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 err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod, 213 hcpu, -1, &nr_calls); 214 if (err == NOTIFY_BAD) { 215 nr_calls--; 216 __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod, 217 hcpu, nr_calls, NULL); 218 printk("%s: attempt to take down CPU %u failed\n", 219 __func__, cpu); 220 err = -EINVAL; 221 goto out_release; 222 } 223 224 /* Ensure that we are not runnable on dying cpu */ 225 cpumask_copy(old_allowed, ¤t->cpus_allowed); 226 set_cpus_allowed_ptr(current, 227 cpumask_of(cpumask_any_but(cpu_online_mask, cpu))); 228 229 err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu)); 230 if (err) { 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_allowed; 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_allowed: 255 set_cpus_allowed_ptr(current, old_allowed); 256 out_release: 257 cpu_hotplug_done(); 258 if (!err) { 259 if (raw_notifier_call_chain(&cpu_chain, CPU_POST_DEAD | mod, 260 hcpu) == NOTIFY_BAD) 261 BUG(); 262 } 263 free_cpumask_var(old_allowed); 264 return err; 265 } 266 267 int __ref cpu_down(unsigned int cpu) 268 { 269 int err; 270 271 err = stop_machine_create(); 272 if (err) 273 return err; 274 cpu_maps_update_begin(); 275 276 if (cpu_hotplug_disabled) { 277 err = -EBUSY; 278 goto out; 279 } 280 281 set_cpu_active(cpu, false); 282 283 /* 284 * Make sure the all cpus did the reschedule and are not 285 * using stale version of the cpu_active_mask. 286 * This is not strictly necessary becuase stop_machine() 287 * that we run down the line already provides the required 288 * synchronization. But it's really a side effect and we do not 289 * want to depend on the innards of the stop_machine here. 290 */ 291 synchronize_sched(); 292 293 err = _cpu_down(cpu, 0); 294 295 if (cpu_online(cpu)) 296 set_cpu_active(cpu, true); 297 298 out: 299 cpu_maps_update_done(); 300 stop_machine_destroy(); 301 return err; 302 } 303 EXPORT_SYMBOL(cpu_down); 304 #endif /*CONFIG_HOTPLUG_CPU*/ 305 306 /* Requires cpu_add_remove_lock to be held */ 307 static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen) 308 { 309 int ret, nr_calls = 0; 310 void *hcpu = (void *)(long)cpu; 311 unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0; 312 313 if (cpu_online(cpu) || !cpu_present(cpu)) 314 return -EINVAL; 315 316 cpu_hotplug_begin(); 317 ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu, 318 -1, &nr_calls); 319 if (ret == NOTIFY_BAD) { 320 nr_calls--; 321 printk("%s: attempt to bring up CPU %u failed\n", 322 __func__, cpu); 323 ret = -EINVAL; 324 goto out_notify; 325 } 326 327 /* Arch-specific enabling code. */ 328 ret = __cpu_up(cpu); 329 if (ret != 0) 330 goto out_notify; 331 BUG_ON(!cpu_online(cpu)); 332 333 set_cpu_active(cpu, true); 334 335 /* Now call notifier in preparation. */ 336 raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu); 337 338 out_notify: 339 if (ret != 0) 340 __raw_notifier_call_chain(&cpu_chain, 341 CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL); 342 cpu_hotplug_done(); 343 344 return ret; 345 } 346 347 int __cpuinit cpu_up(unsigned int cpu) 348 { 349 int err = 0; 350 if (!cpu_possible(cpu)) { 351 printk(KERN_ERR "can't online cpu %d because it is not " 352 "configured as may-hotadd at boot time\n", cpu); 353 #if defined(CONFIG_IA64) || defined(CONFIG_X86_64) 354 printk(KERN_ERR "please check additional_cpus= boot " 355 "parameter\n"); 356 #endif 357 return -EINVAL; 358 } 359 360 cpu_maps_update_begin(); 361 362 if (cpu_hotplug_disabled) { 363 err = -EBUSY; 364 goto out; 365 } 366 367 err = _cpu_up(cpu, 0); 368 369 out: 370 cpu_maps_update_done(); 371 return err; 372 } 373 374 #ifdef CONFIG_PM_SLEEP_SMP 375 static cpumask_var_t frozen_cpus; 376 377 int disable_nonboot_cpus(void) 378 { 379 int cpu, first_cpu, error; 380 381 error = stop_machine_create(); 382 if (error) 383 return error; 384 cpu_maps_update_begin(); 385 first_cpu = cpumask_first(cpu_online_mask); 386 /* We take down all of the non-boot CPUs in one shot to avoid races 387 * with the userspace trying to use the CPU hotplug at the same time 388 */ 389 cpumask_clear(frozen_cpus); 390 printk("Disabling non-boot CPUs ...\n"); 391 for_each_online_cpu(cpu) { 392 if (cpu == first_cpu) 393 continue; 394 error = _cpu_down(cpu, 1); 395 if (!error) { 396 cpumask_set_cpu(cpu, frozen_cpus); 397 printk("CPU%d is down\n", cpu); 398 } else { 399 printk(KERN_ERR "Error taking CPU%d down: %d\n", 400 cpu, error); 401 break; 402 } 403 } 404 if (!error) { 405 BUG_ON(num_online_cpus() > 1); 406 /* Make sure the CPUs won't be enabled by someone else */ 407 cpu_hotplug_disabled = 1; 408 } else { 409 printk(KERN_ERR "Non-boot CPUs are not disabled\n"); 410 } 411 cpu_maps_update_done(); 412 stop_machine_destroy(); 413 return error; 414 } 415 416 void __ref enable_nonboot_cpus(void) 417 { 418 int cpu, error; 419 420 /* Allow everyone to use the CPU hotplug again */ 421 cpu_maps_update_begin(); 422 cpu_hotplug_disabled = 0; 423 if (cpumask_empty(frozen_cpus)) 424 goto out; 425 426 printk("Enabling non-boot CPUs ...\n"); 427 for_each_cpu(cpu, frozen_cpus) { 428 error = _cpu_up(cpu, 1); 429 if (!error) { 430 printk("CPU%d is up\n", cpu); 431 continue; 432 } 433 printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error); 434 } 435 cpumask_clear(frozen_cpus); 436 out: 437 cpu_maps_update_done(); 438 } 439 440 static int alloc_frozen_cpus(void) 441 { 442 if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO)) 443 return -ENOMEM; 444 return 0; 445 } 446 core_initcall(alloc_frozen_cpus); 447 #endif /* CONFIG_PM_SLEEP_SMP */ 448 449 /** 450 * notify_cpu_starting(cpu) - call the CPU_STARTING notifiers 451 * @cpu: cpu that just started 452 * 453 * This function calls the cpu_chain notifiers with CPU_STARTING. 454 * It must be called by the arch code on the new cpu, before the new cpu 455 * enables interrupts and before the "boot" cpu returns from __cpu_up(). 456 */ 457 void __cpuinit notify_cpu_starting(unsigned int cpu) 458 { 459 unsigned long val = CPU_STARTING; 460 461 #ifdef CONFIG_PM_SLEEP_SMP 462 if (frozen_cpus != NULL && cpumask_test_cpu(cpu, frozen_cpus)) 463 val = CPU_STARTING_FROZEN; 464 #endif /* CONFIG_PM_SLEEP_SMP */ 465 raw_notifier_call_chain(&cpu_chain, val, (void *)(long)cpu); 466 } 467 468 #endif /* CONFIG_SMP */ 469 470 /* 471 * cpu_bit_bitmap[] is a special, "compressed" data structure that 472 * represents all NR_CPUS bits binary values of 1<<nr. 473 * 474 * It is used by cpumask_of() to get a constant address to a CPU 475 * mask value that has a single bit set only. 476 */ 477 478 /* cpu_bit_bitmap[0] is empty - so we can back into it */ 479 #define MASK_DECLARE_1(x) [x+1][0] = 1UL << (x) 480 #define MASK_DECLARE_2(x) MASK_DECLARE_1(x), MASK_DECLARE_1(x+1) 481 #define MASK_DECLARE_4(x) MASK_DECLARE_2(x), MASK_DECLARE_2(x+2) 482 #define MASK_DECLARE_8(x) MASK_DECLARE_4(x), MASK_DECLARE_4(x+4) 483 484 const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = { 485 486 MASK_DECLARE_8(0), MASK_DECLARE_8(8), 487 MASK_DECLARE_8(16), MASK_DECLARE_8(24), 488 #if BITS_PER_LONG > 32 489 MASK_DECLARE_8(32), MASK_DECLARE_8(40), 490 MASK_DECLARE_8(48), MASK_DECLARE_8(56), 491 #endif 492 }; 493 EXPORT_SYMBOL_GPL(cpu_bit_bitmap); 494 495 const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL; 496 EXPORT_SYMBOL(cpu_all_bits); 497 498 #ifdef CONFIG_INIT_ALL_POSSIBLE 499 static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly 500 = CPU_BITS_ALL; 501 #else 502 static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly; 503 #endif 504 const struct cpumask *const cpu_possible_mask = to_cpumask(cpu_possible_bits); 505 EXPORT_SYMBOL(cpu_possible_mask); 506 507 static DECLARE_BITMAP(cpu_online_bits, CONFIG_NR_CPUS) __read_mostly; 508 const struct cpumask *const cpu_online_mask = to_cpumask(cpu_online_bits); 509 EXPORT_SYMBOL(cpu_online_mask); 510 511 static DECLARE_BITMAP(cpu_present_bits, CONFIG_NR_CPUS) __read_mostly; 512 const struct cpumask *const cpu_present_mask = to_cpumask(cpu_present_bits); 513 EXPORT_SYMBOL(cpu_present_mask); 514 515 static DECLARE_BITMAP(cpu_active_bits, CONFIG_NR_CPUS) __read_mostly; 516 const struct cpumask *const cpu_active_mask = to_cpumask(cpu_active_bits); 517 EXPORT_SYMBOL(cpu_active_mask); 518 519 void set_cpu_possible(unsigned int cpu, bool possible) 520 { 521 if (possible) 522 cpumask_set_cpu(cpu, to_cpumask(cpu_possible_bits)); 523 else 524 cpumask_clear_cpu(cpu, to_cpumask(cpu_possible_bits)); 525 } 526 527 void set_cpu_present(unsigned int cpu, bool present) 528 { 529 if (present) 530 cpumask_set_cpu(cpu, to_cpumask(cpu_present_bits)); 531 else 532 cpumask_clear_cpu(cpu, to_cpumask(cpu_present_bits)); 533 } 534 535 void set_cpu_online(unsigned int cpu, bool online) 536 { 537 if (online) 538 cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits)); 539 else 540 cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits)); 541 } 542 543 void set_cpu_active(unsigned int cpu, bool active) 544 { 545 if (active) 546 cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits)); 547 else 548 cpumask_clear_cpu(cpu, to_cpumask(cpu_active_bits)); 549 } 550 551 void init_cpu_present(const struct cpumask *src) 552 { 553 cpumask_copy(to_cpumask(cpu_present_bits), src); 554 } 555 556 void init_cpu_possible(const struct cpumask *src) 557 { 558 cpumask_copy(to_cpumask(cpu_possible_bits), src); 559 } 560 561 void init_cpu_online(const struct cpumask *src) 562 { 563 cpumask_copy(to_cpumask(cpu_online_bits), src); 564 } 565