text: // SPDX-License-Identifier: GPL-2.0
  /*
   * 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/kmemleak.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/sched/topology.h>
  #include <linux/sched/signal.h>
  #include <linux/delay.h>
  #include <linux/crash_dump.h>
  #include <linux/prefetch.h>
  
  #include <trace/events/block.h>
  
  #include <linux/blk-mq.h>
  #include <linux/t10-pi.h>
  #include "blk.h"
  #include "blk-mq.h"
  #include "blk-mq-debugfs.h"
  #include "blk-mq-tag.h"
  #include "blk-pm.h"
  #include "blk-stat.h"
  #include "blk-mq-sched.h"
  #include "blk-rq-qos.h"
  
  static void blk_mq_poll_stats_start(struct request_queue *q);
  static void blk_mq_poll_stats_fn(struct blk_stat_callback *cb);
  
  static int blk_mq_poll_stats_bkt(const struct request *rq)
  {
  	int ddir, sectors, bucket;
  
  	ddir = rq_data_dir(rq);
  	sectors = blk_rq_stats_sectors(rq);
  
  	bucket = ddir + 2 * ilog2(sectors);
  
  	if (bucket < 0)
  		return -1;
  	else if (bucket >= BLK_MQ_POLL_STATS_BKTS)
  		return ddir + BLK_MQ_POLL_STATS_BKTS - 2;
  
  	return bucket;
  }
  
  /*
   * Check if any of the ctx, dispatch list or elevator
   * have pending work in this hardware queue.
   */
  static bool blk_mq_hctx_has_pending(struct blk_mq_hw_ctx *hctx)
  {
  	return !list_empty_careful(&hctx->dispatch) ||
  		sbitmap_any_bit_set(&hctx->ctx_map) ||
  			blk_mq_sched_has_work(hctx);
  }
  
  /*
   * 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)
  {
  	const int bit = ctx->index_hw[hctx->type];
  
  	if (!sbitmap_test_bit(&hctx->ctx_map, bit))
  		sbitmap_set_bit(&hctx->ctx_map, bit);
  }
  
  static void blk_mq_hctx_clear_pending(struct blk_mq_hw_ctx *hctx,
  				      struct blk_mq_ctx *ctx)
  {
  	const int bit = ctx->index_hw[hctx->type];
  
  	sbitmap_clear_bit(&hctx->ctx_map, bit);
  }
  
  struct mq_inflight {
  	struct hd_struct *part;
  	unsigned int *inflight;
  };
  
  static bool blk_mq_check_inflight(struct blk_mq_hw_ctx *hctx,
  				  struct request *rq, void *priv,
  				  bool reserved)
  {
  	struct mq_inflight *mi = priv;
  
  	/*
  	 * index[0] counts the specific partition that was asked for.
  	 */
  	if (rq->part == mi->part)
  		mi->inflight[0]++;
  
  	return true;
  }
  
  unsigned int blk_mq_in_flight(struct request_queue *q, struct hd_struct *part)
  {
  	unsigned inflight[2];
  	struct mq_inflight mi = { .part = part, .inflight = inflight, };
  
  	inflight[0] = inflight[1] = 0;
  	blk_mq_queue_tag_busy_iter(q, blk_mq_check_inflight, &mi);
  
  	return inflight[0];
  }
  
  static bool blk_mq_check_inflight_rw(struct blk_mq_hw_ctx *hctx,
  				     struct request *rq, void *priv,
  				     bool reserved)
  {
  	struct mq_inflight *mi = priv;
  
  	if (rq->part == mi->part)
  		mi->inflight[rq_data_dir(rq)]++;
  
  	return true;
  }
  
  void blk_mq_in_flight_rw(struct request_queue *q, struct hd_struct *part,
  			 unsigned int inflight[2])
  {
  	struct mq_inflight mi = { .part = part, .inflight = inflight, };
  
  	inflight[0] = inflight[1] = 0;
  	blk_mq_queue_tag_busy_iter(q, blk_mq_check_inflight_rw, &mi);
  }
  
  void blk_freeze_queue_start(struct request_queue *q)
  {
  	mutex_lock(&q->mq_freeze_lock);
  	if (++q->mq_freeze_depth == 1) {
  		percpu_ref_kill(&q->q_usage_counter);
  		mutex_unlock(&q->mq_freeze_lock);
  		if (queue_is_mq(q))
  			blk_mq_run_hw_queues(q, false);
  	} else {
  		mutex_unlock(&q->mq_freeze_lock);
  	}
  }
  EXPORT_SYMBOL_GPL(blk_freeze_queue_start);
  
  void blk_mq_freeze_queue_wait(struct request_queue *q)
  {
  	wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->q_usage_counter));
  }
  EXPORT_SYMBOL_GPL(blk_mq_freeze_queue_wait);
  
  int blk_mq_freeze_queue_wait_timeout(struct request_queue *q,
  				     unsigned long timeout)
  {
  	return wait_event_timeout(q->mq_freeze_wq,
  					percpu_ref_is_zero(&q->q_usage_counter),
  					timeout);
  }
  EXPORT_SYMBOL_GPL(blk_mq_freeze_queue_wait_timeout);
  
  /*
   * Guarantee no request is in use, so we can change any data structure of
   * the queue afterward.
   */
  void blk_freeze_queue(struct request_queue *q)
  {
  	/*
  	 * In the !blk_mq case we are only calling this to kill the
  	 * q_usage_counter, otherwise this increases the freeze depth
  	 * and waits for it to return to zero.  For this reason there is
  	 * no blk_unfreeze_queue(), and blk_freeze_queue() is not
  	 * exported to drivers as the only user for unfreeze is blk_mq.
  	 */
  	blk_freeze_queue_start(q);
  	blk_mq_freeze_queue_wait(q);
  }
  
  void blk_mq_freeze_queue(struct request_queue *q)
  {
  	/*
  	 * ...just an alias to keep freeze and unfreeze actions balanced
  	 * in the blk_mq_* namespace
  	 */
  	blk_freeze_queue(q);
  }
  EXPORT_SYMBOL_GPL(blk_mq_freeze_queue);
  
  void blk_mq_unfreeze_queue(struct request_queue *q)
  {
  	mutex_lock(&q->mq_freeze_lock);
  	q->mq_freeze_depth--;
  	WARN_ON_ONCE(q->mq_freeze_depth < 0);
  	if (!q->mq_freeze_depth) {
  		percpu_ref_resurrect(&q->q_usage_counter);
  		wake_up_all(&q->mq_freeze_wq);
  	}
  	mutex_unlock(&q->mq_freeze_lock);
  }
  EXPORT_SYMBOL_GPL(blk_mq_unfreeze_queue);
  
  /*
   * FIXME: replace the scsi_internal_device_*block_nowait() calls in the
   * mpt3sas driver such that this function can be removed.
   */
  void blk_mq_quiesce_queue_nowait(struct request_queue *q)
  {
  	blk_queue_flag_set(QUEUE_FLAG_QUIESCED, q);
  }
  EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue_nowait);
  
  /**
   * blk_mq_quiesce_queue() - wait until all ongoing dispatches have finished
   * @q: request queue.
   *
   * Note: this function does not prevent that the struct request end_io()
   * callback function is invoked. Once this function is returned, we make
   * sure no dispatch can happen until the queue is unquiesced via
   * blk_mq_unquiesce_queue().
   */
  void blk_mq_quiesce_queue(struct request_queue *q)
  {
  	struct blk_mq_hw_ctx *hctx;
  	unsigned int i;
  	bool rcu = false;
  
  	blk_mq_quiesce_queue_nowait(q);
  
  	queue_for_each_hw_ctx(q, hctx, i) {
  		if (hctx->flags & BLK_MQ_F_BLOCKING)
  			synchronize_srcu(hctx->srcu);
  		else
  			rcu = true;
  	}
  	if (rcu)
  		synchronize_rcu();
  }
  EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue);
  
  /*
   * blk_mq_unquiesce_queue() - counterpart of blk_mq_quiesce_queue()
   * @q: request queue.
   *
   * This function recovers queue into the state before quiescing
   * which is done by blk_mq_quiesce_queue.
   */
  void blk_mq_unquiesce_queue(struct request_queue *q)
  {
  	blk_queue_flag_clear(QUEUE_FLAG_QUIESCED, q);
  
  	/* dispatch requests which are inserted during quiescing */
  	blk_mq_run_hw_queues(q, true);
  }
  EXPORT_SYMBOL_GPL(blk_mq_unquiesce_queue);
  
  void blk_mq_wake_waiters(struct request_queue *q)
  {
  	struct blk_mq_hw_ctx *hctx;
  	unsigned int i;
  
  	queue_for_each_hw_ctx(q, hctx, i)
  		if (blk_mq_hw_queue_mapped(hctx))
  			blk_mq_tag_wakeup_all(hctx->tags, true);
  }
  
  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);
  
  /*
   * Only need start/end time stamping if we have iostat or
   * blk stats enabled, or using an IO scheduler.
   */
  static inline bool blk_mq_need_time_stamp(struct request *rq)
  {
  	return (rq->rq_flags & (RQF_IO_STAT | RQF_STATS)) || rq->q->elevator;
  }
  
  static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
  		unsigned int tag, unsigned int op, u64 alloc_time_ns)
  {
  	struct blk_mq_tags *tags = blk_mq_tags_from_data(data);
  	struct request *rq = tags->static_rqs[tag];
  	req_flags_t rq_flags = 0;
  
  	if (data->flags & BLK_MQ_REQ_INTERNAL) {
  		rq->tag = -1;
  		rq->internal_tag = tag;
  	} else {
  		if (data->hctx->flags & BLK_MQ_F_TAG_SHARED) {
  			rq_flags = RQF_MQ_INFLIGHT;
  			atomic_inc(&data->hctx->nr_active);
  		}
  		rq->tag = tag;
  		rq->internal_tag = -1;
  		data->hctx->tags->rqs[rq->tag] = rq;
  	}
  
  	/* csd/requeue_work/fifo_time is initialized before use */
  	rq->q = data->q;
  	rq->mq_ctx = data->ctx;
  	rq->mq_hctx = data->hctx;
  	rq->rq_flags = rq_flags;
  	rq->cmd_flags = op;
  	if (data->flags & BLK_MQ_REQ_PREEMPT)
  		rq->rq_flags |= RQF_PREEMPT;
  	if (blk_queue_io_stat(data->q))
  		rq->rq_flags |= RQF_IO_STAT;
  	INIT_LIST_HEAD(&rq->queuelist);
  	INIT_HLIST_NODE(&rq->hash);
  	RB_CLEAR_NODE(&rq->rb_node);
  	rq->rq_disk = NULL;
  	rq->part = NULL;
  #ifdef CONFIG_BLK_RQ_ALLOC_TIME
  	rq->alloc_time_ns = alloc_time_ns;
  #endif
  	if (blk_mq_need_time_stamp(rq))
  		rq->start_time_ns = ktime_get_ns();
  	else
  		rq->start_time_ns = 0;
  	rq->io_start_time_ns = 0;
  	rq->stats_sectors = 0;
  	rq->nr_phys_segments = 0;
  #if defined(CONFIG_BLK_DEV_INTEGRITY)
  	rq->nr_integrity_segments = 0;
  #endif
  	/* tag was already set */
  	rq->extra_len = 0;
  	WRITE_ONCE(rq->deadline, 0);
  
  	rq->timeout = 0;
  
  	rq->end_io = NULL;
  	rq->end_io_data = NULL;
  
  	data->ctx->rq_dispatched[op_is_sync(op)]++;
  	refcount_set(&rq->ref, 1);
  	return rq;
  }
  
  static struct request *blk_mq_get_request(struct request_queue *q,
  					  struct bio *bio,
  					  struct blk_mq_alloc_data *data)
  {
  	struct elevator_queue *e = q->elevator;
  	struct request *rq;
  	unsigned int tag;
  	bool clear_ctx_on_error = false;
  	u64 alloc_time_ns = 0;
  
  	blk_queue_enter_live(q);
  
  	/* alloc_time includes depth and tag waits */
  	if (blk_queue_rq_alloc_time(q))
  		alloc_time_ns = ktime_get_ns();
  
  	data->q = q;
  	if (likely(!data->ctx)) {
  		data->ctx = blk_mq_get_ctx(q);
  		clear_ctx_on_error = true;
  	}
  	if (likely(!data->hctx))
  		data->hctx = blk_mq_map_queue(q, data->cmd_flags,
  						data->ctx);
  	if (data->cmd_flags & REQ_NOWAIT)
  		data->flags |= BLK_MQ_REQ_NOWAIT;
  
  	if (e) {
  		data->flags |= BLK_MQ_REQ_INTERNAL;
  
  		/*
  		 * Flush requests are special and go directly to the
  		 * dispatch list. Don't include reserved tags in the
  		 * limiting, as it isn't useful.
  		 */
  		if (!op_is_flush(data->cmd_flags) &&
  		    e->type->ops.limit_depth &&
  		    !(data->flags & BLK_MQ_REQ_RESERVED))
  			e->type->ops.limit_depth(data->cmd_flags, data);
  	} else {
  		blk_mq_tag_busy(data->hctx);
  	}
  
  	tag = blk_mq_get_tag(data);
  	if (tag == BLK_MQ_TAG_FAIL) {
  		if (clear_ctx_on_error)
  			data->ctx = NULL;
  		blk_queue_exit(q);
  		return NULL;
  	}
  
  	rq = blk_mq_rq_ctx_init(data, tag, data->cmd_flags, alloc_time_ns);
  	if (!op_is_flush(data->cmd_flags)) {
  		rq->elv.icq = NULL;
  		if (e && e->type->ops.prepare_request) {
  			if (e->type->icq_cache)
  				blk_mq_sched_assign_ioc(rq);
  
  			e->type->ops.prepare_request(rq, bio);
  			rq->rq_flags |= RQF_ELVPRIV;
  		}
  	}
  	data->hctx->queued++;
  	return rq;
  }
  
  struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op,
  		blk_mq_req_flags_t flags)
  {
  	struct blk_mq_alloc_data alloc_data = { .flags = flags, .cmd_flags = op };
  	struct request *rq;
  	int ret;
  
  	ret = blk_queue_enter(q, flags);
  	if (ret)
  		return ERR_PTR(ret);
  
  	rq = blk_mq_get_request(q, NULL, &alloc_data);
  	blk_queue_exit(q);
  
  	if (!rq)
  		return ERR_PTR(-EWOULDBLOCK);
  
  	rq->__data_len = 0;
  	rq->__sector = (sector_t) -1;
  	rq->bio = rq->biotail = NULL;
  	return rq;
  }
  EXPORT_SYMBOL(blk_mq_alloc_request);
  
  struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
  	unsigned int op, blk_mq_req_flags_t flags, unsigned int hctx_idx)
  {
  	struct blk_mq_alloc_data alloc_data = { .flags = flags, .cmd_flags = op };
  	struct request *rq;
  	unsigned int cpu;
  	int ret;
  
  	/*
  	 * If the tag allocator sleeps we could get an allocation for a
  	 * different hardware context.  No need to complicate the low level
  	 * allocator for this for the rare use case of a command tied to
  	 * a specific queue.
  	 */
  	if (WARN_ON_ONCE(!(flags & BLK_MQ_REQ_NOWAIT)))
  		return ERR_PTR(-EINVAL);
  
  	if (hctx_idx >= q->nr_hw_queues)
  		return ERR_PTR(-EIO);
  
  	ret = blk_queue_enter(q, flags);
  	if (ret)
  		return ERR_PTR(ret);
  
  	/*
  	 * Check if the hardware context is actually mapped to anything.
  	 * If not tell the caller that it should skip this queue.
  	 */
  	alloc_data.hctx = q->queue_hw_ctx[hctx_idx];
  	if (!blk_mq_hw_queue_mapped(alloc_data.hctx)) {
  		blk_queue_exit(q);
  		return ERR_PTR(-EXDEV);
  	}
  	cpu = cpumask_first_and(alloc_data.hctx->cpumask, cpu_online_mask);
  	alloc_data.ctx = __blk_mq_get_ctx(q, cpu);
  
  	rq = blk_mq_get_request(q, NULL, &alloc_data);
  	blk_queue_exit(q);
  
  	if (!rq)
  		return ERR_PTR(-EWOULDBLOCK);
  
  	return rq;
  }
  EXPORT_SYMBOL_GPL(blk_mq_alloc_request_hctx);
  
  static void __blk_mq_free_request(struct request *rq)
  {
  	struct request_queue *q = rq->q;
  	struct blk_mq_ctx *ctx = rq->mq_ctx;
  	struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
  	const int sched_tag = rq->internal_tag;
  
  	blk_pm_mark_last_busy(rq);
  	rq->mq_hctx = NULL;
  	if (rq->tag != -1)
  		blk_mq_put_tag(hctx, hctx->tags, ctx, rq->tag);
  	if (sched_tag != -1)
  		blk_mq_put_tag(hctx, hctx->sched_tags, ctx, sched_tag);
  	blk_mq_sched_restart(hctx);
  	blk_queue_exit(q);
  }
  
  void blk_mq_free_request(struct request *rq)
  {
  	struct request_queue *q = rq->q;
  	struct elevator_queue *e = q->elevator;
  	struct blk_mq_ctx *ctx = rq->mq_ctx;
  	struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
  
  	if (rq->rq_flags & RQF_ELVPRIV) {
  		if (e && e->type->ops.finish_request)
  			e->type->ops.finish_request(rq);
  		if (rq->elv.icq) {
  			put_io_context(rq->elv.icq->ioc);
  			rq->elv.icq = NULL;
  		}
  	}
  
  	ctx->rq_completed[rq_is_sync(rq)]++;
  	if (rq->rq_flags & RQF_MQ_INFLIGHT)
  		atomic_dec(&hctx->nr_active);
  
  	if (unlikely(laptop_mode && !blk_rq_is_passthrough(rq)))
  		laptop_io_completion(q->backing_dev_info);
  
  	rq_qos_done(q, rq);
  
  	WRITE_ONCE(rq->state, MQ_RQ_IDLE);
  	if (refcount_dec_and_test(&rq->ref))
  		__blk_mq_free_request(rq);
  }
  EXPORT_SYMBOL_GPL(blk_mq_free_request);
  
  inline void __blk_mq_end_request(struct request *rq, blk_status_t error)
  {
  	u64 now = 0;
  
  	if (blk_mq_need_time_stamp(rq))
  		now = ktime_get_ns();
  
  	if (rq->rq_flags & RQF_STATS) {
  		blk_mq_poll_stats_start(rq->q);
  		blk_stat_add(rq, now);
  	}
  
  	if (rq->internal_tag != -1)
  		blk_mq_sched_completed_request(rq, now);
  
  	blk_account_io_done(rq, now);
  
  	if (rq->end_io) {
  		rq_qos_done(rq->q, rq);
  		rq->end_io(rq, error);
  	} else {
  		blk_mq_free_request(rq);
  	}
  }
  EXPORT_SYMBOL(__blk_mq_end_request);
  
  void blk_mq_end_request(struct request *rq, blk_status_t error)
  {
  	if (blk_update_request(rq, error, blk_rq_bytes(rq)))
  		BUG();
  	__blk_mq_end_request(rq, error);
  }
  EXPORT_SYMBOL(blk_mq_end_request);
  
  static void __blk_mq_complete_request_remote(void *data)
  {
  	struct request *rq = data;
  	struct request_queue *q = rq->q;
  
  	q->mq_ops->complete(rq);
  }
  
  static void __blk_mq_complete_request(struct request *rq)
  {
  	struct blk_mq_ctx *ctx = rq->mq_ctx;
  	struct request_queue *q = rq->q;
  	bool shared = false;
  	int cpu;
  
  	WRITE_ONCE(rq->state, MQ_RQ_COMPLETE);
  	/*
  	 * Most of single queue controllers, there is only one irq vector
  	 * for handling IO completion, and the only irq's affinity is set
  	 * as all possible CPUs. On most of ARCHs, this affinity means the
  	 * irq is handled on one specific CPU.
  	 *
  	 * So complete IO reqeust in softirq context in case of single queue
  	 * for not degrading IO performance by irqsoff latency.
  	 */
  	if (q->nr_hw_queues == 1) {
  		__blk_complete_request(rq);
  		return;
  	}
  
  	/*
  	 * For a polled request, always complete locallly, it's pointless
  	 * to redirect the completion.
  	 */
  	if ((rq->cmd_flags & REQ_HIPRI) ||
  	    !test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags)) {
  		q->mq_ops->complete(rq);
  		return;
  	}
  
  	cpu = get_cpu();
  	if (!test_bit(QUEUE_FLAG_SAME_FORCE, &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 {
  		q->mq_ops->complete(rq);
  	}
  	put_cpu();
  }
  
  static void hctx_unlock(struct blk_mq_hw_ctx *hctx, int srcu_idx)
  	__releases(hctx->srcu)
  {
  	if (!(hctx->flags & BLK_MQ_F_BLOCKING))
  		rcu_read_unlock();
  	else
  		srcu_read_unlock(hctx->srcu, srcu_idx);
  }
  
  static void hctx_lock(struct blk_mq_hw_ctx *hctx, int *srcu_idx)
  	__acquires(hctx->srcu)
  {
  	if (!(hctx->flags & BLK_MQ_F_BLOCKING)) {
  		/* shut up gcc false positive */
  		*srcu_idx = 0;
  		rcu_read_lock();
  	} else
  		*srcu_idx = srcu_read_lock(hctx->srcu);
  }
  
  /**
   * 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.
   **/
  bool blk_mq_complete_request(struct request *rq)
  {
  	if (unlikely(blk_should_fake_timeout(rq->q)))
  		return false;
  	__blk_mq_complete_request(rq);
  	return true;
  }
  EXPORT_SYMBOL(blk_mq_complete_request);
  
  int blk_mq_request_started(struct request *rq)
  {
  	return blk_mq_rq_state(rq) != MQ_RQ_IDLE;
  }
  EXPORT_SYMBOL_GPL(blk_mq_request_started);
  
  int blk_mq_request_completed(struct request *rq)
  {
  	return blk_mq_rq_state(rq) == MQ_RQ_COMPLETE;
  }
  EXPORT_SYMBOL_GPL(blk_mq_request_completed);
  
  void blk_mq_start_request(struct request *rq)
  {
  	struct request_queue *q = rq->q;
  
  	trace_block_rq_issue(q, rq);
  
  	if (test_bit(QUEUE_FLAG_STATS, &q->queue_flags)) {
  		rq->io_start_time_ns = ktime_get_ns();
  		rq->stats_sectors = blk_rq_sectors(rq);
  		rq->rq_flags |= RQF_STATS;
  		rq_qos_issue(q, rq);
  	}
  
  	WARN_ON_ONCE(blk_mq_rq_state(rq) != MQ_RQ_IDLE);
  
  	blk_add_timer(rq);
  	WRITE_ONCE(rq->state, MQ_RQ_IN_FLIGHT);
  
  	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++;
  	}
  
  #ifdef CONFIG_BLK_DEV_INTEGRITY
  	if (blk_integrity_rq(rq) && req_op(rq) == REQ_OP_WRITE)
  		q->integrity.profile->prepare_fn(rq);
  #endif
  }
  EXPORT_SYMBOL(blk_mq_start_request);
  
  static void __blk_mq_requeue_request(struct request *rq)
  {
  	struct request_queue *q = rq->q;
  
  	blk_mq_put_driver_tag(rq);
  
  	trace_block_rq_requeue(q, rq);
  	rq_qos_requeue(q, rq);
  
  	if (blk_mq_request_started(rq)) {
  		WRITE_ONCE(rq->state, MQ_RQ_IDLE);
  		rq->rq_flags &= ~RQF_TIMED_OUT;
  		if (q->dma_drain_size && blk_rq_bytes(rq))
  			rq->nr_phys_segments--;
  	}
  }
  
  void blk_mq_requeue_request(struct request *rq, bool kick_requeue_list)
  {
  	__blk_mq_requeue_request(rq);
  
  	/* this request will be re-inserted to io scheduler queue */
  	blk_mq_sched_requeue_request(rq);
  
  	BUG_ON(!list_empty(&rq->queuelist));
  	blk_mq_add_to_requeue_list(rq, true, kick_requeue_list);
  }
  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.work);
  	LIST_HEAD(rq_list);
  	struct request *rq, *next;
  
  	spin_lock_irq(&q->requeue_lock);
  	list_splice_init(&q->requeue_list, &rq_list);
  	spin_unlock_irq(&q->requeue_lock);
  
  	list_for_each_entry_safe(rq, next, &rq_list, queuelist) {
  		if (!(rq->rq_flags & (RQF_SOFTBARRIER | RQF_DONTPREP)))
  			continue;
  
  		rq->rq_flags &= ~RQF_SOFTBARRIER;
  		list_del_init(&rq->queuelist);
  		/*
  		 * If RQF_DONTPREP, rq has contained some driver specific
  		 * data, so insert it to hctx dispatch list to avoid any
  		 * merge.
  		 */
  		if (rq->rq_flags & RQF_DONTPREP)
  			blk_mq_request_bypass_insert(rq, false, false);
  		else
  			blk_mq_sched_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_sched_insert_request(rq, false, false, false);
  	}
  
  	blk_mq_run_hw_queues(q, false);
  }
  
  void blk_mq_add_to_requeue_list(struct request *rq, bool at_head,
  				bool kick_requeue_list)
  {
  	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 insertion from the workqueue.
  	 */
  	BUG_ON(rq->rq_flags & RQF_SOFTBARRIER);
  
  	spin_lock_irqsave(&q->requeue_lock, flags);
  	if (at_head) {
  		rq->rq_flags |= RQF_SOFTBARRIER;
  		list_add(&rq->queuelist, &q->requeue_list);
  	} else {
  		list_add_tail(&rq->queuelist, &q->requeue_list);
  	}
  	spin_unlock_irqrestore(&q->requeue_lock, flags);
  
  	if (kick_requeue_list)
  		blk_mq_kick_requeue_list(q);
  }
  
  void blk_mq_kick_requeue_list(struct request_queue *q)
  {
  	kblockd_mod_delayed_work_on(WORK_CPU_UNBOUND, &q->requeue_work, 0);
  }
  EXPORT_SYMBOL(blk_mq_kick_requeue_list);
  
  void blk_mq_delay_kick_requeue_list(struct request_queue *q,
  				    unsigned long msecs)
  {
  	kblockd_mod_delayed_work_on(WORK_CPU_UNBOUND, &q->requeue_work,
  				    msecs_to_jiffies(msecs));
  }
  EXPORT_SYMBOL(blk_mq_delay_kick_requeue_list);
  
  struct request *blk_mq_tag_to_rq(struct blk_mq_tags *tags, unsigned int tag)
  {
  	if (tag < tags->nr_tags) {
  		prefetch(tags->rqs[tag]);
  		return tags->rqs[tag];
  	}
  
  	return NULL;
  }
  EXPORT_SYMBOL(blk_mq_tag_to_rq);
  
  static bool blk_mq_rq_inflight(struct blk_mq_hw_ctx *hctx, struct request *rq,
  			       void *priv, bool reserved)
  {
  	/*
  	 * If we find a request that isn't idle and the queue matches,
  	 * we know the queue is busy. Return false to stop the iteration.
  	 */
  	if (blk_mq_request_started(rq) && rq->q == hctx->queue) {
  		bool *busy = priv;
  
  		*busy = true;
  		return false;
  	}
  
  	return true;
  }
  
  bool blk_mq_queue_inflight(struct request_queue *q)
  {
  	bool busy = false;
  
  	blk_mq_queue_tag_busy_iter(q, blk_mq_rq_inflight, &busy);
  	return busy;
  }
  EXPORT_SYMBOL_GPL(blk_mq_queue_inflight);
  
  static void blk_mq_rq_timed_out(struct request *req, bool reserved)
  {
  	req->rq_flags |= RQF_TIMED_OUT;
  	if (req->q->mq_ops->timeout) {
  		enum blk_eh_timer_return ret;
  
  		ret = req->q->mq_ops->timeout(req, reserved);
  		if (ret == BLK_EH_DONE)
  			return;
  		WARN_ON_ONCE(ret != BLK_EH_RESET_TIMER);
  	}
  
  	blk_add_timer(req);
  }
  
  static bool blk_mq_req_expired(struct request *rq, unsigned long *next)
  {
  	unsigned long deadline;
  
  	if (blk_mq_rq_state(rq) != MQ_RQ_IN_FLIGHT)
  		return false;
  	if (rq->rq_flags & RQF_TIMED_OUT)
  		return false;
  
  	deadline = READ_ONCE(rq->deadline);
  	if (time_after_eq(jiffies, deadline))
  		return true;
  
  	if (*next == 0)
  		*next = deadline;
  	else if (time_after(*next, deadline))
  		*next = deadline;
  	return false;
  }
  
  static bool blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
  		struct request *rq, void *priv, bool reserved)
  {
  	unsigned long *next = priv;
  
  	/*
  	 * Just do a quick check if it is expired before locking the request in
  	 * so we're not unnecessarilly synchronizing across CPUs.
  	 */
  	if (!blk_mq_req_expired(rq, next))
  		return true;
  
  	/*
  	 * We have reason to believe the request may be expired. Take a
  	 * reference on the request to lock this request lifetime into its
  	 * currently allocated context to prevent it from being reallocated in
  	 * the event the completion by-passes this timeout handler.
  	 *
  	 * If the reference was already released, then the driver beat the
  	 * timeout handler to posting a natural completion.
  	 */
  	if (!refcount_inc_not_zero(&rq->ref))
  		return true;
  
  	/*
  	 * The request is now locked and cannot be reallocated underneath the
  	 * timeout handler's processing. Re-verify this exact request is truly
  	 * expired; if it is not expired, then the request was completed and
  	 * reallocated as a new request.
  	 */
  	if (blk_mq_req_expired(rq, next))
  		blk_mq_rq_timed_out(rq, reserved);
  
  	if (is_flush_rq(rq, hctx))
  		rq->end_io(rq, 0);
  	else if (refcount_dec_and_test(&rq->ref))
  		__blk_mq_free_request(rq);
  
  	return true;
  }
  
  static void blk_mq_timeout_work(struct work_struct *work)
  {
  	struct request_queue *q =
  		container_of(work, struct request_queue, timeout_work);
  	unsigned long next = 0;
  	struct blk_mq_hw_ctx *hctx;
  	int i;
  
  	/* A deadlock might occur if a request is stuck requiring a
  	 * timeout at the same time a queue freeze is waiting
  	 * completion, since the timeout code would not be able to
  	 * acquire the queue reference here.
  	 *
  	 * That's why we don't use blk_queue_enter here; instead, we use
  	 * percpu_ref_tryget directly, because we need to be able to
  	 * obtain a reference even in the short window between the queue
  	 * starting to freeze, by dropping the first reference in
  	 * blk_freeze_queue_start, and the moment the last request is
  	 * consumed, marked by the instant q_usage_counter reaches
  	 * zero.
  	 */
  	if (!percpu_ref_tryget(&q->q_usage_counter))
  		return;
  
  	blk_mq_queue_tag_busy_iter(q, blk_mq_check_expired, &next);
  
  	if (next != 0) {
  		mod_timer(&q->timeout, next);
  	} else {
  		/*
  		 * Request timeouts are handled as a forward rolling timer. If
  		 * we end up here it means that no requests are pending and
  		 * also that no request has been pending for a while. Mark
  		 * each hctx as idle.
  		 */
  		queue_for_each_hw_ctx(q, hctx, i) {
  			/* the hctx may be unmapped, so check it here */
  			if (blk_mq_hw_queue_mapped(hctx))
  				blk_mq_tag_idle(hctx);
  		}
  	}
  	blk_queue_exit(q);
  }
  
  struct flush_busy_ctx_data {
  	struct blk_mq_hw_ctx *hctx;
  	struct list_head *list;
  };
  
  static bool flush_busy_ctx(struct sbitmap *sb, unsigned int bitnr, void *data)
  {
  	struct flush_busy_ctx_data *flush_data = data;
  	struct blk_mq_hw_ctx *hctx = flush_data->hctx;
  	struct blk_mq_ctx *ctx = hctx->ctxs[bitnr];
  	enum hctx_type type = hctx->type;
  
  	spin_lock(&ctx->lock);
  	list_splice_tail_init(&ctx->rq_lists[type], flush_data->list);
  	sbitmap_clear_bit(sb, bitnr);
  	spin_unlock(&ctx->lock);
  	return true;
  }
  
  /*
   * Process software queues that have been marked busy, splicing them
   * to the for-dispatch
   */
  void blk_mq_flush_busy_ctxs(struct blk_mq_hw_ctx *hctx, struct list_head *list)
  {
  	struct flush_busy_ctx_data data = {
  		.hctx = hctx,
  		.list = list,
  	};
  
  	sbitmap_for_each_set(&hctx->ctx_map, flush_busy_ctx, &data);
  }
  EXPORT_SYMBOL_GPL(blk_mq_flush_busy_ctxs);
  
  struct dispatch_rq_data {
  	struct blk_mq_hw_ctx *hctx;
  	struct request *rq;
  };
  
  static bool dispatch_rq_from_ctx(struct sbitmap *sb, unsigned int bitnr,
  		void *data)
  {
  	struct dispatch_rq_data *dispatch_data = data;
  	struct blk_mq_hw_ctx *hctx = dispatch_data->hctx;
  	struct blk_mq_ctx *ctx = hctx->ctxs[bitnr];
  	enum hctx_type type = hctx->type;
  
  	spin_lock(&ctx->lock);
  	if (!list_empty(&ctx->rq_lists[type])) {
  		dispatch_data->rq = list_entry_rq(ctx->rq_lists[type].next);
  		list_del_init(&dispatch_data->rq->queuelist);
  		if (list_empty(&ctx->rq_lists[type]))
  			sbitmap_clear_bit(sb, bitnr);
  	}
  	spin_unlock(&ctx->lock);
  
  	return !dispatch_data->rq;
  }
  
  struct request *blk_mq_dequeue_from_ctx(struct blk_mq_hw_ctx *hctx,
  					struct blk_mq_ctx *start)
  {
  	unsigned off = start ? start->index_hw[hctx->type] : 0;
  	struct dispatch_rq_data data = {
  		.hctx = hctx,
  		.rq   = NULL,
  	};
  
  	__sbitmap_for_each_set(&hctx->ctx_map, off,
  			       dispatch_rq_from_ctx, &data);
  
  	return data.rq;
  }
  
  static inline unsigned int queued_to_index(unsigned int queued)
  {
  	if (!queued)
  		return 0;
  
  	return min(BLK_MQ_MAX_DISPATCH_ORDER - 1, ilog2(queued) + 1);
  }
  
  bool blk_mq_get_driver_tag(struct request *rq)
  {
  	struct blk_mq_alloc_data data = {
  		.q = rq->q,
  		.hctx = rq->mq_hctx,
  		.flags = BLK_MQ_REQ_NOWAIT,
  		.cmd_flags = rq->cmd_flags,
  	};
  	bool shared;
  
  	if (rq->tag != -1)
  		goto done;
  
  	if (blk_mq_tag_is_reserved(data.hctx->sched_tags, rq->internal_tag))
  		data.flags |= BLK_MQ_REQ_RESERVED;
  
  	shared = blk_mq_tag_busy(data.hctx);
  	rq->tag = blk_mq_get_tag(&data);
  	if (rq->tag >= 0) {
  		if (shared) {
  			rq->rq_flags |= RQF_MQ_INFLIGHT;
  			atomic_inc(&data.hctx->nr_active);
  		}
  		data.hctx->tags->rqs[rq->tag] = rq;
  	}
  
  done:
  	return rq->tag != -1;
  }
  
  static int blk_mq_dispatch_wake(wait_queue_entry_t *wait, unsigned mode,
  				int flags, void *key)
  {
  	struct blk_mq_hw_ctx *hctx;
  
  	hctx = container_of(wait, struct blk_mq_hw_ctx, dispatch_wait);
  
  	spin_lock(&hctx->dispatch_wait_lock);
  	if (!list_empty(&wait->entry)) {
  		struct sbitmap_queue *sbq;
  
  		list_del_init(&wait->entry);
  		sbq = &hctx->tags->bitmap_tags;
  		atomic_dec(&sbq->ws_active);
  	}
  	spin_unlock(&hctx->dispatch_wait_lock);
  
  	blk_mq_run_hw_queue(hctx, true);
  	return 1;
  }
  
  /*
   * Mark us waiting for a tag. For shared tags, this involves hooking us into
   * the tag wakeups. For non-shared tags, we can simply mark us needing a
   * restart. For both cases, take care to check the condition again after
   * marking us as waiting.
   */
  static bool blk_mq_mark_tag_wait(struct blk_mq_hw_ctx *hctx,
  				 struct request *rq)
  {
  	struct sbitmap_queue *sbq = &hctx->tags->bitmap_tags;
  	struct wait_queue_head *wq;
  	wait_queue_entry_t *wait;
  	bool ret;
  
  	if (!(hctx->flags & BLK_MQ_F_TAG_SHARED)) {
  		blk_mq_sched_mark_restart_hctx(hctx);
  
  		/*
  		 * It's possible that a tag was freed in the window between the
  		 * allocation failure and adding the hardware queue to the wait
  		 * queue.
  		 *
  		 * Don't clear RESTART here, someone else could have set it.
  		 * At most this will cost an extra queue run.
  		 */
  		return blk_mq_get_driver_tag(rq);
  	}
  
  	wait = &hctx->dispatch_wait;
  	if (!list_empty_careful(&wait->entry))
  		return false;
  
  	wq = &bt_wait_ptr(sbq, hctx)->wait;
  
  	spin_lock_irq(&wq->lock);
  	spin_lock(&hctx->dispatch_wait_lock);
  	if (!list_empty(&wait->entry)) {
  		spin_unlock(&hctx->dispatch_wait_lock);
  		spin_unlock_irq(&wq->lock);
  		return false;
  	}
  
  	atomic_inc(&sbq->ws_active);
  	wait->flags &= ~WQ_FLAG_EXCLUSIVE;
  	__add_wait_queue(wq, wait);
  
  	/*
  	 * It's possible that a tag was freed in the window between the
  	 * allocation failure and adding the hardware queue to the wait
  	 * queue.
  	 */
  	ret = blk_mq_get_driver_tag(rq);
  	if (!ret) {
  		spin_unlock(&hctx->dispatch_wait_lock);
  		spin_unlock_irq(&wq->lock);
  		return false;
  	}
  
  	/*
  	 * We got a tag, remove ourselves from the wait queue to ensure
  	 * someone else gets the wakeup.
  	 */
  	list_del_init(&wait->entry);
  	atomic_dec(&sbq->ws_active);
  	spin_unlock(&hctx->dispatch_wait_lock);
  	spin_unlock_irq(&wq->lock);
  
  	return true;
  }
  
  #define BLK_MQ_DISPATCH_BUSY_EWMA_WEIGHT  8
  #define BLK_MQ_DISPATCH_BUSY_EWMA_FACTOR  4
  /*
   * Update dispatch busy with the Exponential Weighted Moving Average(EWMA):
   * - EWMA is one simple way to compute running average value
   * - weight(7/8 and 1/8) is applied so that it can decrease exponentially
   * - take 4 as factor for avoiding to get too small(0) result, and this
   *   factor doesn't matter because EWMA decreases exponentially
   */
  static void blk_mq_update_dispatch_busy(struct blk_mq_hw_ctx *hctx, bool busy)
  {
  	unsigned int ewma;
  
  	if (hctx->queue->elevator)
  		return;
  
  	ewma = hctx->dispatch_busy;
  
  	if (!ewma && !busy)
  		return;
  
  	ewma *= BLK_MQ_DISPATCH_BUSY_EWMA_WEIGHT - 1;
  	if (busy)
  		ewma += 1 << BLK_MQ_DISPATCH_BUSY_EWMA_FACTOR;
  	ewma /= BLK_MQ_DISPATCH_BUSY_EWMA_WEIGHT;
  
  	hctx->dispatch_busy = ewma;
  }
  
  #define BLK_MQ_RESOURCE_DELAY	3		/* ms units */
  
  /*
   * Returns true if we did some work AND can potentially do more.
   */
  bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
  			     bool got_budget)
  {
  	struct blk_mq_hw_ctx *hctx;
  	struct request *rq, *nxt;
  	bool no_tag = false;
  	int errors, queued;
  	blk_status_t ret = BLK_STS_OK;
  
  	if (list_empty(list))
  		return false;
  
  	WARN_ON(!list_is_singular(list) && got_budget);
  
  	/*
  	 * Now process all the entries, sending them to the driver.
  	 */
  	errors = queued = 0;
  	do {
  		struct blk_mq_queue_data bd;
  
  		rq = list_first_entry(list, struct request, queuelist);
  
  		hctx = rq->mq_hctx;
  		if (!got_budget && !blk_mq_get_dispatch_budget(hctx)) {
  			blk_mq_put_driver_tag(rq);
  			break;
  		}
  
  		if (!blk_mq_get_driver_tag(rq)) {
  			/*
  			 * The initial allocation attempt failed, so we need to
  			 * rerun the hardware queue when a tag is freed. The
  			 * waitqueue takes care of that. If the queue is run
  			 * before we add this entry back on the dispatch list,
  			 * we'll re-run it below.
  			 */
  			if (!blk_mq_mark_tag_wait(hctx, rq)) {
  				blk_mq_put_dispatch_budget(hctx);
  				/*
  				 * For non-shared tags, the RESTART check
  				 * will suffice.
  				 */
  				if (hctx->flags & BLK_MQ_F_TAG_SHARED)
  					no_tag = true;
  				break;
  			}
  		}
  
  		list_del_init(&rq->queuelist);
  
  		bd.rq = rq;
  
  		/*
  		 * Flag last if we have no more requests, or if we have more
  		 * but can't assign a driver tag to it.
  		 */
  		if (list_empty(list))
  			bd.last = true;
  		else {
  			nxt = list_first_entry(list, struct request, queuelist);
  			bd.last = !blk_mq_get_driver_tag(nxt);
  		}
  
  		ret = q->mq_ops->queue_rq(hctx, &bd);
  		if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE) {
  			/*
  			 * If an I/O scheduler has been configured and we got a
  			 * driver tag for the next request already, free it
  			 * again.
  			 */
  			if (!list_empty(list)) {
  				nxt = list_first_entry(list, struct request, queuelist);
  				blk_mq_put_driver_tag(nxt);
  			}
  			list_add(&rq->queuelist, list);
  			__blk_mq_requeue_request(rq);
  			break;
  		}
  
  		if (unlikely(ret != BLK_STS_OK)) {
  			errors++;
  			blk_mq_end_request(rq, BLK_STS_IOERR);
  			continue;
  		}
  
  		queued++;
  	} while (!list_empty(list));
  
  	hctx->dispatched[queued_to_index(queued)]++;
  
  	/*
  	 * Any items that need requeuing? Stuff them into hctx->dispatch,
  	 * that is where we will continue on next queue run.
  	 */
  	if (!list_empty(list)) {
  		bool needs_restart;
  
  		/*
  		 * If we didn't flush the entire list, we could have told
  		 * the driver there was more coming, but that turned out to
  		 * be a lie.
  		 */
  		if (q->mq_ops->commit_rqs)
  			q->mq_ops->commit_rqs(hctx);
  
  		spin_lock(&hctx->lock);
  		list_splice_tail_init(list, &hctx->dispatch);
  		spin_unlock(&hctx->lock);
  
  		/*
  		 * Order adding requests to hctx->dispatch and checking
  		 * SCHED_RESTART flag. The pair of this smp_mb() is the one
  		 * in blk_mq_sched_restart(). Avoid restart code path to
  		 * miss the new added requests to hctx->dispatch, meantime
  		 * SCHED_RESTART is observed here.
  		 */
  		smp_mb();
  
  		/*
  		 * If SCHED_RESTART was set by the caller of this function and
  		 * it is no longer set that means that it was cleared by another
  		 * thread and hence that a queue rerun is needed.
  		 *
  		 * If 'no_tag' is set, that means that we failed getting
  		 * a driver tag with an I/O scheduler attached. If our dispatch
  		 * waitqueue is no longer active, ensure that we run the queue
  		 * AFTER adding our entries back to the list.
  		 *
  		 * If no I/O scheduler has been configured it is possible that
  		 * the hardware queue got stopped and restarted before requests
  		 * were pushed back onto the dispatch list. Rerun the queue to
  		 * avoid starvation. Notes:
  		 * - blk_mq_run_hw_queue() checks whether or not a queue has
  		 *   been stopped before rerunning a queue.
  		 * - Some but not all block drivers stop a queue before
  		 *   returning BLK_STS_RESOURCE. Two exceptions are scsi-mq
  		 *   and dm-rq.
  		 *
  		 * If driver returns BLK_STS_RESOURCE and SCHED_RESTART
  		 * bit is set, run queue after a delay to avoid IO stalls
  		 * that could otherwise occur if the queue is idle.
  		 */
  		needs_restart = blk_mq_sched_needs_restart(hctx);
  		if (!needs_restart ||
  		    (no_tag && list_empty_careful(&hctx->dispatch_wait.entry)))
  			blk_mq_run_hw_queue(hctx, true);
  		else if (needs_restart && (ret == BLK_STS_RESOURCE))
  			blk_mq_delay_run_hw_queue(hctx, BLK_MQ_RESOURCE_DELAY);
  
  		blk_mq_update_dispatch_busy(hctx, true);
  		return false;
  	} else
  		blk_mq_update_dispatch_busy(hctx, false);
  
  	/*
  	 * If the host/device is unable to accept more work, inform the
  	 * caller of that.
  	 */
  	if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE)
  		return false;
  
  	return (queued + errors) != 0;
  }
  
  static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
  {
  	int srcu_idx;
  
  	/*
  	 * We should be running this queue from one of the CPUs that
  	 * are mapped to it.
  	 *
  	 * There are at least two related races now between setting
  	 * hctx->next_cpu from blk_mq_hctx_next_cpu() and running
  	 * __blk_mq_run_hw_queue():
  	 *
  	 * - hctx->next_cpu is found offline in blk_mq_hctx_next_cpu(),
  	 *   but later it becomes online, then this warning is harmless
  	 *   at all
  	 *
  	 * - hctx->next_cpu is found online in blk_mq_hctx_next_cpu(),
  	 *   but later it becomes offline, then the warning can't be
  	 *   triggered, and we depend on blk-mq timeout handler to
  	 *   handle dispatched requests to this hctx
  	 */
  	if (!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask) &&
  		cpu_online(hctx->next_cpu)) {
  		printk(KERN_WARNING "run queue from wrong CPU %d, hctx %s\n",
  			raw_smp_processor_id(),
  			cpumask_empty(hctx->cpumask) ? "inactive": "active");
  		dump_stack();
  	}
  
  	/*
  	 * We can't run the queue inline with ints disabled. Ensure that
  	 * we catch bad users of this early.
  	 */
  	WARN_ON_ONCE(in_interrupt());
  
  	might_sleep_if(hctx->flags & BLK_MQ_F_BLOCKING);
  
  	hctx_lock(hctx, &srcu_idx);
  	blk_mq_sched_dispatch_requests(hctx);
  	hctx_unlock(hctx, srcu_idx);
  }
  
  static inline int blk_mq_first_mapped_cpu(struct blk_mq_hw_ctx *hctx)
  {
  	int cpu = cpumask_first_and(hctx->cpumask, cpu_online_mask);
  
  	if (cpu >= nr_cpu_ids)
  		cpu = cpumask_first(hctx->cpumask);
  	return cpu;
  }
  
  /*
   * 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)
  {
  	bool tried = false;
  	int next_cpu = hctx->next_cpu;
  
  	if (hctx->queue->nr_hw_queues == 1)
  		return WORK_CPU_UNBOUND;
  
  	if (--hctx->next_cpu_batch <= 0) {
  select_cpu:
  		next_cpu = cpumask_next_and(next_cpu, hctx->cpumask,
  				cpu_online_mask);
  		if (next_cpu >= nr_cpu_ids)
  			next_cpu = blk_mq_first_mapped_cpu(hctx);
  		hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;
  	}
  
  	/*
  	 * Do unbound schedule if we can't find a online CPU for this hctx,
  	 * and it should only happen in the path of handling CPU DEAD.
  	 */
  	if (!cpu_online(next_cpu)) {
  		if (!tried) {
  			tried = true;
  			goto select_cpu;
  		}
  
  		/*
  		 * Make sure to re-select CPU next time once after CPUs
  		 * in hctx->cpumask become online again.
  		 */
  		hctx->next_cpu = next_cpu;
  		hctx->next_cpu_batch = 1;
  		return WORK_CPU_UNBOUND;
  	}
  
  	hctx->next_cpu = next_cpu;
  	return next_cpu;
  }
  
  static void __blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async,
  					unsigned long msecs)
  {
  	if (unlikely(blk_mq_hctx_stopped(hctx)))
  		return;
  
  	if (!async && !(hctx->flags & BLK_MQ_F_BLOCKING)) {
  		int cpu = get_cpu();
  		if (cpumask_test_cpu(cpu, hctx->cpumask)) {
  			__blk_mq_run_hw_queue(hctx);
  			put_cpu();
  			return;
  		}
  
  		put_cpu();
  	}
  
  	kblockd_mod_delayed_work_on(blk_mq_hctx_next_cpu(hctx), &hctx->run_work,
  				    msecs_to_jiffies(msecs));
  }
  
  void blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs)
  {
  	__blk_mq_delay_run_hw_queue(hctx, true, msecs);
  }
  EXPORT_SYMBOL(blk_mq_delay_run_hw_queue);
  
  bool blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async)
  {
  	int srcu_idx;
  	bool need_run;
  
  	/*
  	 * When queue is quiesced, we may be switching io scheduler, or
  	 * updating nr_hw_queues, or other things, and we can't run queue
  	 * any more, even __blk_mq_hctx_has_pending() can't be called safely.
  	 *
  	 * And queue will be rerun in blk_mq_unquiesce_queue() if it is
  	 * quiesced.
  	 */
  	hctx_lock(hctx, &srcu_idx);
  	need_run = !blk_queue_quiesced(hctx->queue) &&
  		blk_mq_hctx_has_pending(hctx);
  	hctx_unlock(hctx, srcu_idx);
  
  	if (need_run) {
  		__blk_mq_delay_run_hw_queue(hctx, async, 0);
  		return true;
  	}
  
  	return false;
  }
  EXPORT_SYMBOL(blk_mq_run_hw_queue);
  
  void blk_mq_run_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 (blk_mq_hctx_stopped(hctx))
  			continue;
  
  		blk_mq_run_hw_queue(hctx, async);
  	}
  }
  EXPORT_SYMBOL(blk_mq_run_hw_queues);
  
  /**
   * blk_mq_queue_stopped() - check whether one or more hctxs have been stopped
   * @q: request queue.
   *
   * The caller is responsible for serializing this function against
   * blk_mq_{start,stop}_hw_queue().
   */
  bool blk_mq_queue_stopped(struct request_queue *q)
  {
  	struct blk_mq_hw_ctx *hctx;
  	int i;
  
  	queue_for_each_hw_ctx(q, hctx, i)
  		if (blk_mq_hctx_stopped(hctx))
  			return true;
  
  	return false;
  }
  EXPORT_SYMBOL(blk_mq_queue_stopped);
  
  /*
   * This function is often used for pausing .queue_rq() by driver when
   * there isn't enough resource or some conditions aren't satisfied, and
   * BLK_STS_RESOURCE is usually returned.
   *
   * We do not guarantee that dispatch can be drained or blocked
   * after blk_mq_stop_hw_queue() returns. Please use
   * blk_mq_quiesce_queue() for that requirement.
   */
  void blk_mq_stop_hw_queue(struct blk_mq_hw_ctx *hctx)
  {
  	cancel_delayed_work(&hctx->run_work);
  
  	set_bit(BLK_MQ_S_STOPPED, &hctx->state);
  }
  EXPORT_SYMBOL(blk_mq_stop_hw_queue);
  
  /*
   * This function is often used for pausing .queue_rq() by driver when
   * there isn't enough resource or some conditions aren't satisfied, and
   * BLK_STS_RESOURCE is usually returned.
   *
   * We do not guarantee that dispatch can be drained or blocked
   * after blk_mq_stop_hw_queues() returns. Please use
   * blk_mq_quiesce_queue() for that requirement.
   */
  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, false);
  }
  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_queue(struct blk_mq_hw_ctx *hctx, bool async)
  {
  	if (!blk_mq_hctx_stopped(hctx))
  		return;
  
  	clear_bit(BLK_MQ_S_STOPPED, &hctx->state);
  	blk_mq_run_hw_queue(hctx, async);
  }
  EXPORT_SYMBOL_GPL(blk_mq_start_stopped_hw_queue);
  
  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)
  		blk_mq_start_stopped_hw_queue(hctx, async);
  }
  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);
  
  	/*
  	 * If we are stopped, don't run the queue.
  	 */
  	if (test_bit(BLK_MQ_S_STOPPED, &hctx->state))
  		return;
  
  	__blk_mq_run_hw_queue(hctx);
  }
  
  static inline void __blk_mq_insert_req_list(struct blk_mq_hw_ctx *hctx,
  					    struct request *rq,
  					    bool at_head)
  {
  	struct blk_mq_ctx *ctx = rq->mq_ctx;
  	enum hctx_type type = hctx->type;
  
  	lockdep_assert_held(&ctx->lock);
  
  	trace_block_rq_insert(hctx->queue, rq);
  
  	if (at_head)
  		list_add(&rq->queuelist, &ctx->rq_lists[type]);
  	else
  		list_add_tail(&rq->queuelist, &ctx->rq_lists[type]);
  }
  
  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;
  
  	lockdep_assert_held(&ctx->lock);
  
  	__blk_mq_insert_req_list(hctx, rq, at_head);
  	blk_mq_hctx_mark_pending(hctx, ctx);
  }
  
  /*
   * Should only be used carefully, when the caller knows we want to
   * bypass a potential IO scheduler on the target device.
   */
  void blk_mq_request_bypass_insert(struct request *rq, bool at_head,
  				  bool run_queue)
  {
  	struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
  
  	spin_lock(&hctx->lock);
  	if (at_head)
  		list_add(&rq->queuelist, &hctx->dispatch);
  	else
  		list_add_tail(&rq->queuelist, &hctx->dispatch);
  	spin_unlock(&hctx->lock);
  
  	if (run_queue)
  		blk_mq_run_hw_queue(hctx, false);
  }
  
  void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
  			    struct list_head *list)
  
  {
  	struct request *rq;
  	enum hctx_type type = hctx->type;
  
  	/*
  	 * preemption doesn't flush plug list, so it's possible ctx->cpu is
  	 * offline now
  	 */
  	list_for_each_entry(rq, list, queuelist) {
  		BUG_ON(rq->mq_ctx != ctx);
  		trace_block_rq_insert(hctx->queue, rq);
  	}
  
  	spin_lock(&ctx->lock);
  	list_splice_tail_init(list, &ctx->rq_lists[type]);
  	blk_mq_hctx_mark_pending(hctx, ctx);
  	spin_unlock(&ctx->lock);
  }
  
  static int plug_rq_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);
  
  	if (rqa->mq_ctx < rqb->mq_ctx)
  		return -1;
  	else if (rqa->mq_ctx > rqb->mq_ctx)
  		return 1;
  	else if (rqa->mq_hctx < rqb->mq_hctx)
  		return -1;
  	else if (rqa->mq_hctx > rqb->mq_hctx)
  		return 1;
  
  	return blk_rq_pos(rqa) > blk_rq_pos(rqb);
  }
  
  void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
  {
  	struct blk_mq_hw_ctx *this_hctx;
  	struct blk_mq_ctx *this_ctx;
  	struct request_queue *this_q;
  	struct request *rq;
  	LIST_HEAD(list);
  	LIST_HEAD(rq_list);
  	unsigned int depth;
  
  	list_splice_init(&plug->mq_list, &list);
  
  	if (plug->rq_count > 2 && plug->multiple_queues)
  		list_sort(NULL, &list, plug_rq_cmp);
  
  	plug->rq_count = 0;
  
  	this_q = NULL;
  	this_hctx = 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_hctx != this_hctx || rq->mq_ctx != this_ctx) {
  			if (this_hctx) {
  				trace_block_unplug(this_q, depth, !from_schedule);
  				blk_mq_sched_insert_requests(this_hctx, this_ctx,
  								&rq_list,
  								from_schedule);
  			}
  
  			this_q = rq->q;
  			this_ctx = rq->mq_ctx;
  			this_hctx = rq->mq_hctx;
  			depth = 0;
  		}
  
  		depth++;
  		list_add_tail(&rq->queuelist, &rq_list);
  	}
  
  	/*
  	 * If 'this_hctx' is set, we know we have entries to complete
  	 * on 'rq_list'. Do those.
  	 */
  	if (this_hctx) {
  		trace_block_unplug(this_q, depth, !from_schedule);
  		blk_mq_sched_insert_requests(this_hctx, this_ctx, &rq_list,
  						from_schedule);
  	}
  }
  
  static void blk_mq_bio_to_request(struct request *rq, struct bio *bio,
  		unsigned int nr_segs)
  {
  	if (bio->bi_opf & REQ_RAHEAD)
  		rq->cmd_flags |= REQ_FAILFAST_MASK;
  
  	rq->__sector = bio->bi_iter.bi_sector;
  	rq->write_hint = bio->bi_write_hint;
  	blk_rq_bio_prep(rq, bio, nr_segs);
  
  	blk_account_io_start(rq, true);
  }
  
  static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
  					    struct request *rq,
  					    blk_qc_t *cookie, bool last)
  {
  	struct request_queue *q = rq->q;
  	struct blk_mq_queue_data bd = {
  		.rq = rq,
  		.last = last,
  	};
  	blk_qc_t new_cookie;
  	blk_status_t ret;
  
  	new_cookie = request_to_qc_t(hctx, rq);
  
  	/*
  	 * For OK queue, we are done. For error, caller may kill it.
  	 * Any other error (busy), just add it to our list as we
  	 * previously would have done.
  	 */
  	ret = q->mq_ops->queue_rq(hctx, &bd);
  	switch (ret) {
  	case BLK_STS_OK:
  		blk_mq_update_dispatch_busy(hctx, false);
  		*cookie = new_cookie;
  		break;
  	case BLK_STS_RESOURCE:
  	case BLK_STS_DEV_RESOURCE:
  		blk_mq_update_dispatch_busy(hctx, true);
  		__blk_mq_requeue_request(rq);
  		break;
  	default:
  		blk_mq_update_dispatch_busy(hctx, false);
  		*cookie = BLK_QC_T_NONE;
  		break;
  	}
  
  	return ret;
  }
  
  static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
  						struct request *rq,
  						blk_qc_t *cookie,
  						bool bypass_insert, bool last)
  {
  	struct request_queue *q = rq->q;
  	bool run_queue = true;
  
  	/*
  	 * RCU or SRCU read lock is needed before checking quiesced flag.
  	 *
  	 * When queue is stopped or quiesced, ignore 'bypass_insert' from
  	 * blk_mq_request_issue_directly(), and return BLK_STS_OK to caller,
  	 * and avoid driver to try to dispatch again.
  	 */
  	if (blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)) {
  		run_queue = false;
  		bypass_insert = false;
  		goto insert;
  	}
  
  	if (q->elevator && !bypass_insert)
  		goto insert;
  
  	if (!blk_mq_get_dispatch_budget(hctx))
  		goto insert;
  
  	if (!blk_mq_get_driver_tag(rq)) {
  		blk_mq_put_dispatch_budget(hctx);
  		goto insert;
  	}
  
  	return __blk_mq_issue_directly(hctx, rq, cookie, last);
  insert:
  	if (bypass_insert)
  		return BLK_STS_RESOURCE;
  
  	blk_mq_sched_insert_request(rq, false, run_queue, false);
  
  	return BLK_STS_OK;
  }
  
  static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
  		struct request *rq, blk_qc_t *cookie)
  {
  	blk_status_t ret;
  	int srcu_idx;
  
  	might_sleep_if(hctx->flags & BLK_MQ_F_BLOCKING);
  
  	hctx_lock(hctx, &srcu_idx);
  
  	ret = __blk_mq_try_issue_directly(hctx, rq, cookie, false, true);
  	if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE)
  		blk_mq_request_bypass_insert(rq, false, true);
  	else if (ret != BLK_STS_OK)
  		blk_mq_end_request(rq, ret);
  
  	hctx_unlock(hctx, srcu_idx);
  }
  
  blk_status_t blk_mq_request_issue_directly(struct request *rq, bool last)
  {
  	blk_status_t ret;
  	int srcu_idx;
  	blk_qc_t unused_cookie;
  	struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
  
  	hctx_lock(hctx, &srcu_idx);
  	ret = __blk_mq_try_issue_directly(hctx, rq, &unused_cookie, true, last);
  	hctx_unlock(hctx, srcu_idx);
  
  	return ret;
  }
  
  void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
  		struct list_head *list)
  {
  	while (!list_empty(list)) {
  		blk_status_t ret;
  		struct request *rq = list_first_entry(list, struct request,
  				queuelist);
  
  		list_del_init(&rq->queuelist);
  		ret = blk_mq_request_issue_directly(rq, list_empty(list));
  		if (ret != BLK_STS_OK) {
  			if (ret == BLK_STS_RESOURCE ||
  					ret == BLK_STS_DEV_RESOURCE) {
  				blk_mq_request_bypass_insert(rq, false,
  							list_empty(list));
  				break;
  			}
  			blk_mq_end_request(rq, ret);
  		}
  	}
  
  	/*
  	 * If we didn't flush the entire list, we could have told
  	 * the driver there was more coming, but that turned out to
  	 * be a lie.
  	 */
  	if (!list_empty(list) && hctx->queue->mq_ops->commit_rqs)
  		hctx->queue->mq_ops->commit_rqs(hctx);
  }
  
  static void blk_add_rq_to_plug(struct blk_plug *plug, struct request *rq)
  {
  	list_add_tail(&rq->queuelist, &plug->mq_list);
  	plug->rq_count++;
  	if (!plug->multiple_queues && !list_is_singular(&plug->mq_list)) {
  		struct request *tmp;
  
  		tmp = list_first_entry(&plug->mq_list, struct request,
  						queuelist);
  		if (tmp->q != rq->q)
  			plug->multiple_queues = true;
  	}
  }
  
  static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
  {
  	const int is_sync = op_is_sync(bio->bi_opf);
  	const int is_flush_fua = op_is_flush(bio->bi_opf);
  	struct blk_mq_alloc_data data = { .flags = 0};
  	struct request *rq;
  	struct blk_plug *plug;
  	struct request *same_queue_rq = NULL;
  	unsigned int nr_segs;
  	blk_qc_t cookie;
  
  	blk_queue_bounce(q, &bio);
  	__blk_queue_split(q, &bio, &nr_segs);
  
  	if (!bio_integrity_prep(bio))
  		return BLK_QC_T_NONE;
  
  	if (!is_flush_fua && !blk_queue_nomerges(q) &&
  	    blk_attempt_plug_merge(q, bio, nr_segs, &same_queue_rq))
  		return BLK_QC_T_NONE;
  
  	if (blk_mq_sched_bio_merge(q, bio, nr_segs))
  		return BLK_QC_T_NONE;
  
  	rq_qos_throttle(q, bio);
  
  	data.cmd_flags = bio->bi_opf;
  	rq = blk_mq_get_request(q, bio, &data);
  	if (unlikely(!rq)) {
  		rq_qos_cleanup(q, bio);
  		if (bio->bi_opf & REQ_NOWAIT)
  			bio_wouldblock_error(bio);
  		return BLK_QC_T_NONE;
  	}
  
  	trace_block_getrq(q, bio, bio->bi_opf);
  
  	rq_qos_track(q, rq, bio);
  
  	cookie = request_to_qc_t(data.hctx, rq);
  
  	blk_mq_bio_to_request(rq, bio, nr_segs);
  
  	plug = blk_mq_plug(q, bio);
  	if (unlikely(is_flush_fua)) {
  		/* bypass scheduler for flush rq */
  		blk_insert_flush(rq);
  		blk_mq_run_hw_queue(data.hctx, true);
  	} else if (plug && (q->nr_hw_queues == 1 || q->mq_ops->commit_rqs ||
  				!blk_queue_nonrot(q))) {
  		/*
  		 * Use plugging if we have a ->commit_rqs() hook as well, as
  		 * we know the driver uses bd->last in a smart fashion.
  		 *
  		 * Use normal plugging if this disk is slow HDD, as sequential
  		 * IO may benefit a lot from plug merging.
  		 */
  		unsigned int request_count = plug->rq_count;
  		struct request *last = NULL;
  
  		if (!request_count)
  			trace_block_plug(q);
  		else
  			last = list_entry_rq(plug->mq_list.prev);
  
  		if (request_count >= BLK_MAX_REQUEST_COUNT || (last &&
  		    blk_rq_bytes(last) >= BLK_PLUG_FLUSH_SIZE)) {
  			blk_flush_plug_list(plug, false);
  			trace_block_plug(q);
  		}
  
  		blk_add_rq_to_plug(plug, rq);
  	} else if (q->elevator) {
  		blk_mq_sched_insert_request(rq, false, true, true);
  	} else if (plug && !blk_queue_nomerges(q)) {
  		/*
  		 * We do limited plugging. If the bio can be merged, do that.
  		 * Otherwise the existing request in the plug list will be
  		 * issued. So the plug list will have one request at most
  		 * The plug list might get flushed before this. If that happens,
  		 * the plug list is empty, and same_queue_rq is invalid.
  		 */
  		if (list_empty(&plug->mq_list))
  			same_queue_rq = NULL;
  		if (same_queue_rq) {
  			list_del_init(&same_queue_rq->queuelist);
  			plug->rq_count--;
  		}
  		blk_add_rq_to_plug(plug, rq);
  		trace_block_plug(q);
  
  		if (same_queue_rq) {
  			data.hctx = same_queue_rq->mq_hctx;
  			trace_block_unplug(q, 1, true);
  			blk_mq_try_issue_directly(data.hctx, same_queue_rq,
  					&cookie);
  		}
  	} else if ((q->nr_hw_queues > 1 && is_sync) ||
  			!data.hctx->dispatch_busy) {
  		blk_mq_try_issue_directly(data.hctx, rq, &cookie);
  	} else {
  		blk_mq_sched_insert_request(rq, false, true, true);
  	}
  
  	return cookie;
  }
  
  void blk_mq_free_rqs(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++) {
  			struct request *rq = tags->static_rqs[i];
  
  			if (!rq)
  				continue;
  			set->ops->exit_request(set, rq, hctx_idx);
  			tags->static_rqs[i] = NULL;
  		}
  	}
  
  	while (!list_empty(&tags->page_list)) {
  		page = list_first_entry(&tags->page_list, struct page, lru);
  		list_del_init(&page->lru);
  		/*
  		 * Remove kmemleak object previously allocated in
  		 * blk_mq_alloc_rqs().
  		 */
  		kmemleak_free(page_address(page));
  		__free_pages(page, page->private);
  	}
  }
  
  void blk_mq_free_rq_map(struct blk_mq_tags *tags)
  {
  	kfree(tags->rqs);
  	tags->rqs = NULL;
  	kfree(tags->static_rqs);
  	tags->static_rqs = NULL;
  
  	blk_mq_free_tags(tags);
  }
  
  struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set,
  					unsigned int hctx_idx,
  					unsigned int nr_tags,
  					unsigned int reserved_tags)
  {
  	struct blk_mq_tags *tags;
  	int node;
  
  	node = blk_mq_hw_queue_to_node(&set->map[HCTX_TYPE_DEFAULT], hctx_idx);
  	if (node == NUMA_NO_NODE)
  		node = set->numa_node;
  
  	tags = blk_mq_init_tags(nr_tags, reserved_tags, node,
  				BLK_MQ_FLAG_TO_ALLOC_POLICY(set->flags));
  	if (!tags)
  		return NULL;
  
  	tags->rqs = kcalloc_node(nr_tags, sizeof(struct request *),
  				 GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY,
  				 node);
  	if (!tags->rqs) {
  		blk_mq_free_tags(tags);
  		return NULL;
  	}
  
  	tags->static_rqs = kcalloc_node(nr_tags, sizeof(struct request *),
  					GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY,
  					node);
  	if (!tags->static_rqs) {
  		kfree(tags->rqs);
  		blk_mq_free_tags(tags);
  		return NULL;
  	}
  
  	return tags;
  }
  
  static size_t order_to_size(unsigned int order)
  {
  	return (size_t)PAGE_SIZE << order;
  }
  
  static int blk_mq_init_request(struct blk_mq_tag_set *set, struct request *rq,
  			       unsigned int hctx_idx, int node)
  {
  	int ret;
  
  	if (set->ops->init_request) {
  		ret = set->ops->init_request(set, rq, hctx_idx, node);
  		if (ret)
  			return ret;
  	}
  
  	WRITE_ONCE(rq->state, MQ_RQ_IDLE);
  	return 0;
  }
  
  int blk_mq_alloc_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags,
  		     unsigned int hctx_idx, unsigned int depth)
  {
  	unsigned int i, j, entries_per_page, max_order = 4;
  	size_t rq_size, left;
  	int node;
  
  	node = blk_mq_hw_queue_to_node(&set->map[HCTX_TYPE_DEFAULT], hctx_idx);
  	if (node == NUMA_NO_NODE)
  		node = set->numa_node;
  
  	INIT_LIST_HEAD(&tags->page_list);
  
  	/*
  	 * 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 * depth;
  
  	for (i = 0; i < depth; ) {
  		int this_order = max_order;
  		struct page *page;
  		int to_do;
  		void *p;
  
  		while (this_order && left < order_to_size(this_order - 1))
  			this_order--;
  
  		do {
  			page = alloc_pages_node(node,
  				GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY | __GFP_ZERO,
  				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);
  		/*
  		 * Allow kmemleak to scan these pages as they contain pointers
  		 * to additional allocations like via ops->init_request().
  		 */
  		kmemleak_alloc(p, order_to_size(this_order), 1, GFP_NOIO);
  		entries_per_page = order_to_size(this_order) / rq_size;
  		to_do = min(entries_per_page, depth - i);
  		left -= to_do * rq_size;
  		for (j = 0; j < to_do; j++) {
  			struct request *rq = p;
  
  			tags->static_rqs[i] = rq;
  			if (blk_mq_init_request(set, rq, hctx_idx, node)) {
  				tags->static_rqs[i] = NULL;
  				goto fail;
  			}
  
  			p += rq_size;
  			i++;
  		}
  	}
  	return 0;
  
  fail:
  	blk_mq_free_rqs(set, tags, hctx_idx);
  	return -ENOMEM;
  }
  
  /*
   * 'cpu' is going away. splice any existing rq_list entries from this
   * software queue to the hw queue dispatch list, and ensure that it
   * gets run.
   */
  static int blk_mq_hctx_notify_dead(unsigned int cpu, struct hlist_node *node)
  {
  	struct blk_mq_hw_ctx *hctx;
  	struct blk_mq_ctx *ctx;
  	LIST_HEAD(tmp);
  	enum hctx_type type;
  
  	hctx = hlist_entry_safe(node, struct blk_mq_hw_ctx, cpuhp_dead);
  	ctx = __blk_mq_get_ctx(hctx->queue, cpu);
  	type = hctx->type;
  
  	spin_lock(&ctx->lock);
  	if (!list_empty(&ctx->rq_lists[type])) {
  		list_splice_init(&ctx->rq_lists[type], &tmp);
  		blk_mq_hctx_clear_pending(hctx, ctx);
  	}
  	spin_unlock(&ctx->lock);
  
  	if (list_empty(&tmp))
  		return 0;
  
  	spin_lock(&hctx->lock);
  	list_splice_tail_init(&tmp, &hctx->dispatch);
  	spin_unlock(&hctx->lock);
  
  	blk_mq_run_hw_queue(hctx, true);
  	return 0;
  }
  
  static void blk_mq_remove_cpuhp(struct blk_mq_hw_ctx *hctx)
  {
  	cpuhp_state_remove_instance_nocalls(CPUHP_BLK_MQ_DEAD,
  					    &hctx->cpuhp_dead);
  }
  
  /* hctx->ctxs will be freed in queue's release handler */
  static void blk_mq_exit_hctx(struct request_queue *q,
  		struct blk_mq_tag_set *set,
  		struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
  {
  	if (blk_mq_hw_queue_mapped(hctx))
  		blk_mq_tag_idle(hctx);
  
  	if (set->ops->exit_request)
  		set->ops->exit_request(set, hctx->fq->flush_rq, hctx_idx);
  
  	if (set->ops->exit_hctx)
  		set->ops->exit_hctx(hctx, hctx_idx);
  
  	blk_mq_remove_cpuhp(hctx);
  
  	spin_lock(&q->unused_hctx_lock);
  	list_add(&hctx->hctx_list, &q->unused_hctx_list);
  	spin_unlock(&q->unused_hctx_lock);
  }
  
  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_debugfs_unregister_hctx(hctx);
  		blk_mq_exit_hctx(q, set, hctx, i);
  	}
  }
  
  static int blk_mq_hw_ctx_size(struct blk_mq_tag_set *tag_set)
  {
  	int hw_ctx_size = sizeof(struct blk_mq_hw_ctx);
  
  	BUILD_BUG_ON(ALIGN(offsetof(struct blk_mq_hw_ctx, srcu),
  			   __alignof__(struct blk_mq_hw_ctx)) !=
  		     sizeof(struct blk_mq_hw_ctx));
  
  	if (tag_set->flags & BLK_MQ_F_BLOCKING)
  		hw_ctx_size += sizeof(struct srcu_struct);
  
  	return hw_ctx_size;
  }
  
  static int blk_mq_init_hctx(struct request_queue *q,
  		struct blk_mq_tag_set *set,
  		struct blk_mq_hw_ctx *hctx, unsigned hctx_idx)
  {
  	hctx->queue_num = hctx_idx;
  
  	cpuhp_state_add_instance_nocalls(CPUHP_BLK_MQ_DEAD, &hctx->cpuhp_dead);
  
  	hctx->tags = set->tags[hctx_idx];
  
  	if (set->ops->init_hctx &&
  	    set->ops->init_hctx(hctx, set->driver_data, hctx_idx))
  		goto unregister_cpu_notifier;
  
  	if (blk_mq_init_request(set, hctx->fq->flush_rq, hctx_idx,
  				hctx->numa_node))
  		goto exit_hctx;
  	return 0;
  
   exit_hctx:
  	if (set->ops->exit_hctx)
  		set->ops->exit_hctx(hctx, hctx_idx);
   unregister_cpu_notifier:
  	blk_mq_remove_cpuhp(hctx);
  	return -1;
  }
  
  static struct blk_mq_hw_ctx *
  blk_mq_alloc_hctx(struct request_queue *q, struct blk_mq_tag_set *set,
  		int node)
  {
  	struct blk_mq_hw_ctx *hctx;
  	gfp_t gfp = GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY;
  
  	hctx = kzalloc_node(blk_mq_hw_ctx_size(set), gfp, node);
  	if (!hctx)
  		goto fail_alloc_hctx;
  
  	if (!zalloc_cpumask_var_node(&hctx->cpumask, gfp, node))
  		goto free_hctx;
  
  	atomic_set(&hctx->nr_active, 0);
  	if (node == NUMA_NO_NODE)
  		node = set->numa_node;
  	hctx->numa_node = node;
  
  	INIT_DELAYED_WORK(&hctx->run_work, blk_mq_run_work_fn);
  	spin_lock_init(&hctx->lock);
  	INIT_LIST_HEAD(&hctx->dispatch);
  	hctx->queue = q;
  	hctx->flags = set->flags & ~BLK_MQ_F_TAG_SHARED;
  
  	INIT_LIST_HEAD(&hctx->hctx_list);
  
  	/*
  	 * Allocate space for all possible cpus to avoid allocation at
  	 * runtime
  	 */
  	hctx->ctxs = kmalloc_array_node(nr_cpu_ids, sizeof(void *),
  			gfp, node);
  	if (!hctx->ctxs)
  		goto free_cpumask;
  
  	if (sbitmap_init_node(&hctx->ctx_map, nr_cpu_ids, ilog2(8),
  				gfp, node))
  		goto free_ctxs;
  	hctx->nr_ctx = 0;
  
  	spin_lock_init(&hctx->dispatch_wait_lock);
  	init_waitqueue_func_entry(&hctx->dispatch_wait, blk_mq_dispatch_wake);
  	INIT_LIST_HEAD(&hctx->dispatch_wait.entry);
  
  	hctx->fq = blk_alloc_flush_queue(q, hctx->numa_node, set->cmd_size,
  			gfp);
  	if (!hctx->fq)
  		goto free_bitmap;
  
  	if (hctx->flags & BLK_MQ_F_BLOCKING)
  		init_srcu_struct(hctx->srcu);
  	blk_mq_hctx_kobj_init(hctx);
  
  	return hctx;
  
   free_bitmap:
  	sbitmap_free(&hctx->ctx_map);
   free_ctxs:
  	kfree(hctx->ctxs);
   free_cpumask:
  	free_cpumask_var(hctx->cpumask);
   free_hctx:
  	kfree(hctx);
   fail_alloc_hctx:
  	return NULL;
  }
  
  static void blk_mq_init_cpu_queues(struct request_queue *q,
  				   unsigned int nr_hw_queues)
  {
  	struct blk_mq_tag_set *set = q->tag_set;
  	unsigned int i, j;
  
  	for_each_possible_cpu(i) {
  		struct blk_mq_ctx *__ctx = per_cpu_ptr(q->queue_ctx, i);
  		struct blk_mq_hw_ctx *hctx;
  		int k;
  
  		__ctx->cpu = i;
  		spin_lock_init(&__ctx->lock);
  		for (k = HCTX_TYPE_DEFAULT; k < HCTX_MAX_TYPES; k++)
  			INIT_LIST_HEAD(&__ctx->rq_lists[k]);
  
  		__ctx->queue = q;
  
  		/*
  		 * Set local node, IFF we have more than one hw queue. If
  		 * not, we remain on the home node of the device
  		 */
  		for (j = 0; j < set->nr_maps; j++) {
  			hctx = blk_mq_map_queue_type(q, j, i);
  			if (nr_hw_queues > 1 && hctx->numa_node == NUMA_NO_NODE)
  				hctx->numa_node = local_memory_node(cpu_to_node(i));
  		}
  	}
  }
  
  static bool __blk_mq_alloc_rq_map(struct blk_mq_tag_set *set, int hctx_idx)
  {
  	int ret = 0;
  
  	set->tags[hctx_idx] = blk_mq_alloc_rq_map(set, hctx_idx,
  					set->queue_depth, set->reserved_tags);
  	if (!set->tags[hctx_idx])
  		return false;
  
  	ret = blk_mq_alloc_rqs(set, set->tags[hctx_idx], hctx_idx,
  				set->queue_depth);
  	if (!ret)
  		return true;
  
  	blk_mq_free_rq_map(set->tags[hctx_idx]);
  	set->tags[hctx_idx] = NULL;
  	return false;
  }
  
  static void blk_mq_free_map_and_requests(struct blk_mq_tag_set *set,
  					 unsigned int hctx_idx)
  {
  	if (set->tags && set->tags[hctx_idx]) {
  		blk_mq_free_rqs(set, set->tags[hctx_idx], hctx_idx);
  		blk_mq_free_rq_map(set->tags[hctx_idx]);
  		set->tags[hctx_idx] = NULL;
  	}
  }
  
  static void blk_mq_map_swqueue(struct request_queue *q)
  {
  	unsigned int i, j, hctx_idx;
  	struct blk_mq_hw_ctx *hctx;
  	struct blk_mq_ctx *ctx;
  	struct blk_mq_tag_set *set = q->tag_set;
  
  	queue_for_each_hw_ctx(q, hctx, i) {
  		cpumask_clear(hctx->cpumask);
  		hctx->nr_ctx = 0;
  		hctx->dispatch_from = NULL;
  	}
  
  	/*
  	 * Map software to hardware queues.
  	 *
  	 * If the cpu isn't present, the cpu is mapped to first hctx.
  	 */
  	for_each_possible_cpu(i) {
  
  		ctx = per_cpu_ptr(q->queue_ctx, i);
  		for (j = 0; j < set->nr_maps; j++) {
  			if (!set->map[j].nr_queues) {
  				ctx->hctxs[j] = blk_mq_map_queue_type(q,
  						HCTX_TYPE_DEFAULT, i);
  				continue;
  			}
  			hctx_idx = set->map[j].mq_map[i];
  			/* unmapped hw queue can be remapped after CPU topo changed */
  			if (!set->tags[hctx_idx] &&
  			    !__blk_mq_alloc_rq_map(set, hctx_idx)) {
  				/*
  				 * If tags initialization fail for some hctx,
  				 * that hctx won't be brought online.  In this
  				 * case, remap the current ctx to hctx[0] which
  				 * is guaranteed to always have tags allocated
  				 */
  				set->map[j].mq_map[i] = 0;
  			}
  
  			hctx = blk_mq_map_queue_type(q, j, i);
  			ctx->hctxs[j] = hctx;
  			/*
  			 * If the CPU is already set in the mask, then we've
  			 * mapped this one already. This can happen if
  			 * devices share queues across queue maps.
  			 */
  			if (cpumask_test_cpu(i, hctx->cpumask))
  				continue;
  
  			cpumask_set_cpu(i, hctx->cpumask);
  			hctx->type = j;
  			ctx->index_hw[hctx->type] = hctx->nr_ctx;
  			hctx->ctxs[hctx->nr_ctx++] = ctx;
  
  			/*
  			 * If the nr_ctx type overflows, we have exceeded the
  			 * amount of sw queues we can support.
  			 */
  			BUG_ON(!hctx->nr_ctx);
  		}
  
  		for (; j < HCTX_MAX_TYPES; j++)
  			ctx->hctxs[j] = blk_mq_map_queue_type(q,
  					HCTX_TYPE_DEFAULT, i);
  	}
  
  	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) {
  			/* Never unmap queue 0.  We need it as a
  			 * fallback in case of a new remap fails
  			 * allocation
  			 */
  			if (i && set->tags[i])
  				blk_mq_free_map_and_requests(set, i);
  
  			hctx->tags = NULL;
  			continue;
  		}
  
  		hctx->tags = set->tags[i];
  		WARN_ON(!hctx->tags);
  
  		/*
  		 * Set the map size to the number of mapped software queues.
  		 * This is more accurate and more efficient than looping
  		 * over all possibly mapped software queues.
  		 */
  		sbitmap_resize(&hctx->ctx_map, hctx->nr_ctx);
  
  		/*
  		 * Initialize batch roundrobin counts
  		 */
  		hctx->next_cpu = blk_mq_first_mapped_cpu(hctx);
  		hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;
  	}
  }
  
  /*
   * Caller needs to ensure that we're either frozen/quiesced, or that
   * the queue isn't live yet.
   */
  static void queue_set_hctx_shared(struct request_queue *q, bool shared)
  {
  	struct blk_mq_hw_ctx *hctx;
  	int i;
  
  	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;
  	}
  }
  
  static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set,
  					bool shared)
  {
  	struct request_queue *q;
  
  	lockdep_assert_held(&set->tag_list_lock);
  
  	list_for_each_entry(q, &set->tag_list, tag_set_list) {
  		blk_mq_freeze_queue(q);
  		queue_set_hctx_shared(q, 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_rcu(&q->tag_set_list);
  	if (list_is_singular(&set->tag_list)) {
  		/* just transitioned to unshared */
  		set->flags &= ~BLK_MQ_F_TAG_SHARED;
  		/* update existing queue */
  		blk_mq_update_tag_set_depth(set, false);
  	}
  	mutex_unlock(&set->tag_list_lock);
  	INIT_LIST_HEAD(&q->tag_set_list);
  }
  
  static void blk_mq_add_queue_tag_set(struct blk_mq_tag_set *set,
  				     struct request_queue *q)
  {
  	mutex_lock(&set->tag_list_lock);
  
  	/*
  	 * Check to see if we're transitioning to shared (from 1 to 2 queues).
  	 */
  	if (!list_empty(&set->tag_list) &&
  	    !(set->flags & BLK_MQ_F_TAG_SHARED)) {
  		set->flags |= BLK_MQ_F_TAG_SHARED;
  		/* update existing queue */
  		blk_mq_update_tag_set_depth(set, true);
  	}
  	if (set->flags & BLK_MQ_F_TAG_SHARED)
  		queue_set_hctx_shared(q, true);
  	list_add_tail_rcu(&q->tag_set_list, &set->tag_list);
  
  	mutex_unlock(&set->tag_list_lock);
  }
  
  /* All allocations will be freed in release handler of q->mq_kobj */
  static int blk_mq_alloc_ctxs(struct request_queue *q)
  {
  	struct blk_mq_ctxs *ctxs;
  	int cpu;
  
  	ctxs = kzalloc(sizeof(*ctxs), GFP_KERNEL);
  	if (!ctxs)
  		return -ENOMEM;
  
  	ctxs->queue_ctx = alloc_percpu(struct blk_mq_ctx);
  	if (!ctxs->queue_ctx)
  		goto fail;
  
  	for_each_possible_cpu(cpu) {
  		struct blk_mq_ctx *ctx = per_cpu_ptr(ctxs->queue_ctx, cpu);
  		ctx->ctxs = ctxs;
  	}
  
  	q->mq_kobj = &ctxs->kobj;
  	q->queue_ctx = ctxs->queue_ctx;
  
  	return 0;
   fail:
  	kfree(ctxs);
  	return -ENOMEM;
  }
  
  /*
   * It is the actual release handler for mq, but we do it from
   * request queue's release handler for avoiding use-after-free
   * and headache because q->mq_kobj shouldn't have been introduced,
   * but we can't group ctx/kctx kobj without it.
   */
  void blk_mq_release(struct request_queue *q)
  {
  	struct blk_mq_hw_ctx *hctx, *next;
  	int i;
  
  	queue_for_each_hw_ctx(q, hctx, i)
  		WARN_ON_ONCE(hctx && list_empty(&hctx->hctx_list));
  
  	/* all hctx are in .unused_hctx_list now */
  	list_for_each_entry_safe(hctx, next, &q->unused_hctx_list, hctx_list) {
  		list_del_init(&hctx->hctx_list);
  		kobject_put(&hctx->kobj);
  	}
  
  	kfree(q->queue_hw_ctx);
  
  	/*
  	 * release .mq_kobj and sw queue's kobject now because
  	 * both share lifetime with request queue.
  	 */
  	blk_mq_sysfs_deinit(q);
  }
  
  struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *set)
  {
  	struct request_queue *uninit_q, *q;
  
  	uninit_q = blk_alloc_queue_node(GFP_KERNEL, set->numa_node);
  	if (!uninit_q)
  		return ERR_PTR(-ENOMEM);
  
  	/*
  	 * Initialize the queue without an elevator. device_add_disk() will do
  	 * the initialization.
  	 */
  	q = blk_mq_init_allocated_queue(set, uninit_q, false);
  	if (IS_ERR(q))
  		blk_cleanup_queue(uninit_q);
  
  	return q;
  }
  EXPORT_SYMBOL(blk_mq_init_queue);
  
  /*
   * Helper for setting up a queue with mq ops, given queue depth, and
   * the passed in mq ops flags.
   */
  struct request_queue *blk_mq_init_sq_queue(struct blk_mq_tag_set *set,
  					   const struct blk_mq_ops *ops,
  					   unsigned int queue_depth,
  					   unsigned int set_flags)
  {
  	struct request_queue *q;
  	int ret;
  
  	memset(set, 0, sizeof(*set));
  	set->ops = ops;
  	set->nr_hw_queues = 1;
  	set->nr_maps = 1;
  	set->queue_depth = queue_depth;
  	set->numa_node = NUMA_NO_NODE;
  	set->flags = set_flags;
  
  	ret = blk_mq_alloc_tag_set(set);
  	if (ret)
  		return ERR_PTR(ret);
  
  	q = blk_mq_init_queue(set);
  	if (IS_ERR(q)) {
  		blk_mq_free_tag_set(set);
  		return q;
  	}
  
  	return q;
  }
  EXPORT_SYMBOL(blk_mq_init_sq_queue);
  
  static struct blk_mq_hw_ctx *blk_mq_alloc_and_init_hctx(
  		struct blk_mq_tag_set *set, struct request_queue *q,
  		int hctx_idx, int node)
  {
  	struct blk_mq_hw_ctx *hctx = NULL, *tmp;
  
  	/* reuse dead hctx first */
  	spin_lock(&q->unused_hctx_lock);
  	list_for_each_entry(tmp, &q->unused_hctx_list, hctx_list) {
  		if (tmp->numa_node == node) {
  			hctx = tmp;
  			break;
  		}
  	}
  	if (hctx)
  		list_del_init(&hctx->hctx_list);
  	spin_unlock(&q->unused_hctx_lock);
  
  	if (!hctx)
  		hctx = blk_mq_alloc_hctx(q, set, node);
  	if (!hctx)
  		goto fail;
  
  	if (blk_mq_init_hctx(q, set, hctx, hctx_idx))
  		goto free_hctx;
  
  	return hctx;
  
   free_hctx:
  	kobject_put(&hctx->kobj);
   fail:
  	return NULL;
  }
  
  static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set,
  						struct request_queue *q)
  {
  	int i, j, end;
  	struct blk_mq_hw_ctx **hctxs = q->queue_hw_ctx;
  
  	/* protect against switching io scheduler  */
  	mutex_lock(&q->sysfs_lock);
  	for (i = 0; i < set->nr_hw_queues; i++) {
  		int node;
  		struct blk_mq_hw_ctx *hctx;
  
  		node = blk_mq_hw_queue_to_node(&set->map[HCTX_TYPE_DEFAULT], i);
  		/*
  		 * If the hw queue has been mapped to another numa node,
  		 * we need to realloc the hctx. If allocation fails, fallback
  		 * to use the previous one.
  		 */
  		if (hctxs[i] && (hctxs[i]->numa_node == node))
  			continue;
  
  		hctx = blk_mq_alloc_and_init_hctx(set, q, i, node);
  		if (hctx) {
  			if (hctxs[i])
  				blk_mq_exit_hctx(q, set, hctxs[i], i);
  			hctxs[i] = hctx;
  		} else {
  			if (hctxs[i])
  				pr_warn("Allocate new hctx on node %d fails,\
  						fallback to previous one on node %d\n",
  						node, hctxs[i]->numa_node);
  			else
  				break;
  		}
  	}
  	/*
  	 * Increasing nr_hw_queues fails. Free the newly allocated
  	 * hctxs and keep the previous q->nr_hw_queues.
  	 */
  	if (i != set->nr_hw_queues) {
  		j = q->nr_hw_queues;
  		end = i;
  	} else {
  		j = i;
  		end = q->nr_hw_queues;
  		q->nr_hw_queues = set->nr_hw_queues;
  	}
  
  	for (; j < end; j++) {
  		struct blk_mq_hw_ctx *hctx = hctxs[j];
  
  		if (hctx) {
  			if (hctx->tags)
  				blk_mq_free_map_and_requests(set, j);
  			blk_mq_exit_hctx(q, set, hctx, j);
  			hctxs[j] = NULL;
  		}
  	}
  	mutex_unlock(&q->sysfs_lock);
  }
  
  /*
   * Maximum number of hardware queues we support. For single sets, we'll never
   * have more than the CPUs (software queues). For multiple sets, the tag_set
   * user may have set ->nr_hw_queues larger.
   */
  static unsigned int nr_hw_queues(struct blk_mq_tag_set *set)
  {
  	if (set->nr_maps == 1)
  		return nr_cpu_ids;
  
  	return max(set->nr_hw_queues, nr_cpu_ids);
  }
  
  struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
  						  struct request_queue *q,
  						  bool elevator_init)
  {
  	/* mark the queue as mq asap */
  	q->mq_ops = set->ops;
  
  	q->poll_cb = blk_stat_alloc_callback(blk_mq_poll_stats_fn,
  					     blk_mq_poll_stats_bkt,
  					     BLK_MQ_POLL_STATS_BKTS, q);
  	if (!q->poll_cb)
  		goto err_exit;
  
  	if (blk_mq_alloc_ctxs(q))
  		goto err_poll;
  
  	/* init q->mq_kobj and sw queues' kobjects */
  	blk_mq_sysfs_init(q);
  
  	q->nr_queues = nr_hw_queues(set);
  	q->queue_hw_ctx = kcalloc_node(q->nr_queues, sizeof(*(q->queue_hw_ctx)),
  						GFP_KERNEL, set->numa_node);
  	if (!q->queue_hw_ctx)
  		goto err_sys_init;
  
  	INIT_LIST_HEAD(&q->unused_hctx_list);
  	spin_lock_init(&q->unused_hctx_lock);
  
  	blk_mq_realloc_hw_ctxs(set, q);
  	if (!q->nr_hw_queues)
  		goto err_hctxs;
  
  	INIT_WORK(&q->timeout_work, blk_mq_timeout_work);
  	blk_queue_rq_timeout(q, set->timeout ? set->timeout : 30 * HZ);
  
  	q->tag_set = set;
  
  	q->queue_flags |= QUEUE_FLAG_MQ_DEFAULT;
  	if (set->nr_maps > HCTX_TYPE_POLL &&
  	    set->map[HCTX_TYPE_POLL].nr_queues)
  		blk_queue_flag_set(QUEUE_FLAG_POLL, q);
  
  	q->sg_reserved_size = INT_MAX;
  
  	INIT_DELAYED_WORK(&q->requeue_work, blk_mq_requeue_work);
  	INIT_LIST_HEAD(&q->requeue_list);
  	spin_lock_init(&q->requeue_lock);
  
  	blk_queue_make_request(q, blk_mq_make_request);
  
  	/*
  	 * Do this after blk_queue_make_request() overrides it...
  	 */
  	q->nr_requests = set->queue_depth;
  
  	/*
  	 * Default to classic polling
  	 */
  	q->poll_nsec = BLK_MQ_POLL_CLASSIC;
  
  	blk_mq_init_cpu_queues(q, set->nr_hw_queues);
  	blk_mq_add_queue_tag_set(set, q);
  	blk_mq_map_swqueue(q);
  
  	if (elevator_init)
  		elevator_init_mq(q);
  
  	return q;
  
  err_hctxs:
  	kfree(q->queue_hw_ctx);
  	q->nr_hw_queues = 0;
  err_sys_init:
  	blk_mq_sysfs_deinit(q);
  err_poll:
  	blk_stat_free_callback(q->poll_cb);
  	q->poll_cb = NULL;
  err_exit:
  	q->mq_ops = NULL;
  	return ERR_PTR(-ENOMEM);
  }
  EXPORT_SYMBOL(blk_mq_init_allocated_queue);
  
  /* tags can _not_ be used after returning from blk_mq_exit_queue */
  void blk_mq_exit_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);
  }
  
  static int __blk_mq_alloc_rq_maps(struct blk_mq_tag_set *set)
  {
  	int i;
  
  	for (i = 0; i < set->nr_hw_queues; i++)
  		if (!__blk_mq_alloc_rq_map(set, i))
  			goto out_unwind;
  
  	return 0;
  
  out_unwind:
  	while (--i >= 0)
  		blk_mq_free_rq_map(set->tags[i]);
  
  	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;
  }
  
  static int blk_mq_update_queue_map(struct blk_mq_tag_set *set)
  {
  	/*
  	 * blk_mq_map_queues() and multiple .map_queues() implementations
  	 * expect that set->map[HCTX_TYPE_DEFAULT].nr_queues is set to the
  	 * number of hardware queues.
  	 */
  	if (set->nr_maps == 1)
  		set->map[HCTX_TYPE_DEFAULT].nr_queues = set->nr_hw_queues;
  
  	if (set->ops->map_queues && !is_kdump_kernel()) {
  		int i;
  
  		/*
  		 * transport .map_queues is usually done in the following
  		 * way:
  		 *
  		 * for (queue = 0; queue < set->nr_hw_queues; queue++) {
  		 * 	mask = get_cpu_mask(queue)
  		 * 	for_each_cpu(cpu, mask)
  		 * 		set->map[x].mq_map[cpu] = queue;
  		 * }
  		 *
  		 * When we need to remap, the table has to be cleared for
  		 * killing stale mapping since one CPU may not be mapped
  		 * to any hw queue.
  		 */
  		for (i = 0; i < set->nr_maps; i++)
  			blk_mq_clear_mq_map(&set->map[i]);
  
  		return set->ops->map_queues(set);
  	} else {
  		BUG_ON(set->nr_maps > 1);
  		return blk_mq_map_queues(&set->map[HCTX_TYPE_DEFAULT]);
  	}
  }
  
  /*
   * 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 it's 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)
  {
  	int i, ret;
  
  	BUILD_BUG_ON(BLK_MQ_MAX_DEPTH > 1 << BLK_MQ_UNIQUE_TAG_BITS);
  
  	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->ops->queue_rq)
  		return -EINVAL;
  
  	if (!set->ops->get_budget ^ !set->ops->put_budget)
  		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;
  	}
  
  	if (!set->nr_maps)
  		set->nr_maps = 1;
  	else if (set->nr_maps > HCTX_MAX_TYPES)
  		return -EINVAL;
  
  	/*
  	 * If a crashdump is active, then we are potentially in a very
  	 * memory constrained environment. Limit us to 1 queue and
  	 * 64 tags to prevent using too much memory.
  	 */
  	if (is_kdump_kernel()) {
  		set->nr_hw_queues = 1;
  		set->nr_maps = 1;
  		set->queue_depth = min(64U, set->queue_depth);
  	}
  	/*
  	 * There is no use for more h/w queues than cpus if we just have
  	 * a single map
  	 */
  	if (set->nr_maps == 1 && set->nr_hw_queues > nr_cpu_ids)
  		set->nr_hw_queues = nr_cpu_ids;
  
  	set->tags = kcalloc_node(nr_hw_queues(set), sizeof(struct blk_mq_tags *),
  				 GFP_KERNEL, set->numa_node);
  	if (!set->tags)
  		return -ENOMEM;
  
  	ret = -ENOMEM;
  	for (i = 0; i < set->nr_maps; i++) {
  		set->map[i].mq_map = kcalloc_node(nr_cpu_ids,
  						  sizeof(set->map[i].mq_map[0]),
  						  GFP_KERNEL, set->numa_node);
  		if (!set->map[i].mq_map)
  			goto out_free_mq_map;
  		set->map[i].nr_queues = is_kdump_kernel() ? 1 : set->nr_hw_queues;
  	}
  
  	ret = blk_mq_update_queue_map(set);
  	if (ret)
  		goto out_free_mq_map;
  
  	ret = blk_mq_alloc_rq_maps(set);
  	if (ret)
  		goto out_free_mq_map;
  
  	mutex_init(&set->tag_list_lock);
  	INIT_LIST_HEAD(&set->tag_list);
  
  	return 0;
  
  out_free_mq_map:
  	for (i = 0; i < set->nr_maps; i++) {
  		kfree(set->map[i].mq_map);
  		set->map[i].mq_map = NULL;
  	}
  	kfree(set->tags);
  	set->tags = NULL;
  	return ret;
  }
  EXPORT_SYMBOL(blk_mq_alloc_tag_set);
  
  void blk_mq_free_tag_set(struct blk_mq_tag_set *set)
  {
  	int i, j;
  
  	for (i = 0; i < nr_hw_queues(set); i++)
  		blk_mq_free_map_and_requests(set, i);
  
  	for (j = 0; j < set->nr_maps; j++) {
  		kfree(set->map[j].mq_map);
  		set->map[j].mq_map = NULL;
  	}
  
  	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)
  		return -EINVAL;
  
  	if (q->nr_requests == nr)
  		return 0;
  
  	blk_mq_freeze_queue(q);
  	blk_mq_quiesce_queue(q);
  
  	ret = 0;
  	queue_for_each_hw_ctx(q, hctx, i) {
  		if (!hctx->tags)
  			continue;
  		/*
  		 * If we're using an MQ scheduler, just update the scheduler
  		 * queue depth. This is similar to what the old code would do.
  		 */
  		if (!hctx->sched_tags) {
  			ret = blk_mq_tag_update_depth(hctx, &hctx->tags, nr,
  							false);
  		} else {
  			ret = blk_mq_tag_update_depth(hctx, &hctx->sched_tags,
  							nr, true);
  		}
  		if (ret)
  			break;
  		if (q->elevator && q->elevator->type->ops.depth_updated)
  			q->elevator->type->ops.depth_updated(hctx);
  	}
  
  	if (!ret)
  		q->nr_requests = nr;
  
  	blk_mq_unquiesce_queue(q);
  	blk_mq_unfreeze_queue(q);
  
  	return ret;
  }
  
  /*
   * request_queue and elevator_type pair.
   * It is just used by __blk_mq_update_nr_hw_queues to cache
   * the elevator_type associated with a request_queue.
   */
  struct blk_mq_qe_pair {
  	struct list_head node;
  	struct request_queue *q;
  	struct elevator_type *type;
  };
  
  /*
   * Cache the elevator_type in qe pair list and switch the
   * io scheduler to 'none'
   */
  static bool blk_mq_elv_switch_none(struct list_head *head,
  		struct request_queue *q)
  {
  	struct blk_mq_qe_pair *qe;
  
  	if (!q->elevator)
  		return true;
  
  	qe = kmalloc(sizeof(*qe), GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY);
  	if (!qe)
  		return false;
  
  	INIT_LIST_HEAD(&qe->node);
  	qe->q = q;
  	qe->type = q->elevator->type;
  	list_add(&qe->node, head);
  
  	mutex_lock(&q->sysfs_lock);
  	/*
  	 * After elevator_switch_mq, the previous elevator_queue will be
  	 * released by elevator_release. The reference of the io scheduler
  	 * module get by elevator_get will also be put. So we need to get
  	 * a reference of the io scheduler module here to prevent it to be
  	 * removed.
  	 */
  	__module_get(qe->type->elevator_owner);
  	elevator_switch_mq(q, NULL);
  	mutex_unlock(&q->sysfs_lock);
  
  	return true;
  }
  
  static void blk_mq_elv_switch_back(struct list_head *head,
  		struct request_queue *q)
  {
  	struct blk_mq_qe_pair *qe;
  	struct elevator_type *t = NULL;
  
  	list_for_each_entry(qe, head, node)
  		if (qe->q == q) {
  			t = qe->type;
  			break;
  		}
  
  	if (!t)
  		return;
  
  	list_del(&qe->node);
  	kfree(qe);
  
  	mutex_lock(&q->sysfs_lock);
  	elevator_switch_mq(q, t);
  	mutex_unlock(&q->sysfs_lock);
  }
  
  static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
  							int nr_hw_queues)
  {
  	struct request_queue *q;
  	LIST_HEAD(head);
  	int prev_nr_hw_queues;
  
  	lockdep_assert_held(&set->tag_list_lock);
  
  	if (set->nr_maps == 1 && nr_hw_queues > nr_cpu_ids)
  		nr_hw_queues = nr_cpu_ids;
  	if (nr_hw_queues < 1)
  		return;
  	if (set->nr_maps == 1 && nr_hw_queues == set->nr_hw_queues)
  		return;
  
  	list_for_each_entry(q, &set->tag_list, tag_set_list)
  		blk_mq_freeze_queue(q);
  	/*
  	 * Sync with blk_mq_queue_tag_busy_iter.
  	 */
  	synchronize_rcu();
  	/*
  	 * Switch IO scheduler to 'none', cleaning up the data associated
  	 * with the previous scheduler. We will switch back once we are done
  	 * updating the new sw to hw queue mappings.
  	 */
  	list_for_each_entry(q, &set->tag_list, tag_set_list)
  		if (!blk_mq_elv_switch_none(&head, q))
  			goto switch_back;
  
  	list_for_each_entry(q, &set->tag_list, tag_set_list) {
  		blk_mq_debugfs_unregister_hctxs(q);
  		blk_mq_sysfs_unregister(q);
  	}
  
  	prev_nr_hw_queues = set->nr_hw_queues;
  	set->nr_hw_queues = nr_hw_queues;
  fallback:
  	blk_mq_update_queue_map(set);
  	list_for_each_entry(q, &set->tag_list, tag_set_list) {
  		blk_mq_realloc_hw_ctxs(set, q);
  		if (q->nr_hw_queues != set->nr_hw_queues) {
  			pr_warn("Increasing nr_hw_queues to %d fails, fallback to %d\n",
  					nr_hw_queues, prev_nr_hw_queues);
  			set->nr_hw_queues = prev_nr_hw_queues;
  			blk_mq_map_queues(&set->map[HCTX_TYPE_DEFAULT]);
  			goto fallback;
  		}
  		blk_mq_map_swqueue(q);
  	}
  
  	list_for_each_entry(q, &set->tag_list, tag_set_list) {
  		blk_mq_sysfs_register(q);
  		blk_mq_debugfs_register_hctxs(q);
  	}
  
  switch_back:
  	list_for_each_entry(q, &set->tag_list, tag_set_list)
  		blk_mq_elv_switch_back(&head, q);
  
  	list_for_each_entry(q, &set->tag_list, tag_set_list)
  		blk_mq_unfreeze_queue(q);
  }
  
  void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues)
  {
  	mutex_lock(&set->tag_list_lock);
  	__blk_mq_update_nr_hw_queues(set, nr_hw_queues);
  	mutex_unlock(&set->tag_list_lock);
  }
  EXPORT_SYMBOL_GPL(blk_mq_update_nr_hw_queues);
  
  /* Enable polling stats and return whether they were already enabled. */
  static bool blk_poll_stats_enable(struct request_queue *q)
  {
  	if (test_bit(QUEUE_FLAG_POLL_STATS, &q->queue_flags) ||
  	    blk_queue_flag_test_and_set(QUEUE_FLAG_POLL_STATS, q))
  		return true;
  	blk_stat_add_callback(q, q->poll_cb);
  	return false;
  }
  
  static void blk_mq_poll_stats_start(struct request_queue *q)
  {
  	/*
  	 * We don't arm the callback if polling stats are not enabled or the
  	 * callback is already active.
  	 */
  	if (!test_bit(QUEUE_FLAG_POLL_STATS, &q->queue_flags) ||
  	    blk_stat_is_active(q->poll_cb))
  		return;
  
  	blk_stat_activate_msecs(q->poll_cb, 100);
  }
  
  static void blk_mq_poll_stats_fn(struct blk_stat_callback *cb)
  {
  	struct request_queue *q = cb->data;
  	int bucket;
  
  	for (bucket = 0; bucket < BLK_MQ_POLL_STATS_BKTS; bucket++) {
  		if (cb->stat[bucket].nr_samples)
  			q->poll_stat[bucket] = cb->stat[bucket];
  	}
  }
  
  static unsigned long blk_mq_poll_nsecs(struct request_queue *q,
  				       struct blk_mq_hw_ctx *hctx,
  				       struct request *rq)
  {
  	unsigned long ret = 0;
  	int bucket;
  
  	/*
  	 * If stats collection isn't on, don't sleep but turn it on for
  	 * future users
  	 */
  	if (!blk_poll_stats_enable(q))
  		return 0;
  
  	/*
  	 * As an optimistic guess, use half of the mean service time
  	 * for this type of request. We can (and should) make this smarter.
  	 * For instance, if the completion latencies are tight, we can
  	 * get closer than just half the mean. This is especially
  	 * important on devices where the completion latencies are longer
  	 * than ~10 usec. We do use the stats for the relevant IO size
  	 * if available which does lead to better estimates.
  	 */
  	bucket = blk_mq_poll_stats_bkt(rq);
  	if (bucket < 0)
  		return ret;
  
  	if (q->poll_stat[bucket].nr_samples)
  		ret = (q->poll_stat[bucket].mean + 1) / 2;
  
  	return ret;
  }
  
  static bool blk_mq_poll_hybrid_sleep(struct request_queue *q,
  				     struct blk_mq_hw_ctx *hctx,
  				     struct request *rq)
  {
  	struct hrtimer_sleeper hs;
  	enum hrtimer_mode mode;
  	unsigned int nsecs;
  	ktime_t kt;
  
  	if (rq->rq_flags & RQF_MQ_POLL_SLEPT)
  		return false;
  
  	/*
  	 * If we get here, hybrid polling is enabled. Hence poll_nsec can be:
  	 *
  	 *  0:	use half of prev avg
  	 * >0:	use this specific value
  	 */
  	if (q->poll_nsec > 0)
  		nsecs = q->poll_nsec;
  	else
  		nsecs = blk_mq_poll_nsecs(q, hctx, rq);
  
  	if (!nsecs)
  		return false;
  
  	rq->rq_flags |= RQF_MQ_POLL_SLEPT;
  
  	/*
  	 * This will be replaced with the stats tracking code, using
  	 * 'avg_completion_time / 2' as the pre-sleep target.
  	 */
  	kt = nsecs;
  
  	mode = HRTIMER_MODE_REL;
  	hrtimer_init_sleeper_on_stack(&hs, CLOCK_MONOTONIC, mode);
  	hrtimer_set_expires(&hs.timer, kt);
  
  	do {
  		if (blk_mq_rq_state(rq) == MQ_RQ_COMPLETE)
  			break;
  		set_current_state(TASK_UNINTERRUPTIBLE);
  		hrtimer_sleeper_start_expires(&hs, mode);
  		if (hs.task)
  			io_schedule();
  		hrtimer_cancel(&hs.timer);
  		mode = HRTIMER_MODE_ABS;
  	} while (hs.task && !signal_pending(current));
  
  	__set_current_state(TASK_RUNNING);
  	destroy_hrtimer_on_stack(&hs.timer);
  	return true;
  }
  
  static bool blk_mq_poll_hybrid(struct request_queue *q,
  			       struct blk_mq_hw_ctx *hctx, blk_qc_t cookie)
  {
  	struct request *rq;
  
  	if (q->poll_nsec == BLK_MQ_POLL_CLASSIC)
  		return false;
  
  	if (!blk_qc_t_is_internal(cookie))
  		rq = blk_mq_tag_to_rq(hctx->tags, blk_qc_t_to_tag(cookie));
  	else {
  		rq = blk_mq_tag_to_rq(hctx->sched_tags, blk_qc_t_to_tag(cookie));
  		/*
  		 * With scheduling, if the request has completed, we'll
  		 * get a NULL return here, as we clear the sched tag when
  		 * that happens. The request still remains valid, like always,
  		 * so we should be safe with just the NULL check.
  		 */
  		if (!rq)
  			return false;
  	}
  
  	return blk_mq_poll_hybrid_sleep(q, hctx, rq);
  }
  
  /**
   * blk_poll - poll for IO completions
   * @q:  the queue
   * @cookie: cookie passed back at IO submission time
   * @spin: whether to spin for completions
   *
   * Description:
   *    Poll for completions on the passed in queue. Returns number of
   *    completed entries found. If @spin is true, then blk_poll will continue
   *    looping until at least one completion is found, unless the task is
   *    otherwise marked running (or we need to reschedule).
   */
  int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin)
  {
  	struct blk_mq_hw_ctx *hctx;
  	long state;
  
  	if (!blk_qc_t_valid(cookie) ||
  	    !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
  		return 0;
  
  	if (current->plug)
  		blk_flush_plug_list(current->plug, false);
  
  	hctx = q->queue_hw_ctx[blk_qc_t_to_queue_num(cookie)];
  
  	/*
  	 * If we sleep, have the caller restart the poll loop to reset
  	 * the state. Like for the other success return cases, the
  	 * caller is responsible for checking if the IO completed. If
  	 * the IO isn't complete, we'll get called again and will go
  	 * straight to the busy poll loop.
  	 */
  	if (blk_mq_poll_hybrid(q, hctx, cookie))
  		return 1;
  
  	hctx->poll_considered++;
  
  	state = current->state;
  	do {
  		int ret;
  
  		hctx->poll_invoked++;
  
  		ret = q->mq_ops->poll(hctx);
  		if (ret > 0) {
  			hctx->poll_success++;
  			__set_current_state(TASK_RUNNING);
  			return ret;
  		}
  
  		if (signal_pending_state(state, current))
  			__set_current_state(TASK_RUNNING);
  
  		if (current->state == TASK_RUNNING)
  			return 1;
  		if (ret < 0 || !spin)
  			break;
  		cpu_relax();
  	} while (!need_resched());
  
  	__set_current_state(TASK_RUNNING);
  	return 0;
  }
  EXPORT_SYMBOL_GPL(blk_poll);
  
  unsigned int blk_mq_rq_cpu(struct request *rq)
  {
  	return rq->mq_ctx->cpu;
  }
  EXPORT_SYMBOL(blk_mq_rq_cpu);
  
  static int __init blk_mq_init(void)
  {
  	cpuhp_setup_state_multi(CPUHP_BLK_MQ_DEAD, "block/mq:dead", NULL,
  				blk_mq_hctx_notify_dead);
  	return 0;
  }
  subsys_initcall(blk_mq_init);
  