// SPDX-License-Identifier: GPL-2.0
/*
 * Fast batching percpu counters.
 */

#include <linux/percpu_counter.h>
#include <linux/mutex.h>
#include <linux/init.h>
#include <linux/cpu.h>
#include <linux/module.h>
#include <linux/debugobjects.h>

#ifdef CONFIG_HOTPLUG_CPU
static LIST_HEAD(percpu_counters);
static DEFINE_SPINLOCK(percpu_counters_lock);
#endif

#ifdef CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER

static const struct debug_obj_descr percpu_counter_debug_descr;

static bool percpu_counter_fixup_free(void *addr, enum debug_obj_state state)
{
        struct percpu_counter *fbc = addr;

        switch (state) {
        case ODEBUG_STATE_ACTIVE:
                percpu_counter_destroy(fbc);
                debug_object_free(fbc, &percpu_counter_debug_descr);
                return true;
        default:
                return false;
        }
}

static const struct debug_obj_descr percpu_counter_debug_descr = {
        .name           = "percpu_counter",
        .fixup_free     = percpu_counter_fixup_free,
};

static inline void debug_percpu_counter_activate(struct percpu_counter *fbc)
{
        debug_object_init(fbc, &percpu_counter_debug_descr);
        debug_object_activate(fbc, &percpu_counter_debug_descr);
}

static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
{
        debug_object_deactivate(fbc, &percpu_counter_debug_descr);
        debug_object_free(fbc, &percpu_counter_debug_descr);
}

#else   /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */
static inline void debug_percpu_counter_activate(struct percpu_counter *fbc)
{ }
static inline void debug_percpu_counter_deactivate(struct percpu_counter *fbc)
{ }
#endif  /* CONFIG_DEBUG_OBJECTS_PERCPU_COUNTER */

void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
{
        int cpu;
        unsigned long flags;

        raw_spin_lock_irqsave(&fbc->lock, flags);
        for_each_possible_cpu(cpu) {
                s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
                *pcount = 0;
        }
        fbc->count = amount;
        raw_spin_unlock_irqrestore(&fbc->lock, flags);
}
EXPORT_SYMBOL(percpu_counter_set);

/*
 * This function is both preempt and irq safe. The former is due to explicit
 * preemption disable. The latter is guaranteed by the fact that the slow path
 * is explicitly protected by an irq-safe spinlock whereas the fast patch uses
 * this_cpu_add which is irq-safe by definition. Hence there is no need muck
 * with irq state before calling this one
 */
void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch)
{
        s64 count;

        preempt_disable();
        count = __this_cpu_read(*fbc->counters) + amount;
        if (abs(count) >= batch) {
                unsigned long flags;
                raw_spin_lock_irqsave(&fbc->lock, flags);
                fbc->count += count;
                __this_cpu_sub(*fbc->counters, count - amount);
                raw_spin_unlock_irqrestore(&fbc->lock, flags);
        } else {
                this_cpu_add(*fbc->counters, amount);
        }
        preempt_enable();
}
EXPORT_SYMBOL(percpu_counter_add_batch);

/*
 * For percpu_counter with a big batch, the devication of its count could
 * be big, and there is requirement to reduce the deviation, like when the
 * counter's batch could be runtime decreased to get a better accuracy,
 * which can be achieved by running this sync function on each CPU.
 */
void percpu_counter_sync(struct percpu_counter *fbc)
{
        unsigned long flags;
        s64 count;

        raw_spin_lock_irqsave(&fbc->lock, flags);
        count = __this_cpu_read(*fbc->counters);
        fbc->count += count;
        __this_cpu_sub(*fbc->counters, count);
        raw_spin_unlock_irqrestore(&fbc->lock, flags);
}
EXPORT_SYMBOL(percpu_counter_sync);

/*
 * Add up all the per-cpu counts, return the result.  This is a more accurate
 * but much slower version of percpu_counter_read_positive()
 */
s64 __percpu_counter_sum(struct percpu_counter *fbc)
{
        s64 ret;
        int cpu;
        unsigned long flags;

        raw_spin_lock_irqsave(&fbc->lock, flags);
        ret = fbc->count;
        for_each_online_cpu(cpu) {
                s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
                ret += *pcount;
        }
        raw_spin_unlock_irqrestore(&fbc->lock, flags);
        return ret;
}
EXPORT_SYMBOL(__percpu_counter_sum);

int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp,
                          struct lock_class_key *key)
{
        unsigned long flags __maybe_unused;

        raw_spin_lock_init(&fbc->lock);
        lockdep_set_class(&fbc->lock, key);
        fbc->count = amount;
        fbc->counters = alloc_percpu_gfp(s32, gfp);
        if (!fbc->counters)
                return -ENOMEM;

        debug_percpu_counter_activate(fbc);

#ifdef CONFIG_HOTPLUG_CPU
        INIT_LIST_HEAD(&fbc->list);
        spin_lock_irqsave(&percpu_counters_lock, flags);
        list_add(&fbc->list, &percpu_counters);
        spin_unlock_irqrestore(&percpu_counters_lock, flags);
#endif
        return 0;
}
EXPORT_SYMBOL(__percpu_counter_init);

void percpu_counter_destroy(struct percpu_counter *fbc)
{
        unsigned long flags __maybe_unused;

        if (!fbc->counters)
                return;

        debug_percpu_counter_deactivate(fbc);

#ifdef CONFIG_HOTPLUG_CPU
        spin_lock_irqsave(&percpu_counters_lock, flags);
        list_del(&fbc->list);
        spin_unlock_irqrestore(&percpu_counters_lock, flags);
#endif
        free_percpu(fbc->counters);
        fbc->counters = NULL;
}
EXPORT_SYMBOL(percpu_counter_destroy);

int percpu_counter_batch __read_mostly = 32;
EXPORT_SYMBOL(percpu_counter_batch);

static int compute_batch_value(unsigned int cpu)
{
        int nr = num_online_cpus();

        percpu_counter_batch = max(32, nr*2);
        return 0;
}

static int percpu_counter_cpu_dead(unsigned int cpu)
{
#ifdef CONFIG_HOTPLUG_CPU
        struct percpu_counter *fbc;

        compute_batch_value(cpu);

        spin_lock_irq(&percpu_counters_lock);
        list_for_each_entry(fbc, &percpu_counters, list) {
                s32 *pcount;

                raw_spin_lock(&fbc->lock);
                pcount = per_cpu_ptr(fbc->counters, cpu);
                fbc->count += *pcount;
                *pcount = 0;
                raw_spin_unlock(&fbc->lock);
        }
        spin_unlock_irq(&percpu_counters_lock);
#endif
        return 0;
}

/*
 * Compare counter against given value.
 * Return 1 if greater, 0 if equal and -1 if less
 */
int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch)
{
        s64     count;

        count = percpu_counter_read(fbc);
        /* Check to see if rough count will be sufficient for comparison */
        if (abs(count - rhs) > (batch * num_online_cpus())) {
                if (count > rhs)
                        return 1;
                else
                        return -1;
        }
        /* Need to use precise count */
        count = percpu_counter_sum(fbc);
        if (count > rhs)
                return 1;
        else if (count < rhs)
                return -1;
        else
                return 0;
}
EXPORT_SYMBOL(__percpu_counter_compare);

static int __init percpu_counter_startup(void)
{
        int ret;

        ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "lib/percpu_cnt:online",
                                compute_batch_value, NULL);
        WARN_ON(ret < 0);
        ret = cpuhp_setup_state_nocalls(CPUHP_PERCPU_CNT_DEAD,
                                        "lib/percpu_cnt:dead", NULL,
                                        percpu_counter_cpu_dead);
        WARN_ON(ret < 0);
        return 0;
}
module_init(percpu_counter_startup);