OSCL-LXR linux-6.0.1/​block/​blk-mq.c	Source navigation Diff markup Identifier search General search
	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // 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/sysctl.h>
 #include <linux/sched/topology.h>
 #include <linux/sched/signal.h>
 #include <linux/delay.h>
 #include <linux/crash_dump.h>
 #include <linux/prefetch.h>
 #include <linux/blk-crypto.h>
 #include <linux/part_stat.h>
 
 #include <trace/events/block.h>
 
 #include <linux/blk-mq.h>
 #include <linux/t10-pi.h>
 #include "blk.h"
 #include "blk-mq.h"
 #include "blk-mq-debugfs.h"
 #include "blk-mq-tag.h"
 #include "blk-pm.h"
 #include "blk-stat.h"
 #include "blk-mq-sched.h"
 #include "blk-rq-qos.h"
 #include "blk-ioprio.h"
 
 static DEFINE_PER_CPU(struct llist_head, blk_cpu_done);
 
 static void blk_mq_poll_stats_start(struct request_queue *q);
 static void blk_mq_poll_stats_fn(struct blk_stat_callback *cb);
 
 static int blk_mq_poll_stats_bkt(const struct request *rq)
 {
     int ddir, sectors, bucket;
 
     ddir = rq_data_dir(rq);
     sectors = blk_rq_stats_sectors(rq);
 
     bucket = ddir + 2 * ilog2(sectors);
 
     if (bucket < 0)
         return -1;
     else if (bucket >= BLK_MQ_POLL_STATS_BKTS)
         return ddir + BLK_MQ_POLL_STATS_BKTS - 2;
 
     return bucket;
 }
 
 #define BLK_QC_T_SHIFT      16
 #define BLK_QC_T_INTERNAL   (1U << 31)
 
 static inline struct blk_mq_hw_ctx *blk_qc_to_hctx(struct request_queue *q,
         blk_qc_t qc)
 {
     return xa_load(&q->hctx_table,
             (qc & ~BLK_QC_T_INTERNAL) >> BLK_QC_T_SHIFT);
 }
 
 static inline struct request *blk_qc_to_rq(struct blk_mq_hw_ctx *hctx,
         blk_qc_t qc)
 {
     unsigned int tag = qc & ((1U << BLK_QC_T_SHIFT) - 1);
 
     if (qc & BLK_QC_T_INTERNAL)
         return blk_mq_tag_to_rq(hctx->sched_tags, tag);
     return blk_mq_tag_to_rq(hctx->tags, tag);
 }
 
 static inline blk_qc_t blk_rq_to_qc(struct request *rq)
 {
     return (rq->mq_hctx->queue_num << BLK_QC_T_SHIFT) |
         (rq->tag != -1 ?
          rq->tag : (rq->internal_tag | BLK_QC_T_INTERNAL));
 }
 
 /*
  * 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) &&
         (!mi->part->bd_partno || 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
  * @q: request queue.
  *
  * Note: it is driver's responsibility for making sure that quiesce has
  * been started.
  */
 void blk_mq_wait_quiesce_done(struct request_queue *q)
 {
     if (blk_queue_has_srcu(q))
         synchronize_srcu(q->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);
     blk_mq_wait_quiesce_done(q);
 }
 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_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 = ktime_get_ns();
     rq->part = NULL;
     blk_crypto_rq_set_defaults(rq);
 }
 EXPORT_SYMBOL(blk_rq_init);
 
 static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
         struct blk_mq_tags *tags, unsigned int tag, u64 alloc_time_ns)
 {
     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_ELV)) {
         rq->tag = tag;
         rq->internal_tag = BLK_MQ_NO_TAG;
     } else {
         rq->tag = BLK_MQ_NO_TAG;
         rq->internal_tag = tag;
     }
     rq->timeout = 0;
 
     if (blk_mq_need_time_stamp(rq))
         rq->start_time_ns = ktime_get_ns();
     else
         rq->start_time_ns = 0;
     rq->part = NULL;
 #ifdef CONFIG_BLK_RQ_ALLOC_TIME
     rq->alloc_time_ns = alloc_time_ns;
 #endif
     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_ELV) {
         struct elevator_queue *e = data->q->elevator;
 
         INIT_HLIST_NODE(&rq->hash);
         RB_CLEAR_NODE(&rq->rb_node);
 
         if (!op_is_flush(data->cmd_flags) &&
             e->type->ops.prepare_request) {
             e->type->ops.prepare_request(rq);
             rq->rq_flags |= RQF_ELVPRIV;
         }
     }
 
     return rq;
 }
 
 static inline struct request *
 __blk_mq_alloc_requests_batch(struct blk_mq_alloc_data *data,
         u64 alloc_time_ns)
 {
     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, alloc_time_ns);
         rq_list_add(data->cached_rq, rq);
         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 = ktime_get_ns();
 
     if (data->cmd_flags & REQ_NOWAIT)
         data->flags |= BLK_MQ_REQ_NOWAIT;
 
     if (q->elevator) {
         struct elevator_queue *e = q->elevator;
 
         data->rq_flags |= RQF_ELV;
 
         /*
          * Flush/passthrough requests are special and go directly to the
          * dispatch list. Don't include reserved tags in the
          * limiting, as it isn't useful.
          */
         if (!op_is_flush(data->cmd_flags) &&
             !blk_op_is_passthrough(data->cmd_flags) &&
             e->type->ops.limit_depth &&
             !(data->flags & BLK_MQ_REQ_RESERVED))
             e->type->ops.limit_depth(data->cmd_flags, data);
     }
 
 retry:
     data->ctx = blk_mq_get_ctx(q);
     data->hctx = blk_mq_map_queue(q, data->cmd_flags, data->ctx);
     if (!(data->rq_flags & RQF_ELV))
         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, alloc_time_ns);
         if (rq)
             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;
     }
 
     return blk_mq_rq_ctx_init(data, blk_mq_tags_from_data(data), tag,
                     alloc_time_ns);
 }
 
 struct request *blk_mq_alloc_request(struct request_queue *q, 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    = 1,
     };
     struct request *rq;
     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;
     unsigned int cpu;
     unsigned int tag;
     int ret;
 
     /* alloc_time includes depth and tag waits */
     if (blk_queue_rq_alloc_time(q))
         alloc_time_ns = ktime_get_ns();
 
     /*
      * If the tag allocator sleeps we could get an allocation for a
      * different hardware context.  No need to complicate the low level
      * allocator for this for the rare use case of a command tied to
      * a specific queue.
      */
     if (WARN_ON_ONCE(!(flags & (BLK_MQ_REQ_NOWAIT | BLK_MQ_REQ_RESERVED))))
         return ERR_PTR(-EINVAL);
 
     if (hctx_idx >= q->nr_hw_queues)
         return ERR_PTR(-EIO);
 
     ret = blk_queue_enter(q, flags);
     if (ret)
         return ERR_PTR(ret);
 
     /*
      * Check if the hardware context is actually mapped to anything.
      * If not tell the caller that it should skip this queue.
      */
     ret = -EXDEV;
     data.hctx = 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)
         blk_mq_tag_busy(data.hctx);
     else
         data.rq_flags |= RQF_ELV;
 
     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;
     return blk_mq_rq_ctx_init(&data, blk_mq_tags_from_data(&data), tag,
                     alloc_time_ns);
 
 out_queue_exit:
     blk_queue_exit(q);
     return ERR_PTR(ret);
 }
 EXPORT_SYMBOL_GPL(blk_mq_alloc_request_hctx);
 
 static void __blk_mq_free_request(struct request *rq)
 {
     struct request_queue *q = rq->q;
     struct blk_mq_ctx *ctx = rq->mq_ctx;
     struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
     const int sched_tag = rq->internal_tag;
 
     blk_crypto_free_request(rq);
     blk_pm_mark_last_busy(rq);
     rq->mq_hctx = NULL;
     if (rq->tag != BLK_MQ_NO_TAG)
         blk_mq_put_tag(hctx->tags, ctx, rq->tag);
     if (sched_tag != BLK_MQ_NO_TAG)
         blk_mq_put_tag(hctx->sched_tags, ctx, sched_tag);
     blk_mq_sched_restart(hctx);
     blk_queue_exit(q);
 }
 
 void blk_mq_free_request(struct request *rq)
 {
     struct request_queue *q = rq->q;
     struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
 
     if ((rq->rq_flags & RQF_ELVPRIV) &&
         q->elevator->type->ops.finish_request)
         q->elevator->type->ops.finish_request(rq);
 
     if (rq->rq_flags & RQF_MQ_INFLIGHT)
         __blk_mq_dec_active_requests(hctx);
 
     if (unlikely(laptop_mode && !blk_rq_is_passthrough(rq)))
         laptop_io_completion(q->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 req_bio_endio(struct request *rq, struct bio *bio,
               unsigned int nbytes, blk_status_t error)
 {
     if (unlikely(error)) {
         bio->bi_status = error;
     } else if (req_op(rq) == REQ_OP_ZONE_APPEND) {
         /*
          * Partial zone append completions cannot be supported as the
          * BIO fragments may end up not being written sequentially.
          */
         if (bio->bi_iter.bi_size != nbytes)
             bio->bi_status = BLK_STS_IOERR;
         else
             bio->bi_iter.bi_sector = rq->__sector;
     }
 
     bio_advance(bio, nbytes);
 
     if (unlikely(rq->rq_flags & RQF_QUIET))
         bio_set_flag(bio, BIO_QUIET);
     /* don't actually finish bio if it's part of flush sequence */
     if (bio->bi_iter.bi_size == 0 && !(rq->rq_flags & RQF_FLUSH_SEQ))
         bio_endio(bio);
 }
 
 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;
 
 #ifdef CONFIG_BLK_DEV_INTEGRITY
     if (blk_integrity_rq(req) && req_op(req) == REQ_OP_READ)
         req->q->integrity.profile->complete_fn(req, total_bytes);
 #endif
 
     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);
 
         if (req_op(req) == REQ_OP_ZONE_APPEND)
             bio->bi_iter.bi_sector = req->__sector;
 
         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.
      */
     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)
 {
     int total_bytes;
 
     trace_block_rq_complete(req, error, nr_bytes);
 
     if (!req->bio)
         return false;
 
 #ifdef CONFIG_BLK_DEV_INTEGRITY
     if (blk_integrity_rq(req) && req_op(req) == REQ_OP_READ &&
         error == BLK_STS_OK)
         req->q->integrity.profile->complete_fn(req, nr_bytes);
 #endif
 
     if (unlikely(error && !blk_rq_is_passthrough(req) &&
              !(req->rq_flags & RQF_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 (bio_bytes == bio->bi_iter.bi_size)
             req->bio = bio->bi_next;
 
         /* Completion has already been traced */
         bio_clear_flag(bio, BIO_TRACE_COMPLETION);
         req_bio_endio(req, bio, bio_bytes, error);
 
         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 void __blk_account_io_done(struct request *req, u64 now)
 {
     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_unlock();
 }
 
 static inline void blk_account_io_done(struct request *req, u64 now)
 {
     /*
      * 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))
         __blk_account_io_done(req, now);
 }
 
 static void __blk_account_io_start(struct request *rq)
 {
     /*
      * 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 (rq->bio)
         rq->part = rq->bio->bi_bdev;
     else
         rq->part = rq->q->disk->part0;
 
     part_stat_lock();
     update_io_ticks(rq->part, jiffies, false);
     part_stat_unlock();
 }
 
 static inline void blk_account_io_start(struct request *req)
 {
     if (blk_do_io_stat(req))
         __blk_account_io_start(req);
 }
 
 static inline void __blk_mq_end_request_acct(struct request *rq, u64 now)
 {
     if (rq->rq_flags & RQF_STATS) {
         blk_mq_poll_stats_start(rq->q);
         blk_stat_add(rq, now);
     }
 
     blk_mq_sched_completed_request(rq, now);
     blk_account_io_done(rq, now);
 }
 
 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, ktime_get_ns());
 
     if (rq->end_io) {
         rq_qos_done(rq->q, rq);
         rq->end_io(rq, error);
     } else {
         blk_mq_free_request(rq);
     }
 }
 EXPORT_SYMBOL(__blk_mq_end_request);
 
 void blk_mq_end_request(struct request *rq, blk_status_t error)
 {
     if (blk_update_request(rq, error, blk_rq_bytes(rq)))
         BUG();
     __blk_mq_end_request(rq, error);
 }
 EXPORT_SYMBOL(blk_mq_end_request);
 
 #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;
 
     /*
      * All requests should have been marked as RQF_MQ_INFLIGHT, so
      * update hctx->nr_active in batch
      */
     if (hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED)
         __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 = ktime_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);
 
         rq_qos_done(rq->q, rq);
 
         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?  Complete locally */
     if (cpu == rq->mq_ctx->cpu ||
         (!test_bit(QUEUE_FLAG_SAME_FORCE, &rq->q->queue_flags) &&
          cpus_share_cache(cpu, rq->mq_ctx->cpu)))
         return false;
 
     /* don't try to IPI to an offline CPU */
     return cpu_online(rq->mq_ctx->cpu);
 }
 
 static void blk_mq_complete_send_ipi(struct request *rq)
 {
     struct llist_head *list;
     unsigned int cpu;
 
     cpu = rq->mq_ctx->cpu;
     list = &per_cpu(blk_cpu_done, cpu);
     if (llist_add(&rq->ipi_list, list)) {
         INIT_CSD(&rq->csd, __blk_mq_complete_request_remote, rq);
         smp_call_function_single_async(cpu, &rq->csd);
     }
 }
 
 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 a polled request, always complete locally, it's pointless
      * to redirect the completion.
      */
     if (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)) {
         rq->io_start_time_ns = ktime_get_ns();
         rq->stats_sectors = blk_rq_sectors(rq);
         rq->rq_flags |= RQF_STATS;
         rq_qos_issue(q, rq);
     }
 
     WARN_ON_ONCE(blk_mq_rq_state(rq) != MQ_RQ_IDLE);
 
     blk_add_timer(rq);
     WRITE_ONCE(rq->state, MQ_RQ_IN_FLIGHT);
 
 #ifdef CONFIG_BLK_DEV_INTEGRITY
     if (blk_integrity_rq(rq) && req_op(rq) == REQ_OP_WRITE)
         q->integrity.profile->prepare_fn(rq);
 #endif
     if (rq->bio && rq->bio->bi_opf & REQ_POLLED)
             WRITE_ONCE(rq->bio->bi_cookie, blk_rq_to_qc(rq));
 }
 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);
         trace_block_plug(rq->q);
     }
 
     if (!plug->multiple_queues && last && last->q != rq->q)
         plug->multiple_queues = true;
     if (!plug->has_elevator && (rq->rq_flags & RQF_ELV))
         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)
 {
     WARN_ON(irqs_disabled());
     WARN_ON(!blk_rq_is_passthrough(rq));
 
     blk_account_io_start(rq);
     if (current->plug)
         blk_add_rq_to_plug(current->plug, rq);
     else
         blk_mq_sched_insert_request(rq, at_head, true, false);
 }
 EXPORT_SYMBOL_GPL(blk_execute_rq_nowait);
 
 struct blk_rq_wait {
     struct completion done;
     blk_status_t ret;
 };
 
 static void 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);
 }
 
 static bool blk_rq_is_poll(struct request *rq)
 {
     if (!rq->mq_hctx)
         return false;
     if (rq->mq_hctx->type != HCTX_TYPE_POLL)
         return false;
     if (WARN_ON_ONCE(!rq->bio))
         return false;
     return true;
 }
 
 static void blk_rq_poll_completion(struct request *rq, struct completion *wait)
 {
     do {
         bio_poll(rq->bio, 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_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_sched_insert_request(rq, at_head, true, false);
 
     if (blk_rq_is_poll(rq)) {
         blk_rq_poll_completion(rq, &wait.done);
     } else {
         /*
          * Prevent hang_check timer from firing at us during very long
          * I/O
          */
         unsigned long hang_check = sysctl_hung_task_timeout_secs;
 
         if (hang_check)
             while (!wait_for_completion_io_timeout(&wait.done,
                     hang_check * (HZ/2)))
                 ;
         else
             wait_for_completion_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)
 {
     __blk_mq_requeue_request(rq);
 
     /* this request will be re-inserted to io scheduler queue */
     blk_mq_sched_requeue_request(rq);
 
     blk_mq_add_to_requeue_list(rq, true, kick_requeue_list);
 }
 EXPORT_SYMBOL(blk_mq_requeue_request);
 
 static void blk_mq_requeue_work(struct work_struct *work)
 {
     struct request_queue *q =
         container_of(work, struct request_queue, requeue_work.work);
     LIST_HEAD(rq_list);
     struct request *rq, *next;
 
     spin_lock_irq(&q->requeue_lock);
     list_splice_init(&q->requeue_list, &rq_list);
     spin_unlock_irq(&q->requeue_lock);
 
     list_for_each_entry_safe(rq, next, &rq_list, queuelist) {
         if (!(rq->rq_flags & (RQF_SOFTBARRIER | RQF_DONTPREP)))
             continue;
 
         rq->rq_flags &= ~RQF_SOFTBARRIER;
         list_del_init(&rq->queuelist);
         /*
          * If RQF_DONTPREP, rq has contained some driver specific
          * data, so insert it to hctx dispatch list to avoid any
          * merge.
          */
         if (rq->rq_flags & RQF_DONTPREP)
             blk_mq_request_bypass_insert(rq, false, false);
         else
             blk_mq_sched_insert_request(rq, true, false, false);
     }
 
     while (!list_empty(&rq_list)) {
         rq = list_entry(rq_list.next, struct request, queuelist);
         list_del_init(&rq->queuelist);
         blk_mq_sched_insert_request(rq, false, false, false);
     }
 
     blk_mq_run_hw_queues(q, false);
 }
 
 void blk_mq_add_to_requeue_list(struct request *rq, bool at_head,
                 bool kick_requeue_list)
 {
     struct request_queue *q = rq->q;
     unsigned long flags;
 
     /*
      * We abuse this flag that is otherwise used by the I/O scheduler to
      * request head insertion from the workqueue.
      */
     BUG_ON(rq->rq_flags & RQF_SOFTBARRIER);
 
     spin_lock_irqsave(&q->requeue_lock, flags);
     if (at_head) {
         rq->rq_flags |= RQF_SOFTBARRIER;
         list_add(&rq->queuelist, &q->requeue_list);
     } else {
         list_add_tail(&rq->queuelist, &q->requeue_list);
     }
     spin_unlock_irqrestore(&q->requeue_lock, flags);
 
     if (kick_requeue_list)
         blk_mq_kick_requeue_list(q);
 }
 
 void blk_mq_kick_requeue_list(struct request_queue *q)
 {
     kblockd_mod_delayed_work_on(WORK_CPU_UNBOUND, &q->requeue_work, 0);
 }
 EXPORT_SYMBOL(blk_mq_kick_requeue_list);
 
 void blk_mq_delay_kick_requeue_list(struct request_queue *q,
                     unsigned long msecs)
 {
     kblockd_mod_delayed_work_on(WORK_CPU_UNBOUND, &q->requeue_work,
                     msecs_to_jiffies(msecs));
 }
 EXPORT_SYMBOL(blk_mq_delay_kick_requeue_list);
 
 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.
      */
     if (blk_mq_request_started(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);
 }
 
 static bool blk_mq_req_expired(struct request *rq, unsigned long *next)
 {
     unsigned long deadline;
 
     if (blk_mq_rq_state(rq) != MQ_RQ_IN_FLIGHT)
         return false;
     if (rq->rq_flags & RQF_TIMED_OUT)
         return false;
 
     deadline = READ_ONCE(rq->deadline);
     if (time_after_eq(jiffies, deadline))
         return true;
 
     if (*next == 0)
         *next = deadline;
     else if (time_after(*next, deadline))
         *next = deadline;
     return false;
 }
 
 void blk_mq_put_rq_ref(struct request *rq)
 {
     if (is_flush_rq(rq))
         rq->end_io(rq, 0);
     else if (req_ref_put_and_test(rq))
         __blk_mq_free_request(rq);
 }
 
 static bool blk_mq_check_expired(struct request *rq, void *priv)
 {
     unsigned long *next = 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, next))
         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);
     unsigned long next = 0;
     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;
 
     blk_mq_queue_tag_busy_iter(q, blk_mq_check_expired, &next);
 
     if (next != 0) {
         mod_timer(&q->timeout, next);
     } else {
         /*
          * Request timeouts are handled as a forward rolling timer. If
          * we end up here it means that no requests are pending and
          * also that no request has been pending for a while. Mark
          * each hctx as idle.
          */
         queue_for_each_hw_ctx(q, hctx, i) {
             /* the hctx may be unmapped, so check it here */
             if (blk_mq_hw_queue_mapped(hctx))
                 blk_mq_tag_idle(hctx);
         }
     }
     blk_queue_exit(q);
 }
 
 struct flush_busy_ctx_data {
     struct blk_mq_hw_ctx *hctx;
     struct list_head *list;
 };
 
 static bool flush_busy_ctx(struct sbitmap *sb, unsigned int bitnr, void *data)
 {
     struct flush_busy_ctx_data *flush_data = data;
     struct blk_mq_hw_ctx *hctx = flush_data->hctx;
     struct blk_mq_ctx *ctx = hctx->ctxs[bitnr];
     enum hctx_type type = hctx->type;
 
     spin_lock(&ctx->lock);
     list_splice_tail_init(&ctx->rq_lists[type], flush_data->list);
     sbitmap_clear_bit(sb, bitnr);
     spin_unlock(&ctx->lock);
     return true;
 }
 
 /*
  * Process software queues that have been marked busy, splicing them
  * to the for-dispatch
  */
 void blk_mq_flush_busy_ctxs(struct blk_mq_hw_ctx *hctx, struct list_head *list)
 {
     struct flush_busy_ctx_data data = {
         .hctx = hctx,
         .list = list,
     };
 
     sbitmap_for_each_set(&hctx->ctx_map, flush_busy_ctx, &data);
 }
 EXPORT_SYMBOL_GPL(blk_mq_flush_busy_ctxs);
 
 struct dispatch_rq_data {
     struct blk_mq_hw_ctx *hctx;
     struct request *rq;
 };
 
 static bool dispatch_rq_from_ctx(struct sbitmap *sb, unsigned int bitnr,
         void *data)
 {
     struct dispatch_rq_data *dispatch_data = data;
     struct blk_mq_hw_ctx *hctx = dispatch_data->hctx;
     struct blk_mq_ctx *ctx = hctx->ctxs[bitnr];
     enum hctx_type type = hctx->type;
 
     spin_lock(&ctx->lock);
     if (!list_empty(&ctx->rq_lists[type])) {
         dispatch_data->rq = list_entry_rq(ctx->rq_lists[type].next);
         list_del_init(&dispatch_data->rq->queuelist);
         if (list_empty(&ctx->rq_lists[type]))
             sbitmap_clear_bit(sb, bitnr);
     }
     spin_unlock(&ctx->lock);
 
     return !dispatch_data->rq;
 }
 
 struct request *blk_mq_dequeue_from_ctx(struct blk_mq_hw_ctx *hctx,
                     struct blk_mq_ctx *start)
 {
     unsigned off = start ? start->index_hw[hctx->type] : 0;
     struct dispatch_rq_data data = {
         .hctx = hctx,
         .rq   = NULL,
     };
 
     __sbitmap_for_each_set(&hctx->ctx_map, off,
                    dispatch_rq_from_ctx, &data);
 
     return data.rq;
 }
 
 static 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;
     return true;
 }
 
 bool __blk_mq_get_driver_tag(struct blk_mq_hw_ctx *hctx, struct request *rq)
 {
     if (rq->tag == BLK_MQ_NO_TAG && !__blk_mq_alloc_driver_tag(rq))
         return false;
 
     if ((hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED) &&
             !(rq->rq_flags & RQF_MQ_INFLIGHT)) {
         rq->rq_flags |= RQF_MQ_INFLIGHT;
         __blk_mq_inc_active_requests(hctx);
     }
     hctx->tags->rqs[rq->tag] = rq;
     return true;
 }
 
 static int blk_mq_dispatch_wake(wait_queue_entry_t *wait, unsigned mode,
                 int flags, void *key)
 {
     struct blk_mq_hw_ctx *hctx;
 
     hctx = container_of(wait, struct blk_mq_hw_ctx, dispatch_wait);
 
     spin_lock(&hctx->dispatch_wait_lock);
     if (!list_empty(&wait->entry)) {
         struct sbitmap_queue *sbq;
 
         list_del_init(&wait->entry);
         sbq = &hctx->tags->bitmap_tags;
         atomic_dec(&sbq->ws_active);
     }
     spin_unlock(&hctx->dispatch_wait_lock);
 
     blk_mq_run_hw_queue(hctx, true);
     return 1;
 }
 
 /*
  * Mark us waiting for a tag. For shared tags, this involves hooking us into
  * the tag wakeups. For non-shared tags, we can simply mark us needing a
  * restart. For both cases, take care to check the condition again after
  * marking us as waiting.
  */
 static bool blk_mq_mark_tag_wait(struct blk_mq_hw_ctx *hctx,
                  struct request *rq)
 {
     struct sbitmap_queue *sbq = &hctx->tags->bitmap_tags;
     struct wait_queue_head *wq;
     wait_queue_entry_t *wait;
     bool ret;
 
     if (!(hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED)) {
         blk_mq_sched_mark_restart_hctx(hctx);
 
         /*
          * It's possible that a tag was freed in the window between the
          * allocation failure and adding the hardware queue to the wait
          * queue.
          *
          * Don't clear RESTART here, someone else could have set it.
          * At most this will cost an extra queue run.
          */
         return blk_mq_get_driver_tag(rq);
     }
 
     wait = &hctx->dispatch_wait;
     if (!list_empty_careful(&wait->entry))
         return false;
 
     wq = &bt_wait_ptr(sbq, hctx)->wait;
 
     spin_lock_irq(&wq->lock);
     spin_lock(&hctx->dispatch_wait_lock);
     if (!list_empty(&wait->entry)) {
         spin_unlock(&hctx->dispatch_wait_lock);
         spin_unlock_irq(&wq->lock);
         return false;
     }
 
     atomic_inc(&sbq->ws_active);
     wait->flags &= ~WQ_FLAG_EXCLUSIVE;
     __add_wait_queue(wq, wait);
 
     /*
      * It's possible that a tag was freed in the window between the
      * allocation failure and adding the hardware queue to the wait
      * queue.
      */
     ret = blk_mq_get_driver_tag(rq);
     if (!ret) {
         spin_unlock(&hctx->dispatch_wait_lock);
         spin_unlock_irq(&wq->lock);
         return false;
     }
 
     /*
      * We got a tag, remove ourselves from the wait queue to ensure
      * someone else gets the wakeup.
      */
     list_del_init(&wait->entry);
     atomic_dec(&sbq->ws_active);
     spin_unlock(&hctx->dispatch_wait_lock);
     spin_unlock_irq(&wq->lock);
 
     return true;
 }
 
 #define BLK_MQ_DISPATCH_BUSY_EWMA_WEIGHT  8
 #define BLK_MQ_DISPATCH_BUSY_EWMA_FACTOR  4
 /*
  * Update dispatch busy with the Exponential Weighted Moving Average(EWMA):
  * - EWMA is one simple way to compute running average value
  * - weight(7/8 and 1/8) is applied so that it can decrease exponentially
  * - take 4 as factor for avoiding to get too small(0) result, and this
  *   factor doesn't matter because EWMA decreases exponentially
  */
 static void blk_mq_update_dispatch_busy(struct blk_mq_hw_ctx *hctx, bool busy)
 {
     unsigned int ewma;
 
     ewma = hctx->dispatch_busy;
 
     if (!ewma && !busy)
         return;
 
     ewma *= BLK_MQ_DISPATCH_BUSY_EWMA_WEIGHT - 1;
     if (busy)
         ewma += 1 << BLK_MQ_DISPATCH_BUSY_EWMA_FACTOR;
     ewma /= BLK_MQ_DISPATCH_BUSY_EWMA_WEIGHT;
 
     hctx->dispatch_busy = ewma;
 }
 
 #define BLK_MQ_RESOURCE_DELAY   3       /* ms units */
 
 static void blk_mq_handle_dev_resource(struct request *rq,
                        struct list_head *list)
 {
     struct request *next =
         list_first_entry_or_null(list, struct request, queuelist);
 
     /*
      * If an I/O scheduler has been configured and we got a driver tag for
      * the next request already, free it.
      */
     if (next)
         blk_mq_put_driver_tag(next);
 
     list_add(&rq->queuelist, list);
     __blk_mq_requeue_request(rq);
 }
 
 static void blk_mq_handle_zone_resource(struct request *rq,
                     struct list_head *zone_list)
 {
     /*
      * If we end up here it is because we cannot dispatch a request to a
      * specific zone due to LLD level zone-write locking or other zone
      * related resource not being available. In this case, set the request
      * aside in zone_list for retrying it later.
      */
     list_add(&rq->queuelist, zone_list);
     __blk_mq_requeue_request(rq);
 }
 
 enum prep_dispatch {
     PREP_DISPATCH_OK,
     PREP_DISPATCH_NO_TAG,
     PREP_DISPATCH_NO_BUDGET,
 };
 
 static enum prep_dispatch blk_mq_prep_dispatch_rq(struct request *rq,
                           bool need_budget)
 {
     struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
     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);
     }
 }
 
 /*
  * Returns true if we did some work AND can potentially do more.
  */
 bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
                  unsigned int nr_budgets)
 {
     enum prep_dispatch prep;
     struct request_queue *q = hctx->queue;
     struct request *rq, *nxt;
     int errors, queued;
     blk_status_t ret = BLK_STS_OK;
     LIST_HEAD(zone_list);
     bool needs_resource = false;
 
     if (list_empty(list))
         return false;
 
     /*
      * Now process all the entries, sending them to the driver.
      */
     errors = queued = 0;
     do {
         struct blk_mq_queue_data bd;
 
         rq = list_first_entry(list, struct request, queuelist);
 
         WARN_ON_ONCE(hctx != rq->mq_hctx);
         prep = blk_mq_prep_dispatch_rq(rq, !nr_budgets);
         if (prep != PREP_DISPATCH_OK)
             break;
 
         list_del_init(&rq->queuelist);
 
         bd.rq = rq;
 
         /*
          * Flag last if we have no more requests, or if we have more
          * but can't assign a driver tag to it.
          */
         if (list_empty(list))
             bd.last = true;
         else {
             nxt = list_first_entry(list, struct request, queuelist);
             bd.last = !blk_mq_get_driver_tag(nxt);
         }
 
         /*
          * once the request is queued to lld, no need to cover the
          * budget any more
          */
         if (nr_budgets)
             nr_budgets--;
         ret = q->mq_ops->queue_rq(hctx, &bd);
         switch (ret) {
         case BLK_STS_OK:
             queued++;
             break;
         case BLK_STS_RESOURCE:
             needs_resource = true;
             fallthrough;
         case BLK_STS_DEV_RESOURCE:
             blk_mq_handle_dev_resource(rq, list);
             goto out;
         case BLK_STS_ZONE_RESOURCE:
             /*
              * Move the request to zone_list and keep going through
              * the dispatch list to find more requests the drive can
              * accept.
              */
             blk_mq_handle_zone_resource(rq, &zone_list);
             needs_resource = true;
             break;
         default:
             errors++;
             blk_mq_end_request(rq, ret);
         }
     } while (!list_empty(list));
 out:
     if (!list_empty(&zone_list))
         list_splice_tail_init(&zone_list, list);
 
     /* 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) || errors || needs_resource ||
          ret == BLK_STS_DEV_RESOURCE) && q->mq_ops->commit_rqs && queued)
         q->mq_ops->commit_rqs(hctx);
     /*
      * 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);
 
         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_restart && needs_resource)
             blk_mq_delay_run_hw_queue(hctx, BLK_MQ_RESOURCE_DELAY);
 
         blk_mq_update_dispatch_busy(hctx, true);
         return false;
     } else
         blk_mq_update_dispatch_busy(hctx, false);
 
     return (queued + errors) != 0;
 }
 
 /**
  * __blk_mq_run_hw_queue - Run a hardware queue.
  * @hctx: Pointer to the hardware queue to run.
  *
  * Send pending requests to the hardware.
  */
 static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
 {
     /*
      * We can't run the queue inline with ints disabled. Ensure that
      * we catch bad users of this early.
      */
     WARN_ON_ONCE(in_interrupt());
 
     blk_mq_run_dispatch_ops(hctx->queue,
             blk_mq_sched_dispatch_requests(hctx));
 }
 
 static inline int blk_mq_first_mapped_cpu(struct blk_mq_hw_ctx *hctx)
 {
     int cpu = cpumask_first_and(hctx->cpumask, cpu_online_mask);
 
     if (cpu >= nr_cpu_ids)
         cpu = cpumask_first(hctx->cpumask);
     return cpu;
 }
 
 /*
  * It'd be great if the workqueue API had a way to pass
  * in a mask and had some smarts for more clever placement.
  * For now we just round-robin here, switching for every
  * BLK_MQ_CPU_WORK_BATCH queued items.
  */
 static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
 {
     bool tried = false;
     int next_cpu = hctx->next_cpu;
 
     if (hctx->queue->nr_hw_queues == 1)
         return WORK_CPU_UNBOUND;
 
     if (--hctx->next_cpu_batch <= 0) {
 select_cpu:
         next_cpu = cpumask_next_and(next_cpu, hctx->cpumask,
                 cpu_online_mask);
         if (next_cpu >= nr_cpu_ids)
             next_cpu = blk_mq_first_mapped_cpu(hctx);
         hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;
     }
 
     /*
      * Do unbound schedule if we can't find a online CPU for this hctx,
      * and it should only happen in the path of handling CPU DEAD.
      */
     if (!cpu_online(next_cpu)) {
         if (!tried) {
             tried = true;
             goto select_cpu;
         }
 
         /*
          * Make sure to re-select CPU next time once after CPUs
          * in hctx->cpumask become online again.
          */
         hctx->next_cpu = next_cpu;
         hctx->next_cpu_batch = 1;
         return WORK_CPU_UNBOUND;
     }
 
     hctx->next_cpu = next_cpu;
     return next_cpu;
 }
 
 /**
  * __blk_mq_delay_run_hw_queue - Run (or schedule to run) a hardware queue.
  * @hctx: Pointer to the hardware queue to run.
  * @async: If we want to run the queue asynchronously.
  * @msecs: Milliseconds of delay to wait before running the queue.
  *
  * If !@async, try to run the queue now. Else, run the queue asynchronously and
  * with a delay of @msecs.
  */
 static void __blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async,
                     unsigned long msecs)
 {
     if (unlikely(blk_mq_hctx_stopped(hctx)))
         return;
 
     if (!async && !(hctx->flags & BLK_MQ_F_BLOCKING)) {
         if (cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask)) {
             __blk_mq_run_hw_queue(hctx);
             return;
         }
     }
 
     kblockd_mod_delayed_work_on(blk_mq_hctx_next_cpu(hctx), &hctx->run_work,
                     msecs_to_jiffies(msecs));
 }
 
 /**
  * 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)
 {
     __blk_mq_delay_run_hw_queue(hctx, true, 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;
 
     /*
      * 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)
         __blk_mq_delay_run_hw_queue(hctx, async, 0);
 }
 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, false);
 }
 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);
 }
 EXPORT_SYMBOL(blk_mq_start_stopped_hw_queues);
 
 static void blk_mq_run_work_fn(struct work_struct *work)
 {
     struct blk_mq_hw_ctx *hctx;
 
     hctx = container_of(work, struct blk_mq_hw_ctx, run_work.work);
 
     /*
      * If we are stopped, don't run the queue.
      */
     if (blk_mq_hctx_stopped(hctx))
         return;
 
     __blk_mq_run_hw_queue(hctx);
 }
 
 static inline void __blk_mq_insert_req_list(struct blk_mq_hw_ctx *hctx,
                         struct request *rq,
                         bool at_head)
 {
     struct blk_mq_ctx *ctx = rq->mq_ctx;
     enum hctx_type type = hctx->type;
 
     lockdep_assert_held(&ctx->lock);
 
     trace_block_rq_insert(rq);
 
     if (at_head)
         list_add(&rq->queuelist, &ctx->rq_lists[type]);
     else
         list_add_tail(&rq->queuelist, &ctx->rq_lists[type]);
 }
 
 void __blk_mq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
                  bool at_head)
 {
     struct blk_mq_ctx *ctx = rq->mq_ctx;
 
     lockdep_assert_held(&ctx->lock);
 
     __blk_mq_insert_req_list(hctx, rq, at_head);
     blk_mq_hctx_mark_pending(hctx, ctx);
 }
 
 /**
  * blk_mq_request_bypass_insert - Insert a request at dispatch list.
  * @rq: Pointer to request to be inserted.
  * @at_head: true if the request should be inserted at the head of the list.
  * @run_queue: If we should run the hardware queue after inserting the request.
  *
  * Should only be used carefully, when the caller knows we want to
  * bypass a potential IO scheduler on the target device.
  */
 void blk_mq_request_bypass_insert(struct request *rq, bool at_head,
                   bool run_queue)
 {
     struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
 
     spin_lock(&hctx->lock);
     if (at_head)
         list_add(&rq->queuelist, &hctx->dispatch);
     else
         list_add_tail(&rq->queuelist, &hctx->dispatch);
     spin_unlock(&hctx->lock);
 
     if (run_queue)
         blk_mq_run_hw_queue(hctx, false);
 }
 
 void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
                 struct list_head *list)
 
 {
     struct request *rq;
     enum hctx_type type = hctx->type;
 
     /*
      * preemption doesn't flush plug list, so it's possible ctx->cpu is
      * offline now
      */
     list_for_each_entry(rq, list, queuelist) {
         BUG_ON(rq->mq_ctx != ctx);
         trace_block_rq_insert(rq);
     }
 
     spin_lock(&ctx->lock);
     list_splice_tail_init(list, &ctx->rq_lists[type]);
     blk_mq_hctx_mark_pending(hctx, ctx);
     spin_unlock(&ctx->lock);
 }
 
 static void blk_mq_commit_rqs(struct blk_mq_hw_ctx *hctx, int *queued,
                   bool from_schedule)
 {
     if (hctx->queue->mq_ops->commit_rqs) {
         trace_block_unplug(hctx->queue, *queued, !from_schedule);
         hctx->queue->mq_ops->commit_rqs(hctx);
     }
     *queued = 0;
 }
 
 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;
     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 blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
                         struct request *rq,
                         bool bypass_insert, bool last)
 {
     struct request_queue *q = rq->q;
     bool run_queue = true;
     int budget_token;
 
     /*
      * RCU or SRCU read lock is needed before checking quiesced flag.
      *
      * When queue is stopped or quiesced, ignore 'bypass_insert' from
      * blk_mq_request_issue_directly(), and return BLK_STS_OK to caller,
      * and avoid driver to try to dispatch again.
      */
     if (blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)) {
         run_queue = false;
         bypass_insert = false;
         goto insert;
     }
 
     if ((rq->rq_flags & RQF_ELV) && !bypass_insert)
         goto insert;
 
     budget_token = blk_mq_get_dispatch_budget(q);
     if (budget_token < 0)
         goto insert;
 
     blk_mq_set_rq_budget_token(rq, budget_token);
 
     if (!blk_mq_get_driver_tag(rq)) {
         blk_mq_put_dispatch_budget(q, budget_token);
         goto insert;
     }
 
     return __blk_mq_issue_directly(hctx, rq, last);
 insert:
     if (bypass_insert)
         return BLK_STS_RESOURCE;
 
     blk_mq_sched_insert_request(rq, false, run_queue, false);
 
     return BLK_STS_OK;
 }
 
 /**
  * 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 =
         __blk_mq_try_issue_directly(hctx, rq, false, true);
 
     if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE)
         blk_mq_request_bypass_insert(rq, false, true);
     else if (ret != BLK_STS_OK)
         blk_mq_end_request(rq, ret);
 }
 
 static blk_status_t blk_mq_request_issue_directly(struct request *rq, bool last)
 {
     return __blk_mq_try_issue_directly(rq->mq_hctx, rq, true, last);
 }
 
 static void blk_mq_plug_issue_direct(struct blk_plug *plug, bool from_schedule)
 {
     struct blk_mq_hw_ctx *hctx = NULL;
     struct request *rq;
     int queued = 0;
     int errors = 0;
 
     while ((rq = rq_list_pop(&plug->mq_list))) {
         bool last = rq_list_empty(plug->mq_list);
         blk_status_t ret;
 
         if (hctx != rq->mq_hctx) {
             if (hctx)
                 blk_mq_commit_rqs(hctx, &queued, from_schedule);
             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, false, true);
             blk_mq_commit_rqs(hctx, &queued, from_schedule);
             return;
         default:
             blk_mq_end_request(rq, ret);
             errors++;
             break;
         }
     }
 
     /*
      * 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 (errors)
         blk_mq_commit_rqs(hctx, &queued, from_schedule);
 }
 
 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;
     unsigned int depth = 0;
     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;
         } else if (this_hctx != rq->mq_hctx || this_ctx != rq->mq_ctx) {
             rq_list_add(&requeue_list, rq);
             continue;
         }
         list_add_tail(&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);
     blk_mq_sched_insert_requests(this_hctx, this_ctx, &list, from_sched);
 }
 
 void blk_mq_flush_plug_list(struct blk_plug *plug, bool from_schedule)
 {
     struct request *rq;
 
     if (rq_list_empty(plug->mq_list))
         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.
          *
          * Since we pass off the full list to the driver at this point,
          * we do not increment the active request count for the queue.
          * Bypass shared tags for now because of that.
          */
         if (q->mq_ops->queue_rqs &&
             !(rq->mq_hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED)) {
             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, false));
         if (rq_list_empty(plug->mq_list))
             return;
     }
 
     do {
         blk_mq_dispatch_plug_list(plug, from_schedule);
     } while (!rq_list_empty(plug->mq_list));
 }
 
 void blk_mq_try_issue_list_directly(struct blk_mq_hw_ctx *hctx,
         struct list_head *list)
 {
     int queued = 0;
     int errors = 0;
 
     while (!list_empty(list)) {
         blk_status_t ret;
         struct request *rq = list_first_entry(list, struct request,
                 queuelist);
 
         list_del_init(&rq->queuelist);
         ret = blk_mq_request_issue_directly(rq, list_empty(list));
         if (ret != BLK_STS_OK) {
             errors++;
             if (ret == BLK_STS_RESOURCE ||
                     ret == BLK_STS_DEV_RESOURCE) {
                 blk_mq_request_bypass_insert(rq, false,
                             list_empty(list));
                 break;
             }
             blk_mq_end_request(rq, ret);
         } else
             queued++;
     }
 
     /*
      * 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) || errors) &&
          hctx->queue->mq_ops->commit_rqs && queued)
         hctx->queue->mq_ops->commit_rqs(hctx);
 }
 
 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;
 
     if (unlikely(bio_queue_enter(bio)))
         return NULL;
 
     if (blk_mq_attempt_bio_merge(q, bio, nsegs))
         goto queue_exit;
 
     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);
 queue_exit:
     blk_queue_exit(q);
     return NULL;
 }
 
 static inline struct request *blk_mq_get_cached_request(struct request_queue *q,
         struct blk_plug *plug, struct bio **bio, unsigned int nsegs)
 {
     struct request *rq;
 
     if (!plug)
         return NULL;
     rq = rq_list_peek(&plug->cached_rq);
     if (!rq || rq->q != q)
         return NULL;
 
     if (blk_mq_attempt_bio_merge(q, *bio, nsegs)) {
         *bio = NULL;
         return NULL;
     }
 
     if (blk_mq_get_hctx_type((*bio)->bi_opf) != rq->mq_hctx->type)
         return NULL;
     if (op_is_flush(rq->cmd_flags) != op_is_flush((*bio)->bi_opf))
         return NULL;
 
     /*
      * 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(q, *bio);
 
     rq->cmd_flags = (*bio)->bi_opf;
     INIT_LIST_HEAD(&rq->queuelist);
     return rq;
 }
 
 static void bio_set_ioprio(struct bio *bio)
 {
     /* Nobody set ioprio so far? Initialize it based on task's nice value */
     if (IOPRIO_PRIO_CLASS(bio->bi_ioprio) == IOPRIO_CLASS_NONE)
         bio->bi_ioprio = get_current_ioprio();
     blkcg_set_ioprio(bio);
 }
 
 /**
  * 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 = blk_mq_plug(bio);
     const int is_sync = op_is_sync(bio->bi_opf);
     struct request *rq;
     unsigned int nr_segs = 1;
     blk_status_t ret;
 
     bio = blk_queue_bounce(bio, q);
     if (bio_may_exceed_limits(bio, &q->limits))
         bio = __bio_split_to_limits(bio, &q->limits, &nr_segs);
 
     if (!bio_integrity_prep(bio))
         return;
 
     bio_set_ioprio(bio);
 
     rq = blk_mq_get_cached_request(q, plug, &bio, nr_segs);
     if (!rq) {
         if (!bio)
             return;
         rq = blk_mq_get_new_requests(q, plug, bio, nr_segs);
         if (unlikely(!rq))
             return;
     }
 
     trace_block_getrq(bio);
 
     rq_qos_track(q, rq, bio);
 
     blk_mq_bio_to_request(rq, bio, nr_segs);
 
     ret = blk_crypto_init_request(rq);
     if (ret != BLK_STS_OK) {
         bio->bi_status = ret;
         bio_endio(bio);
         blk_mq_free_request(rq);
         return;
     }
 
     if (op_is_flush(bio->bi_opf)) {
         blk_insert_flush(rq);
         return;
     }
 
     if (plug)
         blk_add_rq_to_plug(plug, rq);
     else if ((rq->rq_flags & RQF_ELV) ||
          (rq->mq_hctx->dispatch_busy &&
           (q->nr_hw_queues == 1 || !is_sync)))
         blk_mq_sched_insert_request(rq, false, true, true);
     else
         blk_mq_run_dispatch_ops(rq->q,
                 blk_mq_try_issue_directly(rq->mq_hctx, rq));
 }
 
 #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(q, req_op(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 > queue_max_segments(q)) {
         printk(KERN_ERR "%s: over max segments limit. (%hu > %hu)\n",
             __func__, rq->nr_phys_segments, queue_max_segments(q));
         return BLK_STS_IOERR;
     }
 
     if (q->disk && should_fail_request(q->disk->part0, blk_rq_bytes(rq)))
         return BLK_STS_IOERR;
 
     if (blk_crypto_insert_cloned_request(rq))
         return BLK_STS_IOERR;
 
     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, ktime_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;
 
     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 a driver tags own mapping */
     if (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) {
         blk_mq_free_tags(tags);
         return NULL;
     }
 
     tags->static_rqs = kcalloc_node(nr_tags, sizeof(struct request *),
                     GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY,
                     node);
     if (!tags->static_rqs) {
         kfree(tags->rqs);
         blk_mq_free_tags(tags);
         return NULL;
     }
 
     return tags;
 }
 
 static 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 inline bool blk_mq_last_cpu_in_hctx(unsigned int cpu,
         struct blk_mq_hw_ctx *hctx)
 {
     if (cpumask_first_and(hctx->cpumask, cpu_online_mask) != cpu)
         return false;
     if (cpumask_next_and(cpu, hctx->cpumask, cpu_online_mask) < nr_cpu_ids)
         return false;
     return true;
 }
 
 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 (!cpumask_test_cpu(cpu, hctx->cpumask) ||
         !blk_mq_last_cpu_in_hctx(cpu, hctx))
         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;
 }
 
 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 (cpumask_test_cpu(cpu, hctx->cpumask))
         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 (!cpumask_test_cpu(cpu, hctx->cpumask))
         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) {
         /*
          * 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);
 
         /*
          * 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 struct request_queue *blk_mq_init_queue_data(struct blk_mq_tag_set *set,
         void *queuedata)
 {
     struct request_queue *q;
     int ret;
 
     q = blk_alloc_queue(set->numa_node, set->flags & BLK_MQ_F_BLOCKING);
     if (!q)
         return ERR_PTR(-ENOMEM);
     q->queuedata = queuedata;
     ret = blk_mq_init_allocated_queue(set, q);
     if (ret) {
         blk_put_queue(q);
         return ERR_PTR(ret);
     }
     return q;
 }
 
 struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *set)
 {
     return blk_mq_init_queue_data(set, NULL);
 }
 EXPORT_SYMBOL(blk_mq_init_queue);
 
 /**
  * blk_mq_destroy_queue - shutdown a request queue
  * @q: request queue to shutdown
  *
  * This shuts down a request queue allocated by blk_mq_init_queue() and drops
  * the initial reference.  All future requests will failed with -ENODEV.
  *
  * 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_freeze_queue(q);
 
     blk_sync_queue(q);
     blk_mq_cancel_work_sync(q);
     blk_mq_exit_queue(q);
 
     /* @q is and will stay empty, shutdown and put */
     blk_put_queue(q);
 }
 EXPORT_SYMBOL(blk_mq_destroy_queue);
 
 struct gendisk *__blk_mq_alloc_disk(struct blk_mq_tag_set *set, void *queuedata,
         struct lock_class_key *lkclass)
 {
     struct request_queue *q;
     struct gendisk *disk;
 
     q = blk_mq_init_queue_data(set, 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);
         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)
 {
     if (!blk_get_queue(q))
         return NULL;
     return __alloc_disk_node(q, NUMA_NO_NODE, lkclass);
 }
 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);
 }
 
 static void blk_mq_update_poll_flag(struct request_queue *q)
 {
     struct blk_mq_tag_set *set = q->tag_set;
 
     if (set->nr_maps > HCTX_TYPE_POLL &&
         set->map[HCTX_TYPE_POLL].nr_queues)
         blk_queue_flag_set(QUEUE_FLAG_POLL, q);
     else
         blk_queue_flag_clear(QUEUE_FLAG_POLL, q);
 }
 
 int blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
         struct request_queue *q)
 {
     WARN_ON_ONCE(blk_queue_has_srcu(q) !=
             !!(set->flags & BLK_MQ_F_BLOCKING));
 
     /* mark the queue as mq asap */
     q->mq_ops = set->ops;
 
     q->poll_cb = blk_stat_alloc_callback(blk_mq_poll_stats_fn,
                          blk_mq_poll_stats_bkt,
                          BLK_MQ_POLL_STATS_BKTS, q);
     if (!q->poll_cb)
         goto err_exit;
 
     if (blk_mq_alloc_ctxs(q))
         goto err_poll;
 
     /* init q->mq_kobj and sw queues' kobjects */
     blk_mq_sysfs_init(q);
 
     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->tag_set = set;
 
     q->queue_flags |= QUEUE_FLAG_MQ_DEFAULT;
     blk_mq_update_poll_flag(q);
 
     INIT_DELAYED_WORK(&q->requeue_work, blk_mq_requeue_work);
     INIT_LIST_HEAD(&q->requeue_list);
     spin_lock_init(&q->requeue_lock);
 
     q->nr_requests = set->queue_depth;
 
     /*
      * Default to classic polling
      */
     q->poll_nsec = BLK_MQ_POLL_CLASSIC;
 
     blk_mq_init_cpu_queues(q, set->nr_hw_queues);
     blk_mq_add_queue_tag_set(set, q);
     blk_mq_map_swqueue(q);
     return 0;
 
 err_hctxs:
     xa_destroy(&q->hctx_table);
     q->nr_hw_queues = 0;
     blk_mq_sysfs_deinit(q);
 err_poll:
     blk_stat_free_callback(q->poll_cb);
     q->poll_cb = NULL;
 err_exit:
     q->mq_ops = NULL;
     return -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 int blk_mq_update_queue_map(struct blk_mq_tag_set *set)
 {
     /*
      * blk_mq_map_queues() and multiple .map_queues() implementations
      * expect that set->map[HCTX_TYPE_DEFAULT].nr_queues is set to the
      * number of hardware queues.
      */
     if (set->nr_maps == 1)
         set->map[HCTX_TYPE_DEFAULT].nr_queues = set->nr_hw_queues;
 
     if (set->ops->map_queues && !is_kdump_kernel()) {
         int i;
 
         /*
          * transport .map_queues is usually done in the following
          * way:
          *
          * for (queue = 0; queue < set->nr_hw_queues; queue++) {
          *  mask = get_cpu_mask(queue)
          *  for_each_cpu(cpu, mask)
          *      set->map[x].mq_map[cpu] = queue;
          * }
          *
          * When we need to remap, the table has to be cleared for
          * killing stale mapping since one CPU may not be mapped
          * to any hw queue.
          */
         for (i = 0; i < set->nr_maps; i++)
             blk_mq_clear_mq_map(&set->map[i]);
 
         return set->ops->map_queues(set);
     } else {
         BUG_ON(set->nr_maps > 1);
         return blk_mq_map_queues(&set->map[HCTX_TYPE_DEFAULT]);
     }
 }
 
 static int blk_mq_realloc_tag_set_tags(struct blk_mq_tag_set *set,
                   int cur_nr_hw_queues, int new_nr_hw_queues)
 {
     struct blk_mq_tags **new_tags;
 
     if (cur_nr_hw_queues >= new_nr_hw_queues)
         return 0;
 
     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, cur_nr_hw_queues *
                sizeof(*set->tags));
     kfree(set->tags);
     set->tags = new_tags;
     set->nr_hw_queues = new_nr_hw_queues;
 
     return 0;
 }
 
 static int blk_mq_alloc_tag_set_tags(struct blk_mq_tag_set *set,
                 int new_nr_hw_queues)
 {
     return blk_mq_realloc_tag_set_tags(set, 0, new_nr_hw_queues);
 }
 
 /*
  * Alloc a tag set to be associated with one or more request queues.
  * May fail with EINVAL for various error conditions. May adjust the
  * requested depth down, if it's too large. In that case, the set
  * value will be stored in set->queue_depth.
  */
 int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set)
 {
     int i, ret;
 
     BUILD_BUG_ON(BLK_MQ_MAX_DEPTH > 1 << BLK_MQ_UNIQUE_TAG_BITS);
 
     if (!set->nr_hw_queues)
         return -EINVAL;
     if (!set->queue_depth)
         return -EINVAL;
     if (set->queue_depth < set->reserved_tags + BLK_MQ_TAG_MIN)
         return -EINVAL;
 
     if (!set->ops->queue_rq)
         return -EINVAL;
 
     if (!set->ops->get_budget ^ !set->ops->put_budget)
         return -EINVAL;
 
     if (set->queue_depth > BLK_MQ_MAX_DEPTH) {
         pr_info("blk-mq: reduced tag depth to %u\n",
             BLK_MQ_MAX_DEPTH);
         set->queue_depth = BLK_MQ_MAX_DEPTH;
     }
 
     if (!set->nr_maps)
         set->nr_maps = 1;
     else if (set->nr_maps > HCTX_MAX_TYPES)
         return -EINVAL;
 
     /*
      * If a crashdump is active, then we are potentially in a very
      * memory constrained environment. Limit us to 1 queue and
      * 64 tags to prevent using too much memory.
      */
     if (is_kdump_kernel()) {
         set->nr_hw_queues = 1;
         set->nr_maps = 1;
         set->queue_depth = min(64U, set->queue_depth);
     }
     /*
      * There is no use for more h/w queues than cpus if we just have
      * a single map
      */
     if (set->nr_maps == 1 && set->nr_hw_queues > nr_cpu_ids)
         set->nr_hw_queues = nr_cpu_ids;
 
     if (blk_mq_alloc_tag_set_tags(set, set->nr_hw_queues) < 0)
         return -ENOMEM;
 
     ret = -ENOMEM;
     for (i = 0; i < set->nr_maps; i++) {
         set->map[i].mq_map = kcalloc_node(nr_cpu_ids,
                           sizeof(set->map[i].mq_map[0]),
                           GFP_KERNEL, set->numa_node);
         if (!set->map[i].mq_map)
             goto out_free_mq_map;
         set->map[i].nr_queues = is_kdump_kernel() ? 1 : set->nr_hw_queues;
     }
 
     ret = blk_mq_update_queue_map(set);
     if (ret)
         goto out_free_mq_map;
 
     ret = blk_mq_alloc_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;
     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;
 }
 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 (!set)
         return -EINVAL;
 
     if (q->nr_requests == nr)
         return 0;
 
     blk_mq_freeze_queue(q);
     blk_mq_quiesce_queue(q);
 
     ret = 0;
     queue_for_each_hw_ctx(q, hctx, i) {
         if (!hctx->tags)
             continue;
         /*
          * If we're using an MQ scheduler, just update the scheduler
          * queue depth. This is similar to what the old code would do.
          */
         if (hctx->sched_tags) {
             ret = blk_mq_tag_update_depth(hctx, &hctx->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);
     blk_mq_unfreeze_queue(q);
 
     return ret;
 }
 
 /*
  * request_queue and elevator_type pair.
  * It is just used by __blk_mq_update_nr_hw_queues to cache
  * the elevator_type associated with a request_queue.
  */
 struct blk_mq_qe_pair {
     struct list_head node;
     struct request_queue *q;
     struct elevator_type *type;
 };
 
 /*
  * Cache the elevator_type in qe pair list and switch the
  * io scheduler to 'none'
  */
 static bool blk_mq_elv_switch_none(struct list_head *head,
         struct request_queue *q)
 {
     struct blk_mq_qe_pair *qe;
 
     if (!q->elevator)
         return true;
 
     qe = kmalloc(sizeof(*qe), GFP_NOIO | __GFP_NOWARN | __GFP_NORETRY);
     if (!qe)
         return false;
 
     /* q->elevator needs protection from ->sysfs_lock */
     mutex_lock(&q->sysfs_lock);
 
     INIT_LIST_HEAD(&qe->node);
     qe->q = q;
     qe->type = q->elevator->type;
     list_add(&qe->node, head);
 
     /*
      * After elevator_switch_mq, the previous elevator_queue will be
      * released by elevator_release. The reference of the io scheduler
      * module get by elevator_get will also be put. So we need to get
      * a reference of the io scheduler module here to prevent it to be
      * removed.
      */
     __module_get(qe->type->elevator_owner);
     elevator_switch_mq(q, NULL);
     mutex_unlock(&q->sysfs_lock);
 
     return true;
 }
 
 static 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_mq(q, t);
     mutex_unlock(&q->sysfs_lock);
 }
 
 static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
                             int nr_hw_queues)
 {
     struct request_queue *q;
     LIST_HEAD(head);
     int prev_nr_hw_queues;
 
     lockdep_assert_held(&set->tag_list_lock);
 
     if (set->nr_maps == 1 && nr_hw_queues > nr_cpu_ids)
         nr_hw_queues = nr_cpu_ids;
     if (nr_hw_queues < 1)
         return;
     if (set->nr_maps == 1 && nr_hw_queues == set->nr_hw_queues)
         return;
 
     list_for_each_entry(q, &set->tag_list, tag_set_list)
         blk_mq_freeze_queue(q);
     /*
      * 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);
     }
 
     prev_nr_hw_queues = set->nr_hw_queues;
     if (blk_mq_realloc_tag_set_tags(set, set->nr_hw_queues, nr_hw_queues) <
         0)
         goto reregister;
 
     set->nr_hw_queues = nr_hw_queues;
 fallback:
     blk_mq_update_queue_map(set);
     list_for_each_entry(q, &set->tag_list, tag_set_list) {
         blk_mq_realloc_hw_ctxs(set, q);
         blk_mq_update_poll_flag(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;
             blk_mq_map_queues(&set->map[HCTX_TYPE_DEFAULT]);
             goto fallback;
         }
         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);
 }
 
 void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues)
 {
     mutex_lock(&set->tag_list_lock);
     __blk_mq_update_nr_hw_queues(set, nr_hw_queues);
     mutex_unlock(&set->tag_list_lock);
 }
 EXPORT_SYMBOL_GPL(blk_mq_update_nr_hw_queues);
 
 /* Enable polling stats and return whether they were already enabled. */
 static bool blk_poll_stats_enable(struct request_queue *q)
 {
     if (q->poll_stat)
         return true;
 
     return blk_stats_alloc_enable(q);
 }
 
 static void blk_mq_poll_stats_start(struct request_queue *q)
 {
     /*
      * We don't arm the callback if polling stats are not enabled or the
      * callback is already active.
      */
     if (!q->poll_stat || blk_stat_is_active(q->poll_cb))
         return;
 
     blk_stat_activate_msecs(q->poll_cb, 100);
 }
 
 static void blk_mq_poll_stats_fn(struct blk_stat_callback *cb)
 {
     struct request_queue *q = cb->data;
     int bucket;
 
     for (bucket = 0; bucket < BLK_MQ_POLL_STATS_BKTS; bucket++) {
         if (cb->stat[bucket].nr_samples)
             q->poll_stat[bucket] = cb->stat[bucket];
     }
 }
 
 static unsigned long blk_mq_poll_nsecs(struct request_queue *q,
                        struct request *rq)
 {
     unsigned long ret = 0;
     int bucket;
 
     /*
      * If stats collection isn't on, don't sleep but turn it on for
      * future users
      */
     if (!blk_poll_stats_enable(q))
         return 0;
 
     /*
      * As an optimistic guess, use half of the mean service time
      * for this type of request. We can (and should) make this smarter.
      * For instance, if the completion latencies are tight, we can
      * get closer than just half the mean. This is especially
      * important on devices where the completion latencies are longer
      * than ~10 usec. We do use the stats for the relevant IO size
      * if available which does lead to better estimates.
      */
     bucket = blk_mq_poll_stats_bkt(rq);
     if (bucket < 0)
         return ret;
 
     if (q->poll_stat[bucket].nr_samples)
         ret = (q->poll_stat[bucket].mean + 1) / 2;
 
     return ret;
 }
 
 static bool blk_mq_poll_hybrid(struct request_queue *q, blk_qc_t qc)
 {
     struct blk_mq_hw_ctx *hctx = blk_qc_to_hctx(q, qc);
     struct request *rq = blk_qc_to_rq(hctx, qc);
     struct hrtimer_sleeper hs;
     enum hrtimer_mode mode;
     unsigned int nsecs;
     ktime_t kt;
 
     /*
      * If a request has completed on queue that uses an I/O scheduler, we
      * won't get back a request from blk_qc_to_rq.
      */
     if (!rq || (rq->rq_flags & RQF_MQ_POLL_SLEPT))
         return false;
 
     /*
      * If we get here, hybrid polling is enabled. Hence poll_nsec can be:
      *
      *  0:  use half of prev avg
      * >0:  use this specific value
      */
     if (q->poll_nsec > 0)
         nsecs = q->poll_nsec;
     else
         nsecs = blk_mq_poll_nsecs(q, rq);
 
     if (!nsecs)
         return false;
 
     rq->rq_flags |= RQF_MQ_POLL_SLEPT;
 
     /*
      * This will be replaced with the stats tracking code, using
      * 'avg_completion_time / 2' as the pre-sleep target.
      */
     kt = nsecs;
 
     mode = HRTIMER_MODE_REL;
     hrtimer_init_sleeper_on_stack(&hs, CLOCK_MONOTONIC, mode);
     hrtimer_set_expires(&hs.timer, kt);
 
     do {
         if (blk_mq_rq_state(rq) == MQ_RQ_COMPLETE)
             break;
         set_current_state(TASK_UNINTERRUPTIBLE);
         hrtimer_sleeper_start_expires(&hs, mode);
         if (hs.task)
             io_schedule();
         hrtimer_cancel(&hs.timer);
         mode = HRTIMER_MODE_ABS;
     } while (hs.task && !signal_pending(current));
 
     __set_current_state(TASK_RUNNING);
     destroy_hrtimer_on_stack(&hs.timer);
 
     /*
      * If we sleep, have the caller restart the poll loop to reset the
      * state.  Like for the other success return cases, the caller is
      * responsible for checking if the IO completed.  If the IO isn't
      * complete, we'll get called again and will go straight to the busy
      * poll loop.
      */
     return true;
 }
 
 static int blk_mq_poll_classic(struct request_queue *q, blk_qc_t cookie,
                    struct io_comp_batch *iob, unsigned int flags)
 {
     struct blk_mq_hw_ctx *hctx = blk_qc_to_hctx(q, cookie);
     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)
 {
     if (!(flags & BLK_POLL_NOSLEEP) &&
         q->poll_nsec != BLK_MQ_POLL_CLASSIC) {
         if (blk_mq_poll_hybrid(q, cookie))
             return 1;
     }
     return blk_mq_poll_classic(q, cookie, iob, flags);
 }
 
 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)
 {
     if (queue_is_mq(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));
     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);