/* * 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> * * This file is released under the GPLv2 and any later version. */#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/lglock.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 */ bool executed; /* actually executed? */ 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 { spinlock_t lock; bool enabled; /* is this stopper enabled? */ struct list_head works; /* list of pending works */}; static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);static DEFINE_PER_CPU(struct task_struct *, cpu_stopper_task);static bool stop_machine_initialized = false; /* * Avoids a race between stop_two_cpus and global stop_cpus, where * the stoppers could get queued up in reverse order, leading to * system deadlock. Using an lglock means stop_two_cpus remains * relatively cheap. */DEFINE_STATIC_LGLOCK(stop_cpus_lock); 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, bool executed){ if (done) { if (executed) done->executed = true; if (atomic_dec_and_test(&done->nr_todo)) complete(&done->completion); }} /* queue @work to @stopper. if offline, @work is completed immediately */static void cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work){ struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu); struct task_struct *p = per_cpu(cpu_stopper_task, cpu); unsigned long flags; spin_lock_irqsave(&stopper->lock, flags); if (stopper->enabled) { list_add_tail(&work->list, &stopper->works); wake_up_process(p); } else cpu_stop_signal_done(work->done, false); spin_unlock_irqrestore(&stopper->lock, flags);} /** * 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); cpu_stop_queue_work(cpu, &work); wait_for_completion(&done.completion); return done.executed ? done.ret : -ENOENT;} /* 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 { int (*fn)(void *); 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(); 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);} /* 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 curstate = MULTI_STOP_NONE; int cpu = smp_processor_id(), err = 0; 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) is_active = cpu == cpumask_first(cpu_online_mask); else is_active = cpumask_test_cpu(cpu, msdata->active_cpus); /* Simple state machine */ do { /* Chill out and ensure we re-read multi_stop_state. */ cpu_relax(); if (msdata->state != curstate) { curstate = msdata->state; 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); } } while (curstate != MULTI_STOP_EXIT); local_irq_restore(flags); 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; preempt_disable(); 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 we observe both CPUs active we know _cpu_down() cannot yet have * queued its stop_machine works and therefore ours will get executed * first. Or its not either one of our CPUs that's getting unplugged, * in which case we don't care. * * This relies on the stopper workqueues to be FIFO. */ if (!cpu_active(cpu1) || !cpu_active(cpu2)) { preempt_enable(); return -ENOENT; } lg_double_lock(&stop_cpus_lock, cpu1, cpu2); cpu_stop_queue_work(cpu1, &work1); cpu_stop_queue_work(cpu2, &work2); lg_double_unlock(&stop_cpus_lock, cpu1, cpu2); preempt_enable(); wait_for_completion(&done.completion); return done.executed ? done.ret : -ENOENT;} /** * 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. */void 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, }; cpu_stop_queue_work(cpu, work_buf);} /* static data for stop_cpus */static DEFINE_MUTEX(stop_cpus_mutex);static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work); static void 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; /* initialize works and done */ for_each_cpu(cpu, cpumask) { work = &per_cpu(stop_cpus_work, cpu); work->fn = fn; work->arg = arg; work->done = done; } /* * 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. */ lg_global_lock(&stop_cpus_lock); for_each_cpu(cpu, cpumask) cpu_stop_queue_work(cpu, &per_cpu(stop_cpus_work, cpu)); lg_global_unlock(&stop_cpus_lock);} 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)); queue_stop_cpus_work(cpumask, fn, arg, &done); wait_for_completion(&done.completion); return done.executed ? done.ret : -ENOENT;} /** * 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. */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;} /** * try_stop_cpus - try to stop multiple cpus * @cpumask: cpus to stop * @fn: function to execute * @arg: argument to @fn * * Identical to stop_cpus() except that it fails with -EAGAIN if * someone else is already using the facility. * * CONTEXT: * Might sleep. * * RETURNS: * -EAGAIN if someone else is already stopping cpus, -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. */int try_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 */ if (!mutex_trylock(&stop_cpus_mutex)) return -EAGAIN; 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; spin_lock_irqsave(&stopper->lock, flags); run = !list_empty(&stopper->works); 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; int ret; repeat: work = NULL; 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); } 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; char ksym_buf[KSYM_NAME_LEN] __maybe_unused; /* cpu stop callbacks are not allowed to sleep */ preempt_disable(); ret = fn(arg); if (ret) done->ret = ret; /* restore preemption and check it's still balanced */ preempt_enable(); WARN_ONCE(preempt_count(), "cpu_stop: %s(%p) leaked preempt count\n", kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL, ksym_buf), arg); cpu_stop_signal_done(done, true); goto repeat; }} 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_task, cpu));} static void cpu_stop_park(unsigned int cpu){ struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu); struct cpu_stop_work *work; unsigned long flags; /* drain remaining works */ spin_lock_irqsave(&stopper->lock, flags); list_for_each_entry(work, &stopper->works, list) cpu_stop_signal_done(work->done, false); stopper->enabled = false; spin_unlock_irqrestore(&stopper->lock, flags);} static void cpu_stop_unpark(unsigned int cpu){ struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu); spin_lock_irq(&stopper->lock); stopper->enabled = true; spin_unlock_irq(&stopper->lock);} static struct smp_hotplug_thread cpu_stop_threads = { .store = &cpu_stopper_task, .thread_should_run = cpu_stop_should_run, .thread_fn = cpu_stopper_thread, .thread_comm = "migration/%u", .create = cpu_stop_create, .setup = cpu_stop_unpark, .park = cpu_stop_park, .pre_unpark = cpu_stop_unpark, .selfparking = true,}; static int __init cpu_stop_init(void){Lines 1–500 of 616. 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/* * 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> * * This file is released under the GPLv2 and any later version. */ #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/lglock.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 */ bool executed; /* actually executed? */ 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 { spinlock_t lock; bool enabled; /* is this stopper enabled? */ struct list_head works; /* list of pending works */ }; static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper); static DEFINE_PER_CPU(struct task_struct *, cpu_stopper_task); static bool stop_machine_initialized = false; /* * Avoids a race between stop_two_cpus and global stop_cpus, where * the stoppers could get queued up in reverse order, leading to * system deadlock. Using an lglock means stop_two_cpus remains * relatively cheap. */ DEFINE_STATIC_LGLOCK(stop_cpus_lock); 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, bool executed) { if (done) { if (executed) done->executed = true; if (atomic_dec_and_test(&done->nr_todo)) complete(&done->completion); } } /* queue @work to @stopper. if offline, @work is completed immediately */ static void cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work) { struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu); struct task_struct *p = per_cpu(cpu_stopper_task, cpu); unsigned long flags; spin_lock_irqsave(&stopper->lock, flags); if (stopper->enabled) { list_add_tail(&work->list, &stopper->works); wake_up_process(p); } else cpu_stop_signal_done(work->done, false); spin_unlock_irqrestore(&stopper->lock, flags); } /** * 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); cpu_stop_queue_work(cpu, &work); wait_for_completion(&done.completion); return done.executed ? done.ret : -ENOENT; } /* 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 { int (*fn)(void *); 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(); 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); } /* 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 curstate = MULTI_STOP_NONE; int cpu = smp_processor_id(), err = 0; 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) is_active = cpu == cpumask_first(cpu_online_mask); else is_active = cpumask_test_cpu(cpu, msdata->active_cpus); /* Simple state machine */ do { /* Chill out and ensure we re-read multi_stop_state. */ cpu_relax(); if (msdata->state != curstate) { curstate = msdata->state; 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); } } while (curstate != MULTI_STOP_EXIT); local_irq_restore(flags); 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; preempt_disable(); 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 we observe both CPUs active we know _cpu_down() cannot yet have * queued its stop_machine works and therefore ours will get executed * first. Or its not either one of our CPUs that's getting unplugged, * in which case we don't care. * * This relies on the stopper workqueues to be FIFO. */ if (!cpu_active(cpu1) || !cpu_active(cpu2)) { preempt_enable(); return -ENOENT; } lg_double_lock(&stop_cpus_lock, cpu1, cpu2); cpu_stop_queue_work(cpu1, &work1); cpu_stop_queue_work(cpu2, &work2); lg_double_unlock(&stop_cpus_lock, cpu1, cpu2); preempt_enable(); wait_for_completion(&done.completion); return done.executed ? done.ret : -ENOENT; } /** * 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. */ void 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, }; cpu_stop_queue_work(cpu, work_buf); } /* static data for stop_cpus */ static DEFINE_MUTEX(stop_cpus_mutex); static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work); static void 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; /* initialize works and done */ for_each_cpu(cpu, cpumask) { work = &per_cpu(stop_cpus_work, cpu); work->fn = fn; work->arg = arg; work->done = done; } /* * 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. */ lg_global_lock(&stop_cpus_lock); for_each_cpu(cpu, cpumask) cpu_stop_queue_work(cpu, &per_cpu(stop_cpus_work, cpu)); lg_global_unlock(&stop_cpus_lock); } 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)); queue_stop_cpus_work(cpumask, fn, arg, &done); wait_for_completion(&done.completion); return done.executed ? done.ret : -ENOENT; } /** * 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. */ 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; } /** * try_stop_cpus - try to stop multiple cpus * @cpumask: cpus to stop * @fn: function to execute * @arg: argument to @fn * * Identical to stop_cpus() except that it fails with -EAGAIN if * someone else is already using the facility. * * CONTEXT: * Might sleep. * * RETURNS: * -EAGAIN if someone else is already stopping cpus, -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. */ int try_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 */ if (!mutex_trylock(&stop_cpus_mutex)) return -EAGAIN; 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; spin_lock_irqsave(&stopper->lock, flags); run = !list_empty(&stopper->works); 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; int ret; repeat: work = NULL; 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); } 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; char ksym_buf[KSYM_NAME_LEN] __maybe_unused; /* cpu stop callbacks are not allowed to sleep */ preempt_disable(); ret = fn(arg); if (ret) done->ret = ret; /* restore preemption and check it's still balanced */ preempt_enable(); WARN_ONCE(preempt_count(), "cpu_stop: %s(%p) leaked preempt count\n", kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL, ksym_buf), arg); cpu_stop_signal_done(done, true); goto repeat; } } 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_task, cpu)); } static void cpu_stop_park(unsigned int cpu) { struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu); struct cpu_stop_work *work; unsigned long flags; /* drain remaining works */ spin_lock_irqsave(&stopper->lock, flags); list_for_each_entry(work, &stopper->works, list) cpu_stop_signal_done(work->done, false); stopper->enabled = false; spin_unlock_irqrestore(&stopper->lock, flags); } static void cpu_stop_unpark(unsigned int cpu) { struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu); spin_lock_irq(&stopper->lock); stopper->enabled = true; spin_unlock_irq(&stopper->lock); } static struct smp_hotplug_thread cpu_stop_threads = { .store = &cpu_stopper_task, .thread_should_run = cpu_stop_should_run, .thread_fn = cpu_stopper_thread, .thread_comm = "migration/%u", .create = cpu_stop_create, .setup = cpu_stop_unpark, .park = cpu_stop_park, .pre_unpark = cpu_stop_unpark, .selfparking = true, }; static int __init cpu_stop_init(void) {