Quelle stop_machine.c Sprache: C

// SPDX-License-Identifier: GPL-2.0-or-later
/*
* kernel/stop_machine.c
*
* Copyright (C) 2008, 2005 IBM Corporation.
* Copyright (C) 2008, 2005 Rusty Russell rusty@rustcorp.com.au
* Copyright (C) 2010 SUSE Linux Products GmbH
* Copyright (C) 2010 Tejun Heo <tj@kernel.org>
*/
#include <linux/compiler.h>
#include <linux/completion.h>
#include <linux/cpu.h>
#include <linux/init.h>
#include <linux/kthread.h>
#include <linux/export.h>
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/stop_machine.h>
#include <linux/interrupt.h>
#include <linux/kallsyms.h>
#include <linux/smpboot.h>
#include <linux/atomic.h>
#include <linux/nmi.h>
#include <linux/sched/wake_q.h>

/*
* Structure to determine completion condition and record errors.  May
* be shared by works on different cpus.
*/
struct cpu_stop_done {
atomic_t  nr_todo; /* nr left to execute */
int   ret;  /* collected return value */
struct completion completion; /* fired if nr_todo reaches 0 */
};

/* the actual stopper, one per every possible cpu, enabled on online cpus */
struct cpu_stopper {
struct task_struct *thread;

raw_spinlock_t  lock;
bool   enabled; /* is this stopper enabled? */
struct list_head works;  /* list of pending works */

struct cpu_stop_work stop_work; /* for stop_cpus */
unsigned long  caller;
cpu_stop_fn_t  fn;
};

static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
static bool stop_machine_initialized = false;

void print_stop_info(const char *log_lvl, struct task_struct *task)
{
/*
* If @task is a stopper task, it cannot migrate and task_cpu() is
* stable.
*/
struct cpu_stopper *stopper = per_cpu_ptr(&cpu_stopper, task_cpu(task));

if (task != stopper->thread)
  return;

printk("%sStopper: %pS <- %pS\n", log_lvl, stopper->fn, (void *)stopper->caller);
}

/* static data for stop_cpus */
static DEFINE_MUTEX(stop_cpus_mutex);
static bool stop_cpus_in_progress;

static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
{
memset(done, 0, sizeof(*done));
atomic_set(&done->nr_todo, nr_todo);
init_completion(&done->completion);
}

/* signal completion unless @done is NULL */
static void cpu_stop_signal_done(struct cpu_stop_done *done)
{
if (atomic_dec_and_test(&done->nr_todo))
  complete(&done->completion);
}

static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
      struct cpu_stop_work *work)
{
list_add_tail(&work->list, &stopper->works);
}

/* queue @work to @stopper.  if offline, @work is completed immediately */
static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
{
struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
unsigned long flags;
bool enabled;

preempt_disable();
raw_spin_lock_irqsave(&stopper->lock, flags);
enabled = stopper->enabled;
if (enabled)
  __cpu_stop_queue_work(stopper, work);
else if (work->done)
  cpu_stop_signal_done(work->done);
raw_spin_unlock_irqrestore(&stopper->lock, flags);

if (enabled)
  wake_up_process(stopper->thread);
preempt_enable();

return enabled;
}

/**
* stop_one_cpu - stop a cpu
* @cpu: cpu to stop
* @fn: function to execute
* @arg: argument to @fn
*
* Execute @fn(@arg) on @cpu.  @fn is run in a process context with
* the highest priority preempting any task on the cpu and
* monopolizing it.  This function returns after the execution is
* complete.
*
* This function doesn't guarantee @cpu stays online till @fn
* completes.  If @cpu goes down in the middle, execution may happen
* partially or fully on different cpus.  @fn should either be ready
* for that or the caller should ensure that @cpu stays online until
* this function completes.
*
* CONTEXT:
* Might sleep.
*
* RETURNS:
* -ENOENT if @fn(@arg) was not executed because @cpu was offline;
* otherwise, the return value of @fn.
*/
int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
{
struct cpu_stop_done done;
struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done, .caller = _RET_IP_ };

cpu_stop_init_done(&done, 1);
if (!cpu_stop_queue_work(cpu, &work))
  return -ENOENT;
/*
* In case @cpu == smp_proccessor_id() we can avoid a sleep+wakeup
* cycle by doing a preemption:
*/
cond_resched();
wait_for_completion(&done.completion);
return done.ret;
}

/* This controls the threads on each CPU. */
enum multi_stop_state {
/* Dummy starting state for thread. */
MULTI_STOP_NONE,
/* Awaiting everyone to be scheduled. */
MULTI_STOP_PREPARE,
/* Disable interrupts. */
MULTI_STOP_DISABLE_IRQ,
/* Run the function */
MULTI_STOP_RUN,
/* Exit */
MULTI_STOP_EXIT,
};

struct multi_stop_data {
cpu_stop_fn_t  fn;
void   *data;
/* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
unsigned int  num_threads;
const struct cpumask *active_cpus;

enum multi_stop_state state;
atomic_t  thread_ack;
};

static void set_state(struct multi_stop_data *msdata,
        enum multi_stop_state newstate)
{
/* Reset ack counter. */
atomic_set(&msdata->thread_ack, msdata->num_threads);
smp_wmb();
WRITE_ONCE(msdata->state, newstate);
}

/* Last one to ack a state moves to the next state. */
static void ack_state(struct multi_stop_data *msdata)
{
if (atomic_dec_and_test(&msdata->thread_ack))
  set_state(msdata, msdata->state + 1);
}

notrace void __weak stop_machine_yield(const struct cpumask *cpumask)
{
cpu_relax();
}

/* This is the cpu_stop function which stops the CPU. */
static int multi_cpu_stop(void *data)
{
struct multi_stop_data *msdata = data;
enum multi_stop_state newstate, curstate = MULTI_STOP_NONE;
int cpu = smp_processor_id(), err = 0;
const struct cpumask *cpumask;
unsigned long flags;
bool is_active;

/*
* When called from stop_machine_from_inactive_cpu(), irq might
* already be disabled.  Save the state and restore it on exit.
*/
local_save_flags(flags);

if (!msdata->active_cpus) {
  cpumask = cpu_online_mask;
  is_active = cpu == cpumask_first(cpumask);
} else {
  cpumask = msdata->active_cpus;
  is_active = cpumask_test_cpu(cpu, cpumask);
}

/* Simple state machine */
do {
  /* Chill out and ensure we re-read multi_stop_state. */
  stop_machine_yield(cpumask);
  newstate = READ_ONCE(msdata->state);
  if (newstate != curstate) {
   curstate = newstate;
   switch (curstate) {
   case MULTI_STOP_DISABLE_IRQ:
    local_irq_disable();
    hard_irq_disable();
    break;
   case MULTI_STOP_RUN:
    if (is_active)
     err = msdata->fn(msdata->data);
    break;
   default:
    break;
   }
   ack_state(msdata);
  } else if (curstate > MULTI_STOP_PREPARE) {
   /*
* At this stage all other CPUs we depend on must spin
* in the same loop. Any reason for hard-lockup should
* be detected and reported on their side.
*/
   touch_nmi_watchdog();
   /* Also suppress RCU CPU stall warnings. */
   rcu_momentary_eqs();
  }
} while (curstate != MULTI_STOP_EXIT);

local_irq_restore(flags);
return err;
}

static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
        int cpu2, struct cpu_stop_work *work2)
{
struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1);
struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);
int err;

retry:
/*
* The waking up of stopper threads has to happen in the same
* scheduling context as the queueing.  Otherwise, there is a
* possibility of one of the above stoppers being woken up by another
* CPU, and preempting us. This will cause us to not wake up the other
* stopper forever.
*/
preempt_disable();
raw_spin_lock_irq(&stopper1->lock);
raw_spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);

if (!stopper1->enabled || !stopper2->enabled) {
  err = -ENOENT;
  goto unlock;
}

/*
* Ensure that if we race with __stop_cpus() the stoppers won't get
* queued up in reverse order leading to system deadlock.
*
* We can't miss stop_cpus_in_progress if queue_stop_cpus_work() has
* queued a work on cpu1 but not on cpu2, we hold both locks.
*
* It can be falsely true but it is safe to spin until it is cleared,
* queue_stop_cpus_work() does everything under preempt_disable().
*/
if (unlikely(stop_cpus_in_progress)) {
  err = -EDEADLK;
  goto unlock;
}

err = 0;
__cpu_stop_queue_work(stopper1, work1);
__cpu_stop_queue_work(stopper2, work2);

unlock:
raw_spin_unlock(&stopper2->lock);
raw_spin_unlock_irq(&stopper1->lock);

if (unlikely(err == -EDEADLK)) {
  preempt_enable();

  while (stop_cpus_in_progress)
   cpu_relax();

  goto retry;
}

if (!err) {
  wake_up_process(stopper1->thread);
  wake_up_process(stopper2->thread);
}
preempt_enable();

return err;
}
/**
* stop_two_cpus - stops two cpus
* @cpu1: the cpu to stop
* @cpu2: the other cpu to stop
* @fn: function to execute
* @arg: argument to @fn
*
* Stops both the current and specified CPU and runs @fn on one of them.
*
* returns when both are completed.
*/
int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
{
struct cpu_stop_done done;
struct cpu_stop_work work1, work2;
struct multi_stop_data msdata;

msdata = (struct multi_stop_data){
  .fn = fn,
  .data = arg,
  .num_threads = 2,
  .active_cpus = cpumask_of(cpu1),
};

work1 = work2 = (struct cpu_stop_work){
  .fn = multi_cpu_stop,
  .arg = &msdata,
  .done = &done,
  .caller = _RET_IP_,
};

cpu_stop_init_done(&done, 2);
set_state(&msdata, MULTI_STOP_PREPARE);

if (cpu1 > cpu2)
  swap(cpu1, cpu2);
if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))
  return -ENOENT;

wait_for_completion(&done.completion);
return done.ret;
}

/**
* stop_one_cpu_nowait - stop a cpu but don't wait for completion
* @cpu: cpu to stop
* @fn: function to execute
* @arg: argument to @fn
* @work_buf: pointer to cpu_stop_work structure
*
* Similar to stop_one_cpu() but doesn't wait for completion.  The
* caller is responsible for ensuring @work_buf is currently unused
* and will remain untouched until stopper starts executing @fn.
*
* CONTEXT:
* Don't care.
*
* RETURNS:
* true if cpu_stop_work was queued successfully and @fn will be called,
* false otherwise.
*/
bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
   struct cpu_stop_work *work_buf)
{
*work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, .caller = _RET_IP_, };
return cpu_stop_queue_work(cpu, work_buf);
}

static bool queue_stop_cpus_work(const struct cpumask *cpumask,
     cpu_stop_fn_t fn, void *arg,
     struct cpu_stop_done *done)
{
struct cpu_stop_work *work;
unsigned int cpu;
bool queued = false;

/*
* Disable preemption while queueing to avoid getting
* preempted by a stopper which might wait for other stoppers
* to enter @fn which can lead to deadlock.
*/
preempt_disable();
stop_cpus_in_progress = true;
barrier();
for_each_cpu(cpu, cpumask) {
  work = &per_cpu(cpu_stopper.stop_work, cpu);
  work->fn = fn;
  work->arg = arg;
  work->done = done;
  work->caller = _RET_IP_;
  if (cpu_stop_queue_work(cpu, work))
   queued = true;
}
barrier();
stop_cpus_in_progress = false;
preempt_enable();

return queued;
}

static int __stop_cpus(const struct cpumask *cpumask,
         cpu_stop_fn_t fn, void *arg)
{
struct cpu_stop_done done;

cpu_stop_init_done(&done, cpumask_weight(cpumask));
if (!queue_stop_cpus_work(cpumask, fn, arg, &done))
  return -ENOENT;
wait_for_completion(&done.completion);
return done.ret;
}

/**
* stop_cpus - stop multiple cpus
* @cpumask: cpus to stop
* @fn: function to execute
* @arg: argument to @fn
*
* Execute @fn(@arg) on online cpus in @cpumask.  On each target cpu,
* @fn is run in a process context with the highest priority
* preempting any task on the cpu and monopolizing it.  This function
* returns after all executions are complete.
*
* This function doesn't guarantee the cpus in @cpumask stay online
* till @fn completes.  If some cpus go down in the middle, execution
* on the cpu may happen partially or fully on different cpus.  @fn
* should either be ready for that or the caller should ensure that
* the cpus stay online until this function completes.
*
* All stop_cpus() calls are serialized making it safe for @fn to wait
* for all cpus to start executing it.
*
* CONTEXT:
* Might sleep.
*
* RETURNS:
* -ENOENT if @fn(@arg) was not executed at all because all cpus in
* @cpumask were offline; otherwise, 0 if all executions of @fn
* returned 0, any non zero return value if any returned non zero.
*/
static int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
{
int ret;

/* static works are used, process one request at a time */
mutex_lock(&stop_cpus_mutex);
ret = __stop_cpus(cpumask, fn, arg);
mutex_unlock(&stop_cpus_mutex);
return ret;
}

static int cpu_stop_should_run(unsigned int cpu)
{
struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
unsigned long flags;
int run;

raw_spin_lock_irqsave(&stopper->lock, flags);
run = !list_empty(&stopper->works);
raw_spin_unlock_irqrestore(&stopper->lock, flags);
return run;
}

static void cpu_stopper_thread(unsigned int cpu)
{
struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
struct cpu_stop_work *work;

repeat:
work = NULL;
raw_spin_lock_irq(&stopper->lock);
if (!list_empty(&stopper->works)) {
  work = list_first_entry(&stopper->works,
     struct cpu_stop_work, list);
  list_del_init(&work->list);
}
raw_spin_unlock_irq(&stopper->lock);

if (work) {
  cpu_stop_fn_t fn = work->fn;
  void *arg = work->arg;
  struct cpu_stop_done *done = work->done;
  int ret;

  /* cpu stop callbacks must not sleep, make in_atomic() == T */
  stopper->caller = work->caller;
  stopper->fn = fn;
  preempt_count_inc();
  ret = fn(arg);
  if (done) {
   if (ret)
    done->ret = ret;
   cpu_stop_signal_done(done);
  }
  preempt_count_dec();
  stopper->fn = NULL;
  stopper->caller = 0;
  WARN_ONCE(preempt_count(),
     "cpu_stop: %ps(%p) leaked preempt count\n", fn, arg);
  goto repeat;
}
}

void stop_machine_park(int cpu)
{
struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
/*
* Lockless. cpu_stopper_thread() will take stopper->lock and flush
* the pending works before it parks, until then it is fine to queue
* the new works.
*/
stopper->enabled = false;
kthread_park(stopper->thread);
}

static void cpu_stop_create(unsigned int cpu)
{
sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
}

static void cpu_stop_park(unsigned int cpu)
{
struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);

WARN_ON(!list_empty(&stopper->works));
}

void stop_machine_unpark(int cpu)
{
struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);

stopper->enabled = true;
kthread_unpark(stopper->thread);
}

static struct smp_hotplug_thread cpu_stop_threads = {
.store   = &cpu_stopper.thread,
.thread_should_run = cpu_stop_should_run,
.thread_fn  = cpu_stopper_thread,
.thread_comm  = "migration/%u",
.create   = cpu_stop_create,
.park   = cpu_stop_park,
.selfparking  = true,
};

static int __init cpu_stop_init(void)
{
unsigned int cpu;

for_each_possible_cpu(cpu) {
  struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);

  raw_spin_lock_init(&stopper->lock);
  INIT_LIST_HEAD(&stopper->works);
}

BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
stop_machine_unpark(raw_smp_processor_id());
stop_machine_initialized = true;
return 0;
}
early_initcall(cpu_stop_init);

int stop_machine_cpuslocked(cpu_stop_fn_t fn, void *data,
       const struct cpumask *cpus)
{
struct multi_stop_data msdata = {
  .fn = fn,
  .data = data,
  .num_threads = num_online_cpus(),
  .active_cpus = cpus,
};

lockdep_assert_cpus_held();

if (!stop_machine_initialized) {
  /*
* Handle the case where stop_machine() is called
* early in boot before stop_machine() has been
* initialized.
*/
  unsigned long flags;
  int ret;

  WARN_ON_ONCE(msdata.num_threads != 1);

  local_irq_save(flags);
  hard_irq_disable();
  ret = (*fn)(data);
  local_irq_restore(flags);

  return ret;
}

/* Set the initial state and stop all online cpus. */
set_state(&msdata, MULTI_STOP_PREPARE);
return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
}

int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
{
int ret;

/* No CPUs can come up or down during this. */
cpus_read_lock();
ret = stop_machine_cpuslocked(fn, data, cpus);
cpus_read_unlock();
return ret;
}
EXPORT_SYMBOL_GPL(stop_machine);

#ifdef CONFIG_SCHED_SMT
int stop_core_cpuslocked(unsigned int cpu, cpu_stop_fn_t fn, void *data)
{
const struct cpumask *smt_mask = cpu_smt_mask(cpu);

struct multi_stop_data msdata = {
  .fn = fn,
  .data = data,
  .num_threads = cpumask_weight(smt_mask),
  .active_cpus = smt_mask,
};

lockdep_assert_cpus_held();

/* Set the initial state and stop all online cpus. */
set_state(&msdata, MULTI_STOP_PREPARE);
return stop_cpus(smt_mask, multi_cpu_stop, &msdata);
}
EXPORT_SYMBOL_GPL(stop_core_cpuslocked);
#endif

/**
* stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
* @fn: the function to run
* @data: the data ptr for the @fn()
* @cpus: the cpus to run the @fn() on (NULL = any online cpu)
*
* This is identical to stop_machine() but can be called from a CPU which
* is not active.  The local CPU is in the process of hotplug (so no other
* CPU hotplug can start) and not marked active and doesn't have enough
* context to sleep.
*
* This function provides stop_machine() functionality for such state by
* using busy-wait for synchronization and executing @fn directly for local
* CPU.
*
* CONTEXT:
* Local CPU is inactive.  Temporarily stops all active CPUs.
*
* RETURNS:
* 0 if all executions of @fn returned 0, any non zero return value if any
* returned non zero.
*/
int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
      const struct cpumask *cpus)
{
struct multi_stop_data msdata = { .fn = fn, .data = data,
         .active_cpus = cpus };
struct cpu_stop_done done;
int ret;

/* Local CPU must be inactive and CPU hotplug in progress. */
BUG_ON(cpu_active(raw_smp_processor_id()));
msdata.num_threads = num_active_cpus() + 1; /* +1 for local */

/* No proper task established and can't sleep - busy wait for lock. */
while (!mutex_trylock(&stop_cpus_mutex))
  cpu_relax();

/* Schedule work on other CPUs and execute directly for local CPU */
set_state(&msdata, MULTI_STOP_PREPARE);
cpu_stop_init_done(&done, num_active_cpus());
queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
        &done);
ret = multi_cpu_stop(&msdata);

/* Busy wait for completion. */
while (!completion_done(&done.completion))
  cpu_relax();

mutex_unlock(&stop_cpus_mutex);
return ret ?: done.ret;
}

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