Quelle cpu.c Sprache: 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/delay.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 <linux/cc_platform.h>
#include <linux/parser.h>

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

#include "smpboot.h"

/**
* struct cpuhp_cpu_state - Per cpu hotplug state storage
* @state: The current cpu state
* @target: The target state
* @fail: Current CPU hotplug callback 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
* @node: Remote CPU node; for multi-instance, do a
* single entry callback for install/remove
* @last: For multi-instance rollback, remember how far we got
* @cb_state: The state for a single callback (install/uninstall)
* @result: Result of the operation
* @ap_sync_state: State for AP synchronization
* @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;
atomic_t  ap_sync_state;
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

/**
* struct 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
* @multi_instance: State has multiple instances which get added afterwards
*/
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;
/* private: */
struct hlist_head list;
/* public: */
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;
}

static bool cpuhp_step_empty(bool bringup, struct cpuhp_step *step)
{
return bringup ? !step->startup.single : !step->teardown.single;
}

/**
* 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.
*
* Return: %0 on success or a negative errno code
*/
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;
  return -EAGAIN;
}

if (cpuhp_step_empty(bringup, step)) {
  WARN_ON_ONCE(1);
  return 0;
}

if (!step->multi_instance) {
  WARN_ON_ONCE(lastp && *lastp);
  cb = bringup ? step->startup.single : step->teardown.single;

  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;

/* 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;
}

/* Synchronization state management */
enum cpuhp_sync_state {
SYNC_STATE_DEAD,
SYNC_STATE_KICKED,
SYNC_STATE_SHOULD_DIE,
SYNC_STATE_ALIVE,
SYNC_STATE_SHOULD_ONLINE,
SYNC_STATE_ONLINE,
};

#ifdef CONFIG_HOTPLUG_CORE_SYNC
/**
* cpuhp_ap_update_sync_state - Update synchronization state during bringup/teardown
* @state: The synchronization state to set
*
* No synchronization point. Just update of the synchronization state, but implies
* a full barrier so that the AP changes are visible before the control CPU proceeds.
*/
static inline void cpuhp_ap_update_sync_state(enum cpuhp_sync_state state)
{
atomic_t *st = this_cpu_ptr(&cpuhp_state.ap_sync_state);

(void)atomic_xchg(st, state);
}

void __weak arch_cpuhp_sync_state_poll(void) { cpu_relax(); }

static bool cpuhp_wait_for_sync_state(unsigned int cpu, enum cpuhp_sync_state state,
          enum cpuhp_sync_state next_state)
{
atomic_t *st = per_cpu_ptr(&cpuhp_state.ap_sync_state, cpu);
ktime_t now, end, start = ktime_get();
int sync;

end = start + 10ULL * NSEC_PER_SEC;

sync = atomic_read(st);
while (1) {
  if (sync == state) {
   if (!atomic_try_cmpxchg(st, &sync, next_state))
    continue;
   return true;
  }

  now = ktime_get();
  if (now > end) {
   /* Timeout. Leave the state unchanged */
   return false;
  } else if (now - start < NSEC_PER_MSEC) {
   /* Poll for one millisecond */
   arch_cpuhp_sync_state_poll();
  } else {
   usleep_range(USEC_PER_MSEC, 2 * USEC_PER_MSEC);
  }
  sync = atomic_read(st);
}
return true;
}
#else  /* CONFIG_HOTPLUG_CORE_SYNC */
static inline void cpuhp_ap_update_sync_state(enum cpuhp_sync_state state) { }
#endif /* !CONFIG_HOTPLUG_CORE_SYNC */

#ifdef CONFIG_HOTPLUG_CORE_SYNC_DEAD
/**
* cpuhp_ap_report_dead - Update synchronization state to DEAD
*
* No synchronization point. Just update of the synchronization state.
*/
void cpuhp_ap_report_dead(void)
{
cpuhp_ap_update_sync_state(SYNC_STATE_DEAD);
}

void __weak arch_cpuhp_cleanup_dead_cpu(unsigned int cpu) { }

/*
* Late CPU shutdown synchronization point. Cannot use cpuhp_state::done_down
* because the AP cannot issue complete() at this stage.
*/
static void cpuhp_bp_sync_dead(unsigned int cpu)
{
atomic_t *st = per_cpu_ptr(&cpuhp_state.ap_sync_state, cpu);
int sync = atomic_read(st);

do {
  /* CPU can have reported dead already. Don't overwrite that! */
  if (sync == SYNC_STATE_DEAD)
   break;
} while (!atomic_try_cmpxchg(st, &sync, SYNC_STATE_SHOULD_DIE));

if (cpuhp_wait_for_sync_state(cpu, SYNC_STATE_DEAD, SYNC_STATE_DEAD)) {
  /* CPU reached dead state. Invoke the cleanup function */
  arch_cpuhp_cleanup_dead_cpu(cpu);
  return;
}

/* No further action possible. Emit message and give up. */
pr_err("CPU%u failed to report dead state\n", cpu);
}
#else /* CONFIG_HOTPLUG_CORE_SYNC_DEAD */
static inline void cpuhp_bp_sync_dead(unsigned int cpu) { }
#endif /* !CONFIG_HOTPLUG_CORE_SYNC_DEAD */

#ifdef CONFIG_HOTPLUG_CORE_SYNC_FULL
/**
* cpuhp_ap_sync_alive - Synchronize AP with the control CPU once it is alive
*
* Updates the AP synchronization state to SYNC_STATE_ALIVE and waits
* for the BP to release it.
*/
void cpuhp_ap_sync_alive(void)
{
atomic_t *st = this_cpu_ptr(&cpuhp_state.ap_sync_state);

cpuhp_ap_update_sync_state(SYNC_STATE_ALIVE);

/* Wait for the control CPU to release it. */
while (atomic_read(st) != SYNC_STATE_SHOULD_ONLINE)
  cpu_relax();
}

static bool cpuhp_can_boot_ap(unsigned int cpu)
{
atomic_t *st = per_cpu_ptr(&cpuhp_state.ap_sync_state, cpu);
int sync = atomic_read(st);

again:
switch (sync) {
case SYNC_STATE_DEAD:
  /* CPU is properly dead */
  break;
case SYNC_STATE_KICKED:
  /* CPU did not come up in previous attempt */
  break;
case SYNC_STATE_ALIVE:
  /* CPU is stuck cpuhp_ap_sync_alive(). */
  break;
default:
  /* CPU failed to report online or dead and is in limbo state. */
  return false;
}

/* Prepare for booting */
if (!atomic_try_cmpxchg(st, &sync, SYNC_STATE_KICKED))
  goto again;

return true;
}

void __weak arch_cpuhp_cleanup_kick_cpu(unsigned int cpu) { }

/*
* Early CPU bringup synchronization point. Cannot use cpuhp_state::done_up
* because the AP cannot issue complete() so early in the bringup.
*/
static int cpuhp_bp_sync_alive(unsigned int cpu)
{
int ret = 0;

if (!IS_ENABLED(CONFIG_HOTPLUG_CORE_SYNC_FULL))
  return 0;

if (!cpuhp_wait_for_sync_state(cpu, SYNC_STATE_ALIVE, SYNC_STATE_SHOULD_ONLINE)) {
  pr_err("CPU%u failed to report alive state\n", cpu);
  ret = -EIO;
}

/* Let the architecture cleanup the kick alive mechanics. */
arch_cpuhp_cleanup_kick_cpu(cpu);
return ret;
}
#else /* CONFIG_HOTPLUG_CORE_SYNC_FULL */
static inline int cpuhp_bp_sync_alive(unsigned int cpu) { return 0; }
static inline bool cpuhp_can_boot_ap(unsigned int cpu) { return true; }
#endif /* !CONFIG_HOTPLUG_CORE_SYNC_FULL */

/* 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);
}

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

/*
* 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);

static bool cpu_hotplug_offline_disabled __ro_after_init;

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);
}
EXPORT_SYMBOL_GPL(lockdep_assert_cpus_held);

#ifdef CONFIG_LOCKDEP
int lockdep_is_cpus_held(void)
{
return percpu_rwsem_is_held(&cpu_hotplug_lock);
}
#endif

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_);
}

/* Declare CPU offlining not supported */
void cpu_hotplug_disable_offlining(void)
{
cpu_maps_update_begin();
cpu_hotplug_offline_disabled = true;
cpu_maps_update_done();
}

/*
* 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;
static unsigned int cpu_smt_max_threads __ro_after_init;
unsigned int cpu_smt_num_threads __read_mostly = UINT_MAX;

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;
}
cpu_smt_num_threads = 1;
}

/*
* The decision whether SMT is supported can only be done after the full
* CPU identification. Called from architecture code.
*/
void __init cpu_smt_set_num_threads(unsigned int num_threads,
        unsigned int max_threads)
{
WARN_ON(!num_threads || (num_threads > max_threads));

if (max_threads == 1)
  cpu_smt_control = CPU_SMT_NOT_SUPPORTED;

cpu_smt_max_threads = max_threads;

/*
* If SMT has been disabled via the kernel command line or SMT is
* not supported, set cpu_smt_num_threads to 1 for consistency.
* If enabled, take the architecture requested number of threads
* to bring up into account.
*/
if (cpu_smt_control != CPU_SMT_ENABLED)
  cpu_smt_num_threads = 1;
else if (num_threads < cpu_smt_num_threads)
  cpu_smt_num_threads = num_threads;
}

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

/*
* For Archicture supporting partial SMT states check if the thread is allowed.
* Otherwise this has already been checked through cpu_smt_max_threads when
* setting the SMT level.
*/
static inline bool cpu_smt_thread_allowed(unsigned int cpu)
{
#ifdef CONFIG_SMT_NUM_THREADS_DYNAMIC
return topology_smt_thread_allowed(cpu);
#else
return true;
#endif
}

static inline bool cpu_bootable(unsigned int cpu)
{
if (cpu_smt_control == CPU_SMT_ENABLED && cpu_smt_thread_allowed(cpu))
  return true;

/* All CPUs are bootable if controls are not configured */
if (cpu_smt_control == CPU_SMT_NOT_IMPLEMENTED)
  return true;

/* All CPUs are bootable if CPU is not SMT capable */
if (cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
  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 supported and not 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_bootable(unsigned int cpu) { return true; }
#endif

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

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

st->target = target;
st->single = false;
st->bringup = bringup;
if (cpu_dying(cpu) != !bringup)
  set_cpu_dying(cpu, !bringup);

return prev_state;
}

static inline void
cpuhp_reset_state(int cpu, struct cpuhp_cpu_state *st,
    enum cpuhp_state prev_state)
{
bool bringup = !st->bringup;

st->target = prev_state;

/*
* Already rolling back. No need invert the bringup value or to change
* the current state.
*/
if (st->rollback)
  return;

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->bringup = bringup;
if (cpu_dying(cpu) != !bringup)
  set_cpu_dying(cpu, !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(int cpu, struct cpuhp_cpu_state *st,
    enum cpuhp_state target)
{
enum cpuhp_state prev_state;
int ret;

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

return ret;
}

static int bringup_wait_for_ap_online(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_bootable() check will now return false if this is not the
* primary sibling.
*/
if (!cpu_bootable(cpu))
  return -ECANCELED;
return 0;
}

#ifdef CONFIG_HOTPLUG_SPLIT_STARTUP
static int cpuhp_kick_ap_alive(unsigned int cpu)
{
if (!cpuhp_can_boot_ap(cpu))
  return -EAGAIN;

return arch_cpuhp_kick_ap_alive(cpu, idle_thread_get(cpu));
}

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

/*
* 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();

ret = cpuhp_bp_sync_alive(cpu);
if (ret)
  goto out_unlock;

ret = bringup_wait_for_ap_online(cpu);
if (ret)
  goto out_unlock;

irq_unlock_sparse();

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

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

out_unlock:
irq_unlock_sparse();
return ret;
}
#else
static int bringup_cpu(unsigned int cpu)
{
struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
struct task_struct *idle = idle_thread_get(cpu);
int ret;

if (!cpuhp_can_boot_ap(cpu))
  return -EAGAIN;

/*
* 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 by acquiring the
* sparse irq lock. Hold it until the upcoming CPU completes the
* startup in cpuhp_online_idle() which allows to avoid
* intermediate synchronization points in the architecture code.
*/
irq_lock_sparse();

ret = __cpu_up(cpu, idle);
if (ret)
  goto out_unlock;

ret = cpuhp_bp_sync_alive(cpu);
if (ret)
  goto out_unlock;

ret = bringup_wait_for_ap_online(cpu);
if (ret)
  goto out_unlock;

irq_unlock_sparse();

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

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

out_unlock:
irq_unlock_sparse();
return ret;
}
#endif

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

/*
* sched_force_init_mm() ensured the use of &init_mm,
* drop that refcount now that the CPU has stopped.
*/
WARN_ON(mm != &init_mm);
idle->active_mm = NULL;
mmdrop_lazy_tlb(mm);

return 0;
}

/*
* Hotplug state machine related functions
*/

/*
* Get the next state to run. Empty ones will be skipped. Returns true if a
* state must be run.
*
* st->state will be modified ahead of time, to match state_to_run, as if it
* has already ran.
*/
static bool cpuhp_next_state(bool bringup,
        enum cpuhp_state *state_to_run,
        struct cpuhp_cpu_state *st,
        enum cpuhp_state target)
{
do {
  if (bringup) {
   if (st->state >= target)
    return false;

   *state_to_run = ++st->state;
  } else {
   if (st->state <= target)
    return false;

   *state_to_run = st->state--;
  }

  if (!cpuhp_step_empty(bringup, cpuhp_get_step(*state_to_run)))
   break;
} while (true);

return true;
}

static int __cpuhp_invoke_callback_range(bool bringup,
      unsigned int cpu,
      struct cpuhp_cpu_state *st,
      enum cpuhp_state target,
      bool nofail)
{
enum cpuhp_state state;
int ret = 0;

while (cpuhp_next_state(bringup, &state, st, target)) {
  int err;

  err = cpuhp_invoke_callback(cpu, state, bringup, NULL, NULL);
  if (!err)
   continue;

  if (nofail) {
   pr_warn("CPU %u %s state %s (%d) failed (%d)\n",
    cpu, bringup ? "UP" : "DOWN",
    cpuhp_get_step(st->state)->name,
    st->state, err);
   ret = -1;
  } else {
   ret = err;
   break;
  }
}

return ret;
}

static inline int cpuhp_invoke_callback_range(bool bringup,
           unsigned int cpu,
           struct cpuhp_cpu_state *st,
           enum cpuhp_state target)
{
return __cpuhp_invoke_callback_range(bringup, cpu, st, target, false);
}

static inline void cpuhp_invoke_callback_range_nofail(bool bringup,
            unsigned int cpu,
            struct cpuhp_cpu_state *st,
            enum cpuhp_state target)
{
__cpuhp_invoke_callback_range(bringup, cpu, st, target, true);
}

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;

ret = cpuhp_invoke_callback_range(true, cpu, st, target);
if (ret) {
  pr_debug("CPU UP failed (%d) CPU %u state %s (%d)\n",
    ret, cpu, cpuhp_get_step(st->state)->name,
    st->state);

  cpuhp_reset_state(cpu, st, prev_state);
  if (can_rollback_cpu(st))
   WARN_ON(cpuhp_invoke_callback_range(false, cpu, st,
           prev_state));
}
return ret;
}

/*
* The cpu hotplug threads manage the bringup and teardown of the cpus
*/
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 {
  st->should_run = cpuhp_next_state(bringup, &state, st, st->target);
  if (!st->should_run)
   goto end;
}

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;
}

end:
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(cpu, 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,
.thread_should_run = cpuhp_should_run,
.thread_fn  = cpuhp_thread_fun,
.thread_comm  = "cpuhp/%u",
.selfparking  = true,
};

static __init void cpuhp_init_state(void)
{
struct cpuhp_cpu_state *st;
int cpu;

for_each_possible_cpu(cpu) {
  st = per_cpu_ptr(&cpuhp_state, cpu);
  init_completion(&st->done_up);
  init_completion(&st->done_down);
}
}

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

#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();

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

/*
* Must be called from CPUHP_TEARDOWN_CPU, which means, as we are going
* down, that the current state is CPUHP_TEARDOWN_CPU - 1.
*/
WARN_ON(st->state != (CPUHP_TEARDOWN_CPU - 1));

/*
* Invoke the former CPU_DYING callbacks. DYING must not fail!
*/
cpuhp_invoke_callback_range_nofail(false, cpu, st, target);

/* 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(st->thread);

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

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(st->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);

cpuhp_bp_sync_dead(cpu);

lockdep_cleanup_dead_cpu(cpu, idle_thread_get(cpu));

/*
* Callbacks must be re-integrated right away to the RCU state machine.
* Otherwise an RCU callback could block a further teardown function
* waiting for its completion.
*/
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);
tick_assert_timekeeping_handover();
rcutree_report_cpu_dead();
st->state = CPUHP_AP_IDLE_DEAD;
/*
* We cannot call complete after rcutree_report_cpu_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 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;

ret = cpuhp_invoke_callback_range(false, cpu, st, target);
if (ret) {
  pr_debug("CPU DOWN failed (%d) CPU %u state %s (%d)\n",
    ret, cpu, cpuhp_get_step(st->state)->name,
    st->state);

  cpuhp_reset_state(cpu, st, prev_state);

  if (st->state < prev_state)
   WARN_ON(cpuhp_invoke_callback_range(true, cpu, st,
           prev_state));
}

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_online_cpus() == 1)
  return -EBUSY;

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

cpus_write_lock();

cpuhp_tasks_frozen = tasks_frozen;

prev_state = cpuhp_set_state(cpu, 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 < prev_state) {
  if (st->state == CPUHP_TEARDOWN_CPU) {
   cpuhp_reset_state(cpu, st, prev_state);
   __cpuhp_kick_ap(st);
  } else {
   WARN(1, "DEAD callback error for CPU%d", cpu);
  }
}

out:
cpus_write_unlock();
arch_smt_update();
return ret;
}

struct cpu_down_work {
unsigned int  cpu;
enum cpuhp_state target;
};

static long __cpu_down_maps_locked(void *arg)
{
struct cpu_down_work *work = arg;

return _cpu_down(work->cpu, 0, work->target);
}

static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
{
struct cpu_down_work work = { .cpu = cpu, .target = target, };

/*
* If the platform does not support hotplug, report it explicitly to
* differentiate it from a transient offlining failure.
*/
if (cpu_hotplug_offline_disabled)
  return -EOPNOTSUPP;
if (cpu_hotplug_disabled)
  return -EBUSY;

/*
* Ensure that the control task does not run on the to be offlined
* CPU to prevent a deadlock against cfs_b->period_timer.
* Also keep at least one housekeeping cpu onlined to avoid generating
* an empty sched_domain span.
*/
for_each_cpu_and(cpu, cpu_online_mask, housekeeping_cpumask(HK_TYPE_DOMAIN)) {
  if (cpu != work.cpu)
   return work_on_cpu(cpu, __cpu_down_maps_locked, &work);
}
return -EBUSY;
}

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.
*
* Return: %0 on success or a negative errno code
*/
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);

rcutree_report_cpu_starting(cpu); /* Enables RCU usage on this CPU. */
cpumask_set_cpu(cpu, &cpus_booted_once_mask);

/*
* STARTING must not fail!
*/
cpuhp_invoke_callback_range_nofail(true, cpu, st, target);
}

/*
* 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;

cpuhp_ap_update_sync_state(SYNC_STATE_ONLINE);

/*
* Unpark 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;
  }

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

cpuhp_tasks_frozen = tasks_frozen;

cpuhp_set_state(cpu, 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();
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);
  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_bootable(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.
*
* Return: %0 on success or a negative errno code
*/
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.
*
* Return: %0 on success or a negative errno code
*/
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;
}

static void __init cpuhp_bringup_mask(const struct cpumask *mask, unsigned int ncpus,
          enum cpuhp_state target)
{
unsigned int cpu;

for_each_cpu(cpu, mask) {
  struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);

  if (cpu_up(cpu, target) && can_rollback_cpu(st)) {
   /*
* If this failed then cpu_up() might have only
* rolled back to CPUHP_BP_KICK_AP for the final
* online. Clean it up. NOOP if already rolled back.
*/
   WARN_ON(cpuhp_invoke_callback_range(false, cpu, st, CPUHP_OFFLINE));
  }

  if (!--ncpus)
   break;
}
}

#ifdef CONFIG_HOTPLUG_PARALLEL
static bool __cpuhp_parallel_bringup __ro_after_init = true;

static int __init parallel_bringup_parse_param(char *arg)
{
return kstrtobool(arg, &__cpuhp_parallel_bringup);
}
early_param("cpuhp.parallel", parallel_bringup_parse_param);

#ifdef CONFIG_HOTPLUG_SMT
static inline bool cpuhp_smt_aware(void)
{
return cpu_smt_max_threads > 1;
}

static inline const struct cpumask *cpuhp_get_primary_thread_mask(void)
{
return cpu_primary_thread_mask;
}
#else
static inline bool cpuhp_smt_aware(void)
{
return false;
}
static inline const struct cpumask *cpuhp_get_primary_thread_mask(void)
{
return cpu_none_mask;
}
#endif

bool __weak arch_cpuhp_init_parallel_bringup(void)
{
return true;
}

/*
* On architectures which have enabled parallel bringup this invokes all BP
* prepare states for each of the to be onlined APs first. The last state
* sends the startup IPI to the APs. The APs proceed through the low level
* bringup code in parallel and then wait for the control CPU to release
* them one by one for the final onlining procedure.
*
* This avoids waiting for each AP to respond to the startup IPI in
* CPUHP_BRINGUP_CPU.
*/
static bool __init cpuhp_bringup_cpus_parallel(unsigned int ncpus)
{
const struct cpumask *mask = cpu_present_mask;

if (__cpuhp_parallel_bringup)
  __cpuhp_parallel_bringup = arch_cpuhp_init_parallel_bringup();
if (!__cpuhp_parallel_bringup)
  return false;

if (cpuhp_smt_aware()) {
  const struct cpumask *pmask = cpuhp_get_primary_thread_mask();
  static struct cpumask tmp_mask __initdata;

  /*
* X86 requires to prevent that SMT siblings stopped while
* the primary thread does a microcode update for various
* reasons. Bring the primary threads up first.
*/
  cpumask_and(&tmp_mask, mask, pmask);
  cpuhp_bringup_mask(&tmp_mask, ncpus, CPUHP_BP_KICK_AP);
  cpuhp_bringup_mask(&tmp_mask, ncpus, CPUHP_ONLINE);
  /* Account for the online CPUs */
  ncpus -= num_online_cpus();
  if (!ncpus)
   return true;
  /* Create the mask for secondary CPUs */
  cpumask_andnot(&tmp_mask, mask, pmask);
  mask = &tmp_mask;
}

/* Bring the not-yet started CPUs up */
cpuhp_bringup_mask(mask, ncpus, CPUHP_BP_KICK_AP);
cpuhp_bringup_mask(mask, ncpus, CPUHP_ONLINE);
return true;
}
#else
static inline bool cpuhp_bringup_cpus_parallel(unsigned int ncpus) { return false; }
#endif /* CONFIG_HOTPLUG_PARALLEL */

void __init bringup_nonboot_cpus(unsigned int max_cpus)
{
if (!max_cpus)
  return;

/* Try parallel bringup optimization if enabled */
if (cpuhp_bringup_cpus_parallel(max_cpus))
  return;

/* Full per CPU serialized bringup */
cpuhp_bringup_mask(cpu_present_mask, max_cpus, 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_TYPE_TIMER))
   primary = housekeeping_any_cpu(HK_TYPE_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 (cpu = nr_cpu_ids - 1; cpu >= 0; cpu--) {
  if (!cpu_online(cpu) || 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_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 = NULL,
},
[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_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,
},

#ifdef CONFIG_HOTPLUG_SPLIT_STARTUP
/*
* Kicks the AP alive. AP will wait in cpuhp_ap_sync_alive() until
* the next step will release it.
*/
[CPUHP_BP_KICK_AP] = {
  .name   = "cpu:kick_ap",
  .startup.single  = cpuhp_kick_ap_alive,
},

/*
* Waits for the AP to reach cpuhp_ap_sync_alive() and then
* releases it for the complete bringup.
*/
[CPUHP_BRINGUP_CPU] = {
  .name   = "cpu:bringup",
  .startup.single  = cpuhp_bringup_ap,
  .teardown.single = finish_cpu,
  .cant_stop  = true,
},
#else
/*
* All-in-one CPU bringup state which includes the kick alive.
*/
[CPUHP_BRINGUP_CPU] = {
  .name   = "cpu:bringup",
  .startup.single  = bringup_cpu,
  .teardown.single = finish_cpu,
  .cant_stop  = true,
},
#endif
/* 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,
},
[CPUHP_AP_HRTIMERS_DYING] = {
  .name   = "hrtimers:dying",
  .startup.single  = hrtimers_cpu_starting,
  .teardown.single = hrtimers_cpu_dying,
},
[CPUHP_AP_TICK_DYING] = {
  .name   = "tick:dying",
  .startup.single  = NULL,
  .teardown.single = tick_cpu_dying,
},
/* Entry state on starting. Interrupts enabled from here on. Transient
* state for synchronsization */
[CPUHP_AP_ONLINE] = {
  .name   = "ap:online",
},
/*
* Handled on control processor until the plugged processor manages
* this itself.
*/
[CPUHP_TEARDOWN_CPU] = {
  .name   = "cpu:teardown",
  .startup.single  = NULL,
  .teardown.single = takedown_cpu,
  .cant_stop  = true,
},

[CPUHP_AP_SCHED_WAIT_EMPTY] = {
  .name   = "sched:waitempty",
  .startup.single  = NULL,
  .teardown.single = sched_cpu_wait_empty,
},

/* 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 (cpuhp_step_empty(bringup, sp))
  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
* @name: Name of the step
* @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.
* Return:
*   On success:
*      Positive state number if @state is CPUHP_AP_ONLINE_DYN or CPUHP_BP_PREPARE_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 || state == CPUHP_BP_PREPARE_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 or CPUHP_BP_PREPARE_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
--> --------------------

--> maximum size reached

--> --------------------

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