// 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 <linux/string_choices.h>

#include <trace/events/ipi.h>
#define CREATE_TRACE_POINTS
#include <trace/events/csd.h>
#undef CREATE_TRACE_POINTS

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

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

struct call_function_data {
        call_single_data_t      __percpu *csd;
        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 DEFINE_PER_CPU(atomic_t, trigger_backtrace) = ATOMIC_INIT(1);

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->csd = alloc_percpu(call_single_data_t);
        if (!cfd->csd) {
                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->csd);
        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.
         *
         * This runs with interrupts disabled inside the stopper task invoked by
         * stop_machine(), ensuring mutually exclusive CPU offlining and IPI flush.
         */
        __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());
}

static __always_inline void
send_call_function_single_ipi(int cpu)
{
        if (call_function_single_prep_ipi(cpu)) {
                trace_ipi_send_cpu(cpu, _RET_IP_,
                                   generic_smp_call_function_single_interrupt);
                arch_send_call_function_single_ipi(cpu);
        }
}

static __always_inline void
send_call_function_ipi_mask(struct cpumask *mask)
{
        trace_ipi_send_cpumask(mask, _RET_IP_,
                               generic_smp_call_function_single_interrupt);
        arch_send_call_function_ipi_mask(mask);
}

static __always_inline void
csd_do_func(smp_call_func_t func, void *info, call_single_data_t *csd)
{
        trace_csd_function_entry(func, csd);
        func(info);
        trace_csd_function_exit(func, csd);
}

#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG

static DEFINE_STATIC_KEY_MAYBE(CONFIG_CSD_LOCK_WAIT_DEBUG_DEFAULT, csdlock_debug_enabled);

/*
 * Parse the csdlock_debug= kernel boot parameter.
 *
 * If you need to restore the old "ext" value that once provided
 * additional debugging information, reapply the following commits:
 *
 * de7b09ef658d ("locking/csd_lock: Prepare more CSD lock debugging")
 * a5aabace5fb8 ("locking/csd_lock: Add more data to CSD lock debugging")
 */
static int __init csdlock_debug(char *str)
{
        int ret;
        unsigned int val = 0;

        ret = get_option(&str, &val);
        if (ret) {
                if (val)
                        static_branch_enable(&csdlock_debug_enabled);
                else
                        static_branch_disable(&csdlock_debug_enabled);
        }

        return 1;
}
__setup("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);

static ulong csd_lock_timeout = 5000;  /* CSD lock timeout in milliseconds. */
module_param(csd_lock_timeout, ulong, 0644);
static int panic_on_ipistall;  /* CSD panic timeout in milliseconds, 300000 for five minutes. */
module_param(panic_on_ipistall, int, 0644);

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;
}

static atomic_t n_csd_lock_stuck;

/**
 * csd_lock_is_stuck - Has a CSD-lock acquisition been stuck too long?
 *
 * Returns @true if a CSD-lock acquisition is stuck and has been stuck
 * long enough for a "non-responsive CSD lock" message to be printed.
 */
bool csd_lock_is_stuck(void)
{
        return !!atomic_read(&n_csd_lock_stuck);
}

/*
 * 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, unsigned long *nmessages)
{
        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);
        unsigned long long csd_lock_timeout_ns = csd_lock_timeout * NSEC_PER_MSEC;

        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);
                atomic_dec(&n_csd_lock_stuck);
                return true;
        }

        ts2 = ktime_get_mono_fast_ns();
        /* How long since we last checked for a stuck CSD lock.*/
        ts_delta = ts2 - *ts1;
        if (likely(ts_delta <= csd_lock_timeout_ns * (*nmessages + 1) *
                               (!*nmessages ? 1 : (ilog2(num_online_cpus()) / 2 + 1)) ||
                   csd_lock_timeout_ns == 0))
                return false;

        if (ts0 > ts2) {
                /* Our own sched_clock went backward; don't blame another CPU. */
                ts_delta = ts0 - ts2;
                pr_alert("sched_clock on CPU %d went backward by %llu ns\n", raw_smp_processor_id(), ts_delta);
                *ts1 = ts2;
                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. */
        /* How long since this CSD lock was stuck. */
        ts_delta = ts2 - ts0;
        pr_alert("csd: %s non-responsive CSD lock (#%d) on CPU#%d, waiting %lld ns for CPU#%02d %pS(%ps).\n",
                 firsttime ? "Detected" : "Continued", *bug_id, raw_smp_processor_id(), (s64)ts_delta,
                 cpu, csd->func, csd->info);
        (*nmessages)++;
        if (firsttime)
                atomic_inc(&n_csd_lock_stuck);
        /*
         * If the CSD lock is still stuck after 5 minutes, it is unlikely
         * to become unstuck. Use a signed comparison to avoid triggering
         * on underflows when the TSC is out of sync between sockets.
         */
        BUG_ON(panic_on_ipistall > 0 && (s64)ts_delta > ((s64)panic_on_ipistall * NSEC_PER_MSEC));
        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 (atomic_cmpxchg_acquire(&per_cpu(trigger_backtrace, cpu), 1, 0))
                        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);
                }
        }
        if (firsttime)
                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)
{
        unsigned long nmessages = 0;
        int bug_id = 0;
        u64 ts0, ts1;

        ts1 = ts0 = ktime_get_mono_fast_ns();
        for (;;) {
                if (csd_lock_wait_toolong(csd, ts0, &ts1, &bug_id, &nmessages))
                        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)
{
        /*
         * We have to check the type of the CSD before queueing it, because
         * once queued it can have its flags cleared by
         *   flush_smp_call_function_queue()
         * even if we haven't sent the smp_call IPI yet (e.g. the stopper
         * executes migration_cpu_stop() on the remote CPU).
         */
        if (trace_csd_queue_cpu_enabled()) {
                call_single_data_t *csd;
                smp_call_func_t func;

                csd = container_of(node, call_single_data_t, node.llist);
                func = CSD_TYPE(csd) == CSD_TYPE_TTWU ?
                        sched_ttwu_pending : csd->func;

                trace_csd_queue_cpu(cpu, _RET_IP_, func, csd);
        }

        /*
         * The list addition should be visible to the target CPU when it pops
         * the head of the list to pull the entry off it in the IPI handler
         * because of normal cache coherency rules implied by the underlying
         * llist ops.
         *
         * 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)
{
        /*
         * Preemption already disabled here so stopper cannot run on this CPU,
         * ensuring mutually exclusive CPU offlining and last IPI flush.
         */
        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);
                csd_do_func(func, info, NULL);
                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;
        atomic_t *tbt;

        lockdep_assert_irqs_disabled();

        /* Allow waiters to send backtrace NMI from here onwards */
        tbt = this_cpu_ptr(&trigger_backtrace);
        atomic_set_release(tbt, 1);

        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 && entry != NULL)) {
                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);
                        csd_do_func(func, info, csd);
                        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);
                                csd_do_func(func, info, csd);
                                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) {
                csd = llist_entry(entry, typeof(*csd), node.llist);
                csd_do_func(sched_ttwu_pending, entry, csd);
        }
}


/**
 * flush_smp_call_function_queue - Flush pending smp-call-function callbacks
 *                                 from task context (idle, migration thread)
 *
 * When TIF_POLLING_NRFLAG is supported and a CPU is in idle and has it
 * set, then remote CPUs can avoid sending IPIs and wake the idle CPU by
 * setting TIF_NEED_RESCHED. The idle task on the woken up CPU has to
 * handle queued SMP function calls before scheduling.
 *
 * The migration thread has to ensure that an eventually pending wakeup has
 * been handled before it migrates a task.
 */
void flush_smp_call_function_queue(void)
{
        unsigned int was_pending;
        unsigned long flags;

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

        local_irq_save(flags);
        /* Get the already pending soft interrupts for RT enabled kernels */
        was_pending = local_softirq_pending();
        __flush_smp_call_function_queue(true);
        if (local_softirq_pending())
                do_softirq_post_smp_call_flush(was_pending);

        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 CPU, as well as CPU
         * removal. This prevents stopper from running on this CPU, thus
         * providing mutual exclusion of the below cpu_online() check and
         * IPI sending ensuring IPI are not missed by CPU going offline.
         */
        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.
 *
 * Return: %0 on success or negative errno value on error
 */
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) nearest cpu in @mask, based on NUMA topology
 */
int smp_call_function_any(const struct cpumask *mask,
                          smp_call_func_t func, void *info, int wait)
{
        unsigned int cpu;
        int ret;

        /* Try for same CPU (cheapest) */
        cpu = get_cpu();
        if (!cpumask_test_cpu(cpu, mask))
                cpu = sched_numa_find_nth_cpu(mask, 0, cpu_to_node(cpu));

        ret = smp_call_function_single(cpu, func, info, wait);
        put_cpu();
        return ret;
}
EXPORT_SYMBOL_GPL(smp_call_function_any);

/*
 * Flags to be used as scf_flags argument of smp_call_function_many_cond().
 *
 * %SCF_WAIT:           Wait until function execution is completed
 * %SCF_RUN_LOCAL:      Run also locally if local cpu is set in cpumask
 */
#define SCF_WAIT        (1U << 0)
#define SCF_RUN_LOCAL   (1U << 1)

static void smp_call_function_many_cond(const struct cpumask *mask,
                                        smp_call_func_t func, void *info,
                                        unsigned int scf_flags,
                                        smp_cond_func_t cond_func)
{
        int cpu, last_cpu, this_cpu = smp_processor_id();
        struct call_function_data *cfd;
        bool wait = scf_flags & SCF_WAIT;
        int nr_cpus = 0;
        bool run_remote = false;

        lockdep_assert_preemption_disabled();

        /*
         * 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.
         */
        if (cpu_online(this_cpu) && !oops_in_progress &&
            !early_boot_irqs_disabled)
                lockdep_assert_irqs_enabled();

        /*
         * 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());

        /* Check if we need remote execution, i.e., any CPU excluding this one. */
        if (cpumask_any_and_but(mask, cpu_online_mask, this_cpu) < nr_cpu_ids) {
                cfd = this_cpu_ptr(&cfd_data);
                cpumask_and(cfd->cpumask, mask, cpu_online_mask);
                __cpumask_clear_cpu(this_cpu, cfd->cpumask);

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

                        if (cond_func && !cond_func(cpu, info)) {
                                __cpumask_clear_cpu(cpu, cfd->cpumask);
                                continue;
                        }

                        /* Work is enqueued on a remote CPU. */
                        run_remote = true;

                        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
                        trace_csd_queue_cpu(cpu, _RET_IP_, func, csd);

                        /*
                         * Kick the remote CPU if this is the first work
                         * item enqueued.
                         */
                        if (llist_add(&csd->node.llist, &per_cpu(call_single_queue, cpu))) {
                                __cpumask_set_cpu(cpu, cfd->cpumask_ipi);
                                nr_cpus++;
                                last_cpu = cpu;
                        }
                }

                /*
                 * Choose the most efficient way to send an IPI. Note that the
                 * number of CPUs might be zero due to concurrent changes to the
                 * provided mask.
                 */
                if (nr_cpus == 1)
                        send_call_function_single_ipi(last_cpu);
                else if (likely(nr_cpus > 1))
                        send_call_function_ipi_mask(cfd->cpumask_ipi);
        }

        /* Check if we need local execution. */
        if ((scf_flags & SCF_RUN_LOCAL) && cpumask_test_cpu(this_cpu, mask) &&
            (!cond_func || cond_func(this_cpu, info))) {
                unsigned long flags;

                local_irq_save(flags);
                csd_do_func(func, info, NULL);
                local_irq_restore(flags);
        }

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

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

/**
 * smp_call_function_many(): Run a function on a set of 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.
 *
 * 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.
 *
 * @func is not called on the local CPU even if @mask contains it.  Consider
 * using on_each_cpu_cond_mask() instead if this is not desirable.
 */
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 * SCF_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 __init 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)
                set_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);

#if (NR_CPUS > 1) && !defined(CONFIG_FORCE_NR_CPUS)
/* Setup number of possible processor ids */
unsigned int nr_cpu_ids __read_mostly = NR_CPUS;
EXPORT_SYMBOL(nr_cpu_ids);
#endif

/* An arch may set nr_cpu_ids earlier if needed, so this would be redundant */
void __init setup_nr_cpu_ids(void)
{
        set_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, str_plural(num_nodes), num_cpus, str_plural(num_cpus));

        /* Any cleanup work */
        smp_cpus_done(setup_max_cpus);
}

/*
 * 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 boolean 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)
{
        unsigned int scf_flags = SCF_RUN_LOCAL;

        if (wait)
                scf_flags |= SCF_WAIT;

        preempt_disable();
        smp_call_function_many_cond(mask, func, info, scf_flags, cond_func);
        preempt_enable();
}
EXPORT_SYMBOL(on_each_cpu_cond_mask);

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;

        for_each_possible_cpu(cpu) {
                preempt_disable();
                if (cpu != smp_processor_id() && cpu_online(cpu))
                        wake_up_if_idle(cpu);
                preempt_enable();
        }
}
EXPORT_SYMBOL_GPL(wake_up_all_idle_cpus);

/**
 * cpus_peek_for_pending_ipi - Check for pending IPI for CPUs
 * @mask: The CPU mask for the CPUs to check.
 *
 * This function walks through the @mask to check if there are any pending IPIs
 * scheduled, for any of the CPUs in the @mask. It does not guarantee
 * correctness as it only provides a racy snapshot.
 *
 * Returns true if there is a pending IPI scheduled and false otherwise.
 */
bool cpus_peek_for_pending_ipi(const struct cpumask *mask)
{
        unsigned int cpu;

        for_each_cpu(cpu, mask) {
                if (!llist_empty(per_cpu_ptr(&call_single_queue, cpu)))
                        return true;
        }

        return false;
}

/**
 * struct smp_call_on_cpu_struct - Call a function on a specific CPU
 * @work: &work_struct
 * @done: &completion to signal
 * @func: function to call
 * @data: function's data argument
 * @ret: return value from @func
 * @cpu: target CPU (%-1 for any 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);
        destroy_work_on_stack(&sscs.work);

        return sscs.ret;
}
EXPORT_SYMBOL_GPL(smp_call_on_cpu);