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