// SPDX-License-Identifier: LGPL-2.1
#define _GNU_SOURCE
#include <assert.h>
#include <pthread.h>
#include <sched.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stddef.h>

#include "../kselftest.h"
#include "rseq.h"

struct percpu_lock_entry {
        intptr_t v;
} __attribute__((aligned(128)));

struct percpu_lock {
        struct percpu_lock_entry c[CPU_SETSIZE];
};

struct test_data_entry {
        intptr_t count;
} __attribute__((aligned(128)));

struct spinlock_test_data {
        struct percpu_lock lock;
        struct test_data_entry c[CPU_SETSIZE];
        int reps;
};

struct percpu_list_node {
        intptr_t data;
        struct percpu_list_node *next;
};

struct percpu_list_entry {
        struct percpu_list_node *head;
} __attribute__((aligned(128)));

struct percpu_list {
        struct percpu_list_entry c[CPU_SETSIZE];
};

/* A simple percpu spinlock.  Returns the cpu lock was acquired on. */
int rseq_this_cpu_lock(struct percpu_lock *lock)
{
        int cpu;

        for (;;) {
                int ret;

                cpu = rseq_cpu_start();
                ret = rseq_cmpeqv_storev(&lock->c[cpu].v,
                                         0, 1, cpu);
                if (rseq_likely(!ret))
                        break;
                /* Retry if comparison fails or rseq aborts. */
        }
        /*
         * Acquire semantic when taking lock after control dependency.
         * Matches rseq_smp_store_release().
         */
        rseq_smp_acquire__after_ctrl_dep();
        return cpu;
}

void rseq_percpu_unlock(struct percpu_lock *lock, int cpu)
{
        assert(lock->c[cpu].v == 1);
        /*
         * Release lock, with release semantic. Matches
         * rseq_smp_acquire__after_ctrl_dep().
         */
        rseq_smp_store_release(&lock->c[cpu].v, 0);
}

void *test_percpu_spinlock_thread(void *arg)
{
        struct spinlock_test_data *data = arg;
        int i, cpu;

        if (rseq_register_current_thread()) {
                fprintf(stderr, "Error: rseq_register_current_thread(...) failed(%d): %s\n",
                        errno, strerror(errno));
                abort();
        }
        for (i = 0; i < data->reps; i++) {
                cpu = rseq_this_cpu_lock(&data->lock);
                data->c[cpu].count++;
                rseq_percpu_unlock(&data->lock, cpu);
        }
        if (rseq_unregister_current_thread()) {
                fprintf(stderr, "Error: rseq_unregister_current_thread(...) failed(%d): %s\n",
                        errno, strerror(errno));
                abort();
        }

        return NULL;
}

/*
 * A simple test which implements a sharded counter using a per-cpu
 * lock.  Obviously real applications might prefer to simply use a
 * per-cpu increment; however, this is reasonable for a test and the
 * lock can be extended to synchronize more complicated operations.
 */
void test_percpu_spinlock(void)
{
        const int num_threads = 200;
        int i;
        uint64_t sum;
        pthread_t test_threads[num_threads];
        struct spinlock_test_data data;

        memset(&data, 0, sizeof(data));
        data.reps = 5000;

        for (i = 0; i < num_threads; i++)
                pthread_create(&test_threads[i], NULL,
                               test_percpu_spinlock_thread, &data);

        for (i = 0; i < num_threads; i++)
                pthread_join(test_threads[i], NULL);

        sum = 0;
        for (i = 0; i < CPU_SETSIZE; i++)
                sum += data.c[i].count;

        assert(sum == (uint64_t)data.reps * num_threads);
}

void this_cpu_list_push(struct percpu_list *list,
                        struct percpu_list_node *node,
                        int *_cpu)
{
        int cpu;

        for (;;) {
                intptr_t *targetptr, newval, expect;
                int ret;

                cpu = rseq_cpu_start();
                /* Load list->c[cpu].head with single-copy atomicity. */
                expect = (intptr_t)RSEQ_READ_ONCE(list->c[cpu].head);
                newval = (intptr_t)node;
                targetptr = (intptr_t *)&list->c[cpu].head;
                node->next = (struct percpu_list_node *)expect;
                ret = rseq_cmpeqv_storev(targetptr, expect, newval, cpu);
                if (rseq_likely(!ret))
                        break;
                /* Retry if comparison fails or rseq aborts. */
        }
        if (_cpu)
                *_cpu = cpu;
}

/*
 * Unlike a traditional lock-less linked list; the availability of a
 * rseq primitive allows us to implement pop without concerns over
 * ABA-type races.
 */
struct percpu_list_node *this_cpu_list_pop(struct percpu_list *list,
                                           int *_cpu)
{
        for (;;) {
                struct percpu_list_node *head;
                intptr_t *targetptr, expectnot, *load;
                off_t offset;
                int ret, cpu;

                cpu = rseq_cpu_start();
                targetptr = (intptr_t *)&list->c[cpu].head;
                expectnot = (intptr_t)NULL;
                offset = offsetof(struct percpu_list_node, next);
                load = (intptr_t *)&head;
                ret = rseq_cmpnev_storeoffp_load(targetptr, expectnot,
                                                 offset, load, cpu);
                if (rseq_likely(!ret)) {
                        if (_cpu)
                                *_cpu = cpu;
                        return head;
                }
                if (ret > 0)
                        return NULL;
                /* Retry if rseq aborts. */
        }
}

/*
 * __percpu_list_pop is not safe against concurrent accesses. Should
 * only be used on lists that are not concurrently modified.
 */
struct percpu_list_node *__percpu_list_pop(struct percpu_list *list, int cpu)
{
        struct percpu_list_node *node;

        node = list->c[cpu].head;
        if (!node)
                return NULL;
        list->c[cpu].head = node->next;
        return node;
}

void *test_percpu_list_thread(void *arg)
{
        int i;
        struct percpu_list *list = (struct percpu_list *)arg;

        if (rseq_register_current_thread()) {
                fprintf(stderr, "Error: rseq_register_current_thread(...) failed(%d): %s\n",
                        errno, strerror(errno));
                abort();
        }

        for (i = 0; i < 100000; i++) {
                struct percpu_list_node *node;

                node = this_cpu_list_pop(list, NULL);
                sched_yield();  /* encourage shuffling */
                if (node)
                        this_cpu_list_push(list, node, NULL);
        }

        if (rseq_unregister_current_thread()) {
                fprintf(stderr, "Error: rseq_unregister_current_thread(...) failed(%d): %s\n",
                        errno, strerror(errno));
                abort();
        }

        return NULL;
}

/* Simultaneous modification to a per-cpu linked list from many threads.  */
void test_percpu_list(void)
{
        int i, j;
        uint64_t sum = 0, expected_sum = 0;
        struct percpu_list list;
        pthread_t test_threads[200];
        cpu_set_t allowed_cpus;

        memset(&list, 0, sizeof(list));

        /* Generate list entries for every usable cpu. */
        sched_getaffinity(0, sizeof(allowed_cpus), &allowed_cpus);
        for (i = 0; i < CPU_SETSIZE; i++) {
                if (!CPU_ISSET(i, &allowed_cpus))
                        continue;
                for (j = 1; j <= 100; j++) {
                        struct percpu_list_node *node;

                        expected_sum += j;

                        node = malloc(sizeof(*node));
                        assert(node);
                        node->data = j;
                        node->next = list.c[i].head;
                        list.c[i].head = node;
                }
        }

        for (i = 0; i < 200; i++)
                pthread_create(&test_threads[i], NULL,
                       test_percpu_list_thread, &list);

        for (i = 0; i < 200; i++)
                pthread_join(test_threads[i], NULL);

        for (i = 0; i < CPU_SETSIZE; i++) {
                struct percpu_list_node *node;

                if (!CPU_ISSET(i, &allowed_cpus))
                        continue;

                while ((node = __percpu_list_pop(&list, i))) {
                        sum += node->data;
                        free(node);
                }
        }

        /*
         * All entries should now be accounted for (unless some external
         * actor is interfering with our allowed affinity while this
         * test is running).
         */
        assert(sum == expected_sum);
}

int main(int argc, char **argv)
{
        if (rseq_register_current_thread()) {
                fprintf(stderr, "Error: rseq_register_current_thread(...) failed(%d): %s\n",
                        errno, strerror(errno));
                goto error;
        }
        printf("spinlock\n");
        test_percpu_spinlock();
        printf("percpu_list\n");
        test_percpu_list();
        if (rseq_unregister_current_thread()) {
                fprintf(stderr, "Error: rseq_unregister_current_thread(...) failed(%d): %s\n",
                        errno, strerror(errno));
                goto error;
        }
        return 0;

error:
        return -1;
}