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cpu.c
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/* CPU control.
* (C) 2001, 2002, 2003, 2004 Rusty Russell
*
* This code is licenced under the GPL.
*/
#include <linux/proc_fs.h>
#include <linux/smp.h>
#include <linux/init.h>
#include <linux/notifier.h>
#include <linux/sched.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/smpboot.h>
#include <linux/relay.h>
#include <linux/slab.h>
#include <trace/events/power.h>
#define CREATE_TRACE_POINTS
#include <trace/events/cpuhp.h>
#include "smpboot.h"
/**
* 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: Signal completion to the issuer of the task
*/
struct cpuhp_cpu_state {
enum cpuhp_state state;
enum cpuhp_state target;
#ifdef CONFIG_SMP
struct task_struct *thread;
bool should_run;
bool rollback;
bool single;
bool bringup;
struct hlist_node *node;
enum cpuhp_state cb_state;
int result;
struct completion done;
#endif
};
static DEFINE_PER_CPU(struct cpuhp_cpu_state, cpuhp_state);
/**
* cpuhp_step - Hotplug state machine step
* @name: Name of the step
* @startup: Startup function of the step
* @teardown: Teardown function of the step
* @skip_onerr: Do not invoke the functions on error rollback
* Will go away once the notifiers are gone
* @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 skip_onerr;
bool cant_stop;
bool multi_instance;
};
static DEFINE_MUTEX(cpuhp_state_mutex);
static struct cpuhp_step cpuhp_bp_states[];
static struct cpuhp_step cpuhp_ap_states[];
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 struct cpuhp_step *cpuhp_get_step(enum cpuhp_state state)
{
struct cpuhp_step *sp;
sp = cpuhp_is_ap_state(state) ? cpuhp_ap_states : cpuhp_bp_states;
return sp + state;
}
/**
* cpuhp_invoke_callback _ Invoke the callbacks for a given state
* @cpu: The cpu for which the callback should be invoked
* @step: The step in the state machine
* @bringup: True if the bringup callback should be invoked
*
* 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 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 (!step->multi_instance) {
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) {
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) {
trace_cpuhp_multi_enter(cpu, st->target, state, cbm, node);
ret = cbm(cpu, node);
trace_cpuhp_exit(cpu, st->state, state, ret);
if (ret)
goto err;
cnt++;
}
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;
cbm(cpu, node);
}
return ret;
}
#ifdef CONFIG_SMP
/* 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.
* The APIs cpu_notifier_register_begin/done() must be used to protect CPU
* hotplug callback (un)registration performed using __register_cpu_notifier()
* or __unregister_cpu_notifier().
*/
void cpu_maps_update_begin(void)
{
mutex_lock(&cpu_add_remove_lock);
}
EXPORT_SYMBOL(cpu_notifier_register_begin);
void cpu_maps_update_done(void)
{
mutex_unlock(&cpu_add_remove_lock);
}
EXPORT_SYMBOL(cpu_notifier_register_done);
static RAW_NOTIFIER_HEAD(cpu_chain);
/* 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
static struct {
struct task_struct *active_writer;
/* wait queue to wake up the active_writer */
wait_queue_head_t wq;
/* verifies that no writer will get active while readers are active */
struct mutex lock;
/*
* Also blocks the new readers during
* an ongoing cpu hotplug operation.
*/
atomic_t refcount;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map dep_map;
#endif
} cpu_hotplug = {
.active_writer = NULL,
.wq = __WAIT_QUEUE_HEAD_INITIALIZER(cpu_hotplug.wq),
.lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),
#ifdef CONFIG_DEBUG_LOCK_ALLOC
.dep_map = STATIC_LOCKDEP_MAP_INIT("cpu_hotplug.dep_map", &cpu_hotplug.dep_map),
#endif
};
/* Lockdep annotations for get/put_online_cpus() and cpu_hotplug_begin/end() */
#define cpuhp_lock_acquire_read() lock_map_acquire_read(&cpu_hotplug.dep_map)
#define cpuhp_lock_acquire_tryread() \
lock_map_acquire_tryread(&cpu_hotplug.dep_map)
#define cpuhp_lock_acquire() lock_map_acquire(&cpu_hotplug.dep_map)
#define cpuhp_lock_release() lock_map_release(&cpu_hotplug.dep_map)
void get_online_cpus(void)
{
might_sleep();
if (cpu_hotplug.active_writer == current)
return;
cpuhp_lock_acquire_read();
mutex_lock(&cpu_hotplug.lock);
atomic_inc(&cpu_hotplug.refcount);
mutex_unlock(&cpu_hotplug.lock);
}
EXPORT_SYMBOL_GPL(get_online_cpus);
void put_online_cpus(void)
{
int refcount;
if (cpu_hotplug.active_writer == current)
return;
refcount = atomic_dec_return(&cpu_hotplug.refcount);
if (WARN_ON(refcount < 0)) /* try to fix things up */
atomic_inc(&cpu_hotplug.refcount);
if (refcount <= 0 && waitqueue_active(&cpu_hotplug.wq))
wake_up(&cpu_hotplug.wq);
cpuhp_lock_release();
}
EXPORT_SYMBOL_GPL(put_online_cpus);
/*
* This ensures that the hotplug operation can begin only when the
* refcount goes to zero.
*
* Note that during a cpu-hotplug operation, the new readers, if any,
* will be blocked by the cpu_hotplug.lock
*
* Since cpu_hotplug_begin() is always called after invoking
* cpu_maps_update_begin(), we can be sure that only one writer is active.
*
* Note that theoretically, there is a possibility of a livelock:
* - Refcount goes to zero, last reader wakes up the sleeping
* writer.
* - Last reader unlocks the cpu_hotplug.lock.
* - A new reader arrives at this moment, bumps up the refcount.
* - The writer acquires the cpu_hotplug.lock finds the refcount
* non zero and goes to sleep again.
*
* However, this is very difficult to achieve in practice since
* get_online_cpus() not an api which is called all that often.
*
*/
void cpu_hotplug_begin(void)
{
DEFINE_WAIT(wait);
cpu_hotplug.active_writer = current;
cpuhp_lock_acquire();
for (;;) {
mutex_lock(&cpu_hotplug.lock);
prepare_to_wait(&cpu_hotplug.wq, &wait, TASK_UNINTERRUPTIBLE);
if (likely(!atomic_read(&cpu_hotplug.refcount)))
break;
mutex_unlock(&cpu_hotplug.lock);
schedule();
}
finish_wait(&cpu_hotplug.wq, &wait);
}
void cpu_hotplug_done(void)
{
cpu_hotplug.active_writer = NULL;
mutex_unlock(&cpu_hotplug.lock);
cpuhp_lock_release();
}
/*
* 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);
#endif /* CONFIG_HOTPLUG_CPU */
/* Need to know about CPUs going up/down? */
int register_cpu_notifier(struct notifier_block *nb)
{
int ret;
cpu_maps_update_begin();
ret = raw_notifier_chain_register(&cpu_chain, nb);
cpu_maps_update_done();
return ret;
}
int __register_cpu_notifier(struct notifier_block *nb)
{
return raw_notifier_chain_register(&cpu_chain, nb);
}
static int __cpu_notify(unsigned long val, unsigned int cpu, int nr_to_call,
int *nr_calls)
{
unsigned long mod = cpuhp_tasks_frozen ? CPU_TASKS_FROZEN : 0;
void *hcpu = (void *)(long)cpu;
int ret;
ret = __raw_notifier_call_chain(&cpu_chain, val | mod, hcpu, nr_to_call,
nr_calls);
return notifier_to_errno(ret);
}
static int cpu_notify(unsigned long val, unsigned int cpu)
{
return __cpu_notify(val, cpu, -1, NULL);
}
static void cpu_notify_nofail(unsigned long val, unsigned int cpu)
{
BUG_ON(cpu_notify(val, cpu));
}
/* Notifier wrappers for transitioning to state machine */
static int notify_prepare(unsigned int cpu)
{
int nr_calls = 0;
int ret;
ret = __cpu_notify(CPU_UP_PREPARE, cpu, -1, &nr_calls);
if (ret) {
nr_calls--;
printk(KERN_WARNING "%s: attempt to bring up CPU %u failed\n",
__func__, cpu);
__cpu_notify(CPU_UP_CANCELED, cpu, nr_calls, NULL);
}
return ret;
}
static int notify_online(unsigned int cpu)
{
cpu_notify(CPU_ONLINE, cpu);
return 0;
}
static void __cpuhp_kick_ap_work(struct cpuhp_cpu_state *st);
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_completion(&st->done);
if (WARN_ON_ONCE((!cpu_online(cpu))))
return -ECANCELED;
/* Unpark the stopper thread and the hotplug thread of the target cpu */
stop_machine_unpark(cpu);
kthread_unpark(st->thread);
/* Should we go further up ? */
if (st->target > CPUHP_AP_ONLINE_IDLE) {
__cpuhp_kick_ap_work(st);
wait_for_completion(&st->done);
}
return st->result;
}
static int bringup_cpu(unsigned int cpu)
{
struct task_struct *idle = idle_thread_get(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();
/* Arch-specific enabling code. */
ret = __cpu_up(cpu, idle);
irq_unlock_sparse();
if (ret) {
cpu_notify(CPU_UP_CANCELED, cpu);
return ret;
}
return bringup_wait_for_ap(cpu);
}
/*
* Hotplug state machine related functions
*/
static void undo_cpu_down(unsigned int cpu, struct cpuhp_cpu_state *st)
{
for (st->state++; st->state < st->target; st->state++) {
struct cpuhp_step *step = cpuhp_get_step(st->state);
if (!step->skip_onerr)
cpuhp_invoke_callback(cpu, st->state, true, 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);
if (ret) {
st->target = prev_state;
undo_cpu_down(cpu, st);
break;
}
}
return ret;
}
static void undo_cpu_up(unsigned int cpu, struct cpuhp_cpu_state *st)
{
for (st->state--; st->state > st->target; st->state--) {
struct cpuhp_step *step = cpuhp_get_step(st->state);
if (!step->skip_onerr)
cpuhp_invoke_callback(cpu, st->state, false, NULL);
}
}
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);
if (ret) {
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);
}
static int cpuhp_should_run(unsigned int cpu)
{
struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
return st->should_run;
}
/* Execute the teardown callbacks. Used to be CPU_DOWN_PREPARE */
static int cpuhp_ap_offline(unsigned int cpu, struct cpuhp_cpu_state *st)
{
enum cpuhp_state target = max((int)st->target, CPUHP_TEARDOWN_CPU);
return cpuhp_down_callbacks(cpu, st, target);
}
/* Execute the online startup callbacks. Used to be CPU_ONLINE */
static int cpuhp_ap_online(unsigned int cpu, struct cpuhp_cpu_state *st)
{
return cpuhp_up_callbacks(cpu, st, st->target);
}
/*
* Execute teardown/startup callbacks on the plugged cpu. Also used to invoke
* callbacks when a state gets [un]installed at runtime.
*/
static void cpuhp_thread_fun(unsigned int cpu)
{
struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
int ret = 0;
/*
* Paired with the mb() in cpuhp_kick_ap_work and
* cpuhp_invoke_ap_callback, so the work set is consistent visible.
*/
smp_mb();
if (!st->should_run)
return;
st->should_run = false;
/* Single callback invocation for [un]install ? */
if (st->single) {
if (st->cb_state < CPUHP_AP_ONLINE) {
local_irq_disable();
ret = cpuhp_invoke_callback(cpu, st->cb_state,
st->bringup, st->node);
local_irq_enable();
} else {
ret = cpuhp_invoke_callback(cpu, st->cb_state,
st->bringup, st->node);
}
} else if (st->rollback) {
BUG_ON(st->state < CPUHP_AP_ONLINE_IDLE);
undo_cpu_down(cpu, st);
/*
* This is a momentary workaround to keep the notifier users
* happy. Will go away once we got rid of the notifiers.
*/
cpu_notify_nofail(CPU_DOWN_FAILED, cpu);
st->rollback = false;
} else {
/* Cannot happen .... */
BUG_ON(st->state < CPUHP_AP_ONLINE_IDLE);
/* Regular hotplug work */
if (st->state < st->target)
ret = cpuhp_ap_online(cpu, st);
else if (st->state > st->target)
ret = cpuhp_ap_offline(cpu, st);
}
st->result = ret;
complete(&st->done);
}
/* 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);
if (!cpu_online(cpu))
return 0;
/*
* 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);
st->cb_state = state;
st->single = true;
st->bringup = bringup;
st->node = node;
/*
* 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_completion(&st->done);
return st->result;
}
/* Regular hotplug invocation of the AP hotplug thread */
static void __cpuhp_kick_ap_work(struct cpuhp_cpu_state *st)
{
st->result = 0;
st->single = false;
/*
* 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);
}
static int cpuhp_kick_ap_work(unsigned int cpu)
{
struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
enum cpuhp_state state = st->state;
trace_cpuhp_enter(cpu, st->target, state, cpuhp_kick_ap_work);
__cpuhp_kick_ap_work(st);
wait_for_completion(&st->done);
trace_cpuhp_exit(cpu, st->state, state, st->result);
return st->result;
}
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));
}
EXPORT_SYMBOL(register_cpu_notifier);
EXPORT_SYMBOL(__register_cpu_notifier);
void unregister_cpu_notifier(struct notifier_block *nb)
{
cpu_maps_update_begin();
raw_notifier_chain_unregister(&cpu_chain, nb);
cpu_maps_update_done();
}
EXPORT_SYMBOL(unregister_cpu_notifier);
void __unregister_cpu_notifier(struct notifier_block *nb)
{
raw_notifier_chain_unregister(&cpu_chain, nb);
}
EXPORT_SYMBOL(__unregister_cpu_notifier);
#ifdef CONFIG_HOTPLUG_CPU
/**
* 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;
cpumask_clear_cpu(cpu, mm_cpumask(t->mm));
task_unlock(t);
}
rcu_read_unlock();
}
static inline void check_for_tasks(int dead_cpu)
{
struct task_struct *g, *p;
read_lock(&tasklist_lock);
for_each_process_thread(g, p) {
if (!p->on_rq)
continue;
/*
* We do the check with unlocked task_rq(p)->lock.
* Order the reading to do not warn about a task,
* which was running on this cpu in the past, and
* it's just been woken on another cpu.
*/
rmb();
if (task_cpu(p) != dead_cpu)
continue;
pr_warn("Task %s (pid=%d) is on cpu %d (state=%ld, flags=%x)\n",
p->comm, task_pid_nr(p), dead_cpu, p->state, p->flags);
}
read_unlock(&tasklist_lock);
}
static int notify_down_prepare(unsigned int cpu)
{
int err, nr_calls = 0;
err = __cpu_notify(CPU_DOWN_PREPARE, cpu, -1, &nr_calls);
if (err) {
nr_calls--;
__cpu_notify(CPU_DOWN_FAILED, cpu, nr_calls, NULL);
pr_warn("%s: attempt to take down CPU %u failed\n",
__func__, cpu);
}
return err;
}
/* 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;
/*
* 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--)
cpuhp_invoke_callback(cpu, st->state, false, NULL);
/* Give up timekeeping duties */
tick_handover_do_timer();
/* 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);
smpboot_park_threads(cpu);
/*
* 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(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 CPUHP_AP_SCHED_MIGRATE_DYING callback 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_completion(&st->done);
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);
return 0;
}
static int notify_dead(unsigned int cpu)
{
cpu_notify_nofail(CPU_DEAD, cpu);
check_for_tasks(cpu);
return 0;
}
static void cpuhp_complete_idle_dead(void *arg)
{
struct cpuhp_cpu_state *st = arg;
complete(&st->done);
}
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);
}
#else
#define notify_down_prepare NULL
#define takedown_cpu NULL
#define notify_dead NULL
#endif
#ifdef CONFIG_HOTPLUG_CPU
/* 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;
bool hasdied = false;
if (num_online_cpus() == 1)
return -EBUSY;
if (!cpu_present(cpu))
return -EINVAL;
cpu_hotplug_begin();
cpuhp_tasks_frozen = tasks_frozen;
prev_state = st->state;
st->target = 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) {
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;
}
/*
* 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) {
st->target = prev_state;
st->rollback = true;
cpuhp_kick_ap_work(cpu);
}
hasdied = prev_state != st->state && st->state == CPUHP_OFFLINE;
out:
cpu_hotplug_done();
/* This post dead nonsense must die */
if (!ret && hasdied)
cpu_notify_nofail(CPU_POST_DEAD, cpu);
return ret;
}
static int do_cpu_down(unsigned int cpu, enum cpuhp_state target)
{
int err;
cpu_maps_update_begin();
if (cpu_hotplug_disabled) {
err = -EBUSY;
goto out;
}
err = _cpu_down(cpu, 0, target);
out:
cpu_maps_update_done();
return err;
}
int cpu_down(unsigned int cpu)
{
return do_cpu_down(cpu, CPUHP_OFFLINE);
}
EXPORT_SYMBOL(cpu_down);
#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);
rcu_cpu_starting(cpu); /* Enables RCU usage on this CPU. */
while (st->state < target) {
st->state++;
cpuhp_invoke_callback(cpu, st->state, true, NULL);
}
}
/*
* Called from the idle task. Wake up the controlling task which brings the
* stopper and 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;