/*      $NetBSD: t_seqlock.c,v 1.2 2022/04/10 11:36:32 riastradh Exp $  */

/*-
 * Copyright (c) 2022 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__RCSID("$NetBSD: t_seqlock.c,v 1.2 2022/04/10 11:36:32 riastradh Exp $");

#include <sys/atomic.h>
#include <sys/param.h>
#include <sys/sysctl.h>

#include <assert.h>
#include <atf-c.h>
#include <err.h>
#include <errno.h>
#include <inttypes.h>
#include <pthread.h>
#include <stdint.h>
#include <stdio.h>
#include <unistd.h>

#ifdef  BROKEN_PRODUCER
#undef  membar_producer
#define membar_producer()       asm volatile("" ::: "memory")
#endif  /* BROKEN_PRODUCER */

#ifdef  BROKEN_CONSUMER
#undef  membar_consumer
#define membar_consumer()       asm volatile("" ::: "memory")
#endif  /* BROKEN_CONSUMER */

volatile sig_atomic_t times_up;

volatile unsigned version;

volatile struct {
        uint64_t s;
} __aligned(COHERENCY_UNIT) stats[16];

uint64_t results[2];

static void *
writer(void *cookie)
{
        uint64_t s;
        unsigned i;

        for (s = 0; !times_up; s++) {
                version |= 1;
                membar_producer();
                for (i = __arraycount(stats); i --> 0;)
                        stats[i].s = s;
                membar_producer();
                version |= 1;
                version += 1;

                /*
                 * Not needed for correctness, but this helps on Cavium
                 * Octeon cnMIPS CPUs which require issuing a sync
                 * plunger to unclog store buffers which can otherwise
                 * stay clogged for hundreds of thousands of cycles,
                 * giving very little concurrency to this test.
                 * Without this, the reader spends most of its time
                 * thinking an update is in progress.
                 */
                membar_producer();
        }

        return NULL;
}

static void *
reader(void *cookie)
{
        uint64_t s;
        unsigned v, result, i;
        volatile unsigned *vp = &version;
        volatile uint64_t t;

        while (!times_up) {
                /*
                 * Prime the cache with possibly stale garbage.
                 */
                t = stats[0].s;

                /*
                 * Normally we would do
                 *
                 *      while ((v = version) & 1)
                 *              SPINLOCK_BACKOFF_HOOK;
                 *
                 * to avoid copying out a version that we know is in
                 * flux, but it's not wrong to copy out a version in
                 * flux -- just wasteful.
                 *
                 * Reading the version unconditionally, and then
                 * copying out the record, better exercises plausible
                 * bugs in PowerPC membars based on `isync' that
                 * provide the desired ordering only if separated from
                 * the load by a conditional branch based on the load.
                 */
                v = *vp;
                membar_consumer();
                s = stats[0].s;
                for (result = 0, i = 1; i < __arraycount(stats); i++)
                        result |= (s != stats[i].s);
                membar_consumer();
                if ((v & ~1u) != *vp)
                        continue;
                results[result]++;
        }

        (void)t;

        return NULL;
}

ATF_TC(seqlock);
ATF_TC_HEAD(seqlock, tc)
{
        atf_tc_set_md_var(tc, "descr",
            "Verify membar_producer/consumer work for seqlocks");
}
ATF_TC_BODY(seqlock, tc)
{
        pthread_t t[2];
        void *(*start[2])(void *) = { &reader, &writer };
        unsigned i;
        int ncpu;
        size_t ncpulen = sizeof(ncpu);
        int error;

        alarm(10);

        if (sysctlbyname("hw.ncpu", &ncpu, &ncpulen, NULL, 0) == -1)
                atf_tc_fail("hw.ncpu: (%d) %s", errno, strerror(errno));
        assert(ncpulen == sizeof(ncpu));
        if (ncpu == 1)
                atf_tc_skip("membar tests are only for multicore systems");

        for (i = 0; i < 2; i++) {
                error = pthread_create(&t[i], NULL, start[i],
                    (void *)(uintptr_t)i);
                if (error)
                        errc(1, error, "pthread_create");
        }
        sleep(5);
        times_up = 1;
        for (i = 0; i < 2; i++) {
                error = pthread_join(t[i], NULL);
                if (error)
                        errc(1, error, "pthread_join");
        }
        ATF_REQUIRE(results[0] != 0);
        ATF_REQUIRE_MSG(results[1] == 0,
            "%"PRIu64" good snapshots, %"PRIu64" bad snapshots",
            results[0], results[1]);
}

ATF_TP_ADD_TCS(tp)
{

        ATF_TP_ADD_TC(tp, seqlock);
        return atf_no_error();
}