// SPDX-License-Identifier: GPL-2.0

#include "blk-rq-qos.h"

/*
 * Increment 'v', if 'v' is below 'below'. Returns true if we succeeded,
 * false if 'v' + 1 would be bigger than 'below'.
 */
static bool atomic_inc_below(atomic_t *v, unsigned int below)
{
        unsigned int cur = atomic_read(v);

        do {
                if (cur >= below)
                        return false;
        } while (!atomic_try_cmpxchg(v, &cur, cur + 1));

        return true;
}

bool rq_wait_inc_below(struct rq_wait *rq_wait, unsigned int limit)
{
        return atomic_inc_below(&rq_wait->inflight, limit);
}

void __rq_qos_cleanup(struct rq_qos *rqos, struct bio *bio)
{
        do {
                if (rqos->ops->cleanup)
                        rqos->ops->cleanup(rqos, bio);
                rqos = rqos->next;
        } while (rqos);
}

void __rq_qos_done(struct rq_qos *rqos, struct request *rq)
{
        do {
                if (rqos->ops->done)
                        rqos->ops->done(rqos, rq);
                rqos = rqos->next;
        } while (rqos);
}

void __rq_qos_issue(struct rq_qos *rqos, struct request *rq)
{
        do {
                if (rqos->ops->issue)
                        rqos->ops->issue(rqos, rq);
                rqos = rqos->next;
        } while (rqos);
}

void __rq_qos_requeue(struct rq_qos *rqos, struct request *rq)
{
        do {
                if (rqos->ops->requeue)
                        rqos->ops->requeue(rqos, rq);
                rqos = rqos->next;
        } while (rqos);
}

void __rq_qos_throttle(struct rq_qos *rqos, struct bio *bio)
{
        do {
                if (rqos->ops->throttle)
                        rqos->ops->throttle(rqos, bio);
                rqos = rqos->next;
        } while (rqos);
}

void __rq_qos_track(struct rq_qos *rqos, struct request *rq, struct bio *bio)
{
        do {
                if (rqos->ops->track)
                        rqos->ops->track(rqos, rq, bio);
                rqos = rqos->next;
        } while (rqos);
}

void __rq_qos_merge(struct rq_qos *rqos, struct request *rq, struct bio *bio)
{
        do {
                if (rqos->ops->merge)
                        rqos->ops->merge(rqos, rq, bio);
                rqos = rqos->next;
        } while (rqos);
}

void __rq_qos_done_bio(struct rq_qos *rqos, struct bio *bio)
{
        do {
                if (rqos->ops->done_bio)
                        rqos->ops->done_bio(rqos, bio);
                rqos = rqos->next;
        } while (rqos);
}

void __rq_qos_queue_depth_changed(struct rq_qos *rqos)
{
        do {
                if (rqos->ops->queue_depth_changed)
                        rqos->ops->queue_depth_changed(rqos);
                rqos = rqos->next;
        } while (rqos);
}

/*
 * Return true, if we can't increase the depth further by scaling
 */
bool rq_depth_calc_max_depth(struct rq_depth *rqd)
{
        unsigned int depth;
        bool ret = false;

        /*
         * For QD=1 devices, this is a special case. It's important for those
         * to have one request ready when one completes, so force a depth of
         * 2 for those devices. On the backend, it'll be a depth of 1 anyway,
         * since the device can't have more than that in flight. If we're
         * scaling down, then keep a setting of 1/1/1.
         */
        if (rqd->queue_depth == 1) {
                if (rqd->scale_step > 0)
                        rqd->max_depth = 1;
                else {
                        rqd->max_depth = 2;
                        ret = true;
                }
        } else {
                /*
                 * scale_step == 0 is our default state. If we have suffered
                 * latency spikes, step will be > 0, and we shrink the
                 * allowed write depths. If step is < 0, we're only doing
                 * writes, and we allow a temporarily higher depth to
                 * increase performance.
                 */
                depth = min_t(unsigned int, rqd->default_depth,
                              rqd->queue_depth);
                if (rqd->scale_step > 0)
                        depth = 1 + ((depth - 1) >> min(31, rqd->scale_step));
                else if (rqd->scale_step < 0) {
                        unsigned int maxd = 3 * rqd->queue_depth / 4;

                        depth = 1 + ((depth - 1) << -rqd->scale_step);
                        if (depth > maxd) {
                                depth = maxd;
                                ret = true;
                        }
                }

                rqd->max_depth = depth;
        }

        return ret;
}

/* Returns true on success and false if scaling up wasn't possible */
bool rq_depth_scale_up(struct rq_depth *rqd)
{
        /*
         * Hit max in previous round, stop here
         */
        if (rqd->scaled_max)
                return false;

        rqd->scale_step--;

        rqd->scaled_max = rq_depth_calc_max_depth(rqd);
        return true;
}

/*
 * Scale rwb down. If 'hard_throttle' is set, do it quicker, since we
 * had a latency violation. Returns true on success and returns false if
 * scaling down wasn't possible.
 */
bool rq_depth_scale_down(struct rq_depth *rqd, bool hard_throttle)
{
        /*
         * Stop scaling down when we've hit the limit. This also prevents
         * ->scale_step from going to crazy values, if the device can't
         * keep up.
         */
        if (rqd->max_depth == 1)
                return false;

        if (rqd->scale_step < 0 && hard_throttle)
                rqd->scale_step = 0;
        else
                rqd->scale_step++;

        rqd->scaled_max = false;
        rq_depth_calc_max_depth(rqd);
        return true;
}

struct rq_qos_wait_data {
        struct wait_queue_entry wq;
        struct rq_wait *rqw;
        acquire_inflight_cb_t *cb;
        void *private_data;
        bool got_token;
};

static int rq_qos_wake_function(struct wait_queue_entry *curr,
                                unsigned int mode, int wake_flags, void *key)
{
        struct rq_qos_wait_data *data = container_of(curr,
                                                     struct rq_qos_wait_data,
                                                     wq);

        /*
         * If we fail to get a budget, return -1 to interrupt the wake up loop
         * in __wake_up_common.
         */
        if (!data->cb(data->rqw, data->private_data))
                return -1;

        data->got_token = true;
        /*
         * autoremove_wake_function() removes the wait entry only when it
         * actually changed the task state. We want the wait always removed.
         * Remove explicitly and use default_wake_function().
         */
        default_wake_function(curr, mode, wake_flags, key);
        /*
         * Note that the order of operations is important as finish_wait()
         * tests whether @curr is removed without grabbing the lock. This
         * should be the last thing to do to make sure we will not have a
         * UAF access to @data. And the semantics of memory barrier in it
         * also make sure the waiter will see the latest @data->got_token
         * once list_empty_careful() in finish_wait() returns true.
         */
        list_del_init_careful(&curr->entry);
        return 1;
}

/**
 * rq_qos_wait - throttle on a rqw if we need to
 * @rqw: rqw to throttle on
 * @private_data: caller provided specific data
 * @acquire_inflight_cb: inc the rqw->inflight counter if we can
 * @cleanup_cb: the callback to cleanup in case we race with a waker
 *
 * This provides a uniform place for the rq_qos users to do their throttling.
 * Since you can end up with a lot of things sleeping at once, this manages the
 * waking up based on the resources available.  The acquire_inflight_cb should
 * inc the rqw->inflight if we have the ability to do so, or return false if not
 * and then we will sleep until the room becomes available.
 *
 * cleanup_cb is in case that we race with a waker and need to cleanup the
 * inflight count accordingly.
 */
void rq_qos_wait(struct rq_wait *rqw, void *private_data,
                 acquire_inflight_cb_t *acquire_inflight_cb,
                 cleanup_cb_t *cleanup_cb)
{
        struct rq_qos_wait_data data = {
                .rqw            = rqw,
                .cb             = acquire_inflight_cb,
                .private_data   = private_data,
                .got_token      = false,
        };
        bool first_waiter;

        /*
         * If there are no waiters in the waiting queue, try to increase the
         * inflight counter if we can. Otherwise, prepare for adding ourselves
         * to the waiting queue.
         */
        if (!waitqueue_active(&rqw->wait) && acquire_inflight_cb(rqw, private_data))
                return;

        init_wait_func(&data.wq, rq_qos_wake_function);
        first_waiter = prepare_to_wait_exclusive(&rqw->wait, &data.wq,
                                                 TASK_UNINTERRUPTIBLE);
        /*
         * Make sure there is at least one inflight process; otherwise, waiters
         * will never be woken up. Since there may be no inflight process before
         * adding ourselves to the waiting queue above, we need to try to
         * increase the inflight counter for ourselves. And it is sufficient to
         * guarantee that at least the first waiter to enter the waiting queue
         * will re-check the waiting condition before going to sleep, thus
         * ensuring forward progress.
         */
        if (!data.got_token && first_waiter && acquire_inflight_cb(rqw, private_data)) {
                finish_wait(&rqw->wait, &data.wq);
                /*
                 * We raced with rq_qos_wake_function() getting a token,
                 * which means we now have two. Put our local token
                 * and wake anyone else potentially waiting for one.
                 *
                 * Enough memory barrier in list_empty_careful() in
                 * finish_wait() is paired with list_del_init_careful()
                 * in rq_qos_wake_function() to make sure we will see
                 * the latest @data->got_token.
                 */
                if (data.got_token)
                        cleanup_cb(rqw, private_data);
                return;
        }

        /* we are now relying on the waker to increase our inflight counter. */
        do {
                if (data.got_token)
                        break;
                io_schedule();
                set_current_state(TASK_UNINTERRUPTIBLE);
        } while (1);
        finish_wait(&rqw->wait, &data.wq);
}

void rq_qos_exit(struct request_queue *q)
{
        mutex_lock(&q->rq_qos_mutex);
        while (q->rq_qos) {
                struct rq_qos *rqos = q->rq_qos;
                q->rq_qos = rqos->next;
                rqos->ops->exit(rqos);
        }
        blk_queue_flag_clear(QUEUE_FLAG_QOS_ENABLED, q);
        mutex_unlock(&q->rq_qos_mutex);
}

int rq_qos_add(struct rq_qos *rqos, struct gendisk *disk, enum rq_qos_id id,
                const struct rq_qos_ops *ops)
{
        struct request_queue *q = disk->queue;
        unsigned int memflags;

        lockdep_assert_held(&q->rq_qos_mutex);

        rqos->disk = disk;
        rqos->id = id;
        rqos->ops = ops;

        /*
         * No IO can be in-flight when adding rqos, so freeze queue, which
         * is fine since we only support rq_qos for blk-mq queue.
         */
        memflags = blk_mq_freeze_queue(q);

        if (rq_qos_id(q, rqos->id))
                goto ebusy;
        rqos->next = q->rq_qos;
        q->rq_qos = rqos;
        blk_queue_flag_set(QUEUE_FLAG_QOS_ENABLED, q);

        blk_mq_unfreeze_queue(q, memflags);
        return 0;
ebusy:
        blk_mq_unfreeze_queue(q, memflags);
        return -EBUSY;
}

void rq_qos_del(struct rq_qos *rqos)
{
        struct request_queue *q = rqos->disk->queue;
        struct rq_qos **cur;
        unsigned int memflags;

        lockdep_assert_held(&q->rq_qos_mutex);

        memflags = blk_mq_freeze_queue(q);
        for (cur = &q->rq_qos; *cur; cur = &(*cur)->next) {
                if (*cur == rqos) {
                        *cur = rqos->next;
                        break;
                }
        }
        if (!q->rq_qos)
                blk_queue_flag_clear(QUEUE_FLAG_QOS_ENABLED, q);
        blk_mq_unfreeze_queue(q, memflags);
}