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1142d810 TH |
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. | |
e5582ca2 | 10 | */ |
1142d810 | 11 | #include <linux/completion.h> |
1da177e4 | 12 | #include <linux/cpu.h> |
1142d810 | 13 | #include <linux/init.h> |
ee527cd3 PB |
14 | #include <linux/kthread.h> |
15 | #include <linux/module.h> | |
1142d810 | 16 | #include <linux/percpu.h> |
ee527cd3 PB |
17 | #include <linux/sched.h> |
18 | #include <linux/stop_machine.h> | |
a12bb444 | 19 | #include <linux/interrupt.h> |
1142d810 | 20 | #include <linux/kallsyms.h> |
a12bb444 | 21 | |
1da177e4 | 22 | #include <asm/atomic.h> |
1142d810 TH |
23 | |
24 | /* | |
25 | * Structure to determine completion condition and record errors. May | |
26 | * be shared by works on different cpus. | |
27 | */ | |
28 | struct 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 */ | |
36 | struct cpu_stopper { | |
37 | spinlock_t lock; | |
38 | struct list_head works; /* list of pending works */ | |
39 | struct task_struct *thread; /* stopper thread */ | |
40 | bool enabled; /* is this stopper enabled? */ | |
41 | }; | |
42 | ||
43 | static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper); | |
44 | ||
45 | static 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 */ | |
53 | static 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 */ | |
64 | static 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 | */ | |
104 | int 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 | */ | |
128 | void 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 */ | |
136 | static DEFINE_MUTEX(stop_cpus_mutex); | |
137 | static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work); | |
138 | ||
139 | int __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 | */ | |
197 | int 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 | */ | |
226 | int 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 | ||
238 | static int cpu_stopper_thread(void *data) | |
239 | { | |
240 | struct cpu_stopper *stopper = data; | |
241 | struct cpu_stop_work *work; | |
242 | int ret; | |
243 | ||
244 | repeat: | |
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 */ | |
291 | static 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); | |
1142d810 TH |
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)); | |
969c7921 | 303 | p = kthread_create(cpu_stopper_thread, stopper, "migration/%d", |
1142d810 TH |
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: | |
54e88fad | 324 | case CPU_POST_DEAD: |
9c6f7e43 IM |
325 | { |
326 | struct cpu_stop_work *work; | |
327 | ||
1142d810 TH |
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; | |
9c6f7e43 | 340 | } |
1142d810 TH |
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 | */ | |
352 | static struct notifier_block __cpuinitdata cpu_stop_cpu_notifier = { | |
353 | .notifier_call = cpu_stop_cpu_callback, | |
354 | .priority = 10, | |
355 | }; | |
356 | ||
357 | static 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 | } | |
379 | early_initcall(cpu_stop_init); | |
1da177e4 | 380 | |
bbf1bb3e TH |
381 | #ifdef CONFIG_STOP_MACHINE |
382 | ||
ffdb5976 | 383 | /* This controls the threads on each CPU. */ |
1da177e4 | 384 | enum stopmachine_state { |
ffdb5976 RR |
385 | /* Dummy starting state for thread. */ |
386 | STOPMACHINE_NONE, | |
387 | /* Awaiting everyone to be scheduled. */ | |
1da177e4 | 388 | STOPMACHINE_PREPARE, |
ffdb5976 | 389 | /* Disable interrupts. */ |
1da177e4 | 390 | STOPMACHINE_DISABLE_IRQ, |
ffdb5976 | 391 | /* Run the function */ |
5c2aed62 | 392 | STOPMACHINE_RUN, |
ffdb5976 | 393 | /* Exit */ |
1da177e4 LT |
394 | STOPMACHINE_EXIT, |
395 | }; | |
396 | ||
5c2aed62 | 397 | struct stop_machine_data { |
3fc1f1e2 TH |
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; | |
ffdb5976 | 406 | }; |
5c2aed62 | 407 | |
3fc1f1e2 TH |
408 | static void set_state(struct stop_machine_data *smdata, |
409 | enum stopmachine_state newstate) | |
1da177e4 | 410 | { |
ffdb5976 | 411 | /* Reset ack counter. */ |
3fc1f1e2 | 412 | atomic_set(&smdata->thread_ack, smdata->num_threads); |
ffdb5976 | 413 | smp_wmb(); |
3fc1f1e2 | 414 | smdata->state = newstate; |
1da177e4 LT |
415 | } |
416 | ||
ffdb5976 | 417 | /* Last one to ack a state moves to the next state. */ |
3fc1f1e2 | 418 | static void ack_state(struct stop_machine_data *smdata) |
1da177e4 | 419 | { |
3fc1f1e2 TH |
420 | if (atomic_dec_and_test(&smdata->thread_ack)) |
421 | set_state(smdata, smdata->state + 1); | |
1da177e4 LT |
422 | } |
423 | ||
3fc1f1e2 TH |
424 | /* This is the cpu_stop function which stops the CPU. */ |
425 | static int stop_machine_cpu_stop(void *data) | |
1da177e4 | 426 | { |
3fc1f1e2 | 427 | struct stop_machine_data *smdata = data; |
ffdb5976 | 428 | enum stopmachine_state curstate = STOPMACHINE_NONE; |
3fc1f1e2 TH |
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); | |
c9583e55 | 436 | |
ffdb5976 RR |
437 | /* Simple state machine */ |
438 | do { | |
439 | /* Chill out and ensure we re-read stopmachine_state. */ | |
3401a61e | 440 | cpu_relax(); |
3fc1f1e2 TH |
441 | if (smdata->state != curstate) { |
442 | curstate = smdata->state; | |
ffdb5976 RR |
443 | switch (curstate) { |
444 | case STOPMACHINE_DISABLE_IRQ: | |
445 | local_irq_disable(); | |
446 | hard_irq_disable(); | |
447 | break; | |
448 | case STOPMACHINE_RUN: | |
3fc1f1e2 TH |
449 | if (is_active) |
450 | err = smdata->fn(smdata->data); | |
ffdb5976 RR |
451 | break; |
452 | default: | |
453 | break; | |
454 | } | |
3fc1f1e2 | 455 | ack_state(smdata); |
ffdb5976 RR |
456 | } |
457 | } while (curstate != STOPMACHINE_EXIT); | |
1da177e4 | 458 | |
1da177e4 | 459 | local_irq_enable(); |
3fc1f1e2 | 460 | return err; |
1da177e4 LT |
461 | } |
462 | ||
41c7bb95 | 463 | int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) |
1da177e4 | 464 | { |
3fc1f1e2 TH |
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); | |
1da177e4 LT |
472 | } |
473 | ||
41c7bb95 | 474 | int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) |
1da177e4 | 475 | { |
1da177e4 LT |
476 | int ret; |
477 | ||
478 | /* No CPUs can come up or down during this. */ | |
86ef5c9a | 479 | get_online_cpus(); |
eeec4fad | 480 | ret = __stop_machine(fn, data, cpus); |
86ef5c9a | 481 | put_online_cpus(); |
1da177e4 LT |
482 | return ret; |
483 | } | |
eeec4fad | 484 | EXPORT_SYMBOL_GPL(stop_machine); |
bbf1bb3e TH |
485 | |
486 | #endif /* CONFIG_STOP_MACHINE */ |