1 /* 2 * Common SMP CPU bringup/teardown functions 3 */ 4 #include <linux/cpu.h> 5 #include <linux/err.h> 6 #include <linux/smp.h> 7 #include <linux/delay.h> 8 #include <linux/init.h> 9 #include <linux/list.h> 10 #include <linux/slab.h> 11 #include <linux/sched.h> 12 #include <linux/export.h> 13 #include <linux/percpu.h> 14 #include <linux/kthread.h> 15 #include <linux/smpboot.h> 16 17 #include "smpboot.h" 18 19 #ifdef CONFIG_SMP 20 21 #ifdef CONFIG_GENERIC_SMP_IDLE_THREAD 22 /* 23 * For the hotplug case we keep the task structs around and reuse 24 * them. 25 */ 26 static DEFINE_PER_CPU(struct task_struct *, idle_threads); 27 28 struct task_struct *idle_thread_get(unsigned int cpu) 29 { 30 struct task_struct *tsk = per_cpu(idle_threads, cpu); 31 32 if (!tsk) 33 return ERR_PTR(-ENOMEM); 34 init_idle(tsk, cpu); 35 return tsk; 36 } 37 38 void __init idle_thread_set_boot_cpu(void) 39 { 40 per_cpu(idle_threads, smp_processor_id()) = current; 41 } 42 43 /** 44 * idle_init - Initialize the idle thread for a cpu 45 * @cpu: The cpu for which the idle thread should be initialized 46 * 47 * Creates the thread if it does not exist. 48 */ 49 static inline void idle_init(unsigned int cpu) 50 { 51 struct task_struct *tsk = per_cpu(idle_threads, cpu); 52 53 if (!tsk) { 54 tsk = fork_idle(cpu); 55 if (IS_ERR(tsk)) 56 pr_err("SMP: fork_idle() failed for CPU %u\n", cpu); 57 else 58 per_cpu(idle_threads, cpu) = tsk; 59 } 60 } 61 62 /** 63 * idle_threads_init - Initialize idle threads for all cpus 64 */ 65 void __init idle_threads_init(void) 66 { 67 unsigned int cpu, boot_cpu; 68 69 boot_cpu = smp_processor_id(); 70 71 for_each_possible_cpu(cpu) { 72 if (cpu != boot_cpu) 73 idle_init(cpu); 74 } 75 } 76 #endif 77 78 #endif /* #ifdef CONFIG_SMP */ 79 80 static LIST_HEAD(hotplug_threads); 81 static DEFINE_MUTEX(smpboot_threads_lock); 82 83 struct smpboot_thread_data { 84 unsigned int cpu; 85 unsigned int status; 86 struct smp_hotplug_thread *ht; 87 }; 88 89 enum { 90 HP_THREAD_NONE = 0, 91 HP_THREAD_ACTIVE, 92 HP_THREAD_PARKED, 93 }; 94 95 /** 96 * smpboot_thread_fn - percpu hotplug thread loop function 97 * @data: thread data pointer 98 * 99 * Checks for thread stop and park conditions. Calls the necessary 100 * setup, cleanup, park and unpark functions for the registered 101 * thread. 102 * 103 * Returns 1 when the thread should exit, 0 otherwise. 104 */ 105 static int smpboot_thread_fn(void *data) 106 { 107 struct smpboot_thread_data *td = data; 108 struct smp_hotplug_thread *ht = td->ht; 109 110 while (1) { 111 set_current_state(TASK_INTERRUPTIBLE); 112 preempt_disable(); 113 if (kthread_should_stop()) { 114 __set_current_state(TASK_RUNNING); 115 preempt_enable(); 116 /* cleanup must mirror setup */ 117 if (ht->cleanup && td->status != HP_THREAD_NONE) 118 ht->cleanup(td->cpu, cpu_online(td->cpu)); 119 kfree(td); 120 return 0; 121 } 122 123 if (kthread_should_park()) { 124 __set_current_state(TASK_RUNNING); 125 preempt_enable(); 126 if (ht->park && td->status == HP_THREAD_ACTIVE) { 127 BUG_ON(td->cpu != smp_processor_id()); 128 ht->park(td->cpu); 129 td->status = HP_THREAD_PARKED; 130 } 131 kthread_parkme(); 132 /* We might have been woken for stop */ 133 continue; 134 } 135 136 BUG_ON(td->cpu != smp_processor_id()); 137 138 /* Check for state change setup */ 139 switch (td->status) { 140 case HP_THREAD_NONE: 141 __set_current_state(TASK_RUNNING); 142 preempt_enable(); 143 if (ht->setup) 144 ht->setup(td->cpu); 145 td->status = HP_THREAD_ACTIVE; 146 continue; 147 148 case HP_THREAD_PARKED: 149 __set_current_state(TASK_RUNNING); 150 preempt_enable(); 151 if (ht->unpark) 152 ht->unpark(td->cpu); 153 td->status = HP_THREAD_ACTIVE; 154 continue; 155 } 156 157 if (!ht->thread_should_run(td->cpu)) { 158 preempt_enable_no_resched(); 159 schedule(); 160 } else { 161 __set_current_state(TASK_RUNNING); 162 preempt_enable(); 163 ht->thread_fn(td->cpu); 164 } 165 } 166 } 167 168 static int 169 __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu) 170 { 171 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); 172 struct smpboot_thread_data *td; 173 174 if (tsk) 175 return 0; 176 177 td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu)); 178 if (!td) 179 return -ENOMEM; 180 td->cpu = cpu; 181 td->ht = ht; 182 183 tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu, 184 ht->thread_comm); 185 if (IS_ERR(tsk)) { 186 kfree(td); 187 return PTR_ERR(tsk); 188 } 189 /* 190 * Park the thread so that it could start right on the CPU 191 * when it is available. 192 */ 193 kthread_park(tsk); 194 get_task_struct(tsk); 195 *per_cpu_ptr(ht->store, cpu) = tsk; 196 if (ht->create) { 197 /* 198 * Make sure that the task has actually scheduled out 199 * into park position, before calling the create 200 * callback. At least the migration thread callback 201 * requires that the task is off the runqueue. 202 */ 203 if (!wait_task_inactive(tsk, TASK_PARKED)) 204 WARN_ON(1); 205 else 206 ht->create(cpu); 207 } 208 return 0; 209 } 210 211 int smpboot_create_threads(unsigned int cpu) 212 { 213 struct smp_hotplug_thread *cur; 214 int ret = 0; 215 216 mutex_lock(&smpboot_threads_lock); 217 list_for_each_entry(cur, &hotplug_threads, list) { 218 ret = __smpboot_create_thread(cur, cpu); 219 if (ret) 220 break; 221 } 222 mutex_unlock(&smpboot_threads_lock); 223 return ret; 224 } 225 226 static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu) 227 { 228 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); 229 230 if (!ht->selfparking) 231 kthread_unpark(tsk); 232 } 233 234 int smpboot_unpark_threads(unsigned int cpu) 235 { 236 struct smp_hotplug_thread *cur; 237 238 mutex_lock(&smpboot_threads_lock); 239 list_for_each_entry(cur, &hotplug_threads, list) 240 if (cpumask_test_cpu(cpu, cur->cpumask)) 241 smpboot_unpark_thread(cur, cpu); 242 mutex_unlock(&smpboot_threads_lock); 243 return 0; 244 } 245 246 static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu) 247 { 248 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); 249 250 if (tsk && !ht->selfparking) 251 kthread_park(tsk); 252 } 253 254 int smpboot_park_threads(unsigned int cpu) 255 { 256 struct smp_hotplug_thread *cur; 257 258 mutex_lock(&smpboot_threads_lock); 259 list_for_each_entry_reverse(cur, &hotplug_threads, list) 260 smpboot_park_thread(cur, cpu); 261 mutex_unlock(&smpboot_threads_lock); 262 return 0; 263 } 264 265 static void smpboot_destroy_threads(struct smp_hotplug_thread *ht) 266 { 267 unsigned int cpu; 268 269 /* We need to destroy also the parked threads of offline cpus */ 270 for_each_possible_cpu(cpu) { 271 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); 272 273 if (tsk) { 274 kthread_stop(tsk); 275 put_task_struct(tsk); 276 *per_cpu_ptr(ht->store, cpu) = NULL; 277 } 278 } 279 } 280 281 /** 282 * smpboot_register_percpu_thread_cpumask - Register a per_cpu thread related 283 * to hotplug 284 * @plug_thread: Hotplug thread descriptor 285 * @cpumask: The cpumask where threads run 286 * 287 * Creates and starts the threads on all online cpus. 288 */ 289 int smpboot_register_percpu_thread_cpumask(struct smp_hotplug_thread *plug_thread, 290 const struct cpumask *cpumask) 291 { 292 unsigned int cpu; 293 int ret = 0; 294 295 if (!alloc_cpumask_var(&plug_thread->cpumask, GFP_KERNEL)) 296 return -ENOMEM; 297 cpumask_copy(plug_thread->cpumask, cpumask); 298 299 get_online_cpus(); 300 mutex_lock(&smpboot_threads_lock); 301 for_each_online_cpu(cpu) { 302 ret = __smpboot_create_thread(plug_thread, cpu); 303 if (ret) { 304 smpboot_destroy_threads(plug_thread); 305 free_cpumask_var(plug_thread->cpumask); 306 goto out; 307 } 308 if (cpumask_test_cpu(cpu, cpumask)) 309 smpboot_unpark_thread(plug_thread, cpu); 310 } 311 list_add(&plug_thread->list, &hotplug_threads); 312 out: 313 mutex_unlock(&smpboot_threads_lock); 314 put_online_cpus(); 315 return ret; 316 } 317 EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread_cpumask); 318 319 /** 320 * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug 321 * @plug_thread: Hotplug thread descriptor 322 * 323 * Stops all threads on all possible cpus. 324 */ 325 void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread) 326 { 327 get_online_cpus(); 328 mutex_lock(&smpboot_threads_lock); 329 list_del(&plug_thread->list); 330 smpboot_destroy_threads(plug_thread); 331 mutex_unlock(&smpboot_threads_lock); 332 put_online_cpus(); 333 free_cpumask_var(plug_thread->cpumask); 334 } 335 EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread); 336 337 /** 338 * smpboot_update_cpumask_percpu_thread - Adjust which per_cpu hotplug threads stay parked 339 * @plug_thread: Hotplug thread descriptor 340 * @new: Revised mask to use 341 * 342 * The cpumask field in the smp_hotplug_thread must not be updated directly 343 * by the client, but only by calling this function. 344 * This function can only be called on a registered smp_hotplug_thread. 345 */ 346 int smpboot_update_cpumask_percpu_thread(struct smp_hotplug_thread *plug_thread, 347 const struct cpumask *new) 348 { 349 struct cpumask *old = plug_thread->cpumask; 350 cpumask_var_t tmp; 351 unsigned int cpu; 352 353 if (!alloc_cpumask_var(&tmp, GFP_KERNEL)) 354 return -ENOMEM; 355 356 get_online_cpus(); 357 mutex_lock(&smpboot_threads_lock); 358 359 /* Park threads that were exclusively enabled on the old mask. */ 360 cpumask_andnot(tmp, old, new); 361 for_each_cpu_and(cpu, tmp, cpu_online_mask) 362 smpboot_park_thread(plug_thread, cpu); 363 364 /* Unpark threads that are exclusively enabled on the new mask. */ 365 cpumask_andnot(tmp, new, old); 366 for_each_cpu_and(cpu, tmp, cpu_online_mask) 367 smpboot_unpark_thread(plug_thread, cpu); 368 369 cpumask_copy(old, new); 370 371 mutex_unlock(&smpboot_threads_lock); 372 put_online_cpus(); 373 374 free_cpumask_var(tmp); 375 376 return 0; 377 } 378 EXPORT_SYMBOL_GPL(smpboot_update_cpumask_percpu_thread); 379 380 static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD); 381 382 /* 383 * Called to poll specified CPU's state, for example, when waiting for 384 * a CPU to come online. 385 */ 386 int cpu_report_state(int cpu) 387 { 388 return atomic_read(&per_cpu(cpu_hotplug_state, cpu)); 389 } 390 391 /* 392 * If CPU has died properly, set its state to CPU_UP_PREPARE and 393 * return success. Otherwise, return -EBUSY if the CPU died after 394 * cpu_wait_death() timed out. And yet otherwise again, return -EAGAIN 395 * if cpu_wait_death() timed out and the CPU still hasn't gotten around 396 * to dying. In the latter two cases, the CPU might not be set up 397 * properly, but it is up to the arch-specific code to decide. 398 * Finally, -EIO indicates an unanticipated problem. 399 * 400 * Note that it is permissible to omit this call entirely, as is 401 * done in architectures that do no CPU-hotplug error checking. 402 */ 403 int cpu_check_up_prepare(int cpu) 404 { 405 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) { 406 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE); 407 return 0; 408 } 409 410 switch (atomic_read(&per_cpu(cpu_hotplug_state, cpu))) { 411 412 case CPU_POST_DEAD: 413 414 /* The CPU died properly, so just start it up again. */ 415 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE); 416 return 0; 417 418 case CPU_DEAD_FROZEN: 419 420 /* 421 * Timeout during CPU death, so let caller know. 422 * The outgoing CPU completed its processing, but after 423 * cpu_wait_death() timed out and reported the error. The 424 * caller is free to proceed, in which case the state 425 * will be reset properly by cpu_set_state_online(). 426 * Proceeding despite this -EBUSY return makes sense 427 * for systems where the outgoing CPUs take themselves 428 * offline, with no post-death manipulation required from 429 * a surviving CPU. 430 */ 431 return -EBUSY; 432 433 case CPU_BROKEN: 434 435 /* 436 * The most likely reason we got here is that there was 437 * a timeout during CPU death, and the outgoing CPU never 438 * did complete its processing. This could happen on 439 * a virtualized system if the outgoing VCPU gets preempted 440 * for more than five seconds, and the user attempts to 441 * immediately online that same CPU. Trying again later 442 * might return -EBUSY above, hence -EAGAIN. 443 */ 444 return -EAGAIN; 445 446 default: 447 448 /* Should not happen. Famous last words. */ 449 return -EIO; 450 } 451 } 452 453 /* 454 * Mark the specified CPU online. 455 * 456 * Note that it is permissible to omit this call entirely, as is 457 * done in architectures that do no CPU-hotplug error checking. 458 */ 459 void cpu_set_state_online(int cpu) 460 { 461 (void)atomic_xchg(&per_cpu(cpu_hotplug_state, cpu), CPU_ONLINE); 462 } 463 464 #ifdef CONFIG_HOTPLUG_CPU 465 466 /* 467 * Wait for the specified CPU to exit the idle loop and die. 468 */ 469 bool cpu_wait_death(unsigned int cpu, int seconds) 470 { 471 int jf_left = seconds * HZ; 472 int oldstate; 473 bool ret = true; 474 int sleep_jf = 1; 475 476 might_sleep(); 477 478 /* The outgoing CPU will normally get done quite quickly. */ 479 if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD) 480 goto update_state; 481 udelay(5); 482 483 /* But if the outgoing CPU dawdles, wait increasingly long times. */ 484 while (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) != CPU_DEAD) { 485 schedule_timeout_uninterruptible(sleep_jf); 486 jf_left -= sleep_jf; 487 if (jf_left <= 0) 488 break; 489 sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10); 490 } 491 update_state: 492 oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu)); 493 if (oldstate == CPU_DEAD) { 494 /* Outgoing CPU died normally, update state. */ 495 smp_mb(); /* atomic_read() before update. */ 496 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD); 497 } else { 498 /* Outgoing CPU still hasn't died, set state accordingly. */ 499 if (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu), 500 oldstate, CPU_BROKEN) != oldstate) 501 goto update_state; 502 ret = false; 503 } 504 return ret; 505 } 506 507 /* 508 * Called by the outgoing CPU to report its successful death. Return 509 * false if this report follows the surviving CPU's timing out. 510 * 511 * A separate "CPU_DEAD_FROZEN" is used when the surviving CPU 512 * timed out. This approach allows architectures to omit calls to 513 * cpu_check_up_prepare() and cpu_set_state_online() without defeating 514 * the next cpu_wait_death()'s polling loop. 515 */ 516 bool cpu_report_death(void) 517 { 518 int oldstate; 519 int newstate; 520 int cpu = smp_processor_id(); 521 522 do { 523 oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu)); 524 if (oldstate != CPU_BROKEN) 525 newstate = CPU_DEAD; 526 else 527 newstate = CPU_DEAD_FROZEN; 528 } while (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu), 529 oldstate, newstate) != oldstate); 530 return newstate == CPU_DEAD; 531 } 532 533 #endif /* #ifdef CONFIG_HOTPLUG_CPU */ 534