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)
{
	struct request *rq;

	if (blk_mq_queue_enter(q))
		return NULL;

	rq = blk_mq_alloc_request_pinned(q, rw, gfp, false);
	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
 */
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_end_io(struct request *rq, int error)
{
	struct bio *bio = rq->bio;
	unsigned int bytes = 0;

	trace_block_rq_complete(rq->q, rq, blk_rq_bytes(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);
}
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);
}

void __blk_mq_complete_request(struct request *rq)
{
	struct blk_mq_ctx *ctx = rq->mq_ctx;
	int cpu;

	if (!ctx->ipi_redirect) {
		rq->q->softirq_done_fn(rq);
		return;
	}

	cpu = get_cpu();
	if (cpu != ctx->cpu && 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();
}

/**
 * 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)
{
	if (unlikely(blk_should_fake_timeout(rq->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);

	/*
	 * 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);

	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--;
}

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, 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:
			/*
			 * 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);
		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);
	}
}

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, 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);

	/*
	 * 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 at_head, 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, at_head);
		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, false);
	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, false);
	}
	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 (bio_integrity_enabled(bio) && bio_integrity_prep(bio)) {
		bio_endio(bio, -EIO);
		return;
	}

	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, false);
	}

	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]];