// SPDX-License-Identifier: GPL-2.0
/*
 * Asynchronous refcounty things
 *
 * Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
 * Copyright 2012 Google, Inc.
 */

#include <linux/closure.h>
#include <linux/debugfs.h>
#include <linux/export.h>
#include <linux/rcupdate.h>
#include <linux/seq_file.h>
#include <linux/sched/debug.h>

static inline void closure_put_after_sub_checks(int flags)
{
        int r = flags & CLOSURE_REMAINING_MASK;

        if (WARN(flags & CLOSURE_GUARD_MASK,
                 "closure has guard bits set: %x (%u)",
                 flags & CLOSURE_GUARD_MASK, (unsigned) __fls(r)))
                r &= ~CLOSURE_GUARD_MASK;

        WARN(!r && (flags & ~CLOSURE_DESTRUCTOR),
             "closure ref hit 0 with incorrect flags set: %x (%u)",
             flags & ~CLOSURE_DESTRUCTOR, (unsigned) __fls(flags));
}

static inline void closure_put_after_sub(struct closure *cl, int flags)
{
        closure_put_after_sub_checks(flags);

        if (!(flags & CLOSURE_REMAINING_MASK)) {
                smp_acquire__after_ctrl_dep();

                cl->closure_get_happened = false;

                if (cl->fn && !(flags & CLOSURE_DESTRUCTOR)) {
                        atomic_set(&cl->remaining,
                                   CLOSURE_REMAINING_INITIALIZER);
                        closure_queue(cl);
                } else {
                        struct closure *parent = cl->parent;
                        closure_fn *destructor = cl->fn;

                        closure_debug_destroy(cl);

                        if (destructor)
                                destructor(&cl->work);

                        if (parent)
                                closure_put(parent);
                }
        }
}

/* For clearing flags with the same atomic op as a put */
void closure_sub(struct closure *cl, int v)
{
        closure_put_after_sub(cl, atomic_sub_return_release(v, &cl->remaining));
}
EXPORT_SYMBOL(closure_sub);

/*
 * closure_put - decrement a closure's refcount
 */
void closure_put(struct closure *cl)
{
        closure_put_after_sub(cl, atomic_dec_return_release(&cl->remaining));
}
EXPORT_SYMBOL(closure_put);

/*
 * closure_wake_up - wake up all closures on a wait list, without memory barrier
 */
void __closure_wake_up(struct closure_waitlist *wait_list)
{
        struct llist_node *list;
        struct closure *cl, *t;
        struct llist_node *reverse = NULL;

        list = llist_del_all(&wait_list->list);

        /* We first reverse the list to preserve FIFO ordering and fairness */
        reverse = llist_reverse_order(list);

        /* Then do the wakeups */
        llist_for_each_entry_safe(cl, t, reverse, list) {
                closure_set_waiting(cl, 0);
                closure_sub(cl, CLOSURE_WAITING + 1);
        }
}
EXPORT_SYMBOL(__closure_wake_up);

/**
 * closure_wait - add a closure to a waitlist
 * @waitlist: will own a ref on @cl, which will be released when
 * closure_wake_up() is called on @waitlist.
 * @cl: closure pointer.
 *
 */
bool closure_wait(struct closure_waitlist *waitlist, struct closure *cl)
{
        if (atomic_read(&cl->remaining) & CLOSURE_WAITING)
                return false;

        cl->closure_get_happened = true;
        closure_set_waiting(cl, _RET_IP_);
        atomic_add(CLOSURE_WAITING + 1, &cl->remaining);
        llist_add(&cl->list, &waitlist->list);

        return true;
}
EXPORT_SYMBOL(closure_wait);

struct closure_syncer {
        struct task_struct      *task;
        int                     done;
};

static CLOSURE_CALLBACK(closure_sync_fn)
{
        struct closure *cl = container_of(ws, struct closure, work);
        struct closure_syncer *s = cl->s;
        struct task_struct *p;

        rcu_read_lock();
        p = READ_ONCE(s->task);
        s->done = 1;
        wake_up_process(p);
        rcu_read_unlock();
}

void __sched __closure_sync(struct closure *cl)
{
        struct closure_syncer s = { .task = current };

        cl->s = &s;
        continue_at(cl, closure_sync_fn, NULL);

        while (1) {
                set_current_state(TASK_UNINTERRUPTIBLE);
                if (s.done)
                        break;
                schedule();
        }

        __set_current_state(TASK_RUNNING);
}
EXPORT_SYMBOL(__closure_sync);

/*
 * closure_return_sync - finish running a closure, synchronously (i.e. waiting
 * for outstanding get()s to finish) and returning once closure refcount is 0.
 *
 * Unlike closure_sync() this doesn't reinit the ref to 1; subsequent
 * closure_get_not_zero() calls waill fail.
 */
void __sched closure_return_sync(struct closure *cl)
{
        struct closure_syncer s = { .task = current };

        cl->s = &s;
        set_closure_fn(cl, closure_sync_fn, NULL);

        unsigned flags = atomic_sub_return_release(1 + CLOSURE_RUNNING - CLOSURE_DESTRUCTOR,
                                                   &cl->remaining);

        closure_put_after_sub_checks(flags);

        if (unlikely(flags & CLOSURE_REMAINING_MASK)) {
                while (1) {
                        set_current_state(TASK_UNINTERRUPTIBLE);
                        if (s.done)
                                break;
                        schedule();
                }

                __set_current_state(TASK_RUNNING);
        }

        if (cl->parent)
                closure_put(cl->parent);
}
EXPORT_SYMBOL(closure_return_sync);

int __sched __closure_sync_timeout(struct closure *cl, unsigned long timeout)
{
        struct closure_syncer s = { .task = current };
        int ret = 0;

        cl->s = &s;
        continue_at(cl, closure_sync_fn, NULL);

        while (1) {
                set_current_state(TASK_UNINTERRUPTIBLE);
                if (s.done)
                        break;
                if (!timeout) {
                        /*
                         * Carefully undo the continue_at() - but only if it
                         * hasn't completed, i.e. the final closure_put() hasn't
                         * happened yet:
                         */
                        unsigned old, new, v = atomic_read(&cl->remaining);
                        do {
                                old = v;
                                if (!old || (old & CLOSURE_RUNNING))
                                        goto success;

                                new = old + CLOSURE_REMAINING_INITIALIZER;
                        } while ((v = atomic_cmpxchg(&cl->remaining, old, new)) != old);
                        ret = -ETIME;
                }

                timeout = schedule_timeout(timeout);
        }
success:
        __set_current_state(TASK_RUNNING);
        return ret;
}
EXPORT_SYMBOL(__closure_sync_timeout);

#ifdef CONFIG_DEBUG_CLOSURES

static LIST_HEAD(closure_list);
static DEFINE_SPINLOCK(closure_list_lock);

void closure_debug_create(struct closure *cl)
{
        unsigned long flags;

        BUG_ON(cl->magic == CLOSURE_MAGIC_ALIVE);
        cl->magic = CLOSURE_MAGIC_ALIVE;

        spin_lock_irqsave(&closure_list_lock, flags);
        list_add(&cl->all, &closure_list);
        spin_unlock_irqrestore(&closure_list_lock, flags);
}
EXPORT_SYMBOL(closure_debug_create);

void closure_debug_destroy(struct closure *cl)
{
        unsigned long flags;

        if (cl->magic == CLOSURE_MAGIC_STACK)
                return;

        BUG_ON(cl->magic != CLOSURE_MAGIC_ALIVE);
        cl->magic = CLOSURE_MAGIC_DEAD;

        spin_lock_irqsave(&closure_list_lock, flags);
        list_del(&cl->all);
        spin_unlock_irqrestore(&closure_list_lock, flags);
}
EXPORT_SYMBOL(closure_debug_destroy);

static int debug_show(struct seq_file *f, void *data)
{
        struct closure *cl;

        spin_lock_irq(&closure_list_lock);

        list_for_each_entry(cl, &closure_list, all) {
                int r = atomic_read(&cl->remaining);

                seq_printf(f, "%p: %pS -> %pS p %p r %i ",
                           cl, (void *) cl->ip, cl->fn, cl->parent,
                           r & CLOSURE_REMAINING_MASK);

                seq_printf(f, "%s%s\n",
                           test_bit(WORK_STRUCT_PENDING_BIT,
                                    work_data_bits(&cl->work)) ? "Q" : "",
                           r & CLOSURE_RUNNING  ? "R" : "");

                if (r & CLOSURE_WAITING)
                        seq_printf(f, " W %pS\n",
                                   (void *) cl->waiting_on);

                seq_putc(f, '\n');
        }

        spin_unlock_irq(&closure_list_lock);
        return 0;
}

DEFINE_SHOW_ATTRIBUTE(debug);

static int __init closure_debug_init(void)
{
        debugfs_create_file("closures", 0400, NULL, NULL, &debug_fops);
        return 0;
}
late_initcall(closure_debug_init)

#endif