linux/kernel/stop_machine.c
Suresh Siddha 192d885742 x86, mtrr: use stop_machine APIs for doing MTRR rendezvous
MTRR rendezvous sequence is not implemened using stop_machine() before, as this
gets called both from the process context aswell as the cpu online paths
(where the cpu has not come online and the interrupts are disabled etc).

Now that we have a new stop_machine_from_inactive_cpu() API, use it for
rendezvous during mtrr init of a logical processor that is coming online.

For the rest (runtime MTRR modification, system boot, resume paths), use
stop_machine() to implement the rendezvous sequence. This will consolidate and
cleanup the code.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Link: http://lkml.kernel.org/r/20110623182057.076997177@sbsiddha-MOBL3.sc.intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
2011-06-27 15:17:13 -07:00

559 lines
15 KiB
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/module.h>
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/stop_machine.h>
#include <linux/interrupt.h>
#include <linux/kallsyms.h>
#include <asm/atomic.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 */
bool executed; /* actually executed? */
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 {
spinlock_t lock;
bool enabled; /* is this stopper enabled? */
struct list_head works; /* list of pending works */
struct task_struct *thread; /* stopper thread */
};
static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
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, bool executed)
{
if (done) {
if (executed)
done->executed = true;
if (atomic_dec_and_test(&done->nr_todo))
complete(&done->completion);
}
}
/* queue @work to @stopper. if offline, @work is completed immediately */
static void cpu_stop_queue_work(struct cpu_stopper *stopper,
struct cpu_stop_work *work)
{
unsigned long flags;
spin_lock_irqsave(&stopper->lock, flags);
if (stopper->enabled) {
list_add_tail(&work->list, &stopper->works);
wake_up_process(stopper->thread);
} else
cpu_stop_signal_done(work->done, false);
spin_unlock_irqrestore(&stopper->lock, flags);
}
/**
* 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);
cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), &work);
wait_for_completion(&done.completion);
return done.executed ? done.ret : -ENOENT;
}
/**
* 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
*
* 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.
*/
void 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, };
cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), work_buf);
}
/* static data for stop_cpus */
static DEFINE_MUTEX(stop_cpus_mutex);
static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work);
static void 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;
/* initialize works and done */
for_each_cpu(cpu, cpumask) {
work = &per_cpu(stop_cpus_work, cpu);
work->fn = fn;
work->arg = arg;
work->done = done;
}
/*
* 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();
for_each_cpu(cpu, cpumask)
cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu),
&per_cpu(stop_cpus_work, cpu));
preempt_enable();
}
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));
queue_stop_cpus_work(cpumask, fn, arg, &done);
wait_for_completion(&done.completion);
return done.executed ? done.ret : -ENOENT;
}
/**
* 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_stopper_thread(void *data)
{
struct cpu_stopper *stopper = data;
struct cpu_stop_work *work;
int ret;
repeat:
set_current_state(TASK_INTERRUPTIBLE); /* mb paired w/ kthread_stop */
if (kthread_should_stop()) {
__set_current_state(TASK_RUNNING);
return 0;
}
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;
char ksym_buf[KSYM_NAME_LEN] __maybe_unused;
__set_current_state(TASK_RUNNING);
/* cpu stop callbacks are not allowed to sleep */
preempt_disable();
ret = fn(arg);
if (ret)
done->ret = ret;
/* restore preemption and check it's still balanced */
preempt_enable();
WARN_ONCE(preempt_count(),
"cpu_stop: %s(%p) leaked preempt count\n",
kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL,
ksym_buf), arg);
cpu_stop_signal_done(done, true);
} else
schedule();
goto repeat;
}
extern void sched_set_stop_task(int cpu, struct task_struct *stop);
/* manage stopper for a cpu, mostly lifted from sched migration thread mgmt */
static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
unsigned long action, void *hcpu)
{
unsigned int cpu = (unsigned long)hcpu;
struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
struct task_struct *p;
switch (action & ~CPU_TASKS_FROZEN) {
case CPU_UP_PREPARE:
BUG_ON(stopper->thread || stopper->enabled ||
!list_empty(&stopper->works));
p = kthread_create_on_node(cpu_stopper_thread,
stopper,
cpu_to_node(cpu),
"migration/%d", cpu);
if (IS_ERR(p))
return notifier_from_errno(PTR_ERR(p));
get_task_struct(p);
kthread_bind(p, cpu);
sched_set_stop_task(cpu, p);
stopper->thread = p;
break;
case CPU_ONLINE:
/* strictly unnecessary, as first user will wake it */
wake_up_process(stopper->thread);
/* mark enabled */
spin_lock_irq(&stopper->lock);
stopper->enabled = true;
spin_unlock_irq(&stopper->lock);
break;
#ifdef CONFIG_HOTPLUG_CPU
case CPU_UP_CANCELED:
case CPU_POST_DEAD:
{
struct cpu_stop_work *work;
sched_set_stop_task(cpu, NULL);
/* kill the stopper */
kthread_stop(stopper->thread);
/* drain remaining works */
spin_lock_irq(&stopper->lock);
list_for_each_entry(work, &stopper->works, list)
cpu_stop_signal_done(work->done, false);
stopper->enabled = false;
spin_unlock_irq(&stopper->lock);
/* release the stopper */
put_task_struct(stopper->thread);
stopper->thread = NULL;
break;
}
#endif
}
return NOTIFY_OK;
}
/*
* Give it a higher priority so that cpu stopper is available to other
* cpu notifiers. It currently shares the same priority as sched
* migration_notifier.
*/
static struct notifier_block __cpuinitdata cpu_stop_cpu_notifier = {
.notifier_call = cpu_stop_cpu_callback,
.priority = 10,
};
static int __init cpu_stop_init(void)
{
void *bcpu = (void *)(long)smp_processor_id();
unsigned int cpu;
int err;
for_each_possible_cpu(cpu) {
struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
spin_lock_init(&stopper->lock);
INIT_LIST_HEAD(&stopper->works);
}
/* start one for the boot cpu */
err = cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_UP_PREPARE,
bcpu);
BUG_ON(err != NOTIFY_OK);
cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu);
register_cpu_notifier(&cpu_stop_cpu_notifier);
return 0;
}
early_initcall(cpu_stop_init);
#ifdef CONFIG_STOP_MACHINE
/* This controls the threads on each CPU. */
enum stopmachine_state {
/* Dummy starting state for thread. */
STOPMACHINE_NONE,
/* Awaiting everyone to be scheduled. */
STOPMACHINE_PREPARE,
/* Disable interrupts. */
STOPMACHINE_DISABLE_IRQ,
/* Run the function */
STOPMACHINE_RUN,
/* Exit */
STOPMACHINE_EXIT,
};
struct stop_machine_data {
int (*fn)(void *);
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 stopmachine_state state;
atomic_t thread_ack;
};
static void set_state(struct stop_machine_data *smdata,
enum stopmachine_state newstate)
{
/* Reset ack counter. */
atomic_set(&smdata->thread_ack, smdata->num_threads);
smp_wmb();
smdata->state = newstate;
}
/* Last one to ack a state moves to the next state. */
static void ack_state(struct stop_machine_data *smdata)
{
if (atomic_dec_and_test(&smdata->thread_ack))
set_state(smdata, smdata->state + 1);
}
/* This is the cpu_stop function which stops the CPU. */
static int stop_machine_cpu_stop(void *data)
{
struct stop_machine_data *smdata = data;
enum stopmachine_state curstate = STOPMACHINE_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 (!smdata->active_cpus)
is_active = cpu == cpumask_first(cpu_online_mask);
else
is_active = cpumask_test_cpu(cpu, smdata->active_cpus);
/* Simple state machine */
do {
/* Chill out and ensure we re-read stopmachine_state. */
cpu_relax();
if (smdata->state != curstate) {
curstate = smdata->state;
switch (curstate) {
case STOPMACHINE_DISABLE_IRQ:
local_irq_disable();
hard_irq_disable();
break;
case STOPMACHINE_RUN:
if (is_active)
err = smdata->fn(smdata->data);
break;
default:
break;
}
ack_state(smdata);
}
} while (curstate != STOPMACHINE_EXIT);
local_irq_restore(flags);
return err;
}
int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
{
struct stop_machine_data smdata = { .fn = fn, .data = data,
.num_threads = num_online_cpus(),
.active_cpus = cpus };
/* Set the initial state and stop all online cpus. */
set_state(&smdata, STOPMACHINE_PREPARE);
return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata);
}
int stop_machine(int (*fn)(void *), 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(int (*fn)(void *), void *data,
const struct cpumask *cpus)
{
struct stop_machine_data smdata = { .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()));
smdata.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(&smdata, STOPMACHINE_PREPARE);
cpu_stop_init_done(&done, num_active_cpus());
queue_stop_cpus_work(cpu_active_mask, stop_machine_cpu_stop, &smdata,
&done);
ret = stop_machine_cpu_stop(&smdata);
/* Busy wait for completion. */
while (!completion_done(&done.completion))
cpu_relax();
mutex_unlock(&stop_cpus_mutex);
return ret ?: done.ret;
}
#endif /* CONFIG_STOP_MACHINE */