xref: /openbmc/linux/kernel/cpu.c (revision 9d56dd3b083a3bec56e9da35ce07baca81030b03)
1 /* CPU control.
2  * (C) 2001, 2002, 2003, 2004 Rusty Russell
3  *
4  * This code is licenced under the GPL.
5  */
6 #include <linux/proc_fs.h>
7 #include <linux/smp.h>
8 #include <linux/init.h>
9 #include <linux/notifier.h>
10 #include <linux/sched.h>
11 #include <linux/unistd.h>
12 #include <linux/cpu.h>
13 #include <linux/module.h>
14 #include <linux/kthread.h>
15 #include <linux/stop_machine.h>
16 #include <linux/mutex.h>
17 
18 #ifdef CONFIG_SMP
19 /* Serializes the updates to cpu_online_mask, cpu_present_mask */
20 static DEFINE_MUTEX(cpu_add_remove_lock);
21 
22 static __cpuinitdata RAW_NOTIFIER_HEAD(cpu_chain);
23 
24 /* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
25  * Should always be manipulated under cpu_add_remove_lock
26  */
27 static int cpu_hotplug_disabled;
28 
29 static struct {
30 	struct task_struct *active_writer;
31 	struct mutex lock; /* Synchronizes accesses to refcount, */
32 	/*
33 	 * Also blocks the new readers during
34 	 * an ongoing cpu hotplug operation.
35 	 */
36 	int refcount;
37 } cpu_hotplug = {
38 	.active_writer = NULL,
39 	.lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),
40 	.refcount = 0,
41 };
42 
43 #ifdef CONFIG_HOTPLUG_CPU
44 
45 void get_online_cpus(void)
46 {
47 	might_sleep();
48 	if (cpu_hotplug.active_writer == current)
49 		return;
50 	mutex_lock(&cpu_hotplug.lock);
51 	cpu_hotplug.refcount++;
52 	mutex_unlock(&cpu_hotplug.lock);
53 
54 }
55 EXPORT_SYMBOL_GPL(get_online_cpus);
56 
57 void put_online_cpus(void)
58 {
59 	if (cpu_hotplug.active_writer == current)
60 		return;
61 	mutex_lock(&cpu_hotplug.lock);
62 	if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
63 		wake_up_process(cpu_hotplug.active_writer);
64 	mutex_unlock(&cpu_hotplug.lock);
65 
66 }
67 EXPORT_SYMBOL_GPL(put_online_cpus);
68 
69 #endif	/* CONFIG_HOTPLUG_CPU */
70 
71 /*
72  * The following two API's must be used when attempting
73  * to serialize the updates to cpu_online_mask, cpu_present_mask.
74  */
75 void cpu_maps_update_begin(void)
76 {
77 	mutex_lock(&cpu_add_remove_lock);
78 }
79 
80 void cpu_maps_update_done(void)
81 {
82 	mutex_unlock(&cpu_add_remove_lock);
83 }
84 
85 /*
86  * This ensures that the hotplug operation can begin only when the
87  * refcount goes to zero.
88  *
89  * Note that during a cpu-hotplug operation, the new readers, if any,
90  * will be blocked by the cpu_hotplug.lock
91  *
92  * Since cpu_hotplug_begin() is always called after invoking
93  * cpu_maps_update_begin(), we can be sure that only one writer is active.
94  *
95  * Note that theoretically, there is a possibility of a livelock:
96  * - Refcount goes to zero, last reader wakes up the sleeping
97  *   writer.
98  * - Last reader unlocks the cpu_hotplug.lock.
99  * - A new reader arrives at this moment, bumps up the refcount.
100  * - The writer acquires the cpu_hotplug.lock finds the refcount
101  *   non zero and goes to sleep again.
102  *
103  * However, this is very difficult to achieve in practice since
104  * get_online_cpus() not an api which is called all that often.
105  *
106  */
107 static void cpu_hotplug_begin(void)
108 {
109 	cpu_hotplug.active_writer = current;
110 
111 	for (;;) {
112 		mutex_lock(&cpu_hotplug.lock);
113 		if (likely(!cpu_hotplug.refcount))
114 			break;
115 		__set_current_state(TASK_UNINTERRUPTIBLE);
116 		mutex_unlock(&cpu_hotplug.lock);
117 		schedule();
118 	}
119 }
120 
121 static void cpu_hotplug_done(void)
122 {
123 	cpu_hotplug.active_writer = NULL;
124 	mutex_unlock(&cpu_hotplug.lock);
125 }
126 /* Need to know about CPUs going up/down? */
127 int __ref register_cpu_notifier(struct notifier_block *nb)
128 {
129 	int ret;
130 	cpu_maps_update_begin();
131 	ret = raw_notifier_chain_register(&cpu_chain, nb);
132 	cpu_maps_update_done();
133 	return ret;
134 }
135 
136 #ifdef CONFIG_HOTPLUG_CPU
137 
138 EXPORT_SYMBOL(register_cpu_notifier);
139 
140 void __ref unregister_cpu_notifier(struct notifier_block *nb)
141 {
142 	cpu_maps_update_begin();
143 	raw_notifier_chain_unregister(&cpu_chain, nb);
144 	cpu_maps_update_done();
145 }
146 EXPORT_SYMBOL(unregister_cpu_notifier);
147 
148 static inline void check_for_tasks(int cpu)
149 {
150 	struct task_struct *p;
151 
152 	write_lock_irq(&tasklist_lock);
153 	for_each_process(p) {
154 		if (task_cpu(p) == cpu &&
155 		    (!cputime_eq(p->utime, cputime_zero) ||
156 		     !cputime_eq(p->stime, cputime_zero)))
157 			printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
158 				(state = %ld, flags = %x) \n",
159 				 p->comm, task_pid_nr(p), cpu,
160 				 p->state, p->flags);
161 	}
162 	write_unlock_irq(&tasklist_lock);
163 }
164 
165 struct take_cpu_down_param {
166 	unsigned long mod;
167 	void *hcpu;
168 };
169 
170 /* Take this CPU down. */
171 static int __ref take_cpu_down(void *_param)
172 {
173 	struct take_cpu_down_param *param = _param;
174 	int err;
175 
176 	/* Ensure this CPU doesn't handle any more interrupts. */
177 	err = __cpu_disable();
178 	if (err < 0)
179 		return err;
180 
181 	raw_notifier_call_chain(&cpu_chain, CPU_DYING | param->mod,
182 				param->hcpu);
183 
184 	/* Force idle task to run as soon as we yield: it should
185 	   immediately notice cpu is offline and die quickly. */
186 	sched_idle_next();
187 	return 0;
188 }
189 
190 /* Requires cpu_add_remove_lock to be held */
191 static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
192 {
193 	int err, nr_calls = 0;
194 	cpumask_var_t old_allowed;
195 	void *hcpu = (void *)(long)cpu;
196 	unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
197 	struct take_cpu_down_param tcd_param = {
198 		.mod = mod,
199 		.hcpu = hcpu,
200 	};
201 
202 	if (num_online_cpus() == 1)
203 		return -EBUSY;
204 
205 	if (!cpu_online(cpu))
206 		return -EINVAL;
207 
208 	if (!alloc_cpumask_var(&old_allowed, GFP_KERNEL))
209 		return -ENOMEM;
210 
211 	cpu_hotplug_begin();
212 	set_cpu_active(cpu, false);
213 	err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
214 					hcpu, -1, &nr_calls);
215 	if (err == NOTIFY_BAD) {
216 		set_cpu_active(cpu, true);
217 
218 		nr_calls--;
219 		__raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
220 					  hcpu, nr_calls, NULL);
221 		printk("%s: attempt to take down CPU %u failed\n",
222 				__func__, cpu);
223 		err = -EINVAL;
224 		goto out_release;
225 	}
226 
227 	/* Ensure that we are not runnable on dying cpu */
228 	cpumask_copy(old_allowed, &current->cpus_allowed);
229 	set_cpus_allowed_ptr(current, cpu_active_mask);
230 
231 	err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
232 	if (err) {
233 		set_cpu_active(cpu, true);
234 		/* CPU didn't die: tell everyone.  Can't complain. */
235 		if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
236 					    hcpu) == NOTIFY_BAD)
237 			BUG();
238 
239 		goto out_allowed;
240 	}
241 	BUG_ON(cpu_online(cpu));
242 
243 	/* Wait for it to sleep (leaving idle task). */
244 	while (!idle_cpu(cpu))
245 		yield();
246 
247 	/* This actually kills the CPU. */
248 	__cpu_die(cpu);
249 
250 	/* CPU is completely dead: tell everyone.  Too late to complain. */
251 	if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD | mod,
252 				    hcpu) == NOTIFY_BAD)
253 		BUG();
254 
255 	check_for_tasks(cpu);
256 
257 out_allowed:
258 	set_cpus_allowed_ptr(current, old_allowed);
259 out_release:
260 	cpu_hotplug_done();
261 	if (!err) {
262 		if (raw_notifier_call_chain(&cpu_chain, CPU_POST_DEAD | mod,
263 					    hcpu) == NOTIFY_BAD)
264 			BUG();
265 	}
266 	free_cpumask_var(old_allowed);
267 	return err;
268 }
269 
270 int __ref cpu_down(unsigned int cpu)
271 {
272 	int err;
273 
274 	err = stop_machine_create();
275 	if (err)
276 		return err;
277 	cpu_maps_update_begin();
278 
279 	if (cpu_hotplug_disabled) {
280 		err = -EBUSY;
281 		goto out;
282 	}
283 
284 	err = _cpu_down(cpu, 0);
285 
286 out:
287 	cpu_maps_update_done();
288 	stop_machine_destroy();
289 	return err;
290 }
291 EXPORT_SYMBOL(cpu_down);
292 #endif /*CONFIG_HOTPLUG_CPU*/
293 
294 /* Requires cpu_add_remove_lock to be held */
295 static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
296 {
297 	int ret, nr_calls = 0;
298 	void *hcpu = (void *)(long)cpu;
299 	unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
300 
301 	if (cpu_online(cpu) || !cpu_present(cpu))
302 		return -EINVAL;
303 
304 	cpu_hotplug_begin();
305 	ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
306 							-1, &nr_calls);
307 	if (ret == NOTIFY_BAD) {
308 		nr_calls--;
309 		printk("%s: attempt to bring up CPU %u failed\n",
310 				__func__, cpu);
311 		ret = -EINVAL;
312 		goto out_notify;
313 	}
314 
315 	/* Arch-specific enabling code. */
316 	ret = __cpu_up(cpu);
317 	if (ret != 0)
318 		goto out_notify;
319 	BUG_ON(!cpu_online(cpu));
320 
321 	set_cpu_active(cpu, true);
322 
323 	/* Now call notifier in preparation. */
324 	raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu);
325 
326 out_notify:
327 	if (ret != 0)
328 		__raw_notifier_call_chain(&cpu_chain,
329 				CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
330 	cpu_hotplug_done();
331 
332 	return ret;
333 }
334 
335 int __cpuinit cpu_up(unsigned int cpu)
336 {
337 	int err = 0;
338 	if (!cpu_possible(cpu)) {
339 		printk(KERN_ERR "can't online cpu %d because it is not "
340 			"configured as may-hotadd at boot time\n", cpu);
341 #if defined(CONFIG_IA64) || defined(CONFIG_X86_64)
342 		printk(KERN_ERR "please check additional_cpus= boot "
343 				"parameter\n");
344 #endif
345 		return -EINVAL;
346 	}
347 
348 	cpu_maps_update_begin();
349 
350 	if (cpu_hotplug_disabled) {
351 		err = -EBUSY;
352 		goto out;
353 	}
354 
355 	err = _cpu_up(cpu, 0);
356 
357 out:
358 	cpu_maps_update_done();
359 	return err;
360 }
361 
362 #ifdef CONFIG_PM_SLEEP_SMP
363 static cpumask_var_t frozen_cpus;
364 
365 int disable_nonboot_cpus(void)
366 {
367 	int cpu, first_cpu, error;
368 
369 	error = stop_machine_create();
370 	if (error)
371 		return error;
372 	cpu_maps_update_begin();
373 	first_cpu = cpumask_first(cpu_online_mask);
374 	/*
375 	 * We take down all of the non-boot CPUs in one shot to avoid races
376 	 * with the userspace trying to use the CPU hotplug at the same time
377 	 */
378 	cpumask_clear(frozen_cpus);
379 
380 	printk("Disabling non-boot CPUs ...\n");
381 	for_each_online_cpu(cpu) {
382 		if (cpu == first_cpu)
383 			continue;
384 		error = _cpu_down(cpu, 1);
385 		if (!error)
386 			cpumask_set_cpu(cpu, frozen_cpus);
387 		else {
388 			printk(KERN_ERR "Error taking CPU%d down: %d\n",
389 				cpu, error);
390 			break;
391 		}
392 	}
393 
394 	if (!error) {
395 		BUG_ON(num_online_cpus() > 1);
396 		/* Make sure the CPUs won't be enabled by someone else */
397 		cpu_hotplug_disabled = 1;
398 	} else {
399 		printk(KERN_ERR "Non-boot CPUs are not disabled\n");
400 	}
401 	cpu_maps_update_done();
402 	stop_machine_destroy();
403 	return error;
404 }
405 
406 void __weak arch_enable_nonboot_cpus_begin(void)
407 {
408 }
409 
410 void __weak arch_enable_nonboot_cpus_end(void)
411 {
412 }
413 
414 void __ref enable_nonboot_cpus(void)
415 {
416 	int cpu, error;
417 
418 	/* Allow everyone to use the CPU hotplug again */
419 	cpu_maps_update_begin();
420 	cpu_hotplug_disabled = 0;
421 	if (cpumask_empty(frozen_cpus))
422 		goto out;
423 
424 	printk("Enabling non-boot CPUs ...\n");
425 
426 	arch_enable_nonboot_cpus_begin();
427 
428 	for_each_cpu(cpu, frozen_cpus) {
429 		error = _cpu_up(cpu, 1);
430 		if (!error) {
431 			printk("CPU%d is up\n", cpu);
432 			continue;
433 		}
434 		printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
435 	}
436 
437 	arch_enable_nonboot_cpus_end();
438 
439 	cpumask_clear(frozen_cpus);
440 out:
441 	cpu_maps_update_done();
442 }
443 
444 static int alloc_frozen_cpus(void)
445 {
446 	if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO))
447 		return -ENOMEM;
448 	return 0;
449 }
450 core_initcall(alloc_frozen_cpus);
451 #endif /* CONFIG_PM_SLEEP_SMP */
452 
453 /**
454  * notify_cpu_starting(cpu) - call the CPU_STARTING notifiers
455  * @cpu: cpu that just started
456  *
457  * This function calls the cpu_chain notifiers with CPU_STARTING.
458  * It must be called by the arch code on the new cpu, before the new cpu
459  * enables interrupts and before the "boot" cpu returns from __cpu_up().
460  */
461 void __cpuinit notify_cpu_starting(unsigned int cpu)
462 {
463 	unsigned long val = CPU_STARTING;
464 
465 #ifdef CONFIG_PM_SLEEP_SMP
466 	if (frozen_cpus != NULL && cpumask_test_cpu(cpu, frozen_cpus))
467 		val = CPU_STARTING_FROZEN;
468 #endif /* CONFIG_PM_SLEEP_SMP */
469 	raw_notifier_call_chain(&cpu_chain, val, (void *)(long)cpu);
470 }
471 
472 #endif /* CONFIG_SMP */
473 
474 /*
475  * cpu_bit_bitmap[] is a special, "compressed" data structure that
476  * represents all NR_CPUS bits binary values of 1<<nr.
477  *
478  * It is used by cpumask_of() to get a constant address to a CPU
479  * mask value that has a single bit set only.
480  */
481 
482 /* cpu_bit_bitmap[0] is empty - so we can back into it */
483 #define MASK_DECLARE_1(x)	[x+1][0] = 1UL << (x)
484 #define MASK_DECLARE_2(x)	MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
485 #define MASK_DECLARE_4(x)	MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
486 #define MASK_DECLARE_8(x)	MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)
487 
488 const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {
489 
490 	MASK_DECLARE_8(0),	MASK_DECLARE_8(8),
491 	MASK_DECLARE_8(16),	MASK_DECLARE_8(24),
492 #if BITS_PER_LONG > 32
493 	MASK_DECLARE_8(32),	MASK_DECLARE_8(40),
494 	MASK_DECLARE_8(48),	MASK_DECLARE_8(56),
495 #endif
496 };
497 EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
498 
499 const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
500 EXPORT_SYMBOL(cpu_all_bits);
501 
502 #ifdef CONFIG_INIT_ALL_POSSIBLE
503 static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly
504 	= CPU_BITS_ALL;
505 #else
506 static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly;
507 #endif
508 const struct cpumask *const cpu_possible_mask = to_cpumask(cpu_possible_bits);
509 EXPORT_SYMBOL(cpu_possible_mask);
510 
511 static DECLARE_BITMAP(cpu_online_bits, CONFIG_NR_CPUS) __read_mostly;
512 const struct cpumask *const cpu_online_mask = to_cpumask(cpu_online_bits);
513 EXPORT_SYMBOL(cpu_online_mask);
514 
515 static DECLARE_BITMAP(cpu_present_bits, CONFIG_NR_CPUS) __read_mostly;
516 const struct cpumask *const cpu_present_mask = to_cpumask(cpu_present_bits);
517 EXPORT_SYMBOL(cpu_present_mask);
518 
519 static DECLARE_BITMAP(cpu_active_bits, CONFIG_NR_CPUS) __read_mostly;
520 const struct cpumask *const cpu_active_mask = to_cpumask(cpu_active_bits);
521 EXPORT_SYMBOL(cpu_active_mask);
522 
523 void set_cpu_possible(unsigned int cpu, bool possible)
524 {
525 	if (possible)
526 		cpumask_set_cpu(cpu, to_cpumask(cpu_possible_bits));
527 	else
528 		cpumask_clear_cpu(cpu, to_cpumask(cpu_possible_bits));
529 }
530 
531 void set_cpu_present(unsigned int cpu, bool present)
532 {
533 	if (present)
534 		cpumask_set_cpu(cpu, to_cpumask(cpu_present_bits));
535 	else
536 		cpumask_clear_cpu(cpu, to_cpumask(cpu_present_bits));
537 }
538 
539 void set_cpu_online(unsigned int cpu, bool online)
540 {
541 	if (online)
542 		cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits));
543 	else
544 		cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits));
545 }
546 
547 void set_cpu_active(unsigned int cpu, bool active)
548 {
549 	if (active)
550 		cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
551 	else
552 		cpumask_clear_cpu(cpu, to_cpumask(cpu_active_bits));
553 }
554 
555 void init_cpu_present(const struct cpumask *src)
556 {
557 	cpumask_copy(to_cpumask(cpu_present_bits), src);
558 }
559 
560 void init_cpu_possible(const struct cpumask *src)
561 {
562 	cpumask_copy(to_cpumask(cpu_possible_bits), src);
563 }
564 
565 void init_cpu_online(const struct cpumask *src)
566 {
567 	cpumask_copy(to_cpumask(cpu_online_bits), src);
568 }
569