1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Common SMP CPU bringup/teardown functions 4 */ 5 #include <linux/cpu.h> 6 #include <linux/err.h> 7 #include <linux/smp.h> 8 #include <linux/delay.h> 9 #include <linux/init.h> 10 #include <linux/list.h> 11 #include <linux/slab.h> 12 #include <linux/sched.h> 13 #include <linux/sched/task.h> 14 #include <linux/export.h> 15 #include <linux/percpu.h> 16 #include <linux/kthread.h> 17 #include <linux/smpboot.h> 18 19 #include "smpboot.h" 20 21 #ifdef CONFIG_SMP 22 23 #ifdef CONFIG_GENERIC_SMP_IDLE_THREAD 24 /* 25 * For the hotplug case we keep the task structs around and reuse 26 * them. 27 */ 28 static DEFINE_PER_CPU(struct task_struct *, idle_threads); 29 30 struct task_struct *idle_thread_get(unsigned int cpu) 31 { 32 struct task_struct *tsk = per_cpu(idle_threads, cpu); 33 34 if (!tsk) 35 return ERR_PTR(-ENOMEM); 36 init_idle(tsk, cpu); 37 return tsk; 38 } 39 40 void __init idle_thread_set_boot_cpu(void) 41 { 42 per_cpu(idle_threads, smp_processor_id()) = current; 43 } 44 45 /** 46 * idle_init - Initialize the idle thread for a cpu 47 * @cpu: The cpu for which the idle thread should be initialized 48 * 49 * Creates the thread if it does not exist. 50 */ 51 static inline void idle_init(unsigned int cpu) 52 { 53 struct task_struct *tsk = per_cpu(idle_threads, cpu); 54 55 if (!tsk) { 56 tsk = fork_idle(cpu); 57 if (IS_ERR(tsk)) 58 pr_err("SMP: fork_idle() failed for CPU %u\n", cpu); 59 else 60 per_cpu(idle_threads, cpu) = tsk; 61 } 62 } 63 64 /** 65 * idle_threads_init - Initialize idle threads for all cpus 66 */ 67 void __init idle_threads_init(void) 68 { 69 unsigned int cpu, boot_cpu; 70 71 boot_cpu = smp_processor_id(); 72 73 for_each_possible_cpu(cpu) { 74 if (cpu != boot_cpu) 75 idle_init(cpu); 76 } 77 } 78 #endif 79 80 #endif /* #ifdef CONFIG_SMP */ 81 82 static LIST_HEAD(hotplug_threads); 83 static DEFINE_MUTEX(smpboot_threads_lock); 84 85 struct smpboot_thread_data { 86 unsigned int cpu; 87 unsigned int status; 88 struct smp_hotplug_thread *ht; 89 }; 90 91 enum { 92 HP_THREAD_NONE = 0, 93 HP_THREAD_ACTIVE, 94 HP_THREAD_PARKED, 95 }; 96 97 /** 98 * smpboot_thread_fn - percpu hotplug thread loop function 99 * @data: thread data pointer 100 * 101 * Checks for thread stop and park conditions. Calls the necessary 102 * setup, cleanup, park and unpark functions for the registered 103 * thread. 104 * 105 * Returns 1 when the thread should exit, 0 otherwise. 106 */ 107 static int smpboot_thread_fn(void *data) 108 { 109 struct smpboot_thread_data *td = data; 110 struct smp_hotplug_thread *ht = td->ht; 111 112 while (1) { 113 set_current_state(TASK_INTERRUPTIBLE); 114 preempt_disable(); 115 if (kthread_should_stop()) { 116 __set_current_state(TASK_RUNNING); 117 preempt_enable(); 118 /* cleanup must mirror setup */ 119 if (ht->cleanup && td->status != HP_THREAD_NONE) 120 ht->cleanup(td->cpu, cpu_online(td->cpu)); 121 kfree(td); 122 return 0; 123 } 124 125 if (kthread_should_park()) { 126 __set_current_state(TASK_RUNNING); 127 preempt_enable(); 128 if (ht->park && td->status == HP_THREAD_ACTIVE) { 129 BUG_ON(td->cpu != smp_processor_id()); 130 ht->park(td->cpu); 131 td->status = HP_THREAD_PARKED; 132 } 133 kthread_parkme(); 134 /* We might have been woken for stop */ 135 continue; 136 } 137 138 BUG_ON(td->cpu != smp_processor_id()); 139 140 /* Check for state change setup */ 141 switch (td->status) { 142 case HP_THREAD_NONE: 143 __set_current_state(TASK_RUNNING); 144 preempt_enable(); 145 if (ht->setup) 146 ht->setup(td->cpu); 147 td->status = HP_THREAD_ACTIVE; 148 continue; 149 150 case HP_THREAD_PARKED: 151 __set_current_state(TASK_RUNNING); 152 preempt_enable(); 153 if (ht->unpark) 154 ht->unpark(td->cpu); 155 td->status = HP_THREAD_ACTIVE; 156 continue; 157 } 158 159 if (!ht->thread_should_run(td->cpu)) { 160 preempt_enable_no_resched(); 161 schedule(); 162 } else { 163 __set_current_state(TASK_RUNNING); 164 preempt_enable(); 165 ht->thread_fn(td->cpu); 166 } 167 } 168 } 169 170 static int 171 __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu) 172 { 173 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); 174 struct smpboot_thread_data *td; 175 176 if (tsk) 177 return 0; 178 179 td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu)); 180 if (!td) 181 return -ENOMEM; 182 td->cpu = cpu; 183 td->ht = ht; 184 185 tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu, 186 ht->thread_comm); 187 if (IS_ERR(tsk)) { 188 kfree(td); 189 return PTR_ERR(tsk); 190 } 191 kthread_set_per_cpu(tsk, cpu); 192 /* 193 * Park the thread so that it could start right on the CPU 194 * when it is available. 195 */ 196 kthread_park(tsk); 197 get_task_struct(tsk); 198 *per_cpu_ptr(ht->store, cpu) = tsk; 199 if (ht->create) { 200 /* 201 * Make sure that the task has actually scheduled out 202 * into park position, before calling the create 203 * callback. At least the migration thread callback 204 * requires that the task is off the runqueue. 205 */ 206 if (!wait_task_inactive(tsk, TASK_PARKED)) 207 WARN_ON(1); 208 else 209 ht->create(cpu); 210 } 211 return 0; 212 } 213 214 int smpboot_create_threads(unsigned int cpu) 215 { 216 struct smp_hotplug_thread *cur; 217 int ret = 0; 218 219 mutex_lock(&smpboot_threads_lock); 220 list_for_each_entry(cur, &hotplug_threads, list) { 221 ret = __smpboot_create_thread(cur, cpu); 222 if (ret) 223 break; 224 } 225 mutex_unlock(&smpboot_threads_lock); 226 return ret; 227 } 228 229 static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu) 230 { 231 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); 232 233 if (!ht->selfparking) 234 kthread_unpark(tsk); 235 } 236 237 int smpboot_unpark_threads(unsigned int cpu) 238 { 239 struct smp_hotplug_thread *cur; 240 241 mutex_lock(&smpboot_threads_lock); 242 list_for_each_entry(cur, &hotplug_threads, list) 243 smpboot_unpark_thread(cur, cpu); 244 mutex_unlock(&smpboot_threads_lock); 245 return 0; 246 } 247 248 static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu) 249 { 250 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); 251 252 if (tsk && !ht->selfparking) 253 kthread_park(tsk); 254 } 255 256 int smpboot_park_threads(unsigned int cpu) 257 { 258 struct smp_hotplug_thread *cur; 259 260 mutex_lock(&smpboot_threads_lock); 261 list_for_each_entry_reverse(cur, &hotplug_threads, list) 262 smpboot_park_thread(cur, cpu); 263 mutex_unlock(&smpboot_threads_lock); 264 return 0; 265 } 266 267 static void smpboot_destroy_threads(struct smp_hotplug_thread *ht) 268 { 269 unsigned int cpu; 270 271 /* We need to destroy also the parked threads of offline cpus */ 272 for_each_possible_cpu(cpu) { 273 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); 274 275 if (tsk) { 276 kthread_stop(tsk); 277 put_task_struct(tsk); 278 *per_cpu_ptr(ht->store, cpu) = NULL; 279 } 280 } 281 } 282 283 /** 284 * smpboot_register_percpu_thread - Register a per_cpu thread related 285 * to hotplug 286 * @plug_thread: Hotplug thread descriptor 287 * 288 * Creates and starts the threads on all online cpus. 289 */ 290 int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread) 291 { 292 unsigned int cpu; 293 int ret = 0; 294 295 get_online_cpus(); 296 mutex_lock(&smpboot_threads_lock); 297 for_each_online_cpu(cpu) { 298 ret = __smpboot_create_thread(plug_thread, cpu); 299 if (ret) { 300 smpboot_destroy_threads(plug_thread); 301 goto out; 302 } 303 smpboot_unpark_thread(plug_thread, cpu); 304 } 305 list_add(&plug_thread->list, &hotplug_threads); 306 out: 307 mutex_unlock(&smpboot_threads_lock); 308 put_online_cpus(); 309 return ret; 310 } 311 EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread); 312 313 /** 314 * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug 315 * @plug_thread: Hotplug thread descriptor 316 * 317 * Stops all threads on all possible cpus. 318 */ 319 void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread) 320 { 321 get_online_cpus(); 322 mutex_lock(&smpboot_threads_lock); 323 list_del(&plug_thread->list); 324 smpboot_destroy_threads(plug_thread); 325 mutex_unlock(&smpboot_threads_lock); 326 put_online_cpus(); 327 } 328 EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread); 329 330 static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD); 331 332 /* 333 * Called to poll specified CPU's state, for example, when waiting for 334 * a CPU to come online. 335 */ 336 int cpu_report_state(int cpu) 337 { 338 return atomic_read(&per_cpu(cpu_hotplug_state, cpu)); 339 } 340 341 /* 342 * If CPU has died properly, set its state to CPU_UP_PREPARE and 343 * return success. Otherwise, return -EBUSY if the CPU died after 344 * cpu_wait_death() timed out. And yet otherwise again, return -EAGAIN 345 * if cpu_wait_death() timed out and the CPU still hasn't gotten around 346 * to dying. In the latter two cases, the CPU might not be set up 347 * properly, but it is up to the arch-specific code to decide. 348 * Finally, -EIO indicates an unanticipated problem. 349 * 350 * Note that it is permissible to omit this call entirely, as is 351 * done in architectures that do no CPU-hotplug error checking. 352 */ 353 int cpu_check_up_prepare(int cpu) 354 { 355 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) { 356 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE); 357 return 0; 358 } 359 360 switch (atomic_read(&per_cpu(cpu_hotplug_state, cpu))) { 361 362 case CPU_POST_DEAD: 363 364 /* The CPU died properly, so just start it up again. */ 365 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE); 366 return 0; 367 368 case CPU_DEAD_FROZEN: 369 370 /* 371 * Timeout during CPU death, so let caller know. 372 * The outgoing CPU completed its processing, but after 373 * cpu_wait_death() timed out and reported the error. The 374 * caller is free to proceed, in which case the state 375 * will be reset properly by cpu_set_state_online(). 376 * Proceeding despite this -EBUSY return makes sense 377 * for systems where the outgoing CPUs take themselves 378 * offline, with no post-death manipulation required from 379 * a surviving CPU. 380 */ 381 return -EBUSY; 382 383 case CPU_BROKEN: 384 385 /* 386 * The most likely reason we got here is that there was 387 * a timeout during CPU death, and the outgoing CPU never 388 * did complete its processing. This could happen on 389 * a virtualized system if the outgoing VCPU gets preempted 390 * for more than five seconds, and the user attempts to 391 * immediately online that same CPU. Trying again later 392 * might return -EBUSY above, hence -EAGAIN. 393 */ 394 return -EAGAIN; 395 396 default: 397 398 /* Should not happen. Famous last words. */ 399 return -EIO; 400 } 401 } 402 403 /* 404 * Mark the specified CPU online. 405 * 406 * Note that it is permissible to omit this call entirely, as is 407 * done in architectures that do no CPU-hotplug error checking. 408 */ 409 void cpu_set_state_online(int cpu) 410 { 411 (void)atomic_xchg(&per_cpu(cpu_hotplug_state, cpu), CPU_ONLINE); 412 } 413 414 #ifdef CONFIG_HOTPLUG_CPU 415 416 /* 417 * Wait for the specified CPU to exit the idle loop and die. 418 */ 419 bool cpu_wait_death(unsigned int cpu, int seconds) 420 { 421 int jf_left = seconds * HZ; 422 int oldstate; 423 bool ret = true; 424 int sleep_jf = 1; 425 426 might_sleep(); 427 428 /* The outgoing CPU will normally get done quite quickly. */ 429 if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD) 430 goto update_state; 431 udelay(5); 432 433 /* But if the outgoing CPU dawdles, wait increasingly long times. */ 434 while (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) != CPU_DEAD) { 435 schedule_timeout_uninterruptible(sleep_jf); 436 jf_left -= sleep_jf; 437 if (jf_left <= 0) 438 break; 439 sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10); 440 } 441 update_state: 442 oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu)); 443 if (oldstate == CPU_DEAD) { 444 /* Outgoing CPU died normally, update state. */ 445 smp_mb(); /* atomic_read() before update. */ 446 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD); 447 } else { 448 /* Outgoing CPU still hasn't died, set state accordingly. */ 449 if (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu), 450 oldstate, CPU_BROKEN) != oldstate) 451 goto update_state; 452 ret = false; 453 } 454 return ret; 455 } 456 457 /* 458 * Called by the outgoing CPU to report its successful death. Return 459 * false if this report follows the surviving CPU's timing out. 460 * 461 * A separate "CPU_DEAD_FROZEN" is used when the surviving CPU 462 * timed out. This approach allows architectures to omit calls to 463 * cpu_check_up_prepare() and cpu_set_state_online() without defeating 464 * the next cpu_wait_death()'s polling loop. 465 */ 466 bool cpu_report_death(void) 467 { 468 int oldstate; 469 int newstate; 470 int cpu = smp_processor_id(); 471 472 do { 473 oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu)); 474 if (oldstate != CPU_BROKEN) 475 newstate = CPU_DEAD; 476 else 477 newstate = CPU_DEAD_FROZEN; 478 } while (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu), 479 oldstate, newstate) != oldstate); 480 return newstate == CPU_DEAD; 481 } 482 483 #endif /* #ifdef CONFIG_HOTPLUG_CPU */ 484