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 /* Serializes the updates to cpu_online_map, cpu_present_map */
19 static DEFINE_MUTEX(cpu_add_remove_lock);
20
21 static __cpuinitdata RAW_NOTIFIER_HEAD(cpu_chain);
22
23 /* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
24 * Should always be manipulated under cpu_add_remove_lock
25 */
26 static int cpu_hotplug_disabled;
27
28 static struct {
29 struct task_struct *active_writer;
30 struct mutex lock; /* Synchronizes accesses to refcount, */
31 /*
32 * Also blocks the new readers during
33 * an ongoing cpu hotplug operation.
34 */
35 int refcount;
36 wait_queue_head_t writer_queue;
37 } cpu_hotplug;
38
39 #define writer_exists() (cpu_hotplug.active_writer != NULL)
40
41 void __init cpu_hotplug_init(void)
42 {
43 cpu_hotplug.active_writer = NULL;
44 mutex_init(&cpu_hotplug.lock);
45 cpu_hotplug.refcount = 0;
46 init_waitqueue_head(&cpu_hotplug.writer_queue);
47 }
48
49 #ifdef CONFIG_HOTPLUG_CPU
50
51 void get_online_cpus(void)
52 {
53 might_sleep();
54 if (cpu_hotplug.active_writer == current)
55 return;
56 mutex_lock(&cpu_hotplug.lock);
57 cpu_hotplug.refcount++;
58 mutex_unlock(&cpu_hotplug.lock);
59
60 }
61 EXPORT_SYMBOL_GPL(get_online_cpus);
62
63 void put_online_cpus(void)
64 {
65 if (cpu_hotplug.active_writer == current)
66 return;
67 mutex_lock(&cpu_hotplug.lock);
68 cpu_hotplug.refcount--;
69
70 if (unlikely(writer_exists()) && !cpu_hotplug.refcount)
71 wake_up(&cpu_hotplug.writer_queue);
72
73 mutex_unlock(&cpu_hotplug.lock);
74
75 }
76 EXPORT_SYMBOL_GPL(put_online_cpus);
77
78 #endif /* CONFIG_HOTPLUG_CPU */
79
80 /*
81 * The following two API's must be used when attempting
82 * to serialize the updates to cpu_online_map, cpu_present_map.
83 */
84 void cpu_maps_update_begin(void)
85 {
86 mutex_lock(&cpu_add_remove_lock);
87 }
88
89 void cpu_maps_update_done(void)
90 {
91 mutex_unlock(&cpu_add_remove_lock);
92 }
93
94 /*
95 * This ensures that the hotplug operation can begin only when the
96 * refcount goes to zero.
97 *
98 * Note that during a cpu-hotplug operation, the new readers, if any,
99 * will be blocked by the cpu_hotplug.lock
100 *
101 * Since cpu_maps_update_begin is always called after invoking
102 * cpu_maps_update_begin, we can be sure that only one writer is active.
103 *
104 * Note that theoretically, there is a possibility of a livelock:
105 * - Refcount goes to zero, last reader wakes up the sleeping
106 * writer.
107 * - Last reader unlocks the cpu_hotplug.lock.
108 * - A new reader arrives at this moment, bumps up the refcount.
109 * - The writer acquires the cpu_hotplug.lock finds the refcount
110 * non zero and goes to sleep again.
111 *
112 * However, this is very difficult to achieve in practice since
113 * get_online_cpus() not an api which is called all that often.
114 *
115 */
116 static void cpu_hotplug_begin(void)
117 {
118 DECLARE_WAITQUEUE(wait, current);
119
120 mutex_lock(&cpu_hotplug.lock);
121
122 cpu_hotplug.active_writer = current;
123 add_wait_queue_exclusive(&cpu_hotplug.writer_queue, &wait);
124 while (cpu_hotplug.refcount) {
125 set_current_state(TASK_UNINTERRUPTIBLE);
126 mutex_unlock(&cpu_hotplug.lock);
127 schedule();
128 mutex_lock(&cpu_hotplug.lock);
129 }
130 remove_wait_queue_locked(&cpu_hotplug.writer_queue, &wait);
131 }
132
133 static void cpu_hotplug_done(void)
134 {
135 cpu_hotplug.active_writer = NULL;
136 mutex_unlock(&cpu_hotplug.lock);
137 }
138 /* Need to know about CPUs going up/down? */
139 int __cpuinit register_cpu_notifier(struct notifier_block *nb)
140 {
141 int ret;
142 cpu_maps_update_begin();
143 ret = raw_notifier_chain_register(&cpu_chain, nb);
144 cpu_maps_update_done();
145 return ret;
146 }
147
148 #ifdef CONFIG_HOTPLUG_CPU
149
150 EXPORT_SYMBOL(register_cpu_notifier);
151
152 void unregister_cpu_notifier(struct notifier_block *nb)
153 {
154 cpu_maps_update_begin();
155 raw_notifier_chain_unregister(&cpu_chain, nb);
156 cpu_maps_update_done();
157 }
158 EXPORT_SYMBOL(unregister_cpu_notifier);
159
160 static inline void check_for_tasks(int cpu)
161 {
162 struct task_struct *p;
163
164 write_lock_irq(&tasklist_lock);
165 for_each_process(p) {
166 if (task_cpu(p) == cpu &&
167 (!cputime_eq(p->utime, cputime_zero) ||
168 !cputime_eq(p->stime, cputime_zero)))
169 printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
170 (state = %ld, flags = %x) \n",
171 p->comm, task_pid_nr(p), cpu,
172 p->state, p->flags);
173 }
174 write_unlock_irq(&tasklist_lock);
175 }
176
177 struct take_cpu_down_param {
178 unsigned long mod;
179 void *hcpu;
180 };
181
182 /* Take this CPU down. */
183 static int take_cpu_down(void *_param)
184 {
185 struct take_cpu_down_param *param = _param;
186 int err;
187
188 raw_notifier_call_chain(&cpu_chain, CPU_DYING | param->mod,
189 param->hcpu);
190 /* Ensure this CPU doesn't handle any more interrupts. */
191 err = __cpu_disable();
192 if (err < 0)
193 return err;
194
195 /* Force idle task to run as soon as we yield: it should
196 immediately notice cpu is offline and die quickly. */
197 sched_idle_next();
198 return 0;
199 }
200
201 /* Requires cpu_add_remove_lock to be held */
202 static int _cpu_down(unsigned int cpu, int tasks_frozen)
203 {
204 int err, nr_calls = 0;
205 struct task_struct *p;
206 cpumask_t old_allowed, tmp;
207 void *hcpu = (void *)(long)cpu;
208 unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
209 struct take_cpu_down_param tcd_param = {
210 .mod = mod,
211 .hcpu = hcpu,
212 };
213
214 if (num_online_cpus() == 1)
215 return -EBUSY;
216
217 if (!cpu_online(cpu))
218 return -EINVAL;
219
220 cpu_hotplug_begin();
221 err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
222 hcpu, -1, &nr_calls);
223 if (err == NOTIFY_BAD) {
224 nr_calls--;
225 __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
226 hcpu, nr_calls, NULL);
227 printk("%s: attempt to take down CPU %u failed\n",
228 __FUNCTION__, cpu);
229 err = -EINVAL;
230 goto out_release;
231 }
232
233 /* Ensure that we are not runnable on dying cpu */
234 old_allowed = current->cpus_allowed;
235 tmp = CPU_MASK_ALL;
236 cpu_clear(cpu, tmp);
237 set_cpus_allowed(current, tmp);
238
239 p = __stop_machine_run(take_cpu_down, &tcd_param, cpu);
240
241 if (IS_ERR(p) || cpu_online(cpu)) {
242 /* CPU didn't die: tell everyone. Can't complain. */
243 if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
244 hcpu) == NOTIFY_BAD)
245 BUG();
246
247 if (IS_ERR(p)) {
248 err = PTR_ERR(p);
249 goto out_allowed;
250 }
251 goto out_thread;
252 }
253
254 /* Wait for it to sleep (leaving idle task). */
255 while (!idle_cpu(cpu))
256 yield();
257
258 /* This actually kills the CPU. */
259 __cpu_die(cpu);
260
261 /* CPU is completely dead: tell everyone. Too late to complain. */
262 if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD | mod,
263 hcpu) == NOTIFY_BAD)
264 BUG();
265
266 check_for_tasks(cpu);
267
268 out_thread:
269 err = kthread_stop(p);
270 out_allowed:
271 set_cpus_allowed(current, old_allowed);
272 out_release:
273 cpu_hotplug_done();
274 return err;
275 }
276
277 int cpu_down(unsigned int cpu)
278 {
279 int err = 0;
280
281 cpu_maps_update_begin();
282 if (cpu_hotplug_disabled)
283 err = -EBUSY;
284 else
285 err = _cpu_down(cpu, 0);
286
287 cpu_maps_update_done();
288 return err;
289 }
290 #endif /*CONFIG_HOTPLUG_CPU*/
291
292 /* Requires cpu_add_remove_lock to be held */
293 static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
294 {
295 int ret, nr_calls = 0;
296 void *hcpu = (void *)(long)cpu;
297 unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
298
299 if (cpu_online(cpu) || !cpu_present(cpu))
300 return -EINVAL;
301
302 cpu_hotplug_begin();
303 ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
304 -1, &nr_calls);
305 if (ret == NOTIFY_BAD) {
306 nr_calls--;
307 printk("%s: attempt to bring up CPU %u failed\n",
308 __FUNCTION__, cpu);
309 ret = -EINVAL;
310 goto out_notify;
311 }
312
313 /* Arch-specific enabling code. */
314 ret = __cpu_up(cpu);
315 if (ret != 0)
316 goto out_notify;
317 BUG_ON(!cpu_online(cpu));
318
319 /* Now call notifier in preparation. */
320 raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu);
321
322 out_notify:
323 if (ret != 0)
324 __raw_notifier_call_chain(&cpu_chain,
325 CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
326 cpu_hotplug_done();
327
328 return ret;
329 }
330
331 int __cpuinit cpu_up(unsigned int cpu)
332 {
333 int err = 0;
334 if (!cpu_isset(cpu, cpu_possible_map)) {
335 printk(KERN_ERR "can't online cpu %d because it is not "
336 "configured as may-hotadd at boot time\n", cpu);
337 #if defined(CONFIG_IA64) || defined(CONFIG_X86_64) || defined(CONFIG_S390)
338 printk(KERN_ERR "please check additional_cpus= boot "
339 "parameter\n");
340 #endif
341 return -EINVAL;
342 }
343
344 cpu_maps_update_begin();
345 if (cpu_hotplug_disabled)
346 err = -EBUSY;
347 else
348 err = _cpu_up(cpu, 0);
349
350 cpu_maps_update_done();
351 return err;
352 }
353
354 #ifdef CONFIG_PM_SLEEP_SMP
355 static cpumask_t frozen_cpus;
356
357 int disable_nonboot_cpus(void)
358 {
359 int cpu, first_cpu, error = 0;
360
361 cpu_maps_update_begin();
362 first_cpu = first_cpu(cpu_online_map);
363 /* We take down all of the non-boot CPUs in one shot to avoid races
364 * with the userspace trying to use the CPU hotplug at the same time
365 */
366 cpus_clear(frozen_cpus);
367 printk("Disabling non-boot CPUs ...\n");
368 for_each_online_cpu(cpu) {
369 if (cpu == first_cpu)
370 continue;
371 error = _cpu_down(cpu, 1);
372 if (!error) {
373 cpu_set(cpu, frozen_cpus);
374 printk("CPU%d is down\n", cpu);
375 } else {
376 printk(KERN_ERR "Error taking CPU%d down: %d\n",
377 cpu, error);
378 break;
379 }
380 }
381 if (!error) {
382 BUG_ON(num_online_cpus() > 1);
383 /* Make sure the CPUs won't be enabled by someone else */
384 cpu_hotplug_disabled = 1;
385 } else {
386 printk(KERN_ERR "Non-boot CPUs are not disabled\n");
387 }
388 cpu_maps_update_done();
389 return error;
390 }
391
392 void __ref enable_nonboot_cpus(void)
393 {
394 int cpu, error;
395
396 /* Allow everyone to use the CPU hotplug again */
397 cpu_maps_update_begin();
398 cpu_hotplug_disabled = 0;
399 if (cpus_empty(frozen_cpus))
400 goto out;
401
402 printk("Enabling non-boot CPUs ...\n");
403 for_each_cpu_mask(cpu, frozen_cpus) {
404 error = _cpu_up(cpu, 1);
405 if (!error) {
406 printk("CPU%d is up\n", cpu);
407 continue;
408 }
409 printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
410 }
411 cpus_clear(frozen_cpus);
412 out:
413 cpu_maps_update_done();
414 }
415 #endif /* CONFIG_PM_SLEEP_SMP */
416
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