diff options
Diffstat (limited to 'kernel/stop_machine.c')
| -rw-r--r-- | kernel/stop_machine.c | 665 |
1 files changed, 665 insertions, 0 deletions
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c new file mode 100644 index 000000000..890b79cf0 --- /dev/null +++ b/kernel/stop_machine.c @@ -0,0 +1,665 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * kernel/stop_machine.c + * + * Copyright (C) 2008, 2005 IBM Corporation. + * Copyright (C) 2008, 2005 Rusty Russell rusty@rustcorp.com.au + * Copyright (C) 2010 SUSE Linux Products GmbH + * Copyright (C) 2010 Tejun Heo <tj@kernel.org> + */ +#include <linux/compiler.h> +#include <linux/completion.h> +#include <linux/cpu.h> +#include <linux/init.h> +#include <linux/kthread.h> +#include <linux/export.h> +#include <linux/percpu.h> +#include <linux/sched.h> +#include <linux/stop_machine.h> +#include <linux/interrupt.h> +#include <linux/kallsyms.h> +#include <linux/smpboot.h> +#include <linux/atomic.h> +#include <linux/nmi.h> +#include <linux/sched/wake_q.h> + +/* + * Structure to determine completion condition and record errors. May + * be shared by works on different cpus. + */ +struct cpu_stop_done { + atomic_t nr_todo; /* nr left to execute */ + int ret; /* collected return value */ + struct completion completion; /* fired if nr_todo reaches 0 */ +}; + +/* the actual stopper, one per every possible cpu, enabled on online cpus */ +struct cpu_stopper { + struct task_struct *thread; + + raw_spinlock_t lock; + bool enabled; /* is this stopper enabled? */ + struct list_head works; /* list of pending works */ + + struct cpu_stop_work stop_work; /* for stop_cpus */ +}; + +static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper); +static bool stop_machine_initialized = false; + +/* static data for stop_cpus */ +static DEFINE_MUTEX(stop_cpus_mutex); +static bool stop_cpus_in_progress; + +static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo) +{ + memset(done, 0, sizeof(*done)); + atomic_set(&done->nr_todo, nr_todo); + init_completion(&done->completion); +} + +/* signal completion unless @done is NULL */ +static void cpu_stop_signal_done(struct cpu_stop_done *done) +{ + if (atomic_dec_and_test(&done->nr_todo)) + complete(&done->completion); +} + +static void __cpu_stop_queue_work(struct cpu_stopper *stopper, + struct cpu_stop_work *work, + struct wake_q_head *wakeq) +{ + list_add_tail(&work->list, &stopper->works); + wake_q_add(wakeq, stopper->thread); +} + +/* queue @work to @stopper. if offline, @work is completed immediately */ +static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work) +{ + struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu); + DEFINE_WAKE_Q(wakeq); + unsigned long flags; + bool enabled; + + preempt_disable(); + raw_spin_lock_irqsave(&stopper->lock, flags); + enabled = stopper->enabled; + if (enabled) + __cpu_stop_queue_work(stopper, work, &wakeq); + else if (work->done) + cpu_stop_signal_done(work->done); + raw_spin_unlock_irqrestore(&stopper->lock, flags); + + wake_up_q(&wakeq); + preempt_enable(); + + return enabled; +} + +/** + * stop_one_cpu - stop a cpu + * @cpu: cpu to stop + * @fn: function to execute + * @arg: argument to @fn + * + * Execute @fn(@arg) on @cpu. @fn is run in a process context with + * the highest priority preempting any task on the cpu and + * monopolizing it. This function returns after the execution is + * complete. + * + * This function doesn't guarantee @cpu stays online till @fn + * completes. If @cpu goes down in the middle, execution may happen + * partially or fully on different cpus. @fn should either be ready + * for that or the caller should ensure that @cpu stays online until + * this function completes. + * + * CONTEXT: + * Might sleep. + * + * RETURNS: + * -ENOENT if @fn(@arg) was not executed because @cpu was offline; + * otherwise, the return value of @fn. + */ +int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg) +{ + struct cpu_stop_done done; + struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done }; + + cpu_stop_init_done(&done, 1); + if (!cpu_stop_queue_work(cpu, &work)) + return -ENOENT; + /* + * In case @cpu == smp_proccessor_id() we can avoid a sleep+wakeup + * cycle by doing a preemption: + */ + cond_resched(); + wait_for_completion(&done.completion); + return done.ret; +} + +/* This controls the threads on each CPU. */ +enum multi_stop_state { + /* Dummy starting state for thread. */ + MULTI_STOP_NONE, + /* Awaiting everyone to be scheduled. */ + MULTI_STOP_PREPARE, + /* Disable interrupts. */ + MULTI_STOP_DISABLE_IRQ, + /* Run the function */ + MULTI_STOP_RUN, + /* Exit */ + MULTI_STOP_EXIT, +}; + +struct multi_stop_data { + cpu_stop_fn_t fn; + void *data; + /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */ + unsigned int num_threads; + const struct cpumask *active_cpus; + + enum multi_stop_state state; + atomic_t thread_ack; +}; + +static void set_state(struct multi_stop_data *msdata, + enum multi_stop_state newstate) +{ + /* Reset ack counter. */ + atomic_set(&msdata->thread_ack, msdata->num_threads); + smp_wmb(); + WRITE_ONCE(msdata->state, newstate); +} + +/* Last one to ack a state moves to the next state. */ +static void ack_state(struct multi_stop_data *msdata) +{ + if (atomic_dec_and_test(&msdata->thread_ack)) + set_state(msdata, msdata->state + 1); +} + +notrace void __weak stop_machine_yield(const struct cpumask *cpumask) +{ + cpu_relax(); +} + +/* This is the cpu_stop function which stops the CPU. */ +static int multi_cpu_stop(void *data) +{ + struct multi_stop_data *msdata = data; + enum multi_stop_state newstate, curstate = MULTI_STOP_NONE; + int cpu = smp_processor_id(), err = 0; + const struct cpumask *cpumask; + unsigned long flags; + bool is_active; + + /* + * When called from stop_machine_from_inactive_cpu(), irq might + * already be disabled. Save the state and restore it on exit. + */ + local_save_flags(flags); + + if (!msdata->active_cpus) { + cpumask = cpu_online_mask; + is_active = cpu == cpumask_first(cpumask); + } else { + cpumask = msdata->active_cpus; + is_active = cpumask_test_cpu(cpu, cpumask); + } + + /* Simple state machine */ + do { + /* Chill out and ensure we re-read multi_stop_state. */ + stop_machine_yield(cpumask); + newstate = READ_ONCE(msdata->state); + if (newstate != curstate) { + curstate = newstate; + switch (curstate) { + case MULTI_STOP_DISABLE_IRQ: + local_irq_disable(); + hard_irq_disable(); + break; + case MULTI_STOP_RUN: + if (is_active) + err = msdata->fn(msdata->data); + break; + default: + break; + } + ack_state(msdata); + } else if (curstate > MULTI_STOP_PREPARE) { + /* + * At this stage all other CPUs we depend on must spin + * in the same loop. Any reason for hard-lockup should + * be detected and reported on their side. + */ + touch_nmi_watchdog(); + } + rcu_momentary_dyntick_idle(); + } while (curstate != MULTI_STOP_EXIT); + + local_irq_restore(flags); + return err; +} + +static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1, + int cpu2, struct cpu_stop_work *work2) +{ + struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1); + struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2); + DEFINE_WAKE_Q(wakeq); + int err; + +retry: + /* + * The waking up of stopper threads has to happen in the same + * scheduling context as the queueing. Otherwise, there is a + * possibility of one of the above stoppers being woken up by another + * CPU, and preempting us. This will cause us to not wake up the other + * stopper forever. + */ + preempt_disable(); + raw_spin_lock_irq(&stopper1->lock); + raw_spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING); + + if (!stopper1->enabled || !stopper2->enabled) { + err = -ENOENT; + goto unlock; + } + + /* + * Ensure that if we race with __stop_cpus() the stoppers won't get + * queued up in reverse order leading to system deadlock. + * + * We can't miss stop_cpus_in_progress if queue_stop_cpus_work() has + * queued a work on cpu1 but not on cpu2, we hold both locks. + * + * It can be falsely true but it is safe to spin until it is cleared, + * queue_stop_cpus_work() does everything under preempt_disable(). + */ + if (unlikely(stop_cpus_in_progress)) { + err = -EDEADLK; + goto unlock; + } + + err = 0; + __cpu_stop_queue_work(stopper1, work1, &wakeq); + __cpu_stop_queue_work(stopper2, work2, &wakeq); + +unlock: + raw_spin_unlock(&stopper2->lock); + raw_spin_unlock_irq(&stopper1->lock); + + if (unlikely(err == -EDEADLK)) { + preempt_enable(); + + while (stop_cpus_in_progress) + cpu_relax(); + + goto retry; + } + + wake_up_q(&wakeq); + preempt_enable(); + + return err; +} +/** + * stop_two_cpus - stops two cpus + * @cpu1: the cpu to stop + * @cpu2: the other cpu to stop + * @fn: function to execute + * @arg: argument to @fn + * + * Stops both the current and specified CPU and runs @fn on one of them. + * + * returns when both are completed. + */ +int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg) +{ + struct cpu_stop_done done; + struct cpu_stop_work work1, work2; + struct multi_stop_data msdata; + + msdata = (struct multi_stop_data){ + .fn = fn, + .data = arg, + .num_threads = 2, + .active_cpus = cpumask_of(cpu1), + }; + + work1 = work2 = (struct cpu_stop_work){ + .fn = multi_cpu_stop, + .arg = &msdata, + .done = &done + }; + + cpu_stop_init_done(&done, 2); + set_state(&msdata, MULTI_STOP_PREPARE); + + if (cpu1 > cpu2) + swap(cpu1, cpu2); + if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2)) + return -ENOENT; + + wait_for_completion(&done.completion); + return done.ret; +} + +/** + * stop_one_cpu_nowait - stop a cpu but don't wait for completion + * @cpu: cpu to stop + * @fn: function to execute + * @arg: argument to @fn + * @work_buf: pointer to cpu_stop_work structure + * + * Similar to stop_one_cpu() but doesn't wait for completion. The + * caller is responsible for ensuring @work_buf is currently unused + * and will remain untouched until stopper starts executing @fn. + * + * CONTEXT: + * Don't care. + * + * RETURNS: + * true if cpu_stop_work was queued successfully and @fn will be called, + * false otherwise. + */ +bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg, + struct cpu_stop_work *work_buf) +{ + *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, }; + return cpu_stop_queue_work(cpu, work_buf); +} + +static bool queue_stop_cpus_work(const struct cpumask *cpumask, + cpu_stop_fn_t fn, void *arg, + struct cpu_stop_done *done) +{ + struct cpu_stop_work *work; + unsigned int cpu; + bool queued = false; + + /* + * Disable preemption while queueing to avoid getting + * preempted by a stopper which might wait for other stoppers + * to enter @fn which can lead to deadlock. + */ + preempt_disable(); + stop_cpus_in_progress = true; + barrier(); + for_each_cpu(cpu, cpumask) { + work = &per_cpu(cpu_stopper.stop_work, cpu); + work->fn = fn; + work->arg = arg; + work->done = done; + if (cpu_stop_queue_work(cpu, work)) + queued = true; + } + barrier(); + stop_cpus_in_progress = false; + preempt_enable(); + + return queued; +} + +static int __stop_cpus(const struct cpumask *cpumask, + cpu_stop_fn_t fn, void *arg) +{ + struct cpu_stop_done done; + + cpu_stop_init_done(&done, cpumask_weight(cpumask)); + if (!queue_stop_cpus_work(cpumask, fn, arg, &done)) + return -ENOENT; + wait_for_completion(&done.completion); + return done.ret; +} + +/** + * stop_cpus - stop multiple cpus + * @cpumask: cpus to stop + * @fn: function to execute + * @arg: argument to @fn + * + * Execute @fn(@arg) on online cpus in @cpumask. On each target cpu, + * @fn is run in a process context with the highest priority + * preempting any task on the cpu and monopolizing it. This function + * returns after all executions are complete. + * + * This function doesn't guarantee the cpus in @cpumask stay online + * till @fn completes. If some cpus go down in the middle, execution + * on the cpu may happen partially or fully on different cpus. @fn + * should either be ready for that or the caller should ensure that + * the cpus stay online until this function completes. + * + * All stop_cpus() calls are serialized making it safe for @fn to wait + * for all cpus to start executing it. + * + * CONTEXT: + * Might sleep. + * + * RETURNS: + * -ENOENT if @fn(@arg) was not executed at all because all cpus in + * @cpumask were offline; otherwise, 0 if all executions of @fn + * returned 0, any non zero return value if any returned non zero. + */ +static int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg) +{ + int ret; + + /* static works are used, process one request at a time */ + mutex_lock(&stop_cpus_mutex); + ret = __stop_cpus(cpumask, fn, arg); + mutex_unlock(&stop_cpus_mutex); + return ret; +} + +static int cpu_stop_should_run(unsigned int cpu) +{ + struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu); + unsigned long flags; + int run; + + raw_spin_lock_irqsave(&stopper->lock, flags); + run = !list_empty(&stopper->works); + raw_spin_unlock_irqrestore(&stopper->lock, flags); + return run; +} + +static void cpu_stopper_thread(unsigned int cpu) +{ + struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu); + struct cpu_stop_work *work; + +repeat: + work = NULL; + raw_spin_lock_irq(&stopper->lock); + if (!list_empty(&stopper->works)) { + work = list_first_entry(&stopper->works, + struct cpu_stop_work, list); + list_del_init(&work->list); + } + raw_spin_unlock_irq(&stopper->lock); + + if (work) { + cpu_stop_fn_t fn = work->fn; + void *arg = work->arg; + struct cpu_stop_done *done = work->done; + int ret; + + /* cpu stop callbacks must not sleep, make in_atomic() == T */ + preempt_count_inc(); + ret = fn(arg); + if (done) { + if (ret) + done->ret = ret; + cpu_stop_signal_done(done); + } + preempt_count_dec(); + WARN_ONCE(preempt_count(), + "cpu_stop: %ps(%p) leaked preempt count\n", fn, arg); + goto repeat; + } +} + +void stop_machine_park(int cpu) +{ + struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu); + /* + * Lockless. cpu_stopper_thread() will take stopper->lock and flush + * the pending works before it parks, until then it is fine to queue + * the new works. + */ + stopper->enabled = false; + kthread_park(stopper->thread); +} + +extern void sched_set_stop_task(int cpu, struct task_struct *stop); + +static void cpu_stop_create(unsigned int cpu) +{ + sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu)); +} + +static void cpu_stop_park(unsigned int cpu) +{ + struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu); + + WARN_ON(!list_empty(&stopper->works)); +} + +void stop_machine_unpark(int cpu) +{ + struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu); + + stopper->enabled = true; + kthread_unpark(stopper->thread); +} + +static struct smp_hotplug_thread cpu_stop_threads = { + .store = &cpu_stopper.thread, + .thread_should_run = cpu_stop_should_run, + .thread_fn = cpu_stopper_thread, + .thread_comm = "migration/%u", + .create = cpu_stop_create, + .park = cpu_stop_park, + .selfparking = true, +}; + +static int __init cpu_stop_init(void) +{ + unsigned int cpu; + + for_each_possible_cpu(cpu) { + struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu); + + raw_spin_lock_init(&stopper->lock); + INIT_LIST_HEAD(&stopper->works); + } + + BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads)); + stop_machine_unpark(raw_smp_processor_id()); + stop_machine_initialized = true; + return 0; +} +early_initcall(cpu_stop_init); + +int stop_machine_cpuslocked(cpu_stop_fn_t fn, void *data, + const struct cpumask *cpus) +{ + struct multi_stop_data msdata = { + .fn = fn, + .data = data, + .num_threads = num_online_cpus(), + .active_cpus = cpus, + }; + + lockdep_assert_cpus_held(); + + if (!stop_machine_initialized) { + /* + * Handle the case where stop_machine() is called + * early in boot before stop_machine() has been + * initialized. + */ + unsigned long flags; + int ret; + + WARN_ON_ONCE(msdata.num_threads != 1); + + local_irq_save(flags); + hard_irq_disable(); + ret = (*fn)(data); + local_irq_restore(flags); + + return ret; + } + + /* Set the initial state and stop all online cpus. */ + set_state(&msdata, MULTI_STOP_PREPARE); + return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata); +} + +int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus) +{ + int ret; + + /* No CPUs can come up or down during this. */ + cpus_read_lock(); + ret = stop_machine_cpuslocked(fn, data, cpus); + cpus_read_unlock(); + return ret; +} +EXPORT_SYMBOL_GPL(stop_machine); + +/** + * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU + * @fn: the function to run + * @data: the data ptr for the @fn() + * @cpus: the cpus to run the @fn() on (NULL = any online cpu) + * + * This is identical to stop_machine() but can be called from a CPU which + * is not active. The local CPU is in the process of hotplug (so no other + * CPU hotplug can start) and not marked active and doesn't have enough + * context to sleep. + * + * This function provides stop_machine() functionality for such state by + * using busy-wait for synchronization and executing @fn directly for local + * CPU. + * + * CONTEXT: + * Local CPU is inactive. Temporarily stops all active CPUs. + * + * RETURNS: + * 0 if all executions of @fn returned 0, any non zero return value if any + * returned non zero. + */ +int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data, + const struct cpumask *cpus) +{ + struct multi_stop_data msdata = { .fn = fn, .data = data, + .active_cpus = cpus }; + struct cpu_stop_done done; + int ret; + + /* Local CPU must be inactive and CPU hotplug in progress. */ + BUG_ON(cpu_active(raw_smp_processor_id())); + msdata.num_threads = num_active_cpus() + 1; /* +1 for local */ + + /* No proper task established and can't sleep - busy wait for lock. */ + while (!mutex_trylock(&stop_cpus_mutex)) + cpu_relax(); + + /* Schedule work on other CPUs and execute directly for local CPU */ + set_state(&msdata, MULTI_STOP_PREPARE); + cpu_stop_init_done(&done, num_active_cpus()); + queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata, + &done); + ret = multi_cpu_stop(&msdata); + + /* Busy wait for completion. */ + while (!completion_done(&done.completion)) + cpu_relax(); + + mutex_unlock(&stop_cpus_mutex); + return ret ?: done.ret; +} |