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 /* 192 * Park the thread so that it could start right on the CPU 193 * when it is available. 194 */ 195 kthread_park(tsk); 196 get_task_struct(tsk); 197 *per_cpu_ptr(ht->store, cpu) = tsk; 198 if (ht->create) { 199 /* 200 * Make sure that the task has actually scheduled out 201 * into park position, before calling the create 202 * callback. At least the migration thread callback 203 * requires that the task is off the runqueue. 204 */ 205 if (!wait_task_inactive(tsk, TASK_PARKED)) 206 WARN_ON(1); 207 else 208 ht->create(cpu); 209 } 210 return 0; 211 } 212 213 int smpboot_create_threads(unsigned int cpu) 214 { 215 struct smp_hotplug_thread *cur; 216 int ret = 0; 217 218 mutex_lock(&smpboot_threads_lock); 219 list_for_each_entry(cur, &hotplug_threads, list) { 220 ret = __smpboot_create_thread(cur, cpu); 221 if (ret) 222 break; 223 } 224 mutex_unlock(&smpboot_threads_lock); 225 return ret; 226 } 227 228 static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu) 229 { 230 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); 231 232 if (!ht->selfparking) 233 kthread_unpark(tsk); 234 } 235 236 int smpboot_unpark_threads(unsigned int cpu) 237 { 238 struct smp_hotplug_thread *cur; 239 240 mutex_lock(&smpboot_threads_lock); 241 list_for_each_entry(cur, &hotplug_threads, list) 242 smpboot_unpark_thread(cur, cpu); 243 mutex_unlock(&smpboot_threads_lock); 244 return 0; 245 } 246 247 static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu) 248 { 249 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); 250 251 if (tsk && !ht->selfparking) 252 kthread_park(tsk); 253 } 254 255 int smpboot_park_threads(unsigned int cpu) 256 { 257 struct smp_hotplug_thread *cur; 258 259 mutex_lock(&smpboot_threads_lock); 260 list_for_each_entry_reverse(cur, &hotplug_threads, list) 261 smpboot_park_thread(cur, cpu); 262 mutex_unlock(&smpboot_threads_lock); 263 return 0; 264 } 265 266 static void smpboot_destroy_threads(struct smp_hotplug_thread *ht) 267 { 268 unsigned int cpu; 269 270 /* We need to destroy also the parked threads of offline cpus */ 271 for_each_possible_cpu(cpu) { 272 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); 273 274 if (tsk) { 275 kthread_stop(tsk); 276 put_task_struct(tsk); 277 *per_cpu_ptr(ht->store, cpu) = NULL; 278 } 279 } 280 } 281 282 /** 283 * smpboot_register_percpu_thread - Register a per_cpu thread related 284 * to hotplug 285 * @plug_thread: Hotplug thread descriptor 286 * 287 * Creates and starts the threads on all online cpus. 288 */ 289 int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread) 290 { 291 unsigned int cpu; 292 int ret = 0; 293 294 get_online_cpus(); 295 mutex_lock(&smpboot_threads_lock); 296 for_each_online_cpu(cpu) { 297 ret = __smpboot_create_thread(plug_thread, cpu); 298 if (ret) { 299 smpboot_destroy_threads(plug_thread); 300 goto out; 301 } 302 smpboot_unpark_thread(plug_thread, cpu); 303 } 304 list_add(&plug_thread->list, &hotplug_threads); 305 out: 306 mutex_unlock(&smpboot_threads_lock); 307 put_online_cpus(); 308 return ret; 309 } 310 EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread); 311 312 /** 313 * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug 314 * @plug_thread: Hotplug thread descriptor 315 * 316 * Stops all threads on all possible cpus. 317 */ 318 void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread) 319 { 320 get_online_cpus(); 321 mutex_lock(&smpboot_threads_lock); 322 list_del(&plug_thread->list); 323 smpboot_destroy_threads(plug_thread); 324 mutex_unlock(&smpboot_threads_lock); 325 put_online_cpus(); 326 } 327 EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread); 328 329 static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD); 330 331 /* 332 * Called to poll specified CPU's state, for example, when waiting for 333 * a CPU to come online. 334 */ 335 int cpu_report_state(int cpu) 336 { 337 return atomic_read(&per_cpu(cpu_hotplug_state, cpu)); 338 } 339 340 /* 341 * If CPU has died properly, set its state to CPU_UP_PREPARE and 342 * return success. Otherwise, return -EBUSY if the CPU died after 343 * cpu_wait_death() timed out. And yet otherwise again, return -EAGAIN 344 * if cpu_wait_death() timed out and the CPU still hasn't gotten around 345 * to dying. In the latter two cases, the CPU might not be set up 346 * properly, but it is up to the arch-specific code to decide. 347 * Finally, -EIO indicates an unanticipated problem. 348 * 349 * Note that it is permissible to omit this call entirely, as is 350 * done in architectures that do no CPU-hotplug error checking. 351 */ 352 int cpu_check_up_prepare(int cpu) 353 { 354 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) { 355 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE); 356 return 0; 357 } 358 359 switch (atomic_read(&per_cpu(cpu_hotplug_state, cpu))) { 360 361 case CPU_POST_DEAD: 362 363 /* The CPU died properly, so just start it up again. */ 364 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE); 365 return 0; 366 367 case CPU_DEAD_FROZEN: 368 369 /* 370 * Timeout during CPU death, so let caller know. 371 * The outgoing CPU completed its processing, but after 372 * cpu_wait_death() timed out and reported the error. The 373 * caller is free to proceed, in which case the state 374 * will be reset properly by cpu_set_state_online(). 375 * Proceeding despite this -EBUSY return makes sense 376 * for systems where the outgoing CPUs take themselves 377 * offline, with no post-death manipulation required from 378 * a surviving CPU. 379 */ 380 return -EBUSY; 381 382 case CPU_BROKEN: 383 384 /* 385 * The most likely reason we got here is that there was 386 * a timeout during CPU death, and the outgoing CPU never 387 * did complete its processing. This could happen on 388 * a virtualized system if the outgoing VCPU gets preempted 389 * for more than five seconds, and the user attempts to 390 * immediately online that same CPU. Trying again later 391 * might return -EBUSY above, hence -EAGAIN. 392 */ 393 return -EAGAIN; 394 395 default: 396 397 /* Should not happen. Famous last words. */ 398 return -EIO; 399 } 400 } 401 402 /* 403 * Mark the specified CPU online. 404 * 405 * Note that it is permissible to omit this call entirely, as is 406 * done in architectures that do no CPU-hotplug error checking. 407 */ 408 void cpu_set_state_online(int cpu) 409 { 410 (void)atomic_xchg(&per_cpu(cpu_hotplug_state, cpu), CPU_ONLINE); 411 } 412 413 #ifdef CONFIG_HOTPLUG_CPU 414 415 /* 416 * Wait for the specified CPU to exit the idle loop and die. 417 */ 418 bool cpu_wait_death(unsigned int cpu, int seconds) 419 { 420 int jf_left = seconds * HZ; 421 int oldstate; 422 bool ret = true; 423 int sleep_jf = 1; 424 425 might_sleep(); 426 427 /* The outgoing CPU will normally get done quite quickly. */ 428 if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD) 429 goto update_state; 430 udelay(5); 431 432 /* But if the outgoing CPU dawdles, wait increasingly long times. */ 433 while (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) != CPU_DEAD) { 434 schedule_timeout_uninterruptible(sleep_jf); 435 jf_left -= sleep_jf; 436 if (jf_left <= 0) 437 break; 438 sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10); 439 } 440 update_state: 441 oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu)); 442 if (oldstate == CPU_DEAD) { 443 /* Outgoing CPU died normally, update state. */ 444 smp_mb(); /* atomic_read() before update. */ 445 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD); 446 } else { 447 /* Outgoing CPU still hasn't died, set state accordingly. */ 448 if (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu), 449 oldstate, CPU_BROKEN) != oldstate) 450 goto update_state; 451 ret = false; 452 } 453 return ret; 454 } 455 456 /* 457 * Called by the outgoing CPU to report its successful death. Return 458 * false if this report follows the surviving CPU's timing out. 459 * 460 * A separate "CPU_DEAD_FROZEN" is used when the surviving CPU 461 * timed out. This approach allows architectures to omit calls to 462 * cpu_check_up_prepare() and cpu_set_state_online() without defeating 463 * the next cpu_wait_death()'s polling loop. 464 */ 465 bool cpu_report_death(void) 466 { 467 int oldstate; 468 int newstate; 469 int cpu = smp_processor_id(); 470 471 do { 472 oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu)); 473 if (oldstate != CPU_BROKEN) 474 newstate = CPU_DEAD; 475 else 476 newstate = CPU_DEAD_FROZEN; 477 } while (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu), 478 oldstate, newstate) != oldstate); 479 return newstate == CPU_DEAD; 480 } 481 482 #endif /* #ifdef CONFIG_HOTPLUG_CPU */ 483