1/* 2 * kernel/stop_machine.c 3 * 4 * Copyright (C) 2008, 2005 IBM Corporation. 5 * Copyright (C) 2008, 2005 Rusty Russell rusty@rustcorp.com.au 6 * Copyright (C) 2010 SUSE Linux Products GmbH 7 * Copyright (C) 2010 Tejun Heo <tj@kernel.org> 8 * 9 * This file is released under the GPLv2 and any later version. 10 */ 11#include <linux/completion.h> 12#include <linux/cpu.h> 13#include <linux/init.h> 14#include <linux/kthread.h> 15#include <linux/module.h> 16#include <linux/percpu.h> 17#include <linux/sched.h> 18#include <linux/stop_machine.h> 19#include <linux/interrupt.h> 20#include <linux/kallsyms.h> 21 22#include <asm/atomic.h> 23 24/* 25 * Structure to determine completion condition and record errors. May 26 * be shared by works on different cpus. 27 */ 28struct cpu_stop_done { 29 atomic_t nr_todo; /* nr left to execute */ 30 bool executed; /* actually executed? */ 31 int ret; /* collected return value */ 32 struct completion completion; /* fired if nr_todo reaches 0 */ 33}; 34 35/* the actual stopper, one per every possible cpu, enabled on online cpus */ 36struct cpu_stopper { 37 spinlock_t lock; 38 bool enabled; /* is this stopper enabled? */ 39 struct list_head works; /* list of pending works */ 40 struct task_struct *thread; /* stopper thread */ 41}; 42 43static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper); 44 45static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo) 46{ 47 memset(done, 0, sizeof(*done)); 48 atomic_set(&done->nr_todo, nr_todo); 49 init_completion(&done->completion); 50} 51 52/* signal completion unless @done is NULL */ 53static void cpu_stop_signal_done(struct cpu_stop_done *done, bool executed) 54{ 55 if (done) { 56 if (executed) 57 done->executed = true; 58 if (atomic_dec_and_test(&done->nr_todo)) 59 complete(&done->completion); 60 } 61} 62 63/* queue @work to @stopper. if offline, @work is completed immediately */ 64static void cpu_stop_queue_work(struct cpu_stopper *stopper, 65 struct cpu_stop_work *work) 66{ 67 unsigned long flags; 68 69 spin_lock_irqsave(&stopper->lock, flags); 70 71 if (stopper->enabled) { 72 list_add_tail(&work->list, &stopper->works); 73 wake_up_process(stopper->thread); 74 } else 75 cpu_stop_signal_done(work->done, false); 76 77 spin_unlock_irqrestore(&stopper->lock, flags); 78} 79 80/** 81 * stop_one_cpu - stop a cpu 82 * @cpu: cpu to stop 83 * @fn: function to execute 84 * @arg: argument to @fn 85 * 86 * Execute @fn(@arg) on @cpu. @fn is run in a process context with 87 * the highest priority preempting any task on the cpu and 88 * monopolizing it. This function returns after the execution is 89 * complete. 90 * 91 * This function doesn't guarantee @cpu stays online till @fn 92 * completes. If @cpu goes down in the middle, execution may happen 93 * partially or fully on different cpus. @fn should either be ready 94 * for that or the caller should ensure that @cpu stays online until 95 * this function completes. 96 * 97 * CONTEXT: 98 * Might sleep. 99 * 100 * RETURNS: 101 * -ENOENT if @fn(@arg) was not executed because @cpu was offline; 102 * otherwise, the return value of @fn. 103 */ 104int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg) 105{ 106 struct cpu_stop_done done; 107 struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done }; 108 109 cpu_stop_init_done(&done, 1); 110 cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), &work); 111 wait_for_completion(&done.completion); 112 return done.executed ? done.ret : -ENOENT; 113} 114 115/** 116 * stop_one_cpu_nowait - stop a cpu but don't wait for completion 117 * @cpu: cpu to stop 118 * @fn: function to execute 119 * @arg: argument to @fn 120 * 121 * Similar to stop_one_cpu() but doesn't wait for completion. The 122 * caller is responsible for ensuring @work_buf is currently unused 123 * and will remain untouched until stopper starts executing @fn. 124 * 125 * CONTEXT: 126 * Don't care. 127 */ 128void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg, 129 struct cpu_stop_work *work_buf) 130{ 131 *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, }; 132 cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), work_buf); 133} 134 135/* static data for stop_cpus */ 136static DEFINE_MUTEX(stop_cpus_mutex); 137static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work); 138 139int __stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg) 140{ 141 struct cpu_stop_work *work; 142 struct cpu_stop_done done; 143 unsigned int cpu; 144 145 /* initialize works and done */ 146 for_each_cpu(cpu, cpumask) { 147 work = &per_cpu(stop_cpus_work, cpu); 148 work->fn = fn; 149 work->arg = arg; 150 work->done = &done; 151 } 152 cpu_stop_init_done(&done, cpumask_weight(cpumask)); 153 154 /* 155 * Disable preemption while queueing to avoid getting 156 * preempted by a stopper which might wait for other stoppers 157 * to enter @fn which can lead to deadlock. 158 */ 159 preempt_disable(); 160 for_each_cpu(cpu, cpumask) 161 cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), 162 &per_cpu(stop_cpus_work, cpu)); 163 preempt_enable(); 164 165 wait_for_completion(&done.completion); 166 return done.executed ? done.ret : -ENOENT; 167} 168 169/** 170 * stop_cpus - stop multiple cpus 171 * @cpumask: cpus to stop 172 * @fn: function to execute 173 * @arg: argument to @fn 174 * 175 * Execute @fn(@arg) on online cpus in @cpumask. On each target cpu, 176 * @fn is run in a process context with the highest priority 177 * preempting any task on the cpu and monopolizing it. This function 178 * returns after all executions are complete. 179 * 180 * This function doesn't guarantee the cpus in @cpumask stay online 181 * till @fn completes. If some cpus go down in the middle, execution 182 * on the cpu may happen partially or fully on different cpus. @fn 183 * should either be ready for that or the caller should ensure that 184 * the cpus stay online until this function completes. 185 * 186 * All stop_cpus() calls are serialized making it safe for @fn to wait 187 * for all cpus to start executing it. 188 * 189 * CONTEXT: 190 * Might sleep. 191 * 192 * RETURNS: 193 * -ENOENT if @fn(@arg) was not executed at all because all cpus in 194 * @cpumask were offline; otherwise, 0 if all executions of @fn 195 * returned 0, any non zero return value if any returned non zero. 196 */ 197int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg) 198{ 199 int ret; 200 201 /* static works are used, process one request at a time */ 202 mutex_lock(&stop_cpus_mutex); 203 ret = __stop_cpus(cpumask, fn, arg); 204 mutex_unlock(&stop_cpus_mutex); 205 return ret; 206} 207 208/** 209 * try_stop_cpus - try to stop multiple cpus 210 * @cpumask: cpus to stop 211 * @fn: function to execute 212 * @arg: argument to @fn 213 * 214 * Identical to stop_cpus() except that it fails with -EAGAIN if 215 * someone else is already using the facility. 216 * 217 * CONTEXT: 218 * Might sleep. 219 * 220 * RETURNS: 221 * -EAGAIN if someone else is already stopping cpus, -ENOENT if 222 * @fn(@arg) was not executed at all because all cpus in @cpumask were 223 * offline; otherwise, 0 if all executions of @fn returned 0, any non 224 * zero return value if any returned non zero. 225 */ 226int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg) 227{ 228 int ret; 229 230 /* static works are used, process one request at a time */ 231 if (!mutex_trylock(&stop_cpus_mutex)) 232 return -EAGAIN; 233 ret = __stop_cpus(cpumask, fn, arg); 234 mutex_unlock(&stop_cpus_mutex); 235 return ret; 236} 237 238static int cpu_stopper_thread(void *data) 239{ 240 struct cpu_stopper *stopper = data; 241 struct cpu_stop_work *work; 242 int ret; 243 244repeat: 245 set_current_state(TASK_INTERRUPTIBLE); /* mb paired w/ kthread_stop */ 246 247 if (kthread_should_stop()) { 248 __set_current_state(TASK_RUNNING); 249 return 0; 250 } 251 252 work = NULL; 253 spin_lock_irq(&stopper->lock); 254 if (!list_empty(&stopper->works)) { 255 work = list_first_entry(&stopper->works, 256 struct cpu_stop_work, list); 257 list_del_init(&work->list); 258 } 259 spin_unlock_irq(&stopper->lock); 260 261 if (work) { 262 cpu_stop_fn_t fn = work->fn; 263 void *arg = work->arg; 264 struct cpu_stop_done *done = work->done; 265 char ksym_buf[KSYM_NAME_LEN]; 266 267 __set_current_state(TASK_RUNNING); 268 269 /* cpu stop callbacks are not allowed to sleep */ 270 preempt_disable(); 271 272 ret = fn(arg); 273 if (ret) 274 done->ret = ret; 275 276 /* restore preemption and check it's still balanced */ 277 preempt_enable(); 278 WARN_ONCE(preempt_count(), 279 "cpu_stop: %s(%p) leaked preempt count\n", 280 kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL, 281 ksym_buf), arg); 282 283 cpu_stop_signal_done(done, true); 284 } else 285 schedule(); 286 287 goto repeat; 288} 289 290/* manage stopper for a cpu, mostly lifted from sched migration thread mgmt */ 291static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb, 292 unsigned long action, void *hcpu) 293{ 294 struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 }; 295 unsigned int cpu = (unsigned long)hcpu; 296 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu); 297 struct task_struct *p; 298 299 switch (action & ~CPU_TASKS_FROZEN) { 300 case CPU_UP_PREPARE: 301 BUG_ON(stopper->thread || stopper->enabled || 302 !list_empty(&stopper->works)); 303 p = kthread_create(cpu_stopper_thread, stopper, "migration/%d", 304 cpu); 305 if (IS_ERR(p)) 306 return NOTIFY_BAD; 307 sched_setscheduler_nocheck(p, SCHED_FIFO, ¶m); 308 get_task_struct(p); 309 stopper->thread = p; 310 break; 311 312 case CPU_ONLINE: 313 kthread_bind(stopper->thread, cpu); 314 /* strictly unnecessary, as first user will wake it */ 315 wake_up_process(stopper->thread); 316 /* mark enabled */ 317 spin_lock_irq(&stopper->lock); 318 stopper->enabled = true; 319 spin_unlock_irq(&stopper->lock); 320 break; 321 322#ifdef CONFIG_HOTPLUG_CPU 323 case CPU_UP_CANCELED: 324 case CPU_POST_DEAD: 325 { 326 struct cpu_stop_work *work; 327 328 /* kill the stopper */ 329 kthread_stop(stopper->thread); 330 /* drain remaining works */ 331 spin_lock_irq(&stopper->lock); 332 list_for_each_entry(work, &stopper->works, list) 333 cpu_stop_signal_done(work->done, false); 334 stopper->enabled = false; 335 spin_unlock_irq(&stopper->lock); 336 /* release the stopper */ 337 put_task_struct(stopper->thread); 338 stopper->thread = NULL; 339 break; 340 } 341#endif 342 } 343 344 return NOTIFY_OK; 345} 346 347/* 348 * Give it a higher priority so that cpu stopper is available to other 349 * cpu notifiers. It currently shares the same priority as sched 350 * migration_notifier. 351 */ 352static struct notifier_block __cpuinitdata cpu_stop_cpu_notifier = { 353 .notifier_call = cpu_stop_cpu_callback, 354 .priority = 10, 355}; 356 357static int __init cpu_stop_init(void) 358{ 359 void *bcpu = (void *)(long)smp_processor_id(); 360 unsigned int cpu; 361 int err; 362 363 for_each_possible_cpu(cpu) { 364 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu); 365 366 spin_lock_init(&stopper->lock); 367 INIT_LIST_HEAD(&stopper->works); 368 } 369 370 /* start one for the boot cpu */ 371 err = cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_UP_PREPARE, 372 bcpu); 373 BUG_ON(err == NOTIFY_BAD); 374 cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu); 375 register_cpu_notifier(&cpu_stop_cpu_notifier); 376 377 return 0; 378} 379early_initcall(cpu_stop_init); 380 381#ifdef CONFIG_STOP_MACHINE 382 383/* This controls the threads on each CPU. */ 384enum stopmachine_state { 385 /* Dummy starting state for thread. */ 386 STOPMACHINE_NONE, 387 /* Awaiting everyone to be scheduled. */ 388 STOPMACHINE_PREPARE, 389 /* Disable interrupts. */ 390 STOPMACHINE_DISABLE_IRQ, 391 /* Run the function */ 392 STOPMACHINE_RUN, 393 /* Exit */ 394 STOPMACHINE_EXIT, 395}; 396 397struct stop_machine_data { 398 int (*fn)(void *); 399 void *data; 400 /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */ 401 unsigned int num_threads; 402 const struct cpumask *active_cpus; 403 404 enum stopmachine_state state; 405 atomic_t thread_ack; 406}; 407 408static void set_state(struct stop_machine_data *smdata, 409 enum stopmachine_state newstate) 410{ 411 /* Reset ack counter. */ 412 atomic_set(&smdata->thread_ack, smdata->num_threads); 413 smp_wmb(); 414 smdata->state = newstate; 415} 416 417/* Last one to ack a state moves to the next state. */ 418static void ack_state(struct stop_machine_data *smdata) 419{ 420 if (atomic_dec_and_test(&smdata->thread_ack)) 421 set_state(smdata, smdata->state + 1); 422} 423 424/* This is the cpu_stop function which stops the CPU. */ 425static int stop_machine_cpu_stop(void *data) 426{ 427 struct stop_machine_data *smdata = data; 428 enum stopmachine_state curstate = STOPMACHINE_NONE; 429 int cpu = smp_processor_id(), err = 0; 430 bool is_active; 431 432 if (!smdata->active_cpus) 433 is_active = cpu == cpumask_first(cpu_online_mask); 434 else 435 is_active = cpumask_test_cpu(cpu, smdata->active_cpus); 436 437 /* Simple state machine */ 438 do { 439 /* Chill out and ensure we re-read stopmachine_state. */ 440 cpu_relax(); 441 if (smdata->state != curstate) { 442 curstate = smdata->state; 443 switch (curstate) { 444 case STOPMACHINE_DISABLE_IRQ: 445 local_irq_disable(); 446 hard_irq_disable(); 447 break; 448 case STOPMACHINE_RUN: 449 if (is_active) 450 err = smdata->fn(smdata->data); 451 break; 452 default: 453 break; 454 } 455 ack_state(smdata); 456 } 457 } while (curstate != STOPMACHINE_EXIT); 458 459 local_irq_enable(); 460 return err; 461} 462 463int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) 464{ 465 struct stop_machine_data smdata = { .fn = fn, .data = data, 466 .num_threads = num_online_cpus(), 467 .active_cpus = cpus }; 468 469 /* Set the initial state and stop all online cpus. */ 470 set_state(&smdata, STOPMACHINE_PREPARE); 471 return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata); 472} 473 474int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) 475{ 476 int ret; 477 478 /* No CPUs can come up or down during this. */ 479 get_online_cpus(); 480 ret = __stop_machine(fn, data, cpus); 481 put_online_cpus(); 482 return ret; 483} 484EXPORT_SYMBOL_GPL(stop_machine); 485 486#endif /* CONFIG_STOP_MACHINE */ 487