup interrupt happens.
168	 */
169	if (idle_should_freeze()) {
170		entered_state = cpuidle_enter_freeze(drv, dev);
171		if (entered_state >= 0) {
172			local_irq_enable();
173			goto exit_idle;
174		}
175
176		next_state = cpuidle_find_deepest_state(drv, dev);
177		call_cpuidle(drv, dev, next_state);
178	} else {
179		/*
180		 * Ask the cpuidle framework to choose a convenient idle state.
181		 */
182		next_state = cpuidle_select(drv, dev);
183		entered_state = call_cpuidle(drv, dev, next_state);
184		/*
185		 * Give the governor an opportunity to reflect on the outcome
186		 */
187		cpuidle_reflect(dev, entered_state);
188	}
189
190exit_idle:
191	__current_set_polling();
192
193	/*
194	 * It is up to the idle functions to reenable local interrupts
195	 */
196	if (WARN_ON_ONCE(irqs_disabled()))
197		local_irq_enable();
198
199	rcu_idle_exit();
200}
201
202DEFINE_PER_CPU(bool, cpu_dead_idle);
203
204/*
205 * Generic idle loop implementation
206 *
207 * Called with polling cleared.
208 */
209static void cpu_idle_loop(void)
210{
211	while (1) {
212		/*
213		 * If the arch has a polling bit, we maintain an invariant:
214		 *
215		 * Our polling bit is clear if we're not scheduled (i.e. if
216		 * rq->curr != rq->idle).  This means that, if rq->idle has
217		 * the polling bit set, then setting need_resched is
218		 * guaranteed to cause the cpu to reschedule.
219		 */
220
221		__current_set_polling();
222		tick_nohz_idle_enter();
223
224		while (!need_resched()) {
225			check_pgt_cache();
226			rmb();
227
228			if (cpu_is_offline(smp_processor_id())) {
229				rcu_cpu_notify(NULL, CPU_DYING_IDLE,
230					       (void *)(long)smp_processor_id());
231				smp_mb(); /* all activity before dead. */
232				this_cpu_write(cpu_dead_idle, true);
233				arch_cpu_idle_dead();
234			}
235
236			local_irq_disable();
237			arch_cpu_idle_enter();
238
239			/*
240			 * In poll mode we reenable interrupts and spin.
241			 *
242			 * Also if we detected in the wakeup from idle
243			 * path that the tick broadcast device expired
244			 * for us, we don't want to go deep idle as we
245			 * know that the IPI is going to arrive right
246			 * away
247			 */
248			if (cpu_idle_force_poll || tick_check_broadcast_expired())
249				cpu_idle_poll();
250			else
251				cpuidle_idle_call();
252
253			arch_cpu_idle_exit();
254		}
255
256		/*
257		 * Since we fell out of the loop above, we know
258		 * TIF_NEED_RESCHED must be set, propagate it into
259		 * PREEMPT_NEED_RESCHED.
260		 *
261		 * This is required because for polling idle loops we will
262		 * not have had an IPI to fold the state for us.
263		 */
264		preempt_set_need_resched();
265		tick_nohz_idle_exit();
266		__current_clr_polling();
267
268		/*
269		 * We promise to call sched_ttwu_pending and reschedule
270		 * if need_resched is set while polling is set.  That
271		 * means that clearing polling needs to be visible
272		 * before doing these things.
273		 */
274		smp_mb__after_atomic();
275
276		sched_ttwu_pending();
277		schedule_preempt_disabled();
278	}
279}
280
281void cpu_startup_entry(enum cpuhp_state state)
282{
283	/*
284	 * This #ifdef needs to die, but it's too late in the cycle to
285	 * make this generic (arm and sh have never invoked the canary
286	 * init for the non boot cpus!). Will be fixed in 3.11
287	 */
288#ifdef CONFIG_X86
289	/*
290	 * If we're the non-boot CPU, nothing set the stack canary up
291	 * for us. The boot CPU already has it initialized but no harm
292	 * in doing it again. This is a good place for updating it, as
293	 * we wont ever return from this function (so the invalid
294	 * canaries already on the stack wont ever trigger).
295	 */
296	boot_init_stack_canary();
297#endif
298	arch_cpu_idle_prepare();
299	cpu_idle_loop();
300}
301