sched: _cpu_down(): Don't play with current->cpus_allowed
[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 #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 && p->state == TASK_RUNNING &&
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         struct task_struct *caller;
167         unsigned long mod;
168         void *hcpu;
169 };
170
171 /* Take this CPU down. */
172 static int __ref take_cpu_down(void *_param)
173 {
174         struct take_cpu_down_param *param = _param;
175         unsigned int cpu = (unsigned long)param->hcpu;
176         int err;
177
178         /* Ensure this CPU doesn't handle any more interrupts. */
179         err = __cpu_disable();
180         if (err < 0)
181                 return err;
182
183         raw_notifier_call_chain(&cpu_chain, CPU_DYING | param->mod,
184                                 param->hcpu);
185
186         if (task_cpu(param->caller) == cpu)
187                 move_task_off_dead_cpu(cpu, param->caller);
188         /* Force idle task to run as soon as we yield: it should
189            immediately notice cpu is offline and die quickly. */
190         sched_idle_next();
191         return 0;
192 }
193
194 /* Requires cpu_add_remove_lock to be held */
195 static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
196 {
197         int err, nr_calls = 0;
198         void *hcpu = (void *)(long)cpu;
199         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
200         struct take_cpu_down_param tcd_param = {
201                 .caller = current,
202                 .mod = mod,
203                 .hcpu = hcpu,
204         };
205
206         if (num_online_cpus() == 1)
207                 return -EBUSY;
208
209         if (!cpu_online(cpu))
210                 return -EINVAL;
211
212         cpu_hotplug_begin();
213         set_cpu_active(cpu, false);
214         err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
215                                         hcpu, -1, &nr_calls);
216         if (err == NOTIFY_BAD) {
217                 set_cpu_active(cpu, true);
218
219                 nr_calls--;
220                 __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
221                                           hcpu, nr_calls, NULL);
222                 printk("%s: attempt to take down CPU %u failed\n",
223                                 __func__, cpu);
224                 err = -EINVAL;
225                 goto out_release;
226         }
227
228         err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
229         if (err) {
230                 set_cpu_active(cpu, true);
231                 /* CPU didn't die: tell everyone.  Can't complain. */
232                 if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
233                                             hcpu) == NOTIFY_BAD)
234                         BUG();
235
236                 goto out_release;
237         }
238         BUG_ON(cpu_online(cpu));
239
240         /* Wait for it to sleep (leaving idle task). */
241         while (!idle_cpu(cpu))
242                 yield();
243
244         /* This actually kills the CPU. */
245         __cpu_die(cpu);
246
247         /* CPU is completely dead: tell everyone.  Too late to complain. */
248         if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD | mod,
249                                     hcpu) == NOTIFY_BAD)
250                 BUG();
251
252         check_for_tasks(cpu);
253
254 out_release:
255         cpu_hotplug_done();
256         if (!err) {
257                 if (raw_notifier_call_chain(&cpu_chain, CPU_POST_DEAD | mod,
258                                             hcpu) == NOTIFY_BAD)
259                         BUG();
260         }
261         return err;
262 }
263
264 int __ref cpu_down(unsigned int cpu)
265 {
266         int err;
267
268         err = stop_machine_create();
269         if (err)
270                 return err;
271         cpu_maps_update_begin();
272
273         if (cpu_hotplug_disabled) {
274                 err = -EBUSY;
275                 goto out;
276         }
277
278         err = _cpu_down(cpu, 0);
279
280 out:
281         cpu_maps_update_done();
282         stop_machine_destroy();
283         return err;
284 }
285 EXPORT_SYMBOL(cpu_down);
286 #endif /*CONFIG_HOTPLUG_CPU*/
287
288 /* Requires cpu_add_remove_lock to be held */
289 static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
290 {
291         int ret, nr_calls = 0;
292         void *hcpu = (void *)(long)cpu;
293         unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
294
295         if (cpu_online(cpu) || !cpu_present(cpu))
296                 return -EINVAL;
297
298         cpu_hotplug_begin();
299         ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
300                                                         -1, &nr_calls);
301         if (ret == NOTIFY_BAD) {
302                 nr_calls--;
303                 printk("%s: attempt to bring up CPU %u failed\n",
304                                 __func__, cpu);
305                 ret = -EINVAL;
306                 goto out_notify;
307         }
308
309         /* Arch-specific enabling code. */
310         ret = __cpu_up(cpu);
311         if (ret != 0)
312                 goto out_notify;
313         BUG_ON(!cpu_online(cpu));
314
315         set_cpu_active(cpu, true);
316
317         /* Now call notifier in preparation. */
318         raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu);
319
320 out_notify:
321         if (ret != 0)
322                 __raw_notifier_call_chain(&cpu_chain,
323                                 CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
324         cpu_hotplug_done();
325
326         return ret;
327 }
328
329 int __cpuinit cpu_up(unsigned int cpu)
330 {
331         int err = 0;
332         if (!cpu_possible(cpu)) {
333                 printk(KERN_ERR "can't online cpu %d because it is not "
334                         "configured as may-hotadd at boot time\n", cpu);
335 #if defined(CONFIG_IA64)
336                 printk(KERN_ERR "please check additional_cpus= boot "
337                                 "parameter\n");
338 #endif
339                 return -EINVAL;
340         }
341
342         cpu_maps_update_begin();
343
344         if (cpu_hotplug_disabled) {
345                 err = -EBUSY;
346                 goto out;
347         }
348
349         err = _cpu_up(cpu, 0);
350
351 out:
352         cpu_maps_update_done();
353         return err;
354 }
355
356 #ifdef CONFIG_PM_SLEEP_SMP
357 static cpumask_var_t frozen_cpus;
358
359 int disable_nonboot_cpus(void)
360 {
361         int cpu, first_cpu, error;
362
363         error = stop_machine_create();
364         if (error)
365                 return error;
366         cpu_maps_update_begin();
367         first_cpu = cpumask_first(cpu_online_mask);
368         /*
369          * We take down all of the non-boot CPUs in one shot to avoid races
370          * with the userspace trying to use the CPU hotplug at the same time
371          */
372         cpumask_clear(frozen_cpus);
373
374         printk("Disabling non-boot CPUs ...\n");
375         for_each_online_cpu(cpu) {
376                 if (cpu == first_cpu)
377                         continue;
378                 error = _cpu_down(cpu, 1);
379                 if (!error)
380                         cpumask_set_cpu(cpu, frozen_cpus);
381                 else {
382                         printk(KERN_ERR "Error taking CPU%d down: %d\n",
383                                 cpu, error);
384                         break;
385                 }
386         }
387
388         if (!error) {
389                 BUG_ON(num_online_cpus() > 1);
390                 /* Make sure the CPUs won't be enabled by someone else */
391                 cpu_hotplug_disabled = 1;
392         } else {
393                 printk(KERN_ERR "Non-boot CPUs are not disabled\n");
394         }
395         cpu_maps_update_done();
396         stop_machine_destroy();
397         return error;
398 }
399
400 void __weak arch_enable_nonboot_cpus_begin(void)
401 {
402 }
403
404 void __weak arch_enable_nonboot_cpus_end(void)
405 {
406 }
407
408 void __ref enable_nonboot_cpus(void)
409 {
410         int cpu, error;
411
412         /* Allow everyone to use the CPU hotplug again */
413         cpu_maps_update_begin();
414         cpu_hotplug_disabled = 0;
415         if (cpumask_empty(frozen_cpus))
416                 goto out;
417
418         printk("Enabling non-boot CPUs ...\n");
419
420         arch_enable_nonboot_cpus_begin();
421
422         for_each_cpu(cpu, frozen_cpus) {
423                 error = _cpu_up(cpu, 1);
424                 if (!error) {
425                         printk("CPU%d is up\n", cpu);
426                         continue;
427                 }
428                 printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
429         }
430
431         arch_enable_nonboot_cpus_end();
432
433         cpumask_clear(frozen_cpus);
434 out:
435         cpu_maps_update_done();
436 }
437
438 static int alloc_frozen_cpus(void)
439 {
440         if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO))
441                 return -ENOMEM;
442         return 0;
443 }
444 core_initcall(alloc_frozen_cpus);
445 #endif /* CONFIG_PM_SLEEP_SMP */
446
447 /**
448  * notify_cpu_starting(cpu) - call the CPU_STARTING notifiers
449  * @cpu: cpu that just started
450  *
451  * This function calls the cpu_chain notifiers with CPU_STARTING.
452  * It must be called by the arch code on the new cpu, before the new cpu
453  * enables interrupts and before the "boot" cpu returns from __cpu_up().
454  */
455 void __cpuinit notify_cpu_starting(unsigned int cpu)
456 {
457         unsigned long val = CPU_STARTING;
458
459 #ifdef CONFIG_PM_SLEEP_SMP
460         if (frozen_cpus != NULL && cpumask_test_cpu(cpu, frozen_cpus))
461                 val = CPU_STARTING_FROZEN;
462 #endif /* CONFIG_PM_SLEEP_SMP */
463         raw_notifier_call_chain(&cpu_chain, val, (void *)(long)cpu);
464 }
465
466 #endif /* CONFIG_SMP */
467
468 /*
469  * cpu_bit_bitmap[] is a special, "compressed" data structure that
470  * represents all NR_CPUS bits binary values of 1<<nr.
471  *
472  * It is used by cpumask_of() to get a constant address to a CPU
473  * mask value that has a single bit set only.
474  */
475
476 /* cpu_bit_bitmap[0] is empty - so we can back into it */
477 #define MASK_DECLARE_1(x)       [x+1][0] = 1UL << (x)
478 #define MASK_DECLARE_2(x)       MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
479 #define MASK_DECLARE_4(x)       MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
480 #define MASK_DECLARE_8(x)       MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)
481
482 const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {
483
484         MASK_DECLARE_8(0),      MASK_DECLARE_8(8),
485         MASK_DECLARE_8(16),     MASK_DECLARE_8(24),
486 #if BITS_PER_LONG > 32
487         MASK_DECLARE_8(32),     MASK_DECLARE_8(40),
488         MASK_DECLARE_8(48),     MASK_DECLARE_8(56),
489 #endif
490 };
491 EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
492
493 const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
494 EXPORT_SYMBOL(cpu_all_bits);
495
496 #ifdef CONFIG_INIT_ALL_POSSIBLE
497 static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly
498         = CPU_BITS_ALL;
499 #else
500 static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly;
501 #endif
502 const struct cpumask *const cpu_possible_mask = to_cpumask(cpu_possible_bits);
503 EXPORT_SYMBOL(cpu_possible_mask);
504
505 static DECLARE_BITMAP(cpu_online_bits, CONFIG_NR_CPUS) __read_mostly;
506 const struct cpumask *const cpu_online_mask = to_cpumask(cpu_online_bits);
507 EXPORT_SYMBOL(cpu_online_mask);
508
509 static DECLARE_BITMAP(cpu_present_bits, CONFIG_NR_CPUS) __read_mostly;
510 const struct cpumask *const cpu_present_mask = to_cpumask(cpu_present_bits);
511 EXPORT_SYMBOL(cpu_present_mask);
512
513 static DECLARE_BITMAP(cpu_active_bits, CONFIG_NR_CPUS) __read_mostly;
514 const struct cpumask *const cpu_active_mask = to_cpumask(cpu_active_bits);
515 EXPORT_SYMBOL(cpu_active_mask);
516
517 void set_cpu_possible(unsigned int cpu, bool possible)
518 {
519         if (possible)
520                 cpumask_set_cpu(cpu, to_cpumask(cpu_possible_bits));
521         else
522                 cpumask_clear_cpu(cpu, to_cpumask(cpu_possible_bits));
523 }
524
525 void set_cpu_present(unsigned int cpu, bool present)
526 {
527         if (present)
528                 cpumask_set_cpu(cpu, to_cpumask(cpu_present_bits));
529         else
530                 cpumask_clear_cpu(cpu, to_cpumask(cpu_present_bits));
531 }
532
533 void set_cpu_online(unsigned int cpu, bool online)
534 {
535         if (online)
536                 cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits));
537         else
538                 cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits));
539 }
540
541 void set_cpu_active(unsigned int cpu, bool active)
542 {
543         if (active)
544                 cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
545         else
546                 cpumask_clear_cpu(cpu, to_cpumask(cpu_active_bits));
547 }
548
549 void init_cpu_present(const struct cpumask *src)
550 {
551         cpumask_copy(to_cpumask(cpu_present_bits), src);
552 }
553
554 void init_cpu_possible(const struct cpumask *src)
555 {
556         cpumask_copy(to_cpumask(cpu_possible_bits), src);
557 }
558
559 void init_cpu_online(const struct cpumask *src)
560 {
561         cpumask_copy(to_cpumask(cpu_online_bits), src);
562 }