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 // SPDX-License-Identifier: GPL-2.0
 /*
  * blk-mq scheduling framework
  *
  * Copyright (C) 2016 Jens Axboe
  */
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/blk-mq.h>
 #include <linux/list_sort.h>
 
 #include <trace/events/block.h>
 
 #include "blk.h"
 #include "blk-mq.h"
 #include "blk-mq-debugfs.h"
 #include "blk-mq-sched.h"
 #include "blk-mq-tag.h"
 #include "blk-wbt.h"
 
 /*
  * Mark a hardware queue as needing a restart. For shared queues, maintain
  * a count of how many hardware queues are marked for restart.
  */
 void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx)
 {
     if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
         return;
 
     set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
 }
 EXPORT_SYMBOL_GPL(blk_mq_sched_mark_restart_hctx);
 
 void __blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
 {
     clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
 
     /*
      * Order clearing SCHED_RESTART and list_empty_careful(&hctx->dispatch)
      * in blk_mq_run_hw_queue(). Its pair is the barrier in
      * blk_mq_dispatch_rq_list(). So dispatch code won't see SCHED_RESTART,
      * meantime new request added to hctx->dispatch is missed to check in
      * blk_mq_run_hw_queue().
      */
     smp_mb();
 
     blk_mq_run_hw_queue(hctx, true);
 }
 
 static int sched_rq_cmp(void *priv, const struct list_head *a,
             const struct list_head *b)
 {
     struct request *rqa = container_of(a, struct request, queuelist);
     struct request *rqb = container_of(b, struct request, queuelist);
 
     return rqa->mq_hctx > rqb->mq_hctx;
 }
 
 static bool blk_mq_dispatch_hctx_list(struct list_head *rq_list)
 {
     struct blk_mq_hw_ctx *hctx =
         list_first_entry(rq_list, struct request, queuelist)->mq_hctx;
     struct request *rq;
     LIST_HEAD(hctx_list);
     unsigned int count = 0;
 
     list_for_each_entry(rq, rq_list, queuelist) {
         if (rq->mq_hctx != hctx) {
             list_cut_before(&hctx_list, rq_list, &rq->queuelist);
             goto dispatch;
         }
         count++;
     }
     list_splice_tail_init(rq_list, &hctx_list);
 
 dispatch:
     return blk_mq_dispatch_rq_list(hctx, &hctx_list, count);
 }
 
 #define BLK_MQ_BUDGET_DELAY 3       /* ms units */
 
 /*
  * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
  * its queue by itself in its completion handler, so we don't need to
  * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
  *
  * Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
  * be run again.  This is necessary to avoid starving flushes.
  */
 static int __blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
 {
     struct request_queue *q = hctx->queue;
     struct elevator_queue *e = q->elevator;
     bool multi_hctxs = false, run_queue = false;
     bool dispatched = false, busy = false;
     unsigned int max_dispatch;
     LIST_HEAD(rq_list);
     int count = 0;
 
     if (hctx->dispatch_busy)
         max_dispatch = 1;
     else
         max_dispatch = hctx->queue->nr_requests;
 
     do {
         struct request *rq;
         int budget_token;
 
         if (e->type->ops.has_work && !e->type->ops.has_work(hctx))
             break;
 
         if (!list_empty_careful(&hctx->dispatch)) {
             busy = true;
             break;
         }
 
         budget_token = blk_mq_get_dispatch_budget(q);
         if (budget_token < 0)
             break;
 
         rq = e->type->ops.dispatch_request(hctx);
         if (!rq) {
             blk_mq_put_dispatch_budget(q, budget_token);
             /*
              * We're releasing without dispatching. Holding the
              * budget could have blocked any "hctx"s with the
              * same queue and if we didn't dispatch then there's
              * no guarantee anyone will kick the queue.  Kick it
              * ourselves.
              */
             run_queue = true;
             break;
         }
 
         blk_mq_set_rq_budget_token(rq, budget_token);
 
         /*
          * Now this rq owns the budget which has to be released
          * if this rq won't be queued to driver via .queue_rq()
          * in blk_mq_dispatch_rq_list().
          */
         list_add_tail(&rq->queuelist, &rq_list);
         count++;
         if (rq->mq_hctx != hctx)
             multi_hctxs = true;
 
         /*
          * If we cannot get tag for the request, stop dequeueing
          * requests from the IO scheduler. We are unlikely to be able
          * to submit them anyway and it creates false impression for
          * scheduling heuristics that the device can take more IO.
          */
         if (!blk_mq_get_driver_tag(rq))
             break;
     } while (count < max_dispatch);
 
     if (!count) {
         if (run_queue)
             blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
     } else if (multi_hctxs) {
         /*
          * Requests from different hctx may be dequeued from some
          * schedulers, such as bfq and deadline.
          *
          * Sort the requests in the list according to their hctx,
          * dispatch batching requests from same hctx at a time.
          */
         list_sort(NULL, &rq_list, sched_rq_cmp);
         do {
             dispatched |= blk_mq_dispatch_hctx_list(&rq_list);
         } while (!list_empty(&rq_list));
     } else {
         dispatched = blk_mq_dispatch_rq_list(hctx, &rq_list, count);
     }
 
     if (busy)
         return -EAGAIN;
     return !!dispatched;
 }
 
 static int blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
 {
     unsigned long end = jiffies + HZ;
     int ret;
 
     do {
         ret = __blk_mq_do_dispatch_sched(hctx);
         if (ret != 1)
             break;
         if (need_resched() || time_is_before_jiffies(end)) {
             blk_mq_delay_run_hw_queue(hctx, 0);
             break;
         }
     } while (1);
 
     return ret;
 }
 
 static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
                       struct blk_mq_ctx *ctx)
 {
     unsigned short idx = ctx->index_hw[hctx->type];
 
     if (++idx == hctx->nr_ctx)
         idx = 0;
 
     return hctx->ctxs[idx];
 }
 
 /*
  * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
  * its queue by itself in its completion handler, so we don't need to
  * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
  *
  * Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
  * be run again.  This is necessary to avoid starving flushes.
  */
 static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
 {
     struct request_queue *q = hctx->queue;
     LIST_HEAD(rq_list);
     struct blk_mq_ctx *ctx = READ_ONCE(hctx->dispatch_from);
     int ret = 0;
     struct request *rq;
 
     do {
         int budget_token;
 
         if (!list_empty_careful(&hctx->dispatch)) {
             ret = -EAGAIN;
             break;
         }
 
         if (!sbitmap_any_bit_set(&hctx->ctx_map))
             break;
 
         budget_token = blk_mq_get_dispatch_budget(q);
         if (budget_token < 0)
             break;
 
         rq = blk_mq_dequeue_from_ctx(hctx, ctx);
         if (!rq) {
             blk_mq_put_dispatch_budget(q, budget_token);
             /*
              * We're releasing without dispatching. Holding the
              * budget could have blocked any "hctx"s with the
              * same queue and if we didn't dispatch then there's
              * no guarantee anyone will kick the queue.  Kick it
              * ourselves.
              */
             blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
             break;
         }
 
         blk_mq_set_rq_budget_token(rq, budget_token);
 
         /*
          * Now this rq owns the budget which has to be released
          * if this rq won't be queued to driver via .queue_rq()
          * in blk_mq_dispatch_rq_list().
          */
         list_add(&rq->queuelist, &rq_list);
 
         /* round robin for fair dispatch */
         ctx = blk_mq_next_ctx(hctx, rq->mq_ctx);
 
     } while (blk_mq_dispatch_rq_list(rq->mq_hctx, &rq_list, 1));
 
     WRITE_ONCE(hctx->dispatch_from, ctx);
     return ret;
 }
 
 static int __blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
 {
     struct request_queue *q = hctx->queue;
     const bool has_sched = q->elevator;
     int ret = 0;
     LIST_HEAD(rq_list);
 
     /*
      * If we have previous entries on our dispatch list, grab them first for
      * more fair dispatch.
      */
     if (!list_empty_careful(&hctx->dispatch)) {
         spin_lock(&hctx->lock);
         if (!list_empty(&hctx->dispatch))
             list_splice_init(&hctx->dispatch, &rq_list);
         spin_unlock(&hctx->lock);
     }
 
     /*
      * Only ask the scheduler for requests, if we didn't have residual
      * requests from the dispatch list. This is to avoid the case where
      * we only ever dispatch a fraction of the requests available because
      * of low device queue depth. Once we pull requests out of the IO
      * scheduler, we can no longer merge or sort them. So it's best to
      * leave them there for as long as we can. Mark the hw queue as
      * needing a restart in that case.
      *
      * We want to dispatch from the scheduler if there was nothing
      * on the dispatch list or we were able to dispatch from the
      * dispatch list.
      */
     if (!list_empty(&rq_list)) {
         blk_mq_sched_mark_restart_hctx(hctx);
         if (blk_mq_dispatch_rq_list(hctx, &rq_list, 0)) {
             if (has_sched)
                 ret = blk_mq_do_dispatch_sched(hctx);
             else
                 ret = blk_mq_do_dispatch_ctx(hctx);
         }
     } else if (has_sched) {
         ret = blk_mq_do_dispatch_sched(hctx);
     } else if (hctx->dispatch_busy) {
         /* dequeue request one by one from sw queue if queue is busy */
         ret = blk_mq_do_dispatch_ctx(hctx);
     } else {
         blk_mq_flush_busy_ctxs(hctx, &rq_list);
         blk_mq_dispatch_rq_list(hctx, &rq_list, 0);
     }
 
     return ret;
 }
 
 void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
 {
     struct request_queue *q = hctx->queue;
 
     /* RCU or SRCU read lock is needed before checking quiesced flag */
     if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
         return;
 
     hctx->run++;
 
     /*
      * A return of -EAGAIN is an indication that hctx->dispatch is not
      * empty and we must run again in order to avoid starving flushes.
      */
     if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN) {
         if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN)
             blk_mq_run_hw_queue(hctx, true);
     }
 }
 
 bool blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio,
         unsigned int nr_segs)
 {
     struct elevator_queue *e = q->elevator;
     struct blk_mq_ctx *ctx;
     struct blk_mq_hw_ctx *hctx;
     bool ret = false;
     enum hctx_type type;
 
     if (e && e->type->ops.bio_merge) {
         ret = e->type->ops.bio_merge(q, bio, nr_segs);
         goto out_put;
     }
 
     ctx = blk_mq_get_ctx(q);
     hctx = blk_mq_map_queue(q, bio->bi_opf, ctx);
     type = hctx->type;
     if (!(hctx->flags & BLK_MQ_F_SHOULD_MERGE) ||
         list_empty_careful(&ctx->rq_lists[type]))
         goto out_put;
 
     /* default per sw-queue merge */
     spin_lock(&ctx->lock);
     /*
      * Reverse check our software queue for entries that we could
      * potentially merge with. Currently includes a hand-wavy stop
      * count of 8, to not spend too much time checking for merges.
      */
     if (blk_bio_list_merge(q, &ctx->rq_lists[type], bio, nr_segs))
         ret = true;
 
     spin_unlock(&ctx->lock);
 out_put:
     return ret;
 }
 
 bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq,
                    struct list_head *free)
 {
     return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq, free);
 }
 EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);
 
 static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
                        struct request *rq)
 {
     /*
      * dispatch flush and passthrough rq directly
      *
      * passthrough request has to be added to hctx->dispatch directly.
      * For some reason, device may be in one situation which can't
      * handle FS request, so STS_RESOURCE is always returned and the
      * FS request will be added to hctx->dispatch. However passthrough
      * request may be required at that time for fixing the problem. If
      * passthrough request is added to scheduler queue, there isn't any
      * chance to dispatch it given we prioritize requests in hctx->dispatch.
      */
     if ((rq->rq_flags & RQF_FLUSH_SEQ) || blk_rq_is_passthrough(rq))
         return true;
 
     return false;
 }
 
 void blk_mq_sched_insert_request(struct request *rq, bool at_head,
                  bool run_queue, bool async)
 {
     struct request_queue *q = rq->q;
     struct elevator_queue *e = q->elevator;
     struct blk_mq_ctx *ctx = rq->mq_ctx;
     struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
 
     WARN_ON(e && (rq->tag != BLK_MQ_NO_TAG));
 
     if (blk_mq_sched_bypass_insert(hctx, rq)) {
         /*
          * Firstly normal IO request is inserted to scheduler queue or
          * sw queue, meantime we add flush request to dispatch queue(
          * hctx->dispatch) directly and there is at most one in-flight
          * flush request for each hw queue, so it doesn't matter to add
          * flush request to tail or front of the dispatch queue.
          *
          * Secondly in case of NCQ, flush request belongs to non-NCQ
          * command, and queueing it will fail when there is any
          * in-flight normal IO request(NCQ command). When adding flush
          * rq to the front of hctx->dispatch, it is easier to introduce
          * extra time to flush rq's latency because of S_SCHED_RESTART
          * compared with adding to the tail of dispatch queue, then
          * chance of flush merge is increased, and less flush requests
          * will be issued to controller. It is observed that ~10% time
          * is saved in blktests block/004 on disk attached to AHCI/NCQ
          * drive when adding flush rq to the front of hctx->dispatch.
          *
          * Simply queue flush rq to the front of hctx->dispatch so that
          * intensive flush workloads can benefit in case of NCQ HW.
          */
         at_head = (rq->rq_flags & RQF_FLUSH_SEQ) ? true : at_head;
         blk_mq_request_bypass_insert(rq, at_head, false);
         goto run;
     }
 
     if (e) {
         LIST_HEAD(list);
 
         list_add(&rq->queuelist, &list);
         e->type->ops.insert_requests(hctx, &list, at_head);
     } else {
         spin_lock(&ctx->lock);
         __blk_mq_insert_request(hctx, rq, at_head);
         spin_unlock(&ctx->lock);
     }
 
 run:
     if (run_queue)
         blk_mq_run_hw_queue(hctx, async);
 }
 
 void blk_mq_sched_insert_requests(struct blk_mq_hw_ctx *hctx,
                   struct blk_mq_ctx *ctx,
                   struct list_head *list, bool run_queue_async)
 {
     struct elevator_queue *e;
     struct request_queue *q = hctx->queue;
 
     /*
      * blk_mq_sched_insert_requests() is called from flush plug
      * context only, and hold one usage counter to prevent queue
      * from being released.
      */
     percpu_ref_get(&q->q_usage_counter);
 
     e = hctx->queue->elevator;
     if (e) {
         e->type->ops.insert_requests(hctx, list, false);
     } else {
         /*
          * try to issue requests directly if the hw queue isn't
          * busy in case of 'none' scheduler, and this way may save
          * us one extra enqueue & dequeue to sw queue.
          */
         if (!hctx->dispatch_busy && !run_queue_async) {
             blk_mq_run_dispatch_ops(hctx->queue,
                 blk_mq_try_issue_list_directly(hctx, list));
             if (list_empty(list))
                 goto out;
         }
         blk_mq_insert_requests(hctx, ctx, list);
     }
 
     blk_mq_run_hw_queue(hctx, run_queue_async);
  out:
     percpu_ref_put(&q->q_usage_counter);
 }
 
 static int blk_mq_sched_alloc_map_and_rqs(struct request_queue *q,
                       struct blk_mq_hw_ctx *hctx,
                       unsigned int hctx_idx)
 {
     if (blk_mq_is_shared_tags(q->tag_set->flags)) {
         hctx->sched_tags = q->sched_shared_tags;
         return 0;
     }
 
     hctx->sched_tags = blk_mq_alloc_map_and_rqs(q->tag_set, hctx_idx,
                             q->nr_requests);
 
     if (!hctx->sched_tags)
         return -ENOMEM;
     return 0;
 }
 
 static void blk_mq_exit_sched_shared_tags(struct request_queue *queue)
 {
     blk_mq_free_rq_map(queue->sched_shared_tags);
     queue->sched_shared_tags = NULL;
 }
 
 /* called in queue's release handler, tagset has gone away */
 static void blk_mq_sched_tags_teardown(struct request_queue *q, unsigned int flags)
 {
     struct blk_mq_hw_ctx *hctx;
     unsigned long i;
 
     queue_for_each_hw_ctx(q, hctx, i) {
         if (hctx->sched_tags) {
             if (!blk_mq_is_shared_tags(flags))
                 blk_mq_free_rq_map(hctx->sched_tags);
             hctx->sched_tags = NULL;
         }
     }
 
     if (blk_mq_is_shared_tags(flags))
         blk_mq_exit_sched_shared_tags(q);
 }
 
 static int blk_mq_init_sched_shared_tags(struct request_queue *queue)
 {
     struct blk_mq_tag_set *set = queue->tag_set;
 
     /*
      * Set initial depth at max so that we don't need to reallocate for
      * updating nr_requests.
      */
     queue->sched_shared_tags = blk_mq_alloc_map_and_rqs(set,
                         BLK_MQ_NO_HCTX_IDX,
                         MAX_SCHED_RQ);
     if (!queue->sched_shared_tags)
         return -ENOMEM;
 
     blk_mq_tag_update_sched_shared_tags(queue);
 
     return 0;
 }
 
 int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
 {
     unsigned int flags = q->tag_set->flags;
     struct blk_mq_hw_ctx *hctx;
     struct elevator_queue *eq;
     unsigned long i;
     int ret;
 
     if (!e) {
         blk_queue_flag_clear(QUEUE_FLAG_SQ_SCHED, q);
         q->elevator = NULL;
         q->nr_requests = q->tag_set->queue_depth;
         return 0;
     }
 
     /*
      * Default to double of smaller one between hw queue_depth and 128,
      * since we don't split into sync/async like the old code did.
      * Additionally, this is a per-hw queue depth.
      */
     q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth,
                    BLKDEV_DEFAULT_RQ);
 
     if (blk_mq_is_shared_tags(flags)) {
         ret = blk_mq_init_sched_shared_tags(q);
         if (ret)
             return ret;
     }
 
     queue_for_each_hw_ctx(q, hctx, i) {
         ret = blk_mq_sched_alloc_map_and_rqs(q, hctx, i);
         if (ret)
             goto err_free_map_and_rqs;
     }
 
     ret = e->ops.init_sched(q, e);
     if (ret)
         goto err_free_map_and_rqs;
 
     mutex_lock(&q->debugfs_mutex);
     blk_mq_debugfs_register_sched(q);
     mutex_unlock(&q->debugfs_mutex);
 
     queue_for_each_hw_ctx(q, hctx, i) {
         if (e->ops.init_hctx) {
             ret = e->ops.init_hctx(hctx, i);
             if (ret) {
                 eq = q->elevator;
                 blk_mq_sched_free_rqs(q);
                 blk_mq_exit_sched(q, eq);
                 kobject_put(&eq->kobj);
                 return ret;
             }
         }
         mutex_lock(&q->debugfs_mutex);
         blk_mq_debugfs_register_sched_hctx(q, hctx);
         mutex_unlock(&q->debugfs_mutex);
     }
 
     return 0;
 
 err_free_map_and_rqs:
     blk_mq_sched_free_rqs(q);
     blk_mq_sched_tags_teardown(q, flags);
 
     q->elevator = NULL;
     return ret;
 }
 
 /*
  * called in either blk_queue_cleanup or elevator_switch, tagset
  * is required for freeing requests
  */
 void blk_mq_sched_free_rqs(struct request_queue *q)
 {
     struct blk_mq_hw_ctx *hctx;
     unsigned long i;
 
     if (blk_mq_is_shared_tags(q->tag_set->flags)) {
         blk_mq_free_rqs(q->tag_set, q->sched_shared_tags,
                 BLK_MQ_NO_HCTX_IDX);
     } else {
         queue_for_each_hw_ctx(q, hctx, i) {
             if (hctx->sched_tags)
                 blk_mq_free_rqs(q->tag_set,
                         hctx->sched_tags, i);
         }
     }
 }
 
 void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
 {
     struct blk_mq_hw_ctx *hctx;
     unsigned long i;
     unsigned int flags = 0;
 
     queue_for_each_hw_ctx(q, hctx, i) {
         mutex_lock(&q->debugfs_mutex);
         blk_mq_debugfs_unregister_sched_hctx(hctx);
         mutex_unlock(&q->debugfs_mutex);
 
         if (e->type->ops.exit_hctx && hctx->sched_data) {
             e->type->ops.exit_hctx(hctx, i);
             hctx->sched_data = NULL;
         }
         flags = hctx->flags;
     }
 
     mutex_lock(&q->debugfs_mutex);
     blk_mq_debugfs_unregister_sched(q);
     mutex_unlock(&q->debugfs_mutex);
 
     if (e->type->ops.exit_sched)
         e->type->ops.exit_sched(e);
     blk_mq_sched_tags_teardown(q, flags);
     q->elevator = NULL;
 }

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