// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright 2023 Red Hat
 */

#include "thread-registry.h"

#include <asm/current.h>
#include <linux/rculist.h>

#include "permassert.h"

/*
 * We need to be careful when using other facilities that may use thread registry functions in
 * their normal operation. For example, we do not want to invoke the logger while holding a lock.
 */

void vdo_initialize_thread_registry(struct thread_registry *registry)
{
        INIT_LIST_HEAD(&registry->links);
        spin_lock_init(&registry->lock);
}

/* Register the current thread and associate it with a data pointer. */
void vdo_register_thread(struct thread_registry *registry,
                         struct registered_thread *new_thread, const void *pointer)
{
        struct registered_thread *thread;
        bool found_it = false;

        INIT_LIST_HEAD(&new_thread->links);
        new_thread->pointer = pointer;
        new_thread->task = current;

        spin_lock(&registry->lock);
        list_for_each_entry(thread, &registry->links, links) {
                if (thread->task == current) {
                        /* There should be no existing entry. */
                        list_del_rcu(&thread->links);
                        found_it = true;
                        break;
                }
        }
        list_add_tail_rcu(&new_thread->links, &registry->links);
        spin_unlock(&registry->lock);

        VDO_ASSERT_LOG_ONLY(!found_it, "new thread not already in registry");
        if (found_it) {
                /* Ensure no RCU iterators see it before re-initializing. */
                synchronize_rcu();
                INIT_LIST_HEAD(&thread->links);
        }
}

void vdo_unregister_thread(struct thread_registry *registry)
{
        struct registered_thread *thread;
        bool found_it = false;

        spin_lock(&registry->lock);
        list_for_each_entry(thread, &registry->links, links) {
                if (thread->task == current) {
                        list_del_rcu(&thread->links);
                        found_it = true;
                        break;
                }
        }
        spin_unlock(&registry->lock);

        VDO_ASSERT_LOG_ONLY(found_it, "thread found in registry");
        if (found_it) {
                /* Ensure no RCU iterators see it before re-initializing. */
                synchronize_rcu();
                INIT_LIST_HEAD(&thread->links);
        }
}

const void *vdo_lookup_thread(struct thread_registry *registry)
{
        struct registered_thread *thread;
        const void *result = NULL;

        rcu_read_lock();
        list_for_each_entry_rcu(thread, &registry->links, links) {
                if (thread->task == current) {
                        result = thread->pointer;
                        break;
                }
        }
        rcu_read_unlock();

        return result;
}