1 // SPDX-License-Identifier: GPL-2.0-only
3 * Common SMP CPU bringup/teardown functions
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>
23 #ifdef CONFIG_GENERIC_SMP_IDLE_THREAD
25 * For the hotplug case we keep the task structs around and reuse
28 static DEFINE_PER_CPU(struct task_struct *, idle_threads);
30 struct task_struct *idle_thread_get(unsigned int cpu)
32 struct task_struct *tsk = per_cpu(idle_threads, cpu);
35 return ERR_PTR(-ENOMEM);
39 void __init idle_thread_set_boot_cpu(void)
41 per_cpu(idle_threads, smp_processor_id()) = current;
45 * idle_init - Initialize the idle thread for a cpu
46 * @cpu: The cpu for which the idle thread should be initialized
48 * Creates the thread if it does not exist.
50 static __always_inline void idle_init(unsigned int cpu)
52 struct task_struct *tsk = per_cpu(idle_threads, cpu);
57 pr_err("SMP: fork_idle() failed for CPU %u\n", cpu);
59 per_cpu(idle_threads, cpu) = tsk;
64 * idle_threads_init - Initialize idle threads for all cpus
66 void __init idle_threads_init(void)
68 unsigned int cpu, boot_cpu;
70 boot_cpu = smp_processor_id();
72 for_each_possible_cpu(cpu) {
79 #endif /* #ifdef CONFIG_SMP */
81 static LIST_HEAD(hotplug_threads);
82 static DEFINE_MUTEX(smpboot_threads_lock);
84 struct smpboot_thread_data {
87 struct smp_hotplug_thread *ht;
97 * smpboot_thread_fn - percpu hotplug thread loop function
98 * @data: thread data pointer
100 * Checks for thread stop and park conditions. Calls the necessary
101 * setup, cleanup, park and unpark functions for the registered
104 * Returns 1 when the thread should exit, 0 otherwise.
106 static int smpboot_thread_fn(void *data)
108 struct smpboot_thread_data *td = data;
109 struct smp_hotplug_thread *ht = td->ht;
112 set_current_state(TASK_INTERRUPTIBLE);
114 if (kthread_should_stop()) {
115 __set_current_state(TASK_RUNNING);
117 /* cleanup must mirror setup */
118 if (ht->cleanup && td->status != HP_THREAD_NONE)
119 ht->cleanup(td->cpu, cpu_online(td->cpu));
124 if (kthread_should_park()) {
125 __set_current_state(TASK_RUNNING);
127 if (ht->park && td->status == HP_THREAD_ACTIVE) {
128 BUG_ON(td->cpu != smp_processor_id());
130 td->status = HP_THREAD_PARKED;
133 /* We might have been woken for stop */
137 BUG_ON(td->cpu != smp_processor_id());
139 /* Check for state change setup */
140 switch (td->status) {
142 __set_current_state(TASK_RUNNING);
146 td->status = HP_THREAD_ACTIVE;
149 case HP_THREAD_PARKED:
150 __set_current_state(TASK_RUNNING);
154 td->status = HP_THREAD_ACTIVE;
158 if (!ht->thread_should_run(td->cpu)) {
159 preempt_enable_no_resched();
162 __set_current_state(TASK_RUNNING);
164 ht->thread_fn(td->cpu);
170 __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
172 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
173 struct smpboot_thread_data *td;
178 td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
184 tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu,
190 kthread_set_per_cpu(tsk, cpu);
192 * Park the thread so that it could start right on the CPU
193 * when it is available.
196 get_task_struct(tsk);
197 *per_cpu_ptr(ht->store, cpu) = tsk;
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.
205 if (!wait_task_inactive(tsk, TASK_PARKED))
213 int smpboot_create_threads(unsigned int cpu)
215 struct smp_hotplug_thread *cur;
218 mutex_lock(&smpboot_threads_lock);
219 list_for_each_entry(cur, &hotplug_threads, list) {
220 ret = __smpboot_create_thread(cur, cpu);
224 mutex_unlock(&smpboot_threads_lock);
228 static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
230 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
232 if (!ht->selfparking)
236 int smpboot_unpark_threads(unsigned int cpu)
238 struct smp_hotplug_thread *cur;
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);
247 static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
249 struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
251 if (tsk && !ht->selfparking)
255 int smpboot_park_threads(unsigned int cpu)
257 struct smp_hotplug_thread *cur;
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);
266 static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
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);
276 put_task_struct(tsk);
277 *per_cpu_ptr(ht->store, cpu) = NULL;
283 * smpboot_register_percpu_thread - Register a per_cpu thread related
285 * @plug_thread: Hotplug thread descriptor
287 * Creates and starts the threads on all online cpus.
289 int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
295 mutex_lock(&smpboot_threads_lock);
296 for_each_online_cpu(cpu) {
297 ret = __smpboot_create_thread(plug_thread, cpu);
299 smpboot_destroy_threads(plug_thread);
302 smpboot_unpark_thread(plug_thread, cpu);
304 list_add(&plug_thread->list, &hotplug_threads);
306 mutex_unlock(&smpboot_threads_lock);
310 EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
313 * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
314 * @plug_thread: Hotplug thread descriptor
316 * Stops all threads on all possible cpus.
318 void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
321 mutex_lock(&smpboot_threads_lock);
322 list_del(&plug_thread->list);
323 smpboot_destroy_threads(plug_thread);
324 mutex_unlock(&smpboot_threads_lock);
327 EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
329 static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD);
332 * Called to poll specified CPU's state, for example, when waiting for
333 * a CPU to come online.
335 int cpu_report_state(int cpu)
337 return atomic_read(&per_cpu(cpu_hotplug_state, cpu));
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.
349 * Note that it is permissible to omit this call entirely, as is
350 * done in architectures that do no CPU-hotplug error checking.
352 int cpu_check_up_prepare(int cpu)
354 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
355 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
359 switch (atomic_read(&per_cpu(cpu_hotplug_state, cpu))) {
363 /* The CPU died properly, so just start it up again. */
364 atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
367 case CPU_DEAD_FROZEN:
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
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.
397 /* Should not happen. Famous last words. */
403 * Mark the specified CPU online.
405 * Note that it is permissible to omit this call entirely, as is
406 * done in architectures that do no CPU-hotplug error checking.
408 void cpu_set_state_online(int cpu)
410 (void)atomic_xchg(&per_cpu(cpu_hotplug_state, cpu), CPU_ONLINE);
413 #ifdef CONFIG_HOTPLUG_CPU
416 * Wait for the specified CPU to exit the idle loop and die.
418 bool cpu_wait_death(unsigned int cpu, int seconds)
420 int jf_left = seconds * HZ;
427 /* The outgoing CPU will normally get done quite quickly. */
428 if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD)
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);
438 sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10);
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);
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)
457 * Called by the outgoing CPU to report its successful death. Return
458 * false if this report follows the surviving CPU's timing out.
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.
465 bool cpu_report_death(void)
469 int cpu = smp_processor_id();
472 oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
473 if (oldstate != CPU_BROKEN)
476 newstate = CPU_DEAD_FROZEN;
477 } while (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
478 oldstate, newstate) != oldstate);
479 return newstate == CPU_DEAD;
482 #endif /* #ifdef CONFIG_HOTPLUG_CPU */