// 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 <linux/blk-crypto.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 DEFINE_PER_CPU(struct list_head, blk_cpu_done);

  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[2];

  };

  static bool blk_mq_check_inflight(struct blk_mq_hw_ctx *hctx,

  				  struct request *rq, void *priv,
  				  bool reserved)
  {
  	struct mq_inflight *mi = priv;

  	if (rq->part == mi->part && blk_mq_rq_state(rq) == MQ_RQ_IN_FLIGHT)

  		mi->inflight[rq_data_dir(rq)]++;

  
  	return true;

  }

  unsigned int blk_mq_in_flight(struct request_queue *q, struct hd_struct *part)

  {

  	struct mq_inflight mi = { .part = part };

  	blk_mq_queue_tag_busy_iter(q, blk_mq_check_inflight, &mi);

  	return mi.inflight[0] + mi.inflight[1];

  }
  
  void blk_mq_in_flight_rw(struct request_queue *q, struct hd_struct *part,
  			 unsigned int inflight[2])
  {

  	struct mq_inflight mi = { .part = part };

  	blk_mq_queue_tag_busy_iter(q, blk_mq_check_inflight, &mi);

  	inflight[0] = mi.inflight[0];
  	inflight[1] = mi.inflight[1];

  }

  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);
  }

  /*

   * 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, u64 alloc_time_ns)

  {

  	struct blk_mq_tags *tags = blk_mq_tags_from_data(data);
  	struct request *rq = tags->static_rqs[tag];

  	if (data->q->elevator) {

  		rq->tag = BLK_MQ_NO_TAG;

  		rq->internal_tag = tag;
  	} else {

  		rq->tag = tag;

  		rq->internal_tag = BLK_MQ_NO_TAG;

  	}

  	/* 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 = 0;

  	rq->cmd_flags = data->cmd_flags;

  	if (data->flags & BLK_MQ_REQ_PM)
  		rq->rq_flags |= RQF_PM;

  	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

  	blk_crypto_rq_set_defaults(rq);

  	/* tag was already set */

  	WRITE_ONCE(rq->deadline, 0);

  	rq->timeout = 0;

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

  	data->ctx->rq_dispatched[op_is_sync(data->cmd_flags)]++;

  	refcount_set(&rq->ref, 1);

  
  	if (!op_is_flush(data->cmd_flags)) {
  		struct elevator_queue *e = data->q->elevator;
  
  		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);
  			rq->rq_flags |= RQF_ELVPRIV;
  		}
  	}
  
  	data->hctx->queued++;

  	return rq;

  }

  static struct request *__blk_mq_alloc_request(struct blk_mq_alloc_data *data)

  {

  	struct request_queue *q = data->q;

  	struct elevator_queue *e = q->elevator;

  	u64 alloc_time_ns = 0;

  	unsigned int tag;

  	/* alloc_time includes depth and tag waits */
  	if (blk_queue_rq_alloc_time(q))
  		alloc_time_ns = ktime_get_ns();

  	if (data->cmd_flags & REQ_NOWAIT)

  		data->flags |= BLK_MQ_REQ_NOWAIT;

  
  	if (e) {

  		/*
  		 * 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);

  	}

  retry:

  	data->ctx = blk_mq_get_ctx(q);
  	data->hctx = blk_mq_map_queue(q, data->cmd_flags, data->ctx);

  	if (!e)

  		blk_mq_tag_busy(data->hctx);

  	/*
  	 * Waiting allocations only fail because of an inactive hctx.  In that
  	 * case just retry the hctx assignment and tag allocation as CPU hotplug
  	 * should have migrated us to an online CPU by now.
  	 */

  	tag = blk_mq_get_tag(data);

  	if (tag == BLK_MQ_NO_TAG) {
  		if (data->flags & BLK_MQ_REQ_NOWAIT)
  			return NULL;
  
  		/*
  		 * Give up the CPU and sleep for a random short time to ensure
  		 * that thread using a realtime scheduling class are migrated

  		 * off the CPU, and thus off the hctx that is going away.

  		 */
  		msleep(3);
  		goto retry;
  	}

  	return blk_mq_rq_ctx_init(data, tag, alloc_time_ns);

  }

  struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op,

  		blk_mq_req_flags_t flags)

  {

  	struct blk_mq_alloc_data data = {
  		.q		= q,
  		.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_alloc_request(&data);

  	if (!rq)

  		goto out_queue_exit;

  	rq->__data_len = 0;
  	rq->__sector = (sector_t) -1;
  	rq->bio = rq->biotail = NULL;

  	return rq;

  out_queue_exit:
  	blk_queue_exit(q);
  	return ERR_PTR(-EWOULDBLOCK);

  }

  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 data = {
  		.q		= q,
  		.flags		= flags,
  		.cmd_flags	= op,
  	};

  	u64 alloc_time_ns = 0;

  	unsigned int cpu;

  	unsigned int tag;

  	int ret;

  	/* alloc_time includes depth and tag waits */
  	if (blk_queue_rq_alloc_time(q))
  		alloc_time_ns = ktime_get_ns();

  	/*
  	 * 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 | BLK_MQ_REQ_RESERVED))))

  		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.
  	 */

  	ret = -EXDEV;

  	data.hctx = q->queue_hw_ctx[hctx_idx];
  	if (!blk_mq_hw_queue_mapped(data.hctx))

  		goto out_queue_exit;

  	cpu = cpumask_first_and(data.hctx->cpumask, cpu_online_mask);
  	data.ctx = __blk_mq_get_ctx(q, cpu);

  	if (!q->elevator)

  		blk_mq_tag_busy(data.hctx);

  	ret = -EWOULDBLOCK;

  	tag = blk_mq_get_tag(&data);
  	if (tag == BLK_MQ_NO_TAG)

  		goto out_queue_exit;

  	return blk_mq_rq_ctx_init(&data, tag, alloc_time_ns);

  out_queue_exit:
  	blk_queue_exit(q);
  	return ERR_PTR(ret);

  }
  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_crypto_free_request(rq);

  	blk_pm_mark_last_busy(rq);

  	rq->mq_hctx = NULL;

  	if (rq->tag != BLK_MQ_NO_TAG)

  		blk_mq_put_tag(hctx->tags, ctx, rq->tag);

  	if (sched_tag != BLK_MQ_NO_TAG)

  		blk_mq_put_tag(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)

  		__blk_mq_dec_active_requests(hctx);

  	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);

  	}

  	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);

  /*
   * Softirq action handler - move entries to local list and loop over them
   * while passing them to the queue registered handler.
   */
  static __latent_entropy void blk_done_softirq(struct softirq_action *h)

  {

  	struct list_head *cpu_list, local_list;

  	local_irq_disable();
  	cpu_list = this_cpu_ptr(&blk_cpu_done);
  	list_replace_init(cpu_list, &local_list);
  	local_irq_enable();
  
  	while (!list_empty(&local_list)) {
  		struct request *rq;
  
  		rq = list_entry(local_list.next, struct request, ipi_list);
  		list_del_init(&rq->ipi_list);
  		rq->q->mq_ops->complete(rq);
  	}

  }

  static void blk_mq_trigger_softirq(struct request *rq)

  {

  	struct list_head *list;
  	unsigned long flags;

  	local_irq_save(flags);
  	list = this_cpu_ptr(&blk_cpu_done);

  	list_add_tail(&rq->ipi_list, list);

  	/*
  	 * If the list only contains our just added request, signal a raise of
  	 * the softirq.  If there are already entries there, someone already
  	 * raised the irq but it hasn't run yet.
  	 */

  	if (list->next == &rq->ipi_list)
  		raise_softirq_irqoff(BLOCK_SOFTIRQ);

  	local_irq_restore(flags);

  }

  static int blk_softirq_cpu_dead(unsigned int cpu)
  {
  	/*
  	 * If a CPU goes away, splice its entries to the current CPU
  	 * and trigger a run of the softirq
  	 */
  	local_irq_disable();
  	list_splice_init(&per_cpu(blk_cpu_done, cpu),
  			 this_cpu_ptr(&blk_cpu_done));
  	raise_softirq_irqoff(BLOCK_SOFTIRQ);
  	local_irq_enable();
  
  	return 0;
  }

  
  static void __blk_mq_complete_request_remote(void *data)

  {

  	struct request *rq = data;

  	/*

  	 * For most of single queue controllers, there is only one irq vector
  	 * for handling I/O completion, and the only irq's affinity is set
  	 * to all possible CPUs.  On most of ARCHs, this affinity means the irq
  	 * is handled on one specific CPU.

  	 *

  	 * So complete I/O requests in softirq context in case of single queue
  	 * devices to avoid degrading I/O performance due to irqsoff latency.

  	 */

  	if (rq->q->nr_hw_queues == 1)
  		blk_mq_trigger_softirq(rq);
  	else
  		rq->q->mq_ops->complete(rq);

  }

  static inline bool blk_mq_complete_need_ipi(struct request *rq)
  {
  	int cpu = raw_smp_processor_id();
  
  	if (!IS_ENABLED(CONFIG_SMP) ||
  	    !test_bit(QUEUE_FLAG_SAME_COMP, &rq->q->queue_flags))
  		return false;
  
  	/* same CPU or cache domain?  Complete locally */
  	if (cpu == rq->mq_ctx->cpu ||
  	    (!test_bit(QUEUE_FLAG_SAME_FORCE, &rq->q->queue_flags) &&
  	     cpus_share_cache(cpu, rq->mq_ctx->cpu)))
  		return false;
  
  	/* don't try to IPI to an offline CPU */
  	return cpu_online(rq->mq_ctx->cpu);
  }

  bool blk_mq_complete_request_remote(struct request *rq)

  {

  	WRITE_ONCE(rq->state, MQ_RQ_COMPLETE);

  	/*
  	 * For a polled request, always complete locallly, it's pointless
  	 * to redirect the completion.
  	 */

  	if (rq->cmd_flags & REQ_HIPRI)
  		return false;

  	if (blk_mq_complete_need_ipi(rq)) {

  		rq->csd.func = __blk_mq_complete_request_remote;

  		rq->csd.info = rq;
  		rq->csd.flags = 0;

  		smp_call_function_single_async(rq->mq_ctx->cpu, &rq->csd);

  	} else {

  		if (rq->q->nr_hw_queues > 1)
  			return false;
  		blk_mq_trigger_softirq(rq);

  	}

  
  	return true;
  }
  EXPORT_SYMBOL_GPL(blk_mq_complete_request_remote);
  
  /**
   * blk_mq_complete_request - end I/O on a request
   * @rq:		the request being processed
   *
   * Description:
   *	Complete a request by scheduling the ->complete_rq operation.
   **/
  void blk_mq_complete_request(struct request *rq)
  {
  	if (!blk_mq_complete_request_remote(rq))
  		rq->q->mq_ops->complete(rq);

  }

  EXPORT_SYMBOL(blk_mq_complete_request);

  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_start_request - Start processing a request
   * @rq: Pointer to request to be started
   *
   * Function used by device drivers to notify the block layer that a request
   * is going to be processed now, so blk layer can do proper initializations
   * such as starting the timeout timer.
   */

  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);

  #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;

  	}

  }

  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);

  }

  static bool __blk_mq_get_driver_tag(struct request *rq)
  {

  	struct sbitmap_queue *bt = rq->mq_hctx->tags->bitmap_tags;

  	unsigned int tag_offset = rq->mq_hctx->tags->nr_reserved_tags;

  	int tag;

  	blk_mq_tag_busy(rq->mq_hctx);

  	if (blk_mq_tag_is_reserved(rq->mq_hctx->sched_tags, rq->internal_tag)) {

  		bt = rq->mq_hctx->tags->breserved_tags;

  		tag_offset = 0;

  	} else {
  		if (!hctx_may_queue(rq->mq_hctx, bt))
  			return false;

  	}

  	tag = __sbitmap_queue_get(bt);
  	if (tag == BLK_MQ_NO_TAG)
  		return false;
  
  	rq->tag = tag + tag_offset;

  	return true;
  }
  
  static bool blk_mq_get_driver_tag(struct request *rq)
  {

  	struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
  
  	if (rq->tag == BLK_MQ_NO_TAG && !__blk_mq_get_driver_tag(rq))
  		return false;

  	if ((hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED) &&

  			!(rq->rq_flags & RQF_MQ_INFLIGHT)) {
  		rq->rq_flags |= RQF_MQ_INFLIGHT;

  		__blk_mq_inc_active_requests(hctx);

  	}
  	hctx->tags->rqs[rq->tag] = rq;
  	return true;

  }

  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_QUEUE_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 */

  static void blk_mq_handle_dev_resource(struct request *rq,
  				       struct list_head *list)
  {
  	struct request *next =
  		list_first_entry_or_null(list, struct request, queuelist);
  
  	/*
  	 * If an I/O scheduler has been configured and we got a driver tag for
  	 * the next request already, free it.
  	 */
  	if (next)
  		blk_mq_put_driver_tag(next);
  
  	list_add(&rq->queuelist, list);
  	__blk_mq_requeue_request(rq);
  }

  static void blk_mq_handle_zone_resource(struct request *rq,
  					struct list_head *zone_list)
  {
  	/*
  	 * If we end up here it is because we cannot dispatch a request to a
  	 * specific zone due to LLD level zone-write locking or other zone
  	 * related resource not being available. In this case, set the request
  	 * aside in zone_list for retrying it later.
  	 */
  	list_add(&rq->queuelist, zone_list);
  	__blk_mq_requeue_request(rq);
  }

  enum prep_dispatch {
  	PREP_DISPATCH_OK,
  	PREP_DISPATCH_NO_TAG,
  	PREP_DISPATCH_NO_BUDGET,
  };
  
  static enum prep_dispatch blk_mq_prep_dispatch_rq(struct request *rq,
  						  bool need_budget)
  {
  	struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
  
  	if (need_budget && !blk_mq_get_dispatch_budget(rq->q)) {
  		blk_mq_put_driver_tag(rq);
  		return PREP_DISPATCH_NO_BUDGET;
  	}
  
  	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)) {

  			/*
  			 * All budgets not got from this function will be put
  			 * together during handling partial dispatch
  			 */
  			if (need_budget)
  				blk_mq_put_dispatch_budget(rq->q);

  			return PREP_DISPATCH_NO_TAG;
  		}
  	}
  
  	return PREP_DISPATCH_OK;
  }

  /* release all allocated budgets before calling to blk_mq_dispatch_rq_list */
  static void blk_mq_release_budgets(struct request_queue *q,
  		unsigned int nr_budgets)
  {
  	int i;
  
  	for (i = 0; i < nr_budgets; i++)
  		blk_mq_put_dispatch_budget(q);
  }

  /*
   * Returns true if we did some work AND can potentially do more.
   */

  bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,

  			     unsigned int nr_budgets)

  {

  	enum prep_dispatch prep;

  	struct request_queue *q = hctx->queue;

  	struct request *rq, *nxt;

  	int errors, queued;

  	blk_status_t ret = BLK_STS_OK;

  	LIST_HEAD(zone_list);

  	if (list_empty(list))
  		return false;

  	/*

  	 * 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);

  		WARN_ON_ONCE(hctx != rq->mq_hctx);

  		prep = blk_mq_prep_dispatch_rq(rq, !nr_budgets);

  		if (prep != PREP_DISPATCH_OK)

  			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);

  		}

  		/*
  		 * once the request is queued to lld, no need to cover the
  		 * budget any more
  		 */
  		if (nr_budgets)
  			nr_budgets--;

  		ret = q->mq_ops->queue_rq(hctx, &bd);

  		switch (ret) {
  		case BLK_STS_OK:
  			queued++;

  			break;

  		case BLK_STS_RESOURCE:
  		case BLK_STS_DEV_RESOURCE:
  			blk_mq_handle_dev_resource(rq, list);
  			goto out;
  		case BLK_STS_ZONE_RESOURCE:

  			/*
  			 * Move the request to zone_list and keep going through
  			 * the dispatch list to find more requests the drive can
  			 * accept.
  			 */
  			blk_mq_handle_zone_resource(rq, &zone_list);

  			break;
  		default:

  			errors++;

  			blk_mq_end_request(rq, BLK_STS_IOERR);

  		}

  	} while (!list_empty(list));

  out:

  	if (!list_empty(&zone_list))
  		list_splice_tail_init(&zone_list, list);

  	hctx->dispatched[queued_to_index(queued)]++;