[mirror_ubuntu-jammy-kernel.git] / kernel / smp.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Generic helpers for smp ipi calls
 *
 * (C) Jens Axboe <jens.axboe@oracle.com> 2008
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/irq_work.h>
#include <linux/rcupdate.h>
#include <linux/rculist.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/percpu.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/gfp.h>
#include <linux/smp.h>
#include <linux/cpu.h>
#include <linux/sched.h>
#include <linux/sched/idle.h>
#include <linux/hypervisor.h>
#include <linux/sched/clock.h>
#include <linux/nmi.h>
#include <linux/sched/debug.h>
#include <linux/jump_label.h>

#include "smpboot.h"
#include "sched/smp.h"

#define CSD_TYPE(_csd)  ((_csd)->node.u_flags & CSD_FLAG_TYPE_MASK)

struct cfd_percpu {
        call_single_data_t      csd;
};

struct call_function_data {
        struct cfd_percpu       __percpu *pcpu;
        cpumask_var_t           cpumask;
        cpumask_var_t           cpumask_ipi;
};

static DEFINE_PER_CPU_ALIGNED(struct call_function_data, cfd_data);

static DEFINE_PER_CPU_SHARED_ALIGNED(struct llist_head, call_single_queue);

static void flush_smp_call_function_queue(bool warn_cpu_offline);

int smpcfd_prepare_cpu(unsigned int cpu)
{
        struct call_function_data *cfd = &per_cpu(cfd_data, cpu);

        if (!zalloc_cpumask_var_node(&cfd->cpumask, GFP_KERNEL,
                                     cpu_to_node(cpu)))
                return -ENOMEM;
        if (!zalloc_cpumask_var_node(&cfd->cpumask_ipi, GFP_KERNEL,
                                     cpu_to_node(cpu))) {
                free_cpumask_var(cfd->cpumask);
                return -ENOMEM;
        }
        cfd->pcpu = alloc_percpu(struct cfd_percpu);
        if (!cfd->pcpu) {
                free_cpumask_var(cfd->cpumask);
                free_cpumask_var(cfd->cpumask_ipi);
                return -ENOMEM;
        }

        return 0;
}

int smpcfd_dead_cpu(unsigned int cpu)
{
        struct call_function_data *cfd = &per_cpu(cfd_data, cpu);

        free_cpumask_var(cfd->cpumask);
        free_cpumask_var(cfd->cpumask_ipi);
        free_percpu(cfd->pcpu);
        return 0;
}

int smpcfd_dying_cpu(unsigned int cpu)
{
        /*
         * The IPIs for the smp-call-function callbacks queued by other
         * CPUs might arrive late, either due to hardware latencies or
         * because this CPU disabled interrupts (inside stop-machine)
         * before the IPIs were sent. So flush out any pending callbacks
         * explicitly (without waiting for the IPIs to arrive), to
         * ensure that the outgoing CPU doesn't go offline with work
         * still pending.
         */
        flush_smp_call_function_queue(false);
        irq_work_run();
        return 0;
}

void __init call_function_init(void)
{
        int i;

        for_each_possible_cpu(i)
                init_llist_head(&per_cpu(call_single_queue, i));

        smpcfd_prepare_cpu(smp_processor_id());
}

#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG

static DEFINE_STATIC_KEY_FALSE(csdlock_debug_enabled);

static int __init csdlock_debug(char *str)
{
        unsigned int val = 0;

        get_option(&str, &val);
        if (val)
                static_branch_enable(&csdlock_debug_enabled);

        return 0;
}
early_param("csdlock_debug", csdlock_debug);

static DEFINE_PER_CPU(call_single_data_t *, cur_csd);
static DEFINE_PER_CPU(smp_call_func_t, cur_csd_func);
static DEFINE_PER_CPU(void *, cur_csd_info);

#define CSD_LOCK_TIMEOUT (5ULL * NSEC_PER_SEC)
static atomic_t csd_bug_count = ATOMIC_INIT(0);

/* Record current CSD work for current CPU, NULL to erase. */
static void __csd_lock_record(call_single_data_t *csd)
{
        if (!csd) {
                smp_mb(); /* NULL cur_csd after unlock. */
                __this_cpu_write(cur_csd, NULL);
                return;
        }
        __this_cpu_write(cur_csd_func, csd->func);
        __this_cpu_write(cur_csd_info, csd->info);
        smp_wmb(); /* func and info before csd. */
        __this_cpu_write(cur_csd, csd);
        smp_mb(); /* Update cur_csd before function call. */
                  /* Or before unlock, as the case may be. */
}

static __always_inline void csd_lock_record(call_single_data_t *csd)
{
        if (static_branch_unlikely(&csdlock_debug_enabled))
                __csd_lock_record(csd);
}

static int csd_lock_wait_getcpu(call_single_data_t *csd)
{
        unsigned int csd_type;

        csd_type = CSD_TYPE(csd);
        if (csd_type == CSD_TYPE_ASYNC || csd_type == CSD_TYPE_SYNC)
                return csd->node.dst; /* Other CSD_TYPE_ values might not have ->dst. */
        return -1;
}

/*
 * Complain if too much time spent waiting.  Note that only
 * the CSD_TYPE_SYNC/ASYNC types provide the destination CPU,
 * so waiting on other types gets much less information.
 */
static bool csd_lock_wait_toolong(call_single_data_t *csd, u64 ts0, u64 *ts1, int *bug_id)
{
        int cpu = -1;
        int cpux;
        bool firsttime;
        u64 ts2, ts_delta;
        call_single_data_t *cpu_cur_csd;
        unsigned int flags = READ_ONCE(csd->node.u_flags);

        if (!(flags & CSD_FLAG_LOCK)) {
                if (!unlikely(*bug_id))
                        return true;
                cpu = csd_lock_wait_getcpu(csd);
                pr_alert("csd: CSD lock (#%d) got unstuck on CPU#%02d, CPU#%02d released the lock.\n",
                         *bug_id, raw_smp_processor_id(), cpu);
                return true;
        }

        ts2 = sched_clock();
        ts_delta = ts2 - *ts1;
        if (likely(ts_delta <= CSD_LOCK_TIMEOUT))
                return false;

        firsttime = !*bug_id;
        if (firsttime)
                *bug_id = atomic_inc_return(&csd_bug_count);
        cpu = csd_lock_wait_getcpu(csd);
        if (WARN_ONCE(cpu < 0 || cpu >= nr_cpu_ids, "%s: cpu = %d\n", __func__, cpu))
                cpux = 0;
        else
                cpux = cpu;
        cpu_cur_csd = smp_load_acquire(&per_cpu(cur_csd, cpux)); /* Before func and info. */
        pr_alert("csd: %s non-responsive CSD lock (#%d) on CPU#%d, waiting %llu ns for CPU#%02d %pS(%ps).\n",
                 firsttime ? "Detected" : "Continued", *bug_id, raw_smp_processor_id(), ts2 - ts0,
                 cpu, csd->func, csd->info);
        if (cpu_cur_csd && csd != cpu_cur_csd) {
                pr_alert("\tcsd: CSD lock (#%d) handling prior %pS(%ps) request.\n",
                         *bug_id, READ_ONCE(per_cpu(cur_csd_func, cpux)),
                         READ_ONCE(per_cpu(cur_csd_info, cpux)));
        } else {
                pr_alert("\tcsd: CSD lock (#%d) %s.\n",
                         *bug_id, !cpu_cur_csd ? "unresponsive" : "handling this request");
        }
        if (cpu >= 0) {
                if (!trigger_single_cpu_backtrace(cpu))
                        dump_cpu_task(cpu);
                if (!cpu_cur_csd) {
                        pr_alert("csd: Re-sending CSD lock (#%d) IPI from CPU#%02d to CPU#%02d\n", *bug_id, raw_smp_processor_id(), cpu);
                        arch_send_call_function_single_ipi(cpu);
                }
        }
        dump_stack();
        *ts1 = ts2;

        return false;
}

/*
 * 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_wait(call_single_data_t *csd)
{
        int bug_id = 0;
        u64 ts0, ts1;

        ts1 = ts0 = sched_clock();
        for (;;) {
                if (csd_lock_wait_toolong(csd, ts0, &ts1, &bug_id))
                        break;
                cpu_relax();
        }
        smp_acquire__after_ctrl_dep();
}

static __always_inline void csd_lock_wait(call_single_data_t *csd)
{
        if (static_branch_unlikely(&csdlock_debug_enabled)) {
                __csd_lock_wait(csd);
                return;
        }

        smp_cond_load_acquire(&csd->node.u_flags, !(VAL & CSD_FLAG_LOCK));
}
#else
static void csd_lock_record(call_single_data_t *csd)
{
}

static __always_inline void csd_lock_wait(call_single_data_t *csd)
{
        smp_cond_load_acquire(&csd->node.u_flags, !(VAL & CSD_FLAG_LOCK));
}
#endif

static __always_inline void csd_lock(call_single_data_t *csd)
{
        csd_lock_wait(csd);
        csd->node.u_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_t structure:
         */
        smp_wmb();
}

static __always_inline void csd_unlock(call_single_data_t *csd)
{
        WARN_ON(!(csd->node.u_flags & CSD_FLAG_LOCK));

        /*
         * ensure we're all done before releasing data:
         */
        smp_store_release(&csd->node.u_flags, 0);
}

static DEFINE_PER_CPU_SHARED_ALIGNED(call_single_data_t, csd_data);

void __smp_call_single_queue(int cpu, struct llist_node *node)
{
        /*
         * 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 (llist_add(node, &per_cpu(call_single_queue, cpu)))
                send_call_function_single_ipi(cpu);
}

/*
 * Insert a previously allocated call_single_data_t element
 * for execution on the given CPU. data must already have
 * ->func, ->info, and ->flags set.
 */
static int generic_exec_single(int cpu, call_single_data_t *csd)
{
        if (cpu == smp_processor_id()) {
                smp_call_func_t func = csd->func;
                void *info = csd->info;
                unsigned long flags;

                /*
                 * We can unlock early even for the synchronous on-stack case,
                 * since we're doing this from the same CPU..
                 */
                csd_lock_record(csd);
                csd_unlock(csd);
                local_irq_save(flags);
                func(info);
                csd_lock_record(NULL);
                local_irq_restore(flags);
                return 0;
        }

        if ((unsigned)cpu >= nr_cpu_ids || !cpu_online(cpu)) {
                csd_unlock(csd);
                return -ENXIO;
        }

        __smp_call_single_queue(cpu, &csd->node.llist);

        return 0;
}

/**
 * generic_smp_call_function_single_interrupt - Execute SMP IPI callbacks
 *
 * Invoked by arch to handle an IPI for call function single.
 * Must be called with interrupts disabled.
 */
void generic_smp_call_function_single_interrupt(void)
{
        flush_smp_call_function_queue(true);
}

/**
 * flush_smp_call_function_queue - Flush pending smp-call-function callbacks
 *
 * @warn_cpu_offline: If set to 'true', warn if callbacks were queued on an
 *                    offline CPU. Skip this check if set to 'false'.
 *
 * Flush any pending smp-call-function callbacks queued on this CPU. This is
 * invoked by the generic IPI handler, as well as by a CPU about to go offline,
 * to ensure that all pending IPI callbacks are run before it goes completely
 * offline.
 *
 * Loop through the call_single_queue and run all the queued callbacks.
 * Must be called with interrupts disabled.
 */
static void flush_smp_call_function_queue(bool warn_cpu_offline)
{
        call_single_data_t *csd, *csd_next;
        struct llist_node *entry, *prev;
        struct llist_head *head;
        static bool warned;

        lockdep_assert_irqs_disabled();

        head = this_cpu_ptr(&call_single_queue);
        entry = llist_del_all(head);
        entry = llist_reverse_order(entry);

        /* There shouldn't be any pending callbacks on an offline CPU. */
        if (unlikely(warn_cpu_offline && !cpu_online(smp_processor_id()) &&
                     !warned && !llist_empty(head))) {
                warned = true;
                WARN(1, "IPI on offline CPU %d\n", smp_processor_id());

                /*
                 * We don't have to use the _safe() variant here
                 * because we are not invoking the IPI handlers yet.
                 */
                llist_for_each_entry(csd, entry, node.llist) {
                        switch (CSD_TYPE(csd)) {
                        case CSD_TYPE_ASYNC:
                        case CSD_TYPE_SYNC:
                        case CSD_TYPE_IRQ_WORK:
                                pr_warn("IPI callback %pS sent to offline CPU\n",
                                        csd->func);
                                break;

                        case CSD_TYPE_TTWU:
                                pr_warn("IPI task-wakeup sent to offline CPU\n");
                                break;

                        default:
                                pr_warn("IPI callback, unknown type %d, sent to offline CPU\n",
                                        CSD_TYPE(csd));
                                break;
                        }
                }
        }

        /*
         * First; run all SYNC callbacks, people are waiting for us.
         */
        prev = NULL;
        llist_for_each_entry_safe(csd, csd_next, entry, node.llist) {
                /* Do we wait until *after* callback? */
                if (CSD_TYPE(csd) == CSD_TYPE_SYNC) {
                        smp_call_func_t func = csd->func;
                        void *info = csd->info;

                        if (prev) {
                                prev->next = &csd_next->node.llist;
                        } else {
                                entry = &csd_next->node.llist;
                        }

                        csd_lock_record(csd);
                        func(info);
                        csd_unlock(csd);
                        csd_lock_record(NULL);
                } else {
                        prev = &csd->node.llist;
                }
        }

        if (!entry)
                return;

        /*
         * Second; run all !SYNC callbacks.
         */
        prev = NULL;
        llist_for_each_entry_safe(csd, csd_next, entry, node.llist) {
                int type = CSD_TYPE(csd);

                if (type != CSD_TYPE_TTWU) {
                        if (prev) {
                                prev->next = &csd_next->node.llist;
                        } else {
                                entry = &csd_next->node.llist;
                        }

                        if (type == CSD_TYPE_ASYNC) {
                                smp_call_func_t func = csd->func;
                                void *info = csd->info;

                                csd_lock_record(csd);
                                csd_unlock(csd);
                                func(info);
                                csd_lock_record(NULL);
                        } else if (type == CSD_TYPE_IRQ_WORK) {
                                irq_work_single(csd);
                        }

                } else {
                        prev = &csd->node.llist;
                }
        }

        /*
         * Third; only CSD_TYPE_TTWU is left, issue those.
         */
        if (entry)
                sched_ttwu_pending(entry);
}

void flush_smp_call_function_from_idle(void)
{
        unsigned long flags;

        if (llist_empty(this_cpu_ptr(&call_single_queue)))
                return;

        local_irq_save(flags);
        flush_smp_call_function_queue(true);
        if (local_softirq_pending())
                do_softirq();

        local_irq_restore(flags);
}

/*
 * 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)
{
        call_single_data_t *csd;
        call_single_data_t csd_stack = {
                .node = { .u_flags = CSD_FLAG_LOCK | CSD_TYPE_SYNC, },
        };
        int this_cpu;
        int err;

        /*
         * 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);

        /*
         * When @wait we can deadlock when we interrupt between llist_add() and
         * arch_send_call_function_ipi*(); when !@wait we can deadlock due to
         * csd_lock() on because the interrupt context uses the same csd
         * storage.
         */
        WARN_ON_ONCE(!in_task());

        csd = &csd_stack;
        if (!wait) {
                csd = this_cpu_ptr(&csd_data);
                csd_lock(csd);
        }

        csd->func = func;
        csd->info = info;
#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG
        csd->node.src = smp_processor_id();
        csd->node.dst = cpu;
#endif

        err = generic_exec_single(cpu, csd);

        if (wait)
                csd_lock_wait(csd);

        put_cpu();

        return err;
}
EXPORT_SYMBOL(smp_call_function_single);

/**
 * smp_call_function_single_async(): Run an asynchronous function on a
 *                               specific CPU.
 * @cpu: The CPU to run on.
 * @csd: Pre-allocated and setup data structure
 *
 * Like smp_call_function_single(), but the call is asynchonous and
 * can thus be done from contexts with disabled interrupts.
 *
 * The caller passes his own pre-allocated data structure
 * (ie: embedded in an object) and is responsible for synchronizing it
 * such that the IPIs performed on the @csd are strictly serialized.
 *
 * If the function is called with one csd which has not yet been
 * processed by previous call to smp_call_function_single_async(), the
 * function will return immediately with -EBUSY showing that the csd
 * object is still in progress.
 *
 * NOTE: Be careful, there is unfortunately no current debugging facility to
 * validate the correctness of this serialization.
 */
int smp_call_function_single_async(int cpu, call_single_data_t *csd)
{
        int err = 0;

        preempt_disable();

        if (csd->node.u_flags & CSD_FLAG_LOCK) {
                err = -EBUSY;
                goto out;
        }

        csd->node.u_flags = CSD_FLAG_LOCK;
        smp_wmb();

        err = generic_exec_single(cpu, csd);

out:
        preempt_enable();

        return err;
}
EXPORT_SYMBOL_GPL(smp_call_function_single_async);

/*
 * 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).
 *
 * 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);

static void smp_call_function_many_cond(const struct cpumask *mask,
                                        smp_call_func_t func, void *info,
                                        bool wait, smp_cond_func_t cond_func)
{
        struct call_function_data *cfd;
        int 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);

        /*
         * When @wait we can deadlock when we interrupt between llist_add() and
         * arch_send_call_function_ipi*(); when !@wait we can deadlock due to
         * csd_lock() on because the interrupt context uses the same csd
         * storage.
         */
        WARN_ON_ONCE(!in_task());

        /* 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) {
                if (!cond_func || cond_func(cpu, info))
                        smp_call_function_single(cpu, func, info, wait);
                return;
        }

        cfd = this_cpu_ptr(&cfd_data);

        cpumask_and(cfd->cpumask, mask, cpu_online_mask);
        __cpumask_clear_cpu(this_cpu, cfd->cpumask);

        /* Some callers race with other cpus changing the passed mask */
        if (unlikely(!cpumask_weight(cfd->cpumask)))
                return;

        cpumask_clear(cfd->cpumask_ipi);
        for_each_cpu(cpu, cfd->cpumask) {
                call_single_data_t *csd = &per_cpu_ptr(cfd->pcpu, cpu)->csd;

                if (cond_func && !cond_func(cpu, info))
                        continue;

                csd_lock(csd);
                if (wait)
                        csd->node.u_flags |= CSD_TYPE_SYNC;
                csd->func = func;
                csd->info = info;
#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG
                csd->node.src = smp_processor_id();
                csd->node.dst = cpu;
#endif
                if (llist_add(&csd->node.llist, &per_cpu(call_single_queue, cpu)))
                        __cpumask_set_cpu(cpu, cfd->cpumask_ipi);
        }

        /* Send a message to all CPUs in the map */
        arch_send_call_function_ipi_mask(cfd->cpumask_ipi);

        if (wait) {
                for_each_cpu(cpu, cfd->cpumask) {
                        call_single_data_t *csd;

                        csd = &per_cpu_ptr(cfd->pcpu, cpu)->csd;
                        csd_lock_wait(csd);
                }
        }
}

/**
 * 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)
{
        smp_call_function_many_cond(mask, func, info, wait, NULL);
}
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.
 */
void 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();
}
EXPORT_SYMBOL(smp_call_function);

/* 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;

        if (get_option(&str, &nr_cpus) && 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 */
unsigned 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)
{
        int num_nodes, num_cpus;

        idle_threads_init();
        cpuhp_threads_init();

        pr_info("Bringing up secondary CPUs ...\n");

        bringup_nonboot_cpus(setup_max_cpus);

        num_nodes = num_online_nodes();
        num_cpus  = num_online_cpus();
        pr_info("Brought up %d node%s, %d CPU%s\n",
                num_nodes, (num_nodes > 1 ? "s" : ""),
                num_cpus,  (num_cpus  > 1 ? "s" : ""));

        /* Any cleanup work */
        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().
 */
void on_each_cpu(smp_call_func_t func, void *info, int wait)
{
        unsigned long flags;

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

/**
 * on_each_cpu_mask(): Run a function on processors specified by
 * cpumask, which may include the local processor.
 * @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.  The
 * exception is that it may be used during early boot while
 * early_boot_irqs_disabled is set.
 */
void on_each_cpu_mask(const struct cpumask *mask, smp_call_func_t func,
                        void *info, bool wait)
{
        int cpu = get_cpu();

        smp_call_function_many(mask, func, info, wait);
        if (cpumask_test_cpu(cpu, mask)) {
                unsigned long flags;
                local_irq_save(flags);
                func(info);
                local_irq_restore(flags);
        }
        put_cpu();
}
EXPORT_SYMBOL(on_each_cpu_mask);

/*
 * on_each_cpu_cond(): Call a function on each processor for which
 * the supplied function cond_func returns true, optionally waiting
 * for all the required CPUs to finish. This may include the local
 * processor.
 * @cond_func:  A callback function that is passed a cpu id and
 *              the info parameter. The function is called
 *              with preemption disabled. The function should
 *              return a blooean value indicating whether to IPI
 *              the specified CPU.
 * @func:       The function to run on all applicable CPUs.
 *              This must be fast and non-blocking.
 * @info:       An arbitrary pointer to pass to both functions.
 * @wait:       If true, wait (atomically) until function has
 *              completed on other CPUs.
 *
 * Preemption is disabled to protect against CPUs going offline but not online.
 * CPUs going online during the call will not be seen or sent an IPI.
 *
 * You must not call this function with disabled interrupts or
 * from a hardware interrupt handler or from a bottom half handler.
 */
void on_each_cpu_cond_mask(smp_cond_func_t cond_func, smp_call_func_t func,
                           void *info, bool wait, const struct cpumask *mask)
{
        int cpu = get_cpu();

        smp_call_function_many_cond(mask, func, info, wait, cond_func);
        if (cpumask_test_cpu(cpu, mask) && cond_func(cpu, info)) {
                unsigned long flags;

                local_irq_save(flags);
                func(info);
                local_irq_restore(flags);
        }
        put_cpu();
}
EXPORT_SYMBOL(on_each_cpu_cond_mask);

void on_each_cpu_cond(smp_cond_func_t cond_func, smp_call_func_t func,
                      void *info, bool wait)
{
        on_each_cpu_cond_mask(cond_func, func, info, wait, cpu_online_mask);
}
EXPORT_SYMBOL(on_each_cpu_cond);

static void do_nothing(void *unused)
{
}

/**
 * kick_all_cpus_sync - Force all cpus out of idle
 *
 * Used to synchronize the update of pm_idle function pointer. It's
 * called after the pointer is updated and returns after the dummy
 * callback function has been executed on all cpus. The execution of
 * the function can only happen on the remote cpus after they have
 * left the idle function which had been called via pm_idle function
 * pointer. So it's guaranteed that nothing uses the previous pointer
 * anymore.
 */
void kick_all_cpus_sync(void)
{
        /* Make sure the change is visible before we kick the cpus */
        smp_mb();
        smp_call_function(do_nothing, NULL, 1);
}
EXPORT_SYMBOL_GPL(kick_all_cpus_sync);

/**
 * wake_up_all_idle_cpus - break all cpus out of idle
 * wake_up_all_idle_cpus try to break all cpus which is in idle state even
 * including idle polling cpus, for non-idle cpus, we will do nothing
 * for them.
 */
void wake_up_all_idle_cpus(void)
{
        int cpu;

        preempt_disable();
        for_each_online_cpu(cpu) {
                if (cpu == smp_processor_id())
                        continue;

                wake_up_if_idle(cpu);
        }
        preempt_enable();
}
EXPORT_SYMBOL_GPL(wake_up_all_idle_cpus);

/**
 * smp_call_on_cpu - Call a function on a specific cpu
 *
 * Used to call a function on a specific cpu and wait for it to return.
 * Optionally make sure the call is done on a specified physical cpu via vcpu
 * pinning in order to support virtualized environments.
 */
struct smp_call_on_cpu_struct {
        struct work_struct      work;
        struct completion       done;
        int                     (*func)(void *);
        void                    *data;
        int                     ret;
        int                     cpu;
};

static void smp_call_on_cpu_callback(struct work_struct *work)
{
        struct smp_call_on_cpu_struct *sscs;

        sscs = container_of(work, struct smp_call_on_cpu_struct, work);
        if (sscs->cpu >= 0)
                hypervisor_pin_vcpu(sscs->cpu);
        sscs->ret = sscs->func(sscs->data);
        if (sscs->cpu >= 0)
                hypervisor_pin_vcpu(-1);

        complete(&sscs->done);
}

int smp_call_on_cpu(unsigned int cpu, int (*func)(void *), void *par, bool phys)
{
        struct smp_call_on_cpu_struct sscs = {
                .done = COMPLETION_INITIALIZER_ONSTACK(sscs.done),
                .func = func,
                .data = par,
                .cpu  = phys ? cpu : -1,
        };

        INIT_WORK_ONSTACK(&sscs.work, smp_call_on_cpu_callback);

        if (cpu >= nr_cpu_ids || !cpu_online(cpu))
                return -ENXIO;

        queue_work_on(cpu, system_wq, &sscs.work);
        wait_for_completion(&sscs.done);

        return sscs.ret;
}
EXPORT_SYMBOL_GPL(smp_call_on_cpu);