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 } cpu_hotplug; 37 38 void __init cpu_hotplug_init(void) 39 { 40 cpu_hotplug.active_writer = NULL; 41 mutex_init(&cpu_hotplug.lock); 42 cpu_hotplug.refcount = 0; 43 } 44 45 #ifdef CONFIG_HOTPLUG_CPU 46 47 void get_online_cpus(void) 48 { 49 might_sleep(); 50 if (cpu_hotplug.active_writer == current) 51 return; 52 mutex_lock(&cpu_hotplug.lock); 53 cpu_hotplug.refcount++; 54 mutex_unlock(&cpu_hotplug.lock); 55 56 } 57 EXPORT_SYMBOL_GPL(get_online_cpus); 58 59 void put_online_cpus(void) 60 { 61 if (cpu_hotplug.active_writer == current) 62 return; 63 mutex_lock(&cpu_hotplug.lock); 64 if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer)) 65 wake_up_process(cpu_hotplug.active_writer); 66 mutex_unlock(&cpu_hotplug.lock); 67 68 } 69 EXPORT_SYMBOL_GPL(put_online_cpus); 70 71 #endif /* CONFIG_HOTPLUG_CPU */ 72 73 /* 74 * The following two API's must be used when attempting 75 * to serialize the updates to cpu_online_map, cpu_present_map. 76 */ 77 void cpu_maps_update_begin(void) 78 { 79 mutex_lock(&cpu_add_remove_lock); 80 } 81 82 void cpu_maps_update_done(void) 83 { 84 mutex_unlock(&cpu_add_remove_lock); 85 } 86 87 /* 88 * This ensures that the hotplug operation can begin only when the 89 * refcount goes to zero. 90 * 91 * Note that during a cpu-hotplug operation, the new readers, if any, 92 * will be blocked by the cpu_hotplug.lock 93 * 94 * Since cpu_hotplug_begin() is always called after invoking 95 * cpu_maps_update_begin(), we can be sure that only one writer is active. 96 * 97 * Note that theoretically, there is a possibility of a livelock: 98 * - Refcount goes to zero, last reader wakes up the sleeping 99 * writer. 100 * - Last reader unlocks the cpu_hotplug.lock. 101 * - A new reader arrives at this moment, bumps up the refcount. 102 * - The writer acquires the cpu_hotplug.lock finds the refcount 103 * non zero and goes to sleep again. 104 * 105 * However, this is very difficult to achieve in practice since 106 * get_online_cpus() not an api which is called all that often. 107 * 108 */ 109 static void cpu_hotplug_begin(void) 110 { 111 cpu_hotplug.active_writer = current; 112 113 for (;;) { 114 mutex_lock(&cpu_hotplug.lock); 115 if (likely(!cpu_hotplug.refcount)) 116 break; 117 __set_current_state(TASK_UNINTERRUPTIBLE); 118 mutex_unlock(&cpu_hotplug.lock); 119 schedule(); 120 } 121 } 122 123 static void cpu_hotplug_done(void) 124 { 125 cpu_hotplug.active_writer = NULL; 126 mutex_unlock(&cpu_hotplug.lock); 127 } 128 /* Need to know about CPUs going up/down? */ 129 int __ref register_cpu_notifier(struct notifier_block *nb) 130 { 131 int ret; 132 cpu_maps_update_begin(); 133 ret = raw_notifier_chain_register(&cpu_chain, nb); 134 cpu_maps_update_done(); 135 return ret; 136 } 137 138 #ifdef CONFIG_HOTPLUG_CPU 139 140 EXPORT_SYMBOL(register_cpu_notifier); 141 142 void __ref unregister_cpu_notifier(struct notifier_block *nb) 143 { 144 cpu_maps_update_begin(); 145 raw_notifier_chain_unregister(&cpu_chain, nb); 146 cpu_maps_update_done(); 147 } 148 EXPORT_SYMBOL(unregister_cpu_notifier); 149 150 static inline void check_for_tasks(int cpu) 151 { 152 struct task_struct *p; 153 154 write_lock_irq(&tasklist_lock); 155 for_each_process(p) { 156 if (task_cpu(p) == cpu && 157 (!cputime_eq(p->utime, cputime_zero) || 158 !cputime_eq(p->stime, cputime_zero))) 159 printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\ 160 (state = %ld, flags = %x) \n", 161 p->comm, task_pid_nr(p), cpu, 162 p->state, p->flags); 163 } 164 write_unlock_irq(&tasklist_lock); 165 } 166 167 struct take_cpu_down_param { 168 unsigned long mod; 169 void *hcpu; 170 }; 171 172 /* Take this CPU down. */ 173 static int __ref take_cpu_down(void *_param) 174 { 175 struct take_cpu_down_param *param = _param; 176 int err; 177 178 raw_notifier_call_chain(&cpu_chain, CPU_DYING | param->mod, 179 param->hcpu); 180 /* Ensure this CPU doesn't handle any more interrupts. */ 181 err = __cpu_disable(); 182 if (err < 0) 183 return err; 184 185 /* Force idle task to run as soon as we yield: it should 186 immediately notice cpu is offline and die quickly. */ 187 sched_idle_next(); 188 return 0; 189 } 190 191 /* Requires cpu_add_remove_lock to be held */ 192 static int __ref _cpu_down(unsigned int cpu, int tasks_frozen) 193 { 194 int err, nr_calls = 0; 195 struct task_struct *p; 196 cpumask_t old_allowed, tmp; 197 void *hcpu = (void *)(long)cpu; 198 unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0; 199 struct take_cpu_down_param tcd_param = { 200 .mod = mod, 201 .hcpu = hcpu, 202 }; 203 204 if (num_online_cpus() == 1) 205 return -EBUSY; 206 207 if (!cpu_online(cpu)) 208 return -EINVAL; 209 210 cpu_hotplug_begin(); 211 err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod, 212 hcpu, -1, &nr_calls); 213 if (err == NOTIFY_BAD) { 214 nr_calls--; 215 __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod, 216 hcpu, nr_calls, NULL); 217 printk("%s: attempt to take down CPU %u failed\n", 218 __func__, cpu); 219 err = -EINVAL; 220 goto out_release; 221 } 222 223 /* Ensure that we are not runnable on dying cpu */ 224 old_allowed = current->cpus_allowed; 225 cpus_setall(tmp); 226 cpu_clear(cpu, tmp); 227 set_cpus_allowed_ptr(current, &tmp); 228 229 p = __stop_machine_run(take_cpu_down, &tcd_param, cpu); 230 231 if (IS_ERR(p) || cpu_online(cpu)) { 232 /* CPU didn't die: tell everyone. Can't complain. */ 233 if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod, 234 hcpu) == NOTIFY_BAD) 235 BUG(); 236 237 if (IS_ERR(p)) { 238 err = PTR_ERR(p); 239 goto out_allowed; 240 } 241 goto out_thread; 242 } 243 244 /* Wait for it to sleep (leaving idle task). */ 245 while (!idle_cpu(cpu)) 246 yield(); 247 248 /* This actually kills the CPU. */ 249 __cpu_die(cpu); 250 251 /* CPU is completely dead: tell everyone. Too late to complain. */ 252 if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD | mod, 253 hcpu) == NOTIFY_BAD) 254 BUG(); 255 256 check_for_tasks(cpu); 257 258 out_thread: 259 err = kthread_stop(p); 260 out_allowed: 261 set_cpus_allowed_ptr(current, &old_allowed); 262 out_release: 263 cpu_hotplug_done(); 264 return err; 265 } 266 267 int __ref cpu_down(unsigned int cpu) 268 { 269 int err = 0; 270 271 cpu_maps_update_begin(); 272 if (cpu_hotplug_disabled) 273 err = -EBUSY; 274 else 275 err = _cpu_down(cpu, 0); 276 277 cpu_maps_update_done(); 278 return err; 279 } 280 #endif /*CONFIG_HOTPLUG_CPU*/ 281 282 /* Requires cpu_add_remove_lock to be held */ 283 static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen) 284 { 285 int ret, nr_calls = 0; 286 void *hcpu = (void *)(long)cpu; 287 unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0; 288 289 if (cpu_online(cpu) || !cpu_present(cpu)) 290 return -EINVAL; 291 292 cpu_hotplug_begin(); 293 ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu, 294 -1, &nr_calls); 295 if (ret == NOTIFY_BAD) { 296 nr_calls--; 297 printk("%s: attempt to bring up CPU %u failed\n", 298 __func__, cpu); 299 ret = -EINVAL; 300 goto out_notify; 301 } 302 303 /* Arch-specific enabling code. */ 304 ret = __cpu_up(cpu); 305 if (ret != 0) 306 goto out_notify; 307 BUG_ON(!cpu_online(cpu)); 308 309 /* Now call notifier in preparation. */ 310 raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu); 311 312 out_notify: 313 if (ret != 0) 314 __raw_notifier_call_chain(&cpu_chain, 315 CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL); 316 cpu_hotplug_done(); 317 318 return ret; 319 } 320 321 int __cpuinit cpu_up(unsigned int cpu) 322 { 323 int err = 0; 324 if (!cpu_isset(cpu, cpu_possible_map)) { 325 printk(KERN_ERR "can't online cpu %d because it is not " 326 "configured as may-hotadd at boot time\n", cpu); 327 #if defined(CONFIG_IA64) || defined(CONFIG_X86_64) || defined(CONFIG_S390) 328 printk(KERN_ERR "please check additional_cpus= boot " 329 "parameter\n"); 330 #endif 331 return -EINVAL; 332 } 333 334 cpu_maps_update_begin(); 335 if (cpu_hotplug_disabled) 336 err = -EBUSY; 337 else 338 err = _cpu_up(cpu, 0); 339 340 cpu_maps_update_done(); 341 return err; 342 } 343 344 #ifdef CONFIG_PM_SLEEP_SMP 345 static cpumask_t frozen_cpus; 346 347 int disable_nonboot_cpus(void) 348 { 349 int cpu, first_cpu, error = 0; 350 351 cpu_maps_update_begin(); 352 first_cpu = first_cpu(cpu_online_map); 353 /* We take down all of the non-boot CPUs in one shot to avoid races 354 * with the userspace trying to use the CPU hotplug at the same time 355 */ 356 cpus_clear(frozen_cpus); 357 printk("Disabling non-boot CPUs ...\n"); 358 for_each_online_cpu(cpu) { 359 if (cpu == first_cpu) 360 continue; 361 error = _cpu_down(cpu, 1); 362 if (!error) { 363 cpu_set(cpu, frozen_cpus); 364 printk("CPU%d is down\n", cpu); 365 } else { 366 printk(KERN_ERR "Error taking CPU%d down: %d\n", 367 cpu, error); 368 break; 369 } 370 } 371 if (!error) { 372 BUG_ON(num_online_cpus() > 1); 373 /* Make sure the CPUs won't be enabled by someone else */ 374 cpu_hotplug_disabled = 1; 375 } else { 376 printk(KERN_ERR "Non-boot CPUs are not disabled\n"); 377 } 378 cpu_maps_update_done(); 379 return error; 380 } 381 382 void __ref enable_nonboot_cpus(void) 383 { 384 int cpu, error; 385 386 /* Allow everyone to use the CPU hotplug again */ 387 cpu_maps_update_begin(); 388 cpu_hotplug_disabled = 0; 389 if (cpus_empty(frozen_cpus)) 390 goto out; 391 392 printk("Enabling non-boot CPUs ...\n"); 393 for_each_cpu_mask(cpu, frozen_cpus) { 394 error = _cpu_up(cpu, 1); 395 if (!error) { 396 printk("CPU%d is up\n", cpu); 397 continue; 398 } 399 printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error); 400 } 401 cpus_clear(frozen_cpus); 402 out: 403 cpu_maps_update_done(); 404 } 405 #endif /* CONFIG_PM_SLEEP_SMP */ 406