TOMOYO Linux Cross Reference
Linux/block/blk-mq.c

   // 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/blk-integrity.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/interrupt.h>
  #include <linux/llist.h>
  #include <linux/cpu.h>
  #include <linux/cache.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 <linux/part_stat.h>
  #include <linux/sched/isolation.h>
  
  #include <trace/events/block.h>
  
  #include <linux/t10-pi.h>
  #include "blk.h"
  #include "blk-mq.h"
  #include "blk-mq-debugfs.h"
  #include "blk-pm.h"
  #include "blk-stat.h"
  #include "blk-mq-sched.h"
  #include "blk-rq-qos.h"
  
  static DEFINE_PER_CPU(struct llist_head, blk_cpu_done);
  static DEFINE_PER_CPU(call_single_data_t, blk_cpu_csd);
  
  static void blk_mq_insert_request(struct request *rq, blk_insert_t flags);
  static void blk_mq_request_bypass_insert(struct request *rq,
                  blk_insert_t flags);
  static void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
                  struct list_head *list);
  static int blk_hctx_poll(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
                           struct io_comp_batch *iob, unsigned int flags);
  
  /*
   * 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 block_device *part;
          unsigned int inflight[2];
  };
  
  static bool blk_mq_check_inflight(struct request *rq, void *priv)
  {
          struct mq_inflight *mi = priv;
  
          if (rq->part && blk_do_io_stat(rq) &&
              (!bdev_is_partition(mi->part) || 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 block_device *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 block_device *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, bool force_atomic)
 {
         mutex_lock(&q->mq_freeze_lock);
         if (force_atomic)
                 q->q_usage_counter.data->force_atomic = true;
         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);
 }
 
 void blk_mq_unfreeze_queue(struct request_queue *q)
 {
         __blk_mq_unfreeze_queue(q, false);
 }
 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)
 {
         unsigned long flags;
 
         spin_lock_irqsave(&q->queue_lock, flags);
         if (!q->quiesce_depth++)
                 blk_queue_flag_set(QUEUE_FLAG_QUIESCED, q);
         spin_unlock_irqrestore(&q->queue_lock, flags);
 }
 EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue_nowait);
 
 /**
  * blk_mq_wait_quiesce_done() - wait until in-progress quiesce is done
  * @set: tag_set to wait on
  *
  * Note: it is driver's responsibility for making sure that quiesce has
  * been started on or more of the request_queues of the tag_set.  This
  * function only waits for the quiesce on those request_queues that had
  * the quiesce flag set using blk_mq_quiesce_queue_nowait.
  */
 void blk_mq_wait_quiesce_done(struct blk_mq_tag_set *set)
 {
         if (set->flags & BLK_MQ_F_BLOCKING)
                 synchronize_srcu(set->srcu);
         else
                 synchronize_rcu();
 }
 EXPORT_SYMBOL_GPL(blk_mq_wait_quiesce_done);
 
 /**
  * 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)
 {
         blk_mq_quiesce_queue_nowait(q);
         /* nothing to wait for non-mq queues */
         if (queue_is_mq(q))
                 blk_mq_wait_quiesce_done(q->tag_set);
 }
 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)
 {
         unsigned long flags;
         bool run_queue = false;
 
         spin_lock_irqsave(&q->queue_lock, flags);
         if (WARN_ON_ONCE(q->quiesce_depth <= 0)) {
                 ;
         } else if (!--q->quiesce_depth) {
                 blk_queue_flag_clear(QUEUE_FLAG_QUIESCED, q);
                 run_queue = true;
         }
         spin_unlock_irqrestore(&q->queue_lock, flags);
 
         /* dispatch requests which are inserted during quiescing */
         if (run_queue)
                 blk_mq_run_hw_queues(q, true);
 }
 EXPORT_SYMBOL_GPL(blk_mq_unquiesce_queue);
 
 void blk_mq_quiesce_tagset(struct blk_mq_tag_set *set)
 {
         struct request_queue *q;
 
         mutex_lock(&set->tag_list_lock);
         list_for_each_entry(q, &set->tag_list, tag_set_list) {
                 if (!blk_queue_skip_tagset_quiesce(q))
                         blk_mq_quiesce_queue_nowait(q);
         }
         blk_mq_wait_quiesce_done(set);
         mutex_unlock(&set->tag_list_lock);
 }
 EXPORT_SYMBOL_GPL(blk_mq_quiesce_tagset);
 
 void blk_mq_unquiesce_tagset(struct blk_mq_tag_set *set)
 {
         struct request_queue *q;
 
         mutex_lock(&set->tag_list_lock);
         list_for_each_entry(q, &set->tag_list, tag_set_list) {
                 if (!blk_queue_skip_tagset_quiesce(q))
                         blk_mq_unquiesce_queue(q);
         }
         mutex_unlock(&set->tag_list_lock);
 }
 EXPORT_SYMBOL_GPL(blk_mq_unquiesce_tagset);
 
 void blk_mq_wake_waiters(struct request_queue *q)
 {
         struct blk_mq_hw_ctx *hctx;
         unsigned long i;
 
         queue_for_each_hw_ctx(q, hctx, i)
                 if (blk_mq_hw_queue_mapped(hctx))
                         blk_mq_tag_wakeup_all(hctx->tags, true);
 }
 
 void blk_rq_init(struct request_queue *q, struct request *rq)
 {
         memset(rq, 0, sizeof(*rq));
 
         INIT_LIST_HEAD(&rq->queuelist);
         rq->q = q;
         rq->__sector = (sector_t) -1;
         INIT_HLIST_NODE(&rq->hash);
         RB_CLEAR_NODE(&rq->rb_node);
         rq->tag = BLK_MQ_NO_TAG;
         rq->internal_tag = BLK_MQ_NO_TAG;
         rq->start_time_ns = blk_time_get_ns();
         rq->part = NULL;
         blk_crypto_rq_set_defaults(rq);
 }
 EXPORT_SYMBOL(blk_rq_init);
 
 /* Set start and alloc time when the allocated request is actually used */
 static inline void blk_mq_rq_time_init(struct request *rq, u64 alloc_time_ns)
 {
         if (blk_mq_need_time_stamp(rq))
                 rq->start_time_ns = blk_time_get_ns();
         else
                 rq->start_time_ns = 0;
 
 #ifdef CONFIG_BLK_RQ_ALLOC_TIME
         if (blk_queue_rq_alloc_time(rq->q))
                 rq->alloc_time_ns = alloc_time_ns ?: rq->start_time_ns;
         else
                 rq->alloc_time_ns = 0;
 #endif
 }
 
 static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
                 struct blk_mq_tags *tags, unsigned int tag)
 {
         struct blk_mq_ctx *ctx = data->ctx;
         struct blk_mq_hw_ctx *hctx = data->hctx;
         struct request_queue *q = data->q;
         struct request *rq = tags->static_rqs[tag];
 
         rq->q = q;
         rq->mq_ctx = ctx;
         rq->mq_hctx = hctx;
         rq->cmd_flags = data->cmd_flags;
 
         if (data->flags & BLK_MQ_REQ_PM)
                 data->rq_flags |= RQF_PM;
         if (blk_queue_io_stat(q))
                 data->rq_flags |= RQF_IO_STAT;
         rq->rq_flags = data->rq_flags;
 
         if (data->rq_flags & RQF_SCHED_TAGS) {
                 rq->tag = BLK_MQ_NO_TAG;
                 rq->internal_tag = tag;
         } else {
                 rq->tag = tag;
                 rq->internal_tag = BLK_MQ_NO_TAG;
         }
         rq->timeout = 0;
 
         rq->part = NULL;
         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
         rq->end_io = NULL;
         rq->end_io_data = NULL;
 
         blk_crypto_rq_set_defaults(rq);
         INIT_LIST_HEAD(&rq->queuelist);
         /* tag was already set */
         WRITE_ONCE(rq->deadline, 0);
         req_ref_set(rq, 1);
 
         if (rq->rq_flags & RQF_USE_SCHED) {
                 struct elevator_queue *e = data->q->elevator;
 
                 INIT_HLIST_NODE(&rq->hash);
                 RB_CLEAR_NODE(&rq->rb_node);
 
                 if (e->type->ops.prepare_request)
                         e->type->ops.prepare_request(rq);
         }
 
         return rq;
 }
 
 static inline struct request *
 __blk_mq_alloc_requests_batch(struct blk_mq_alloc_data *data)
 {
         unsigned int tag, tag_offset;
         struct blk_mq_tags *tags;
         struct request *rq;
         unsigned long tag_mask;
         int i, nr = 0;
 
         tag_mask = blk_mq_get_tags(data, data->nr_tags, &tag_offset);
         if (unlikely(!tag_mask))
                 return NULL;
 
         tags = blk_mq_tags_from_data(data);
         for (i = 0; tag_mask; i++) {
                 if (!(tag_mask & (1UL << i)))
                         continue;
                 tag = tag_offset + i;
                 prefetch(tags->static_rqs[tag]);
                 tag_mask &= ~(1UL << i);
                 rq = blk_mq_rq_ctx_init(data, tags, tag);
                 rq_list_add(data->cached_rq, rq);
                 nr++;
         }
         if (!(data->rq_flags & RQF_SCHED_TAGS))
                 blk_mq_add_active_requests(data->hctx, nr);
         /* caller already holds a reference, add for remainder */
         percpu_ref_get_many(&data->q->q_usage_counter, nr - 1);
         data->nr_tags -= nr;
 
         return rq_list_pop(data->cached_rq);
 }
 
 static struct request *__blk_mq_alloc_requests(struct blk_mq_alloc_data *data)
 {
         struct request_queue *q = data->q;
         u64 alloc_time_ns = 0;
         struct request *rq;
         unsigned int tag;
 
         /* alloc_time includes depth and tag waits */
         if (blk_queue_rq_alloc_time(q))
                 alloc_time_ns = blk_time_get_ns();
 
         if (data->cmd_flags & REQ_NOWAIT)
                 data->flags |= BLK_MQ_REQ_NOWAIT;
 
 retry:
         data->ctx = blk_mq_get_ctx(q);
         data->hctx = blk_mq_map_queue(q, data->cmd_flags, data->ctx);
 
         if (q->elevator) {
                 /*
                  * All requests use scheduler tags when an I/O scheduler is
                  * enabled for the queue.
                  */
                 data->rq_flags |= RQF_SCHED_TAGS;
 
                 /*
                  * Flush/passthrough requests are special and go directly to the
                  * dispatch list.
                  */
                 if ((data->cmd_flags & REQ_OP_MASK) != REQ_OP_FLUSH &&
                     !blk_op_is_passthrough(data->cmd_flags)) {
                         struct elevator_mq_ops *ops = &q->elevator->type->ops;
 
                         WARN_ON_ONCE(data->flags & BLK_MQ_REQ_RESERVED);
 
                         data->rq_flags |= RQF_USE_SCHED;
                         if (ops->limit_depth)
                                 ops->limit_depth(data->cmd_flags, data);
                 }
         } else {
                 blk_mq_tag_busy(data->hctx);
         }
 
         if (data->flags & BLK_MQ_REQ_RESERVED)
                 data->rq_flags |= RQF_RESV;
 
         /*
          * Try batched alloc if we want more than 1 tag.
          */
         if (data->nr_tags > 1) {
                 rq = __blk_mq_alloc_requests_batch(data);
                 if (rq) {
                         blk_mq_rq_time_init(rq, alloc_time_ns);
                         return rq;
                 }
                 data->nr_tags = 1;
         }
 
         /*
          * 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;
         }
 
         if (!(data->rq_flags & RQF_SCHED_TAGS))
                 blk_mq_inc_active_requests(data->hctx);
         rq = blk_mq_rq_ctx_init(data, blk_mq_tags_from_data(data), tag);
         blk_mq_rq_time_init(rq, alloc_time_ns);
         return rq;
 }
 
 static struct request *blk_mq_rq_cache_fill(struct request_queue *q,
                                             struct blk_plug *plug,
                                             blk_opf_t opf,
                                             blk_mq_req_flags_t flags)
 {
         struct blk_mq_alloc_data data = {
                 .q              = q,
                 .flags          = flags,
                 .cmd_flags      = opf,
                 .nr_tags        = plug->nr_ios,
                 .cached_rq      = &plug->cached_rq,
         };
         struct request *rq;
 
         if (blk_queue_enter(q, flags))
                 return NULL;
 
         plug->nr_ios = 1;
 
         rq = __blk_mq_alloc_requests(&data);
         if (unlikely(!rq))
                 blk_queue_exit(q);
         return rq;
 }
 
 static struct request *blk_mq_alloc_cached_request(struct request_queue *q,
                                                    blk_opf_t opf,
                                                    blk_mq_req_flags_t flags)
 {
         struct blk_plug *plug = current->plug;
         struct request *rq;
 
         if (!plug)
                 return NULL;
 
         if (rq_list_empty(plug->cached_rq)) {
                 if (plug->nr_ios == 1)
                         return NULL;
                 rq = blk_mq_rq_cache_fill(q, plug, opf, flags);
                 if (!rq)
                         return NULL;
         } else {
                 rq = rq_list_peek(&plug->cached_rq);
                 if (!rq || rq->q != q)
                         return NULL;
 
                 if (blk_mq_get_hctx_type(opf) != rq->mq_hctx->type)
                         return NULL;
                 if (op_is_flush(rq->cmd_flags) != op_is_flush(opf))
                         return NULL;
 
                 plug->cached_rq = rq_list_next(rq);
                 blk_mq_rq_time_init(rq, 0);
         }
 
         rq->cmd_flags = opf;
         INIT_LIST_HEAD(&rq->queuelist);
         return rq;
 }
 
 struct request *blk_mq_alloc_request(struct request_queue *q, blk_opf_t opf,
                 blk_mq_req_flags_t flags)
 {
         struct request *rq;
 
         rq = blk_mq_alloc_cached_request(q, opf, flags);
         if (!rq) {
                 struct blk_mq_alloc_data data = {
                         .q              = q,
                         .flags          = flags,
                         .cmd_flags      = opf,
                         .nr_tags        = 1,
                 };
                 int ret;
 
                 ret = blk_queue_enter(q, flags);
                 if (ret)
                         return ERR_PTR(ret);
 
                 rq = __blk_mq_alloc_requests(&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,
         blk_opf_t opf, blk_mq_req_flags_t flags, unsigned int hctx_idx)
 {
         struct blk_mq_alloc_data data = {
                 .q              = q,
                 .flags          = flags,
                 .cmd_flags      = opf,
                 .nr_tags        = 1,
         };
         u64 alloc_time_ns = 0;
         struct request *rq;
         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 = blk_time_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)) ||
             WARN_ON_ONCE(!(flags & 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 = xa_load(&q->hctx_table, hctx_idx);
         if (!blk_mq_hw_queue_mapped(data.hctx))
                 goto out_queue_exit;
         cpu = cpumask_first_and(data.hctx->cpumask, cpu_online_mask);
         if (cpu >= nr_cpu_ids)
                 goto out_queue_exit;
         data.ctx = __blk_mq_get_ctx(q, cpu);
 
         if (q->elevator)
                 data.rq_flags |= RQF_SCHED_TAGS;
         else
                 blk_mq_tag_busy(data.hctx);
 
         if (flags & BLK_MQ_REQ_RESERVED)
                 data.rq_flags |= RQF_RESV;
 
         ret = -EWOULDBLOCK;
         tag = blk_mq_get_tag(&data);
         if (tag == BLK_MQ_NO_TAG)
                 goto out_queue_exit;
         if (!(data.rq_flags & RQF_SCHED_TAGS))
                 blk_mq_inc_active_requests(data.hctx);
         rq = blk_mq_rq_ctx_init(&data, blk_mq_tags_from_data(&data), tag);
         blk_mq_rq_time_init(rq, alloc_time_ns);
         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(ret);
 }
 EXPORT_SYMBOL_GPL(blk_mq_alloc_request_hctx);
 
 static void blk_mq_finish_request(struct request *rq)
 {
         struct request_queue *q = rq->q;
 
         blk_zone_finish_request(rq);
 
         if (rq->rq_flags & RQF_USE_SCHED) {
                 q->elevator->type->ops.finish_request(rq);
                 /*
                  * For postflush request that may need to be
                  * completed twice, we should clear this flag
                  * to avoid double finish_request() on the rq.
                  */
                 rq->rq_flags &= ~RQF_USE_SCHED;
         }
 }
 
 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_dec_active_requests(hctx);
                 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;
 
         blk_mq_finish_request(rq);
 
         if (unlikely(laptop_mode && !blk_rq_is_passthrough(rq)))
                 laptop_io_completion(q->disk->bdi);
 
         rq_qos_done(q, rq);
 
         WRITE_ONCE(rq->state, MQ_RQ_IDLE);
         if (req_ref_put_and_test(rq))
                 __blk_mq_free_request(rq);
 }
 EXPORT_SYMBOL_GPL(blk_mq_free_request);
 
 void blk_mq_free_plug_rqs(struct blk_plug *plug)
 {
         struct request *rq;
 
         while ((rq = rq_list_pop(&plug->cached_rq)) != NULL)
                 blk_mq_free_request(rq);
 }
 
 void blk_dump_rq_flags(struct request *rq, char *msg)
 {
         printk(KERN_INFO "%s: dev %s: flags=%llx\n", msg,
                 rq->q->disk ? rq->q->disk->disk_name : "?",
                 (__force unsigned long long) rq->cmd_flags);
 
         printk(KERN_INFO "  sector %llu, nr/cnr %u/%u\n",
                (unsigned long long)blk_rq_pos(rq),
                blk_rq_sectors(rq), blk_rq_cur_sectors(rq));
         printk(KERN_INFO "  bio %p, biotail %p, len %u\n",
                rq->bio, rq->biotail, blk_rq_bytes(rq));
 }
 EXPORT_SYMBOL(blk_dump_rq_flags);
 
 static void blk_account_io_completion(struct request *req, unsigned int bytes)
 {
         if (req->part && blk_do_io_stat(req)) {
                 const int sgrp = op_stat_group(req_op(req));
 
                 part_stat_lock();
                 part_stat_add(req->part, sectors[sgrp], bytes >> 9);
                 part_stat_unlock();
         }
 }
 
 static void blk_print_req_error(struct request *req, blk_status_t status)
 {
         printk_ratelimited(KERN_ERR
                 "%s error, dev %s, sector %llu op 0x%x:(%s) flags 0x%x "
                 "phys_seg %u prio class %u\n",
                 blk_status_to_str(status),
                 req->q->disk ? req->q->disk->disk_name : "?",
                 blk_rq_pos(req), (__force u32)req_op(req),
                 blk_op_str(req_op(req)),
                 (__force u32)(req->cmd_flags & ~REQ_OP_MASK),
                 req->nr_phys_segments,
                 IOPRIO_PRIO_CLASS(req->ioprio));
 }
 
 /*
  * Fully end IO on a request. Does not support partial completions, or
  * errors.
  */
 static void blk_complete_request(struct request *req)
 {
         const bool is_flush = (req->rq_flags & RQF_FLUSH_SEQ) != 0;
         int total_bytes = blk_rq_bytes(req);
         struct bio *bio = req->bio;
 
         trace_block_rq_complete(req, BLK_STS_OK, total_bytes);
 
         if (!bio)
                 return;
 
         if (blk_integrity_rq(req) && req_op(req) == REQ_OP_READ)
                 blk_integrity_complete(req, total_bytes);
 
         /*
          * Upper layers may call blk_crypto_evict_key() anytime after the last
          * bio_endio().  Therefore, the keyslot must be released before that.
          */
         blk_crypto_rq_put_keyslot(req);
 
         blk_account_io_completion(req, total_bytes);
 
         do {
                 struct bio *next = bio->bi_next;
 
                 /* Completion has already been traced */
                 bio_clear_flag(bio, BIO_TRACE_COMPLETION);
 
                 blk_zone_update_request_bio(req, bio);
 
                 if (!is_flush)
                         bio_endio(bio);
                 bio = next;
         } while (bio);
 
         /*
          * Reset counters so that the request stacking driver
          * can find how many bytes remain in the request
          * later.
          */
         if (!req->end_io) {
                 req->bio = NULL;
                 req->__data_len = 0;
         }
 }
 
 /**
  * blk_update_request - Complete multiple bytes without completing the request
  * @req:      the request being processed
  * @error:    block status code
  * @nr_bytes: number of bytes to complete for @req
  *
  * Description:
  *     Ends I/O on a number of bytes attached to @req, but doesn't complete
  *     the request structure even if @req doesn't have leftover.
  *     If @req has leftover, sets it up for the next range of segments.
  *
  *     Passing the result of blk_rq_bytes() as @nr_bytes guarantees
  *     %false return from this function.
  *
  * Note:
  *      The RQF_SPECIAL_PAYLOAD flag is ignored on purpose in this function
  *      except in the consistency check at the end of this function.
  *
  * Return:
  *     %false - this request doesn't have any more data
  *     %true  - this request has more data
  **/
 bool blk_update_request(struct request *req, blk_status_t error,
                 unsigned int nr_bytes)
 {
         bool is_flush = req->rq_flags & RQF_FLUSH_SEQ;
         bool quiet = req->rq_flags & RQF_QUIET;
         int total_bytes;
 
         trace_block_rq_complete(req, error, nr_bytes);
 
         if (!req->bio)
                 return false;
 
         if (blk_integrity_rq(req) && req_op(req) == REQ_OP_READ &&
             error == BLK_STS_OK)
                 blk_integrity_complete(req, nr_bytes);
 
         /*
          * Upper layers may call blk_crypto_evict_key() anytime after the last
          * bio_endio().  Therefore, the keyslot must be released before that.
          */
         if (blk_crypto_rq_has_keyslot(req) && nr_bytes >= blk_rq_bytes(req))
                 __blk_crypto_rq_put_keyslot(req);
 
         if (unlikely(error && !blk_rq_is_passthrough(req) && !quiet) &&
             !test_bit(GD_DEAD, &req->q->disk->state)) {
                 blk_print_req_error(req, error);
                 trace_block_rq_error(req, error, nr_bytes);
         }
 
         blk_account_io_completion(req, nr_bytes);
 
         total_bytes = 0;
         while (req->bio) {
                 struct bio *bio = req->bio;
                 unsigned bio_bytes = min(bio->bi_iter.bi_size, nr_bytes);
 
                 if (unlikely(error))
                         bio->bi_status = error;
 
                 if (bio_bytes == bio->bi_iter.bi_size) {
                         req->bio = bio->bi_next;
                 } else if (bio_is_zone_append(bio) && error == BLK_STS_OK) {
                         /*
                          * Partial zone append completions cannot be supported
                          * as the BIO fragments may end up not being written
                          * sequentially.
                          */
                         bio->bi_status = BLK_STS_IOERR;
                 }
 
                 /* Completion has already been traced */
                 bio_clear_flag(bio, BIO_TRACE_COMPLETION);
                 if (unlikely(quiet))
                         bio_set_flag(bio, BIO_QUIET);
 
                 bio_advance(bio, bio_bytes);
 
                 /* Don't actually finish bio if it's part of flush sequence */
                 if (!bio->bi_iter.bi_size) {
                         blk_zone_update_request_bio(req, bio);
                         if (!is_flush)
                                 bio_endio(bio);
                 }
 
                 total_bytes += bio_bytes;
                 nr_bytes -= bio_bytes;
 
                 if (!nr_bytes)
                         break;
         }
 
         /*
          * completely done
          */
         if (!req->bio) {
                 /*
                  * Reset counters so that the request stacking driver
                  * can find how many bytes remain in the request
                  * later.
                  */
                 req->__data_len = 0;
                 return false;
         }
 
         req->__data_len -= total_bytes;
 
         /* update sector only for requests with clear definition of sector */
         if (!blk_rq_is_passthrough(req))
                 req->__sector += total_bytes >> 9;
 
         /* mixed attributes always follow the first bio */
         if (req->rq_flags & RQF_MIXED_MERGE) {
                 req->cmd_flags &= ~REQ_FAILFAST_MASK;
                 req->cmd_flags |= req->bio->bi_opf & REQ_FAILFAST_MASK;
         }
 
         if (!(req->rq_flags & RQF_SPECIAL_PAYLOAD)) {
                 /*
                  * If total number of sectors is less than the first segment
                  * size, something has gone terribly wrong.
                  */
                 if (blk_rq_bytes(req) < blk_rq_cur_bytes(req)) {
                         blk_dump_rq_flags(req, "request botched");
                         req->__data_len = blk_rq_cur_bytes(req);
                 }
 
                 /* recalculate the number of segments */
                 req->nr_phys_segments = blk_recalc_rq_segments(req);
         }
 
         return true;
 }
 EXPORT_SYMBOL_GPL(blk_update_request);
 
 static inline void blk_account_io_done(struct request *req, u64 now)
 {
         trace_block_io_done(req);
 
         /*
          * Account IO completion.  flush_rq isn't accounted as a
          * normal IO on queueing nor completion.  Accounting the
          * containing request is enough.
          */
         if (blk_do_io_stat(req) && req->part &&
             !(req->rq_flags & RQF_FLUSH_SEQ)) {
                 const int sgrp = op_stat_group(req_op(req));
 
                 part_stat_lock();
                 update_io_ticks(req->part, jiffies, true);
                 part_stat_inc(req->part, ios[sgrp]);
                 part_stat_add(req->part, nsecs[sgrp], now - req->start_time_ns);
                 part_stat_local_dec(req->part,
                                     in_flight[op_is_write(req_op(req))]);
                 part_stat_unlock();
         }
 }
 
 static inline void blk_account_io_start(struct request *req)
 {
         trace_block_io_start(req);
 
         if (blk_do_io_stat(req)) {
                 /*
                  * All non-passthrough requests are created from a bio with one
                  * exception: when a flush command that is part of a flush sequence
                  * generated by the state machine in blk-flush.c is cloned onto the
                  * lower device by dm-multipath we can get here without a bio.
                  */
                 if (req->bio)
                         req->part = req->bio->bi_bdev;
                 else
                         req->part = req->q->disk->part0;
 
                 part_stat_lock();
                 update_io_ticks(req->part, jiffies, false);
                 part_stat_local_inc(req->part,
                                     in_flight[op_is_write(req_op(req))]);
                 part_stat_unlock();
         }
 }
 
 static inline void __blk_mq_end_request_acct(struct request *rq, u64 now)
 {
         if (rq->rq_flags & RQF_STATS)
                 blk_stat_add(rq, now);
 
         blk_mq_sched_completed_request(rq, now);
         blk_account_io_done(rq, now);
 }
 
 inline void __blk_mq_end_request(struct request *rq, blk_status_t error)
 {
         if (blk_mq_need_time_stamp(rq))
                 __blk_mq_end_request_acct(rq, blk_time_get_ns());
 
         blk_mq_finish_request(rq);
 
         if (rq->end_io) {
                 rq_qos_done(rq->q, rq);
                 if (rq->end_io(rq, error) == RQ_END_IO_FREE)
                         blk_mq_free_request(rq);
         } 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);
 
 #define TAG_COMP_BATCH          32
 
 static inline void blk_mq_flush_tag_batch(struct blk_mq_hw_ctx *hctx,
                                           int *tag_array, int nr_tags)
 {
         struct request_queue *q = hctx->queue;
 
         blk_mq_sub_active_requests(hctx, nr_tags);
 
         blk_mq_put_tags(hctx->tags, tag_array, nr_tags);
         percpu_ref_put_many(&q->q_usage_counter, nr_tags);
 }
 
 void blk_mq_end_request_batch(struct io_comp_batch *iob)
 {
         int tags[TAG_COMP_BATCH], nr_tags = 0;
         struct blk_mq_hw_ctx *cur_hctx = NULL;
         struct request *rq;
         u64 now = 0;
 
         if (iob->need_ts)
                 now = blk_time_get_ns();
 
         while ((rq = rq_list_pop(&iob->req_list)) != NULL) {
                 prefetch(rq->bio);
                 prefetch(rq->rq_next);
 
                 blk_complete_request(rq);
                 if (iob->need_ts)
                         __blk_mq_end_request_acct(rq, now);
 
                 blk_mq_finish_request(rq);
 
                 rq_qos_done(rq->q, rq);
 
                 /*
                  * If end_io handler returns NONE, then it still has
                  * ownership of the request.
                  */
                 if (rq->end_io && rq->end_io(rq, 0) == RQ_END_IO_NONE)
                         continue;
 
                 WRITE_ONCE(rq->state, MQ_RQ_IDLE);
                 if (!req_ref_put_and_test(rq))
                         continue;
 
                 blk_crypto_free_request(rq);
                 blk_pm_mark_last_busy(rq);
 
                 if (nr_tags == TAG_COMP_BATCH || cur_hctx != rq->mq_hctx) {
                         if (cur_hctx)
                                 blk_mq_flush_tag_batch(cur_hctx, tags, nr_tags);
                         nr_tags = 0;
                         cur_hctx = rq->mq_hctx;
                 }
                 tags[nr_tags++] = rq->tag;
         }
 
         if (nr_tags)
                 blk_mq_flush_tag_batch(cur_hctx, tags, nr_tags);
 }
 EXPORT_SYMBOL_GPL(blk_mq_end_request_batch);
 
 static void blk_complete_reqs(struct llist_head *list)
 {
         struct llist_node *entry = llist_reverse_order(llist_del_all(list));
         struct request *rq, *next;
 
         llist_for_each_entry_safe(rq, next, entry, ipi_list)
                 rq->q->mq_ops->complete(rq);
 }
 
 static __latent_entropy void blk_done_softirq(struct softirq_action *h)
 {
         blk_complete_reqs(this_cpu_ptr(&blk_cpu_done));
 }
 
 static int blk_softirq_cpu_dead(unsigned int cpu)
 {
         blk_complete_reqs(&per_cpu(blk_cpu_done, cpu));
         return 0;
 }
 
 static void __blk_mq_complete_request_remote(void *data)
 {
         __raise_softirq_irqoff(BLOCK_SOFTIRQ);
 }
 
 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;
         /*
          * With force threaded interrupts enabled, raising softirq from an SMP
          * function call will always result in waking the ksoftirqd thread.
          * This is probably worse than completing the request on a different
          * cache domain.
          */
         if (force_irqthreads())
                 return false;
 
         /* same CPU or cache domain and capacity?  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) &&
              cpus_equal_capacity(cpu, rq->mq_ctx->cpu)))
                 return false;
 
         /* don't try to IPI to an offline CPU */
         return cpu_online(rq->mq_ctx->cpu);
 }
 
 static void blk_mq_complete_send_ipi(struct request *rq)
 {
         unsigned int cpu;
 
         cpu = rq->mq_ctx->cpu;
         if (llist_add(&rq->ipi_list, &per_cpu(blk_cpu_done, cpu)))
                 smp_call_function_single_async(cpu, &per_cpu(blk_cpu_csd, cpu));
 }
 
 static void blk_mq_raise_softirq(struct request *rq)
 {
         struct llist_head *list;
 
         preempt_disable();
         list = this_cpu_ptr(&blk_cpu_done);
         if (llist_add(&rq->ipi_list, list))
                 raise_softirq(BLOCK_SOFTIRQ);
         preempt_enable();
 }
 
 bool blk_mq_complete_request_remote(struct request *rq)
 {
         WRITE_ONCE(rq->state, MQ_RQ_COMPLETE);
 
         /*
          * For request which hctx has only one ctx mapping,
          * or a polled request, always complete locally,
          * it's pointless to redirect the completion.
          */
         if ((rq->mq_hctx->nr_ctx == 1 &&
              rq->mq_ctx->cpu == raw_smp_processor_id()) ||
              rq->cmd_flags & REQ_POLLED)
                 return false;
 
         if (blk_mq_complete_need_ipi(rq)) {
                 blk_mq_complete_send_ipi(rq);
                 return true;
         }
 
         if (rq->q->nr_hw_queues == 1) {
                 blk_mq_raise_softirq(rq);
                 return true;
         }
         return false;
 }
 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);
 
 /**
  * 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(rq);
 
         if (test_bit(QUEUE_FLAG_STATS, &q->queue_flags) &&
             !blk_rq_is_passthrough(rq)) {
                 rq->io_start_time_ns = blk_time_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);
         rq->mq_hctx->tags->rqs[rq->tag] = rq;
 
         if (blk_integrity_rq(rq) && req_op(rq) == REQ_OP_WRITE)
                 blk_integrity_prepare(rq);
 
         if (rq->bio && rq->bio->bi_opf & REQ_POLLED)
                 WRITE_ONCE(rq->bio->bi_cookie, rq->mq_hctx->queue_num);
 }
 EXPORT_SYMBOL(blk_mq_start_request);
 
 /*
  * Allow 2x BLK_MAX_REQUEST_COUNT requests on plug queue for multiple
  * queues. This is important for md arrays to benefit from merging
  * requests.
  */
 static inline unsigned short blk_plug_max_rq_count(struct blk_plug *plug)
 {
         if (plug->multiple_queues)
                 return BLK_MAX_REQUEST_COUNT * 2;
         return BLK_MAX_REQUEST_COUNT;
 }
 
 static void blk_add_rq_to_plug(struct blk_plug *plug, struct request *rq)
 {
         struct request *last = rq_list_peek(&plug->mq_list);
 
         if (!plug->rq_count) {
                 trace_block_plug(rq->q);
         } else if (plug->rq_count >= blk_plug_max_rq_count(plug) ||
                    (!blk_queue_nomerges(rq->q) &&
                     blk_rq_bytes(last) >= BLK_PLUG_FLUSH_SIZE)) {
                 blk_mq_flush_plug_list(plug, false);
                 last = NULL;
                 trace_block_plug(rq->q);
         }
 
         if (!plug->multiple_queues && last && last->q != rq->q)
                 plug->multiple_queues = true;
         /*
          * Any request allocated from sched tags can't be issued to
          * ->queue_rqs() directly
          */
         if (!plug->has_elevator && (rq->rq_flags & RQF_SCHED_TAGS))
                 plug->has_elevator = true;
         rq->rq_next = NULL;
         rq_list_add(&plug->mq_list, rq);
         plug->rq_count++;
 }
 
 /**
  * blk_execute_rq_nowait - insert a request to I/O scheduler for execution
  * @rq:         request to insert
  * @at_head:    insert request at head or tail of queue
  *
  * Description:
  *    Insert a fully prepared request at the back of the I/O scheduler queue
  *    for execution.  Don't wait for completion.
  *
  * Note:
  *    This function will invoke @done directly if the queue is dead.
  */
 void blk_execute_rq_nowait(struct request *rq, bool at_head)
 {
         struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
 
         WARN_ON(irqs_disabled());
         WARN_ON(!blk_rq_is_passthrough(rq));
 
         blk_account_io_start(rq);
 
         if (current->plug && !at_head) {
                 blk_add_rq_to_plug(current->plug, rq);
                 return;
         }
 
         blk_mq_insert_request(rq, at_head ? BLK_MQ_INSERT_AT_HEAD : 0);
         blk_mq_run_hw_queue(hctx, hctx->flags & BLK_MQ_F_BLOCKING);
 }
 EXPORT_SYMBOL_GPL(blk_execute_rq_nowait);
 
 struct blk_rq_wait {
         struct completion done;
         blk_status_t ret;
 };
 
 static enum rq_end_io_ret blk_end_sync_rq(struct request *rq, blk_status_t ret)
 {
         struct blk_rq_wait *wait = rq->end_io_data;
 
         wait->ret = ret;
         complete(&wait->done);
         return RQ_END_IO_NONE;
 }
 
 bool blk_rq_is_poll(struct request *rq)
 {
         if (!rq->mq_hctx)
                 return false;
         if (rq->mq_hctx->type != HCTX_TYPE_POLL)
                 return false;
         return true;
 }
 EXPORT_SYMBOL_GPL(blk_rq_is_poll);
 
 static void blk_rq_poll_completion(struct request *rq, struct completion *wait)
 {
         do {
                 blk_hctx_poll(rq->q, rq->mq_hctx, NULL, 0);
                 cond_resched();
         } while (!completion_done(wait));
 }
 
 /**
  * blk_execute_rq - insert a request into queue for execution
  * @rq:         request to insert
  * @at_head:    insert request at head or tail of queue
  *
  * Description:
  *    Insert a fully prepared request at the back of the I/O scheduler queue
  *    for execution and wait for completion.
  * Return: The blk_status_t result provided to blk_mq_end_request().
  */
 blk_status_t blk_execute_rq(struct request *rq, bool at_head)
 {
         struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
         struct blk_rq_wait wait = {
                 .done = COMPLETION_INITIALIZER_ONSTACK(wait.done),
         };
 
         WARN_ON(irqs_disabled());
         WARN_ON(!blk_rq_is_passthrough(rq));
 
         rq->end_io_data = &wait;
         rq->end_io = blk_end_sync_rq;
 
         blk_account_io_start(rq);
         blk_mq_insert_request(rq, at_head ? BLK_MQ_INSERT_AT_HEAD : 0);
         blk_mq_run_hw_queue(hctx, false);
 
         if (blk_rq_is_poll(rq))
                 blk_rq_poll_completion(rq, &wait.done);
         else
                 blk_wait_io(&wait.done);
 
         return wait.ret;
 }
 EXPORT_SYMBOL(blk_execute_rq);
 
 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(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)
 {
         struct request_queue *q = rq->q;
         unsigned long flags;
 
         __blk_mq_requeue_request(rq);
 
         /* this request will be re-inserted to io scheduler queue */
         blk_mq_sched_requeue_request(rq);
 
         spin_lock_irqsave(&q->requeue_lock, flags);
         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);
 }
 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);
         LIST_HEAD(flush_list);
         struct request *rq;
 
         spin_lock_irq(&q->requeue_lock);
         list_splice_init(&q->requeue_list, &rq_list);
         list_splice_init(&q->flush_list, &flush_list);
         spin_unlock_irq(&q->requeue_lock);
 
         while (!list_empty(&rq_list)) {
                 rq = list_entry(rq_list.next, struct request, queuelist);
                 /*
                  * If RQF_DONTPREP ist set, the request has been started by the
                  * driver already and might have driver-specific data allocated
                  * already.  Insert it into the hctx dispatch list to avoid
                  * block layer merges for the request.
                  */
                 if (rq->rq_flags & RQF_DONTPREP) {
                         list_del_init(&rq->queuelist);
                         blk_mq_request_bypass_insert(rq, 0);
                 } else {
                         list_del_init(&rq->queuelist);
                         blk_mq_insert_request(rq, BLK_MQ_INSERT_AT_HEAD);
                 }
         }
 
         while (!list_empty(&flush_list)) {
                 rq = list_entry(flush_list.next, struct request, queuelist);
                 list_del_init(&rq->queuelist);
                 blk_mq_insert_request(rq, 0);
         }
 
         blk_mq_run_hw_queues(q, false);
 }
 
 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);
 
 static bool blk_is_flush_data_rq(struct request *rq)
 {
         return (rq->rq_flags & RQF_FLUSH_SEQ) && !is_flush_rq(rq);
 }
 
 static bool blk_mq_rq_inflight(struct request *rq, void *priv)
 {
         /*
          * If we find a request that isn't idle we know the queue is busy
          * as it's checked in the iter.
          * Return false to stop the iteration.
          *
          * In case of queue quiesce, if one flush data request is completed,
          * don't count it as inflight given the flush sequence is suspended,
          * and the original flush data request is invisible to driver, just
          * like other pending requests because of quiesce
          */
         if (blk_mq_request_started(rq) && !(blk_queue_quiesced(rq->q) &&
                                 blk_is_flush_data_rq(rq) &&
                                 blk_mq_request_completed(rq))) {
                 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)
 {
         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);
                 if (ret == BLK_EH_DONE)
                         return;
                 WARN_ON_ONCE(ret != BLK_EH_RESET_TIMER);
         }
 
         blk_add_timer(req);
 }
 
 struct blk_expired_data {
         bool has_timedout_rq;
         unsigned long next;
         unsigned long timeout_start;
 };
 
 static bool blk_mq_req_expired(struct request *rq, struct blk_expired_data *expired)
 {
         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(expired->timeout_start, deadline))
                 return true;
 
         if (expired->next == 0)
                 expired->next = deadline;
         else if (time_after(expired->next, deadline))
                 expired->next = deadline;
         return false;
 }
 
 void blk_mq_put_rq_ref(struct request *rq)
 {
         if (is_flush_rq(rq)) {
                 if (rq->end_io(rq, 0) == RQ_END_IO_FREE)
                         blk_mq_free_request(rq);
         } else if (req_ref_put_and_test(rq)) {
                 __blk_mq_free_request(rq);
         }
 }
 
 static bool blk_mq_check_expired(struct request *rq, void *priv)
 {
         struct blk_expired_data *expired = priv;
 
         /*
          * blk_mq_queue_tag_busy_iter() has locked the request, so it cannot
          * be reallocated underneath the timeout handler's processing, then
          * the expire check is reliable. If the request is not expired, then
          * it was completed and reallocated as a new request after returning
          * from blk_mq_check_expired().
          */
         if (blk_mq_req_expired(rq, expired)) {
                 expired->has_timedout_rq = true;
                 return false;
         }
         return true;
 }
 
 static bool blk_mq_handle_expired(struct request *rq, void *priv)
 {
         struct blk_expired_data *expired = priv;
 
         if (blk_mq_req_expired(rq, expired))
                 blk_mq_rq_timed_out(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);
         struct blk_expired_data expired = {
                 .timeout_start = jiffies,
         };
         struct blk_mq_hw_ctx *hctx;
         unsigned long 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;
 
         /* check if there is any timed-out request */
         blk_mq_queue_tag_busy_iter(q, blk_mq_check_expired, &expired);
         if (expired.has_timedout_rq) {
                 /*
                  * Before walking tags, we must ensure any submit started
                  * before the current time has finished. Since the submit
                  * uses srcu or rcu, wait for a synchronization point to
                  * ensure all running submits have finished
                  */
                 blk_mq_wait_quiesce_done(q->tag_set);
 
                 expired.next = 0;
                 blk_mq_queue_tag_busy_iter(q, blk_mq_handle_expired, &expired);
         }
 
         if (expired.next != 0) {
                 mod_timer(&q->timeout, expired.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;
 }
 
 bool __blk_mq_alloc_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;
         blk_mq_inc_active_requests(rq->mq_hctx);
         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;
         struct wait_queue_head *wq;
         wait_queue_entry_t *wait;
         bool ret;
 
         if (!(hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED) &&
             !(blk_mq_is_shared_tags(hctx->flags))) {
                 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;
 
         if (blk_mq_tag_is_reserved(rq->mq_hctx->sched_tags, rq->internal_tag))
                 sbq = &hctx->tags->breserved_tags;
         else
                 sbq = &hctx->tags->bitmap_tags;
         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);
 
         /*
          * Add one explicit barrier since blk_mq_get_driver_tag() may
          * not imply barrier in case of failure.
          *
          * Order adding us to wait queue and allocating driver tag.
          *
          * The pair is the one implied in sbitmap_queue_wake_up() which
          * orders clearing sbitmap tag bits and waitqueue_active() in
          * __sbitmap_queue_wake_up(), since waitqueue_active() is lockless
          *
          * Otherwise, re-order of adding wait queue and getting driver tag
          * may cause __sbitmap_queue_wake_up() to wake up nothing because
          * the waitqueue_active() may not observe us in wait queue.
          */
         smp_mb();
 
         /*
          * 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;
 
         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)
 {
         list_add(&rq->queuelist, 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;
         int budget_token = -1;
 
         if (need_budget) {
                 budget_token = blk_mq_get_dispatch_budget(rq->q);
                 if (budget_token < 0) {
                         blk_mq_put_driver_tag(rq);
                         return PREP_DISPATCH_NO_BUDGET;
                 }
                 blk_mq_set_rq_budget_token(rq, budget_token);
         }
 
         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, budget_token);
                         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,
                 struct list_head *list)
 {
         struct request *rq;
 
         list_for_each_entry(rq, list, queuelist) {
                 int budget_token = blk_mq_get_rq_budget_token(rq);
 
                 if (budget_token >= 0)
                         blk_mq_put_dispatch_budget(q, budget_token);
         }
 }
 
 /*
  * blk_mq_commit_rqs will notify driver using bd->last that there is no
  * more requests. (See comment in struct blk_mq_ops for commit_rqs for
  * details)
  * Attention, we should explicitly call this in unusual cases:
  *  1) did not queue everything initially scheduled to queue
  *  2) the last attempt to queue a request failed
  */
 static void blk_mq_commit_rqs(struct blk_mq_hw_ctx *hctx, int queued,
                               bool from_schedule)
 {
         if (hctx->queue->mq_ops->commit_rqs && queued) {
                 trace_block_unplug(hctx->queue, queued, !from_schedule);
                 hctx->queue->mq_ops->commit_rqs(hctx);
         }
 }
 
 /*
  * 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;
         int queued;
         blk_status_t ret = BLK_STS_OK;
         bool needs_resource = false;
 
         if (list_empty(list))
                 return false;
 
         /*
          * Now process all the entries, sending them to the driver.
          */
         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;
                 bd.last = list_empty(list);
 
                 /*
                  * 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:
                         needs_resource = true;
                         fallthrough;
                 case BLK_STS_DEV_RESOURCE:
                         blk_mq_handle_dev_resource(rq, list);
                         goto out;
                 default:
                         blk_mq_end_request(rq, ret);
                 }
         } while (!list_empty(list));
 out:
         /* 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) || ret != BLK_STS_OK)
                 blk_mq_commit_rqs(hctx, queued, false);
 
         /*
          * 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;
                 /* For non-shared tags, the RESTART check will suffice */
                 bool no_tag = prep == PREP_DISPATCH_NO_TAG &&
                         ((hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED) ||
                         blk_mq_is_shared_tags(hctx->flags));
 
                 if (nr_budgets)
                         blk_mq_release_budgets(q, list);
 
                 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.  We'll do
                  * similar if we couldn't get budget or couldn't lock a zone
                  * and SCHED_RESTART is set.
                  */
                 needs_restart = blk_mq_sched_needs_restart(hctx);
                 if (prep == PREP_DISPATCH_NO_BUDGET)
                         needs_resource = true;
                 if (!needs_restart ||
                     (no_tag && list_empty_careful(&hctx->dispatch_wait.entry)))
                         blk_mq_run_hw_queue(hctx, true);
                 else if (needs_resource)
                         blk_mq_delay_run_hw_queue(hctx, BLK_MQ_RESOURCE_DELAY);
 
                 blk_mq_update_dispatch_busy(hctx, true);
                 return false;
         }
 
         blk_mq_update_dispatch_busy(hctx, false);
         return true;
 }
 
 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;
 }
 
 /*
  * ->next_cpu is always calculated from hctx->cpumask, so simply use
  * it for speeding up the check
  */
 static bool blk_mq_hctx_empty_cpumask(struct blk_mq_hw_ctx *hctx)
 {
         return hctx->next_cpu >= nr_cpu_ids;
 }
 
 /*
  * 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;
 
         /* Switch to unbound if no allowable CPUs in this hctx */
         if (hctx->queue->nr_hw_queues == 1 || blk_mq_hctx_empty_cpumask(hctx))
                 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;
 }
 
 /**
  * blk_mq_delay_run_hw_queue - Run a hardware queue asynchronously.
  * @hctx: Pointer to the hardware queue to run.
  * @msecs: Milliseconds of delay to wait before running the queue.
  *
  * Run a hardware queue asynchronously with a delay of @msecs.
  */
 void blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs)
 {
         if (unlikely(blk_mq_hctx_stopped(hctx)))
                 return;
         kblockd_mod_delayed_work_on(blk_mq_hctx_next_cpu(hctx), &hctx->run_work,
                                     msecs_to_jiffies(msecs));
 }
 EXPORT_SYMBOL(blk_mq_delay_run_hw_queue);
 
 /**
  * blk_mq_run_hw_queue - Start to run a hardware queue.
  * @hctx: Pointer to the hardware queue to run.
  * @async: If we want to run the queue asynchronously.
  *
  * Check if the request queue is not in a quiesced state and if there are
  * pending requests to be sent. If this is true, run the queue to send requests
  * to hardware.
  */
 void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async)
 {
         bool need_run;
 
         /*
          * We can't run the queue inline with interrupts disabled.
          */
         WARN_ON_ONCE(!async && in_interrupt());
 
         might_sleep_if(!async && hctx->flags & BLK_MQ_F_BLOCKING);
 
         /*
          * 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.
          */
         __blk_mq_run_dispatch_ops(hctx->queue, false,
                 need_run = !blk_queue_quiesced(hctx->queue) &&
                 blk_mq_hctx_has_pending(hctx));
 
         if (!need_run)
                 return;
 
         if (async || !cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask)) {
                 blk_mq_delay_run_hw_queue(hctx, 0);
                 return;
         }
 
         blk_mq_run_dispatch_ops(hctx->queue,
                                 blk_mq_sched_dispatch_requests(hctx));
 }
 EXPORT_SYMBOL(blk_mq_run_hw_queue);
 
 /*
  * Return prefered queue to dispatch from (if any) for non-mq aware IO
  * scheduler.
  */
 static struct blk_mq_hw_ctx *blk_mq_get_sq_hctx(struct request_queue *q)
 {
         struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
         /*
          * If the IO scheduler does not respect hardware queues when
          * dispatching, we just don't bother with multiple HW queues and
          * dispatch from hctx for the current CPU since running multiple queues
          * just causes lock contention inside the scheduler and pointless cache
          * bouncing.
          */
         struct blk_mq_hw_ctx *hctx = ctx->hctxs[HCTX_TYPE_DEFAULT];
 
         if (!blk_mq_hctx_stopped(hctx))
                 return hctx;
         return NULL;
 }
 
 /**
  * blk_mq_run_hw_queues - Run all hardware queues in a request queue.
  * @q: Pointer to the request queue to run.
  * @async: If we want to run the queue asynchronously.
  */
 void blk_mq_run_hw_queues(struct request_queue *q, bool async)
 {
         struct blk_mq_hw_ctx *hctx, *sq_hctx;
         unsigned long i;
 
         sq_hctx = NULL;
         if (blk_queue_sq_sched(q))
                 sq_hctx = blk_mq_get_sq_hctx(q);
         queue_for_each_hw_ctx(q, hctx, i) {
                 if (blk_mq_hctx_stopped(hctx))
                         continue;
                 /*
                  * Dispatch from this hctx either if there's no hctx preferred
                  * by IO scheduler or if it has requests that bypass the
                  * scheduler.
                  */
                 if (!sq_hctx || sq_hctx == hctx ||
                     !list_empty_careful(&hctx->dispatch))
                         blk_mq_run_hw_queue(hctx, async);
         }
 }
 EXPORT_SYMBOL(blk_mq_run_hw_queues);
 
 /**
  * blk_mq_delay_run_hw_queues - Run all hardware queues asynchronously.
  * @q: Pointer to the request queue to run.
  * @msecs: Milliseconds of delay to wait before running the queues.
  */
 void blk_mq_delay_run_hw_queues(struct request_queue *q, unsigned long msecs)
 {
         struct blk_mq_hw_ctx *hctx, *sq_hctx;
         unsigned long i;
 
         sq_hctx = NULL;
         if (blk_queue_sq_sched(q))
                 sq_hctx = blk_mq_get_sq_hctx(q);
         queue_for_each_hw_ctx(q, hctx, i) {
                 if (blk_mq_hctx_stopped(hctx))
                         continue;
                 /*
                  * If there is already a run_work pending, leave the
                  * pending delay untouched. Otherwise, a hctx can stall
                  * if another hctx is re-delaying the other's work
                  * before the work executes.
                  */
                 if (delayed_work_pending(&hctx->run_work))
                         continue;
                 /*
                  * Dispatch from this hctx either if there's no hctx preferred
                  * by IO scheduler or if it has requests that bypass the
                  * scheduler.
                  */
                 if (!sq_hctx || sq_hctx == hctx ||
                     !list_empty_careful(&hctx->dispatch))
                         blk_mq_delay_run_hw_queue(hctx, msecs);
         }
 }
 EXPORT_SYMBOL(blk_mq_delay_run_hw_queues);
 
 /*
  * 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;
         unsigned long 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, hctx->flags & BLK_MQ_F_BLOCKING);
 }
 EXPORT_SYMBOL(blk_mq_start_hw_queue);
 
 void blk_mq_start_hw_queues(struct request_queue *q)
 {
         struct blk_mq_hw_ctx *hctx;
         unsigned long 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;
         unsigned long i;
 
         queue_for_each_hw_ctx(q, hctx, i)
                 blk_mq_start_stopped_hw_queue(hctx, async ||
                                         (hctx->flags & BLK_MQ_F_BLOCKING));
 }
 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 =
                 container_of(work, struct blk_mq_hw_ctx, run_work.work);
 
         blk_mq_run_dispatch_ops(hctx->queue,
                                 blk_mq_sched_dispatch_requests(hctx));
 }
 
 /**
  * blk_mq_request_bypass_insert - Insert a request at dispatch list.
  * @rq: Pointer to request to be inserted.
  * @flags: BLK_MQ_INSERT_*
  *
  * Should only be used carefully, when the caller knows we want to
  * bypass a potential IO scheduler on the target device.
  */
 static void blk_mq_request_bypass_insert(struct request *rq, blk_insert_t flags)
 {
         struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
 
         spin_lock(&hctx->lock);
         if (flags & BLK_MQ_INSERT_AT_HEAD)
                 list_add(&rq->queuelist, &hctx->dispatch);
         else
                 list_add_tail(&rq->queuelist, &hctx->dispatch);
         spin_unlock(&hctx->lock);
 }
 
 static void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx,
                 struct blk_mq_ctx *ctx, struct list_head *list,
                 bool run_queue_async)
 {
         struct request *rq;
         enum hctx_type type = hctx->type;
 
         /*
          * Try to issue requests directly if the hw queue isn't busy to save an
          * extra enqueue & dequeue to the sw queue.
          */
         if (!hctx->dispatch_busy && !run_queue_async) {
                 blk_mq_run_dispatch_ops(hctx->queue,
                         blk_mq_try_issue_list_directly(hctx, list));
                 if (list_empty(list))
                         goto out;
         }
 
         /*
          * 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(rq);
                 if (rq->cmd_flags & REQ_NOWAIT)
                         run_queue_async = true;
         }
 
         spin_lock(&ctx->lock);
         list_splice_tail_init(list, &ctx->rq_lists[type]);
         blk_mq_hctx_mark_pending(hctx, ctx);
         spin_unlock(&ctx->lock);
 out:
         blk_mq_run_hw_queue(hctx, run_queue_async);
 }
 
 static void blk_mq_insert_request(struct request *rq, blk_insert_t flags)
 {
         struct request_queue *q = rq->q;
         struct blk_mq_ctx *ctx = rq->mq_ctx;
         struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
 
         if (blk_rq_is_passthrough(rq)) {
                 /*
                  * Passthrough request have to be added to hctx->dispatch
                  * directly.  The device may be in a situation where it can't
                  * handle FS request, and always returns BLK_STS_RESOURCE for
                  * them, which gets them added to hctx->dispatch.
                  *
                  * If a passthrough request is required to unblock the queues,
                  * and it is added to the scheduler queue, there is no chance to
                  * dispatch it given we prioritize requests in hctx->dispatch.
                  */
                 blk_mq_request_bypass_insert(rq, flags);
         } else if (req_op(rq) == REQ_OP_FLUSH) {
                 /*
                  * Firstly normal IO request is inserted to scheduler queue or
                  * sw queue, meantime we add flush request to dispatch queue(
                  * hctx->dispatch) directly and there is at most one in-flight
                  * flush request for each hw queue, so it doesn't matter to add
                  * flush request to tail or front of the dispatch queue.
                  *
                  * Secondly in case of NCQ, flush request belongs to non-NCQ
                  * command, and queueing it will fail when there is any
                  * in-flight normal IO request(NCQ command). When adding flush
                  * rq to the front of hctx->dispatch, it is easier to introduce
                  * extra time to flush rq's latency because of S_SCHED_RESTART
                  * compared with adding to the tail of dispatch queue, then
                  * chance of flush merge is increased, and less flush requests
                  * will be issued to controller. It is observed that ~10% time
                  * is saved in blktests block/004 on disk attached to AHCI/NCQ
                  * drive when adding flush rq to the front of hctx->dispatch.
                  *
                  * Simply queue flush rq to the front of hctx->dispatch so that
                  * intensive flush workloads can benefit in case of NCQ HW.
                  */
                 blk_mq_request_bypass_insert(rq, BLK_MQ_INSERT_AT_HEAD);
         } else if (q->elevator) {
                 LIST_HEAD(list);
 
                 WARN_ON_ONCE(rq->tag != BLK_MQ_NO_TAG);
 
                 list_add(&rq->queuelist, &list);
                 q->elevator->type->ops.insert_requests(hctx, &list, flags);
         } else {
                 trace_block_rq_insert(rq);
 
                 spin_lock(&ctx->lock);
                 if (flags & BLK_MQ_INSERT_AT_HEAD)
                         list_add(&rq->queuelist, &ctx->rq_lists[hctx->type]);
                 else
                         list_add_tail(&rq->queuelist,
                                       &ctx->rq_lists[hctx->type]);
                 blk_mq_hctx_mark_pending(hctx, ctx);
                 spin_unlock(&ctx->lock);
         }
 }
 
 static void blk_mq_bio_to_request(struct request *rq, struct bio *bio,
                 unsigned int nr_segs)
 {
         int err;
 
         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);
 
         /* This can't fail, since GFP_NOIO includes __GFP_DIRECT_RECLAIM. */
         err = blk_crypto_rq_bio_prep(rq, bio, GFP_NOIO);
         WARN_ON_ONCE(err);
 
         blk_account_io_start(rq);
 }
 
 static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
                                             struct request *rq, bool last)
 {
         struct request_queue *q = rq->q;
         struct blk_mq_queue_data bd = {
                 .rq = rq,
                 .last = last,
         };
         blk_status_t ret;
 
         /*
          * 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);
                 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);
                 break;
         }
 
         return ret;
 }
 
 static bool blk_mq_get_budget_and_tag(struct request *rq)
 {
         int budget_token;
 
         budget_token = blk_mq_get_dispatch_budget(rq->q);
         if (budget_token < 0)
                 return false;
         blk_mq_set_rq_budget_token(rq, budget_token);
         if (!blk_mq_get_driver_tag(rq)) {
                 blk_mq_put_dispatch_budget(rq->q, budget_token);
                 return false;
         }
         return true;
 }
 
 /**
  * blk_mq_try_issue_directly - Try to send a request directly to device driver.
  * @hctx: Pointer of the associated hardware queue.
  * @rq: Pointer to request to be sent.
  *
  * If the device has enough resources to accept a new request now, send the
  * request directly to device driver. Else, insert at hctx->dispatch queue, so
  * we can try send it another time in the future. Requests inserted at this
  * queue have higher priority.
  */
 static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
                 struct request *rq)
 {
         blk_status_t ret;
 
         if (blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(rq->q)) {
                 blk_mq_insert_request(rq, 0);
                 return;
         }
 
         if ((rq->rq_flags & RQF_USE_SCHED) || !blk_mq_get_budget_and_tag(rq)) {
                 blk_mq_insert_request(rq, 0);
                 blk_mq_run_hw_queue(hctx, rq->cmd_flags & REQ_NOWAIT);
                 return;
         }
 
         ret = __blk_mq_issue_directly(hctx, rq, true);
         switch (ret) {
         case BLK_STS_OK:
                 break;
         case BLK_STS_RESOURCE:
         case BLK_STS_DEV_RESOURCE:
                 blk_mq_request_bypass_insert(rq, 0);
                 blk_mq_run_hw_queue(hctx, false);
                 break;
         default:
                 blk_mq_end_request(rq, ret);
                 break;
         }
 }
 
 static blk_status_t blk_mq_request_issue_directly(struct request *rq, bool last)
 {
         struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
 
         if (blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(rq->q)) {
                 blk_mq_insert_request(rq, 0);
                 return BLK_STS_OK;
         }
 
         if (!blk_mq_get_budget_and_tag(rq))
                 return BLK_STS_RESOURCE;
         return __blk_mq_issue_directly(hctx, rq, last);
 }
 
 static void blk_mq_plug_issue_direct(struct blk_plug *plug)
 {
         struct blk_mq_hw_ctx *hctx = NULL;
         struct request *rq;
         int queued = 0;
         blk_status_t ret = BLK_STS_OK;
 
         while ((rq = rq_list_pop(&plug->mq_list))) {
                 bool last = rq_list_empty(plug->mq_list);
 
                 if (hctx != rq->mq_hctx) {
                         if (hctx) {
                                 blk_mq_commit_rqs(hctx, queued, false);
                                 queued = 0;
                         }
                         hctx = rq->mq_hctx;
                 }
 
                 ret = blk_mq_request_issue_directly(rq, last);
                 switch (ret) {
                 case BLK_STS_OK:
                         queued++;
                         break;
                 case BLK_STS_RESOURCE:
                 case BLK_STS_DEV_RESOURCE:
                         blk_mq_request_bypass_insert(rq, 0);
                         blk_mq_run_hw_queue(hctx, false);
                         goto out;
                 default:
                         blk_mq_end_request(rq, ret);
                         break;
                 }
         }
 
 out:
         if (ret != BLK_STS_OK)
                 blk_mq_commit_rqs(hctx, queued, false);
 }
 
 static void __blk_mq_flush_plug_list(struct request_queue *q,
                                      struct blk_plug *plug)
 {
         if (blk_queue_quiesced(q))
                 return;
         q->mq_ops->queue_rqs(&plug->mq_list);
 }
 
 static void blk_mq_dispatch_plug_list(struct blk_plug *plug, bool from_sched)
 {
         struct blk_mq_hw_ctx *this_hctx = NULL;
         struct blk_mq_ctx *this_ctx = NULL;
         struct request *requeue_list = NULL;
         struct request **requeue_lastp = &requeue_list;
         unsigned int depth = 0;
         bool is_passthrough = false;
         LIST_HEAD(list);
 
         do {
                 struct request *rq = rq_list_pop(&plug->mq_list);
 
                 if (!this_hctx) {
                         this_hctx = rq->mq_hctx;
                         this_ctx = rq->mq_ctx;
                         is_passthrough = blk_rq_is_passthrough(rq);
                 } else if (this_hctx != rq->mq_hctx || this_ctx != rq->mq_ctx ||
                            is_passthrough != blk_rq_is_passthrough(rq)) {
                         rq_list_add_tail(&requeue_lastp, rq);
                         continue;
                 }
                 list_add(&rq->queuelist, &list);
                 depth++;
         } while (!rq_list_empty(plug->mq_list));
 
         plug->mq_list = requeue_list;
         trace_block_unplug(this_hctx->queue, depth, !from_sched);
 
         percpu_ref_get(&this_hctx->queue->q_usage_counter);
         /* passthrough requests should never be issued to the I/O scheduler */
         if (is_passthrough) {
                 spin_lock(&this_hctx->lock);
                 list_splice_tail_init(&list, &this_hctx->dispatch);
                 spin_unlock(&this_hctx->lock);
                 blk_mq_run_hw_queue(this_hctx, from_sched);
         } else if (this_hctx->queue->elevator) {
                 this_hctx->queue->elevator->type->ops.insert_requests(this_hctx,
                                 &list, 0);
                 blk_mq_run_hw_queue(this_hctx, from_sched);
         } else {
                 blk_mq_insert_requests(this_hctx, this_ctx, &list, from_sched);
         }
         percpu_ref_put(&this_hctx->queue->q_usage_counter);
 }
 
 void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 {
         struct request *rq;
 
         /*
          * We may have been called recursively midway through handling
          * plug->mq_list via a schedule() in the driver's queue_rq() callback.
          * To avoid mq_list changing under our feet, clear rq_count early and
          * bail out specifically if rq_count is 0 rather than checking
          * whether the mq_list is empty.
          */
         if (plug->rq_count == 0)
                 return;
         plug->rq_count = 0;
 
         if (!plug->multiple_queues && !plug->has_elevator && !from_schedule) {
                 struct request_queue *q;
 
                 rq = rq_list_peek(&plug->mq_list);
                 q = rq->q;
 
                 /*
                  * Peek first request and see if we have a ->queue_rqs() hook.
                  * If we do, we can dispatch the whole plug list in one go. We
                  * already know at this point that all requests belong to the
                  * same queue, caller must ensure that's the case.
                  */
                 if (q->mq_ops->queue_rqs) {
                         blk_mq_run_dispatch_ops(q,
                                 __blk_mq_flush_plug_list(q, plug));
                         if (rq_list_empty(plug->mq_list))
                                 return;
                 }
 
                 blk_mq_run_dispatch_ops(q,
                                 blk_mq_plug_issue_direct(plug));
                 if (rq_list_empty(plug->mq_list))
                         return;
         }
 
         do {
                 blk_mq_dispatch_plug_list(plug, from_schedule);
         } while (!rq_list_empty(plug->mq_list));
 }
 
 static void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
                 struct list_head *list)
 {
         int queued = 0;
         blk_status_t ret = BLK_STS_OK;
 
         while (!list_empty(list)) {
                 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));
                 switch (ret) {
                 case BLK_STS_OK:
                         queued++;
                         break;
                 case BLK_STS_RESOURCE:
                 case BLK_STS_DEV_RESOURCE:
                         blk_mq_request_bypass_insert(rq, 0);
                         if (list_empty(list))
                                 blk_mq_run_hw_queue(hctx, false);
                         goto out;
                 default:
                         blk_mq_end_request(rq, ret);
                         break;
                 }
         }
 
 out:
         if (ret != BLK_STS_OK)
                 blk_mq_commit_rqs(hctx, queued, false);
 }
 
 static bool blk_mq_attempt_bio_merge(struct request_queue *q,
                                      struct bio *bio, unsigned int nr_segs)
 {
         if (!blk_queue_nomerges(q) && bio_mergeable(bio)) {
                 if (blk_attempt_plug_merge(q, bio, nr_segs))
                         return true;
                 if (blk_mq_sched_bio_merge(q, bio, nr_segs))
                         return true;
         }
         return false;
 }
 
 static struct request *blk_mq_get_new_requests(struct request_queue *q,
                                                struct blk_plug *plug,
                                                struct bio *bio,
                                                unsigned int nsegs)
 {
         struct blk_mq_alloc_data data = {
                 .q              = q,
                 .nr_tags        = 1,
                 .cmd_flags      = bio->bi_opf,
         };
         struct request *rq;
 
         rq_qos_throttle(q, bio);
 
         if (plug) {
                 data.nr_tags = plug->nr_ios;
                 plug->nr_ios = 1;
                 data.cached_rq = &plug->cached_rq;
         }
 
         rq = __blk_mq_alloc_requests(&data);
         if (rq)
                 return rq;
         rq_qos_cleanup(q, bio);
         if (bio->bi_opf & REQ_NOWAIT)
                 bio_wouldblock_error(bio);
         return NULL;
 }
 
 /*
  * Check if there is a suitable cached request and return it.
  */
 static struct request *blk_mq_peek_cached_request(struct blk_plug *plug,
                 struct request_queue *q, blk_opf_t opf)
 {
         enum hctx_type type = blk_mq_get_hctx_type(opf);
         struct request *rq;
 
         if (!plug)
                 return NULL;
         rq = rq_list_peek(&plug->cached_rq);
         if (!rq || rq->q != q)
                 return NULL;
         if (type != rq->mq_hctx->type &&
             (type != HCTX_TYPE_READ || rq->mq_hctx->type != HCTX_TYPE_DEFAULT))
                 return NULL;
         if (op_is_flush(rq->cmd_flags) != op_is_flush(opf))
                 return NULL;
         return rq;
 }
 
 static void blk_mq_use_cached_rq(struct request *rq, struct blk_plug *plug,
                 struct bio *bio)
 {
         WARN_ON_ONCE(rq_list_peek(&plug->cached_rq) != rq);
 
         /*
          * If any qos ->throttle() end up blocking, we will have flushed the
          * plug and hence killed the cached_rq list as well. Pop this entry
          * before we throttle.
          */
         plug->cached_rq = rq_list_next(rq);
         rq_qos_throttle(rq->q, bio);
 
         blk_mq_rq_time_init(rq, 0);
         rq->cmd_flags = bio->bi_opf;
         INIT_LIST_HEAD(&rq->queuelist);
 }
 
 static bool bio_unaligned(const struct bio *bio, struct request_queue *q)
 {
         unsigned int bs_mask = queue_logical_block_size(q) - 1;
 
         /* .bi_sector of any zero sized bio need to be initialized */
         if ((bio->bi_iter.bi_size & bs_mask) ||
             ((bio->bi_iter.bi_sector << SECTOR_SHIFT) & bs_mask))
                 return true;
         return false;
 }
 
 /**
  * blk_mq_submit_bio - Create and send a request to block device.
  * @bio: Bio pointer.
  *
  * Builds up a request structure from @q and @bio and send to the device. The
  * request may not be queued directly to hardware if:
  * * This request can be merged with another one
  * * We want to place request at plug queue for possible future merging
  * * There is an IO scheduler active at this queue
  *
  * It will not queue the request if there is an error with the bio, or at the
  * request creation.
  */
 void blk_mq_submit_bio(struct bio *bio)
 {
         struct request_queue *q = bdev_get_queue(bio->bi_bdev);
         struct blk_plug *plug = current->plug;
         const int is_sync = op_is_sync(bio->bi_opf);
         struct blk_mq_hw_ctx *hctx;
         unsigned int nr_segs = 1;
         struct request *rq;
         blk_status_t ret;
 
         /*
          * If the plug has a cached request for this queue, try to use it.
          */
         rq = blk_mq_peek_cached_request(plug, q, bio->bi_opf);
 
         /*
          * A BIO that was released from a zone write plug has already been
          * through the preparation in this function, already holds a reference
          * on the queue usage counter, and is the only write BIO in-flight for
          * the target zone. Go straight to preparing a request for it.
          */
         if (bio_zone_write_plugging(bio)) {
                 nr_segs = bio->__bi_nr_segments;
                 if (rq)
                         blk_queue_exit(q);
                 goto new_request;
         }
 
         bio = blk_queue_bounce(bio, q);
 
         /*
          * The cached request already holds a q_usage_counter reference and we
          * don't have to acquire a new one if we use it.
          */
         if (!rq) {
                 if (unlikely(bio_queue_enter(bio)))
                         return;
         }
 
         /*
          * Device reconfiguration may change logical block size, so alignment
          * check has to be done with queue usage counter held
          */
         if (unlikely(bio_unaligned(bio, q))) {
                 bio_io_error(bio);
                 goto queue_exit;
         }
 
         if (unlikely(bio_may_exceed_limits(bio, &q->limits))) {
                 bio = __bio_split_to_limits(bio, &q->limits, &nr_segs);
                 if (!bio)
                         goto queue_exit;
         }
         if (!bio_integrity_prep(bio))
                 goto queue_exit;
 
         if (blk_mq_attempt_bio_merge(q, bio, nr_segs))
                 goto queue_exit;
 
         if (blk_queue_is_zoned(q) && blk_zone_plug_bio(bio, nr_segs))
                 goto queue_exit;
 
 new_request:
         if (!rq) {
                 rq = blk_mq_get_new_requests(q, plug, bio, nr_segs);
                 if (unlikely(!rq))
                         goto queue_exit;
         } else {
                 blk_mq_use_cached_rq(rq, plug, bio);
         }
 
         trace_block_getrq(bio);
 
         rq_qos_track(q, rq, bio);
 
         blk_mq_bio_to_request(rq, bio, nr_segs);
 
         ret = blk_crypto_rq_get_keyslot(rq);
         if (ret != BLK_STS_OK) {
                 bio->bi_status = ret;
                 bio_endio(bio);
                 blk_mq_free_request(rq);
                 return;
         }
 
         if (bio_zone_write_plugging(bio))
                 blk_zone_write_plug_init_request(rq);
 
         if (op_is_flush(bio->bi_opf) && blk_insert_flush(rq))
                 return;
 
         if (plug) {
                 blk_add_rq_to_plug(plug, rq);
                 return;
         }
 
         hctx = rq->mq_hctx;
         if ((rq->rq_flags & RQF_USE_SCHED) ||
             (hctx->dispatch_busy && (q->nr_hw_queues == 1 || !is_sync))) {
                 blk_mq_insert_request(rq, 0);
                 blk_mq_run_hw_queue(hctx, true);
         } else {
                 blk_mq_run_dispatch_ops(q, blk_mq_try_issue_directly(hctx, rq));
         }
         return;
 
 queue_exit:
         /*
          * Don't drop the queue reference if we were trying to use a cached
          * request and thus didn't acquire one.
          */
         if (!rq)
                 blk_queue_exit(q);
 }
 
 #ifdef CONFIG_BLK_MQ_STACKING
 /**
  * blk_insert_cloned_request - Helper for stacking drivers to submit a request
  * @rq: the request being queued
  */
 blk_status_t blk_insert_cloned_request(struct request *rq)
 {
         struct request_queue *q = rq->q;
         unsigned int max_sectors = blk_queue_get_max_sectors(rq);
         unsigned int max_segments = blk_rq_get_max_segments(rq);
         blk_status_t ret;
 
         if (blk_rq_sectors(rq) > max_sectors) {
                 /*
                  * SCSI device does not have a good way to return if
                  * Write Same/Zero is actually supported. If a device rejects
                  * a non-read/write command (discard, write same,etc.) the
                  * low-level device driver will set the relevant queue limit to
                  * 0 to prevent blk-lib from issuing more of the offending
                  * operations. Commands queued prior to the queue limit being
                  * reset need to be completed with BLK_STS_NOTSUPP to avoid I/O
                  * errors being propagated to upper layers.
                  */
                 if (max_sectors == 0)
                         return BLK_STS_NOTSUPP;
 
                 printk(KERN_ERR "%s: over max size limit. (%u > %u)\n",
                         __func__, blk_rq_sectors(rq), max_sectors);
                 return BLK_STS_IOERR;
         }
 
         /*
          * The queue settings related to segment counting may differ from the
          * original queue.
          */
         rq->nr_phys_segments = blk_recalc_rq_segments(rq);
         if (rq->nr_phys_segments > max_segments) {
                 printk(KERN_ERR "%s: over max segments limit. (%u > %u)\n",
                         __func__, rq->nr_phys_segments, max_segments);
                 return BLK_STS_IOERR;
         }
 
         if (q->disk && should_fail_request(q->disk->part0, blk_rq_bytes(rq)))
                 return BLK_STS_IOERR;
 
         ret = blk_crypto_rq_get_keyslot(rq);
         if (ret != BLK_STS_OK)
                 return ret;
 
         blk_account_io_start(rq);
 
         /*
          * Since we have a scheduler attached on the top device,
          * bypass a potential scheduler on the bottom device for
          * insert.
          */
         blk_mq_run_dispatch_ops(q,
                         ret = blk_mq_request_issue_directly(rq, true));
         if (ret)
                 blk_account_io_done(rq, blk_time_get_ns());
         return ret;
 }
 EXPORT_SYMBOL_GPL(blk_insert_cloned_request);
 
 /**
  * blk_rq_unprep_clone - Helper function to free all bios in a cloned request
  * @rq: the clone request to be cleaned up
  *
  * Description:
  *     Free all bios in @rq for a cloned request.
  */
 void blk_rq_unprep_clone(struct request *rq)
 {
         struct bio *bio;
 
         while ((bio = rq->bio) != NULL) {
                 rq->bio = bio->bi_next;
 
                 bio_put(bio);
         }
 }
 EXPORT_SYMBOL_GPL(blk_rq_unprep_clone);
 
 /**
  * blk_rq_prep_clone - Helper function to setup clone request
  * @rq: the request to be setup
  * @rq_src: original request to be cloned
  * @bs: bio_set that bios for clone are allocated from
  * @gfp_mask: memory allocation mask for bio
  * @bio_ctr: setup function to be called for each clone bio.
  *           Returns %0 for success, non %0 for failure.
  * @data: private data to be passed to @bio_ctr
  *
  * Description:
  *     Clones bios in @rq_src to @rq, and copies attributes of @rq_src to @rq.
  *     Also, pages which the original bios are pointing to are not copied
  *     and the cloned bios just point same pages.
  *     So cloned bios must be completed before original bios, which means
  *     the caller must complete @rq before @rq_src.
  */
 int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
                       struct bio_set *bs, gfp_t gfp_mask,
                       int (*bio_ctr)(struct bio *, struct bio *, void *),
                       void *data)
 {
         struct bio *bio, *bio_src;
 
         if (!bs)
                 bs = &fs_bio_set;
 
         __rq_for_each_bio(bio_src, rq_src) {
                 bio = bio_alloc_clone(rq->q->disk->part0, bio_src, gfp_mask,
                                       bs);
                 if (!bio)
                         goto free_and_out;
 
                 if (bio_ctr && bio_ctr(bio, bio_src, data))
                         goto free_and_out;
 
                 if (rq->bio) {
                         rq->biotail->bi_next = bio;
                         rq->biotail = bio;
                 } else {
                         rq->bio = rq->biotail = bio;
                 }
                 bio = NULL;
         }
 
         /* Copy attributes of the original request to the clone request. */
         rq->__sector = blk_rq_pos(rq_src);
         rq->__data_len = blk_rq_bytes(rq_src);
         if (rq_src->rq_flags & RQF_SPECIAL_PAYLOAD) {
                 rq->rq_flags |= RQF_SPECIAL_PAYLOAD;
                 rq->special_vec = rq_src->special_vec;
         }
         rq->nr_phys_segments = rq_src->nr_phys_segments;
         rq->ioprio = rq_src->ioprio;
         rq->write_hint = rq_src->write_hint;
 
         if (rq->bio && blk_crypto_rq_bio_prep(rq, rq->bio, gfp_mask) < 0)
                 goto free_and_out;
 
         return 0;
 
 free_and_out:
         if (bio)
                 bio_put(bio);
         blk_rq_unprep_clone(rq);
 
         return -ENOMEM;
 }
 EXPORT_SYMBOL_GPL(blk_rq_prep_clone);
 #endif /* CONFIG_BLK_MQ_STACKING */
 
 /*
  * Steal bios from a request and add them to a bio list.
  * The request must not have been partially completed before.
  */
 void blk_steal_bios(struct bio_list *list, struct request *rq)
 {
         if (rq->bio) {
                 if (list->tail)
                         list->tail->bi_next = rq->bio;
                 else
                         list->head = rq->bio;
                 list->tail = rq->biotail;
 
                 rq->bio = NULL;
                 rq->biotail = NULL;
         }
 
         rq->__data_len = 0;
 }
 EXPORT_SYMBOL_GPL(blk_steal_bios);
 
 static size_t order_to_size(unsigned int order)
 {
         return (size_t)PAGE_SIZE << order;
 }
 
 /* called before freeing request pool in @tags */
 static void blk_mq_clear_rq_mapping(struct blk_mq_tags *drv_tags,
                                     struct blk_mq_tags *tags)
 {
         struct page *page;
         unsigned long flags;
 
         /*
          * There is no need to clear mapping if driver tags is not initialized
          * or the mapping belongs to the driver tags.
          */
         if (!drv_tags || drv_tags == tags)
                 return;
 
         list_for_each_entry(page, &tags->page_list, lru) {
                 unsigned long start = (unsigned long)page_address(page);
                 unsigned long end = start + order_to_size(page->private);
                 int i;
 
                 for (i = 0; i < drv_tags->nr_tags; i++) {
                         struct request *rq = drv_tags->rqs[i];
                         unsigned long rq_addr = (unsigned long)rq;
 
                         if (rq_addr >= start && rq_addr < end) {
                                 WARN_ON_ONCE(req_ref_read(rq) != 0);
                                 cmpxchg(&drv_tags->rqs[i], rq, NULL);
                         }
                 }
         }
 
         /*
          * Wait until all pending iteration is done.
          *
          * Request reference is cleared and it is guaranteed to be observed
          * after the ->lock is released.
          */
         spin_lock_irqsave(&drv_tags->lock, flags);
         spin_unlock_irqrestore(&drv_tags->lock, flags);
 }
 
 void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags,
                      unsigned int hctx_idx)
 {
         struct blk_mq_tags *drv_tags;
         struct page *page;
 
         if (list_empty(&tags->page_list))
                 return;
 
         if (blk_mq_is_shared_tags(set->flags))
                 drv_tags = set->shared_tags;
         else
                 drv_tags = set->tags[hctx_idx];
 
         if (tags->static_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;
                 }
         }
 
         blk_mq_clear_rq_mapping(drv_tags, tags);
 
         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);
 }
 
 static enum hctx_type hctx_idx_to_type(struct blk_mq_tag_set *set,
                 unsigned int hctx_idx)
 {
         int i;
 
         for (i = 0; i < set->nr_maps; i++) {
                 unsigned int start = set->map[i].queue_offset;
                 unsigned int end = start + set->map[i].nr_queues;
 
                 if (hctx_idx >= start && hctx_idx < end)
                         break;
         }
 
         if (i >= set->nr_maps)
                 i = HCTX_TYPE_DEFAULT;
 
         return i;
 }
 
 static int blk_mq_get_hctx_node(struct blk_mq_tag_set *set,
                 unsigned int hctx_idx)
 {
         enum hctx_type type = hctx_idx_to_type(set, hctx_idx);
 
         return blk_mq_hw_queue_to_node(&set->map[type], hctx_idx);
 }
 
 static 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)
 {
         int node = blk_mq_get_hctx_node(set, hctx_idx);
         struct blk_mq_tags *tags;
 
         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)
                 goto err_free_tags;
 
         tags->static_rqs = kcalloc_node(nr_tags, sizeof(struct request *),
                                         GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY,
                                         node);
         if (!tags->static_rqs)
                 goto err_free_rqs;
 
         return tags;
 
 err_free_rqs:
         kfree(tags->rqs);
 err_free_tags:
         blk_mq_free_tags(tags);
         return NULL;
 }
 
 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;
 }
 
 static 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;
         int node = blk_mq_get_hctx_node(set, hctx_idx);
         size_t rq_size, left;
 
         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;
 }
 
 struct rq_iter_data {
         struct blk_mq_hw_ctx *hctx;
         bool has_rq;
 };
 
 static bool blk_mq_has_request(struct request *rq, void *data)
 {
         struct rq_iter_data *iter_data = data;
 
         if (rq->mq_hctx != iter_data->hctx)
                 return true;
         iter_data->has_rq = true;
         return false;
 }
 
 static bool blk_mq_hctx_has_requests(struct blk_mq_hw_ctx *hctx)
 {
         struct blk_mq_tags *tags = hctx->sched_tags ?
                         hctx->sched_tags : hctx->tags;
         struct rq_iter_data data = {
                 .hctx   = hctx,
         };
 
         blk_mq_all_tag_iter(tags, blk_mq_has_request, &data);
         return data.has_rq;
 }
 
 static bool blk_mq_hctx_has_online_cpu(struct blk_mq_hw_ctx *hctx,
                 unsigned int this_cpu)
 {
         enum hctx_type type = hctx->type;
         int cpu;
 
         /*
          * hctx->cpumask has to rule out isolated CPUs, but userspace still
          * might submit IOs on these isolated CPUs, so use the queue map to
          * check if all CPUs mapped to this hctx are offline
          */
         for_each_online_cpu(cpu) {
                 struct blk_mq_hw_ctx *h = blk_mq_map_queue_type(hctx->queue,
                                 type, cpu);
 
                 if (h != hctx)
                         continue;
 
                 /* this hctx has at least one online CPU */
                 if (this_cpu != cpu)
                         return true;
         }
 
         return false;
 }
 
 static int blk_mq_hctx_notify_offline(unsigned int cpu, struct hlist_node *node)
 {
         struct blk_mq_hw_ctx *hctx = hlist_entry_safe(node,
                         struct blk_mq_hw_ctx, cpuhp_online);
 
         if (blk_mq_hctx_has_online_cpu(hctx, cpu))
                 return 0;
 
         /*
          * Prevent new request from being allocated on the current hctx.
          *
          * The smp_mb__after_atomic() Pairs with the implied barrier in
          * test_and_set_bit_lock in sbitmap_get().  Ensures the inactive flag is
          * seen once we return from the tag allocator.
          */
         set_bit(BLK_MQ_S_INACTIVE, &hctx->state);
         smp_mb__after_atomic();
 
         /*
          * Try to grab a reference to the queue and wait for any outstanding
          * requests.  If we could not grab a reference the queue has been
          * frozen and there are no requests.
          */
         if (percpu_ref_tryget(&hctx->queue->q_usage_counter)) {
                 while (blk_mq_hctx_has_requests(hctx))
                         msleep(5);
                 percpu_ref_put(&hctx->queue->q_usage_counter);
         }
 
         return 0;
 }
 
 /*
  * Check if one CPU is mapped to the specified hctx
  *
  * Isolated CPUs have been ruled out from hctx->cpumask, which is supposed
  * to be used for scheduling kworker only. For other usage, please call this
  * helper for checking if one CPU belongs to the specified hctx
  */
 static bool blk_mq_cpu_mapped_to_hctx(unsigned int cpu,
                 const struct blk_mq_hw_ctx *hctx)
 {
         struct blk_mq_hw_ctx *mapped_hctx = blk_mq_map_queue_type(hctx->queue,
                         hctx->type, cpu);
 
         return mapped_hctx == hctx;
 }
 
 static int blk_mq_hctx_notify_online(unsigned int cpu, struct hlist_node *node)
 {
         struct blk_mq_hw_ctx *hctx = hlist_entry_safe(node,
                         struct blk_mq_hw_ctx, cpuhp_online);
 
         if (blk_mq_cpu_mapped_to_hctx(cpu, hctx))
                 clear_bit(BLK_MQ_S_INACTIVE, &hctx->state);
         return 0;
 }
 
 /*
  * '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);
         if (!blk_mq_cpu_mapped_to_hctx(cpu, hctx))
                 return 0;
 
         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)
 {
         if (!(hctx->flags & BLK_MQ_F_STACKING))
                 cpuhp_state_remove_instance_nocalls(CPUHP_AP_BLK_MQ_ONLINE,
                                                     &hctx->cpuhp_online);
         cpuhp_state_remove_instance_nocalls(CPUHP_BLK_MQ_DEAD,
                                             &hctx->cpuhp_dead);
 }
 
 /*
  * Before freeing hw queue, clearing the flush request reference in
  * tags->rqs[] for avoiding potential UAF.
  */
 static void blk_mq_clear_flush_rq_mapping(struct blk_mq_tags *tags,
                 unsigned int queue_depth, struct request *flush_rq)
 {
         int i;
         unsigned long flags;
 
         /* The hw queue may not be mapped yet */
         if (!tags)
                 return;
 
         WARN_ON_ONCE(req_ref_read(flush_rq) != 0);
 
         for (i = 0; i < queue_depth; i++)
                 cmpxchg(&tags->rqs[i], flush_rq, NULL);
 
         /*
          * Wait until all pending iteration is done.
          *
          * Request reference is cleared and it is guaranteed to be observed
          * after the ->lock is released.
          */
         spin_lock_irqsave(&tags->lock, flags);
         spin_unlock_irqrestore(&tags->lock, flags);
 }
 
 /* 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)
 {
         struct request *flush_rq = hctx->fq->flush_rq;
 
         if (blk_mq_hw_queue_mapped(hctx))
                 blk_mq_tag_idle(hctx);
 
         if (blk_queue_init_done(q))
                 blk_mq_clear_flush_rq_mapping(set->tags[hctx_idx],
                                 set->queue_depth, flush_rq);
         if (set->ops->exit_request)
                 set->ops->exit_request(set, flush_rq, hctx_idx);
 
         if (set->ops->exit_hctx)
                 set->ops->exit_hctx(hctx, hctx_idx);
 
         blk_mq_remove_cpuhp(hctx);
 
         xa_erase(&q->hctx_table, hctx_idx);
 
         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 long i;
 
         queue_for_each_hw_ctx(q, hctx, i) {
                 if (i == nr_queue)
                         break;
                 blk_mq_exit_hctx(q, set, hctx, i);
         }
 }
 
 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;
 
         if (!(hctx->flags & BLK_MQ_F_STACKING))
                 cpuhp_state_add_instance_nocalls(CPUHP_AP_BLK_MQ_ONLINE,
                                 &hctx->cpuhp_online);
         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;
 
         if (xa_insert(&q->hctx_table, hctx_idx, hctx, GFP_KERNEL))
                 goto exit_flush_rq;
 
         return 0;
 
  exit_flush_rq:
         if (set->ops->exit_request)
                 set->ops->exit_request(set, hctx->fq->flush_rq, hctx_idx);
  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(sizeof(struct blk_mq_hw_ctx), 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_QUEUE_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, false, false))
                 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(hctx->numa_node, set->cmd_size, gfp);
         if (!hctx->fq)
                 goto free_bitmap;
 
         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 = cpu_to_node(i);
                 }
         }
 }
 
 struct blk_mq_tags *blk_mq_alloc_map_and_rqs(struct blk_mq_tag_set *set,
                                              unsigned int hctx_idx,
                                              unsigned int depth)
 {
         struct blk_mq_tags *tags;
         int ret;
 
         tags = blk_mq_alloc_rq_map(set, hctx_idx, depth, set->reserved_tags);
         if (!tags)
                 return NULL;
 
         ret = blk_mq_alloc_rqs(set, tags, hctx_idx, depth);
         if (ret) {
                 blk_mq_free_rq_map(tags);
                 return NULL;
         }
 
         return tags;
 }
 
 static bool __blk_mq_alloc_map_and_rqs(struct blk_mq_tag_set *set,
                                        int hctx_idx)
 {
         if (blk_mq_is_shared_tags(set->flags)) {
                 set->tags[hctx_idx] = set->shared_tags;
 
                 return true;
         }
 
         set->tags[hctx_idx] = blk_mq_alloc_map_and_rqs(set, hctx_idx,
                                                        set->queue_depth);
 
         return set->tags[hctx_idx];
 }
 
 void blk_mq_free_map_and_rqs(struct blk_mq_tag_set *set,
                              struct blk_mq_tags *tags,
                              unsigned int hctx_idx)
 {
         if (tags) {
                 blk_mq_free_rqs(set, tags, hctx_idx);
                 blk_mq_free_rq_map(tags);
         }
 }
 
 static void __blk_mq_free_map_and_rqs(struct blk_mq_tag_set *set,
                                       unsigned int hctx_idx)
 {
         if (!blk_mq_is_shared_tags(set->flags))
                 blk_mq_free_map_and_rqs(set, set->tags[hctx_idx], hctx_idx);
 
         set->tags[hctx_idx] = NULL;
 }
 
 static void blk_mq_map_swqueue(struct request_queue *q)
 {
         unsigned int j, hctx_idx;
         unsigned long i;
         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_map_and_rqs(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) {
                 int cpu;
 
                 /*
                  * 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)
                                 __blk_mq_free_map_and_rqs(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);
 
                 /*
                  * Rule out isolated CPUs from hctx->cpumask to avoid
                  * running block kworker on isolated CPUs
                  */
                 for_each_cpu(cpu, hctx->cpumask) {
                         if (cpu_is_isolated(cpu))
                                 cpumask_clear_cpu(cpu, hctx->cpumask);
                 }
 
                 /*
                  * 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;
         unsigned long i;
 
         queue_for_each_hw_ctx(q, hctx, i) {
                 if (shared) {
                         hctx->flags |= BLK_MQ_F_TAG_QUEUE_SHARED;
                 } else {
                         blk_mq_tag_idle(hctx);
                         hctx->flags &= ~BLK_MQ_F_TAG_QUEUE_SHARED;
                 }
         }
 }
 
 static void blk_mq_update_tag_set_shared(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(&q->tag_set_list);
         if (list_is_singular(&set->tag_list)) {
                 /* just transitioned to unshared */
                 set->flags &= ~BLK_MQ_F_TAG_QUEUE_SHARED;
                 /* update existing queue */
                 blk_mq_update_tag_set_shared(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_QUEUE_SHARED)) {
                 set->flags |= BLK_MQ_F_TAG_QUEUE_SHARED;
                 /* update existing queue */
                 blk_mq_update_tag_set_shared(set, true);
         }
         if (set->flags & BLK_MQ_F_TAG_QUEUE_SHARED)
                 queue_set_hctx_shared(q, true);
         list_add_tail(&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;
         unsigned long 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);
         }
 
         xa_destroy(&q->hctx_table);
 
         /*
          * release .mq_kobj and sw queue's kobject now because
          * both share lifetime with request queue.
          */
         blk_mq_sysfs_deinit(q);
 }
 
 static bool blk_mq_can_poll(struct blk_mq_tag_set *set)
 {
         return set->nr_maps > HCTX_TYPE_POLL &&
                 set->map[HCTX_TYPE_POLL].nr_queues;
 }
 
 struct request_queue *blk_mq_alloc_queue(struct blk_mq_tag_set *set,
                 struct queue_limits *lim, void *queuedata)
 {
         struct queue_limits default_lim = { };
         struct request_queue *q;
         int ret;
 
         if (!lim)
                 lim = &default_lim;
         lim->features |= BLK_FEAT_IO_STAT | BLK_FEAT_NOWAIT;
         if (blk_mq_can_poll(set))
                 lim->features |= BLK_FEAT_POLL;
 
         q = blk_alloc_queue(lim, set->numa_node);
         if (IS_ERR(q))
                 return q;
         q->queuedata = queuedata;
         ret = blk_mq_init_allocated_queue(set, q);
         if (ret) {
                 blk_put_queue(q);
                 return ERR_PTR(ret);
         }
         return q;
 }
 EXPORT_SYMBOL(blk_mq_alloc_queue);
 
 /**
  * blk_mq_destroy_queue - shutdown a request queue
  * @q: request queue to shutdown
  *
  * This shuts down a request queue allocated by blk_mq_alloc_queue(). All future
  * requests will be failed with -ENODEV. The caller is responsible for dropping
  * the reference from blk_mq_alloc_queue() by calling blk_put_queue().
  *
  * Context: can sleep
  */
 void blk_mq_destroy_queue(struct request_queue *q)
 {
         WARN_ON_ONCE(!queue_is_mq(q));
         WARN_ON_ONCE(blk_queue_registered(q));
 
         might_sleep();
 
         blk_queue_flag_set(QUEUE_FLAG_DYING, q);
         blk_queue_start_drain(q);
         blk_mq_freeze_queue_wait(q);
 
         blk_sync_queue(q);
         blk_mq_cancel_work_sync(q);
         blk_mq_exit_queue(q);
 }
 EXPORT_SYMBOL(blk_mq_destroy_queue);
 
 struct gendisk *__blk_mq_alloc_disk(struct blk_mq_tag_set *set,
                 struct queue_limits *lim, void *queuedata,
                 struct lock_class_key *lkclass)
 {
         struct request_queue *q;
         struct gendisk *disk;
 
         q = blk_mq_alloc_queue(set, lim, queuedata);
         if (IS_ERR(q))
                 return ERR_CAST(q);
 
         disk = __alloc_disk_node(q, set->numa_node, lkclass);
         if (!disk) {
                 blk_mq_destroy_queue(q);
                 blk_put_queue(q);
                 return ERR_PTR(-ENOMEM);
         }
         set_bit(GD_OWNS_QUEUE, &disk->state);
         return disk;
 }
 EXPORT_SYMBOL(__blk_mq_alloc_disk);
 
 struct gendisk *blk_mq_alloc_disk_for_queue(struct request_queue *q,
                 struct lock_class_key *lkclass)
 {
         struct gendisk *disk;
 
         if (!blk_get_queue(q))
                 return NULL;
         disk = __alloc_disk_node(q, NUMA_NO_NODE, lkclass);
         if (!disk)
                 blk_put_queue(q);
         return disk;
 }
 EXPORT_SYMBOL(blk_mq_alloc_disk_for_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)
 {
         struct blk_mq_hw_ctx *hctx;
         unsigned long i, j;
 
         /* protect against switching io scheduler  */
         mutex_lock(&q->sysfs_lock);
         for (i = 0; i < set->nr_hw_queues; i++) {
                 int old_node;
                 int node = blk_mq_get_hctx_node(set, i);
                 struct blk_mq_hw_ctx *old_hctx = xa_load(&q->hctx_table, i);
 
                 if (old_hctx) {
                         old_node = old_hctx->numa_node;
                         blk_mq_exit_hctx(q, set, old_hctx, i);
                 }
 
                 if (!blk_mq_alloc_and_init_hctx(set, q, i, node)) {
                         if (!old_hctx)
                                 break;
                         pr_warn("Allocate new hctx on node %d fails, fallback to previous one on node %d\n",
                                         node, old_node);
                         hctx = blk_mq_alloc_and_init_hctx(set, q, i, old_node);
                         WARN_ON_ONCE(!hctx);
                 }
         }
         /*
          * 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;
         } else {
                 j = i;
                 q->nr_hw_queues = set->nr_hw_queues;
         }
 
         xa_for_each_start(&q->hctx_table, j, hctx, j)
                 blk_mq_exit_hctx(q, set, hctx, j);
         mutex_unlock(&q->sysfs_lock);
 }
 
 int blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
                 struct request_queue *q)
 {
         /* mark the queue as mq asap */
         q->mq_ops = set->ops;
 
         /*
          * ->tag_set has to be setup before initialize hctx, which cpuphp
          * handler needs it for checking queue mapping
          */
         q->tag_set = set;
 
         if (blk_mq_alloc_ctxs(q))
                 goto err_exit;
 
         /* init q->mq_kobj and sw queues' kobjects */
         blk_mq_sysfs_init(q);
 
         INIT_LIST_HEAD(&q->unused_hctx_list);
         spin_lock_init(&q->unused_hctx_lock);
 
         xa_init(&q->hctx_table);
 
         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->queue_flags |= QUEUE_FLAG_MQ_DEFAULT;
 
         INIT_DELAYED_WORK(&q->requeue_work, blk_mq_requeue_work);
         INIT_LIST_HEAD(&q->flush_list);
         INIT_LIST_HEAD(&q->requeue_list);
         spin_lock_init(&q->requeue_lock);
 
         q->nr_requests = set->queue_depth;
 
         blk_mq_init_cpu_queues(q, set->nr_hw_queues);
         blk_mq_add_queue_tag_set(set, q);
         blk_mq_map_swqueue(q);
         return 0;
 
 err_hctxs:
         blk_mq_release(q);
 err_exit:
         q->mq_ops = NULL;
         return -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;
 
         /* Checks hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED. */
         blk_mq_exit_hw_queues(q, set, set->nr_hw_queues);
         /* May clear BLK_MQ_F_TAG_QUEUE_SHARED in hctx->flags. */
         blk_mq_del_queue_tag_set(q);
 }
 
 static int __blk_mq_alloc_rq_maps(struct blk_mq_tag_set *set)
 {
         int i;
 
         if (blk_mq_is_shared_tags(set->flags)) {
                 set->shared_tags = blk_mq_alloc_map_and_rqs(set,
                                                 BLK_MQ_NO_HCTX_IDX,
                                                 set->queue_depth);
                 if (!set->shared_tags)
                         return -ENOMEM;
         }
 
         for (i = 0; i < set->nr_hw_queues; i++) {
                 if (!__blk_mq_alloc_map_and_rqs(set, i))
                         goto out_unwind;
                 cond_resched();
         }
 
         return 0;
 
 out_unwind:
         while (--i >= 0)
                 __blk_mq_free_map_and_rqs(set, i);
 
         if (blk_mq_is_shared_tags(set->flags)) {
                 blk_mq_free_map_and_rqs(set, set->shared_tags,
                                         BLK_MQ_NO_HCTX_IDX);
         }
 
         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_set_map_and_rqs(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 void 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) {
                 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]);
 
                 set->ops->map_queues(set);
         } else {
                 BUG_ON(set->nr_maps > 1);
                 blk_mq_map_queues(&set->map[HCTX_TYPE_DEFAULT]);
         }
 }
 
 static int blk_mq_realloc_tag_set_tags(struct blk_mq_tag_set *set,
                                        int new_nr_hw_queues)
 {
         struct blk_mq_tags **new_tags;
         int i;
 
         if (set->nr_hw_queues >= new_nr_hw_queues)
                 goto done;
 
         new_tags = kcalloc_node(new_nr_hw_queues, sizeof(struct blk_mq_tags *),
                                 GFP_KERNEL, set->numa_node);
         if (!new_tags)
                 return -ENOMEM;
 
         if (set->tags)
                 memcpy(new_tags, set->tags, set->nr_hw_queues *
                        sizeof(*set->tags));
         kfree(set->tags);
         set->tags = new_tags;
 
         for (i = set->nr_hw_queues; i < new_nr_hw_queues; i++) {
                 if (!__blk_mq_alloc_map_and_rqs(set, i)) {
                         while (--i >= set->nr_hw_queues)
                                 __blk_mq_free_map_and_rqs(set, i);
                         return -ENOMEM;
                 }
                 cond_resched();
         }
 
 done:
         set->nr_hw_queues = new_nr_hw_queues;
         return 0;
 }
 
 /*
  * Alloc a tag set to be associated with one or more request queues.
  * May fail with EINVAL for various error conditions. May adjust the
  * requested depth down, if 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  64 tags to prevent
          * using too much memory.
          */
         if (is_kdump_kernel())
                 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;
 
         if (set->flags & BLK_MQ_F_BLOCKING) {
                 set->srcu = kmalloc(sizeof(*set->srcu), GFP_KERNEL);
                 if (!set->srcu)
                         return -ENOMEM;
                 ret = init_srcu_struct(set->srcu);
                 if (ret)
                         goto out_free_srcu;
         }
 
         ret = -ENOMEM;
         set->tags = kcalloc_node(set->nr_hw_queues,
                                  sizeof(struct blk_mq_tags *), GFP_KERNEL,
                                  set->numa_node);
         if (!set->tags)
                 goto out_cleanup_srcu;
 
         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 = set->nr_hw_queues;
         }
 
         blk_mq_update_queue_map(set);
 
         ret = blk_mq_alloc_set_map_and_rqs(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;
 out_cleanup_srcu:
         if (set->flags & BLK_MQ_F_BLOCKING)
                 cleanup_srcu_struct(set->srcu);
 out_free_srcu:
         if (set->flags & BLK_MQ_F_BLOCKING)
                 kfree(set->srcu);
         return ret;
 }
 EXPORT_SYMBOL(blk_mq_alloc_tag_set);
 
 /* allocate and initialize a tagset for a simple single-queue device */
 int blk_mq_alloc_sq_tag_set(struct blk_mq_tag_set *set,
                 const struct blk_mq_ops *ops, unsigned int queue_depth,
                 unsigned int set_flags)
 {
         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;
         return blk_mq_alloc_tag_set(set);
 }
 EXPORT_SYMBOL_GPL(blk_mq_alloc_sq_tag_set);
 
 void blk_mq_free_tag_set(struct blk_mq_tag_set *set)
 {
         int i, j;
 
         for (i = 0; i < set->nr_hw_queues; i++)
                 __blk_mq_free_map_and_rqs(set, i);
 
         if (blk_mq_is_shared_tags(set->flags)) {
                 blk_mq_free_map_and_rqs(set, set->shared_tags,
                                         BLK_MQ_NO_HCTX_IDX);
         }
 
         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;
         if (set->flags & BLK_MQ_F_BLOCKING) {
                 cleanup_srcu_struct(set->srcu);
                 kfree(set->srcu);
         }
 }
 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 ret;
         unsigned long i;
 
         if (WARN_ON_ONCE(!q->mq_freeze_depth))
                 return -EINVAL;
 
         if (!set)
                 return -EINVAL;
 
         if (q->nr_requests == nr)
                 return 0;
 
         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->sched_tags,
                                                       nr, true);
                 } else {
                         ret = blk_mq_tag_update_depth(hctx, &hctx->tags, nr,
                                                       false);
                 }
                 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;
                 if (blk_mq_is_shared_tags(set->flags)) {
                         if (q->elevator)
                                 blk_mq_tag_update_sched_shared_tags(q);
                         else
                                 blk_mq_tag_resize_shared_tags(set, nr);
                 }
         }
 
         blk_mq_unquiesce_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;
 
         qe = kmalloc(sizeof(*qe), GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY);
         if (!qe)
                 return false;
 
         /* q->elevator needs protection from ->sysfs_lock */
         mutex_lock(&q->sysfs_lock);
 
         /* the check has to be done with holding sysfs_lock */
         if (!q->elevator) {
                 kfree(qe);
                 goto unlock;
         }
 
         INIT_LIST_HEAD(&qe->node);
         qe->q = q;
         qe->type = q->elevator->type;
         /* keep a reference to the elevator module as we'll switch back */
         __elevator_get(qe->type);
         list_add(&qe->node, head);
         elevator_disable(q);
 unlock:
         mutex_unlock(&q->sysfs_lock);
 
         return true;
 }
 
 static struct blk_mq_qe_pair *blk_lookup_qe_pair(struct list_head *head,
                                                 struct request_queue *q)
 {
         struct blk_mq_qe_pair *qe;
 
         list_for_each_entry(qe, head, node)
                 if (qe->q == q)
                         return qe;
 
         return NULL;
 }
 
 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;
 
         qe = blk_lookup_qe_pair(head, q);
         if (!qe)
                 return;
         t = qe->type;
         list_del(&qe->node);
         kfree(qe);
 
         mutex_lock(&q->sysfs_lock);
         elevator_switch(q, t);
         /* drop the reference acquired in blk_mq_elv_switch_none */
         elevator_put(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 = set->nr_hw_queues;
         int i;
 
         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);
         /*
          * 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_hctxs(q);
         }
 
         if (blk_mq_realloc_tag_set_tags(set, nr_hw_queues) < 0)
                 goto reregister;
 
 fallback:
         blk_mq_update_queue_map(set);
         list_for_each_entry(q, &set->tag_list, tag_set_list) {
                 struct queue_limits lim;
 
                 blk_mq_realloc_hw_ctxs(set, q);
 
                 if (q->nr_hw_queues != set->nr_hw_queues) {
                         int i = prev_nr_hw_queues;
 
                         pr_warn("Increasing nr_hw_queues to %d fails, fallback to %d\n",
                                         nr_hw_queues, prev_nr_hw_queues);
                         for (; i < set->nr_hw_queues; i++)
                                 __blk_mq_free_map_and_rqs(set, i);
 
                         set->nr_hw_queues = prev_nr_hw_queues;
                         goto fallback;
                 }
                 lim = queue_limits_start_update(q);
                 if (blk_mq_can_poll(set))
                         lim.features |= BLK_FEAT_POLL;
                 else
                         lim.features &= ~BLK_FEAT_POLL;
                 if (queue_limits_commit_update(q, &lim) < 0)
                         pr_warn("updating the poll flag failed\n");
                 blk_mq_map_swqueue(q);
         }
 
 reregister:
         list_for_each_entry(q, &set->tag_list, tag_set_list) {
                 blk_mq_sysfs_register_hctxs(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);
 
         /* Free the excess tags when nr_hw_queues shrink. */
         for (i = set->nr_hw_queues; i < prev_nr_hw_queues; i++)
                 __blk_mq_free_map_and_rqs(set, i);
 }
 
 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);
 
 static int blk_hctx_poll(struct request_queue *q, struct blk_mq_hw_ctx *hctx,
                          struct io_comp_batch *iob, unsigned int flags)
 {
         long state = get_current_state();
         int ret;
 
         do {
                 ret = q->mq_ops->poll(hctx, iob);
                 if (ret > 0) {
                         __set_current_state(TASK_RUNNING);
                         return ret;
                 }
 
                 if (signal_pending_state(state, current))
                         __set_current_state(TASK_RUNNING);
                 if (task_is_running(current))
                         return 1;
 
                 if (ret < 0 || (flags & BLK_POLL_ONESHOT))
                         break;
                 cpu_relax();
         } while (!need_resched());
 
         __set_current_state(TASK_RUNNING);
         return 0;
 }
 
 int blk_mq_poll(struct request_queue *q, blk_qc_t cookie,
                 struct io_comp_batch *iob, unsigned int flags)
 {
         struct blk_mq_hw_ctx *hctx = xa_load(&q->hctx_table, cookie);
 
         return blk_hctx_poll(q, hctx, iob, flags);
 }
 
 int blk_rq_poll(struct request *rq, struct io_comp_batch *iob,
                 unsigned int poll_flags)
 {
         struct request_queue *q = rq->q;
         int ret;
 
         if (!blk_rq_is_poll(rq))
                 return 0;
         if (!percpu_ref_tryget(&q->q_usage_counter))
                 return 0;
 
         ret = blk_hctx_poll(q, rq->mq_hctx, iob, poll_flags);
         blk_queue_exit(q);
 
         return ret;
 }
 EXPORT_SYMBOL_GPL(blk_rq_poll);
 
 unsigned int blk_mq_rq_cpu(struct request *rq)
 {
         return rq->mq_ctx->cpu;
 }
 EXPORT_SYMBOL(blk_mq_rq_cpu);
 
 void blk_mq_cancel_work_sync(struct request_queue *q)
 {
         struct blk_mq_hw_ctx *hctx;
         unsigned long i;
 
         cancel_delayed_work_sync(&q->requeue_work);
 
         queue_for_each_hw_ctx(q, hctx, i)
                 cancel_delayed_work_sync(&hctx->run_work);
 }
 
 static int __init blk_mq_init(void)
 {
         int i;
 
         for_each_possible_cpu(i)
                 init_llist_head(&per_cpu(blk_cpu_done, i));
         for_each_possible_cpu(i)
                 INIT_CSD(&per_cpu(blk_cpu_csd, i),
                          __blk_mq_complete_request_remote, NULL);
         open_softirq(BLOCK_SOFTIRQ, blk_done_softirq);
 
         cpuhp_setup_state_nocalls(CPUHP_BLOCK_SOFTIRQ_DEAD,
                                   "block/softirq:dead", NULL,
                                   blk_softirq_cpu_dead);
         cpuhp_setup_state_multi(CPUHP_BLK_MQ_DEAD, "block/mq:dead", NULL,
                                 blk_mq_hctx_notify_dead);
         cpuhp_setup_state_multi(CPUHP_AP_BLK_MQ_ONLINE, "block/mq:online",
                                 blk_mq_hctx_notify_online,
                                 blk_mq_hctx_notify_offline);
         return 0;
 }
 subsys_initcall(blk_mq_init);