/* SPDX-License-Identifier: GPL-2.0 */
/*
 * Stress concurrent SCX_KICK_WAIT calls to reproduce wait-cycle deadlock.
 *
 * Three CPUs are designated from userspace. Every enqueue from one of the
 * three CPUs kicks the next CPU in the ring with SCX_KICK_WAIT, creating a
 * persistent A -> B -> C -> A wait cycle pressure.
 */
#include <scx/common.bpf.h>

char _license[] SEC("license") = "GPL";

const volatile s32 test_cpu_a;
const volatile s32 test_cpu_b;
const volatile s32 test_cpu_c;

u64 nr_enqueues;
u64 nr_wait_kicks;

UEI_DEFINE(uei);

static s32 target_cpu(s32 cpu)
{
        if (cpu == test_cpu_a)
                return test_cpu_b;
        if (cpu == test_cpu_b)
                return test_cpu_c;
        if (cpu == test_cpu_c)
                return test_cpu_a;
        return -1;
}

void BPF_STRUCT_OPS(cyclic_kick_wait_enqueue, struct task_struct *p,
                    u64 enq_flags)
{
        s32 this_cpu = bpf_get_smp_processor_id();
        s32 tgt;

        __sync_fetch_and_add(&nr_enqueues, 1);

        if (p->flags & PF_KTHREAD) {
                scx_bpf_dsq_insert(p, SCX_DSQ_LOCAL, SCX_SLICE_INF,
                                   enq_flags | SCX_ENQ_PREEMPT);
                return;
        }

        scx_bpf_dsq_insert(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, enq_flags);

        tgt = target_cpu(this_cpu);
        if (tgt < 0 || tgt == this_cpu)
                return;

        __sync_fetch_and_add(&nr_wait_kicks, 1);
        scx_bpf_kick_cpu(tgt, SCX_KICK_WAIT);
}

void BPF_STRUCT_OPS(cyclic_kick_wait_exit, struct scx_exit_info *ei)
{
        UEI_RECORD(uei, ei);
}

SEC(".struct_ops.link")
struct sched_ext_ops cyclic_kick_wait_ops = {
        .enqueue                = cyclic_kick_wait_enqueue,
        .exit                   = cyclic_kick_wait_exit,
        .name                   = "cyclic_kick_wait",
        .timeout_ms             = 1000U,
};