https://github.com/torvalds/linux
Tip revision: a99cde438de0c4c0cecc1d1af1a55a75b10bfdef authored by Linus Torvalds on 04 July 2016, 06:01:00 UTC
Linux 4.7-rc6
Linux 4.7-rc6
Tip revision: a99cde4
stop_machine.c
/*
* kernel/stop_machine.c
*
* Copyright (C) 2008, 2005 IBM Corporation.
* Copyright (C) 2008, 2005 Rusty Russell rusty@rustcorp.com.au
* Copyright (C) 2010 SUSE Linux Products GmbH
* Copyright (C) 2010 Tejun Heo <tj@kernel.org>
*
* This file is released under the GPLv2 and any later version.
*/
#include <linux/completion.h>
#include <linux/cpu.h>
#include <linux/init.h>
#include <linux/kthread.h>
#include <linux/export.h>
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/stop_machine.h>
#include <linux/interrupt.h>
#include <linux/kallsyms.h>
#include <linux/smpboot.h>
#include <linux/atomic.h>
#include <linux/lglock.h>
/*
* Structure to determine completion condition and record errors. May
* be shared by works on different cpus.
*/
struct cpu_stop_done {
atomic_t nr_todo; /* nr left to execute */
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;
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 */
};
static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
static bool stop_machine_initialized = false;
/*
* Avoids a race between stop_two_cpus and global stop_cpus, where
* the stoppers could get queued up in reverse order, leading to
* system deadlock. Using an lglock means stop_two_cpus remains
* relatively cheap.
*/
DEFINE_STATIC_LGLOCK(stop_cpus_lock);
static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
{
memset(done, 0, sizeof(*done));
atomic_set(&done->nr_todo, nr_todo);
init_completion(&done->completion);
}
/* signal completion unless @done is NULL */
static void cpu_stop_signal_done(struct cpu_stop_done *done)
{
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);
wake_up_process(stopper->thread);
}
/* 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;
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);
spin_unlock_irqrestore(&stopper->lock, flags);
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 };
cpu_stop_init_done(&done, 1);
if (!cpu_stop_queue_work(cpu, &work))
return -ENOENT;
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();
msdata->state = newstate;
}
/* Last one to ack a state moves to the next state. */
static void ack_state(struct multi_stop_data *msdata)
{
if (atomic_dec_and_test(&msdata->thread_ack))
set_state(msdata, msdata->state + 1);
}
/* This is the cpu_stop function which stops the CPU. */
static int multi_cpu_stop(void *data)
{
struct multi_stop_data *msdata = data;
enum multi_stop_state curstate = MULTI_STOP_NONE;
int cpu = smp_processor_id(), err = 0;
unsigned long flags;
bool is_active;
/*
* When called from stop_machine_from_inactive_cpu(), irq might
* already be disabled. Save the state and restore it on exit.
*/
local_save_flags(flags);
if (!msdata->active_cpus)
is_active = cpu == cpumask_first(cpu_online_mask);
else
is_active = cpumask_test_cpu(cpu, msdata->active_cpus);
/* Simple state machine */
do {
/* Chill out and ensure we re-read multi_stop_state. */
cpu_relax();
if (msdata->state != curstate) {
curstate = msdata->state;
switch (curstate) {
case MULTI_STOP_DISABLE_IRQ:
local_irq_disable();
hard_irq_disable();
break;
case MULTI_STOP_RUN:
if (is_active)
err = msdata->fn(msdata->data);
break;
default:
break;
}
ack_state(msdata);
}
} while (curstate != MULTI_STOP_EXIT);
local_irq_restore(flags);
return err;
}
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;
lg_double_lock(&stop_cpus_lock, cpu1, cpu2);
spin_lock_irq(&stopper1->lock);
spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);
err = -ENOENT;
if (!stopper1->enabled || !stopper2->enabled)
goto unlock;
err = 0;
__cpu_stop_queue_work(stopper1, work1);
__cpu_stop_queue_work(stopper2, work2);
unlock:
spin_unlock(&stopper2->lock);
spin_unlock_irq(&stopper1->lock);
lg_double_unlock(&stop_cpus_lock, cpu1, cpu2);
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
};
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, };
return cpu_stop_queue_work(cpu, work_buf);
}
/* static data for stop_cpus */
static DEFINE_MUTEX(stop_cpus_mutex);
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.
*/
lg_global_lock(&stop_cpus_lock);
for_each_cpu(cpu, cpumask) {
work = &per_cpu(cpu_stopper.stop_work, cpu);
work->fn = fn;
work->arg = arg;
work->done = done;
if (cpu_stop_queue_work(cpu, work))
queued = true;
}
lg_global_unlock(&stop_cpus_lock);
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.
*/
int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
{
int ret;
/* static works are used, process one request at a time */
mutex_lock(&stop_cpus_mutex);
ret = __stop_cpus(cpumask, fn, arg);
mutex_unlock(&stop_cpus_mutex);
return ret;
}
/**
* try_stop_cpus - try to stop multiple cpus
* @cpumask: cpus to stop
* @fn: function to execute
* @arg: argument to @fn
*
* Identical to stop_cpus() except that it fails with -EAGAIN if
* someone else is already using the facility.
*
* CONTEXT:
* Might sleep.
*
* RETURNS:
* -EAGAIN if someone else is already stopping cpus, -ENOENT if
* @fn(@arg) was not executed at all because all cpus in @cpumask were
* offline; otherwise, 0 if all executions of @fn returned 0, any non
* zero return value if any returned non zero.
*/
int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
{
int ret;
/* static works are used, process one request at a time */
if (!mutex_trylock(&stop_cpus_mutex))
return -EAGAIN;
ret = __stop_cpus(cpumask, fn, arg);
mutex_unlock(&stop_cpus_mutex);
return ret;
}
static int cpu_stop_should_run(unsigned int cpu)
{
struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
unsigned long flags;
int run;
spin_lock_irqsave(&stopper->lock, flags);
run = !list_empty(&stopper->works);
spin_unlock_irqrestore(&stopper->lock, flags);
return run;
}
static void cpu_stopper_thread(unsigned int cpu)
{
struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
struct cpu_stop_work *work;
repeat:
work = NULL;
spin_lock_irq(&stopper->lock);
if (!list_empty(&stopper->works)) {
work = list_first_entry(&stopper->works,
struct cpu_stop_work, list);
list_del_init(&work->list);
}
spin_unlock_irq(&stopper->lock);
if (work) {
cpu_stop_fn_t fn = work->fn;
void *arg = work->arg;
struct cpu_stop_done *done = work->done;
int ret;
/* cpu stop callbacks must not sleep, make in_atomic() == T */
preempt_count_inc();
ret = fn(arg);
if (done) {
if (ret)
done->ret = ret;
cpu_stop_signal_done(done);
}
preempt_count_dec();
WARN_ONCE(preempt_count(),
"cpu_stop: %pf(%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);
}
extern void sched_set_stop_task(int cpu, struct task_struct *stop);
static void cpu_stop_create(unsigned int cpu)
{
sched_set_stop_task(cpu, per_cpu(cpu_stopper.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);
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);
static int __stop_machine(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,
};
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. */
get_online_cpus();
ret = __stop_machine(fn, data, cpus);
put_online_cpus();
return ret;
}
EXPORT_SYMBOL_GPL(stop_machine);
/**
* 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;
}