Merge branch 'linus' into cpus4096
[linux-2.6.git] / kernel / cpu.c
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 /*
19  * Represents all cpu's present in the system
20  * In systems capable of hotplug, this map could dynamically grow
21  * as new cpu's are detected in the system via any platform specific
22  * method, such as ACPI for e.g.
23  */
24 cpumask_t cpu_present_map __read_mostly;
25 EXPORT_SYMBOL(cpu_present_map);
26
27 #ifndef CONFIG_SMP
28
29 /*
30  * Represents all cpu's that are currently online.
31  */
32 cpumask_t cpu_online_map __read_mostly = CPU_MASK_ALL;
33 EXPORT_SYMBOL(cpu_online_map);
34
35 cpumask_t cpu_possible_map __read_mostly = CPU_MASK_ALL;
36 EXPORT_SYMBOL(cpu_possible_map);
37
38 #else /* CONFIG_SMP */
39
40 /* Serializes the updates to cpu_online_map, cpu_present_map */
41 static DEFINE_MUTEX(cpu_add_remove_lock);
42
43 static __cpuinitdata RAW_NOTIFIER_HEAD(cpu_chain);
44
45 /* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
46  * Should always be manipulated under cpu_add_remove_lock
47  */
48 static int cpu_hotplug_disabled;
49
50 static struct {
51         struct task_struct *active_writer;
52         struct mutex lock; /* Synchronizes accesses to refcount, */
53         /*
54          * Also blocks the new readers during
55          * an ongoing cpu hotplug operation.
56          */
57         int refcount;
58 } cpu_hotplug;
59
60 void __init cpu_hotplug_init(void)
61 {
62         cpu_hotplug.active_writer = NULL;
63         mutex_init(&cpu_hotplug.lock);
64         cpu_hotplug.refcount = 0;
65 }
66
67 #ifdef CONFIG_HOTPLUG_CPU
68
69 void get_online_cpus(void)
70 {
71         might_sleep();
72         if (cpu_hotplug.active_writer == current)
73                 return;
74         mutex_lock(&cpu_hotplug.lock);
75         cpu_hotplug.refcount++;
76         mutex_unlock(&cpu_hotplug.lock);
77
78 }
79 EXPORT_SYMBOL_GPL(get_online_cpus);
80
81 void put_online_cpus(void)
82 {
83         if (cpu_hotplug.active_writer == current)
84                 return;
85         mutex_lock(&cpu_hotplug.lock);
86         if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
87                 wake_up_process(cpu_hotplug.active_writer);
88         mutex_unlock(&cpu_hotplug.lock);
89
90 }
91 EXPORT_SYMBOL_GPL(put_online_cpus);
92
93 #endif  /* CONFIG_HOTPLUG_CPU */
94
95 /*
96  * The following two API's must be used when attempting
97  * to serialize the updates to cpu_online_map, cpu_present_map.
98  */
99 void cpu_maps_update_begin(void)
100 {
101         mutex_lock(&cpu_add_remove_lock);
102 }
103
104 void cpu_maps_update_done(void)
105 {
106         mutex_unlock(&cpu_add_remove_lock);
107 }
108
109 /*
110  * This ensures that the hotplug operation can begin only when the
111  * refcount goes to zero.
112  *
113  * Note that during a cpu-hotplug operation, the new readers, if any,
114  * will be blocked by the cpu_hotplug.lock
115  *
116  * Since cpu_hotplug_begin() is always called after invoking
117  * cpu_maps_update_begin(), we can be sure that only one writer is active.
118  *
119  * Note that theoretically, there is a possibility of a livelock:
120  * - Refcount goes to zero, last reader wakes up the sleeping
121  *   writer.
122  * - Last reader unlocks the cpu_hotplug.lock.
123  * - A new reader arrives at this moment, bumps up the refcount.
124  * - The writer acquires the cpu_hotplug.lock finds the refcount
125  *   non zero and goes to sleep again.
126  *
127  * However, this is very difficult to achieve in practice since
128  * get_online_cpus() not an api which is called all that often.
129  *
130  */
131 static void cpu_hotplug_begin(void)
132 {
133         cpu_hotplug.active_writer = current;
134
135         for (;;) {
136                 mutex_lock(&cpu_hotplug.lock);
137                 if (likely(!cpu_hotplug.refcount))
138                         break;
139                 __set_current_state(TASK_UNINTERRUPTIBLE);
140                 mutex_unlock(&cpu_hotplug.lock);
141                 schedule();
142         }
143 }
144
145 static void cpu_hotplug_done(void)
146 {
147         cpu_hotplug.active_writer = NULL;
148         mutex_unlock(&cpu_hotplug.lock);
149 }
150 /* Need to know about CPUs going up/down? */
151 int __ref register_cpu_notifier(struct notifier_block *nb)
152 {
153         int ret;
154         cpu_maps_update_begin();
155         ret = raw_notifier_chain_register(&cpu_chain, nb);
156         cpu_maps_update_done();
157         return ret;
158 }
159
160 #ifdef CONFIG_HOTPLUG_CPU
161
162 EXPORT_SYMBOL(register_cpu_notifier);
163
164 void __ref unregister_cpu_notifier(struct notifier_block *nb)
165 {
166         cpu_maps_update_begin();
167         raw_notifier_chain_unregister(&cpu_chain, nb);
168         cpu_maps_update_done();
169 }
170 EXPORT_SYMBOL(unregister_cpu_notifier);
171
172 static inline void check_for_tasks(int cpu)
173 {
174         struct task_struct *p;
175
176         write_lock_irq(&tasklist_lock);
177         for_each_process(p) {
178                 if (task_cpu(p) == cpu &&
179                     (!cputime_eq(p->utime, cputime_zero) ||
180                      !cputime_eq(p->stime, cputime_zero)))
181                         printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
182                                 (state = %ld, flags = %x) \n",
183                                  p->comm, task_pid_nr(p), cpu,
184                                  p->state, p->flags);
185         }
186         write_unlock_irq(&tasklist_lock);
187 }
188
189 struct take_cpu_down_param {
190         unsigned long mod;
191         void *hcpu;
192 };
193
194 /* Take this CPU down. */
195 static int __ref take_cpu_down(void *_param)
196 {
197         struct take_cpu_down_param *param = _param;
198         int err;
199
200         raw_notifier_call_chain(&cpu_chain, CPU_DYING | param->mod,
201                                 param->hcpu);
202         /* Ensure this CPU doesn't handle any more interrupts. */
203         err = __cpu_disable();
204         if (err < 0)
205                 return err;
206
207         /* Force idle task to run as soon as we yield: it should
208            immediately notice cpu is offline and die quickly. */
209         sched_idle_next();
210         return 0;
211 }
212
213 /* Requires cpu_add_remove_lock to be held */
214 static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
215 {
216         int err, nr_calls = 0;
217         struct task_struct *p;
218         cpumask_t old_allowed, tmp;
219         void *hcpu = (void *)(long)cpu;
220         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
221         struct take_cpu_down_param tcd_param = {
222                 .mod = mod,
223                 .hcpu = hcpu,
224         };
225
226         if (num_online_cpus() == 1)
227                 return -EBUSY;
228
229         if (!cpu_online(cpu))
230                 return -EINVAL;
231
232         cpu_hotplug_begin();
233         err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
234                                         hcpu, -1, &nr_calls);
235         if (err == NOTIFY_BAD) {
236                 nr_calls--;
237                 __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
238                                           hcpu, nr_calls, NULL);
239                 printk("%s: attempt to take down CPU %u failed\n",
240                                 __func__, cpu);
241                 err = -EINVAL;
242                 goto out_release;
243         }
244
245         /* Ensure that we are not runnable on dying cpu */
246         old_allowed = current->cpus_allowed;
247         cpus_setall(tmp);
248         cpu_clear(cpu, tmp);
249         set_cpus_allowed_ptr(current, &tmp);
250
251         p = __stop_machine_run(take_cpu_down, &tcd_param, cpu);
252
253         if (IS_ERR(p) || cpu_online(cpu)) {
254                 /* CPU didn't die: tell everyone.  Can't complain. */
255                 if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
256                                             hcpu) == NOTIFY_BAD)
257                         BUG();
258
259                 if (IS_ERR(p)) {
260                         err = PTR_ERR(p);
261                         goto out_allowed;
262                 }
263                 goto out_thread;
264         }
265
266         /* Wait for it to sleep (leaving idle task). */
267         while (!idle_cpu(cpu))
268                 yield();
269
270         /* This actually kills the CPU. */
271         __cpu_die(cpu);
272
273         /* CPU is completely dead: tell everyone.  Too late to complain. */
274         if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD | mod,
275                                     hcpu) == NOTIFY_BAD)
276                 BUG();
277
278         check_for_tasks(cpu);
279
280 out_thread:
281         err = kthread_stop(p);
282 out_allowed:
283         set_cpus_allowed_ptr(current, &old_allowed);
284 out_release:
285         cpu_hotplug_done();
286         return err;
287 }
288
289 int __ref cpu_down(unsigned int cpu)
290 {
291         int err = 0;
292
293         cpu_maps_update_begin();
294         if (cpu_hotplug_disabled)
295                 err = -EBUSY;
296         else
297                 err = _cpu_down(cpu, 0);
298
299         cpu_maps_update_done();
300         return err;
301 }
302 #endif /*CONFIG_HOTPLUG_CPU*/
303
304 /* Requires cpu_add_remove_lock to be held */
305 static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
306 {
307         int ret, nr_calls = 0;
308         void *hcpu = (void *)(long)cpu;
309         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
310
311         if (cpu_online(cpu) || !cpu_present(cpu))
312                 return -EINVAL;
313
314         cpu_hotplug_begin();
315         ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
316                                                         -1, &nr_calls);
317         if (ret == NOTIFY_BAD) {
318                 nr_calls--;
319                 printk("%s: attempt to bring up CPU %u failed\n",
320                                 __func__, cpu);
321                 ret = -EINVAL;
322                 goto out_notify;
323         }
324
325         /* Arch-specific enabling code. */
326         ret = __cpu_up(cpu);
327         if (ret != 0)
328                 goto out_notify;
329         BUG_ON(!cpu_online(cpu));
330
331         /* Now call notifier in preparation. */
332         raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu);
333
334 out_notify:
335         if (ret != 0)
336                 __raw_notifier_call_chain(&cpu_chain,
337                                 CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
338         cpu_hotplug_done();
339
340         return ret;
341 }
342
343 int __cpuinit cpu_up(unsigned int cpu)
344 {
345         int err = 0;
346         if (!cpu_isset(cpu, cpu_possible_map)) {
347                 printk(KERN_ERR "can't online cpu %d because it is not "
348                         "configured as may-hotadd at boot time\n", cpu);
349 #if defined(CONFIG_IA64) || defined(CONFIG_X86_64) || defined(CONFIG_S390)
350                 printk(KERN_ERR "please check additional_cpus= boot "
351                                 "parameter\n");
352 #endif
353                 return -EINVAL;
354         }
355
356         cpu_maps_update_begin();
357         if (cpu_hotplug_disabled)
358                 err = -EBUSY;
359         else
360                 err = _cpu_up(cpu, 0);
361
362         cpu_maps_update_done();
363         return err;
364 }
365
366 #ifdef CONFIG_PM_SLEEP_SMP
367 static cpumask_t frozen_cpus;
368
369 int disable_nonboot_cpus(void)
370 {
371         int cpu, first_cpu, error = 0;
372
373         cpu_maps_update_begin();
374         first_cpu = first_cpu(cpu_online_map);
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         cpus_clear(frozen_cpus);
379         printk("Disabling non-boot CPUs ...\n");
380         for_each_online_cpu(cpu) {
381                 if (cpu == first_cpu)
382                         continue;
383                 error = _cpu_down(cpu, 1);
384                 if (!error) {
385                         cpu_set(cpu, frozen_cpus);
386                         printk("CPU%d is down\n", cpu);
387                 } else {
388                         printk(KERN_ERR "Error taking CPU%d down: %d\n",
389                                 cpu, error);
390                         break;
391                 }
392         }
393         if (!error) {
394                 BUG_ON(num_online_cpus() > 1);
395                 /* Make sure the CPUs won't be enabled by someone else */
396                 cpu_hotplug_disabled = 1;
397         } else {
398                 printk(KERN_ERR "Non-boot CPUs are not disabled\n");
399         }
400         cpu_maps_update_done();
401         return error;
402 }
403
404 void __ref enable_nonboot_cpus(void)
405 {
406         int cpu, error;
407
408         /* Allow everyone to use the CPU hotplug again */
409         cpu_maps_update_begin();
410         cpu_hotplug_disabled = 0;
411         if (cpus_empty(frozen_cpus))
412                 goto out;
413
414         printk("Enabling non-boot CPUs ...\n");
415         for_each_cpu_mask_nr(cpu, frozen_cpus) {
416                 error = _cpu_up(cpu, 1);
417                 if (!error) {
418                         printk("CPU%d is up\n", cpu);
419                         continue;
420                 }
421                 printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
422         }
423         cpus_clear(frozen_cpus);
424 out:
425         cpu_maps_update_done();
426 }
427 #endif /* CONFIG_PM_SLEEP_SMP */
428
429 #endif /* CONFIG_SMP */