/*
* Generic helpers for smp ipi calls
*
* (C) Jens Axboe <jens.axboe@oracle.com> 2008
*
*/
#include <linux/init.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/rcupdate.h>
#include <linux/rculist.h>
#include <linux/smp.h>
static DEFINE_PER_CPU(struct call_single_queue, call_single_queue);
static LIST_HEAD(call_function_queue);
__cacheline_aligned_in_smp DEFINE_SPINLOCK(call_function_lock);
enum {
CSD_FLAG_WAIT = 0x01,
CSD_FLAG_ALLOC = 0x02,
};
struct call_function_data {
struct call_single_data csd;
spinlock_t lock;
unsigned int refs;
cpumask_t cpumask;
struct rcu_head rcu_head;
};
struct call_single_queue {
struct list_head list;
spinlock_t lock;
};
static int __cpuinit init_call_single_data(void)
{
int i;
for_each_possible_cpu(i) {
struct call_single_queue *q = &per_cpu(call_single_queue, i);
spin_lock_init(&q->lock);
INIT_LIST_HEAD(&q->list);
}
return 0;
}
early_initcall(init_call_single_data);
static void csd_flag_wait(struct call_single_data *data)
{
/* Wait for response */
do {
/*
* We need to see the flags store in the IPI handler
*/
smp_mb();
if (!(data->flags & CSD_FLAG_WAIT))
break;
cpu_relax();
} while (1);
}
/*
* Insert a previously allocated call_single_data element for execution
* on the given CPU. data must already have ->func, ->info, and ->flags set.
*/
static void generic_exec_single(int cpu, struct call_single_data *data)
{
struct call_single_queue *dst = &per_cpu(call_single_queue, cpu);
int wait = data->flags & CSD_FLAG_WAIT, ipi;
unsigned long flags;
spin_lock_irqsave(&dst->lock, flags);
ipi = list_empty(&dst->list);
list_add_tail(&data->list, &dst->list);
spin_unlock_irqrestore(&dst->lock, flags);
if (ipi)
arch_send_call_function_single_ipi(cpu);
if (wait)
csd_flag_wait(data);
}
static void rcu_free_call_data(struct rcu_head *head)
{
struct call_function_data *data;
data = container_of(head, struct call_function_data, rcu_head);
kfree(data);
}
/*
* Invoked by arch to handle an IPI for call function. Must be called with
* interrupts disabled.
*/
void generic_smp_call_function_interrupt(void)
{
struct call_function_data *data;
int cpu = get_cpu();
/*
* It's ok to use list_for_each_rcu() here even though we may delete
* 'pos', since list_del_rcu() doesn't clear ->next
*/
rcu_read_lock();
list_for_each_entry_rcu(data, &call_function_queue, csd.list) {
int refs;
if (!cpu_isset(cpu, data->cpumask))
continue;
data->csd.func(data->csd.info);
spin_lock(&data->lock);
cpu_clear(cpu, data->cpumask);
WARN_ON(data->refs == 0);
data->refs--;
refs = data->refs;
spin_unlock(&data->lock);
if (refs)
continue;
spin_lock(&call_function_lock);
list_del_rcu(&data->csd.list);
spin_unlock(&call_function_lock);
if (data->csd.flags & CSD_FLAG_WAIT) {
/*
* serialize stores to data with the flag clear
* and wakeup
*/
smp_wmb();
data->csd.flags &= ~CSD_FLAG_WAIT;
}
if (data->csd.flags & CSD_FLAG_ALLOC)
call_rcu(&data->rcu_head, rcu_free_call_data);
}
rcu_read_unlock();
put_cpu();
}
/*
* Invoked by arch to handle an IPI for call function single. Must be called
* from the arch with interrupts disabled.
*/
void generic_smp_call_function_single_interrupt(void)
{
struct call_single_queue *q = &__get_cpu_var(call_single_queue);
LIST_HEAD(list);
/*
* Need to see other stores to list head for checking whether
* list is empty without holding q->lock
*/
smp_mb();
while (!list_empty(&q->list)) {
unsigned int data_flags;
spin_lock(&q->lock);
list_replace_init(&q->list, &list);
spin_unlock(&q->lock);
while (!list_empty(&list)) {
struct call_single_data *data;
data = list_entry(list.next, struct call_single_data,
list);
list_del(&data->list);
/*
* 'data' can be invalid after this call if
* flags == 0 (when called through
* generic_exec_single(), so save them away before
* making the call.
*/
data_flags = data->flags;
data->func(data->info);
if (data_flags & CSD_FLAG_WAIT) {
smp_wmb();
data->flags &= ~CSD_FLAG_WAIT;
} else if (data_flags & CSD_FLAG_ALLOC)
kfree(data);
}
/*
* See comment on outer loop
*/
smp_mb();
}
}
/*
* smp_call_function_single - Run a function on a specific CPU
* @func: The function to run. This must be fast and non-blocking.
* @info: An arbitrary pointer to pass to the function.
* @wait: If true, wait until function has completed on other CPUs.
*
* Returns 0 on success, else a negative status code. Note that @wait
* will be implicitly turned on in case of allocation failures, since
* we fall back to on-stack allocation.
*/
int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
int wait)
{
struct call_single_data d;
unsigned long flags;
/* prevent preemption and reschedule on another processor,
as well as CPU removal */
int me = get_cpu();
int err = 0;
/* Can deadlock when called with interrupts disabled */
WARN_ON(irqs_disabled());
if (cpu == me) {
local_irq_save(flags);
func(info);
local_irq_restore(flags);
} else if ((unsigned)cpu < NR_CPUS && cpu_online(cpu)) {
struct call_single_data *data = NULL;
if (!wait) {
data = kmalloc(sizeof(*data), GFP_ATOMIC);
if (data)
data->flags = CSD_FLAG_ALLOC;
}
if (!data) {
data = &d;
data->flags = CSD_FLAG_WAIT;
}
data->func = func;
data->info = info;
generic_exec_single(cpu, data);
} else {
err = -ENXIO; /* CPU not online */
}
put_cpu();
return err;
}
EXPORT_SYMBOL(smp_call_function_single);
/**
* __smp_call_function_single(): Run a function on another CPU
* @cpu: The CPU to run on.
* @data: Pre-allocated and setup data structure
*
* Like smp_call_function_single(), but allow caller to pass in a pre-allocated
* data structure. Useful for embedding @data inside other structures, for
* instance.
*
*/
void __smp_call_function_single(int cpu, struct call_single_data *data)
{
/* Can deadlock when called with interrupts disabled */
WARN_ON((data->flags & CSD_FLAG_WAIT) && irqs_disabled());
generic_exec_single(cpu, data);
}
/* Dummy function */
static void quiesce_dummy(void *unused)
{
}
/*
* Ensure stack based data used in call function mask is safe to free.
*
* This is needed by smp_call_function_mask when using on-stack data, because
* a single call function queue is shared by all CPUs, and any CPU may pick up
* the data item on the queue at any time before it is deleted. So we need to
* ensure that all CPUs have transitioned through a quiescent state after
* this call.
*
* This is a very slow function, implemented by sending synchronous IPIs to
* all possible CPUs. For this reason, we have to alloc data rather than use
* stack based data even in the case of synchronous calls. The stack based
* data is then just used for deadlock/oom fallback which will be very rare.
*
* If a faster scheme can be made, we could go back to preferring stack based
* data -- the data allocation/free is non-zero cost.
*/
static void smp_call_function_mask_quiesce_stack(cpumask_t mask)
{
struct call_single_data data;
int cpu;
data.func = quiesce_dummy;
data.info = NULL;
for_each_cpu_mask(cpu, mask) {
data.flags = CSD_FLAG_WAIT;
generic_exec_single(cpu, &data);
}
}
/**
* smp_call_function_mask(): Run a function on a set of other CPUs.
* @mask: The set of cpus to run on.
* @func: The function to run. This must be fast and non-blocking.
* @info: An arbitrary pointer to pass to the function.
* @wait: If true, wait (atomically) until function has completed on other CPUs.
*
* Returns 0 on success, else a negative status code.
*
* If @wait is true, then returns once @func has returned. Note that @wait
* will be implicitly turned on in case of allocation failures, since
* we fall back to on-stack allocation.
*
* You must not call this function with disabled interrupts or from a
* hardware interrupt handler or from a bottom half handler. Preemption
* must be disabled when calling this function.
*/
int smp_call_function_mask(cpumask_t mask, void (*func)(void *), void *info,
int wait)
{
struct call_function_data d;
struct call_function_data *data = NULL;
cpumask_t allbutself;
unsigned long flags;
int cpu, num_cpus;
int slowpath = 0;
/* Can deadlock when called with interrupts disabled */
WARN_ON(irqs_disabled());
cpu = smp_processor_id();
allbutself = cpu_online_map;
cpu_clear(cpu, allbutself);
cpus_and(mask, mask, allbutself);
num_cpus = cpus_weight(mask);
/*
* If zero CPUs, return. If just a single CPU, turn this request
* into a targetted single call instead since it's faster.
*/
if (!num_cpus)
return 0;
else if (num_cpus == 1) {
cpu = first_cpu(mask);
return smp_call_function_single(cpu, func, info, wait);
}
data = kmalloc(sizeof(*data), GFP_ATOMIC);
if (data) {
data->csd.flags = CSD_FLAG_ALLOC;
if (wait)
data->csd.flags |= CSD_FLAG_WAIT;
} else {
data = &d;
data->csd.flags = CSD_FLAG_WAIT;
wait = 1;
slowpath = 1;
}
spin_lock_init(&data->lock);
data->csd.func = func;
data->csd.info = info;
data->refs = num_cpus;
data->cpumask = mask;
spin_lock_irqsave(&call_function_lock, flags);
list_add_tail_rcu(&data->csd.list, &call_function_queue);
spin_unlock_irqrestore(&call_function_lock, flags);
/* Send a message to all CPUs in the map */
arch_send_call_function_ipi(mask);
/* optionally wait for the CPUs to complete */
if (wait) {
csd_flag_wait(&data->csd);
if (unlikely(slowpath))
smp_call_function_mask_quiesce_stack(mask);
}
return 0;
}
EXPORT_SYMBOL(smp_call_function_mask);
/**
* smp_call_function(): Run a function on all other CPUs.
* @func: The function to run. This must be fast and non-blocking.
* @info: An arbitrary pointer to pass to the function.
* @wait: If true, wait (atomically) until function has completed on other CPUs.
*
* Returns 0 on success, else a negative status code.
*
* If @wait is true, then returns once @func has returned; otherwise
* it returns just before the target cpu calls @func. In case of allocation
* failure, @wait will be implicitly turned on.
*
* You must not call this function with disabled interrupts or from a
* hardware interrupt handler or from a bottom half handler.
*/
int smp_call_function(void (*func)(void *), void *info, int wait)
{
int ret;
preempt_disable();
ret = smp_call_function_mask(cpu_online_map, func, info, wait);
preempt_enable();
return ret;
}
EXPORT_SYMBOL(smp_call_function);
void ipi_call_lock(void)
{
spin_lock(&call_function_lock);
}
void ipi_call_unlock(void)
{
spin_unlock(&call_function_lock);
}
void ipi_call_lock_irq(void)
{
spin_lock_irq(&call_function_lock);
}
void ipi_call_unlock_irq(void)
{
spin_unlock_irq(&call_function_lock);
}
