/*
 * Generic helpers for smp ipi calls
 *
 * (C) Jens Axboe <jens.axboe@oracle.com> 2008
 */
#include <linux/rcupdate.h>
#include <linux/rculist.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/init.h>
#include <linux/gfp.h>
#include <linux/smp.h>
#include <linux/cpu.h>
#include <linux/sched.h>
#include <linux/nmi.h>

#ifdef CONFIG_USE_GENERIC_SMP_HELPERS
static struct {
	struct list_head	queue;
	raw_spinlock_t		lock;
} call_function __cacheline_aligned_in_smp =
	{
		.queue		= LIST_HEAD_INIT(call_function.queue),
		.lock		= __RAW_SPIN_LOCK_UNLOCKED(call_function.lock),
	};

enum {
	CSD_FLAG_LOCK		= 0x01,
};

struct call_function_data {
	struct call_single_data	csd;
	atomic_t		refs;
	cpumask_var_t		cpumask;
};

static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_function_data, cfd_data);

struct call_single_queue {
	struct list_head	list;
	raw_spinlock_t		lock;
};

static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_single_queue, call_single_queue);

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 (!zalloc_cpumask_var_node(&cfd->cpumask, GFP_KERNEL,
				cpu_to_node(cpu)))
			return notifier_from_errno(-ENOMEM);
		break;

#ifdef CONFIG_HOTPLUG_CPU
	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);

		raw_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);

#define CPU_UNSPEC (-1)

#define CSD_LOCK_TIMEOUT 500ULL      /* Locking timeout in ms */
#define CSD_LOCK_TIMEOUT_MAXRETRY 3  /* How often to retry an IPI on timeout */

/* Print this ID in every printk line we output, to be able to easily sort them apart: */
static atomic_t csd_bug_count = ATOMIC_INIT(0);
static DEFINE_PER_CPU(bool, csd_locked_up);

static bool csd_is_queued_on(struct call_single_data *csd, int cpu)
{
	struct call_single_queue *dst =
		&per_cpu(call_single_queue, cpu);
	struct call_single_data *queued_csd;
	unsigned long flags;
	bool csd_found;

	csd_found = false;
	raw_spin_lock_irqsave(&dst->lock, flags);
	list_for_each_entry(queued_csd, &dst->list, list) {
		if (queued_csd == csd) {
			csd_found = true;
			break;
		}
	}
	raw_spin_unlock_irqrestore(&dst->lock, flags);

	return csd_found;
}

struct csd_retry_info {
	int id;
	int nretries;
};

static bool csd_check_timeout(struct call_single_data *csd, int cpu,
			      unsigned long long *ts0, struct csd_retry_info *retry)
{
	int this_cpu = raw_smp_processor_id();
	unsigned long long ts1, ts_delta, ts_delta_s;
	unsigned int ts_delta_ms;
	bool csd_is_queued;

	pr_info_once("csd: CSD deadlock debugging initiated!\n");

	ts1 = div_u64(sched_clock(), 1000000);

	/* Init timeout on first invocation */
	if (unlikely(*ts0 == 0)) {
		*ts0 = ts1;
		return false;
	}

	ts_delta = ts1 - *ts0;
	if (likely(ts_delta < CSD_LOCK_TIMEOUT))
		return false;

	/* Uh oh, it took too long. */

	/* Panic on excessive timeout loop */
	if (retry->nretries++ == CSD_LOCK_TIMEOUT_MAXRETRY)
		goto panic;

	if (!retry->id)
		retry->id = atomic_inc_return(&csd_bug_count);

	ts_delta_s = div_u64_rem(ts_delta, 1000, &ts_delta_ms);
	pr_emerg("csd: Detected non-responsive CSD lock (#%d) for %pf on CPU#%02d, waiting %Lu.%03u secs for CPU#%02d\n",
		retry->id, csd->func, this_cpu,
		ts_delta_s, ts_delta_ms, cpu);

	if (cpu < 0) {
		csd_is_queued = false;
	} else {
		/* For single calls, we may be able to recover */
		csd_is_queued = csd_is_queued_on(csd, cpu);
		pr_emerg("csd: Locked CSD #%d %sfound in CSD queue of target CPU#%d\n",
				retry->id,
				csd_is_queued ? "" : "NOT ",
				cpu);
		per_cpu(csd_locked_up, cpu) = true;
	}

	if (retry->nretries == 1) {
		dump_stack();
		trigger_allbutself_cpu_backtrace();
		add_taint(TAINT_WARN);
	}

	if (!csd_is_queued)
		goto panic;

	/* Try to recover */

	pr_alert("csd: Re-sending CSD lock (#%d) IPI from CPU#%02d to CPU#%02d\n",
			retry->id, this_cpu, cpu);
	arch_send_call_function_single_ipi(cpu);

	/* Re-init timeout */
	*ts0 = ts1;

	return true;
panic:
	panic("csd: CSD lockup on CPU#%d \n", this_cpu);
	return true;
}

static void csd_end_timeout(struct call_single_data *csd, int cpu,
			    struct csd_retry_info *retry)
{
	if (likely(retry->nretries == 0))
		return;

	if (cpu >= 0)
		per_cpu(csd_locked_up, cpu) = false;

	pr_warn("csd: CSD lock (#%d) on CPU#%02d got unstuck by CPU#%02d. Phew!\n",
			retry->id, raw_smp_processor_id(), cpu);
}

enum csd_lock_context {
	CSD_ASYNC,
	CSD_ENTER,
	CSD_LEAVE
};

#ifdef DEBUG_CSD_LOCKUP_TESTING
/* Support for interactive debugging on developer machine.  Not useful on a
 * customer's fritzbox since it requires local shell access.
 *
 * For testing the CSD lockup diagnostics, expose a module parameter that can
 * be used to trigger a CSD lockup.
 *
 * This uses an int type to interface with the module_param API, and maps it
 * to an atomic_t internally.
 */
#define DEFINE_UINT_ARG(varname, argdesc)		\
static unsigned int varname##_arg;			\
static atomic_t varname = ATOMIC_INIT(0);		\
							\
static int varname##_set_arg(const char *arg,		\
		const struct kernel_param *kp)		\
{							\
	int ret;					\
							\
	ret = param_set_uint(arg, kp);			\
	atomic_set(&varname, varname##_arg);		\
							\
	return ret;					\
}							\
							\
static struct kernel_param_ops varname##_ops = {	\
	.get = param_get_uint,				\
	.set = varname##_set_arg,			\
};							\
							\
module_param_cb(varname, &varname##_ops, &varname##_arg, 0644); \
MODULE_PARM_DESC(varname, argdesc)

DEFINE_UINT_ARG(csd_lockup_one_sync_enter,
		"Trigger #cnt repeated CSD timeouts when entering one synchronous smp call");
DEFINE_UINT_ARG(csd_lockup_one_sync_leave,
		"Trigger #cnt repeated CSD timeouts when leaving one synchronous smp call");
DEFINE_UINT_ARG(csd_lockup_one_async,
		"Trigger #cnt repeated CSD timeouts for one async smp call");
DEFINE_UINT_ARG(csd_forget_one_sync,
		"Forget to enqueue the CSD of one synchronous smp call");
DEFINE_UINT_ARG(csd_forget_one_async,
		"Forget to enqueue the CSD of one async smp call");

static bool csd_should_lockup(enum csd_lock_context ctx)
{
	atomic_t *ctxtab[] = {
		[CSD_ASYNC] = &csd_lockup_one_async,
		[CSD_ENTER] = &csd_lockup_one_sync_enter,
		[CSD_LEAVE] = &csd_lockup_one_sync_leave,
	};

	atomic_t *val = ctxtab[ctx];

	return atomic_xchg(val, 0);
}

static bool csd_should_forget(enum csd_lock_context ctx)
{
	atomic_t *val = ctx == CSD_ASYNC ?
		&csd_forget_one_async : &csd_forget_one_sync;

	return atomic_xchg(val, 0);
}
#else
static bool csd_should_lockup(enum csd_lock_context ctx) { return false; }
static bool csd_should_forget(enum csd_lock_context ctx) { return false; }
#endif

/*
 * 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.
 *
 * ( The overhead of deadlock detection is not a big problem, this is a
 *   cpu_relax() loop that is actively wasting CPU cycles to poll for
 *   completion. )
 */
static void csd_lock_wait(struct call_single_data *csd, int cpu,
			  enum csd_lock_context ctx)
{
	struct csd_retry_info retry = {0};
	unsigned long long ts0 = 0;
	unsigned int do_lockup = 0;
	bool timeout;

	/* Lockup injection test? */
	if (cpu >= 0)
		do_lockup = csd_should_lockup(ctx);
	if (do_lockup)
		pr_alert("csd: Initiating %s CSD lockup loop test on %s (%u iterations)\n",
				ctx == CSD_ASYNC ? "async" : "sync",
				ctx == CSD_LEAVE ? "leave" : "enter",
				do_lockup);

	while (ACCESS_ONCE(csd->flags) & CSD_FLAG_LOCK || do_lockup) {
		timeout = csd_check_timeout(csd, cpu, &ts0, &retry);
		if (unlikely(timeout && do_lockup)) {
			--do_lockup;
			pr_alert("csd: lockup test timeout (#%u remaining)\n", do_lockup);
		}
		cpu_relax();
	}

	csd_end_timeout(csd, cpu, &retry);
}

static void csd_lock(struct call_single_data *data, int cpu,
		     enum csd_lock_context ctx)
{
	csd_lock_wait(data, cpu, ctx);
	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, int wait)
{
	struct call_single_queue *dst = &per_cpu(call_single_queue, cpu);
	enum csd_lock_context ctx = wait ? CSD_ENTER : CSD_ASYNC;
	unsigned long flags;
	int ipi;

	if (csd_should_forget(ctx)) {
		pr_alert("csd: Forgetting %s CSD calling %pf on CPU#%d\n",
				ctx == CSD_ASYNC ? "async" : "sync",
				data->func, cpu);
		goto leave_wait;
	}

	raw_spin_lock_irqsave(&dst->lock, flags);
	ipi = list_empty(&dst->list);
	list_add_tail(&data->list, &dst->list);
	raw_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...
	 */

	/* AVM: We're seeing lockups here, so better safe than sorry */
	smp_mb();

	if (ipi)
		arch_send_call_function_single_ipi(cpu);
leave_wait:
	if (wait)
		csd_lock_wait(data, cpu, CSD_LEAVE);
}

/*
 * 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 = smp_processor_id();

	/*
	 * Shouldn't receive this interrupt on a cpu that is not yet online.
	 */
	WARN_ON_ONCE(!cpu_online(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;
		smp_call_func_t func;

		/*
		 * Since we walk the list without any locks, we might
		 * see an entry that was completed, removed from the
		 * list and is in the process of being reused.
		 *
		 * We must check that the cpu is in the cpumask before
		 * checking the refs, and both must be set before
		 * executing the callback on this cpu.
		 */

		if (!cpumask_test_cpu(cpu, data->cpumask))
			continue;

		smp_rmb();

		if (atomic_read(&data->refs) == 0)
			continue;

		func = data->csd.func;		/* save for later warn */
		func(data->csd.info);

		/*
		 * If the cpu mask is not still set then func enabled
		 * interrupts (BUG), and this cpu took another smp call
		 * function interrupt and executed func(info) twice
		 * on this cpu.  That nested execution decremented refs.
		 */
		if (!cpumask_test_and_clear_cpu(cpu, data->cpumask)) {
			WARN(1, "%pf enabled interrupts and double executed\n", func);
			continue;
		}

		refs = atomic_dec_return(&data->refs);
		WARN_ON(refs < 0);

		if (refs)
			continue;

		WARN_ON(!cpumask_empty(data->cpumask));

		raw_spin_lock(&call_function.lock);
		list_del_rcu(&data->csd.list);
		raw_spin_unlock(&call_function.lock);

		csd_unlock(&data->csd);
	}

}

/*
 * 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);
	unsigned int data_flags;
	LIST_HEAD(list);

	if (__get_cpu_var(csd_locked_up))
		printk("CSD: Function call IPI callback on CPU#%d\n",
				raw_smp_processor_id());

	/*
	 * Shouldn't receive this interrupt on a cpu that is not yet online.
	 */
	WARN_ON_ONCE(!cpu_online(smp_processor_id()));

	raw_spin_lock(&q->lock);
	list_replace_init(&q->list, &list);
	raw_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);

		/*
		 * Unlocked CSDs are valid through generic_exec_single():
		 */
		if (data_flags & CSD_FLAG_LOCK)
			csd_unlock(data);
	}
}

static DEFINE_PER_CPU_SHARED_ALIGNED(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.
 */
int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
			     int wait)
{
	struct call_single_data d = {
		.flags = 0,
	};
	unsigned long flags;
	int this_cpu;
	int err = 0;

	/*
	 * prevent preemption and reschedule on another processor,
	 * as well as CPU removal
	 */
	this_cpu = get_cpu();

	/*
	 * Can deadlock when called with interrupts disabled.
	 * We allow cpu's that are not yet online though, as no one else can
	 * send smp call function interrupt to this cpu and as such deadlocks
	 * can't happen.
	 */
	WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
		     && !oops_in_progress);

	if (cpu == this_cpu) {
		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 = &d;
			enum csd_lock_context ctx = wait ? CSD_ENTER : CSD_ASYNC;

			if (!wait)
				data = &__get_cpu_var(csd_data);

			csd_lock(data, cpu, ctx);

			data->func = func;
			data->info = info;
			generic_exec_single(cpu, data, wait);
		} else {
			err = -ENXIO;	/* CPU not online */
		}
	}

	put_cpu();

	return err;
}
EXPORT_SYMBOL(smp_call_function_single);

/*
 * smp_call_function_any - Run a function on any of the given cpus
 * @mask: The mask of cpus it can 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 until function has completed.
 *
 * Returns 0 on success, else a negative status code (if no cpus were online).
 * Note that @wait will be implicitly turned on in case of allocation failures,
 * since we fall back to on-stack allocation.
 *
 * Selection preference:
 *	1) current cpu if in @mask
 *	2) any cpu of current node if in @mask
 *	3) any other online cpu in @mask
 */
int smp_call_function_any(const struct cpumask *mask,
			  smp_call_func_t func, void *info, int wait)
{
	unsigned int cpu;
	const struct cpumask *nodemask;
	int ret;

	/* Try for same CPU (cheapest) */
	cpu = get_cpu();
	if (cpumask_test_cpu(cpu, mask))
		goto call;

	/* Try for same node. */
	nodemask = cpumask_of_node(cpu_to_node(cpu));
	for (cpu = cpumask_first_and(nodemask, mask); cpu < nr_cpu_ids;
	     cpu = cpumask_next_and(cpu, nodemask, mask)) {
		if (cpu_online(cpu))
			goto call;
	}

	/* Any online will do: smp_call_function_single handles nr_cpu_ids. */
	cpu = cpumask_any_and(mask, cpu_online_mask);
call:
	ret = smp_call_function_single(cpu, func, info, wait);
	put_cpu();
	return ret;
}
EXPORT_SYMBOL_GPL(smp_call_function_any);

/**
 * __smp_call_function_single(): Run a function on a specific CPU
 * @cpu: The CPU to run on.
 * @data: Pre-allocated and setup data structure
 * @wait: If true, wait until function has completed on specified CPU.
 *
 * 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,
				int wait)
{
	unsigned int this_cpu;
	unsigned long flags;

	this_cpu = get_cpu();
	/*
	 * Can deadlock when called with interrupts disabled.
	 * We allow cpu's that are not yet online though, as no one else can
	 * send smp call function interrupt to this cpu and as such deadlocks
	 * can't happen.
	 */
	WARN_ON_ONCE(cpu_online(smp_processor_id()) && wait && irqs_disabled()
		     && !oops_in_progress);

	if (cpu == this_cpu) {
		local_irq_save(flags);
		data->func(data->info);
		local_irq_restore(flags);
	} else {
		enum csd_lock_context ctx = wait ? CSD_ENTER : CSD_ASYNC;

		csd_lock(data, cpu, ctx);
		generic_exec_single(cpu, data, wait);
	}
	put_cpu();
}

/**
 * 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.
 *
 * 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,
			    smp_call_func_t func, void *info, bool wait)
{
	struct call_function_data *data;
	unsigned long flags;
	int refs, cpu, next_cpu, this_cpu = smp_processor_id();

	/*
	 * Can deadlock when called with interrupts disabled.
	 * We allow cpu's that are not yet online though, as no one else can
	 * send smp call function interrupt to this cpu and as such deadlocks
	 * can't happen.
	 */
	WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
		     && !oops_in_progress && !early_boot_irqs_disabled);

	/* Try to fastpath.  So, what's a CPU they want? Ignoring this one. */
	cpu = cpumask_first_and(mask, cpu_online_mask);
	if (cpu == this_cpu)
		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 == this_cpu)
		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, CPU_UNSPEC, wait ? CSD_ENTER : CSD_ASYNC);

	/* This BUG_ON verifies our reuse assertions and can be removed */
	BUG_ON(atomic_read(&data->refs) || !cpumask_empty(data->cpumask));

	/*
	 * The global call function queue list add and delete are protected
	 * by a lock, but the list is traversed without any lock, relying
	 * on the rcu list add and delete to allow safe concurrent traversal.
	 * We reuse the call function data without waiting for any grace
	 * period after some other cpu removes it from the global queue.
	 * This means a cpu might find our data block as it is being
	 * filled out.
	 *
	 * We hold off the interrupt handler on the other cpu by
	 * ordering our writes to the cpu mask vs our setting of the
	 * refs counter.  We assert only the cpu owning the data block
	 * will set a bit in cpumask, and each bit will only be cleared
	 * by the subject cpu.  Each cpu must first find its bit is
	 * set and then check that refs is set indicating the element is
	 * ready to be processed, otherwise it must skip the entry.
	 *
	 * On the previous iteration refs was set to 0 by another cpu.
	 * To avoid the use of transitivity, set the counter to 0 here
	 * so the wmb will pair with the rmb in the interrupt handler.
	 */
	atomic_set(&data->refs, 0);	/* convert 3rd to 1st party write */

	data->csd.func = func;
	data->csd.info = info;

	/* Ensure 0 refs is visible before mask.  Also orders func and info */
	smp_wmb();

	/* We rely on the "and" being processed before the store */
	cpumask_and(data->cpumask, mask, cpu_online_mask);
	cpumask_clear_cpu(this_cpu, data->cpumask);
	refs = cpumask_weight(data->cpumask);

	/* Some callers race with other cpus changing the passed mask */
	if (unlikely(!refs)) {
		csd_unlock(&data->csd);
		return;
	}

	raw_spin_lock_irqsave(&call_function.lock, flags);
	/*
	 * 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);
	/*
	 * We rely on the wmb() in list_add_rcu to complete our writes
	 * to the cpumask before this write to refs, which indicates
	 * data is on the list and is ready to be processed.
	 */
	atomic_set(&data->refs, refs);
	raw_spin_unlock_irqrestore(&call_function.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_lock_wait(&data->csd, CPU_UNSPEC, CSD_LEAVE);
}
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.
 *
 * 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(smp_call_func_t func, 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)
{
	raw_spin_lock(&call_function.lock);
}

void ipi_call_unlock(void)
{
	raw_spin_unlock(&call_function.lock);
}

void ipi_call_lock_irq(void)
{
	raw_spin_lock_irq(&call_function.lock);
}

void ipi_call_unlock_irq(void)
{
	raw_spin_unlock_irq(&call_function.lock);
}
#endif /* USE_GENERIC_SMP_HELPERS */

/* Setup configured maximum number of CPUs to activate */
unsigned int setup_max_cpus = NR_CPUS;
EXPORT_SYMBOL(setup_max_cpus);


/*
 * Setup routine for controlling SMP activation
 *
 * Command-line option of "nosmp" or "maxcpus=0" will disable SMP
 * activation entirely (the MPS table probe still happens, though).
 *
 * Command-line option of "maxcpus=<NUM>", where <NUM> is an integer
 * greater than 0, limits the maximum number of CPUs activated in
 * SMP mode to <NUM>.
 */

void __weak arch_disable_smp_support(void) { }

static int __init nosmp(char *str)
{
	setup_max_cpus = 0;
	arch_disable_smp_support();

	return 0;
}

early_param("nosmp", nosmp);

/* this is hard limit */
static int __init nrcpus(char *str)
{
	int nr_cpus;

	get_option(&str, &nr_cpus);
	if (nr_cpus > 0 && nr_cpus < nr_cpu_ids)
		nr_cpu_ids = nr_cpus;

	return 0;
}

early_param("nr_cpus", nrcpus);

static int __init maxcpus(char *str)
{
	get_option(&str, &setup_max_cpus);
	if (setup_max_cpus == 0)
		arch_disable_smp_support();

	return 0;
}

early_param("maxcpus", maxcpus);

/* Setup number of possible processor ids */
int nr_cpu_ids __read_mostly = NR_CPUS;
EXPORT_SYMBOL(nr_cpu_ids);

/* An arch may set nr_cpu_ids earlier if needed, so this would be redundant */
void __init setup_nr_cpu_ids(void)
{
	nr_cpu_ids = find_last_bit(cpumask_bits(cpu_possible_mask),NR_CPUS) + 1;
}

/* Called by boot processor to activate the rest. */
void __init smp_init(void)
{
	unsigned int cpu;

	/* FIXME: This should be done in userspace --RR */
	for_each_present_cpu(cpu) {
		if (num_online_cpus() >= setup_max_cpus)
			break;
		if (!cpu_online(cpu))
			cpu_up(cpu);
	}

	/* Any cleanup work */
	printk(KERN_INFO "Brought up %ld CPUs\n", (long)num_online_cpus());
	smp_cpus_done(setup_max_cpus);
}

/*
 * Call a function on all processors.  May be used during early boot while
 * early_boot_irqs_disabled is set.  Use local_irq_save/restore() instead
 * of local_irq_disable/enable().
 */
int on_each_cpu(void (*func) (void *info), void *info, int wait)
{
	unsigned long flags;
	int ret = 0;

	preempt_disable();
	ret = smp_call_function(func, info, wait);
	local_irq_save(flags);
	func(info);
	local_irq_restore(flags);
	preempt_enable();
	return ret;
}
EXPORT_SYMBOL(on_each_cpu);