// SPDX-License-Identifier: GPL-2.0
/*
 * blk-mq scheduling framework
 *
 * Copyright (C) 2016 Jens Axboe
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/list_sort.h>

#include <trace/events/block.h>

#include "blk.h"
#include "blk-mq.h"
#include "blk-mq-debugfs.h"
#include "blk-mq-sched.h"
#include "blk-wbt.h"

/*
 * Mark a hardware queue as needing a restart.
 */
void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx)
{
        if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
                return;

        set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
}
EXPORT_SYMBOL_GPL(blk_mq_sched_mark_restart_hctx);

void __blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
{
        clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);

        /*
         * Order clearing SCHED_RESTART and list_empty_careful(&hctx->dispatch)
         * in blk_mq_run_hw_queue(). Its pair is the barrier in
         * blk_mq_dispatch_rq_list(). So dispatch code won't see SCHED_RESTART,
         * meantime new request added to hctx->dispatch is missed to check in
         * blk_mq_run_hw_queue().
         */
        smp_mb();

        blk_mq_run_hw_queue(hctx, true);
}

static int sched_rq_cmp(void *priv, const struct list_head *a,
                        const struct list_head *b)
{
        struct request *rqa = container_of(a, struct request, queuelist);
        struct request *rqb = container_of(b, struct request, queuelist);

        return rqa->mq_hctx > rqb->mq_hctx;
}

static bool blk_mq_dispatch_hctx_list(struct list_head *rq_list)
{
        struct blk_mq_hw_ctx *hctx =
                list_first_entry(rq_list, struct request, queuelist)->mq_hctx;
        struct request *rq;
        LIST_HEAD(hctx_list);
        unsigned int count = 0;

        list_for_each_entry(rq, rq_list, queuelist) {
                if (rq->mq_hctx != hctx) {
                        list_cut_before(&hctx_list, rq_list, &rq->queuelist);
                        goto dispatch;
                }
                count++;
        }
        list_splice_tail_init(rq_list, &hctx_list);

dispatch:
        return blk_mq_dispatch_rq_list(hctx, &hctx_list, count);
}

#define BLK_MQ_BUDGET_DELAY     3               /* ms units */

/*
 * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
 * its queue by itself in its completion handler, so we don't need to
 * restart queue if .get_budget() fails to get the budget.
 *
 * Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
 * be run again.  This is necessary to avoid starving flushes.
 */
static int __blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
{
        struct request_queue *q = hctx->queue;
        struct elevator_queue *e = q->elevator;
        bool multi_hctxs = false, run_queue = false;
        bool dispatched = false, busy = false;
        unsigned int max_dispatch;
        LIST_HEAD(rq_list);
        int count = 0;

        if (hctx->dispatch_busy)
                max_dispatch = 1;
        else
                max_dispatch = hctx->queue->nr_requests;

        do {
                struct request *rq;
                int budget_token;

                if (e->type->ops.has_work && !e->type->ops.has_work(hctx))
                        break;

                if (!list_empty_careful(&hctx->dispatch)) {
                        busy = true;
                        break;
                }

                budget_token = blk_mq_get_dispatch_budget(q);
                if (budget_token < 0)
                        break;

                rq = e->type->ops.dispatch_request(hctx);
                if (!rq) {
                        blk_mq_put_dispatch_budget(q, budget_token);
                        /*
                         * We're releasing without dispatching. Holding the
                         * budget could have blocked any "hctx"s with the
                         * same queue and if we didn't dispatch then there's
                         * no guarantee anyone will kick the queue.  Kick it
                         * ourselves.
                         */
                        run_queue = true;
                        break;
                }

                blk_mq_set_rq_budget_token(rq, budget_token);

                /*
                 * Now this rq owns the budget which has to be released
                 * if this rq won't be queued to driver via .queue_rq()
                 * in blk_mq_dispatch_rq_list().
                 */
                list_add_tail(&rq->queuelist, &rq_list);
                count++;
                if (rq->mq_hctx != hctx)
                        multi_hctxs = true;

                /*
                 * If we cannot get tag for the request, stop dequeueing
                 * requests from the IO scheduler. We are unlikely to be able
                 * to submit them anyway and it creates false impression for
                 * scheduling heuristics that the device can take more IO.
                 */
                if (!blk_mq_get_driver_tag(rq))
                        break;
        } while (count < max_dispatch);

        if (!count) {
                if (run_queue)
                        blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
        } else if (multi_hctxs) {
                /*
                 * Requests from different hctx may be dequeued from some
                 * schedulers, such as bfq and deadline.
                 *
                 * Sort the requests in the list according to their hctx,
                 * dispatch batching requests from same hctx at a time.
                 */
                list_sort(NULL, &rq_list, sched_rq_cmp);
                do {
                        dispatched |= blk_mq_dispatch_hctx_list(&rq_list);
                } while (!list_empty(&rq_list));
        } else {
                dispatched = blk_mq_dispatch_rq_list(hctx, &rq_list, count);
        }

        if (busy)
                return -EAGAIN;
        return !!dispatched;
}

static int blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
{
        unsigned long end = jiffies + HZ;
        int ret;

        do {
                ret = __blk_mq_do_dispatch_sched(hctx);
                if (ret != 1)
                        break;
                if (need_resched() || time_is_before_jiffies(end)) {
                        blk_mq_delay_run_hw_queue(hctx, 0);
                        break;
                }
        } while (1);

        return ret;
}

static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
                                          struct blk_mq_ctx *ctx)
{
        unsigned short idx = ctx->index_hw[hctx->type];

        if (++idx == hctx->nr_ctx)
                idx = 0;

        return hctx->ctxs[idx];
}

/*
 * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
 * its queue by itself in its completion handler, so we don't need to
 * restart queue if .get_budget() fails to get the budget.
 *
 * Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
 * be run again.  This is necessary to avoid starving flushes.
 */
static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
{
        struct request_queue *q = hctx->queue;
        LIST_HEAD(rq_list);
        struct blk_mq_ctx *ctx = READ_ONCE(hctx->dispatch_from);
        int ret = 0;
        struct request *rq;

        do {
                int budget_token;

                if (!list_empty_careful(&hctx->dispatch)) {
                        ret = -EAGAIN;
                        break;
                }

                if (!sbitmap_any_bit_set(&hctx->ctx_map))
                        break;

                budget_token = blk_mq_get_dispatch_budget(q);
                if (budget_token < 0)
                        break;

                rq = blk_mq_dequeue_from_ctx(hctx, ctx);
                if (!rq) {
                        blk_mq_put_dispatch_budget(q, budget_token);
                        /*
                         * We're releasing without dispatching. Holding the
                         * budget could have blocked any "hctx"s with the
                         * same queue and if we didn't dispatch then there's
                         * no guarantee anyone will kick the queue.  Kick it
                         * ourselves.
                         */
                        blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
                        break;
                }

                blk_mq_set_rq_budget_token(rq, budget_token);

                /*
                 * Now this rq owns the budget which has to be released
                 * if this rq won't be queued to driver via .queue_rq()
                 * in blk_mq_dispatch_rq_list().
                 */
                list_add(&rq->queuelist, &rq_list);

                /* round robin for fair dispatch */
                ctx = blk_mq_next_ctx(hctx, rq->mq_ctx);

        } while (blk_mq_dispatch_rq_list(rq->mq_hctx, &rq_list, 1));

        WRITE_ONCE(hctx->dispatch_from, ctx);
        return ret;
}

static int __blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
{
        bool need_dispatch = false;
        LIST_HEAD(rq_list);

        /*
         * If we have previous entries on our dispatch list, grab them first for
         * more fair dispatch.
         */
        if (!list_empty_careful(&hctx->dispatch)) {
                spin_lock(&hctx->lock);
                if (!list_empty(&hctx->dispatch))
                        list_splice_init(&hctx->dispatch, &rq_list);
                spin_unlock(&hctx->lock);
        }

        /*
         * Only ask the scheduler for requests, if we didn't have residual
         * requests from the dispatch list. This is to avoid the case where
         * we only ever dispatch a fraction of the requests available because
         * of low device queue depth. Once we pull requests out of the IO
         * scheduler, we can no longer merge or sort them. So it's best to
         * leave them there for as long as we can. Mark the hw queue as
         * needing a restart in that case.
         *
         * We want to dispatch from the scheduler if there was nothing
         * on the dispatch list or we were able to dispatch from the
         * dispatch list.
         */
        if (!list_empty(&rq_list)) {
                blk_mq_sched_mark_restart_hctx(hctx);
                if (!blk_mq_dispatch_rq_list(hctx, &rq_list, 0))
                        return 0;
                need_dispatch = true;
        } else {
                need_dispatch = hctx->dispatch_busy;
        }

        if (hctx->queue->elevator)
                return blk_mq_do_dispatch_sched(hctx);

        /* dequeue request one by one from sw queue if queue is busy */
        if (need_dispatch)
                return blk_mq_do_dispatch_ctx(hctx);
        blk_mq_flush_busy_ctxs(hctx, &rq_list);
        blk_mq_dispatch_rq_list(hctx, &rq_list, 0);
        return 0;
}

void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
{
        struct request_queue *q = hctx->queue;

        /* RCU or SRCU read lock is needed before checking quiesced flag */
        if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
                return;

        hctx->run++;

        /*
         * A return of -EAGAIN is an indication that hctx->dispatch is not
         * empty and we must run again in order to avoid starving flushes.
         */
        if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN) {
                if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN)
                        blk_mq_run_hw_queue(hctx, true);
        }
}

bool blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio,
                unsigned int nr_segs)
{
        struct elevator_queue *e = q->elevator;
        struct blk_mq_ctx *ctx;
        struct blk_mq_hw_ctx *hctx;
        bool ret = false;
        enum hctx_type type;

        if (e && e->type->ops.bio_merge) {
                ret = e->type->ops.bio_merge(q, bio, nr_segs);
                goto out_put;
        }

        ctx = blk_mq_get_ctx(q);
        hctx = blk_mq_map_queue(q, bio->bi_opf, ctx);
        type = hctx->type;
        if (!(hctx->flags & BLK_MQ_F_SHOULD_MERGE) ||
            list_empty_careful(&ctx->rq_lists[type]))
                goto out_put;

        /* default per sw-queue merge */
        spin_lock(&ctx->lock);
        /*
         * Reverse check our software queue for entries that we could
         * potentially merge with. Currently includes a hand-wavy stop
         * count of 8, to not spend too much time checking for merges.
         */
        if (blk_bio_list_merge(q, &ctx->rq_lists[type], bio, nr_segs))
                ret = true;

        spin_unlock(&ctx->lock);
out_put:
        return ret;
}

bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq,
                                   struct list_head *free)
{
        return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq, free);
}
EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);

static int blk_mq_sched_alloc_map_and_rqs(struct request_queue *q,
                                          struct blk_mq_hw_ctx *hctx,
                                          unsigned int hctx_idx)
{
        if (blk_mq_is_shared_tags(q->tag_set->flags)) {
                hctx->sched_tags = q->sched_shared_tags;
                return 0;
        }

        hctx->sched_tags = blk_mq_alloc_map_and_rqs(q->tag_set, hctx_idx,
                                                    q->nr_requests);

        if (!hctx->sched_tags)
                return -ENOMEM;
        return 0;
}

static void blk_mq_exit_sched_shared_tags(struct request_queue *queue)
{
        blk_mq_free_rq_map(queue->sched_shared_tags);
        queue->sched_shared_tags = NULL;
}

/* called in queue's release handler, tagset has gone away */
static void blk_mq_sched_tags_teardown(struct request_queue *q, unsigned int flags)
{
        struct blk_mq_hw_ctx *hctx;
        unsigned long i;

        queue_for_each_hw_ctx(q, hctx, i) {
                if (hctx->sched_tags) {
                        if (!blk_mq_is_shared_tags(flags))
                                blk_mq_free_rq_map(hctx->sched_tags);
                        hctx->sched_tags = NULL;
                }
        }

        if (blk_mq_is_shared_tags(flags))
                blk_mq_exit_sched_shared_tags(q);
}

static int blk_mq_init_sched_shared_tags(struct request_queue *queue)
{
        struct blk_mq_tag_set *set = queue->tag_set;

        /*
         * Set initial depth at max so that we don't need to reallocate for
         * updating nr_requests.
         */
        queue->sched_shared_tags = blk_mq_alloc_map_and_rqs(set,
                                                BLK_MQ_NO_HCTX_IDX,
                                                MAX_SCHED_RQ);
        if (!queue->sched_shared_tags)
                return -ENOMEM;

        blk_mq_tag_update_sched_shared_tags(queue);

        return 0;
}

/* caller must have a reference to @e, will grab another one if successful */
int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
{
        unsigned int flags = q->tag_set->flags;
        struct blk_mq_hw_ctx *hctx;
        struct elevator_queue *eq;
        unsigned long i;
        int ret;

        /*
         * Default to double of smaller one between hw queue_depth and 128,
         * since we don't split into sync/async like the old code did.
         * Additionally, this is a per-hw queue depth.
         */
        q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth,
                                   BLKDEV_DEFAULT_RQ);

        if (blk_mq_is_shared_tags(flags)) {
                ret = blk_mq_init_sched_shared_tags(q);
                if (ret)
                        return ret;
        }

        queue_for_each_hw_ctx(q, hctx, i) {
                ret = blk_mq_sched_alloc_map_and_rqs(q, hctx, i);
                if (ret)
                        goto err_free_map_and_rqs;
        }

        ret = e->ops.init_sched(q, e);
        if (ret)
                goto err_free_map_and_rqs;

        mutex_lock(&q->debugfs_mutex);
        blk_mq_debugfs_register_sched(q);
        mutex_unlock(&q->debugfs_mutex);

        queue_for_each_hw_ctx(q, hctx, i) {
                if (e->ops.init_hctx) {
                        ret = e->ops.init_hctx(hctx, i);
                        if (ret) {
                                eq = q->elevator;
                                blk_mq_sched_free_rqs(q);
                                blk_mq_exit_sched(q, eq);
                                kobject_put(&eq->kobj);
                                return ret;
                        }
                }
                mutex_lock(&q->debugfs_mutex);
                blk_mq_debugfs_register_sched_hctx(q, hctx);
                mutex_unlock(&q->debugfs_mutex);
        }

        return 0;

err_free_map_and_rqs:
        blk_mq_sched_free_rqs(q);
        blk_mq_sched_tags_teardown(q, flags);

        q->elevator = NULL;
        return ret;
}

/*
 * called in either blk_queue_cleanup or elevator_switch, tagset
 * is required for freeing requests
 */
void blk_mq_sched_free_rqs(struct request_queue *q)
{
        struct blk_mq_hw_ctx *hctx;
        unsigned long i;

        if (blk_mq_is_shared_tags(q->tag_set->flags)) {
                blk_mq_free_rqs(q->tag_set, q->sched_shared_tags,
                                BLK_MQ_NO_HCTX_IDX);
        } else {
                queue_for_each_hw_ctx(q, hctx, i) {
                        if (hctx->sched_tags)
                                blk_mq_free_rqs(q->tag_set,
                                                hctx->sched_tags, i);
                }
        }
}

void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
{
        struct blk_mq_hw_ctx *hctx;
        unsigned long i;
        unsigned int flags = 0;

        queue_for_each_hw_ctx(q, hctx, i) {
                mutex_lock(&q->debugfs_mutex);
                blk_mq_debugfs_unregister_sched_hctx(hctx);
                mutex_unlock(&q->debugfs_mutex);

                if (e->type->ops.exit_hctx && hctx->sched_data) {
                        e->type->ops.exit_hctx(hctx, i);
                        hctx->sched_data = NULL;
                }
                flags = hctx->flags;
        }

        mutex_lock(&q->debugfs_mutex);
        blk_mq_debugfs_unregister_sched(q);
        mutex_unlock(&q->debugfs_mutex);

        if (e->type->ops.exit_sched)
                e->type->ops.exit_sched(e);
        blk_mq_sched_tags_teardown(q, flags);
        q->elevator = NULL;
}