// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2007 Oracle.  All rights reserved.
 * Copyright (C) 2014 Fujitsu.  All rights reserved.
 */

#include <linux/kthread.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/freezer.h>
#include <trace/events/btrfs.h>
#include "async-thread.h"

enum {
        WORK_DONE_BIT,
        WORK_ORDER_DONE_BIT,
};

#define NO_THRESHOLD (-1)
#define DEFAULT_THRESHOLD (32)

struct btrfs_workqueue {
        struct workqueue_struct *normal_wq;

        /* File system this workqueue services */
        struct btrfs_fs_info *fs_info;

        /* List head pointing to ordered work list */
        struct list_head ordered_list;

        /* Spinlock for ordered_list */
        spinlock_t list_lock;

        /* Thresholding related variants */
        atomic_t pending;

        /* Up limit of concurrency workers */
        int limit_active;

        /* Current number of concurrency workers */
        int current_active;

        /* Threshold to change current_active */
        int thresh;
        unsigned int count;
        spinlock_t thres_lock;
};

struct btrfs_fs_info * __pure btrfs_workqueue_owner(const struct btrfs_workqueue *wq)
{
        return wq->fs_info;
}

struct btrfs_fs_info * __pure btrfs_work_owner(const struct btrfs_work *work)
{
        return work->wq->fs_info;
}

bool btrfs_workqueue_normal_congested(const struct btrfs_workqueue *wq)
{
        /*
         * We could compare wq->pending with num_online_cpus()
         * to support "thresh == NO_THRESHOLD" case, but it requires
         * moving up atomic_inc/dec in thresh_queue/exec_hook. Let's
         * postpone it until someone needs the support of that case.
         */
        if (wq->thresh == NO_THRESHOLD)
                return false;

        return atomic_read(&wq->pending) > wq->thresh * 2;
}

static void btrfs_init_workqueue(struct btrfs_workqueue *wq,
                                 struct btrfs_fs_info *fs_info)
{
        wq->fs_info = fs_info;
        atomic_set(&wq->pending, 0);
        INIT_LIST_HEAD(&wq->ordered_list);
        spin_lock_init(&wq->list_lock);
        spin_lock_init(&wq->thres_lock);
}

struct btrfs_workqueue *btrfs_alloc_workqueue(struct btrfs_fs_info *fs_info,
                                              const char *name, unsigned int flags,
                                              int limit_active, int thresh)
{
        struct btrfs_workqueue *ret = kzalloc_obj(*ret);

        if (!ret)
                return NULL;

        btrfs_init_workqueue(ret, fs_info);

        ret->limit_active = limit_active;
        if (thresh == 0)
                thresh = DEFAULT_THRESHOLD;
        /* For low threshold, disabling threshold is a better choice */
        if (thresh < DEFAULT_THRESHOLD) {
                ret->current_active = limit_active;
                ret->thresh = NO_THRESHOLD;
        } else {
                /*
                 * For threshold-able wq, let its concurrency grow on demand.
                 * Use minimal max_active at alloc time to reduce resource
                 * usage.
                 */
                ret->current_active = 1;
                ret->thresh = thresh;
        }

        ret->normal_wq = alloc_workqueue("btrfs-%s", flags, ret->current_active,
                                         name);
        if (!ret->normal_wq) {
                kfree(ret);
                return NULL;
        }

        trace_btrfs_workqueue_alloc(ret, name);
        return ret;
}

struct btrfs_workqueue *btrfs_alloc_ordered_workqueue(
                                struct btrfs_fs_info *fs_info, const char *name,
                                unsigned int flags)
{
        struct btrfs_workqueue *ret;

        ret = kzalloc_obj(*ret);
        if (!ret)
                return NULL;

        btrfs_init_workqueue(ret, fs_info);

        /* Ordered workqueues don't allow @max_active adjustments. */
        ret->limit_active = 1;
        ret->current_active = 1;
        ret->thresh = NO_THRESHOLD;

        ret->normal_wq = alloc_ordered_workqueue("btrfs-%s", flags, name);
        if (!ret->normal_wq) {
                kfree(ret);
                return NULL;
        }

        trace_btrfs_workqueue_alloc(ret, name);
        return ret;
}

/*
 * Hook for threshold which will be called in btrfs_queue_work.
 * This hook WILL be called in IRQ handler context,
 * so workqueue_set_max_active MUST NOT be called in this hook
 */
static inline void thresh_queue_hook(struct btrfs_workqueue *wq)
{
        if (wq->thresh == NO_THRESHOLD)
                return;
        atomic_inc(&wq->pending);
}

/*
 * Hook for threshold which will be called before executing the work,
 * This hook is called in kthread content.
 * So workqueue_set_max_active is called here.
 */
static inline void thresh_exec_hook(struct btrfs_workqueue *wq)
{
        int new_current_active;
        long pending;
        bool need_change = false;

        if (wq->thresh == NO_THRESHOLD)
                return;

        atomic_dec(&wq->pending);
        spin_lock(&wq->thres_lock);
        /*
         * Use wq->count to limit the calling frequency of
         * workqueue_set_max_active.
         */
        wq->count++;
        wq->count %= (wq->thresh / 4);
        if (!wq->count)
                goto  out;
        new_current_active = wq->current_active;

        /*
         * pending may be changed later, but it's OK since we really
         * don't need it so accurate to calculate new_max_active.
         */
        pending = atomic_read(&wq->pending);
        if (pending > wq->thresh)
                new_current_active++;
        if (pending < wq->thresh / 2)
                new_current_active--;
        new_current_active = clamp_val(new_current_active, 1, wq->limit_active);
        if (new_current_active != wq->current_active)  {
                need_change = true;
                wq->current_active = new_current_active;
        }
out:
        spin_unlock(&wq->thres_lock);

        if (need_change)
                workqueue_set_max_active(wq->normal_wq, wq->current_active);
}

static void run_ordered_work(struct btrfs_workqueue *wq,
                             struct btrfs_work *self)
{
        struct list_head *list = &wq->ordered_list;
        struct btrfs_work *work;
        spinlock_t *lock = &wq->list_lock;
        unsigned long flags;
        bool free_self = false;

        while (1) {
                spin_lock_irqsave(lock, flags);
                if (list_empty(list))
                        break;
                work = list_first_entry(list, struct btrfs_work, ordered_list);
                if (!test_bit(WORK_DONE_BIT, &work->flags))
                        break;
                /*
                 * Orders all subsequent loads after reading WORK_DONE_BIT,
                 * paired with the smp_mb__before_atomic in btrfs_work_helper
                 * this guarantees that the ordered function will see all
                 * updates from ordinary work function.
                 */
                smp_rmb();

                /*
                 * we are going to call the ordered done function, but
                 * we leave the work item on the list as a barrier so
                 * that later work items that are done don't have their
                 * functions called before this one returns
                 */
                if (test_and_set_bit(WORK_ORDER_DONE_BIT, &work->flags))
                        break;
                trace_btrfs_ordered_sched(work);
                spin_unlock_irqrestore(lock, flags);
                work->ordered_func(work, false);

                /* now take the lock again and drop our item from the list */
                spin_lock_irqsave(lock, flags);
                list_del(&work->ordered_list);
                spin_unlock_irqrestore(lock, flags);

                if (work == self) {
                        /*
                         * This is the work item that the worker is currently
                         * executing.
                         *
                         * The kernel workqueue code guarantees non-reentrancy
                         * of work items. I.e., if a work item with the same
                         * address and work function is queued twice, the second
                         * execution is blocked until the first one finishes. A
                         * work item may be freed and recycled with the same
                         * work function; the workqueue code assumes that the
                         * original work item cannot depend on the recycled work
                         * item in that case (see find_worker_executing_work()).
                         *
                         * Note that different types of Btrfs work can depend on
                         * each other, and one type of work on one Btrfs
                         * filesystem may even depend on the same type of work
                         * on another Btrfs filesystem via, e.g., a loop device.
                         * Therefore, we must not allow the current work item to
                         * be recycled until we are really done, otherwise we
                         * break the above assumption and can deadlock.
                         */
                        free_self = true;
                } else {
                        /*
                         * We don't want to call the ordered free functions with
                         * the lock held.
                         */
                        work->ordered_func(work, true);
                        /* NB: work must not be dereferenced past this point. */
                        trace_btrfs_all_work_done(wq->fs_info, work);
                }
        }
        spin_unlock_irqrestore(lock, flags);

        if (free_self) {
                self->ordered_func(self, true);
                /* NB: self must not be dereferenced past this point. */
                trace_btrfs_all_work_done(wq->fs_info, self);
        }
}

static void btrfs_work_helper(struct work_struct *normal_work)
{
        struct btrfs_work *work = container_of(normal_work, struct btrfs_work,
                                               normal_work);
        struct btrfs_workqueue *wq = work->wq;
        bool need_order = false;

        /*
         * We should not touch things inside work in the following cases:
         * 1) after work->func() if it has no ordered_func(..., true) to free
         *    Since the struct is freed in work->func().
         * 2) after setting WORK_DONE_BIT
         *    The work may be freed in other threads almost instantly.
         * So we save the needed things here.
         */
        if (work->ordered_func)
                need_order = true;

        trace_btrfs_work_sched(work);
        thresh_exec_hook(wq);
        work->func(work);
        if (need_order) {
                /*
                 * Ensures all memory accesses done in the work function are
                 * ordered before setting the WORK_DONE_BIT. Ensuring the thread
                 * which is going to executed the ordered work sees them.
                 * Pairs with the smp_rmb in run_ordered_work.
                 */
                smp_mb__before_atomic();
                set_bit(WORK_DONE_BIT, &work->flags);
                run_ordered_work(wq, work);
        } else {
                /* NB: work must not be dereferenced past this point. */
                trace_btrfs_all_work_done(wq->fs_info, work);
        }
}

void btrfs_init_work(struct btrfs_work *work, btrfs_func_t func,
                     btrfs_ordered_func_t ordered_func)
{
        work->func = func;
        work->ordered_func = ordered_func;
        INIT_WORK(&work->normal_work, btrfs_work_helper);
        INIT_LIST_HEAD(&work->ordered_list);
        work->flags = 0;
}

void btrfs_queue_work(struct btrfs_workqueue *wq, struct btrfs_work *work)
{
        unsigned long flags;

        work->wq = wq;
        thresh_queue_hook(wq);
        if (work->ordered_func) {
                spin_lock_irqsave(&wq->list_lock, flags);
                list_add_tail(&work->ordered_list, &wq->ordered_list);
                spin_unlock_irqrestore(&wq->list_lock, flags);
        }
        trace_btrfs_work_queued(work);
        queue_work(wq->normal_wq, &work->normal_work);
}

void btrfs_destroy_workqueue(struct btrfs_workqueue *wq)
{
        if (!wq)
                return;
        destroy_workqueue(wq->normal_wq);
        trace_btrfs_workqueue_destroy(wq);
        kfree(wq);
}

void btrfs_workqueue_set_max(struct btrfs_workqueue *wq, int limit_active)
{
        if (wq)
                wq->limit_active = limit_active;
}

void btrfs_flush_workqueue(struct btrfs_workqueue *wq)
{
        flush_workqueue(wq->normal_wq);
}