Merge tag 'nfs-for-3.17-5' of git://git.linux-nfs.org/projects/trondmy/linux-nfs

[deliverable/linux.git] / block / blk-mq.c

/*
 * Block multiqueue core code
 *
 * Copyright (C) 2013-2014 Jens Axboe
 * Copyright (C) 2013-2014 Christoph Hellwig
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/backing-dev.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/mm.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/workqueue.h>
#include <linux/smp.h>
#include <linux/llist.h>
#include <linux/list_sort.h>
#include <linux/cpu.h>
#include <linux/cache.h>
#include <linux/sched/sysctl.h>
#include <linux/delay.h>

#include <trace/events/block.h>

#include <linux/blk-mq.h>
#include "blk.h"
#include "blk-mq.h"
#include "blk-mq-tag.h"

static DEFINE_MUTEX(all_q_mutex);
static LIST_HEAD(all_q_list);

static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx);

/*
 * Check if any of the ctx's have pending work in this hardware queue
 */
static bool blk_mq_hctx_has_pending(struct blk_mq_hw_ctx *hctx)
{
        unsigned int i;

        for (i = 0; i < hctx->ctx_map.map_size; i++)
                if (hctx->ctx_map.map[i].word)
                        return true;

        return false;
}

static inline struct blk_align_bitmap *get_bm(struct blk_mq_hw_ctx *hctx,
                                              struct blk_mq_ctx *ctx)
{
        return &hctx->ctx_map.map[ctx->index_hw / hctx->ctx_map.bits_per_word];
}

#define CTX_TO_BIT(hctx, ctx)   \
        ((ctx)->index_hw & ((hctx)->ctx_map.bits_per_word - 1))

/*
 * Mark this ctx as having pending work in this hardware queue
 */
static void blk_mq_hctx_mark_pending(struct blk_mq_hw_ctx *hctx,
                                     struct blk_mq_ctx *ctx)
{
        struct blk_align_bitmap *bm = get_bm(hctx, ctx);

        if (!test_bit(CTX_TO_BIT(hctx, ctx), &bm->word))
                set_bit(CTX_TO_BIT(hctx, ctx), &bm->word);
}

static void blk_mq_hctx_clear_pending(struct blk_mq_hw_ctx *hctx,
                                      struct blk_mq_ctx *ctx)
{
        struct blk_align_bitmap *bm = get_bm(hctx, ctx);

        clear_bit(CTX_TO_BIT(hctx, ctx), &bm->word);
}

static int blk_mq_queue_enter(struct request_queue *q)
{
        while (true) {
                int ret;

                if (percpu_ref_tryget_live(&q->mq_usage_counter))
                        return 0;

                ret = wait_event_interruptible(q->mq_freeze_wq,
                                !q->mq_freeze_depth || blk_queue_dying(q));
                if (blk_queue_dying(q))
                        return -ENODEV;
                if (ret)
                        return ret;
        }
}

static void blk_mq_queue_exit(struct request_queue *q)
{
        percpu_ref_put(&q->mq_usage_counter);
}

static void blk_mq_usage_counter_release(struct percpu_ref *ref)
{
        struct request_queue *q =
                container_of(ref, struct request_queue, mq_usage_counter);

        wake_up_all(&q->mq_freeze_wq);
}

/*
 * Guarantee no request is in use, so we can change any data structure of
 * the queue afterward.
 */
void blk_mq_freeze_queue(struct request_queue *q)
{
        bool freeze;

        spin_lock_irq(q->queue_lock);
        freeze = !q->mq_freeze_depth++;
        spin_unlock_irq(q->queue_lock);

        if (freeze) {
                percpu_ref_kill(&q->mq_usage_counter);
                blk_mq_run_queues(q, false);
        }
        wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->mq_usage_counter));
}

static void blk_mq_unfreeze_queue(struct request_queue *q)
{
        bool wake;

        spin_lock_irq(q->queue_lock);
        wake = !--q->mq_freeze_depth;
        WARN_ON_ONCE(q->mq_freeze_depth < 0);
        spin_unlock_irq(q->queue_lock);
        if (wake) {
                percpu_ref_reinit(&q->mq_usage_counter);
                wake_up_all(&q->mq_freeze_wq);
        }
}

bool blk_mq_can_queue(struct blk_mq_hw_ctx *hctx)
{
        return blk_mq_has_free_tags(hctx->tags);
}
EXPORT_SYMBOL(blk_mq_can_queue);

static void blk_mq_rq_ctx_init(struct request_queue *q, struct blk_mq_ctx *ctx,
                               struct request *rq, unsigned int rw_flags)
{
        if (blk_queue_io_stat(q))
                rw_flags |= REQ_IO_STAT;

        INIT_LIST_HEAD(&rq->queuelist);
        /* csd/requeue_work/fifo_time is initialized before use */
        rq->q = q;
        rq->mq_ctx = ctx;
        rq->cmd_flags |= rw_flags;
        /* do not touch atomic flags, it needs atomic ops against the timer */
        rq->cpu = -1;
        INIT_HLIST_NODE(&rq->hash);
        RB_CLEAR_NODE(&rq->rb_node);
        rq->rq_disk = NULL;
        rq->part = NULL;
        rq->start_time = jiffies;
#ifdef CONFIG_BLK_CGROUP
        rq->rl = NULL;
        set_start_time_ns(rq);
        rq->io_start_time_ns = 0;
#endif
        rq->nr_phys_segments = 0;
#if defined(CONFIG_BLK_DEV_INTEGRITY)
        rq->nr_integrity_segments = 0;
#endif
        rq->special = NULL;
        /* tag was already set */
        rq->errors = 0;

        rq->cmd = rq->__cmd;

        rq->extra_len = 0;
        rq->sense_len = 0;
        rq->resid_len = 0;
        rq->sense = NULL;

        INIT_LIST_HEAD(&rq->timeout_list);
        rq->timeout = 0;

        rq->end_io = NULL;
        rq->end_io_data = NULL;
        rq->next_rq = NULL;

        ctx->rq_dispatched[rw_is_sync(rw_flags)]++;
}

static struct request *
__blk_mq_alloc_request(struct blk_mq_alloc_data *data, int rw)
{
        struct request *rq;
        unsigned int tag;

        tag = blk_mq_get_tag(data);
        if (tag != BLK_MQ_TAG_FAIL) {
                rq = data->hctx->tags->rqs[tag];

                rq->cmd_flags = 0;
                if (blk_mq_tag_busy(data->hctx)) {
                        rq->cmd_flags = REQ_MQ_INFLIGHT;
                        atomic_inc(&data->hctx->nr_active);
                }

                rq->tag = tag;
                blk_mq_rq_ctx_init(data->q, data->ctx, rq, rw);
                return rq;
        }

        return NULL;
}

struct request *blk_mq_alloc_request(struct request_queue *q, int rw, gfp_t gfp,
                bool reserved)
{
        struct blk_mq_ctx *ctx;
        struct blk_mq_hw_ctx *hctx;
        struct request *rq;
        struct blk_mq_alloc_data alloc_data;

        if (blk_mq_queue_enter(q))
                return NULL;

        ctx = blk_mq_get_ctx(q);
        hctx = q->mq_ops->map_queue(q, ctx->cpu);
        blk_mq_set_alloc_data(&alloc_data, q, gfp & ~__GFP_WAIT,
                        reserved, ctx, hctx);

        rq = __blk_mq_alloc_request(&alloc_data, rw);
        if (!rq && (gfp & __GFP_WAIT)) {
                __blk_mq_run_hw_queue(hctx);
                blk_mq_put_ctx(ctx);

                ctx = blk_mq_get_ctx(q);
                hctx = q->mq_ops->map_queue(q, ctx->cpu);
                blk_mq_set_alloc_data(&alloc_data, q, gfp, reserved, ctx,
                                hctx);
                rq =  __blk_mq_alloc_request(&alloc_data, rw);
                ctx = alloc_data.ctx;
        }
        blk_mq_put_ctx(ctx);
        return rq;
}
EXPORT_SYMBOL(blk_mq_alloc_request);

static void __blk_mq_free_request(struct blk_mq_hw_ctx *hctx,
                                  struct blk_mq_ctx *ctx, struct request *rq)
{
        const int tag = rq->tag;
        struct request_queue *q = rq->q;

        if (rq->cmd_flags & REQ_MQ_INFLIGHT)
                atomic_dec(&hctx->nr_active);

        clear_bit(REQ_ATOM_STARTED, &rq->atomic_flags);
        blk_mq_put_tag(hctx, tag, &ctx->last_tag);
        blk_mq_queue_exit(q);
}

void blk_mq_free_request(struct request *rq)
{
        struct blk_mq_ctx *ctx = rq->mq_ctx;
        struct blk_mq_hw_ctx *hctx;
        struct request_queue *q = rq->q;

        ctx->rq_completed[rq_is_sync(rq)]++;

        hctx = q->mq_ops->map_queue(q, ctx->cpu);
        __blk_mq_free_request(hctx, ctx, rq);
}

/*
 * Clone all relevant state from a request that has been put on hold in
 * the flush state machine into the preallocated flush request that hangs
 * off the request queue.
 *
 * For a driver the flush request should be invisible, that's why we are
 * impersonating the original request here.
 */
void blk_mq_clone_flush_request(struct request *flush_rq,
                struct request *orig_rq)
{
        struct blk_mq_hw_ctx *hctx =
                orig_rq->q->mq_ops->map_queue(orig_rq->q, orig_rq->mq_ctx->cpu);

        flush_rq->mq_ctx = orig_rq->mq_ctx;
        flush_rq->tag = orig_rq->tag;
        memcpy(blk_mq_rq_to_pdu(flush_rq), blk_mq_rq_to_pdu(orig_rq),
                hctx->cmd_size);
}

inline void __blk_mq_end_io(struct request *rq, int error)
{
        blk_account_io_done(rq);

        if (rq->end_io) {
                rq->end_io(rq, error);
        } else {
                if (unlikely(blk_bidi_rq(rq)))
                        blk_mq_free_request(rq->next_rq);
                blk_mq_free_request(rq);
        }
}
EXPORT_SYMBOL(__blk_mq_end_io);

void blk_mq_end_io(struct request *rq, int error)
{
        if (blk_update_request(rq, error, blk_rq_bytes(rq)))
                BUG();
        __blk_mq_end_io(rq, error);
}
EXPORT_SYMBOL(blk_mq_end_io);

static void __blk_mq_complete_request_remote(void *data)
{
        struct request *rq = data;

        rq->q->softirq_done_fn(rq);
}

static void blk_mq_ipi_complete_request(struct request *rq)
{
        struct blk_mq_ctx *ctx = rq->mq_ctx;
        bool shared = false;
        int cpu;

        if (!test_bit(QUEUE_FLAG_SAME_COMP, &rq->q->queue_flags)) {
                rq->q->softirq_done_fn(rq);
                return;
        }

        cpu = get_cpu();
        if (!test_bit(QUEUE_FLAG_SAME_FORCE, &rq->q->queue_flags))
                shared = cpus_share_cache(cpu, ctx->cpu);

        if (cpu != ctx->cpu && !shared && cpu_online(ctx->cpu)) {
                rq->csd.func = __blk_mq_complete_request_remote;
                rq->csd.info = rq;
                rq->csd.flags = 0;
                smp_call_function_single_async(ctx->cpu, &rq->csd);
        } else {
                rq->q->softirq_done_fn(rq);
        }
        put_cpu();
}

void __blk_mq_complete_request(struct request *rq)
{
        struct request_queue *q = rq->q;

        if (!q->softirq_done_fn)
                blk_mq_end_io(rq, rq->errors);
        else
                blk_mq_ipi_complete_request(rq);
}

/**
 * blk_mq_complete_request - end I/O on a request
 * @rq:         the request being processed
 *
 * Description:
 *      Ends all I/O on a request. It does not handle partial completions.
 *      The actual completion happens out-of-order, through a IPI handler.
 **/
void blk_mq_complete_request(struct request *rq)
{
        struct request_queue *q = rq->q;

        if (unlikely(blk_should_fake_timeout(q)))
                return;
        if (!blk_mark_rq_complete(rq))
                __blk_mq_complete_request(rq);
}
EXPORT_SYMBOL(blk_mq_complete_request);

static void blk_mq_start_request(struct request *rq, bool last)
{
        struct request_queue *q = rq->q;

        trace_block_rq_issue(q, rq);

        rq->resid_len = blk_rq_bytes(rq);
        if (unlikely(blk_bidi_rq(rq)))
                rq->next_rq->resid_len = blk_rq_bytes(rq->next_rq);

        blk_add_timer(rq);

        /*
         * Mark us as started and clear complete. Complete might have been
         * set if requeue raced with timeout, which then marked it as
         * complete. So be sure to clear complete again when we start
         * the request, otherwise we'll ignore the completion event.
         */
        if (!test_bit(REQ_ATOM_STARTED, &rq->atomic_flags))
                set_bit(REQ_ATOM_STARTED, &rq->atomic_flags);
        if (test_bit(REQ_ATOM_COMPLETE, &rq->atomic_flags))
                clear_bit(REQ_ATOM_COMPLETE, &rq->atomic_flags);

        if (q->dma_drain_size && blk_rq_bytes(rq)) {
                /*
                 * Make sure space for the drain appears.  We know we can do
                 * this because max_hw_segments has been adjusted to be one
                 * fewer than the device can handle.
                 */
                rq->nr_phys_segments++;
        }

        /*
         * Flag the last request in the series so that drivers know when IO
         * should be kicked off, if they don't do it on a per-request basis.
         *
         * Note: the flag isn't the only condition drivers should do kick off.
         * If drive is busy, the last request might not have the bit set.
         */
        if (last)
                rq->cmd_flags |= REQ_END;
}

static void __blk_mq_requeue_request(struct request *rq)
{
        struct request_queue *q = rq->q;

        trace_block_rq_requeue(q, rq);
        clear_bit(REQ_ATOM_STARTED, &rq->atomic_flags);

        rq->cmd_flags &= ~REQ_END;

        if (q->dma_drain_size && blk_rq_bytes(rq))
                rq->nr_phys_segments--;
}

void blk_mq_requeue_request(struct request *rq)
{
        __blk_mq_requeue_request(rq);
        blk_clear_rq_complete(rq);

        BUG_ON(blk_queued_rq(rq));
        blk_mq_add_to_requeue_list(rq, true);
}
EXPORT_SYMBOL(blk_mq_requeue_request);

static void blk_mq_requeue_work(struct work_struct *work)
{
        struct request_queue *q =
                container_of(work, struct request_queue, requeue_work);
        LIST_HEAD(rq_list);
        struct request *rq, *next;
        unsigned long flags;

        spin_lock_irqsave(&q->requeue_lock, flags);
        list_splice_init(&q->requeue_list, &rq_list);
        spin_unlock_irqrestore(&q->requeue_lock, flags);

        list_for_each_entry_safe(rq, next, &rq_list, queuelist) {
                if (!(rq->cmd_flags & REQ_SOFTBARRIER))
                        continue;

                rq->cmd_flags &= ~REQ_SOFTBARRIER;
                list_del_init(&rq->queuelist);
                blk_mq_insert_request(rq, true, false, false);
        }

        while (!list_empty(&rq_list)) {
                rq = list_entry(rq_list.next, struct request, queuelist);
                list_del_init(&rq->queuelist);
                blk_mq_insert_request(rq, false, false, false);
        }

        blk_mq_run_queues(q, false);
}

void blk_mq_add_to_requeue_list(struct request *rq, bool at_head)
{
        struct request_queue *q = rq->q;
        unsigned long flags;

        /*
         * We abuse this flag that is otherwise used by the I/O scheduler to
         * request head insertation from the workqueue.
         */
        BUG_ON(rq->cmd_flags & REQ_SOFTBARRIER);

        spin_lock_irqsave(&q->requeue_lock, flags);
        if (at_head) {
                rq->cmd_flags |= REQ_SOFTBARRIER;
                list_add(&rq->queuelist, &q->requeue_list);
        } else {
                list_add_tail(&rq->queuelist, &q->requeue_list);
        }
        spin_unlock_irqrestore(&q->requeue_lock, flags);
}
EXPORT_SYMBOL(blk_mq_add_to_requeue_list);

void blk_mq_kick_requeue_list(struct request_queue *q)
{
        kblockd_schedule_work(&q->requeue_work);
}
EXPORT_SYMBOL(blk_mq_kick_requeue_list);

static inline bool is_flush_request(struct request *rq, unsigned int tag)
{
        return ((rq->cmd_flags & REQ_FLUSH_SEQ) &&
                        rq->q->flush_rq->tag == tag);
}

struct request *blk_mq_tag_to_rq(struct blk_mq_tags *tags, unsigned int tag)
{
        struct request *rq = tags->rqs[tag];

        if (!is_flush_request(rq, tag))
                return rq;

        return rq->q->flush_rq;
}
EXPORT_SYMBOL(blk_mq_tag_to_rq);

struct blk_mq_timeout_data {
        struct blk_mq_hw_ctx *hctx;
        unsigned long *next;
        unsigned int *next_set;
};

static void blk_mq_timeout_check(void *__data, unsigned long *free_tags)
{
        struct blk_mq_timeout_data *data = __data;
        struct blk_mq_hw_ctx *hctx = data->hctx;
        unsigned int tag;

         /* It may not be in flight yet (this is where
         * the REQ_ATOMIC_STARTED flag comes in). The requests are
         * statically allocated, so we know it's always safe to access the
         * memory associated with a bit offset into ->rqs[].
         */
        tag = 0;
        do {
                struct request *rq;

                tag = find_next_zero_bit(free_tags, hctx->tags->nr_tags, tag);
                if (tag >= hctx->tags->nr_tags)
                        break;

                rq = blk_mq_tag_to_rq(hctx->tags, tag++);
                if (rq->q != hctx->queue)
                        continue;
                if (!test_bit(REQ_ATOM_STARTED, &rq->atomic_flags))
                        continue;

                blk_rq_check_expired(rq, data->next, data->next_set);
        } while (1);
}

static void blk_mq_hw_ctx_check_timeout(struct blk_mq_hw_ctx *hctx,
                                        unsigned long *next,
                                        unsigned int *next_set)
{
        struct blk_mq_timeout_data data = {
                .hctx           = hctx,
                .next           = next,
                .next_set       = next_set,
        };

        /*
         * Ask the tagging code to iterate busy requests, so we can
         * check them for timeout.
         */
        blk_mq_tag_busy_iter(hctx->tags, blk_mq_timeout_check, &data);
}

static enum blk_eh_timer_return blk_mq_rq_timed_out(struct request *rq)
{
        struct request_queue *q = rq->q;

        /*
         * We know that complete is set at this point. If STARTED isn't set
         * anymore, then the request isn't active and the "timeout" should
         * just be ignored. This can happen due to the bitflag ordering.
         * Timeout first checks if STARTED is set, and if it is, assumes
         * the request is active. But if we race with completion, then
         * we both flags will get cleared. So check here again, and ignore
         * a timeout event with a request that isn't active.
         */
        if (!test_bit(REQ_ATOM_STARTED, &rq->atomic_flags))
                return BLK_EH_NOT_HANDLED;

        if (!q->mq_ops->timeout)
                return BLK_EH_RESET_TIMER;

        return q->mq_ops->timeout(rq);
}

static void blk_mq_rq_timer(unsigned long data)
{
        struct request_queue *q = (struct request_queue *) data;
        struct blk_mq_hw_ctx *hctx;
        unsigned long next = 0;
        int i, next_set = 0;

        queue_for_each_hw_ctx(q, hctx, i) {
                /*
                 * If not software queues are currently mapped to this
                 * hardware queue, there's nothing to check
                 */
                if (!hctx->nr_ctx || !hctx->tags)
                        continue;

                blk_mq_hw_ctx_check_timeout(hctx, &next, &next_set);
        }

        if (next_set) {
                next = blk_rq_timeout(round_jiffies_up(next));
                mod_timer(&q->timeout, next);
        } else {
                queue_for_each_hw_ctx(q, hctx, i)
                        blk_mq_tag_idle(hctx);
        }
}

/*
 * 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.
 */
static bool blk_mq_attempt_merge(struct request_queue *q,
                                 struct blk_mq_ctx *ctx, struct bio *bio)
{
        struct request *rq;
        int checked = 8;

        list_for_each_entry_reverse(rq, &ctx->rq_list, queuelist) {
                int el_ret;

                if (!checked--)
                        break;

                if (!blk_rq_merge_ok(rq, bio))
                        continue;

                el_ret = blk_try_merge(rq, bio);
                if (el_ret == ELEVATOR_BACK_MERGE) {
                        if (bio_attempt_back_merge(q, rq, bio)) {
                                ctx->rq_merged++;
                                return true;
                        }
                        break;
                } else if (el_ret == ELEVATOR_FRONT_MERGE) {
                        if (bio_attempt_front_merge(q, rq, bio)) {
                                ctx->rq_merged++;
                                return true;
                        }
                        break;
                }
        }

        return false;
}

/*
 * Process software queues that have been marked busy, splicing them
 * to the for-dispatch
 */
static void flush_busy_ctxs(struct blk_mq_hw_ctx *hctx, struct list_head *list)
{
        struct blk_mq_ctx *ctx;
        int i;

        for (i = 0; i < hctx->ctx_map.map_size; i++) {
                struct blk_align_bitmap *bm = &hctx->ctx_map.map[i];
                unsigned int off, bit;

                if (!bm->word)
                        continue;

                bit = 0;
                off = i * hctx->ctx_map.bits_per_word;
                do {
                        bit = find_next_bit(&bm->word, bm->depth, bit);
                        if (bit >= bm->depth)
                                break;

                        ctx = hctx->ctxs[bit + off];
                        clear_bit(bit, &bm->word);
                        spin_lock(&ctx->lock);
                        list_splice_tail_init(&ctx->rq_list, list);
                        spin_unlock(&ctx->lock);

                        bit++;
                } while (1);
        }
}

/*
 * Run this hardware queue, pulling any software queues mapped to it in.
 * Note that this function currently has various problems around ordering
 * of IO. In particular, we'd like FIFO behaviour on handling existing
 * items on the hctx->dispatch list. Ignore that for now.
 */
static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
{
        struct request_queue *q = hctx->queue;
        struct request *rq;
        LIST_HEAD(rq_list);
        int queued;

        WARN_ON(!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask));

        if (unlikely(test_bit(BLK_MQ_S_STOPPED, &hctx->state)))
                return;

        hctx->run++;

        /*
         * Touch any software queue that has pending entries.
         */
        flush_busy_ctxs(hctx, &rq_list);

        /*
         * If we have previous entries on our dispatch list, grab them
         * and stuff them at the front 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);
        }

        /*
         * Now process all the entries, sending them to the driver.
         */
        queued = 0;
        while (!list_empty(&rq_list)) {
                int ret;

                rq = list_first_entry(&rq_list, struct request, queuelist);
                list_del_init(&rq->queuelist);

                blk_mq_start_request(rq, list_empty(&rq_list));

                ret = q->mq_ops->queue_rq(hctx, rq);
                switch (ret) {
                case BLK_MQ_RQ_QUEUE_OK:
                        queued++;
                        continue;
                case BLK_MQ_RQ_QUEUE_BUSY:
                        list_add(&rq->queuelist, &rq_list);
                        __blk_mq_requeue_request(rq);
                        break;
                default:
                        pr_err("blk-mq: bad return on queue: %d\n", ret);
                case BLK_MQ_RQ_QUEUE_ERROR:
                        rq->errors = -EIO;
                        blk_mq_end_io(rq, rq->errors);
                        break;
                }

                if (ret == BLK_MQ_RQ_QUEUE_BUSY)
                        break;
        }

        if (!queued)
                hctx->dispatched[0]++;
        else if (queued < (1 << (BLK_MQ_MAX_DISPATCH_ORDER - 1)))
                hctx->dispatched[ilog2(queued) + 1]++;

        /*
         * Any items that need requeuing? Stuff them into hctx->dispatch,
         * that is where we will continue on next queue run.
         */
        if (!list_empty(&rq_list)) {
                spin_lock(&hctx->lock);
                list_splice(&rq_list, &hctx->dispatch);
                spin_unlock(&hctx->lock);
        }
}

/*
 * It'd be great if the workqueue API had a way to pass
 * in a mask and had some smarts for more clever placement.
 * For now we just round-robin here, switching for every
 * BLK_MQ_CPU_WORK_BATCH queued items.
 */
static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
{
        int cpu = hctx->next_cpu;

        if (--hctx->next_cpu_batch <= 0) {
                int next_cpu;

                next_cpu = cpumask_next(hctx->next_cpu, hctx->cpumask);
                if (next_cpu >= nr_cpu_ids)
                        next_cpu = cpumask_first(hctx->cpumask);

                hctx->next_cpu = next_cpu;
                hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;
        }

        return cpu;
}

void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async)
{
        if (unlikely(test_bit(BLK_MQ_S_STOPPED, &hctx->state)))
                return;

        if (!async && cpumask_test_cpu(smp_processor_id(), hctx->cpumask))
                __blk_mq_run_hw_queue(hctx);
        else if (hctx->queue->nr_hw_queues == 1)
                kblockd_schedule_delayed_work(&hctx->run_work, 0);
        else {
                unsigned int cpu;

                cpu = blk_mq_hctx_next_cpu(hctx);
                kblockd_schedule_delayed_work_on(cpu, &hctx->run_work, 0);
        }
}

void blk_mq_run_queues(struct request_queue *q, bool async)
{
        struct blk_mq_hw_ctx *hctx;
        int i;

        queue_for_each_hw_ctx(q, hctx, i) {
                if ((!blk_mq_hctx_has_pending(hctx) &&
                    list_empty_careful(&hctx->dispatch)) ||
                    test_bit(BLK_MQ_S_STOPPED, &hctx->state))
                        continue;

                preempt_disable();
                blk_mq_run_hw_queue(hctx, async);
                preempt_enable();
        }
}
EXPORT_SYMBOL(blk_mq_run_queues);

void blk_mq_stop_hw_queue(struct blk_mq_hw_ctx *hctx)
{
        cancel_delayed_work(&hctx->run_work);
        cancel_delayed_work(&hctx->delay_work);
        set_bit(BLK_MQ_S_STOPPED, &hctx->state);
}
EXPORT_SYMBOL(blk_mq_stop_hw_queue);

void blk_mq_stop_hw_queues(struct request_queue *q)
{
        struct blk_mq_hw_ctx *hctx;
        int i;

        queue_for_each_hw_ctx(q, hctx, i)
                blk_mq_stop_hw_queue(hctx);
}
EXPORT_SYMBOL(blk_mq_stop_hw_queues);

void blk_mq_start_hw_queue(struct blk_mq_hw_ctx *hctx)
{
        clear_bit(BLK_MQ_S_STOPPED, &hctx->state);

        preempt_disable();
        blk_mq_run_hw_queue(hctx, false);
        preempt_enable();
}
EXPORT_SYMBOL(blk_mq_start_hw_queue);

void blk_mq_start_hw_queues(struct request_queue *q)
{
        struct blk_mq_hw_ctx *hctx;
        int i;

        queue_for_each_hw_ctx(q, hctx, i)
                blk_mq_start_hw_queue(hctx);
}
EXPORT_SYMBOL(blk_mq_start_hw_queues);


void blk_mq_start_stopped_hw_queues(struct request_queue *q, bool async)
{
        struct blk_mq_hw_ctx *hctx;
        int i;

        queue_for_each_hw_ctx(q, hctx, i) {
                if (!test_bit(BLK_MQ_S_STOPPED, &hctx->state))
                        continue;

                clear_bit(BLK_MQ_S_STOPPED, &hctx->state);
                preempt_disable();
                blk_mq_run_hw_queue(hctx, async);
                preempt_enable();
        }
}
EXPORT_SYMBOL(blk_mq_start_stopped_hw_queues);

static void blk_mq_run_work_fn(struct work_struct *work)
{
        struct blk_mq_hw_ctx *hctx;

        hctx = container_of(work, struct blk_mq_hw_ctx, run_work.work);

        __blk_mq_run_hw_queue(hctx);
}

static void blk_mq_delay_work_fn(struct work_struct *work)
{
        struct blk_mq_hw_ctx *hctx;

        hctx = container_of(work, struct blk_mq_hw_ctx, delay_work.work);

        if (test_and_clear_bit(BLK_MQ_S_STOPPED, &hctx->state))
                __blk_mq_run_hw_queue(hctx);
}

void blk_mq_delay_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs)
{
        unsigned long tmo = msecs_to_jiffies(msecs);

        if (hctx->queue->nr_hw_queues == 1)
                kblockd_schedule_delayed_work(&hctx->delay_work, tmo);
        else {
                unsigned int cpu;

                cpu = blk_mq_hctx_next_cpu(hctx);
                kblockd_schedule_delayed_work_on(cpu, &hctx->delay_work, tmo);
        }
}
EXPORT_SYMBOL(blk_mq_delay_queue);

static void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx,
                                    struct request *rq, bool at_head)
{
        struct blk_mq_ctx *ctx = rq->mq_ctx;

        trace_block_rq_insert(hctx->queue, rq);

        if (at_head)
                list_add(&rq->queuelist, &ctx->rq_list);
        else
                list_add_tail(&rq->queuelist, &ctx->rq_list);

        blk_mq_hctx_mark_pending(hctx, ctx);
}

void blk_mq_insert_request(struct request *rq, bool at_head, bool run_queue,
                bool async)
{
        struct request_queue *q = rq->q;
        struct blk_mq_hw_ctx *hctx;
        struct blk_mq_ctx *ctx = rq->mq_ctx, *current_ctx;

        current_ctx = blk_mq_get_ctx(q);
        if (!cpu_online(ctx->cpu))
                rq->mq_ctx = ctx = current_ctx;

        hctx = q->mq_ops->map_queue(q, ctx->cpu);

        if (rq->cmd_flags & (REQ_FLUSH | REQ_FUA) &&
            !(rq->cmd_flags & (REQ_FLUSH_SEQ))) {
                blk_insert_flush(rq);
        } else {
                spin_lock(&ctx->lock);
                __blk_mq_insert_request(hctx, rq, at_head);
                spin_unlock(&ctx->lock);
        }

        if (run_queue)
                blk_mq_run_hw_queue(hctx, async);

        blk_mq_put_ctx(current_ctx);
}

static void blk_mq_insert_requests(struct request_queue *q,
                                     struct blk_mq_ctx *ctx,
                                     struct list_head *list,
                                     int depth,
                                     bool from_schedule)

{
        struct blk_mq_hw_ctx *hctx;
        struct blk_mq_ctx *current_ctx;

        trace_block_unplug(q, depth, !from_schedule);

        current_ctx = blk_mq_get_ctx(q);

        if (!cpu_online(ctx->cpu))
                ctx = current_ctx;
        hctx = q->mq_ops->map_queue(q, ctx->cpu);

        /*
         * preemption doesn't flush plug list, so it's possible ctx->cpu is
         * offline now
         */
        spin_lock(&ctx->lock);
        while (!list_empty(list)) {
                struct request *rq;

                rq = list_first_entry(list, struct request, queuelist);
                list_del_init(&rq->queuelist);
                rq->mq_ctx = ctx;
                __blk_mq_insert_request(hctx, rq, false);
        }
        spin_unlock(&ctx->lock);

        blk_mq_run_hw_queue(hctx, from_schedule);
        blk_mq_put_ctx(current_ctx);
}

static int plug_ctx_cmp(void *priv, struct list_head *a, 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_ctx < rqb->mq_ctx ||
                 (rqa->mq_ctx == rqb->mq_ctx &&
                  blk_rq_pos(rqa) < blk_rq_pos(rqb)));
}

void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
{
        struct blk_mq_ctx *this_ctx;
        struct request_queue *this_q;
        struct request *rq;
        LIST_HEAD(list);
        LIST_HEAD(ctx_list);
        unsigned int depth;

        list_splice_init(&plug->mq_list, &list);

        list_sort(NULL, &list, plug_ctx_cmp);

        this_q = NULL;
        this_ctx = NULL;
        depth = 0;

        while (!list_empty(&list)) {
                rq = list_entry_rq(list.next);
                list_del_init(&rq->queuelist);
                BUG_ON(!rq->q);
                if (rq->mq_ctx != this_ctx) {
                        if (this_ctx) {
                                blk_mq_insert_requests(this_q, this_ctx,
                                                        &ctx_list, depth,
                                                        from_schedule);
                        }

                        this_ctx = rq->mq_ctx;
                        this_q = rq->q;
                        depth = 0;
                }

                depth++;
                list_add_tail(&rq->queuelist, &ctx_list);
        }

        /*
         * If 'this_ctx' is set, we know we have entries to complete
         * on 'ctx_list'. Do those.
         */
        if (this_ctx) {
                blk_mq_insert_requests(this_q, this_ctx, &ctx_list, depth,
                                       from_schedule);
        }
}

static void blk_mq_bio_to_request(struct request *rq, struct bio *bio)
{
        init_request_from_bio(rq, bio);

        if (blk_do_io_stat(rq))
                blk_account_io_start(rq, 1);
}

static inline bool hctx_allow_merges(struct blk_mq_hw_ctx *hctx)
{
        return (hctx->flags & BLK_MQ_F_SHOULD_MERGE) &&
                !blk_queue_nomerges(hctx->queue);
}

static inline bool blk_mq_merge_queue_io(struct blk_mq_hw_ctx *hctx,
                                         struct blk_mq_ctx *ctx,
                                         struct request *rq, struct bio *bio)
{
        if (!hctx_allow_merges(hctx)) {
                blk_mq_bio_to_request(rq, bio);
                spin_lock(&ctx->lock);
insert_rq:
                __blk_mq_insert_request(hctx, rq, false);
                spin_unlock(&ctx->lock);
                return false;
        } else {
                struct request_queue *q = hctx->queue;

                spin_lock(&ctx->lock);
                if (!blk_mq_attempt_merge(q, ctx, bio)) {
                        blk_mq_bio_to_request(rq, bio);
                        goto insert_rq;
                }

                spin_unlock(&ctx->lock);
                __blk_mq_free_request(hctx, ctx, rq);
                return true;
        }
}

struct blk_map_ctx {
        struct blk_mq_hw_ctx *hctx;
        struct blk_mq_ctx *ctx;
};

static struct request *blk_mq_map_request(struct request_queue *q,
                                          struct bio *bio,
                                          struct blk_map_ctx *data)
{
        struct blk_mq_hw_ctx *hctx;
        struct blk_mq_ctx *ctx;
        struct request *rq;
        int rw = bio_data_dir(bio);
        struct blk_mq_alloc_data alloc_data;

        if (unlikely(blk_mq_queue_enter(q))) {
                bio_endio(bio, -EIO);
                return NULL;
        }

        ctx = blk_mq_get_ctx(q);
        hctx = q->mq_ops->map_queue(q, ctx->cpu);

        if (rw_is_sync(bio->bi_rw))
                rw |= REQ_SYNC;

        trace_block_getrq(q, bio, rw);
        blk_mq_set_alloc_data(&alloc_data, q, GFP_ATOMIC, false, ctx,
                        hctx);
        rq = __blk_mq_alloc_request(&alloc_data, rw);
        if (unlikely(!rq)) {
                __blk_mq_run_hw_queue(hctx);
                blk_mq_put_ctx(ctx);
                trace_block_sleeprq(q, bio, rw);

                ctx = blk_mq_get_ctx(q);
                hctx = q->mq_ops->map_queue(q, ctx->cpu);
                blk_mq_set_alloc_data(&alloc_data, q,
                                __GFP_WAIT|GFP_ATOMIC, false, ctx, hctx);
                rq = __blk_mq_alloc_request(&alloc_data, rw);
                ctx = alloc_data.ctx;
                hctx = alloc_data.hctx;
        }

        hctx->queued++;
        data->hctx = hctx;
        data->ctx = ctx;
        return rq;
}

/*
 * Multiple hardware queue variant. This will not use per-process plugs,
 * but will attempt to bypass the hctx queueing if we can go straight to
 * hardware for SYNC IO.
 */
static void blk_mq_make_request(struct request_queue *q, struct bio *bio)
{
        const int is_sync = rw_is_sync(bio->bi_rw);
        const int is_flush_fua = bio->bi_rw & (REQ_FLUSH | REQ_FUA);
        struct blk_map_ctx data;
        struct request *rq;

        blk_queue_bounce(q, &bio);

        if (bio_integrity_enabled(bio) && bio_integrity_prep(bio)) {
                bio_endio(bio, -EIO);
                return;
        }

        rq = blk_mq_map_request(q, bio, &data);
        if (unlikely(!rq))
                return;

        if (unlikely(is_flush_fua)) {
                blk_mq_bio_to_request(rq, bio);
                blk_insert_flush(rq);
                goto run_queue;
        }

        if (is_sync) {
                int ret;

                blk_mq_bio_to_request(rq, bio);
                blk_mq_start_request(rq, true);

                /*
                 * For OK queue, we are done. For error, kill it. Any other
                 * error (busy), just add it to our list as we previously
                 * would have done
                 */
                ret = q->mq_ops->queue_rq(data.hctx, rq);
                if (ret == BLK_MQ_RQ_QUEUE_OK)
                        goto done;
                else {
                        __blk_mq_requeue_request(rq);

                        if (ret == BLK_MQ_RQ_QUEUE_ERROR) {
                                rq->errors = -EIO;
                                blk_mq_end_io(rq, rq->errors);
                                goto done;
                        }
                }
        }

        if (!blk_mq_merge_queue_io(data.hctx, data.ctx, rq, bio)) {
                /*
                 * For a SYNC request, send it to the hardware immediately. For
                 * an ASYNC request, just ensure that we run it later on. The
                 * latter allows for merging opportunities and more efficient
                 * dispatching.
                 */
run_queue:
                blk_mq_run_hw_queue(data.hctx, !is_sync || is_flush_fua);
        }
done:
        blk_mq_put_ctx(data.ctx);
}

/*
 * Single hardware queue variant. This will attempt to use any per-process
 * plug for merging and IO deferral.
 */
static void blk_sq_make_request(struct request_queue *q, struct bio *bio)
{
        const int is_sync = rw_is_sync(bio->bi_rw);
        const int is_flush_fua = bio->bi_rw & (REQ_FLUSH | REQ_FUA);
        unsigned int use_plug, request_count = 0;
        struct blk_map_ctx data;
        struct request *rq;

        /*
         * If we have multiple hardware queues, just go directly to
         * one of those for sync IO.
         */
        use_plug = !is_flush_fua && !is_sync;

        blk_queue_bounce(q, &bio);

        if (bio_integrity_enabled(bio) && bio_integrity_prep(bio)) {
                bio_endio(bio, -EIO);
                return;
        }

        if (use_plug && !blk_queue_nomerges(q) &&
            blk_attempt_plug_merge(q, bio, &request_count))
                return;

        rq = blk_mq_map_request(q, bio, &data);
        if (unlikely(!rq))
                return;

        if (unlikely(is_flush_fua)) {
                blk_mq_bio_to_request(rq, bio);
                blk_insert_flush(rq);
                goto run_queue;
        }

        /*
         * A task plug currently exists. Since this is completely lockless,
         * utilize that to temporarily store requests until the task is
         * either done or scheduled away.
         */
        if (use_plug) {
                struct blk_plug *plug = current->plug;

                if (plug) {
                        blk_mq_bio_to_request(rq, bio);
                        if (list_empty(&plug->mq_list))
                                trace_block_plug(q);
                        else if (request_count >= BLK_MAX_REQUEST_COUNT) {
                                blk_flush_plug_list(plug, false);
                                trace_block_plug(q);
                        }
                        list_add_tail(&rq->queuelist, &plug->mq_list);
                        blk_mq_put_ctx(data.ctx);
                        return;
                }
        }

        if (!blk_mq_merge_queue_io(data.hctx, data.ctx, rq, bio)) {
                /*
                 * For a SYNC request, send it to the hardware immediately. For
                 * an ASYNC request, just ensure that we run it later on. The
                 * latter allows for merging opportunities and more efficient
                 * dispatching.
                 */
run_queue:
                blk_mq_run_hw_queue(data.hctx, !is_sync || is_flush_fua);
        }

        blk_mq_put_ctx(data.ctx);
}

/*
 * Default mapping to a software queue, since we use one per CPU.
 */
struct blk_mq_hw_ctx *blk_mq_map_queue(struct request_queue *q, const int cpu)
{
        return q->queue_hw_ctx[q->mq_map[cpu]];
}
EXPORT_SYMBOL(blk_mq_map_queue);

static void blk_mq_free_rq_map(struct blk_mq_tag_set *set,
                struct blk_mq_tags *tags, unsigned int hctx_idx)
{
        struct page *page;

        if (tags->rqs && set->ops->exit_request) {
                int i;

                for (i = 0; i < tags->nr_tags; i++) {
                        if (!tags->rqs[i])
                                continue;
                        set->ops->exit_request(set->driver_data, tags->rqs[i],
                                                hctx_idx, i);
                        tags->rqs[i] = NULL;
                }
        }

        while (!list_empty(&tags->page_list)) {
                page = list_first_entry(&tags->page_list, struct page, lru);
                list_del_init(&page->lru);
                __free_pages(page, page->private);
        }

        kfree(tags->rqs);

        blk_mq_free_tags(tags);
}

static size_t order_to_size(unsigned int order)
{
        return (size_t)PAGE_SIZE << order;
}

static struct blk_mq_tags *blk_mq_init_rq_map(struct blk_mq_tag_set *set,
                unsigned int hctx_idx)
{
        struct blk_mq_tags *tags;
        unsigned int i, j, entries_per_page, max_order = 4;
        size_t rq_size, left;

        tags = blk_mq_init_tags(set->queue_depth, set->reserved_tags,
                                set->numa_node);
        if (!tags)
                return NULL;

        INIT_LIST_HEAD(&tags->page_list);

        tags->rqs = kzalloc_node(set->queue_depth * sizeof(struct request *),
                                 GFP_KERNEL | __GFP_NOWARN | __GFP_NORETRY,
                                 set->numa_node);
        if (!tags->rqs) {
                blk_mq_free_tags(tags);
                return NULL;
        }

        /*
         * rq_size is the size of the request plus driver payload, rounded
         * to the cacheline size
         */
        rq_size = round_up(sizeof(struct request) + set->cmd_size,
                                cache_line_size());
        left = rq_size * set->queue_depth;

        for (i = 0; i < set->queue_depth; ) {
                int this_order = max_order;
                struct page *page;
                int to_do;
                void *p;

                while (left < order_to_size(this_order - 1) && this_order)
                        this_order--;

                do {
                        page = alloc_pages_node(set->numa_node,
                                GFP_KERNEL | __GFP_NOWARN | __GFP_NORETRY,
                                this_order);
                        if (page)
                                break;
                        if (!this_order--)
                                break;
                        if (order_to_size(this_order) < rq_size)
                                break;
                } while (1);

                if (!page)
                        goto fail;

                page->private = this_order;
                list_add_tail(&page->lru, &tags->page_list);

                p = page_address(page);
                entries_per_page = order_to_size(this_order) / rq_size;
                to_do = min(entries_per_page, set->queue_depth - i);
                left -= to_do * rq_size;
                for (j = 0; j < to_do; j++) {
                        tags->rqs[i] = p;
                        if (set->ops->init_request) {
                                if (set->ops->init_request(set->driver_data,
                                                tags->rqs[i], hctx_idx, i,
                                                set->numa_node)) {
                                        tags->rqs[i] = NULL;
                                        goto fail;
                                }
                        }

                        p += rq_size;
                        i++;
                }
        }

        return tags;

fail:
        blk_mq_free_rq_map(set, tags, hctx_idx);
        return NULL;
}

static void blk_mq_free_bitmap(struct blk_mq_ctxmap *bitmap)
{
        kfree(bitmap->map);
}

static int blk_mq_alloc_bitmap(struct blk_mq_ctxmap *bitmap, int node)
{
        unsigned int bpw = 8, total, num_maps, i;

        bitmap->bits_per_word = bpw;

        num_maps = ALIGN(nr_cpu_ids, bpw) / bpw;
        bitmap->map = kzalloc_node(num_maps * sizeof(struct blk_align_bitmap),
                                        GFP_KERNEL, node);
        if (!bitmap->map)
                return -ENOMEM;

        bitmap->map_size = num_maps;

        total = nr_cpu_ids;
        for (i = 0; i < num_maps; i++) {
                bitmap->map[i].depth = min(total, bitmap->bits_per_word);
                total -= bitmap->map[i].depth;
        }

        return 0;
}

static int blk_mq_hctx_cpu_offline(struct blk_mq_hw_ctx *hctx, int cpu)
{
        struct request_queue *q = hctx->queue;
        struct blk_mq_ctx *ctx;
        LIST_HEAD(tmp);

        /*
         * Move ctx entries to new CPU, if this one is going away.
         */
        ctx = __blk_mq_get_ctx(q, cpu);

        spin_lock(&ctx->lock);
        if (!list_empty(&ctx->rq_list)) {
                list_splice_init(&ctx->rq_list, &tmp);
                blk_mq_hctx_clear_pending(hctx, ctx);
        }
        spin_unlock(&ctx->lock);

        if (list_empty(&tmp))
                return NOTIFY_OK;

        ctx = blk_mq_get_ctx(q);
        spin_lock(&ctx->lock);

        while (!list_empty(&tmp)) {
                struct request *rq;

                rq = list_first_entry(&tmp, struct request, queuelist);
                rq->mq_ctx = ctx;
                list_move_tail(&rq->queuelist, &ctx->rq_list);
        }

        hctx = q->mq_ops->map_queue(q, ctx->cpu);
        blk_mq_hctx_mark_pending(hctx, ctx);

        spin_unlock(&ctx->lock);

        blk_mq_run_hw_queue(hctx, true);
        blk_mq_put_ctx(ctx);
        return NOTIFY_OK;
}

static int blk_mq_hctx_cpu_online(struct blk_mq_hw_ctx *hctx, int cpu)
{
        struct request_queue *q = hctx->queue;
        struct blk_mq_tag_set *set = q->tag_set;

        if (set->tags[hctx->queue_num])
                return NOTIFY_OK;

        set->tags[hctx->queue_num] = blk_mq_init_rq_map(set, hctx->queue_num);
        if (!set->tags[hctx->queue_num])
                return NOTIFY_STOP;

        hctx->tags = set->tags[hctx->queue_num];
        return NOTIFY_OK;
}

static int blk_mq_hctx_notify(void *data, unsigned long action,
                              unsigned int cpu)
{
        struct blk_mq_hw_ctx *hctx = data;

        if (action == CPU_DEAD || action == CPU_DEAD_FROZEN)
                return blk_mq_hctx_cpu_offline(hctx, cpu);
        else if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN)
                return blk_mq_hctx_cpu_online(hctx, cpu);

        return NOTIFY_OK;
}

static void blk_mq_exit_hw_queues(struct request_queue *q,
                struct blk_mq_tag_set *set, int nr_queue)
{
        struct blk_mq_hw_ctx *hctx;
        unsigned int i;

        queue_for_each_hw_ctx(q, hctx, i) {
                if (i == nr_queue)
                        break;

                blk_mq_tag_idle(hctx);

                if (set->ops->exit_hctx)
                        set->ops->exit_hctx(hctx, i);

                blk_mq_unregister_cpu_notifier(&hctx->cpu_notifier);
                kfree(hctx->ctxs);
                blk_mq_free_bitmap(&hctx->ctx_map);
        }

}

static void blk_mq_free_hw_queues(struct request_queue *q,
                struct blk_mq_tag_set *set)
{
        struct blk_mq_hw_ctx *hctx;
        unsigned int i;

        queue_for_each_hw_ctx(q, hctx, i) {
                free_cpumask_var(hctx->cpumask);
                kfree(hctx);
        }
}

static int blk_mq_init_hw_queues(struct request_queue *q,
                struct blk_mq_tag_set *set)
{
        struct blk_mq_hw_ctx *hctx;
        unsigned int i;

        /*
         * Initialize hardware queues
         */
        queue_for_each_hw_ctx(q, hctx, i) {
                int node;

                node = hctx->numa_node;
                if (node == NUMA_NO_NODE)
                        node = hctx->numa_node = set->numa_node;

                INIT_DELAYED_WORK(&hctx->run_work, blk_mq_run_work_fn);
                INIT_DELAYED_WORK(&hctx->delay_work, blk_mq_delay_work_fn);
                spin_lock_init(&hctx->lock);
                INIT_LIST_HEAD(&hctx->dispatch);
                hctx->queue = q;
                hctx->queue_num = i;
                hctx->flags = set->flags;
                hctx->cmd_size = set->cmd_size;

                blk_mq_init_cpu_notifier(&hctx->cpu_notifier,
                                                blk_mq_hctx_notify, hctx);
                blk_mq_register_cpu_notifier(&hctx->cpu_notifier);

                hctx->tags = set->tags[i];

                /*
                 * Allocate space for all possible cpus to avoid allocation at
                 * runtime
                 */
                hctx->ctxs = kmalloc_node(nr_cpu_ids * sizeof(void *),
                                                GFP_KERNEL, node);
                if (!hctx->ctxs)
                        break;

                if (blk_mq_alloc_bitmap(&hctx->ctx_map, node))
                        break;

                hctx->nr_ctx = 0;

                if (set->ops->init_hctx &&
                    set->ops->init_hctx(hctx, set->driver_data, i))
                        break;
        }

        if (i == q->nr_hw_queues)
                return 0;

        /*
         * Init failed
         */
        blk_mq_exit_hw_queues(q, set, i);

        return 1;
}

static void blk_mq_init_cpu_queues(struct request_queue *q,
                                   unsigned int nr_hw_queues)
{
        unsigned int i;

        for_each_possible_cpu(i) {
                struct blk_mq_ctx *__ctx = per_cpu_ptr(q->queue_ctx, i);
                struct blk_mq_hw_ctx *hctx;

                memset(__ctx, 0, sizeof(*__ctx));
                __ctx->cpu = i;
                spin_lock_init(&__ctx->lock);
                INIT_LIST_HEAD(&__ctx->rq_list);
                __ctx->queue = q;

                /* If the cpu isn't online, the cpu is mapped to first hctx */
                if (!cpu_online(i))
                        continue;

                hctx = q->mq_ops->map_queue(q, i);
                cpumask_set_cpu(i, hctx->cpumask);
                hctx->nr_ctx++;

                /*
                 * Set local node, IFF we have more than one hw queue. If
                 * not, we remain on the home node of the device
                 */
                if (nr_hw_queues > 1 && hctx->numa_node == NUMA_NO_NODE)
                        hctx->numa_node = cpu_to_node(i);
        }
}

static void blk_mq_map_swqueue(struct request_queue *q)
{
        unsigned int i;
        struct blk_mq_hw_ctx *hctx;
        struct blk_mq_ctx *ctx;

        queue_for_each_hw_ctx(q, hctx, i) {
                cpumask_clear(hctx->cpumask);
                hctx->nr_ctx = 0;
        }

        /*
         * Map software to hardware queues
         */
        queue_for_each_ctx(q, ctx, i) {
                /* If the cpu isn't online, the cpu is mapped to first hctx */
                if (!cpu_online(i))
                        continue;

                hctx = q->mq_ops->map_queue(q, i);
                cpumask_set_cpu(i, hctx->cpumask);
                ctx->index_hw = hctx->nr_ctx;
                hctx->ctxs[hctx->nr_ctx++] = ctx;
        }

        queue_for_each_hw_ctx(q, hctx, i) {
                /*
                 * If no software queues are mapped to this hardware queue,
                 * disable it and free the request entries.
                 */
                if (!hctx->nr_ctx) {
                        struct blk_mq_tag_set *set = q->tag_set;

                        if (set->tags[i]) {
                                blk_mq_free_rq_map(set, set->tags[i], i);
                                set->tags[i] = NULL;
                                hctx->tags = NULL;
                        }
                        continue;
                }

                /*
                 * Initialize batch roundrobin counts
                 */
                hctx->next_cpu = cpumask_first(hctx->cpumask);
                hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;
        }
}

static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set)
{
        struct blk_mq_hw_ctx *hctx;
        struct request_queue *q;
        bool shared;
        int i;

        if (set->tag_list.next == set->tag_list.prev)
                shared = false;
        else
                shared = true;

        list_for_each_entry(q, &set->tag_list, tag_set_list) {
                blk_mq_freeze_queue(q);

                queue_for_each_hw_ctx(q, hctx, i) {
                        if (shared)
                                hctx->flags |= BLK_MQ_F_TAG_SHARED;
                        else
                                hctx->flags &= ~BLK_MQ_F_TAG_SHARED;
                }
                blk_mq_unfreeze_queue(q);
        }
}

static void blk_mq_del_queue_tag_set(struct request_queue *q)
{
        struct blk_mq_tag_set *set = q->tag_set;

        mutex_lock(&set->tag_list_lock);
        list_del_init(&q->tag_set_list);
        blk_mq_update_tag_set_depth(set);
        mutex_unlock(&set->tag_list_lock);
}

static void blk_mq_add_queue_tag_set(struct blk_mq_tag_set *set,
                                     struct request_queue *q)
{
        q->tag_set = set;

        mutex_lock(&set->tag_list_lock);
        list_add_tail(&q->tag_set_list, &set->tag_list);
        blk_mq_update_tag_set_depth(set);
        mutex_unlock(&set->tag_list_lock);
}

struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *set)
{
        struct blk_mq_hw_ctx **hctxs;
        struct blk_mq_ctx __percpu *ctx;
        struct request_queue *q;
        unsigned int *map;
        int i;

        ctx = alloc_percpu(struct blk_mq_ctx);
        if (!ctx)
                return ERR_PTR(-ENOMEM);

        hctxs = kmalloc_node(set->nr_hw_queues * sizeof(*hctxs), GFP_KERNEL,
                        set->numa_node);

        if (!hctxs)
                goto err_percpu;

        map = blk_mq_make_queue_map(set);
        if (!map)
                goto err_map;

        for (i = 0; i < set->nr_hw_queues; i++) {
                int node = blk_mq_hw_queue_to_node(map, i);

                hctxs[i] = kzalloc_node(sizeof(struct blk_mq_hw_ctx),
                                        GFP_KERNEL, node);
                if (!hctxs[i])
                        goto err_hctxs;

                if (!zalloc_cpumask_var(&hctxs[i]->cpumask, GFP_KERNEL))
                        goto err_hctxs;

                atomic_set(&hctxs[i]->nr_active, 0);
                hctxs[i]->numa_node = node;
                hctxs[i]->queue_num = i;
        }

        q = blk_alloc_queue_node(GFP_KERNEL, set->numa_node);
        if (!q)
                goto err_hctxs;

        if (percpu_ref_init(&q->mq_usage_counter, blk_mq_usage_counter_release))
                goto err_map;

        setup_timer(&q->timeout, blk_mq_rq_timer, (unsigned long) q);
        blk_queue_rq_timeout(q, 30000);

        q->nr_queues = nr_cpu_ids;
        q->nr_hw_queues = set->nr_hw_queues;
        q->mq_map = map;

        q->queue_ctx = ctx;
        q->queue_hw_ctx = hctxs;

        q->mq_ops = set->ops;
        q->queue_flags |= QUEUE_FLAG_MQ_DEFAULT;

        if (!(set->flags & BLK_MQ_F_SG_MERGE))
                q->queue_flags |= 1 << QUEUE_FLAG_NO_SG_MERGE;

        q->sg_reserved_size = INT_MAX;

        INIT_WORK(&q->requeue_work, blk_mq_requeue_work);
        INIT_LIST_HEAD(&q->requeue_list);
        spin_lock_init(&q->requeue_lock);

        if (q->nr_hw_queues > 1)
                blk_queue_make_request(q, blk_mq_make_request);
        else
                blk_queue_make_request(q, blk_sq_make_request);

        blk_queue_rq_timed_out(q, blk_mq_rq_timed_out);
        if (set->timeout)
                blk_queue_rq_timeout(q, set->timeout);

        /*
         * Do this after blk_queue_make_request() overrides it...
         */
        q->nr_requests = set->queue_depth;

        if (set->ops->complete)
                blk_queue_softirq_done(q, set->ops->complete);

        blk_mq_init_flush(q);
        blk_mq_init_cpu_queues(q, set->nr_hw_queues);

        q->flush_rq = kzalloc(round_up(sizeof(struct request) +
                                set->cmd_size, cache_line_size()),
                                GFP_KERNEL);
        if (!q->flush_rq)
                goto err_hw;

        if (blk_mq_init_hw_queues(q, set))
                goto err_flush_rq;

        mutex_lock(&all_q_mutex);
        list_add_tail(&q->all_q_node, &all_q_list);
        mutex_unlock(&all_q_mutex);

        blk_mq_add_queue_tag_set(set, q);

        blk_mq_map_swqueue(q);

        return q;

err_flush_rq:
        kfree(q->flush_rq);
err_hw:
        blk_cleanup_queue(q);
err_hctxs:
        kfree(map);
        for (i = 0; i < set->nr_hw_queues; i++) {
                if (!hctxs[i])
                        break;
                free_cpumask_var(hctxs[i]->cpumask);
                kfree(hctxs[i]);
        }
err_map:
        kfree(hctxs);
err_percpu:
        free_percpu(ctx);
        return ERR_PTR(-ENOMEM);
}
EXPORT_SYMBOL(blk_mq_init_queue);

void blk_mq_free_queue(struct request_queue *q)
{
        struct blk_mq_tag_set   *set = q->tag_set;

        blk_mq_del_queue_tag_set(q);

        blk_mq_exit_hw_queues(q, set, set->nr_hw_queues);
        blk_mq_free_hw_queues(q, set);

        percpu_ref_exit(&q->mq_usage_counter);

        free_percpu(q->queue_ctx);
        kfree(q->queue_hw_ctx);
        kfree(q->mq_map);

        q->queue_ctx = NULL;
        q->queue_hw_ctx = NULL;
        q->mq_map = NULL;

        mutex_lock(&all_q_mutex);
        list_del_init(&q->all_q_node);
        mutex_unlock(&all_q_mutex);
}

/* Basically redo blk_mq_init_queue with queue frozen */
static void blk_mq_queue_reinit(struct request_queue *q)
{
        blk_mq_freeze_queue(q);

        blk_mq_sysfs_unregister(q);

        blk_mq_update_queue_map(q->mq_map, q->nr_hw_queues);

        /*
         * redo blk_mq_init_cpu_queues and blk_mq_init_hw_queues. FIXME: maybe
         * we should change hctx numa_node according to new topology (this
         * involves free and re-allocate memory, worthy doing?)
         */

        blk_mq_map_swqueue(q);

        blk_mq_sysfs_register(q);

        blk_mq_unfreeze_queue(q);
}

static int blk_mq_queue_reinit_notify(struct notifier_block *nb,
                                      unsigned long action, void *hcpu)
{
        struct request_queue *q;

        /*
         * Before new mappings are established, hotadded cpu might already
         * start handling requests. This doesn't break anything as we map
         * offline CPUs to first hardware queue. We will re-init the queue
         * below to get optimal settings.
         */
        if (action != CPU_DEAD && action != CPU_DEAD_FROZEN &&
            action != CPU_ONLINE && action != CPU_ONLINE_FROZEN)
                return NOTIFY_OK;

        mutex_lock(&all_q_mutex);
        list_for_each_entry(q, &all_q_list, all_q_node)
                blk_mq_queue_reinit(q);
        mutex_unlock(&all_q_mutex);
        return NOTIFY_OK;
}

static int __blk_mq_alloc_rq_maps(struct blk_mq_tag_set *set)
{
        int i;

        for (i = 0; i < set->nr_hw_queues; i++) {
                set->tags[i] = blk_mq_init_rq_map(set, i);
                if (!set->tags[i])
                        goto out_unwind;
        }

        return 0;

out_unwind:
        while (--i >= 0)
                blk_mq_free_rq_map(set, set->tags[i], i);

        set->tags = NULL;
        return -ENOMEM;
}

/*
 * Allocate the request maps associated with this tag_set. Note that this
 * may reduce the depth asked for, if memory is tight. set->queue_depth
 * will be updated to reflect the allocated depth.
 */
static int blk_mq_alloc_rq_maps(struct blk_mq_tag_set *set)
{
        unsigned int depth;
        int err;

        depth = set->queue_depth;
        do {
                err = __blk_mq_alloc_rq_maps(set);
                if (!err)
                        break;

                set->queue_depth >>= 1;
                if (set->queue_depth < set->reserved_tags + BLK_MQ_TAG_MIN) {
                        err = -ENOMEM;
                        break;
                }
        } while (set->queue_depth);

        if (!set->queue_depth || err) {
                pr_err("blk-mq: failed to allocate request map\n");
                return -ENOMEM;
        }

        if (depth != set->queue_depth)
                pr_info("blk-mq: reduced tag depth (%u -> %u)\n",
                                                depth, set->queue_depth);

        return 0;
}

/*
 * Alloc a tag set to be associated with one or more request queues.
 * May fail with EINVAL for various error conditions. May adjust the
 * requested depth down, if if it too large. In that case, the set
 * value will be stored in set->queue_depth.
 */
int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set)
{
        if (!set->nr_hw_queues)
                return -EINVAL;
        if (!set->queue_depth)
                return -EINVAL;
        if (set->queue_depth < set->reserved_tags + BLK_MQ_TAG_MIN)
                return -EINVAL;

        if (!set->nr_hw_queues || !set->ops->queue_rq || !set->ops->map_queue)
                return -EINVAL;

        if (set->queue_depth > BLK_MQ_MAX_DEPTH) {
                pr_info("blk-mq: reduced tag depth to %u\n",
                        BLK_MQ_MAX_DEPTH);
                set->queue_depth = BLK_MQ_MAX_DEPTH;
        }

        set->tags = kmalloc_node(set->nr_hw_queues *
                                 sizeof(struct blk_mq_tags *),
                                 GFP_KERNEL, set->numa_node);
        if (!set->tags)
                return -ENOMEM;

        if (blk_mq_alloc_rq_maps(set))
                goto enomem;

        mutex_init(&set->tag_list_lock);
        INIT_LIST_HEAD(&set->tag_list);

        return 0;
enomem:
        kfree(set->tags);
        set->tags = NULL;
        return -ENOMEM;
}
EXPORT_SYMBOL(blk_mq_alloc_tag_set);

void blk_mq_free_tag_set(struct blk_mq_tag_set *set)
{
        int i;

        for (i = 0; i < set->nr_hw_queues; i++) {
                if (set->tags[i])
                        blk_mq_free_rq_map(set, set->tags[i], i);
        }

        kfree(set->tags);
        set->tags = NULL;
}
EXPORT_SYMBOL(blk_mq_free_tag_set);

int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
{
        struct blk_mq_tag_set *set = q->tag_set;
        struct blk_mq_hw_ctx *hctx;
        int i, ret;

        if (!set || nr > set->queue_depth)
                return -EINVAL;

        ret = 0;
        queue_for_each_hw_ctx(q, hctx, i) {
                ret = blk_mq_tag_update_depth(hctx->tags, nr);
                if (ret)
                        break;
        }

        if (!ret)
                q->nr_requests = nr;

        return ret;
}

void blk_mq_disable_hotplug(void)
{
        mutex_lock(&all_q_mutex);
}

void blk_mq_enable_hotplug(void)
{
        mutex_unlock(&all_q_mutex);
}

static int __init blk_mq_init(void)
{
        blk_mq_cpu_init();

        hotcpu_notifier(blk_mq_queue_reinit_notify, 0);

        return 0;
}
subsys_initcall(blk_mq_init);