// 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);

/*
 * Add to a counter while respecting batch size.
 *
 * There are 2 implementations, both dealing with the following problem:
 *
 * The decision slow path/fast path and the actual update must be atomic.
 * Otherwise a call in process context could check the current values and
 * decide that the fast path can be used. If now an interrupt occurs before
 * the this_cpu_add(), and the interrupt updates this_cpu(*fbc->counters),
 * then the this_cpu_add() that is executed after the interrupt has completed
 * can produce values larger than "batch" or even overflows.
 */
#ifdef CONFIG_HAVE_CMPXCHG_LOCAL
/*
 * Safety against interrupts is achieved in 2 ways:
 * 1. the fast path uses local cmpxchg (note: no lock prefix)
 * 2. the slow path operates with interrupts disabled
 */
void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch)
{
        s64 count;
        unsigned long flags;

        count = this_cpu_read(*fbc->counters);
        do {
                if (unlikely(abs(count + amount) >= batch)) {
                        raw_spin_lock_irqsave(&fbc->lock, flags);
                        /*
                         * Note: by now we might have migrated to another CPU
                         * or the value might have changed.
                         */
                        count = __this_cpu_read(*fbc->counters);
                        fbc->count += count + amount;
                        __this_cpu_sub(*fbc->counters, count);
                        raw_spin_unlock_irqrestore(&fbc->lock, flags);
                        return;
                }
        } while (!this_cpu_try_cmpxchg(*fbc->counters, &count, count + amount));
}
#else
/*
 * local_irq_save() is used to make the function irq safe:
 * - The slow path would be ok as protected by an irq-safe spinlock.
 * - this_cpu_add would be ok as it is irq-safe by definition.
 */
void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch)
{
        s64 count;
        unsigned long flags;

        local_irq_save(flags);
        count = __this_cpu_read(*fbc->counters) + amount;
        if (abs(count) >= batch) {
                raw_spin_lock(&fbc->lock);
                fbc->count += count;
                __this_cpu_sub(*fbc->counters, count - amount);
                raw_spin_unlock(&fbc->lock);
        } else {
                this_cpu_add(*fbc->counters, amount);
        }
        local_irq_restore(flags);
}
#endif
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().
 *
 * We use the cpu mask of (cpu_online_mask | cpu_dying_mask) to capture sums
 * from CPUs that are in the process of being taken offline. Dying cpus have
 * been removed from the online mask, but may not have had the hotplug dead
 * notifier called to fold the percpu count back into the global counter sum.
 * By including dying CPUs in the iteration mask, we avoid this race condition
 * so __percpu_counter_sum() just does the right thing when CPUs are being taken
 * offline.
 */
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_cpu_or(cpu, cpu_online_mask, cpu_dying_mask) {
                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_many(struct percpu_counter *fbc, s64 amount,
                               gfp_t gfp, u32 nr_counters,
                               struct lock_class_key *key)
{
        unsigned long flags __maybe_unused;
        size_t counter_size;
        s32 __percpu *counters;
        u32 i;

        counter_size = ALIGN(sizeof(*counters), __alignof__(*counters));
        counters = __alloc_percpu_gfp(nr_counters * counter_size,
                                      __alignof__(*counters), gfp);
        if (!counters) {
                fbc[0].counters = NULL;
                return -ENOMEM;
        }

        for (i = 0; i < nr_counters; i++) {
                raw_spin_lock_init(&fbc[i].lock);
                lockdep_set_class(&fbc[i].lock, key);
#ifdef CONFIG_HOTPLUG_CPU
                INIT_LIST_HEAD(&fbc[i].list);
#endif
                fbc[i].count = amount;
                fbc[i].counters = (void __percpu *)counters + i * counter_size;

                debug_percpu_counter_activate(&fbc[i]);
        }

#ifdef CONFIG_HOTPLUG_CPU
        spin_lock_irqsave(&percpu_counters_lock, flags);
        for (i = 0; i < nr_counters; i++)
                list_add(&fbc[i].list, &percpu_counters);
        spin_unlock_irqrestore(&percpu_counters_lock, flags);
#endif
        return 0;
}
EXPORT_SYMBOL(__percpu_counter_init_many);

void percpu_counter_destroy_many(struct percpu_counter *fbc, u32 nr_counters)
{
        unsigned long flags __maybe_unused;
        u32 i;

        if (WARN_ON_ONCE(!fbc))
                return;

        if (!fbc[0].counters)
                return;

        for (i = 0; i < nr_counters; i++)
                debug_percpu_counter_deactivate(&fbc[i]);

#ifdef CONFIG_HOTPLUG_CPU
        spin_lock_irqsave(&percpu_counters_lock, flags);
        for (i = 0; i < nr_counters; i++)
                list_del(&fbc[i].list);
        spin_unlock_irqrestore(&percpu_counters_lock, flags);
#endif

        free_percpu(fbc[0].counters);

        for (i = 0; i < nr_counters; i++)
                fbc[i].counters = NULL;
}
EXPORT_SYMBOL(percpu_counter_destroy_many);

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);

/*
 * Compare counter, and add amount if total is: less than or equal to limit if
 * amount is positive, or greater than or equal to limit if amount is negative.
 * Return true if amount is added, or false if total would be beyond the limit.
 *
 * Negative limit is allowed, but unusual.
 * When negative amounts (subs) are given to percpu_counter_limited_add(),
 * the limit would most naturally be 0 - but other limits are also allowed.
 *
 * Overflow beyond S64_MAX is not allowed for: counter, limit and amount
 * are all assumed to be sane (far from S64_MIN and S64_MAX).
 */
bool __percpu_counter_limited_add(struct percpu_counter *fbc,
                                  s64 limit, s64 amount, s32 batch)
{
        s64 count;
        s64 unknown;
        unsigned long flags;
        bool good = false;

        if (amount == 0)
                return true;

        local_irq_save(flags);
        unknown = batch * num_online_cpus();
        count = __this_cpu_read(*fbc->counters);

        /* Skip taking the lock when safe */
        if (abs(count + amount) <= batch &&
            ((amount > 0 && fbc->count + unknown <= limit) ||
             (amount < 0 && fbc->count - unknown >= limit))) {
                this_cpu_add(*fbc->counters, amount);
                local_irq_restore(flags);
                return true;
        }

        raw_spin_lock(&fbc->lock);
        count = fbc->count + amount;

        /* Skip percpu_counter_sum() when safe */
        if (amount > 0) {
                if (count - unknown > limit)
                        goto out;
                if (count + unknown <= limit)
                        good = true;
        } else {
                if (count + unknown < limit)
                        goto out;
                if (count - unknown >= limit)
                        good = true;
        }

        if (!good) {
                s32 *pcount;
                int cpu;

                for_each_cpu_or(cpu, cpu_online_mask, cpu_dying_mask) {
                        pcount = per_cpu_ptr(fbc->counters, cpu);
                        count += *pcount;
                }
                if (amount > 0) {
                        if (count > limit)
                                goto out;
                } else {
                        if (count < limit)
                                goto out;
                }
                good = true;
        }

        count = __this_cpu_read(*fbc->counters);
        fbc->count += count + amount;
        __this_cpu_sub(*fbc->counters, count);
out:
        raw_spin_unlock(&fbc->lock);
        local_irq_restore(flags);
        return good;
}

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);