// SPDX-License-Identifier: GPL-2.0-only /* * Common SMP CPU bringup/teardown functions */ #include <linux/cpu.h> #include <linux/err.h> #include <linux/smp.h> #include <linux/delay.h> #include <linux/init.h> #include <linux/list.h> #include <linux/slab.h> #include <linux/sched.h> #include <linux/sched/task.h> #include <linux/export.h> #include <linux/percpu.h> #include <linux/kthread.h> #include <linux/smpboot.h> #include "smpboot.h" #ifdef CONFIG_SMP #ifdef CONFIG_GENERIC_SMP_IDLE_THREAD /* * For the hotplug case we keep the task structs around and reuse * them. */ static DEFINE_PER_CPU(struct task_struct *, idle_threads); struct task_struct *idle_thread_get(unsigned int cpu) { struct task_struct *tsk = per_cpu(idle_threads, cpu); if (!tsk) return ERR_PTR(-ENOMEM); return tsk; } void __init idle_thread_set_boot_cpu(void) { per_cpu(idle_threads, smp_processor_id()) = current; } /** * idle_init - Initialize the idle thread for a cpu * @cpu: The cpu for which the idle thread should be initialized * * Creates the thread if it does not exist. */ static __always_inline void idle_init(unsigned int cpu) { struct task_struct *tsk = per_cpu(idle_threads, cpu); if (!tsk) { tsk = fork_idle(cpu); if (IS_ERR(tsk)) pr_err("SMP: fork_idle() failed for CPU %u\n", cpu); else per_cpu(idle_threads, cpu) = tsk; } } /** * idle_threads_init - Initialize idle threads for all cpus */ void __init idle_threads_init(void) { unsigned int cpu, boot_cpu; boot_cpu = smp_processor_id(); for_each_possible_cpu(cpu) { if (cpu != boot_cpu) idle_init(cpu); } } #endif #endif /* #ifdef CONFIG_SMP */ static LIST_HEAD(hotplug_threads); static DEFINE_MUTEX(smpboot_threads_lock); struct smpboot_thread_data { unsigned int cpu; unsigned int status; struct smp_hotplug_thread *ht; }; enum { HP_THREAD_NONE = 0, HP_THREAD_ACTIVE, HP_THREAD_PARKED, }; /** * smpboot_thread_fn - percpu hotplug thread loop function * @data: thread data pointer * * Checks for thread stop and park conditions. Calls the necessary * setup, cleanup, park and unpark functions for the registered * thread. * * Returns 1 when the thread should exit, 0 otherwise. */ static int smpboot_thread_fn(void *data) { struct smpboot_thread_data *td = data; struct smp_hotplug_thread *ht = td->ht; while (1) { set_current_state(TASK_INTERRUPTIBLE); preempt_disable(); if (kthread_should_stop()) { __set_current_state(TASK_RUNNING); preempt_enable(); /* cleanup must mirror setup */ if (ht->cleanup && td->status != HP_THREAD_NONE) ht->cleanup(td->cpu, cpu_online(td->cpu)); kfree(td); return 0; } if (kthread_should_park()) { __set_current_state(TASK_RUNNING); preempt_enable(); if (ht->park && td->status == HP_THREAD_ACTIVE) { BUG_ON(td->cpu != smp_processor_id()); ht->park(td->cpu); td->status = HP_THREAD_PARKED; } kthread_parkme(); /* We might have been woken for stop */ continue; } BUG_ON(td->cpu != smp_processor_id()); /* Check for state change setup */ switch (td->status) { case HP_THREAD_NONE: __set_current_state(TASK_RUNNING); preempt_enable(); if (ht->setup) ht->setup(td->cpu); td->status = HP_THREAD_ACTIVE; continue; case HP_THREAD_PARKED: __set_current_state(TASK_RUNNING); preempt_enable(); if (ht->unpark) ht->unpark(td->cpu); td->status = HP_THREAD_ACTIVE; continue; } if (!ht->thread_should_run(td->cpu)) { preempt_enable_no_resched(); schedule(); } else { __set_current_state(TASK_RUNNING); preempt_enable(); ht->thread_fn(td->cpu); } } } static int __smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu) { struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); struct smpboot_thread_data *td; if (tsk) return 0; td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu)); if (!td) return -ENOMEM; td->cpu = cpu; td->ht = ht; tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu, ht->thread_comm); if (IS_ERR(tsk)) { kfree(td); return PTR_ERR(tsk); } kthread_set_per_cpu(tsk, cpu); /* * Park the thread so that it could start right on the CPU * when it is available. */ kthread_park(tsk); get_task_struct(tsk); *per_cpu_ptr(ht->store, cpu) = tsk; if (ht->create) { /* * Make sure that the task has actually scheduled out * into park position, before calling the create * callback. At least the migration thread callback * requires that the task is off the runqueue. */ if (!wait_task_inactive(tsk, TASK_PARKED)) WARN_ON(1); else ht->create(cpu); } return 0; } int smpboot_create_threads(unsigned int cpu) { struct smp_hotplug_thread *cur; int ret = 0; mutex_lock(&smpboot_threads_lock); list_for_each_entry(cur, &hotplug_threads, list) { ret = __smpboot_create_thread(cur, cpu); if (ret) break; } mutex_unlock(&smpboot_threads_lock); return ret; } static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu) { struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); if (!ht->selfparking) kthread_unpark(tsk); } int smpboot_unpark_threads(unsigned int cpu) { struct smp_hotplug_thread *cur; mutex_lock(&smpboot_threads_lock); list_for_each_entry(cur, &hotplug_threads, list) smpboot_unpark_thread(cur, cpu); mutex_unlock(&smpboot_threads_lock); return 0; } static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu) { struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); if (tsk && !ht->selfparking) kthread_park(tsk); } int smpboot_park_threads(unsigned int cpu) { struct smp_hotplug_thread *cur; mutex_lock(&smpboot_threads_lock); list_for_each_entry_reverse(cur, &hotplug_threads, list) smpboot_park_thread(cur, cpu); mutex_unlock(&smpboot_threads_lock); return 0; } static void smpboot_destroy_threads(struct smp_hotplug_thread *ht) { unsigned int cpu; /* We need to destroy also the parked threads of offline cpus */ for_each_possible_cpu(cpu) { struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu); if (tsk) { kthread_stop(tsk); put_task_struct(tsk); *per_cpu_ptr(ht->store, cpu) = NULL; } } } /** * smpboot_register_percpu_thread - Register a per_cpu thread related * to hotplug * @plug_thread: Hotplug thread descriptor * * Creates and starts the threads on all online cpus. */ int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread) { unsigned int cpu; int ret = 0; cpus_read_lock(); mutex_lock(&smpboot_threads_lock); for_each_online_cpu(cpu) { ret = __smpboot_create_thread(plug_thread, cpu); if (ret) { smpboot_destroy_threads(plug_thread); goto out; } smpboot_unpark_thread(plug_thread, cpu); } list_add(&plug_thread->list, &hotplug_threads); out: mutex_unlock(&smpboot_threads_lock); cpus_read_unlock(); return ret; } EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread); /** * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug * @plug_thread: Hotplug thread descriptor * * Stops all threads on all possible cpus. */ void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread) { cpus_read_lock(); mutex_lock(&smpboot_threads_lock); list_del(&plug_thread->list); smpboot_destroy_threads(plug_thread); mutex_unlock(&smpboot_threads_lock); cpus_read_unlock(); } EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread); static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD); /* * Called to poll specified CPU's state, for example, when waiting for * a CPU to come online. */ int cpu_report_state(int cpu) { return atomic_read(&per_cpu(cpu_hotplug_state, cpu)); } /* * If CPU has died properly, set its state to CPU_UP_PREPARE and * return success. Otherwise, return -EBUSY if the CPU died after * cpu_wait_death() timed out. And yet otherwise again, return -EAGAIN * if cpu_wait_death() timed out and the CPU still hasn't gotten around * to dying. In the latter two cases, the CPU might not be set up * properly, but it is up to the arch-specific code to decide. * Finally, -EIO indicates an unanticipated problem. * * Note that it is permissible to omit this call entirely, as is * done in architectures that do no CPU-hotplug error checking. */ int cpu_check_up_prepare(int cpu) { if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) { atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE); return 0; } switch (atomic_read(&per_cpu(cpu_hotplug_state, cpu))) { case CPU_POST_DEAD: /* The CPU died properly, so just start it up again. */ atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE); return 0; case CPU_DEAD_FROZEN: /* * Timeout during CPU death, so let caller know. * The outgoing CPU completed its processing, but after * cpu_wait_death() timed out and reported the error. The * caller is free to proceed, in which case the state * will be reset properly by cpu_set_state_online(). * Proceeding despite this -EBUSY return makes sense * for systems where the outgoing CPUs take themselves * offline, with no post-death manipulation required from * a surviving CPU. */ return -EBUSY; case CPU_BROKEN: /* * The most likely reason we got here is that there was * a timeout during CPU death, and the outgoing CPU never * did complete its processing. This could happen on * a virtualized system if the outgoing VCPU gets preempted * for more than five seconds, and the user attempts to * immediately online that same CPU. Trying again later * might return -EBUSY above, hence -EAGAIN. */ return -EAGAIN; case CPU_UP_PREPARE: /* * Timeout while waiting for the CPU to show up. Allow to try * again later. */ return 0; default: /* Should not happen. Famous last words. */ return -EIO; } } /* * Mark the specified CPU online. * * Note that it is permissible to omit this call entirely, as is * done in architectures that do no CPU-hotplug error checking. */ void cpu_set_state_online(int cpu) { (void)atomic_xchg(&per_cpu(cpu_hotplug_state, cpu), CPU_ONLINE); } #ifdef CONFIG_HOTPLUG_CPU /* * Wait for the specified CPU to exit the idle loop and die. */ bool cpu_wait_death(unsigned int cpu, int seconds) { int jf_left = seconds * HZ; int oldstate; bool ret = true; int sleep_jf = 1; might_sleep(); /* The outgoing CPU will normally get done quite quickly. */ if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD) goto update_state_early; udelay(5); /* But if the outgoing CPU dawdles, wait increasingly long times. */ while (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) != CPU_DEAD) { schedule_timeout_uninterruptible(sleep_jf); jf_left -= sleep_jf; if (jf_left <= 0) break; sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10); } update_state_early: oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu)); update_state: if (oldstate == CPU_DEAD) { /* Outgoing CPU died normally, update state. */ smp_mb(); /* atomic_read() before update. */ atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD); } else { /* Outgoing CPU still hasn't died, set state accordingly. */ if (!atomic_try_cmpxchg(&per_cpu(cpu_hotplug_state, cpu), &oldstate, CPU_BROKEN)) goto update_state; ret = false; } return ret; } /* * Called by the outgoing CPU to report its successful death. Return * false if this report follows the surviving CPU's timing out. * * A separate "CPU_DEAD_FROZEN" is used when the surviving CPU * timed out. This approach allows architectures to omit calls to * cpu_check_up_prepare() and cpu_set_state_online() without defeating * the next cpu_wait_death()'s polling loop. */ bool cpu_report_death(void) { int oldstate; int newstate; int cpu = smp_processor_id(); oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu)); do { if (oldstate != CPU_BROKEN) newstate = CPU_DEAD; else newstate = CPU_DEAD_FROZEN; } while (!atomic_try_cmpxchg(&per_cpu(cpu_hotplug_state, cpu), &oldstate, newstate)); return newstate == CPU_DEAD; } #endif /* #ifdef CONFIG_HOTPLUG_CPU */