sdk_linux/kernel/cpu.c

/* CPU control.
 * (C) 2001, 2002, 2003, 2004 Rusty Russell
 *
 * This code is licenced under the GPL.
 */
#include <linux/sched/mm.h>
#include <linux/proc_fs.h>
#include <linux/smp.h>
#include <linux/init.h>
#include <linux/notifier.h>
#include <linux/sched/signal.h>
#include <linux/sched/hotplug.h>
#include <linux/sched/isolation.h>
#include <linux/sched/task.h>
#include <linux/sched/smt.h>
#include <linux/unistd.h>
#include <linux/cpu.h>
#include <linux/oom.h>
#include <linux/rcupdate.h>
#include <linux/export.h>
#include <linux/bug.h>
#include <linux/kthread.h>
#include <linux/stop_machine.h>
#include <linux/mutex.h>
#include <linux/gfp.h>
#include <linux/suspend.h>
#include <linux/lockdep.h>
#include <linux/tick.h>
#include <linux/irq.h>
#include <linux/nmi.h>
#include <linux/smpboot.h>
#include <linux/relay.h>
#include <linux/slab.h>
#include <linux/scs.h>
#include <linux/percpu-rwsem.h>
#include <linux/cpuset.h>
#include <linux/random.h>

#include <trace/events/power.h>
#define CREATE_TRACE_POINTS
#include <trace/events/cpuhp.h>

#undef CREATE_TRACE_POINTS

#include "smpboot.h"

#define CPU_PAGE_SIZE_OFF_TWO 2

/**
 * cpuhp_cpu_state - Per cpu hotplug state storage
 * @state:    The current cpu state
 * @target:    The target state
 * @thread:    Pointer to the hotplug thread
 * @should_run:    Thread should execute
 * @rollback:    Perform a rollback
 * @single:    Single callback invocation
 * @bringup:    Single callback bringup or teardown selector
 * @cb_state:    The state for a single callback (install/uninstall)
 * @result:    Result of the operation
 * @done_up:    Signal completion to the issuer of the task for cpu-up
 * @done_down:    Signal completion to the issuer of the task for cpu-down
 */
struct cpuhp_cpu_state {
    enum cpuhp_state state;
    enum cpuhp_state target;
    enum cpuhp_state fail;
#ifdef CONFIG_SMP
    struct task_struct *thread;
    bool should_run;
    bool rollback;
    bool single;
    bool bringup;
    struct hlist_node *node;
    struct hlist_node *last;
    enum cpuhp_state cb_state;
    int result;
    struct completion done_up;
    struct completion done_down;
#endif
};

static DEFINE_PER_CPU(struct cpuhp_cpu_state, cpuhp_state) = {
    .fail = CPUHP_INVALID,
};

#ifdef CONFIG_SMP
cpumask_t cpus_booted_once_mask;
#endif

#if defined(CONFIG_LOCKDEP) && defined(CONFIG_SMP)
static struct lockdep_map cpuhp_state_up_map = STATIC_LOCKDEP_MAP_INIT("cpuhp_state-up", &cpuhp_state_up_map);
static struct lockdep_map cpuhp_state_down_map = STATIC_LOCKDEP_MAP_INIT("cpuhp_state-down", &cpuhp_state_down_map);

static inline void cpuhp_lock_acquire(bool bringup)
{
    lock_map_acquire(bringup ? &cpuhp_state_up_map : &cpuhp_state_down_map);
}

static inline void cpuhp_lock_release(bool bringup)
{
    lock_map_release(bringup ? &cpuhp_state_up_map : &cpuhp_state_down_map);
}
#else

static inline void cpuhp_lock_acquire(bool bringup)
{
}
static inline void cpuhp_lock_release(bool bringup)
{
}

#endif

/**
 * cpuhp_step - Hotplug state machine step
 * @name:    Name of the step
 * @startup:    Startup function of the step
 * @teardown:    Teardown function of the step
 * @cant_stop:    Bringup/teardown can't be stopped at this step
 */
struct cpuhp_step {
    const char *name;
    union {
        int (*single)(unsigned int cpu);
        int (*multi)(unsigned int cpu, struct hlist_node *node);
    } startup;
    union {
        int (*single)(unsigned int cpu);
        int (*multi)(unsigned int cpu, struct hlist_node *node);
    } teardown;
    struct hlist_head list;
    bool cant_stop;
    bool multi_instance;
};

static DEFINE_MUTEX(cpuhp_state_mutex);
static struct cpuhp_step cpuhp_hp_states[];

static struct cpuhp_step *cpuhp_get_step(enum cpuhp_state state)
{
    return cpuhp_hp_states + state;
}

/**
 * cpuhp_invoke_callback _ Invoke the callbacks for a given state
 * @cpu:    The cpu for which the callback should be invoked
 * @state:    The state to do callbacks for
 * @bringup:    True if the bringup callback should be invoked
 * @node:    For multi-instance, do a single entry callback for install/remove
 * @lastp:    For multi-instance rollback, remember how far we got
 *
 * Called from cpu hotplug and from the state register machinery.
 */
static int cpuhp_invoke_callback(unsigned int cpu, enum cpuhp_state state, bool bringup, struct hlist_node *node,
                                 struct hlist_node **lastp)
{
    struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    struct cpuhp_step *step = cpuhp_get_step(state);
    int (*cbm)(unsigned int cpu, struct hlist_node *node);
    int (*cb)(unsigned int cpu);
    int ret, cnt;

    if (st->fail == state) {
        st->fail = CPUHP_INVALID;

        if (!(bringup ? step->startup.single : step->teardown.single)) {
            return 0;
        }

        return -EAGAIN;
    }

    if (!step->multi_instance) {
        WARN_ON_ONCE(lastp && *lastp);
        cb = bringup ? step->startup.single : step->teardown.single;
        if (!cb) {
            return 0;
        }
        trace_cpuhp_enter(cpu, st->target, state, cb);
        ret = cb(cpu);
        trace_cpuhp_exit(cpu, st->state, state, ret);
        return ret;
    }
    cbm = bringup ? step->startup.multi : step->teardown.multi;
    if (!cbm) {
        return 0;
    }

    /* Single invocation for instance add/remove */
    if (node) {
        WARN_ON_ONCE(lastp && *lastp);
        trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
        ret = cbm(cpu, node);
        trace_cpuhp_exit(cpu, st->state, state, ret);
        return ret;
    }

    /* State transition. Invoke on all instances */
    cnt = 0;
    hlist_for_each(node, &step->list)
    {
        if (lastp && node == *lastp) {
            break;
        }

        trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
        ret = cbm(cpu, node);
        trace_cpuhp_exit(cpu, st->state, state, ret);
        if (ret) {
            if (!lastp) {
                goto err;
            }

            *lastp = node;
            return ret;
        }
        cnt++;
    }
    if (lastp) {
        *lastp = NULL;
    }
    return 0;
err:
    /* Rollback the instances if one failed */
    cbm = !bringup ? step->startup.multi : step->teardown.multi;
    if (!cbm) {
        return ret;
    }

    hlist_for_each(node, &step->list)
    {
        if (!cnt--) {
            break;
        }

        trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
        ret = cbm(cpu, node);
        trace_cpuhp_exit(cpu, st->state, state, ret);
        /*
         * Rollback must not fail,
         */
        WARN_ON_ONCE(ret);
    }
    return ret;
}

#ifdef CONFIG_SMP
static bool cpuhp_is_ap_state(enum cpuhp_state state)
{
    /*
     * The extra check for CPUHP_TEARDOWN_CPU is only for documentation
     * purposes as that state is handled explicitly in cpu_down.
     */
    return state > CPUHP_BRINGUP_CPU && state != CPUHP_TEARDOWN_CPU;
}

static inline void wait_for_ap_thread(struct cpuhp_cpu_state *st, bool bringup)
{
    struct completion *done = bringup ? &st->done_up : &st->done_down;
    wait_for_completion(done);
}

static inline void complete_ap_thread(struct cpuhp_cpu_state *st, bool bringup)
{
    struct completion *done = bringup ? &st->done_up : &st->done_down;
    complete(done);
}

/*
 * The former STARTING/DYING states, ran with IRQs disabled and must not fail.
 */
static bool cpuhp_is_atomic_state(enum cpuhp_state state)
{
    return CPUHP_AP_IDLE_DEAD <= state && state < CPUHP_AP_ONLINE;
}

/* Serializes the updates to cpu_online_mask, cpu_present_mask */
static DEFINE_MUTEX(cpu_add_remove_lock);
bool cpuhp_tasks_frozen;
EXPORT_SYMBOL_GPL(cpuhp_tasks_frozen);

/*
 * The following two APIs (cpu_maps_update_begin/done) must be used when
 * attempting to serialize the updates to cpu_online_mask & cpu_present_mask.
 */
void cpu_maps_update_begin(void)
{
    mutex_lock(&cpu_add_remove_lock);
}
EXPORT_SYMBOL_GPL(cpu_maps_update_begin);

void cpu_maps_update_done(void)
{
    mutex_unlock(&cpu_add_remove_lock);
}
EXPORT_SYMBOL_GPL(cpu_maps_update_done);

/*
 * If set, cpu_up and cpu_down will return -EBUSY and do nothing.
 * Should always be manipulated under cpu_add_remove_lock
 */
static int cpu_hotplug_disabled;

#ifdef CONFIG_HOTPLUG_CPU

DEFINE_STATIC_PERCPU_RWSEM(cpu_hotplug_lock);

void cpus_read_lock(void)
{
    percpu_down_read(&cpu_hotplug_lock);
}
EXPORT_SYMBOL_GPL(cpus_read_lock);

int cpus_read_trylock(void)
{
    return percpu_down_read_trylock(&cpu_hotplug_lock);
}
EXPORT_SYMBOL_GPL(cpus_read_trylock);

void cpus_read_unlock(void)
{
    percpu_up_read(&cpu_hotplug_lock);
}
EXPORT_SYMBOL_GPL(cpus_read_unlock);

void cpus_write_lock(void)
{
    percpu_down_write(&cpu_hotplug_lock);
}

void cpus_write_unlock(void)
{
    percpu_up_write(&cpu_hotplug_lock);
}

void lockdep_assert_cpus_held(void)
{
    /*
     * We can't have hotplug operations before userspace starts running,
     * and some init codepaths will knowingly not take the hotplug lock.
     * This is all valid, so mute lockdep until it makes sense to report
     * unheld locks.
     */
    if (system_state < SYSTEM_RUNNING) {
        return;
    }

    percpu_rwsem_assert_held(&cpu_hotplug_lock);
}

static void lockdep_acquire_cpus_lock(void)
{
    rwsem_acquire(&cpu_hotplug_lock.dep_map, 0, 0, _THIS_IP_);
}

static void lockdep_release_cpus_lock(void)
{
    rwsem_release(&cpu_hotplug_lock.dep_map, _THIS_IP_);
}

/*
 * Wait for currently running CPU hotplug operations to complete (if any) and
 * disable future CPU hotplug (from sysfs). The 'cpu_add_remove_lock' protects
 * the 'cpu_hotplug_disabled' flag. The same lock is also acquired by the
 * hotplug path before performing hotplug operations. So acquiring that lock
 * guarantees mutual exclusion from any currently running hotplug operations.
 */
void cpu_hotplug_disable(void)
{
    cpu_maps_update_begin();
    cpu_hotplug_disabled++;
    cpu_maps_update_done();
}
EXPORT_SYMBOL_GPL(cpu_hotplug_disable);

static void _cpu_hotplug_enable(void)
{
    if (WARN_ONCE(!cpu_hotplug_disabled, "Unbalanced cpu hotplug enable\n")) {
        return;
    }
    cpu_hotplug_disabled--;
}

void cpu_hotplug_enable(void)
{
    cpu_maps_update_begin();
    _cpu_hotplug_enable();
    cpu_maps_update_done();
}
EXPORT_SYMBOL_GPL(cpu_hotplug_enable);

#else

static void lockdep_acquire_cpus_lock(void)
{
}

static void lockdep_release_cpus_lock(void)
{
}

#endif /* CONFIG_HOTPLUG_CPU */

/*
 * Architectures that need SMT-specific errata handling during SMT hotplug
 * should override this.
 */
void __weak arch_smt_update(void)
{
}

#ifdef CONFIG_HOTPLUG_SMT
enum cpuhp_smt_control cpu_smt_control __read_mostly = CPU_SMT_ENABLED;

void __init cpu_smt_disable(bool force)
{
    if (!cpu_smt_possible()) {
        return;
    }

    if (force) {
        pr_info("SMT: Force disabled\n");
        cpu_smt_control = CPU_SMT_FORCE_DISABLED;
    } else {
        pr_info("SMT: disabled\n");
        cpu_smt_control = CPU_SMT_DISABLED;
    }
}

/*
 * The decision whether SMT is supported can only be done after the full
 * CPU identification. Called from architecture code.
 */
void __init cpu_smt_check_topology(void)
{
    if (!topology_smt_supported()) {
        cpu_smt_control = CPU_SMT_NOT_SUPPORTED;
    }
}

static int __init smt_cmdline_disable(char *str)
{
    cpu_smt_disable(str && !strcmp(str, "force"));
    return 0;
}
early_param("nosmt", smt_cmdline_disable);

static inline bool cpu_smt_allowed(unsigned int cpu)
{
    if (cpu_smt_control == CPU_SMT_ENABLED) {
        return true;
    }

    if (topology_is_primary_thread(cpu)) {
        return true;
    }

    /*
     * On x86 it's required to boot all logical CPUs at least once so
     * that the init code can get a chance to set CR4.MCE on each
     * CPU. Otherwise, a broadcasted MCE observing CR4.MCE=0b on any
     * core will shutdown the machine.
     */
    return !cpumask_test_cpu(cpu, &cpus_booted_once_mask);
}

/* Returns true if SMT is not supported of forcefully (irreversibly) disabled */
bool cpu_smt_possible(void)
{
    return cpu_smt_control != CPU_SMT_FORCE_DISABLED && cpu_smt_control != CPU_SMT_NOT_SUPPORTED;
}
EXPORT_SYMBOL_GPL(cpu_smt_possible);
#else
static inline bool cpu_smt_allowed(unsigned int cpu)
{
    return true;
}
#endif

static inline enum cpuhp_state cpuhp_set_state(struct cpuhp_cpu_state *st, enum cpuhp_state target)
{
    enum cpuhp_state prev_state = st->state;

    st->rollback = false;
    st->last = NULL;

    st->target = target;
    st->single = false;
    st->bringup = st->state < target;

    return prev_state;
}

static inline void cpuhp_reset_state(struct cpuhp_cpu_state *st, enum cpuhp_state prev_state)
{
    st->rollback = true;

    /*
     * If we have st->last we need to undo partial multi_instance of this
     * state first. Otherwise start undo at the previous state.
     */
    if (!st->last) {
        if (st->bringup) {
            st->state--;
        } else {
            st->state++;
        }
    }

    st->target = prev_state;
    st->bringup = !st->bringup;
}

/* Regular hotplug invocation of the AP hotplug thread */
static void _cpuhp_kick_ap(struct cpuhp_cpu_state *st)
{
    if (!st->single && st->state == st->target) {
        return;
    }

    st->result = 0;
    /*
     * Make sure the above stores are visible before should_run becomes
     * true. Paired with the mb() above in cpuhp_thread_fun()
     */
    smp_mb();
    st->should_run = true;
    wake_up_process(st->thread);
    wait_for_ap_thread(st, st->bringup);
}

static int cpuhp_kick_ap(struct cpuhp_cpu_state *st, enum cpuhp_state target)
{
    enum cpuhp_state prev_state;
    int ret;

    prev_state = cpuhp_set_state(st, target);
    _cpuhp_kick_ap(st);
    if ((ret = st->result)) {
        cpuhp_reset_state(st, prev_state);
        _cpuhp_kick_ap(st);
    }

    return ret;
}

static int bringup_wait_for_ap(unsigned int cpu)
{
    struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);

    /* Wait for the CPU to reach CPUHP_AP_ONLINE_IDLE */
    wait_for_ap_thread(st, true);
    if (WARN_ON_ONCE((!cpu_online(cpu)))) {
        return -ECANCELED;
    }

    /* Unpark the hotplug thread of the target cpu */
    kthread_unpark(st->thread);

    /*
     * SMT soft disabling on X86 requires to bring the CPU out of the
     * BIOS 'wait for SIPI' state in order to set the CR4.MCE bit.  The
     * CPU marked itself as booted_once in notify_cpu_starting() so the
     * cpu_smt_allowed() check will now return false if this is not the
     * primary sibling.
     */
    if (!cpu_smt_allowed(cpu)) {
        return -ECANCELED;
    }

    if (st->target <= CPUHP_AP_ONLINE_IDLE) {
        return 0;
    }

    return cpuhp_kick_ap(st, st->target);
}

static int bringup_cpu(unsigned int cpu)
{
    struct task_struct *idle = idle_thread_get(cpu);
    int ret;

    /*
     * Reset stale stack state from the last time this CPU was online.
     */
    scs_task_reset(idle);
    kasan_unpoison_task_stack(idle);

    /*
     * Some architectures have to walk the irq descriptors to
     * setup the vector space for the cpu which comes online.
     * Prevent irq alloc/free across the bringup.
     */
    irq_lock_sparse();

    /* Arch-specific enabling code. */
    ret = __cpu_up(cpu, idle);
    irq_unlock_sparse();
    if (ret) {
        return ret;
    }
    return bringup_wait_for_ap(cpu);
}

static int finish_cpu(unsigned int cpu)
{
    struct task_struct *idle = idle_thread_get(cpu);
    struct mm_struct *mm = idle->active_mm;

    /*
     * idle_task_exit() will have switched to &init_mm, now
     * clean up any remaining active_mm state.
     */
    if (mm != &init_mm) {
        idle->active_mm = &init_mm;
    }
    mmdrop(mm);
    return 0;
}

/*
 * Hotplug state machine related functions
 */

static void undo_cpu_up(unsigned int cpu, struct cpuhp_cpu_state *st)
{
    for (st->state--; st->state > st->target; st->state--) {
        cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
    }
}

static inline bool can_rollback_cpu(struct cpuhp_cpu_state *st)
{
    if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
        return true;
    }
    /*
     * When CPU hotplug is disabled, then taking the CPU down is not
     * possible because takedown_cpu() and the architecture and
     * subsystem specific mechanisms are not available. So the CPU
     * which would be completely unplugged again needs to stay around
     * in the current state.
     */
    return st->state <= CPUHP_BRINGUP_CPU;
}

static int cpuhp_up_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st, enum cpuhp_state target)
{
    enum cpuhp_state prev_state = st->state;
    int ret = 0;

    while (st->state < target) {
        st->state++;
        ret = cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
        if (ret) {
            if (can_rollback_cpu(st)) {
                st->target = prev_state;
                undo_cpu_up(cpu, st);
            }
            break;
        }
    }
    return ret;
}

/*
 * The cpu hotplug threads manage the bringup and teardown of the cpus
 */
static void cpuhp_create(unsigned int cpu)
{
    struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);

    init_completion(&st->done_up);
    init_completion(&st->done_down);
}

static int cpuhp_should_run(unsigned int cpu)
{
    struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);

    return st->should_run;
}

/*
 * Execute teardown/startup callbacks on the plugged cpu. Also used to invoke
 * callbacks when a state gets [un]installed at runtime.
 *
 * Each invocation of this function by the smpboot thread does a single AP
 * state callback.
 *
 * It has 3 modes of operation:
 *  - single: runs st->cb_state
 *  - up:     runs ++st->state, while st->state < st->target
 *  - down:   runs st->state--, while st->state > st->target
 *
 * When complete or on error, should_run is cleared and the completion is fired.
 */
static void cpuhp_thread_fun(unsigned int cpu)
{
    struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
    bool bringup = st->bringup;
    enum cpuhp_state state;

    if (WARN_ON_ONCE(!st->should_run)) {
        return;
    }

    /*
     * ACQUIRE for the cpuhp_should_run() load of ->should_run. Ensures
     * that if we see ->should_run we also see the rest of the state.
     */
    smp_mb();

    /*
     * The BP holds the hotplug lock, but we're now running on the AP,
     * ensure that anybody asserting the lock is held, will actually find
     * it so.
     */
    lockdep_acquire_cpus_lock();
    cpuhp_lock_acquire(bringup);

    if (st->single) {
        state = st->cb_state;
        st->should_run = false;
    } else {
        if (bringup) {
            st->state++;
            state = st->state;
            st->should_run = (st->state < st->target);
            WARN_ON_ONCE(st->state > st->target);
        } else {
            state = st->state;
            st->state--;
            st->should_run = (st->state > st->target);
            WARN_ON_ONCE(st->state < st->target);
        }
    }

    WARN_ON_ONCE(!cpuhp_is_ap_state(state));

    if (cpuhp_is_atomic_state(state)) {
        local_irq_disable();
        st->result = cpuhp_invoke_callback(cpu, state, bringup, st->node, &st->last);
        local_irq_enable();

        /*
         * STARTING/DYING must not fail!
         */
        WARN_ON_ONCE(st->result);
    } else {
        st->result = cpuhp_invoke_callback(cpu, state, bringup, st->node, &st->last);
    }

    if (st->result) {
        /*
         * If we fail on a rollback, we're up a creek without no
         * paddle, no way forward, no way back. We loose, thanks for
         * playing.
         */
        WARN_ON_ONCE(st->rollback);
        st->should_run = false;
    }

    cpuhp_lock_release(bringup);
    lockdep_release_cpus_lock();

    if (!st->should_run) {
        complete_ap_thread(st, bringup);
    }
}

/* Invoke a single callback on a remote cpu */
static int cpuhp_invoke_ap_callback(int cpu, enum cpuhp_state state, bool bringup, struct hlist_node *node)
{
    struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    int ret;

    if (!cpu_online(cpu)) {
        return 0;
    }

    cpuhp_lock_acquire(false);
    cpuhp_lock_release(false);

    cpuhp_lock_acquire(true);
    cpuhp_lock_release(true);

    /*
     * If we are up and running, use the hotplug thread. For early calls
     * we invoke the thread function directly.
     */
    if (!st->thread) {
        return cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
    }

    st->rollback = false;
    st->last = NULL;

    st->node = node;
    st->bringup = bringup;
    st->cb_state = state;
    st->single = true;

    _cpuhp_kick_ap(st);

    /*
     * If we failed and did a partial, do a rollback.
     */
    if ((ret = st->result) && st->last) {
        st->rollback = true;
        st->bringup = !bringup;

        _cpuhp_kick_ap(st);
    }

    /*
     * Clean up the leftovers so the next hotplug operation wont use stale
     * data.
     */
    st->node = st->last = NULL;
    return ret;
}

static int cpuhp_kick_ap_work(unsigned int cpu)
{
    struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    enum cpuhp_state prev_state = st->state;
    int ret;

    cpuhp_lock_acquire(false);
    cpuhp_lock_release(false);

    cpuhp_lock_acquire(true);
    cpuhp_lock_release(true);

    trace_cpuhp_enter(cpu, st->target, prev_state, cpuhp_kick_ap_work);
    ret = cpuhp_kick_ap(st, st->target);
    trace_cpuhp_exit(cpu, st->state, prev_state, ret);

    return ret;
}

static struct smp_hotplug_thread cpuhp_threads = {
    .store = &cpuhp_state.thread,
    .create = &cpuhp_create,
    .thread_should_run = cpuhp_should_run,
    .thread_fn = cpuhp_thread_fun,
    .thread_comm = "cpuhp/%u",
    .selfparking = true,
};

void __init cpuhp_threads_init(void)
{
    BUG_ON(smpboot_register_percpu_thread(&cpuhp_threads));
    kthread_unpark(this_cpu_read(cpuhp_state.thread));
}

/*
 *
 * Serialize hotplug trainwrecks outside of the cpu_hotplug_lock
 * protected region.
 *
 * The operation is still serialized against concurrent CPU hotplug via
 * cpu_add_remove_lock, i.e. CPU map protection.  But it is _not_
 * serialized against other hotplug related activity like adding or
 * removing of state callbacks and state instances, which invoke either the
 * startup or the teardown callback of the affected state.
 *
 * This is required for subsystems which are unfixable vs. CPU hotplug and
 * evade lock inversion problems by scheduling work which has to be
 * completed _before_ cpu_up()/_cpu_down() returns.
 *
 * Don't even think about adding anything to this for any new code or even
 * drivers. It's only purpose is to keep existing lock order trainwrecks
 * working.
 *
 * For cpu_down() there might be valid reasons to finish cleanups which are
 * not required to be done under cpu_hotplug_lock, but that's a different
 * story and would be not invoked via this.
 */
static void cpu_up_down_serialize_trainwrecks(bool tasks_frozen)
{
    /*
     * cpusets delegate hotplug operations to a worker to "solve" the
     * lock order problems. Wait for the worker, but only if tasks are
     * _not_ frozen (suspend, hibernate) as that would wait forever.
     *
     * The wait is required because otherwise the hotplug operation
     * returns with inconsistent state, which could even be observed in
     * user space when a new CPU is brought up. The CPU plug uevent
     * would be delivered and user space reacting on it would fail to
     * move tasks to the newly plugged CPU up to the point where the
     * work has finished because up to that point the newly plugged CPU
     * is not assignable in cpusets/cgroups. On unplug that's not
     * necessarily a visible issue, but it is still inconsistent state,
     * which is the real problem which needs to be "fixed". This can't
     * prevent the transient state between scheduling the work and
     * returning from waiting for it.
     */
    if (!tasks_frozen) {
        cpuset_wait_for_hotplug();
    }
}

#ifdef CONFIG_HOTPLUG_CPU
#ifndef arch_clear_mm_cpumask_cpu
#define arch_clear_mm_cpumask_cpu(cpu, mm) cpumask_clear_cpu(cpu, mm_cpumask(mm))
#endif

/**
 * clear_tasks_mm_cpumask - Safely clear tasks' mm_cpumask for a CPU
 * @cpu: a CPU id
 *
 * This function walks all processes, finds a valid mm struct for each one and
 * then clears a corresponding bit in mm's cpumask.  While this all sounds
 * trivial, there are various non-obvious corner cases, which this function
 * tries to solve in a safe manner.
 *
 * Also note that the function uses a somewhat relaxed locking scheme, so it may
 * be called only for an already offlined CPU.
 */
void clear_tasks_mm_cpumask(int cpu)
{
    struct task_struct *p;

    /*
     * This function is called after the cpu is taken down and marked
     * offline, so its not like new tasks will ever get this cpu set in
     * their mm mask. -- Peter Zijlstra
     * Thus, we may use rcu_read_lock() here, instead of grabbing
     * full-fledged tasklist_lock.
     */
    WARN_ON(cpu_online(cpu));
    rcu_read_lock();
    for_each_process(p)
    {
        struct task_struct *t;

        /*
         * Main thread might exit, but other threads may still have
         * a valid mm. Find one.
         */
        t = find_lock_task_mm(p);
        if (!t) {
            continue;
        }
        arch_clear_mm_cpumask_cpu(cpu, t->mm);
        task_unlock(t);
    }
    rcu_read_unlock();
}

/* Take this CPU down. */
static int take_cpu_down(void *_param)
{
    struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
    enum cpuhp_state target = max((int)st->target, CPUHP_AP_OFFLINE);
    int err, cpu = smp_processor_id();
    int ret;

    /* Ensure this CPU doesn't handle any more interrupts. */
    err = __cpu_disable();
    if (err < 0) {
        return err;
    }

    /*
     * We get here while we are in CPUHP_TEARDOWN_CPU state and we must not
     * do this step again.
     */
    WARN_ON(st->state != CPUHP_TEARDOWN_CPU);
    st->state--;
    /* Invoke the former CPU_DYING callbacks */
    for (; st->state > target; st->state--) {
        ret = cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
        /*
         * DYING must not fail!
         */
        WARN_ON_ONCE(ret);
    }

    /* Give up timekeeping duties */
    tick_handover_do_timer();
    /* Remove CPU from timer broadcasting */
    tick_offline_cpu(cpu);
    /* Park the stopper thread */
    stop_machine_park(cpu);
    return 0;
}

static int takedown_cpu(unsigned int cpu)
{
    struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    int err;

    /* Park the smpboot threads */
    kthread_park(per_cpu_ptr(&cpuhp_state, cpu)->thread);

    /*
     * Prevent irq alloc/free while the dying cpu reorganizes the
     * interrupt affinities.
     */
    irq_lock_sparse();

    /*
     * So now all preempt/rcu users must observe !cpu_active().
     */
    err = stop_machine_cpuslocked(take_cpu_down, NULL, cpumask_of(cpu));
    if (err) {
        /* CPU refused to die */
        irq_unlock_sparse();
        /* Unpark the hotplug thread so we can rollback there */
        kthread_unpark(per_cpu_ptr(&cpuhp_state, cpu)->thread);
        return err;
    }
    BUG_ON(cpu_online(cpu));

    /*
     * The teardown callback for CPUHP_AP_SCHED_STARTING will have removed
     * all runnable tasks from the CPU, there's only the idle task left now
     * that the migration thread is done doing the stop_machine thing.
     *
     * Wait for the stop thread to go away.
     */
    wait_for_ap_thread(st, false);
    BUG_ON(st->state != CPUHP_AP_IDLE_DEAD);

    /* Interrupts are moved away from the dying cpu, reenable alloc/free */
    irq_unlock_sparse();

    hotplug_cpu__broadcast_tick_pull(cpu);
    /* This actually kills the CPU. */
    __cpu_die(cpu);

    tick_cleanup_dead_cpu(cpu);
    rcutree_migrate_callbacks(cpu);
    return 0;
}

static void cpuhp_complete_idle_dead(void *arg)
{
    struct cpuhp_cpu_state *st = arg;

    complete_ap_thread(st, false);
}

void cpuhp_report_idle_dead(void)
{
    struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);

    BUG_ON(st->state != CPUHP_AP_OFFLINE);
    rcu_report_dead(smp_processor_id());
    st->state = CPUHP_AP_IDLE_DEAD;
    /*
     * We cannot call complete after rcu_report_dead() so we delegate it
     * to an online cpu.
     */
    smp_call_function_single(cpumask_first(cpu_online_mask), cpuhp_complete_idle_dead, st, 0);
}

static void undo_cpu_down(unsigned int cpu, struct cpuhp_cpu_state *st)
{
    for (st->state++; st->state < st->target; st->state++) {
        cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
    }
}

static int cpuhp_down_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st, enum cpuhp_state target)
{
    enum cpuhp_state prev_state = st->state;
    int ret = 0;

    for (; st->state > target; st->state--) {
        ret = cpuhp_invoke_callback(cpu, st->state, false, NULL, NULL);
        if (ret) {
            st->target = prev_state;
            if (st->state < prev_state) {
                undo_cpu_down(cpu, st);
            }
            break;
        }
    }
    return ret;
}

/* Requires cpu_add_remove_lock to be held */
static int __ref _cpu_down(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
{
    struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    int prev_state, ret = 0;

    if (num_active_cpus() == 1 && cpu_active(cpu)) {
        return -EBUSY;
    }

    if (!cpu_present(cpu)) {
        return -EINVAL;
    }

#ifdef CONFIG_CPU_ISOLATION_OPT
    if (!tasks_frozen && !cpu_isolated(cpu) && num_online_uniso_cpus() == 1) {
        return -EBUSY;
    }
#endif

    cpus_write_lock();

    cpuhp_tasks_frozen = tasks_frozen;

    prev_state = cpuhp_set_state(st, target);
    /*
     * If the current CPU state is in the range of the AP hotplug thread,
     * then we need to kick the thread.
     */
    if (st->state > CPUHP_TEARDOWN_CPU) {
        st->target = max((int)target, CPUHP_TEARDOWN_CPU);
        ret = cpuhp_kick_ap_work(cpu);
        /*
         * The AP side has done the error rollback already. Just
         * return the error code..
         */
        if (ret) {
            goto out;
        }

        /*
         * We might have stopped still in the range of the AP hotplug
         * thread. Nothing to do anymore.
         */
        if (st->state > CPUHP_TEARDOWN_CPU) {
            goto out;
        }

        st->target = target;
    }
    /*
     * The AP brought itself down to CPUHP_TEARDOWN_CPU. So we need
     * to do the further cleanups.
     */
    ret = cpuhp_down_callbacks(cpu, st, target);
    if (ret && st->state == CPUHP_TEARDOWN_CPU && st->state < prev_state) {
        cpuhp_reset_state(st, prev_state);
        _cpuhp_kick_ap(st);
    }

out:
    cpus_write_unlock();
    /*
     * Do post unplug cleanup. This is still protected against
     * concurrent CPU hotplug via cpu_add_remove_lock.
     */
    lockup_detector_cleanup();
    arch_smt_update();
    cpu_up_down_serialize_trainwrecks(tasks_frozen);
    return ret;
}

static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
{
    if (cpu_hotplug_disabled) {
        return -EBUSY;
    }
    return _cpu_down(cpu, 0, target);
}

static int cpu_down(unsigned int cpu, enum cpuhp_state target)
{
    int err;

    cpu_maps_update_begin();
    err = cpu_down_maps_locked(cpu, target);
    cpu_maps_update_done();
    return err;
}

/**
 * cpu_device_down - Bring down a cpu device
 * @dev: Pointer to the cpu device to offline
 *
 * This function is meant to be used by device core cpu subsystem only.
 *
 * Other subsystems should use remove_cpu() instead.
 */
int cpu_device_down(struct device *dev)
{
    return cpu_down(dev->id, CPUHP_OFFLINE);
}

int remove_cpu(unsigned int cpu)
{
    int ret;

    lock_device_hotplug();
    ret = device_offline(get_cpu_device(cpu));
    unlock_device_hotplug();

    return ret;
}
EXPORT_SYMBOL_GPL(remove_cpu);

void smp_shutdown_nonboot_cpus(unsigned int primary_cpu)
{
    unsigned int cpu;
    int error;

    cpu_maps_update_begin();

    /*
     * Make certain the cpu I'm about to reboot on is online.
     *
     * This is inline to what migrate_to_reboot_cpu() already do.
     */
    if (!cpu_online(primary_cpu)) {
        primary_cpu = cpumask_first(cpu_online_mask);
    }

    for_each_online_cpu(cpu)
    {
        if (cpu == primary_cpu) {
            continue;
        }

        error = cpu_down_maps_locked(cpu, CPUHP_OFFLINE);
        if (error) {
            pr_err("Failed to offline CPU%d - error=%d", cpu, error);
            break;
        }
    }

    /*
     * Ensure all but the reboot CPU are offline.
     */
    BUG_ON(num_online_cpus() > 1);

    /*
     * Make sure the CPUs won't be enabled by someone else after this
     * point. Kexec will reboot to a new kernel shortly resetting
     * everything along the way.
     */
    cpu_hotplug_disabled++;

    cpu_maps_update_done();
}

#else
#define takedown_cpu NULL
#endif /* CONFIG_HOTPLUG_CPU */

/**
 * notify_cpu_starting(cpu) - Invoke the callbacks on the starting CPU
 * @cpu: cpu that just started
 *
 * It must be called by the arch code on the new cpu, before the new cpu
 * enables interrupts and before the "boot" cpu returns from __cpu_up().
 */
void notify_cpu_starting(unsigned int cpu)
{
    struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    enum cpuhp_state target = min((int)st->target, CPUHP_AP_ONLINE);
    int ret;

    rcu_cpu_starting(cpu); /* Enables RCU usage on this CPU. */
    cpumask_set_cpu(cpu, &cpus_booted_once_mask);
    while (st->state < target) {
        st->state++;
        ret = cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
        /*
         * STARTING must not fail!
         */
        WARN_ON_ONCE(ret);
    }
}

/*
 * Called from the idle task. Wake up the controlling task which brings the
 * hotplug thread of the upcoming CPU up and then delegates the rest of the
 * online bringup to the hotplug thread.
 */
void cpuhp_online_idle(enum cpuhp_state state)
{
    struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);

    /* Happens for the boot cpu */
    if (state != CPUHP_AP_ONLINE_IDLE) {
        return;
    }

    /*
     * Unpart the stopper thread before we start the idle loop (and start
     * scheduling); this ensures the stopper task is always available.
     */
    stop_machine_unpark(smp_processor_id());

    st->state = CPUHP_AP_ONLINE_IDLE;
    complete_ap_thread(st, true);
}

/* Requires cpu_add_remove_lock to be held */
static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
{
    struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
    struct task_struct *idle;
    int ret = 0;

    cpus_write_lock();

    if (!cpu_present(cpu)) {
        ret = -EINVAL;
        goto out;
    }

    /*
     * The caller of cpu_up() might have raced with another
     * caller. Nothing to do.
     */
    if (st->state >= target) {
        goto out;
    }

    if (st->state == CPUHP_OFFLINE) {
        /* Let it fail before we try to bring the cpu up */
        idle = idle_thread_get(cpu);
        if (IS_ERR(idle)) {
            ret = PTR_ERR(idle);
            goto out;
        }
    }

    cpuhp_tasks_frozen = tasks_frozen;

    cpuhp_set_state(st, target);
    /*
     * If the current CPU state is in the range of the AP hotplug thread,
     * then we need to kick the thread once more.
     */
    if (st->state > CPUHP_BRINGUP_CPU) {
        ret = cpuhp_kick_ap_work(cpu);
        /*
         * The AP side has done the error rollback already. Just
         * return the error code..
         */
        if (ret) {
            goto out;
        }
    }

    /*
     * Try to reach the target state. We max out on the BP at
     * CPUHP_BRINGUP_CPU. After that the AP hotplug thread is
     * responsible for bringing it up to the target state.
     */
    target = min((int)target, CPUHP_BRINGUP_CPU);
    ret = cpuhp_up_callbacks(cpu, st, target);
out:
    cpus_write_unlock();
    arch_smt_update();
    cpu_up_down_serialize_trainwrecks(tasks_frozen);
    return ret;
}

static int cpu_up(unsigned int cpu, enum cpuhp_state target)
{
    int err = 0;

    if (!cpu_possible(cpu)) {
        pr_err("can't online cpu %d because it is not configured as may-hotadd at boot time\n", cpu);
#if defined(CONFIG_IA64)
        pr_err("please check additional_cpus= boot parameter\n");
#endif
        return -EINVAL;
    }

    err = try_online_node(cpu_to_node(cpu));
    if (err) {
        return err;
    }

    cpu_maps_update_begin();

    if (cpu_hotplug_disabled) {
        err = -EBUSY;
        goto out;
    }
    if (!cpu_smt_allowed(cpu)) {
        err = -EPERM;
        goto out;
    }

    err = _cpu_up(cpu, 0, target);
out:
    cpu_maps_update_done();
    return err;
}

/**
 * cpu_device_up - Bring up a cpu device
 * @dev: Pointer to the cpu device to online
 *
 * This function is meant to be used by device core cpu subsystem only.
 *
 * Other subsystems should use add_cpu() instead.
 */
int cpu_device_up(struct device *dev)
{
    return cpu_up(dev->id, CPUHP_ONLINE);
}

int add_cpu(unsigned int cpu)
{
    int ret;

    lock_device_hotplug();
    ret = device_online(get_cpu_device(cpu));
    unlock_device_hotplug();

    return ret;
}
EXPORT_SYMBOL_GPL(add_cpu);

/**
 * bringup_hibernate_cpu - Bring up the CPU that we hibernated on
 * @sleep_cpu: The cpu we hibernated on and should be brought up.
 *
 * On some architectures like arm64, we can hibernate on any CPU, but on
 * wake up the CPU we hibernated on might be offline as a side effect of
 * using maxcpus= for example.
 */
int bringup_hibernate_cpu(unsigned int sleep_cpu)
{
    int ret;

    if (!cpu_online(sleep_cpu)) {
        pr_info("Hibernated on a CPU that is offline! Bringing CPU up.\n");
        ret = cpu_up(sleep_cpu, CPUHP_ONLINE);
        if (ret) {
            pr_err("Failed to bring hibernate-CPU up!\n");
            return ret;
        }
    }
    return 0;
}

void bringup_nonboot_cpus(unsigned int setup_max_cpus)
{
    unsigned int cpu;

    for_each_present_cpu(cpu)
    {
        if (num_online_cpus() >= setup_max_cpus) {
            break;
        }
        if (!cpu_online(cpu)) {
            cpu_up(cpu, CPUHP_ONLINE);
        }
    }
}

#ifdef CONFIG_PM_SLEEP_SMP
static cpumask_var_t frozen_cpus;

int freeze_secondary_cpus(int primary)
{
    int cpu, error = 0;

    cpu_maps_update_begin();
    if (primary == -1) {
        primary = cpumask_first(cpu_online_mask);
        if (!housekeeping_cpu(primary, HK_FLAG_TIMER)) {
            primary = housekeeping_any_cpu(HK_FLAG_TIMER);
        }
    } else {
        if (!cpu_online(primary)) {
            primary = cpumask_first(cpu_online_mask);
        }
    }

    /*
     * We take down all of the non-boot CPUs in one shot to avoid races
     * with the userspace trying to use the CPU hotplug at the same time
     */
    cpumask_clear(frozen_cpus);

    pr_info("Disabling non-boot CPUs ...\n");
    for_each_online_cpu(cpu)
    {
        if (cpu == primary) {
            continue;
        }

        if (pm_wakeup_pending()) {
            pr_info("Wakeup pending. Abort CPU freeze\n");
            error = -EBUSY;
            break;
        }

        trace_suspend_resume(TPS("CPU_OFF"), cpu, true);
        error = _cpu_down(cpu, 1, CPUHP_OFFLINE);
        trace_suspend_resume(TPS("CPU_OFF"), cpu, false);
        if (!error) {
            cpumask_set_cpu(cpu, frozen_cpus);
        } else {
            pr_err("Error taking CPU%d down: %d\n", cpu, error);
            break;
        }
    }

    if (!error) {
        BUG_ON(num_online_cpus() > 1);
    } else {
        pr_err("Non-boot CPUs are not disabled\n");
    }

    /*
     * Make sure the CPUs won't be enabled by someone else. We need to do
     * this even in case of failure as all freeze_secondary_cpus() users are
     * supposed to do thaw_secondary_cpus() on the failure path.
     */
    cpu_hotplug_disabled++;

    cpu_maps_update_done();
    return error;
}

void __weak arch_thaw_secondary_cpus_begin(void)
{
}

void __weak arch_thaw_secondary_cpus_end(void)
{
}

void thaw_secondary_cpus(void)
{
    int cpu, error;

    /* Allow everyone to use the CPU hotplug again */
    cpu_maps_update_begin();
    _cpu_hotplug_enable();
    if (cpumask_empty(frozen_cpus)) {
        goto out;
    }

    pr_info("Enabling non-boot CPUs ...\n");

    arch_thaw_secondary_cpus_begin();

    for_each_cpu(cpu, frozen_cpus)
    {
        trace_suspend_resume(TPS("CPU_ON"), cpu, true);
        error = _cpu_up(cpu, 1, CPUHP_ONLINE);
        trace_suspend_resume(TPS("CPU_ON"), cpu, false);
        if (!error) {
            pr_info("CPU%d is up\n", cpu);
            continue;
        }
        pr_warn("Error taking CPU%d up: %d\n", cpu, error);
    }

    arch_thaw_secondary_cpus_end();

    cpumask_clear(frozen_cpus);
out:
    cpu_maps_update_done();
}

static int __init alloc_frozen_cpus(void)
{
    if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL | __GFP_ZERO)) {
        return -ENOMEM;
    }
    return 0;
}
core_initcall(alloc_frozen_cpus);

/*
 * When callbacks for CPU hotplug notifications are being executed, we must
 * ensure that the state of the system with respect to the tasks being frozen
 * or not, as reported by the notification, remains unchanged *throughout the
 * duration* of the execution of the callbacks.
 * Hence we need to prevent the freezer from racing with regular CPU hotplug.
 *
 * This synchronization is implemented by mutually excluding regular CPU
 * hotplug and Suspend/Hibernate call paths by hooking onto the Suspend/
 * Hibernate notifications.
 */
static int cpu_hotplug_pm_callback(struct notifier_block *nb, unsigned long action, void *ptr)
{
    switch (action) {
        case PM_SUSPEND_PREPARE:
        case PM_HIBERNATION_PREPARE:
            cpu_hotplug_disable();
            break;

        case PM_POST_SUSPEND:
        case PM_POST_HIBERNATION:
            cpu_hotplug_enable();
            break;

        default:
            return NOTIFY_DONE;
    }

    return NOTIFY_OK;
}

static int __init cpu_hotplug_pm_sync_init(void)
{
    /*
     * cpu_hotplug_pm_callback has higher priority than x86
     * bsp_pm_callback which depends on cpu_hotplug_pm_callback
     * to disable cpu hotplug to avoid cpu hotplug race.
     */
    pm_notifier(cpu_hotplug_pm_callback, 0);
    return 0;
}
core_initcall(cpu_hotplug_pm_sync_init);

#endif /* CONFIG_PM_SLEEP_SMP */

int __boot_cpu_id;

#endif /* CONFIG_SMP */

/* Boot processor state steps */
static struct cpuhp_step cpuhp_hp_states[] = {
    [CPUHP_OFFLINE] =
        {
            .name = "offline",
            .startup.single = NULL,
            .teardown.single = NULL,
        },
#ifdef CONFIG_SMP
    [CPUHP_CREATE_THREADS] =
        {
            .name = "threads:prepare",
            .startup.single = smpboot_create_threads,
            .teardown.single = NULL,
            .cant_stop = true,
        },
    [CPUHP_PERF_PREPARE] =
        {
            .name = "perf:prepare",
            .startup.single = perf_event_init_cpu,
            .teardown.single = perf_event_exit_cpu,
        },
    [CPUHP_RANDOM_PREPARE] = {
        .name			= "random:prepare",
        .startup.single		= random_prepare_cpu,
        .teardown.single	= NULL,
    },

    [CPUHP_WORKQUEUE_PREP] =
        {
            .name = "workqueue:prepare",
            .startup.single = workqueue_prepare_cpu,
            .teardown.single = NULL,
        },
    [CPUHP_HRTIMERS_PREPARE] =
        {
            .name = "hrtimers:prepare",
            .startup.single = hrtimers_prepare_cpu,
            .teardown.single = hrtimers_dead_cpu,
        },
    [CPUHP_SMPCFD_PREPARE] =
        {
            .name = "smpcfd:prepare",
            .startup.single = smpcfd_prepare_cpu,
            .teardown.single = smpcfd_dead_cpu,
        },
    [CPUHP_RELAY_PREPARE] =
        {
            .name = "relay:prepare",
            .startup.single = relay_prepare_cpu,
            .teardown.single = NULL,
        },
    [CPUHP_SLAB_PREPARE] =
        {
            .name = "slab:prepare",
            .startup.single = slab_prepare_cpu,
            .teardown.single = slab_dead_cpu,
        },
    [CPUHP_RCUTREE_PREP] =
        {
            .name = "RCU/tree:prepare",
            .startup.single = rcutree_prepare_cpu,
            .teardown.single = rcutree_dead_cpu,
        },
    /*
     * On the tear-down path, timers_dead_cpu() must be invoked
     * before blk_mq_queue_reinit_notify() from notify_dead(),
     * otherwise a RCU stall occurs.
     */
    [CPUHP_TIMERS_PREPARE] =
        {
            .name = "timers:prepare",
            .startup.single = timers_prepare_cpu,
            .teardown.single = timers_dead_cpu,
        },
    /* Kicks the plugged cpu into life */
    [CPUHP_BRINGUP_CPU] =
        {
            .name = "cpu:bringup",
            .startup.single = bringup_cpu,
            .teardown.single = finish_cpu,
            .cant_stop = true,
        },
    /* Final state before CPU kills itself */
    [CPUHP_AP_IDLE_DEAD] =
        {
            .name = "idle:dead",
        },
    /*
     * Last state before CPU enters the idle loop to die. Transient state
     * for synchronization.
     */
    [CPUHP_AP_OFFLINE] =
        {
            .name = "ap:offline",
            .cant_stop = true,
        },
    /* First state is scheduler control. Interrupts are disabled */
    [CPUHP_AP_SCHED_STARTING] =
        {
            .name = "sched:starting",
            .startup.single = sched_cpu_starting,
            .teardown.single = sched_cpu_dying,
        },
    [CPUHP_AP_RCUTREE_DYING] =
        {
            .name = "RCU/tree:dying",
            .startup.single = NULL,
            .teardown.single = rcutree_dying_cpu,
        },
    [CPUHP_AP_SMPCFD_DYING] =
        {
            .name = "smpcfd:dying",
            .startup.single = NULL,
            .teardown.single = smpcfd_dying_cpu,
        },
    /* Entry state on starting. Interrupts enabled from here on. Transient
     * state for synchronsization */
    [CPUHP_AP_ONLINE] =
        {
            .name = "ap:online",
        },
    /*
     * Handled on controll processor until the plugged processor manages
     * this itself.
     */
    [CPUHP_TEARDOWN_CPU] =
        {
            .name = "cpu:teardown",
            .startup.single = NULL,
            .teardown.single = takedown_cpu,
            .cant_stop = true,
        },
    /* Handle smpboot threads park/unpark */
    [CPUHP_AP_SMPBOOT_THREADS] =
        {
            .name = "smpboot/threads:online",
            .startup.single = smpboot_unpark_threads,
            .teardown.single = smpboot_park_threads,
        },
    [CPUHP_AP_IRQ_AFFINITY_ONLINE] =
        {
            .name = "irq/affinity:online",
            .startup.single = irq_affinity_online_cpu,
            .teardown.single = NULL,
        },
    [CPUHP_AP_PERF_ONLINE] =
        {
            .name = "perf:online",
            .startup.single = perf_event_init_cpu,
            .teardown.single = perf_event_exit_cpu,
        },
    [CPUHP_AP_WATCHDOG_ONLINE] =
        {
            .name = "lockup_detector:online",
            .startup.single = lockup_detector_online_cpu,
            .teardown.single = lockup_detector_offline_cpu,
        },
    [CPUHP_AP_WORKQUEUE_ONLINE] =
        {
            .name = "workqueue:online",
            .startup.single = workqueue_online_cpu,
            .teardown.single = workqueue_offline_cpu,
        },
    [CPUHP_AP_RANDOM_ONLINE] = {
        .name			= "random:online",
        .startup.single		= random_online_cpu,
        .teardown.single	= NULL,
    },
    [CPUHP_AP_RCUTREE_ONLINE] =
        {
            .name = "RCU/tree:online",
            .startup.single = rcutree_online_cpu,
            .teardown.single = rcutree_offline_cpu,
        },
#endif
/*
 * The dynamically registered state space is here
 */

#ifdef CONFIG_SMP
    /* Last state is scheduler control setting the cpu active */
    [CPUHP_AP_ACTIVE] =
        {
            .name = "sched:active",
            .startup.single = sched_cpu_activate,
            .teardown.single = sched_cpu_deactivate,
        },
#endif

    /* CPU is fully up and running. */
    [CPUHP_ONLINE] =
        {
            .name = "online",
            .startup.single = NULL,
            .teardown.single = NULL,
        },
};

/* Sanity check for callbacks */
static int cpuhp_cb_check(enum cpuhp_state state)
{
    if (state <= CPUHP_OFFLINE || state >= CPUHP_ONLINE) {
        return -EINVAL;
    }
    return 0;
}

/*
 * Returns a free for dynamic slot assignment of the Online state. The states
 * are protected by the cpuhp_slot_states mutex and an empty slot is identified
 * by having no name assigned.
 */
static int cpuhp_reserve_state(enum cpuhp_state state)
{
    enum cpuhp_state i, end;
    struct cpuhp_step *step;

    switch (state) {
        case CPUHP_AP_ONLINE_DYN:
            step = cpuhp_hp_states + CPUHP_AP_ONLINE_DYN;
            end = CPUHP_AP_ONLINE_DYN_END;
            break;
        case CPUHP_BP_PREPARE_DYN:
            step = cpuhp_hp_states + CPUHP_BP_PREPARE_DYN;
            end = CPUHP_BP_PREPARE_DYN_END;
            break;
        default:
            return -EINVAL;
    }

    for (i = state; i <= end; i++, step++) {
        if (!step->name) {
            return i;
        }
    }
    WARN(1, "No more dynamic states available for CPU hotplug\n");
    return -ENOSPC;
}

static int cpuhp_store_callbacks(enum cpuhp_state state, const char *name, int (*startup)(unsigned int cpu),
                                 int (*teardown)(unsigned int cpu), bool multi_instance)
{
    /* (Un)Install the callbacks for further cpu hotplug operations */
    struct cpuhp_step *sp;
    int ret = 0;

    /*
     * If name is NULL, then the state gets removed.
     *
     * CPUHP_AP_ONLINE_DYN and CPUHP_BP_PREPARE_DYN are handed out on
     * the first allocation from these dynamic ranges, so the removal
     * would trigger a new allocation and clear the wrong (already
     * empty) state, leaving the callbacks of the to be cleared state
     * dangling, which causes wreckage on the next hotplug operation.
     */
    if (name && (state == CPUHP_AP_ONLINE_DYN || state == CPUHP_BP_PREPARE_DYN)) {
        ret = cpuhp_reserve_state(state);
        if (ret < 0) {
            return ret;
        }
        state = ret;
    }
    sp = cpuhp_get_step(state);
    if (name && sp->name) {
        return -EBUSY;
    }

    sp->startup.single = startup;
    sp->teardown.single = teardown;
    sp->name = name;
    sp->multi_instance = multi_instance;
    INIT_HLIST_HEAD(&sp->list);
    return ret;
}

static void *cpuhp_get_teardown_cb(enum cpuhp_state state)
{
    return cpuhp_get_step(state)->teardown.single;
}

/*
 * Call the startup/teardown function for a step either on the AP or
 * on the current CPU.
 */
static int cpuhp_issue_call(int cpu, enum cpuhp_state state, bool bringup, struct hlist_node *node)
{
    struct cpuhp_step *sp = cpuhp_get_step(state);
    int ret;

    /*
     * If there's nothing to do, we done.
     * Relies on the union for multi_instance.
     */
    if ((bringup && !sp->startup.single) || (!bringup && !sp->teardown.single)) {
        return 0;
    }
    /*
     * The non AP bound callbacks can fail on bringup. On teardown
     * e.g. module removal we crash for now.
     */
#ifdef CONFIG_SMP
    if (cpuhp_is_ap_state(state)) {
        ret = cpuhp_invoke_ap_callback(cpu, state, bringup, node);
    } else {
        ret = cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
    }
#else
    ret = cpuhp_invoke_callback(cpu, state, bringup, node, NULL);
#endif
    BUG_ON(ret && !bringup);
    return ret;
}

/*
 * Called from __cpuhp_setup_state on a recoverable failure.
 *
 * Note: The teardown callbacks for rollback are not allowed to fail!
 */
static void cpuhp_rollback_install(int failedcpu, enum cpuhp_state state, struct hlist_node *node)
{
    int cpu;

    /* Roll back the already executed steps on the other cpus */
    for_each_present_cpu(cpu)
    {
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
        int cpustate = st->state;

        if (cpu >= failedcpu) {
            break;
        }

        /* Did we invoke the startup call on that cpu ? */
        if (cpustate >= state) {
            cpuhp_issue_call(cpu, state, false, node);
        }
    }
}

int __cpuhp_state_add_instance_cpuslocked(enum cpuhp_state state, struct hlist_node *node, bool invoke)
{
    struct cpuhp_step *sp;
    int cpu;
    int ret;

    lockdep_assert_cpus_held();

    sp = cpuhp_get_step(state);
    if (sp->multi_instance == false) {
        return -EINVAL;
    }

    mutex_lock(&cpuhp_state_mutex);

    if (!invoke || !sp->startup.multi) {
        goto add_node;
    }

    /*
     * Try to call the startup callback for each present cpu
     * depending on the hotplug state of the cpu.
     */
    for_each_present_cpu(cpu)
    {
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
        int cpustate = st->state;

        if (cpustate < state) {
            continue;
        }

        ret = cpuhp_issue_call(cpu, state, true, node);
        if (ret) {
            if (sp->teardown.multi) {
                cpuhp_rollback_install(cpu, state, node);
            }
            goto unlock;
        }
    }
add_node:
    ret = 0;
    hlist_add_head(node, &sp->list);
unlock:
    mutex_unlock(&cpuhp_state_mutex);
    return ret;
}

int __cpuhp_state_add_instance(enum cpuhp_state state, struct hlist_node *node, bool invoke)
{
    int ret;

    cpus_read_lock();
    ret = __cpuhp_state_add_instance_cpuslocked(state, node, invoke);
    cpus_read_unlock();
    return ret;
}
EXPORT_SYMBOL_GPL(__cpuhp_state_add_instance);

/**
 * __cpuhp_setup_state_cpuslocked - Setup the callbacks for an hotplug machine state
 * @state:        The state to setup
 * @invoke:        If true, the startup function is invoked for cpus where
 *            cpu state >= @state
 * @startup:        startup callback function
 * @teardown:        teardown callback function
 * @multi_instance:    State is set up for multiple instances which get
 *            added afterwards.
 *
 * The caller needs to hold cpus read locked while calling this function.
 * Returns:
 *   On success:
 *      Positive state number if @state is CPUHP_AP_ONLINE_DYN
 *      0 for all other states
 *   On failure: proper (negative) error code
 */
int __cpuhp_setup_state_cpuslocked(enum cpuhp_state state, const char *name, bool invoke,
                                   int (*startup)(unsigned int cpu), int (*teardown)(unsigned int cpu),
                                   bool multi_instance)
{
    int cpu, ret = 0;
    bool dynstate;

    lockdep_assert_cpus_held();

    if (cpuhp_cb_check(state) || !name) {
        return -EINVAL;
    }

    mutex_lock(&cpuhp_state_mutex);

    ret = cpuhp_store_callbacks(state, name, startup, teardown, multi_instance);

    dynstate = state == CPUHP_AP_ONLINE_DYN;
    if (ret > 0 && dynstate) {
        state = ret;
        ret = 0;
    }

    if (ret || !invoke || !startup) {
        goto out;
    }

    /*
     * Try to call the startup callback for each present cpu
     * depending on the hotplug state of the cpu.
     */
    for_each_present_cpu(cpu)
    {
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
        int cpustate = st->state;

        if (cpustate < state) {
            continue;
        }

        ret = cpuhp_issue_call(cpu, state, true, NULL);
        if (ret) {
            if (teardown) {
                cpuhp_rollback_install(cpu, state, NULL);
            }
            cpuhp_store_callbacks(state, NULL, NULL, NULL, false);
            goto out;
        }
    }
out:
    mutex_unlock(&cpuhp_state_mutex);
    /*
     * If the requested state is CPUHP_AP_ONLINE_DYN, return the
     * dynamically allocated state in case of success.
     */
    if (!ret && dynstate) {
        return state;
    }
    return ret;
}
EXPORT_SYMBOL(__cpuhp_setup_state_cpuslocked);

int __cpuhp_setup_state(enum cpuhp_state state, const char *name, bool invoke, int (*startup)(unsigned int cpu),
                        int (*teardown)(unsigned int cpu), bool multi_instance)
{
    int ret;

    cpus_read_lock();
    ret = __cpuhp_setup_state_cpuslocked(state, name, invoke, startup, teardown, multi_instance);
    cpus_read_unlock();
    return ret;
}
EXPORT_SYMBOL(__cpuhp_setup_state);

int __cpuhp_state_remove_instance(enum cpuhp_state state, struct hlist_node *node, bool invoke)
{
    struct cpuhp_step *sp = cpuhp_get_step(state);
    int cpu;

    BUG_ON(cpuhp_cb_check(state));

    if (!sp->multi_instance) {
        return -EINVAL;
    }

    cpus_read_lock();
    mutex_lock(&cpuhp_state_mutex);

    if (!invoke || !cpuhp_get_teardown_cb(state)) {
        goto remove;
    }
    /*
     * Call the teardown callback for each present cpu depending
     * on the hotplug state of the cpu. This function is not
     * allowed to fail currently!
     */
    for_each_present_cpu(cpu)
    {
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
        int cpustate = st->state;

        if (cpustate >= state) {
            cpuhp_issue_call(cpu, state, false, node);
        }
    }

remove:
    hlist_del(node);
    mutex_unlock(&cpuhp_state_mutex);
    cpus_read_unlock();

    return 0;
}
EXPORT_SYMBOL_GPL(__cpuhp_state_remove_instance);

/**
 * __cpuhp_remove_state_cpuslocked - Remove the callbacks for an hotplug machine state
 * @state:    The state to remove
 * @invoke:    If true, the teardown function is invoked for cpus where
 *        cpu state >= @state
 *
 * The caller needs to hold cpus read locked while calling this function.
 * The teardown callback is currently not allowed to fail. Think
 * about module removal!
 */
void __cpuhp_remove_state_cpuslocked(enum cpuhp_state state, bool invoke)
{
    struct cpuhp_step *sp = cpuhp_get_step(state);
    int cpu;

    BUG_ON(cpuhp_cb_check(state));

    lockdep_assert_cpus_held();

    mutex_lock(&cpuhp_state_mutex);
    if (sp->multi_instance) {
        WARN(!hlist_empty(&sp->list), "Error: Removing state %d which has instances left.\n", state);
        goto remove;
    }

    if (!invoke || !cpuhp_get_teardown_cb(state)) {
        goto remove;
    }

    /*
     * Call the teardown callback for each present cpu depending
     * on the hotplug state of the cpu. This function is not
     * allowed to fail currently!
     */
    for_each_present_cpu(cpu)
    {
        struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
        int cpustate = st->state;

        if (cpustate >= state) {
            cpuhp_issue_call(cpu, state, false, NULL);
        }
    }
remove:
    cpuhp_store_callbacks(state, NULL, NULL, NULL, false);
    mutex_unlock(&cpuhp_state_mutex);
}
EXPORT_SYMBOL(__cpuhp_remove_state_cpuslocked);

void __cpuhp_remove_state(enum cpuhp_state state, bool invoke)
{
    cpus_read_lock();
    __cpuhp_remove_state_cpuslocked(state, invoke);
    cpus_read_unlock();
}
EXPORT_SYMBOL(__cpuhp_remove_state);

#ifdef CONFIG_HOTPLUG_SMT
static void cpuhp_offline_cpu_device(unsigned int cpu)
{
    struct device *dev = get_cpu_device(cpu);

    dev->offline = true;
    /* Tell user space about the state change */
    kobject_uevent(&dev->kobj, KOBJ_OFFLINE);
}

static void cpuhp_online_cpu_device(unsigned int cpu)
{
    struct device *dev = get_cpu_device(cpu);

    dev->offline = false;
    /* Tell user space about the state change */
    kobject_uevent(&dev->kobj, KOBJ_ONLINE);
}

int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
{
    int cpu, ret = 0;

    cpu_maps_update_begin();
    for_each_online_cpu(cpu)
    {
        if (topology_is_primary_thread(cpu)) {
            continue;
        }
        ret = cpu_down_maps_locked(cpu, CPUHP_OFFLINE);
        if (ret) {
            break;
        }
        /*
         * As this needs to hold the cpu maps lock it's impossible
         * to call device_offline() because that ends up calling
         * cpu_down() which takes cpu maps lock. cpu maps lock
         * needs to be held as this might race against in kernel
         * abusers of the hotplug machinery (thermal management).
         *
         * So nothing would update device:offline state. That would
         * leave the sysfs entry stale and prevent onlining after
         * smt control has been changed to 'off' again. This is
         * called under the sysfs hotplug lock, so it is properly
         * serialized against the regular offline usage.
         */
        cpuhp_offline_cpu_device(cpu);
    }
    if (!ret) {
        cpu_smt_control = ctrlval;
    }
    cpu_maps_update_done();
    return ret;
}

int cpuhp_smt_enable(void)
{
    int cpu, ret = 0;

    cpu_maps_update_begin();
    cpu_smt_control = CPU_SMT_ENABLED;
    for_each_present_cpu(cpu)
    {
        /* Skip online CPUs and CPUs on offline nodes */
        if (cpu_online(cpu) || !node_online(cpu_to_node(cpu))) {
            continue;
        }
        ret = _cpu_up(cpu, 0, CPUHP_ONLINE);
        if (ret) {
            break;
        }
        /* See comment in cpuhp_smt_disable() */
        cpuhp_online_cpu_device(cpu);
    }
    cpu_maps_update_done();
    return ret;
}
#endif

#if defined(CONFIG_SYSFS) && defined(CONFIG_HOTPLUG_CPU)
static ssize_t show_cpuhp_state(struct device *dev, struct device_attribute *attr, char *buf)
{
    struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);

    return sprintf(buf, "%d\n", st->state);
}
static DEVICE_ATTR(state, 0444, show_cpuhp_state, NULL);

static ssize_t write_cpuhp_target(struct device *dev, struct device_attribute *attr, const char *buf, size_t count)
{
    struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
    struct cpuhp_step *sp;
    int target, ret;

    ret = kstrtoint(buf, 10, &target);
    if (ret) {
        return ret;
    }

#ifdef CONFIG_CPU_HOTPLUG_STATE_CONTROL
    if (target < CPUHP_OFFLINE || target > CPUHP_ONLINE) {
        return -EINVAL;
    }
#else
    if (target != CPUHP_OFFLINE && target != CPUHP_ONLINE) {
        return -EINVAL;
    }
#endif

    ret = lock_device_hotplug_sysfs();
    if (ret) {
        return ret;
    }

    mutex_lock(&cpuhp_state_mutex);
    sp = cpuhp_get_step(target);
    ret = !sp->name || sp->cant_stop ? -EINVAL : 0;
    mutex_unlock(&cpuhp_state_mutex);
    if (ret) {
        goto out;
    }

    if (st->state < target) {
        ret = cpu_up(dev->id, target);
    } else {
        ret = cpu_down(dev->id, target);
    }
out:
    unlock_device_hotplug();
    return ret ? ret : count;
}

static ssize_t show_cpuhp_target(struct device *dev, struct device_attribute *attr, char *buf)
{
    struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);

    return sprintf(buf, "%d\n", st->target);
}
static DEVICE_ATTR(target, 0644, show_cpuhp_target, write_cpuhp_target);

static ssize_t write_cpuhp_fail(struct device *dev, struct device_attribute *attr, const char *buf, size_t count)
{
    struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
    struct cpuhp_step *sp;
    int fail, ret;

    ret = kstrtoint(buf, 10, &fail);
    if (ret) {
        return ret;
    }

    if (fail < CPUHP_OFFLINE || fail > CPUHP_ONLINE) {
        return -EINVAL;
    }

    /*
     * Cannot fail STARTING/DYING callbacks.
     */
    if (cpuhp_is_atomic_state(fail)) {
        return -EINVAL;
    }

    /*
     * Cannot fail anything that doesn't have callbacks.
     */
    mutex_lock(&cpuhp_state_mutex);
    sp = cpuhp_get_step(fail);
    if (!sp->startup.single && !sp->teardown.single) {
        ret = -EINVAL;
    }
    mutex_unlock(&cpuhp_state_mutex);
    if (ret) {
        return ret;
    }

    st->fail = fail;

    return count;
}

static ssize_t show_cpuhp_fail(struct device *dev, struct device_attribute *attr, char *buf)
{
    struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);

    return sprintf(buf, "%d\n", st->fail);
}

static DEVICE_ATTR(fail, 0644, show_cpuhp_fail, write_cpuhp_fail);

static struct attribute *cpuhp_cpu_attrs[] = {&dev_attr_state.attr, &dev_attr_target.attr, &dev_attr_fail.attr, NULL};

static const struct attribute_group cpuhp_cpu_attr_group = {.attrs = cpuhp_cpu_attrs, .name = "hotplug", NULL};

static ssize_t show_cpuhp_states(struct device *dev, struct device_attribute *attr, char *buf)
{
    ssize_t cur, res = 0;
    int i;

    mutex_lock(&cpuhp_state_mutex);
    for (i = CPUHP_OFFLINE; i <= CPUHP_ONLINE; i++) {
        struct cpuhp_step *sp = cpuhp_get_step(i);

        if (sp->name) {
            cur = sprintf(buf, "%3d: %s\n", i, sp->name);
            buf += cur;
            res += cur;
        }
    }
    mutex_unlock(&cpuhp_state_mutex);
    return res;
}
static DEVICE_ATTR(states, 0444, show_cpuhp_states, NULL);

static struct attribute *cpuhp_cpu_root_attrs[] = {&dev_attr_states.attr, NULL};

static const struct attribute_group cpuhp_cpu_root_attr_group = {
    .attrs = cpuhp_cpu_root_attrs, .name = "hotplug", NULL};

#ifdef CONFIG_HOTPLUG_SMT

static ssize_t _store_smt_control(struct device *dev, struct device_attribute *attr, const char *buf, size_t count)
{
    int ctrlval, ret;

    if (sysfs_streq(buf, "on")) {
        ctrlval = CPU_SMT_ENABLED;
    } else if (sysfs_streq(buf, "off")) {
        ctrlval = CPU_SMT_DISABLED;
    } else if (sysfs_streq(buf, "forceoff")) {
        ctrlval = CPU_SMT_FORCE_DISABLED;
    } else {
        return -EINVAL;
    }

    if (cpu_smt_control == CPU_SMT_FORCE_DISABLED) {
        return -EPERM;
    }

    if (cpu_smt_control == CPU_SMT_NOT_SUPPORTED) {
        return -ENODEV;
    }

    ret = lock_device_hotplug_sysfs();
    if (ret) {
        return ret;
    }

    if (ctrlval != cpu_smt_control) {
        switch (ctrlval) {
            case CPU_SMT_ENABLED:
                ret = cpuhp_smt_enable();
                break;
            case CPU_SMT_DISABLED:
            case CPU_SMT_FORCE_DISABLED:
                ret = cpuhp_smt_disable(ctrlval);
                break;
        }
    }

    unlock_device_hotplug();
    return ret ? ret : count;
}

#else  /* !CONFIG_HOTPLUG_SMT */
static ssize_t _store_smt_control(struct device *dev, struct device_attribute *attr, const char *buf, size_t count)
{
    return -ENODEV;
}
#endif /* CONFIG_HOTPLUG_SMT */

static const char *smt_states[] = {
    [CPU_SMT_ENABLED] = "on",
    [CPU_SMT_DISABLED] = "off",
    [CPU_SMT_FORCE_DISABLED] = "forceoff",
    [CPU_SMT_NOT_SUPPORTED] = "notsupported",
    [CPU_SMT_NOT_IMPLEMENTED] = "notimplemented",
};

static ssize_t show_smt_control(struct device *dev, struct device_attribute *attr, char *buf)
{
    const char *state = smt_states[cpu_smt_control];

    return snprintf(buf, PAGE_SIZE - CPU_PAGE_SIZE_OFF_TWO, "%s\n", state);
}

static ssize_t store_smt_control(struct device *dev, struct device_attribute *attr, const char *buf, size_t count)
{
    return _store_smt_control(dev, attr, buf, count);
}
static DEVICE_ATTR(control, 0644, show_smt_control, store_smt_control);

static ssize_t show_smt_active(struct device *dev, struct device_attribute *attr, char *buf)
{
    return snprintf(buf, PAGE_SIZE - CPU_PAGE_SIZE_OFF_TWO, "%d\n", sched_smt_active());
}
static DEVICE_ATTR(active, 0444, show_smt_active, NULL);

static struct attribute *cpuhp_smt_attrs[] = {&dev_attr_control.attr, &dev_attr_active.attr, NULL};

static const struct attribute_group cpuhp_smt_attr_group = {.attrs = cpuhp_smt_attrs, .name = "smt", NULL};

static int __init cpu_smt_sysfs_init(void)
{
    return sysfs_create_group(&cpu_subsys.dev_root->kobj, &cpuhp_smt_attr_group);
}

static int __init cpuhp_sysfs_init(void)
{
    int cpu, ret;

    ret = cpu_smt_sysfs_init();
    if (ret) {
        return ret;
    }

    ret = sysfs_create_group(&cpu_subsys.dev_root->kobj, &cpuhp_cpu_root_attr_group);
    if (ret) {
        return ret;
    }

    for_each_possible_cpu(cpu)
    {
        struct device *dev = get_cpu_device(cpu);

        if (!dev) {
            continue;
        }
        ret = sysfs_create_group(&dev->kobj, &cpuhp_cpu_attr_group);
        if (ret) {
            return ret;
        }
    }
    return 0;
}
device_initcall(cpuhp_sysfs_init);
#endif /* CONFIG_SYSFS && CONFIG_HOTPLUG_CPU */

/*
 * cpu_bit_bitmap[] is a special, "compressed" data structure that
 * represents all NR_CPUS bits binary values of 1<<nr.
 *
 * It is used by cpumask_of() to get a constant address to a CPU
 * mask value that has a single bit set only.
 */

/* cpu_bit_bitmap[0] is empty - so we can back into it */
#define MASK_DECLARE_1(x) [(x) + 1][0] = (1UL << (x))
#define MASK_DECLARE_2(x) MASK_DECLARE_1(x), MASK_DECLARE_1((x) + 1)
#define MASK_DECLARE_4(x) MASK_DECLARE_2(x), MASK_DECLARE_2((x) + 2)
#define MASK_DECLARE_8(x) MASK_DECLARE_4(x), MASK_DECLARE_4((x) + 4)

const unsigned long cpu_bit_bitmap[BITS_PER_LONG + 1][BITS_TO_LONGS(NR_CPUS)] = {

    MASK_DECLARE_8(0),  MASK_DECLARE_8(8),  MASK_DECLARE_8(16), MASK_DECLARE_8(24),
#if BITS_PER_LONG > 32
    MASK_DECLARE_8(32), MASK_DECLARE_8(40), MASK_DECLARE_8(48), MASK_DECLARE_8(56),
#endif
};
EXPORT_SYMBOL_GPL(cpu_bit_bitmap);

const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
EXPORT_SYMBOL(cpu_all_bits);

#ifdef CONFIG_INIT_ALL_POSSIBLE
struct cpumask __cpu_possible_mask __read_mostly = {CPU_BITS_ALL};
#else
struct cpumask __cpu_possible_mask __read_mostly;
#endif
EXPORT_SYMBOL(__cpu_possible_mask);

struct cpumask __cpu_online_mask __read_mostly;
EXPORT_SYMBOL(__cpu_online_mask);

struct cpumask __cpu_present_mask __read_mostly;
EXPORT_SYMBOL(__cpu_present_mask);

struct cpumask __cpu_active_mask __read_mostly;
EXPORT_SYMBOL(__cpu_active_mask);

#ifdef CONFIG_CPU_ISOLATION_OPT
struct cpumask __cpu_isolated_mask __read_mostly;
EXPORT_SYMBOL(__cpu_isolated_mask);
#endif

atomic_t __num_online_cpus __read_mostly;
EXPORT_SYMBOL(__num_online_cpus);

void init_cpu_present(const struct cpumask *src)
{
    cpumask_copy(&__cpu_present_mask, src);
}

void init_cpu_possible(const struct cpumask *src)
{
    cpumask_copy(&__cpu_possible_mask, src);
}

void init_cpu_online(const struct cpumask *src)
{
    cpumask_copy(&__cpu_online_mask, src);
}

#ifdef CONFIG_CPU_ISOLATION_OPT
void init_cpu_isolated(const struct cpumask *src)
{
    cpumask_copy(&__cpu_isolated_mask, src);
}
#endif

void set_cpu_online(unsigned int cpu, bool online)
{
    /*
     * atomic_inc/dec() is required to handle the horrid abuse of this
     * function by the reboot and kexec code which invoke it from
     * IPI/NMI broadcasts when shutting down CPUs. Invocation from
     * regular CPU hotplug is properly serialized.
     *
     * Note, that the fact that __num_online_cpus is of type atomic_t
     * does not protect readers which are not serialized against
     * concurrent hotplug operations.
     */
    if (online) {
        if (!cpumask_test_and_set_cpu(cpu, &__cpu_online_mask)) {
            atomic_inc(&__num_online_cpus);
        }
    } else {
        if (cpumask_test_and_clear_cpu(cpu, &__cpu_online_mask)) {
            atomic_dec(&__num_online_cpus);
        }
    }
}

/*
 * Activate the first processor.
 */
void __init boot_cpu_init(void)
{
    int cpu = smp_processor_id();

    /* Mark the boot cpu "present", "online" etc for SMP and UP case */
    set_cpu_online(cpu, true);
    set_cpu_active(cpu, true);
    set_cpu_present(cpu, true);
    set_cpu_possible(cpu, true);

#ifdef CONFIG_SMP
    __boot_cpu_id = cpu;
#endif
}

/*
 * Must be called _AFTER_ setting up the per_cpu areas
 */
void __init boot_cpu_hotplug_init(void)
{
#ifdef CONFIG_SMP
    cpumask_set_cpu(smp_processor_id(), &cpus_booted_once_mask);
#endif
    this_cpu_write(cpuhp_state.state, CPUHP_ONLINE);
}

/*
 * These are used for a global "mitigations=" cmdline option for toggling
 * optional CPU mitigations.
 */
enum cpu_mitigations {
    CPU_MITIGATIONS_OFF,
    CPU_MITIGATIONS_AUTO,
    CPU_MITIGATIONS_AUTO_NOSMT,
};

static enum cpu_mitigations cpu_mitigations __ro_after_init = CPU_MITIGATIONS_AUTO;

static int __init mitigations_parse_cmdline(char *arg)
{
    if (!strcmp(arg, "off")) {
        cpu_mitigations = CPU_MITIGATIONS_OFF;
    } else if (!strcmp(arg, "auto")) {
        cpu_mitigations = CPU_MITIGATIONS_AUTO;
    } else if (!strcmp(arg, "auto,nosmt")) {
        cpu_mitigations = CPU_MITIGATIONS_AUTO_NOSMT;
    } else {
        pr_crit("Unsupported mitigations=%s, system may still be vulnerable\n", arg);
    }

    return 0;
}
early_param("mitigations", mitigations_parse_cmdline);

/* mitigations=off */
bool cpu_mitigations_off(void)
{
    return cpu_mitigations == CPU_MITIGATIONS_OFF;
}
EXPORT_SYMBOL_GPL(cpu_mitigations_off);

/* mitigations=auto,nosmt */
bool cpu_mitigations_auto_nosmt(void)
{
    return cpu_mitigations == CPU_MITIGATIONS_AUTO_NOSMT;
}
EXPORT_SYMBOL_GPL(cpu_mitigations_auto_nosmt);