Remove the use of kmalloc() from the smp_call_function_*()
calls.
Steven's generic-ipi patch (d7240b98
: generic-ipi: use per cpu
data for single cpu ipi calls) started the discussion on the use
of kmalloc() in this code and fixed the
smp_call_function_single(.wait=0) fallback case.
In this patch we complete this by also providing means for the
_many() call, which fully removes the need for kmalloc() in this
code.
The problem with the _many() call is that other cpus might still
be observing our entry when we're done with it. It solved this
by dynamically allocating data elements and RCU-freeing it.
We solve it by using a single per-cpu entry which provides
static storage and solves one half of the problem (avoiding
referencing freed data).
The other half, ensuring the queue iteration it still possible,
is done by placing re-used entries at the head of the list. This
means that if someone was still iterating that entry when it got
moved, he will now re-visit the entries on the list he had
already seen, but avoids skipping over entries like would have
happened had we placed the new entry at the end.
Furthermore, visiting entries twice is not a problem, since we
remove our cpu from the entry's cpumask once its called.
Many thanks to Oleg for his suggestions and him poking holes in
my earlier attempts.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
505 lines
13 KiB
C
505 lines
13 KiB
C
/*
|
|
* 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>
|
|
#include <linux/cpu.h>
|
|
|
|
static DEFINE_PER_CPU(struct call_single_queue, call_single_queue);
|
|
|
|
static struct {
|
|
struct list_head queue;
|
|
spinlock_t lock;
|
|
} call_function __cacheline_aligned_in_smp = {
|
|
.queue = LIST_HEAD_INIT(call_function.queue),
|
|
.lock = __SPIN_LOCK_UNLOCKED(call_function.lock),
|
|
};
|
|
|
|
enum {
|
|
CSD_FLAG_WAIT = 0x01,
|
|
CSD_FLAG_LOCK = 0x02,
|
|
};
|
|
|
|
struct call_function_data {
|
|
struct call_single_data csd;
|
|
spinlock_t lock;
|
|
unsigned int refs;
|
|
cpumask_var_t cpumask;
|
|
};
|
|
|
|
struct call_single_queue {
|
|
struct list_head list;
|
|
spinlock_t lock;
|
|
};
|
|
|
|
static DEFINE_PER_CPU(struct call_function_data, cfd_data) = {
|
|
.lock = __SPIN_LOCK_UNLOCKED(cfd_data.lock),
|
|
};
|
|
|
|
static int
|
|
hotplug_cfd(struct notifier_block *nfb, unsigned long action, void *hcpu)
|
|
{
|
|
long cpu = (long)hcpu;
|
|
struct call_function_data *cfd = &per_cpu(cfd_data, cpu);
|
|
|
|
switch (action) {
|
|
case CPU_UP_PREPARE:
|
|
case CPU_UP_PREPARE_FROZEN:
|
|
if (!alloc_cpumask_var_node(&cfd->cpumask, GFP_KERNEL,
|
|
cpu_to_node(cpu)))
|
|
return NOTIFY_BAD;
|
|
break;
|
|
|
|
#ifdef CONFIG_CPU_HOTPLUG
|
|
case CPU_UP_CANCELED:
|
|
case CPU_UP_CANCELED_FROZEN:
|
|
|
|
case CPU_DEAD:
|
|
case CPU_DEAD_FROZEN:
|
|
free_cpumask_var(cfd->cpumask);
|
|
break;
|
|
#endif
|
|
};
|
|
|
|
return NOTIFY_OK;
|
|
}
|
|
|
|
static struct notifier_block __cpuinitdata hotplug_cfd_notifier = {
|
|
.notifier_call = hotplug_cfd,
|
|
};
|
|
|
|
static int __cpuinit init_call_single_data(void)
|
|
{
|
|
void *cpu = (void *)(long)smp_processor_id();
|
|
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);
|
|
}
|
|
|
|
hotplug_cfd(&hotplug_cfd_notifier, CPU_UP_PREPARE, cpu);
|
|
register_cpu_notifier(&hotplug_cfd_notifier);
|
|
|
|
return 0;
|
|
}
|
|
early_initcall(init_call_single_data);
|
|
|
|
/*
|
|
* csd_wait/csd_complete are used for synchronous ipi calls
|
|
*/
|
|
static void csd_wait_prepare(struct call_single_data *data)
|
|
{
|
|
data->flags |= CSD_FLAG_WAIT;
|
|
}
|
|
|
|
static void csd_complete(struct call_single_data *data)
|
|
{
|
|
if (data->flags & CSD_FLAG_WAIT) {
|
|
/*
|
|
* ensure we're all done before saying we are
|
|
*/
|
|
smp_mb();
|
|
data->flags &= ~CSD_FLAG_WAIT;
|
|
}
|
|
}
|
|
|
|
static void csd_wait(struct call_single_data *data)
|
|
{
|
|
while (data->flags & CSD_FLAG_WAIT)
|
|
cpu_relax();
|
|
}
|
|
|
|
/*
|
|
* csd_lock/csd_unlock used to serialize access to per-cpu csd resources
|
|
*
|
|
* For non-synchronous ipi calls the csd can still be in use by the previous
|
|
* function call. For multi-cpu calls its even more interesting as we'll have
|
|
* to ensure no other cpu is observing our csd.
|
|
*/
|
|
static void csd_lock(struct call_single_data *data)
|
|
{
|
|
while (data->flags & CSD_FLAG_LOCK)
|
|
cpu_relax();
|
|
data->flags = CSD_FLAG_LOCK;
|
|
|
|
/*
|
|
* prevent CPU from reordering the above assignment to ->flags
|
|
* with any subsequent assignments to other fields of the
|
|
* specified call_single_data structure.
|
|
*/
|
|
|
|
smp_mb();
|
|
}
|
|
|
|
static void csd_unlock(struct call_single_data *data)
|
|
{
|
|
WARN_ON(!(data->flags & CSD_FLAG_LOCK));
|
|
/*
|
|
* ensure we're all done before releasing data
|
|
*/
|
|
smp_mb();
|
|
data->flags &= ~CSD_FLAG_LOCK;
|
|
}
|
|
|
|
/*
|
|
* 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);
|
|
|
|
/*
|
|
* The list addition should be visible before sending the IPI
|
|
* handler locks the list to pull the entry off it because of
|
|
* normal cache coherency rules implied by spinlocks.
|
|
*
|
|
* If IPIs can go out of order to the cache coherency protocol
|
|
* in an architecture, sufficient synchronisation should be added
|
|
* to arch code to make it appear to obey cache coherency WRT
|
|
* locking and barrier primitives. Generic code isn't really equipped
|
|
* to do the right thing...
|
|
*/
|
|
|
|
if (ipi)
|
|
arch_send_call_function_single_ipi(cpu);
|
|
|
|
if (wait)
|
|
csd_wait(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();
|
|
|
|
/*
|
|
* Ensure entry is visible on call_function_queue after we have
|
|
* entered the IPI. See comment in smp_call_function_many.
|
|
* If we don't have this, then we may miss an entry on the list
|
|
* and never get another IPI to process it.
|
|
*/
|
|
smp_mb();
|
|
|
|
/*
|
|
* It's ok to use list_for_each_rcu() here even though we may delete
|
|
* 'pos', since list_del_rcu() doesn't clear ->next
|
|
*/
|
|
list_for_each_entry_rcu(data, &call_function.queue, csd.list) {
|
|
int refs;
|
|
|
|
spin_lock(&data->lock);
|
|
if (!cpumask_test_cpu(cpu, data->cpumask)) {
|
|
spin_unlock(&data->lock);
|
|
continue;
|
|
}
|
|
cpumask_clear_cpu(cpu, data->cpumask);
|
|
spin_unlock(&data->lock);
|
|
|
|
data->csd.func(data->csd.info);
|
|
|
|
spin_lock(&data->lock);
|
|
WARN_ON(data->refs == 0);
|
|
refs = --data->refs;
|
|
if (!refs) {
|
|
spin_lock(&call_function.lock);
|
|
list_del_rcu(&data->csd.list);
|
|
spin_unlock(&call_function.lock);
|
|
}
|
|
spin_unlock(&data->lock);
|
|
|
|
if (refs)
|
|
continue;
|
|
|
|
csd_complete(&data->csd);
|
|
csd_unlock(&data->csd);
|
|
}
|
|
|
|
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);
|
|
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)
|
|
csd_complete(data);
|
|
|
|
/*
|
|
* Unlocked CSDs are valid through generic_exec_single()
|
|
*/
|
|
if (data_flags & CSD_FLAG_LOCK)
|
|
csd_unlock(data);
|
|
}
|
|
}
|
|
|
|
static DEFINE_PER_CPU(struct call_single_data, csd_data);
|
|
|
|
/*
|
|
* 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 = {
|
|
.flags = 0,
|
|
};
|
|
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_cpu_ids && cpu_online(cpu)) {
|
|
struct call_single_data *data;
|
|
|
|
if (!wait) {
|
|
/*
|
|
* We are calling a function on a single CPU
|
|
* and we are not going to wait for it to finish.
|
|
* We use a per cpu data to pass the information to
|
|
* that CPU. Since all callers of this code will
|
|
* use the same data, we must synchronize the
|
|
* callers to prevent a new caller from corrupting
|
|
* the data before the callee can access it.
|
|
*
|
|
* The CSD_FLAG_LOCK is used to let us know when
|
|
* the IPI handler is done with the data.
|
|
* The first caller will set it, and the callee
|
|
* will clear it. The next caller must wait for
|
|
* it to clear before we set it again. This
|
|
* will make sure the callee is done with the
|
|
* data before a new caller will use it.
|
|
*/
|
|
data = &__get_cpu_var(csd_data);
|
|
csd_lock(data);
|
|
} else {
|
|
data = &d;
|
|
csd_wait_prepare(data);
|
|
}
|
|
|
|
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);
|
|
}
|
|
|
|
/* FIXME: Shim for archs using old arch_send_call_function_ipi API. */
|
|
#ifndef arch_send_call_function_ipi_mask
|
|
#define arch_send_call_function_ipi_mask(maskp) \
|
|
arch_send_call_function_ipi(*(maskp))
|
|
#endif
|
|
|
|
/**
|
|
* smp_call_function_many(): Run a function on a set of other CPUs.
|
|
* @mask: The set of cpus to run on (only runs on online subset).
|
|
* @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.
|
|
*
|
|
* 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.
|
|
*/
|
|
void smp_call_function_many(const struct cpumask *mask,
|
|
void (*func)(void *), void *info,
|
|
bool wait)
|
|
{
|
|
struct call_function_data *data;
|
|
unsigned long flags;
|
|
int cpu, next_cpu, me = smp_processor_id();
|
|
|
|
/* Can deadlock when called with interrupts disabled */
|
|
WARN_ON(irqs_disabled());
|
|
|
|
/* So, what's a CPU they want? Ignoring this one. */
|
|
cpu = cpumask_first_and(mask, cpu_online_mask);
|
|
if (cpu == me)
|
|
cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
|
|
/* No online cpus? We're done. */
|
|
if (cpu >= nr_cpu_ids)
|
|
return;
|
|
|
|
/* Do we have another CPU which isn't us? */
|
|
next_cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
|
|
if (next_cpu == me)
|
|
next_cpu = cpumask_next_and(next_cpu, mask, cpu_online_mask);
|
|
|
|
/* Fastpath: do that cpu by itself. */
|
|
if (next_cpu >= nr_cpu_ids) {
|
|
smp_call_function_single(cpu, func, info, wait);
|
|
return;
|
|
}
|
|
|
|
data = &__get_cpu_var(cfd_data);
|
|
csd_lock(&data->csd);
|
|
|
|
spin_lock_irqsave(&data->lock, flags);
|
|
if (wait)
|
|
csd_wait_prepare(&data->csd);
|
|
|
|
data->csd.func = func;
|
|
data->csd.info = info;
|
|
cpumask_and(data->cpumask, mask, cpu_online_mask);
|
|
cpumask_clear_cpu(me, data->cpumask);
|
|
data->refs = cpumask_weight(data->cpumask);
|
|
|
|
spin_lock(&call_function.lock);
|
|
/*
|
|
* Place entry at the _HEAD_ of the list, so that any cpu still
|
|
* observing the entry in generic_smp_call_function_interrupt() will
|
|
* not miss any other list entries.
|
|
*/
|
|
list_add_rcu(&data->csd.list, &call_function.queue);
|
|
spin_unlock(&call_function.lock);
|
|
spin_unlock_irqrestore(&data->lock, flags);
|
|
|
|
/*
|
|
* Make the list addition visible before sending the ipi.
|
|
* (IPIs must obey or appear to obey normal Linux cache coherency
|
|
* rules -- see comment in generic_exec_single).
|
|
*/
|
|
smp_mb();
|
|
|
|
/* Send a message to all CPUs in the map */
|
|
arch_send_call_function_ipi_mask(data->cpumask);
|
|
|
|
/* optionally wait for the CPUs to complete */
|
|
if (wait)
|
|
csd_wait(&data->csd);
|
|
}
|
|
EXPORT_SYMBOL(smp_call_function_many);
|
|
|
|
/**
|
|
* 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.
|
|
*
|
|
* 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)
|
|
{
|
|
preempt_disable();
|
|
smp_call_function_many(cpu_online_mask, func, info, wait);
|
|
preempt_enable();
|
|
return 0;
|
|
}
|
|
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);
|
|
}
|