Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

[linux/fpc-iii.git] / block / blk-mq.c

#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);

static struct blk_mq_ctx *__blk_mq_get_ctx(struct request_queue *q,
                                           unsigned int cpu)
{
        return per_cpu_ptr(q->queue_ctx, cpu);
}

/*
 * This assumes per-cpu software queueing queues. They could be per-node
 * as well, for instance. For now this is hardcoded as-is. Note that we don't
 * care about preemption, since we know the ctx's are persistent. This does
 * mean that we can't rely on ctx always matching the currently running CPU.
 */
static struct blk_mq_ctx *blk_mq_get_ctx(struct request_queue *q)
{
        return __blk_mq_get_ctx(q, get_cpu());
}

static void blk_mq_put_ctx(struct blk_mq_ctx *ctx)
{
        put_cpu();
}

/*
 * 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->nr_ctx_map; i++)
                if (hctx->ctx_map[i])
                        return true;

        return false;
}

/*
 * 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)
{
        if (!test_bit(ctx->index_hw, hctx->ctx_map))
                set_bit(ctx->index_hw, hctx->ctx_map);
}

static struct request *blk_mq_alloc_rq(struct blk_mq_hw_ctx *hctx, gfp_t gfp,
                                       bool reserved)
{
        struct request *rq;
        unsigned int tag;

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

                return rq;
        }

        return NULL;
}

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

        __percpu_counter_add(&q->mq_usage_counter, 1, 1000000);
        smp_wmb();
        /* we have problems to freeze the queue if it's initializing */
        if (!blk_queue_bypass(q) || !blk_queue_init_done(q))
                return 0;

        __percpu_counter_add(&q->mq_usage_counter, -1, 1000000);

        spin_lock_irq(q->queue_lock);
        ret = wait_event_interruptible_lock_irq(q->mq_freeze_wq,
                !blk_queue_bypass(q) || blk_queue_dying(q),
                *q->queue_lock);
        /* inc usage with lock hold to avoid freeze_queue runs here */
        if (!ret && !blk_queue_dying(q))
                __percpu_counter_add(&q->mq_usage_counter, 1, 1000000);
        else if (blk_queue_dying(q))
                ret = -ENODEV;
        spin_unlock_irq(q->queue_lock);

        return ret;
}

static void blk_mq_queue_exit(struct request_queue *q)
{
        __percpu_counter_add(&q->mq_usage_counter, -1, 1000000);
}

static void __blk_mq_drain_queue(struct request_queue *q)
{
        while (true) {
                s64 count;

                spin_lock_irq(q->queue_lock);
                count = percpu_counter_sum(&q->mq_usage_counter);
                spin_unlock_irq(q->queue_lock);

                if (count == 0)
                        break;
                blk_mq_run_queues(q, false);
                msleep(10);
        }
}

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

        spin_lock_irq(q->queue_lock);
        drain = !q->bypass_depth++;
        queue_flag_set(QUEUE_FLAG_BYPASS, q);
        spin_unlock_irq(q->queue_lock);

        if (drain)
                __blk_mq_drain_queue(q);
}

void blk_mq_drain_queue(struct request_queue *q)
{
        __blk_mq_drain_queue(q);
}

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

        spin_lock_irq(q->queue_lock);
        if (!--q->bypass_depth) {
                queue_flag_clear(QUEUE_FLAG_BYPASS, q);
                wake = true;
        }
        WARN_ON_ONCE(q->bypass_depth < 0);
        spin_unlock_irq(q->queue_lock);
        if (wake)
                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;

        rq->mq_ctx = ctx;
        rq->cmd_flags = rw_flags;
        rq->start_time = jiffies;
        set_start_time_ns(rq);
        ctx->rq_dispatched[rw_is_sync(rw_flags)]++;
}

static struct request *__blk_mq_alloc_request(struct blk_mq_hw_ctx *hctx,
                                              gfp_t gfp, bool reserved)
{
        return blk_mq_alloc_rq(hctx, gfp, reserved);
}

static struct request *blk_mq_alloc_request_pinned(struct request_queue *q,
                                                   int rw, gfp_t gfp,
                                                   bool reserved)
{
        struct request *rq;

        do {
                struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
                struct blk_mq_hw_ctx *hctx = q->mq_ops->map_queue(q, ctx->cpu);

                rq = __blk_mq_alloc_request(hctx, gfp & ~__GFP_WAIT, reserved);
                if (rq) {
                        blk_mq_rq_ctx_init(q, ctx, rq, rw);
                        break;
                }

                blk_mq_put_ctx(ctx);
                if (!(gfp & __GFP_WAIT))
                        break;

                __blk_mq_run_hw_queue(hctx);
                blk_mq_wait_for_tags(hctx->tags);
        } while (1);

        return rq;
}

struct request *blk_mq_alloc_request(struct request_queue *q, int rw,
                gfp_t gfp, bool reserved)
{
        struct request *rq;

        if (blk_mq_queue_enter(q))
                return NULL;

        rq = blk_mq_alloc_request_pinned(q, rw, gfp, reserved);
        if (rq)
                blk_mq_put_ctx(rq->mq_ctx);
        return rq;
}

struct request *blk_mq_alloc_reserved_request(struct request_queue *q, int rw,
                                              gfp_t gfp)
{
        struct request *rq;

        if (blk_mq_queue_enter(q))
                return NULL;

        rq = blk_mq_alloc_request_pinned(q, rw, gfp, true);
        if (rq)
                blk_mq_put_ctx(rq->mq_ctx);
        return rq;
}
EXPORT_SYMBOL(blk_mq_alloc_reserved_request);

/*
 * Re-init and set pdu, if we have it
 */
static void blk_mq_rq_init(struct blk_mq_hw_ctx *hctx, struct request *rq)
{
        blk_rq_init(hctx->queue, rq);

        if (hctx->cmd_size)
                rq->special = blk_mq_rq_to_pdu(rq);
}

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;

        blk_mq_rq_init(hctx, rq);
        blk_mq_put_tag(hctx->tags, 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);
}

static void blk_mq_bio_endio(struct request *rq, struct bio *bio, int error)
{
        if (error)
                clear_bit(BIO_UPTODATE, &bio->bi_flags);
        else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
                error = -EIO;

        if (unlikely(rq->cmd_flags & REQ_QUIET))
                set_bit(BIO_QUIET, &bio->bi_flags);

        /* don't actually finish bio if it's part of flush sequence */
        if (!(rq->cmd_flags & REQ_FLUSH_SEQ))
                bio_endio(bio, error);
}

void blk_mq_complete_request(struct request *rq, int error)
{
        struct bio *bio = rq->bio;
        unsigned int bytes = 0;

        trace_block_rq_complete(rq->q, rq);

        while (bio) {
                struct bio *next = bio->bi_next;

                bio->bi_next = NULL;
                bytes += bio->bi_iter.bi_size;
                blk_mq_bio_endio(rq, bio, error);
                bio = next;
        }

        blk_account_io_completion(rq, bytes);

        blk_account_io_done(rq);

        if (rq->end_io)
                rq->end_io(rq, error);
        else
                blk_mq_free_request(rq);
}

void __blk_mq_end_io(struct request *rq, int error)
{
        if (!blk_mark_rq_complete(rq))
                blk_mq_complete_request(rq, error);
}

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

        __blk_mq_end_io(rq, rq->errors);
}

/*
 * End IO on this request on a multiqueue enabled driver. We'll either do
 * it directly inline, or punt to a local IPI handler on the matching
 * remote CPU.
 */
void blk_mq_end_io(struct request *rq, int error)
{
        struct blk_mq_ctx *ctx = rq->mq_ctx;
        int cpu;

        if (!ctx->ipi_redirect)
                return __blk_mq_end_io(rq, error);

        cpu = get_cpu();
        if (cpu != ctx->cpu && cpu_online(ctx->cpu)) {
                rq->errors = error;
                rq->csd.func = blk_mq_end_io_remote;
                rq->csd.info = rq;
                rq->csd.flags = 0;
                __smp_call_function_single(ctx->cpu, &rq->csd, 0);
        } else {
                __blk_mq_end_io(rq, error);
        }
        put_cpu();
}
EXPORT_SYMBOL(blk_mq_end_io);

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

        trace_block_rq_issue(q, rq);

        /*
         * Just mark start time and set the started bit. Due to memory
         * ordering, we know we'll see the correct deadline as long as
         * REQ_ATOMIC_STARTED is seen.
         */
        rq->deadline = jiffies + q->rq_timeout;
        set_bit(REQ_ATOM_STARTED, &rq->atomic_flags);
}

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);
}

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->queue_depth, tag);
                if (tag >= hctx->queue_depth)
                        break;

                rq = hctx->rqs[tag++];

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

        if (next_set)
                mod_timer(&q->timeout, round_jiffies_up(next));
}

/*
 * 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;
}

void blk_mq_add_timer(struct request *rq)
{
        __blk_add_timer(rq, NULL);
}

/*
 * 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 blk_mq_ctx *ctx;
        struct request *rq;
        LIST_HEAD(rq_list);
        int bit, queued;

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

        hctx->run++;

        /*
         * Touch any software queue that has pending entries.
         */
        for_each_set_bit(bit, hctx->ctx_map, hctx->nr_ctx) {
                clear_bit(bit, hctx->ctx_map);
                ctx = hctx->ctxs[bit];
                BUG_ON(bit != ctx->index_hw);

                spin_lock(&ctx->lock);
                list_splice_tail_init(&ctx->rq_list, &rq_list);
                spin_unlock(&ctx->lock);
        }

        /*
         * 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);
        }

        /*
         * Delete and return all entries from our dispatch list
         */
        queued = 0;

        /*
         * Now process all the entries, sending them to the driver.
         */
        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);

                /*
                 * Last request in the series. Flag it as such, this
                 * enables drivers to 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 (list_empty(&rq_list))
                        rq->cmd_flags |= REQ_END;

                ret = q->mq_ops->queue_rq(hctx, rq);
                switch (ret) {
                case BLK_MQ_RQ_QUEUE_OK:
                        queued++;
                        continue;
                case BLK_MQ_RQ_QUEUE_BUSY:
                        /*
                         * FIXME: we should have a mechanism to stop the queue
                         * like blk_stop_queue, otherwise we will waste cpu
                         * time
                         */
                        list_add(&rq->queuelist, &rq_list);
                        blk_mq_requeue_request(rq);
                        break;
                default:
                        pr_err("blk-mq: bad return on queue: %d\n", ret);
                        rq->errors = -EIO;
                case BLK_MQ_RQ_QUEUE_ERROR:
                        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);
        }
}

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

        if (!async)
                __blk_mq_run_hw_queue(hctx);
        else {
                struct request_queue *q = hctx->queue;

                kblockd_schedule_delayed_work(q, &hctx->delayed_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->flags))
                        continue;

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

void blk_mq_stop_hw_queue(struct blk_mq_hw_ctx *hctx)
{
        cancel_delayed_work(&hctx->delayed_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);
        __blk_mq_run_hw_queue(hctx);
}
EXPORT_SYMBOL(blk_mq_start_hw_queue);

void blk_mq_start_stopped_hw_queues(struct request_queue *q)
{
        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);
                blk_mq_run_hw_queue(hctx, true);
        }
}
EXPORT_SYMBOL(blk_mq_start_stopped_hw_queues);

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

        hctx = container_of(work, struct blk_mq_hw_ctx, delayed_work.work);
        __blk_mq_run_hw_queue(hctx);
}

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

        trace_block_rq_insert(hctx->queue, rq);

        list_add_tail(&rq->queuelist, &ctx->rq_list);
        blk_mq_hctx_mark_pending(hctx, ctx);

        /*
         * We do this early, to ensure we are on the right CPU.
         */
        blk_mq_add_timer(rq);
}

void blk_mq_insert_request(struct request_queue *q, struct request *rq,
                           bool run_queue)
{
        struct blk_mq_hw_ctx *hctx;
        struct blk_mq_ctx *ctx, *current_ctx;

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

        if (rq->cmd_flags & (REQ_FLUSH | REQ_FUA)) {
                blk_insert_flush(rq);
        } else {
                current_ctx = blk_mq_get_ctx(q);

                if (!cpu_online(ctx->cpu)) {
                        ctx = current_ctx;
                        hctx = q->mq_ops->map_queue(q, ctx->cpu);
                        rq->mq_ctx = ctx;
                }
                spin_lock(&ctx->lock);
                __blk_mq_insert_request(hctx, rq);
                spin_unlock(&ctx->lock);

                blk_mq_put_ctx(current_ctx);
        }

        if (run_queue)
                __blk_mq_run_hw_queue(hctx);
}
EXPORT_SYMBOL(blk_mq_insert_request);

/*
 * This is a special version of blk_mq_insert_request to bypass FLUSH request
 * check. Should only be used internally.
 */
void blk_mq_run_request(struct request *rq, bool run_queue, bool async)
{
        struct request_queue *q = rq->q;
        struct blk_mq_hw_ctx *hctx;
        struct blk_mq_ctx *ctx, *current_ctx;

        current_ctx = blk_mq_get_ctx(q);

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

        /* ctx->cpu might be offline */
        spin_lock(&ctx->lock);
        __blk_mq_insert_request(hctx, rq);
        spin_unlock(&ctx->lock);

        blk_mq_put_ctx(current_ctx);

        if (run_queue)
                blk_mq_run_hw_queue(hctx, async);
}

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);
        }
        spin_unlock(&ctx->lock);

        blk_mq_put_ctx(current_ctx);

        blk_mq_run_hw_queue(hctx, from_schedule);
}

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);
        blk_account_io_start(rq, 1);
}

static void blk_mq_make_request(struct request_queue *q, struct bio *bio)
{
        struct blk_mq_hw_ctx *hctx;
        struct blk_mq_ctx *ctx;
        const int is_sync = rw_is_sync(bio->bi_rw);
        const int is_flush_fua = bio->bi_rw & (REQ_FLUSH | REQ_FUA);
        int rw = bio_data_dir(bio);
        struct request *rq;
        unsigned int use_plug, request_count = 0;

        /*
         * If we have multiple hardware queues, just go directly to
         * one of those for sync IO.
         */
        use_plug = !is_flush_fua && ((q->nr_hw_queues == 1) || !is_sync);

        blk_queue_bounce(q, &bio);

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

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

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

        trace_block_getrq(q, bio, rw);
        rq = __blk_mq_alloc_request(hctx, GFP_ATOMIC, false);
        if (likely(rq))
                blk_mq_rq_ctx_init(q, ctx, rq, rw);
        else {
                blk_mq_put_ctx(ctx);
                trace_block_sleeprq(q, bio, rw);
                rq = blk_mq_alloc_request_pinned(q, rw, __GFP_WAIT|GFP_ATOMIC,
                                                        false);
                ctx = rq->mq_ctx;
                hctx = q->mq_ops->map_queue(q, ctx->cpu);
        }

        hctx->queued++;

        if (unlikely(is_flush_fua)) {
                blk_mq_bio_to_request(rq, bio);
                blk_mq_put_ctx(ctx);
                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(ctx);
                        return;
                }
        }

        spin_lock(&ctx->lock);

        if ((hctx->flags & BLK_MQ_F_SHOULD_MERGE) &&
            blk_mq_attempt_merge(q, ctx, bio))
                __blk_mq_free_request(hctx, ctx, rq);
        else {
                blk_mq_bio_to_request(rq, bio);
                __blk_mq_insert_request(hctx, rq);
        }

        spin_unlock(&ctx->lock);
        blk_mq_put_ctx(ctx);

        /*
         * 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(hctx, !is_sync || is_flush_fua);
}

/*
 * 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);

struct blk_mq_hw_ctx *blk_mq_alloc_single_hw_queue(struct blk_mq_reg *reg,
                                                   unsigned int hctx_index)
{
        return kmalloc_node(sizeof(struct blk_mq_hw_ctx),
                                GFP_KERNEL | __GFP_ZERO, reg->numa_node);
}
EXPORT_SYMBOL(blk_mq_alloc_single_hw_queue);

void blk_mq_free_single_hw_queue(struct blk_mq_hw_ctx *hctx,
                                 unsigned int hctx_index)
{
        kfree(hctx);
}
EXPORT_SYMBOL(blk_mq_free_single_hw_queue);

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

        if (action != CPU_DEAD && action != CPU_DEAD_FROZEN)
                return;

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

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

        if (list_empty(&tmp))
                return;

        ctx = blk_mq_get_ctx(hctx->queue);
        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);
        }

        blk_mq_hctx_mark_pending(hctx, ctx);

        spin_unlock(&ctx->lock);
        blk_mq_put_ctx(ctx);
}

static void blk_mq_init_hw_commands(struct blk_mq_hw_ctx *hctx,
                                    void (*init)(void *, struct blk_mq_hw_ctx *,
                                        struct request *, unsigned int),
                                    void *data)
{
        unsigned int i;

        for (i = 0; i < hctx->queue_depth; i++) {
                struct request *rq = hctx->rqs[i];

                init(data, hctx, rq, i);
        }
}

void blk_mq_init_commands(struct request_queue *q,
                          void (*init)(void *, struct blk_mq_hw_ctx *,
                                        struct request *, unsigned int),
                          void *data)
{
        struct blk_mq_hw_ctx *hctx;
        unsigned int i;

        queue_for_each_hw_ctx(q, hctx, i)
                blk_mq_init_hw_commands(hctx, init, data);
}
EXPORT_SYMBOL(blk_mq_init_commands);

static void blk_mq_free_rq_map(struct blk_mq_hw_ctx *hctx)
{
        struct page *page;

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

        kfree(hctx->rqs);

        if (hctx->tags)
                blk_mq_free_tags(hctx->tags);
}

static size_t order_to_size(unsigned int order)
{
        size_t ret = PAGE_SIZE;

        while (order--)
                ret *= 2;

        return ret;
}

static int blk_mq_init_rq_map(struct blk_mq_hw_ctx *hctx,
                              unsigned int reserved_tags, int node)
{
        unsigned int i, j, entries_per_page, max_order = 4;
        size_t rq_size, left;

        INIT_LIST_HEAD(&hctx->page_list);

        hctx->rqs = kmalloc_node(hctx->queue_depth * sizeof(struct request *),
                                        GFP_KERNEL, node);
        if (!hctx->rqs)
                return -ENOMEM;

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

        for (i = 0; i < hctx->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(node, GFP_KERNEL, this_order);
                        if (page)
                                break;
                        if (!this_order--)
                                break;
                        if (order_to_size(this_order) < rq_size)
                                break;
                } while (1);

                if (!page)
                        break;

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

                p = page_address(page);
                entries_per_page = order_to_size(this_order) / rq_size;
                to_do = min(entries_per_page, hctx->queue_depth - i);
                left -= to_do * rq_size;
                for (j = 0; j < to_do; j++) {
                        hctx->rqs[i] = p;
                        blk_mq_rq_init(hctx, hctx->rqs[i]);
                        p += rq_size;
                        i++;
                }
        }

        if (i < (reserved_tags + BLK_MQ_TAG_MIN))
                goto err_rq_map;
        else if (i != hctx->queue_depth) {
                hctx->queue_depth = i;
                pr_warn("%s: queue depth set to %u because of low memory\n",
                                        __func__, i);
        }

        hctx->tags = blk_mq_init_tags(hctx->queue_depth, reserved_tags, node);
        if (!hctx->tags) {
err_rq_map:
                blk_mq_free_rq_map(hctx);
                return -ENOMEM;
        }

        return 0;
}

static int blk_mq_init_hw_queues(struct request_queue *q,
                                 struct blk_mq_reg *reg, void *driver_data)
{
        struct blk_mq_hw_ctx *hctx;
        unsigned int i, j;

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

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

                INIT_DELAYED_WORK(&hctx->delayed_work, blk_mq_work_fn);
                spin_lock_init(&hctx->lock);
                INIT_LIST_HEAD(&hctx->dispatch);
                hctx->queue = q;
                hctx->queue_num = i;
                hctx->flags = reg->flags;
                hctx->queue_depth = reg->queue_depth;
                hctx->cmd_size = reg->cmd_size;

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

                if (blk_mq_init_rq_map(hctx, reg->reserved_tags, node))
                        break;

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

                num_maps = ALIGN(nr_cpu_ids, BITS_PER_LONG) / BITS_PER_LONG;
                hctx->ctx_map = kzalloc_node(num_maps * sizeof(unsigned long),
                                                GFP_KERNEL, node);
                if (!hctx->ctx_map)
                        break;

                hctx->nr_ctx_map = num_maps;
                hctx->nr_ctx = 0;

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

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

        /*
         * Init failed
         */
        queue_for_each_hw_ctx(q, hctx, j) {
                if (i == j)
                        break;

                if (reg->ops->exit_hctx)
                        reg->ops->exit_hctx(hctx, j);

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

        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 */
                hctx = q->mq_ops->map_queue(q, i);
                hctx->nr_ctx++;

                if (!cpu_online(i))
                        continue;

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

struct request_queue *blk_mq_init_queue(struct blk_mq_reg *reg,
                                        void *driver_data)
{
        struct blk_mq_hw_ctx **hctxs;
        struct blk_mq_ctx *ctx;
        struct request_queue *q;
        int i;

        if (!reg->nr_hw_queues ||
            !reg->ops->queue_rq || !reg->ops->map_queue ||
            !reg->ops->alloc_hctx || !reg->ops->free_hctx)
                return ERR_PTR(-EINVAL);

        if (!reg->queue_depth)
                reg->queue_depth = BLK_MQ_MAX_DEPTH;
        else if (reg->queue_depth > BLK_MQ_MAX_DEPTH) {
                pr_err("blk-mq: queuedepth too large (%u)\n", reg->queue_depth);
                reg->queue_depth = BLK_MQ_MAX_DEPTH;
        }

        /*
         * Set aside a tag for flush requests.  It will only be used while
         * another flush request is in progress but outside the driver.
         *
         * TODO: only allocate if flushes are supported
         */
        reg->queue_depth++;
        reg->reserved_tags++;

        if (reg->queue_depth < (reg->reserved_tags + BLK_MQ_TAG_MIN))
                return ERR_PTR(-EINVAL);

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

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

        if (!hctxs)
                goto err_percpu;

        for (i = 0; i < reg->nr_hw_queues; i++) {
                hctxs[i] = reg->ops->alloc_hctx(reg, i);
                if (!hctxs[i])
                        goto err_hctxs;

                hctxs[i]->numa_node = NUMA_NO_NODE;
                hctxs[i]->queue_num = i;
        }

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

        q->mq_map = blk_mq_make_queue_map(reg);
        if (!q->mq_map)
                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 = reg->nr_hw_queues;

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

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

        blk_queue_make_request(q, blk_mq_make_request);
        blk_queue_rq_timed_out(q, reg->ops->timeout);
        if (reg->timeout)
                blk_queue_rq_timeout(q, reg->timeout);

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

        if (blk_mq_init_hw_queues(q, reg, driver_data))
                goto err_hw;

        blk_mq_map_swqueue(q);

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

        return q;
err_hw:
        kfree(q->mq_map);
err_map:
        blk_cleanup_queue(q);
err_hctxs:
        for (i = 0; i < reg->nr_hw_queues; i++) {
                if (!hctxs[i])
                        break;
                reg->ops->free_hctx(hctxs[i], i);
        }
        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_hw_ctx *hctx;
        int i;

        queue_for_each_hw_ctx(q, hctx, i) {
                kfree(hctx->ctx_map);
                kfree(hctx->ctxs);
                blk_mq_free_rq_map(hctx);
                blk_mq_unregister_cpu_notifier(&hctx->cpu_notifier);
                if (q->mq_ops->exit_hctx)
                        q->mq_ops->exit_hctx(hctx, i);
                q->mq_ops->free_hctx(hctx, i);
        }

        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_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_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 mapping is 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 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 __init blk_mq_init(void)
{
        blk_mq_cpu_init();

        /* Must be called after percpu_counter_hotcpu_callback() */
        hotcpu_notifier(blk_mq_queue_reinit_notify, -10);

        return 0;
}
subsys_initcall(blk_mq_init);