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 #include <linux/ftrace.h>
18
19 /* Serializes the updates to cpu_online_map, cpu_present_map */
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 wait_queue_head_t writer_queue;
38 } cpu_hotplug;
39
40 #define writer_exists() (cpu_hotplug.active_writer != NULL)
41
42 void __init cpu_hotplug_init(void)
43 {
44 cpu_hotplug.active_writer = NULL;
45 mutex_init(&cpu_hotplug.lock);
46 cpu_hotplug.refcount = 0;
47 init_waitqueue_head(&cpu_hotplug.writer_queue);
48 }
49
50 #ifdef CONFIG_HOTPLUG_CPU
51
52 void get_online_cpus(void)
53 {
54 might_sleep();
55 if (cpu_hotplug.active_writer == current)
56 return;
57 mutex_lock(&cpu_hotplug.lock);
58 cpu_hotplug.refcount++;
59 mutex_unlock(&cpu_hotplug.lock);
60
61 }
62 EXPORT_SYMBOL_GPL(get_online_cpus);
63
64 void put_online_cpus(void)
65 {
66 if (cpu_hotplug.active_writer == current)
67 return;
68 mutex_lock(&cpu_hotplug.lock);
69 cpu_hotplug.refcount--;
70
71 if (unlikely(writer_exists()) && !cpu_hotplug.refcount)
72 wake_up(&cpu_hotplug.writer_queue);
73
74 mutex_unlock(&cpu_hotplug.lock);
75
76 }
77 EXPORT_SYMBOL_GPL(put_online_cpus);
78
79 #endif /* CONFIG_HOTPLUG_CPU */
80
81 /*
82 * The following two API's must be used when attempting
83 * to serialize the updates to cpu_online_map, cpu_present_map.
84 */
85 void cpu_maps_update_begin(void)
86 {
87 mutex_lock(&cpu_add_remove_lock);
88 }
89
90 void cpu_maps_update_done(void)
91 {
92 mutex_unlock(&cpu_add_remove_lock);
93 }
94
95 /*
96 * This ensures that the hotplug operation can begin only when the
97 * refcount goes to zero.
98 *
99 * Note that during a cpu-hotplug operation, the new readers, if any,
100 * will be blocked by the cpu_hotplug.lock
101 *
102 * Since cpu_maps_update_begin is always called after invoking
103 * cpu_maps_update_begin, we can be sure that only one writer is active.
104 *
105 * Note that theoretically, there is a possibility of a livelock:
106 * - Refcount goes to zero, last reader wakes up the sleeping
107 * writer.
108 * - Last reader unlocks the cpu_hotplug.lock.
109 * - A new reader arrives at this moment, bumps up the refcount.
110 * - The writer acquires the cpu_hotplug.lock finds the refcount
111 * non zero and goes to sleep again.
112 *
113 * However, this is very difficult to achieve in practice since
114 * get_online_cpus() not an api which is called all that often.
115 *
116 */
117 static void cpu_hotplug_begin(void)
118 {
119 DECLARE_WAITQUEUE(wait, current);
120
121 mutex_lock(&cpu_hotplug.lock);
122
123 cpu_hotplug.active_writer = current;
124 add_wait_queue_exclusive(&cpu_hotplug.writer_queue, &wait);
125 while (cpu_hotplug.refcount) {
126 set_current_state(TASK_UNINTERRUPTIBLE);
127 mutex_unlock(&cpu_hotplug.lock);
128 schedule();
129 mutex_lock(&cpu_hotplug.lock);
130 }
131 remove_wait_queue_locked(&cpu_hotplug.writer_queue, &wait);
132 }
133
134 static void cpu_hotplug_done(void)
135 {
136 cpu_hotplug.active_writer = NULL;
137 mutex_unlock(&cpu_hotplug.lock);
138 }
139 /* Need to know about CPUs going up/down? */
140 int __cpuinit register_cpu_notifier(struct notifier_block *nb)
141 {
142 int ret;
143 cpu_maps_update_begin();
144 ret = raw_notifier_chain_register(&cpu_chain, nb);
145 cpu_maps_update_done();
146 return ret;
147 }
148
149 #ifdef CONFIG_HOTPLUG_CPU
150
151 EXPORT_SYMBOL(register_cpu_notifier);
152
153 void unregister_cpu_notifier(struct notifier_block *nb)
154 {
155 cpu_maps_update_begin();
156 raw_notifier_chain_unregister(&cpu_chain, nb);
157 cpu_maps_update_done();
158 }
159 EXPORT_SYMBOL(unregister_cpu_notifier);
160
161 static inline void check_for_tasks(int cpu)
162 {
163 struct task_struct *p;
164
165 write_lock_irq(&tasklist_lock);
166 for_each_process(p) {
167 if (task_cpu(p) == cpu &&
168 (!cputime_eq(p->utime, cputime_zero) ||
169 !cputime_eq(p->stime, cputime_zero)))
170 printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
171 (state = %ld, flags = %x) \n",
172 p->comm, task_pid_nr(p), cpu,
173 p->state, p->flags);
174 }
175 write_unlock_irq(&tasklist_lock);
176 }
177
178 struct take_cpu_down_param {
179 unsigned long mod;
180 void *hcpu;
181 };
182
183 /* Take this CPU down. */
184 static int take_cpu_down(void *_param)
185 {
186 struct take_cpu_down_param *param = _param;
187 int err;
188
189 raw_notifier_call_chain(&cpu_chain, CPU_DYING | param->mod,
190 param->hcpu);
191 /* Ensure this CPU doesn't handle any more interrupts. */
192 err = __cpu_disable();
193 if (err < 0)
194 return err;
195
196 /* Force idle task to run as soon as we yield: it should
197 immediately notice cpu is offline and die quickly. */
198 sched_idle_next();
199 return 0;
200 }
201
202 /* Requires cpu_add_remove_lock to be held */
203 static int _cpu_down(unsigned int cpu, int tasks_frozen)
204 {
205 int err, nr_calls = 0;
206 struct task_struct *p;
207 cpumask_t old_allowed, tmp;
208 void *hcpu = (void *)(long)cpu;
209 unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
210 struct take_cpu_down_param tcd_param = {
211 .mod = mod,
212 .hcpu = hcpu,
213 };
214
215 if (num_online_cpus() == 1)
216 return -EBUSY;
217
218 if (!cpu_online(cpu))
219 return -EINVAL;
220
221 cpu_hotplug_begin();
222 err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
223 hcpu, -1, &nr_calls);
224 if (err == NOTIFY_BAD) {
225 nr_calls--;
226 __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
227 hcpu, nr_calls, NULL);
228 printk("%s: attempt to take down CPU %u failed\n",
229 __FUNCTION__, cpu);
230 err = -EINVAL;
231 goto out_release;
232 }
233
234 /* Ensure that we are not runnable on dying cpu */
235 old_allowed = current->cpus_allowed;
236 tmp = CPU_MASK_ALL;
237 cpu_clear(cpu, tmp);
238 set_cpus_allowed(current, tmp);
239
240 p = __stop_machine_run(take_cpu_down, &tcd_param, cpu);
241
242 if (IS_ERR(p) || cpu_online(cpu)) {
243 /* CPU didn't die: tell everyone. Can't complain. */
244 if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
245 hcpu) == NOTIFY_BAD)
246 BUG();
247
248 if (IS_ERR(p)) {
249 err = PTR_ERR(p);
250 goto out_allowed;
251 }
252 goto out_thread;
253 }
254
255 /* Wait for it to sleep (leaving idle task). */
256 while (!idle_cpu(cpu))
257 yield();
258
259 /* This actually kills the CPU. */
260 __cpu_die(cpu);
261
262 /* CPU is completely dead: tell everyone. Too late to complain. */
263 if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD | mod,
264 hcpu) == NOTIFY_BAD)
265 BUG();
266
267 check_for_tasks(cpu);
268
269 out_thread:
270 err = kthread_stop(p);
271 out_allowed:
272 set_cpus_allowed(current, old_allowed);
273 out_release:
274 cpu_hotplug_done();
275 return err;
276 }
277
278 int cpu_down(unsigned int cpu)
279 {
280 int err = 0;
281
282 cpu_maps_update_begin();
283 if (cpu_hotplug_disabled)
284 err = -EBUSY;
285 else
286 err = _cpu_down(cpu, 0);
287
288 cpu_maps_update_done();
289 return err;
290 }
291 #endif /*CONFIG_HOTPLUG_CPU*/
292
293 /* Requires cpu_add_remove_lock to be held */
294 static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
295 {
296 int ret, nr_calls = 0;
297 void *hcpu = (void *)(long)cpu;
298 unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
299
300 if (cpu_online(cpu) || !cpu_present(cpu))
301 return -EINVAL;
302
303 cpu_hotplug_begin();
304 ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
305 -1, &nr_calls);
306 if (ret == NOTIFY_BAD) {
307 nr_calls--;
308 printk("%s: attempt to bring up CPU %u failed\n",
309 __FUNCTION__, cpu);
310 ret = -EINVAL;
311 goto out_notify;
312 }
313
314 /*
315 * Disable function tracing while bringing up a new CPU.
316 * We don't want to trace functions that can not handle a
317 * smp_processor_id() call.
318 */
319 ftrace_disable();
320
321 /* Arch-specific enabling code. */
322 ret = __cpu_up(cpu);
323 ftrace_enable();
324 if (ret != 0)
325 goto out_notify;
326 BUG_ON(!cpu_online(cpu));
327
328 /* Now call notifier in preparation. */
329 raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu);
330
331 out_notify:
332 if (ret != 0)
333 __raw_notifier_call_chain(&cpu_chain,
334 CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
335 cpu_hotplug_done();
336
337 return ret;
338 }
339
340 int __cpuinit cpu_up(unsigned int cpu)
341 {
342 int err = 0;
343 if (!cpu_isset(cpu, cpu_possible_map)) {
344 printk(KERN_ERR "can't online cpu %d because it is not "
345 "configured as may-hotadd at boot time\n", cpu);
346 #if defined(CONFIG_IA64) || defined(CONFIG_X86_64) || defined(CONFIG_S390)
347 printk(KERN_ERR "please check additional_cpus= boot "
348 "parameter\n");
349 #endif
350 return -EINVAL;
351 }
352
353 cpu_maps_update_begin();
354 if (cpu_hotplug_disabled)
355 err = -EBUSY;
356 else
357 err = _cpu_up(cpu, 0);
358
359 cpu_maps_update_done();
360 return err;
361 }
362
363 #ifdef CONFIG_PM_SLEEP_SMP
364 static cpumask_t frozen_cpus;
365
366 int disable_nonboot_cpus(void)
367 {
368 int cpu, first_cpu, error = 0;
369
370 cpu_maps_update_begin();
371 first_cpu = first_cpu(cpu_online_map);
372 /* We take down all of the non-boot CPUs in one shot to avoid races
373 * with the userspace trying to use the CPU hotplug at the same time
374 */
375 cpus_clear(frozen_cpus);
376 printk("Disabling non-boot CPUs ...\n");
377 for_each_online_cpu(cpu) {
378 if (cpu == first_cpu)
379 continue;
380 error = _cpu_down(cpu, 1);
381 if (!error) {
382 cpu_set(cpu, frozen_cpus);
383 printk("CPU%d is down\n", cpu);
384 } else {
385 printk(KERN_ERR "Error taking CPU%d down: %d\n",
386 cpu, error);
387 break;
388 }
389 }
390 if (!error) {
391 BUG_ON(num_online_cpus() > 1);
392 /* Make sure the CPUs won't be enabled by someone else */
393 cpu_hotplug_disabled = 1;
394 } else {
395 printk(KERN_ERR "Non-boot CPUs are not disabled\n");
396 }
397 cpu_maps_update_done();
398 return error;
399 }
400
401 void __ref enable_nonboot_cpus(void)
402 {
403 int cpu, error;
404
405 /* Allow everyone to use the CPU hotplug again */
406 cpu_maps_update_begin();
407 cpu_hotplug_disabled = 0;
408 if (cpus_empty(frozen_cpus))
409 goto out;
410
411 printk("Enabling non-boot CPUs ...\n");
412 for_each_cpu_mask(cpu, frozen_cpus) {
413 error = _cpu_up(cpu, 1);
414 if (!error) {
415 printk("CPU%d is up\n", cpu);
416 continue;
417 }
418 printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
419 }
420 cpus_clear(frozen_cpus);
421 out:
422 cpu_maps_update_done();
423 }
424 #endif /* CONFIG_PM_SLEEP_SMP */
425
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