kernel/sched/idle.c

   1 /*
   2  * Generic entry point for the idle threads
   3  */
   4 #include <linux/sched.h>
   5 #include <linux/sched/idle.h>
   6 #include <linux/cpu.h>
   7 #include <linux/cpuidle.h>
   8 #include <linux/cpuhotplug.h>
   9 #include <linux/tick.h>
  10 #include <linux/mm.h>
  11 #include <linux/stackprotector.h>
  12 #include <linux/suspend.h>
  13 #include <linux/livepatch.h>
  14
  15 #include <asm/tlb.h>
  16
  17 #include <trace/events/power.h>
  18
  19 #include "sched.h"
  20
  21 /* Linker adds these: start and end of __cpuidle functions */
  22 extern char __cpuidle_text_start[], __cpuidle_text_end[];
  23
  24 /**
  25  * sched_idle_set_state - Record idle state for the current CPU.
  26  * @idle_state: State to record.
  27  */
  28 void sched_idle_set_state(struct cpuidle_state *idle_state)
  29 {
  30         idle_set_state(this_rq(), idle_state);
  31 }
  32
  33 static int __read_mostly cpu_idle_force_poll;
  34
  35 void cpu_idle_poll_ctrl(bool enable)
  36 {
  37         if (enable) {
  38                 cpu_idle_force_poll++;
  39         } else {
  40                 cpu_idle_force_poll--;
  41                 WARN_ON_ONCE(cpu_idle_force_poll < 0);
  42         }
  43 }
  44
  45 #ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
  46 static int __init cpu_idle_poll_setup(char *__unused)
  47 {
  48         cpu_idle_force_poll = 1;
  49         return 1;
  50 }
  51 __setup("nohlt", cpu_idle_poll_setup);
  52
  53 static int __init cpu_idle_nopoll_setup(char *__unused)
  54 {
  55         cpu_idle_force_poll = 0;
  56         return 1;
  57 }
  58 __setup("hlt", cpu_idle_nopoll_setup);
  59 #endif
  60
  61 static noinline int __cpuidle cpu_idle_poll(void)
  62 {
  63         rcu_idle_enter();
  64         trace_cpu_idle_rcuidle(0, smp_processor_id());
  65         local_irq_enable();
  66         stop_critical_timings();
  67         while (!tif_need_resched() &&
  68                 (cpu_idle_force_poll || tick_check_broadcast_expired()))
  69                 cpu_relax();
  70         start_critical_timings();
  71         trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
  72         rcu_idle_exit();
  73         return 1;
  74 }
  75
  76 /* Weak implementations for optional arch specific functions */
  77 void __weak arch_cpu_idle_prepare(void) { }
  78 void __weak arch_cpu_idle_enter(void) { }
  79 void __weak arch_cpu_idle_exit(void) { }
  80 void __weak arch_cpu_idle_dead(void) { }
  81 void __weak arch_cpu_idle(void)
  82 {
  83         cpu_idle_force_poll = 1;
  84         local_irq_enable();
  85 }
  86
  87 /**
  88  * default_idle_call - Default CPU idle routine.
  89  *
  90  * To use when the cpuidle framework cannot be used.
  91  */
  92 void __cpuidle default_idle_call(void)
  93 {
  94         if (current_clr_polling_and_test()) {
  95                 local_irq_enable();
  96         } else {
  97                 stop_critical_timings();
  98                 arch_cpu_idle();
  99                 start_critical_timings();
 100         }
 101 }
 102
 103 static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
 104                       int next_state)
 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  */
 133 static void cpuidle_idle_call(void)
 134 {
 135         struct cpuidle_device *dev = cpuidle_get_device();
 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 ("s2idle") 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
 170         if (idle_should_enter_s2idle() || dev->use_deepest_state) {
 171                 if (idle_should_enter_s2idle()) {
 172                         entered_state = cpuidle_enter_s2idle(drv, dev);
 173                         if (entered_state > 0) {
 174                                 local_irq_enable();
 175                                 goto exit_idle;
 176                         }
 177                 }
 178
 179                 next_state = cpuidle_find_deepest_state(drv, dev);
 180                 call_cpuidle(drv, dev, next_state);
 181         } else {
 182                 /*
 183                  * Ask the cpuidle framework to choose a convenient idle state.
 184                  */
 185                 next_state = cpuidle_select(drv, dev);
 186                 entered_state = call_cpuidle(drv, dev, next_state);
 187                 /*
 188                  * Give the governor an opportunity to reflect on the outcome
 189                  */
 190                 cpuidle_reflect(dev, entered_state);
 191         }
 192
 193 exit_idle:
 194         __current_set_polling();
 195
 196         /*
 197          * It is up to the idle functions to reenable local interrupts
 198          */
 199         if (WARN_ON_ONCE(irqs_disabled()))
 200                 local_irq_enable();
 201
 202         rcu_idle_exit();
 203 }
 204
 205 /*
 206  * Generic idle loop implementation
 207  *
 208  * Called with polling cleared.
 209  */
 210 static void do_idle(void)
 211 {
 212         int cpu = smp_processor_id();
 213         /*
 214          * If the arch has a polling bit, we maintain an invariant:
 215          *
 216          * Our polling bit is clear if we're not scheduled (i.e. if rq->curr !=
 217          * rq->idle). This means that, if rq->idle has the polling bit set,
 218          * then setting need_resched is guaranteed to cause the CPU to
 219          * reschedule.
 220          */
 221
 222         __current_set_polling();
 223         tick_nohz_idle_enter();
 224
 225         while (!need_resched()) {
 226                 check_pgt_cache();
 227                 rmb();
 228
 229                 if (cpu_is_offline(cpu)) {
 230                         cpuhp_report_idle_dead();
 231                         arch_cpu_idle_dead();
 232                 }
 233
 234                 local_irq_disable();
 235                 arch_cpu_idle_enter();
 236
 237                 /*
 238                  * In poll mode we reenable interrupts and spin. Also if we
 239                  * detected in the wakeup from idle path that the tick
 240                  * broadcast device expired for us, we don't want to go deep
 241                  * idle as we know that the IPI is going to arrive right away.
 242                  */
 243                 if (cpu_idle_force_poll || tick_check_broadcast_expired())
 244                         cpu_idle_poll();
 245                 else
 246                         cpuidle_idle_call();
 247                 arch_cpu_idle_exit();
 248         }
 249
 250         /*
 251          * Since we fell out of the loop above, we know TIF_NEED_RESCHED must
 252          * be set, propagate it into PREEMPT_NEED_RESCHED.
 253          *
 254          * This is required because for polling idle loops we will not have had
 255          * an IPI to fold the state for us.
 256          */
 257         preempt_set_need_resched();
 258         tick_nohz_idle_exit();
 259         __current_clr_polling();
 260
 261         /*
 262          * We promise to call sched_ttwu_pending() and reschedule if
 263          * need_resched() is set while polling is set. That means that clearing
 264          * polling needs to be visible before doing these things.
 265          */
 266         smp_mb__after_atomic();
 267
 268         sched_ttwu_pending();
 269         schedule_idle();
 270
 271         if (unlikely(klp_patch_pending(current)))
 272                 klp_update_patch_state(current);
 273 }
 274
 275 bool cpu_in_idle(unsigned long pc)
 276 {
 277         return pc >= (unsigned long)__cpuidle_text_start &&
 278                 pc < (unsigned long)__cpuidle_text_end;
 279 }
 280
 281 struct idle_timer {
 282         struct hrtimer timer;
 283         int done;
 284 };
 285
 286 static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer)
 287 {
 288         struct idle_timer *it = container_of(timer, struct idle_timer, timer);
 289
 290         WRITE_ONCE(it->done, 1);
 291         set_tsk_need_resched(current);
 292
 293         return HRTIMER_NORESTART;
 294 }
 295
 296 void play_idle(unsigned long duration_ms)
 297 {
 298         struct idle_timer it;
 299
 300         /*
 301          * Only FIFO tasks can disable the tick since they don't need the forced
 302          * preemption.
 303          */
 304         WARN_ON_ONCE(current->policy != SCHED_FIFO);
 305         WARN_ON_ONCE(current->nr_cpus_allowed != 1);
 306         WARN_ON_ONCE(!(current->flags & PF_KTHREAD));
 307         WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));
 308         WARN_ON_ONCE(!duration_ms);
 309
 310         rcu_sleep_check();
 311         preempt_disable();
 312         current->flags |= PF_IDLE;
 313         cpuidle_use_deepest_state(true);
 314
 315         it.done = 0;
 316         hrtimer_init_on_stack(&it.timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 317         it.timer.function = idle_inject_timer_fn;
 318         hrtimer_start(&it.timer, ms_to_ktime(duration_ms), HRTIMER_MODE_REL_PINNED);
 319
 320         while (!READ_ONCE(it.done))
 321                 do_idle();
 322
 323         cpuidle_use_deepest_state(false);
 324         current->flags &= ~PF_IDLE;
 325
 326         preempt_fold_need_resched();
 327         preempt_enable();
 328 }
 329 EXPORT_SYMBOL_GPL(play_idle);
 330
 331 void cpu_startup_entry(enum cpuhp_state state)
 332 {
 333         /*
 334          * This #ifdef needs to die, but it's too late in the cycle to
 335          * make this generic (arm and sh have never invoked the canary
 336          * init for the non boot cpus!). Will be fixed in 3.11
 337          */
 338 #ifdef CONFIG_X86
 339         /*
 340          * If we're the non-boot CPU, nothing set the stack canary up
 341          * for us. The boot CPU already has it initialized but no harm
 342          * in doing it again. This is a good place for updating it, as
 343          * we wont ever return from this function (so the invalid
 344          * canaries already on the stack wont ever trigger).
 345          */
 346         boot_init_stack_canary();
 347 #endif
 348         arch_cpu_idle_prepare();
 349         cpuhp_online_idle(state);
 350         while (1)
 351                 do_idle();
 352 }