block/blk-mq-sched.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * blk-mq scheduling framework
   4  *
   5  * Copyright (C) 2016 Jens Axboe
   6  */
   7 #include <linux/kernel.h>
   8 #include <linux/module.h>
   9 #include <linux/blk-mq.h>
  10
  11 #include <trace/events/block.h>
  12
  13 #include "blk.h"
  14 #include "blk-mq.h"
  15 #include "blk-mq-debugfs.h"
  16 #include "blk-mq-sched.h"
  17 #include "blk-mq-tag.h"
  18 #include "blk-wbt.h"
  19
  20 void blk_mq_sched_free_hctx_data(struct request_queue *q,
  21                                  void (*exit)(struct blk_mq_hw_ctx *))
  22 {
  23         struct blk_mq_hw_ctx *hctx;
  24         int i;
  25
  26         queue_for_each_hw_ctx(q, hctx, i) {
  27                 if (exit && hctx->sched_data)
  28                         exit(hctx);
  29                 kfree(hctx->sched_data);
  30                 hctx->sched_data = NULL;
  31         }
  32 }
  33 EXPORT_SYMBOL_GPL(blk_mq_sched_free_hctx_data);
  34
  35 void blk_mq_sched_assign_ioc(struct request *rq)
  36 {
  37         struct request_queue *q = rq->q;
  38         struct io_context *ioc;
  39         struct io_cq *icq;
  40
  41         /*
  42          * May not have an IO context if it's a passthrough request
  43          */
  44         ioc = current->io_context;
  45         if (!ioc)
  46                 return;
  47
  48         spin_lock_irq(&q->queue_lock);
  49         icq = ioc_lookup_icq(ioc, q);
  50         spin_unlock_irq(&q->queue_lock);
  51
  52         if (!icq) {
  53                 icq = ioc_create_icq(ioc, q, GFP_ATOMIC);
  54                 if (!icq)
  55                         return;
  56         }
  57         get_io_context(icq->ioc);
  58         rq->elv.icq = icq;
  59 }
  60
  61 /*
  62  * Mark a hardware queue as needing a restart. For shared queues, maintain
  63  * a count of how many hardware queues are marked for restart.
  64  */
  65 void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx)
  66 {
  67         if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
  68                 return;
  69
  70         set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
  71 }
  72 EXPORT_SYMBOL_GPL(blk_mq_sched_mark_restart_hctx);
  73
  74 void blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
  75 {
  76         if (!test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
  77                 return;
  78         clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
  79
  80         blk_mq_run_hw_queue(hctx, true);
  81 }
  82
  83 #define BLK_MQ_BUDGET_DELAY     3               /* ms units */
  84
  85 /*
  86  * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
  87  * its queue by itself in its completion handler, so we don't need to
  88  * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
  89  *
  90  * Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
  91  * be run again.  This is necessary to avoid starving flushes.
  92  */
  93 static int blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
  94 {
  95         struct request_queue *q = hctx->queue;
  96         struct elevator_queue *e = q->elevator;
  97         LIST_HEAD(rq_list);
  98         int ret = 0;
  99
 100         do {
 101                 struct request *rq;
 102
 103                 if (e->type->ops.has_work && !e->type->ops.has_work(hctx))
 104                         break;
 105
 106                 if (!list_empty_careful(&hctx->dispatch)) {
 107                         ret = -EAGAIN;
 108                         break;
 109                 }
 110
 111                 if (!blk_mq_get_dispatch_budget(hctx))
 112                         break;
 113
 114                 rq = e->type->ops.dispatch_request(hctx);
 115                 if (!rq) {
 116                         blk_mq_put_dispatch_budget(hctx);
 117                         /*
 118                          * We're releasing without dispatching. Holding the
 119                          * budget could have blocked any "hctx"s with the
 120                          * same queue and if we didn't dispatch then there's
 121                          * no guarantee anyone will kick the queue.  Kick it
 122                          * ourselves.
 123                          */
 124                         blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
 125                         break;
 126                 }
 127
 128                 /*
 129                  * Now this rq owns the budget which has to be released
 130                  * if this rq won't be queued to driver via .queue_rq()
 131                  * in blk_mq_dispatch_rq_list().
 132                  */
 133                 list_add(&rq->queuelist, &rq_list);
 134         } while (blk_mq_dispatch_rq_list(q, &rq_list, true));
 135
 136         return ret;
 137 }
 138
 139 static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
 140                                           struct blk_mq_ctx *ctx)
 141 {
 142         unsigned short idx = ctx->index_hw[hctx->type];
 143
 144         if (++idx == hctx->nr_ctx)
 145                 idx = 0;
 146
 147         return hctx->ctxs[idx];
 148 }
 149
 150 /*
 151  * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
 152  * its queue by itself in its completion handler, so we don't need to
 153  * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
 154  *
 155  * Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
 156  * to be run again.  This is necessary to avoid starving flushes.
 157  */
 158 static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
 159 {
 160         struct request_queue *q = hctx->queue;
 161         LIST_HEAD(rq_list);
 162         struct blk_mq_ctx *ctx = READ_ONCE(hctx->dispatch_from);
 163         int ret = 0;
 164
 165         do {
 166                 struct request *rq;
 167
 168                 if (!list_empty_careful(&hctx->dispatch)) {
 169                         ret = -EAGAIN;
 170                         break;
 171                 }
 172
 173                 if (!sbitmap_any_bit_set(&hctx->ctx_map))
 174                         break;
 175
 176                 if (!blk_mq_get_dispatch_budget(hctx))
 177                         break;
 178
 179                 rq = blk_mq_dequeue_from_ctx(hctx, ctx);
 180                 if (!rq) {
 181                         blk_mq_put_dispatch_budget(hctx);
 182                         /*
 183                          * We're releasing without dispatching. Holding the
 184                          * budget could have blocked any "hctx"s with the
 185                          * same queue and if we didn't dispatch then there's
 186                          * no guarantee anyone will kick the queue.  Kick it
 187                          * ourselves.
 188                          */
 189                         blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
 190                         break;
 191                 }
 192
 193                 /*
 194                  * Now this rq owns the budget which has to be released
 195                  * if this rq won't be queued to driver via .queue_rq()
 196                  * in blk_mq_dispatch_rq_list().
 197                  */
 198                 list_add(&rq->queuelist, &rq_list);
 199
 200                 /* round robin for fair dispatch */
 201                 ctx = blk_mq_next_ctx(hctx, rq->mq_ctx);
 202
 203         } while (blk_mq_dispatch_rq_list(q, &rq_list, true));
 204
 205         WRITE_ONCE(hctx->dispatch_from, ctx);
 206         return ret;
 207 }
 208
 209 static int __blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
 210 {
 211         struct request_queue *q = hctx->queue;
 212         struct elevator_queue *e = q->elevator;
 213         const bool has_sched_dispatch = e && e->type->ops.dispatch_request;
 214         int ret = 0;
 215         LIST_HEAD(rq_list);
 216
 217         /*
 218          * If we have previous entries on our dispatch list, grab them first for
 219          * more fair dispatch.
 220          */
 221         if (!list_empty_careful(&hctx->dispatch)) {
 222                 spin_lock(&hctx->lock);
 223                 if (!list_empty(&hctx->dispatch))
 224                         list_splice_init(&hctx->dispatch, &rq_list);
 225                 spin_unlock(&hctx->lock);
 226         }
 227
 228         /*
 229          * Only ask the scheduler for requests, if we didn't have residual
 230          * requests from the dispatch list. This is to avoid the case where
 231          * we only ever dispatch a fraction of the requests available because
 232          * of low device queue depth. Once we pull requests out of the IO
 233          * scheduler, we can no longer merge or sort them. So it's best to
 234          * leave them there for as long as we can. Mark the hw queue as
 235          * needing a restart in that case.
 236          *
 237          * We want to dispatch from the scheduler if there was nothing
 238          * on the dispatch list or we were able to dispatch from the
 239          * dispatch list.
 240          */
 241         if (!list_empty(&rq_list)) {
 242                 blk_mq_sched_mark_restart_hctx(hctx);
 243                 if (blk_mq_dispatch_rq_list(q, &rq_list, false)) {
 244                         if (has_sched_dispatch)
 245                                 ret = blk_mq_do_dispatch_sched(hctx);
 246                         else
 247                                 ret = blk_mq_do_dispatch_ctx(hctx);
 248                 }
 249         } else if (has_sched_dispatch) {
 250                 ret = blk_mq_do_dispatch_sched(hctx);
 251         } else if (hctx->dispatch_busy) {
 252                 /* dequeue request one by one from sw queue if queue is busy */
 253                 ret = blk_mq_do_dispatch_ctx(hctx);
 254         } else {
 255                 blk_mq_flush_busy_ctxs(hctx, &rq_list);
 256                 blk_mq_dispatch_rq_list(q, &rq_list, false);
 257         }
 258
 259         return ret;
 260 }
 261
 262 void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
 263 {
 264         struct request_queue *q = hctx->queue;
 265
 266         /* RCU or SRCU read lock is needed before checking quiesced flag */
 267         if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
 268                 return;
 269
 270         hctx->run++;
 271
 272         /*
 273          * A return of -EAGAIN is an indication that hctx->dispatch is not
 274          * empty and we must run again in order to avoid starving flushes.
 275          */
 276         if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN) {
 277                 if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN)
 278                         blk_mq_run_hw_queue(hctx, true);
 279         }
 280 }
 281
 282 bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
 283                 unsigned int nr_segs, struct request **merged_request)
 284 {
 285         struct request *rq;
 286
 287         switch (elv_merge(q, &rq, bio)) {
 288         case ELEVATOR_BACK_MERGE:
 289                 if (!blk_mq_sched_allow_merge(q, rq, bio))
 290                         return false;
 291                 if (!bio_attempt_back_merge(rq, bio, nr_segs))
 292                         return false;
 293                 *merged_request = attempt_back_merge(q, rq);
 294                 if (!*merged_request)
 295                         elv_merged_request(q, rq, ELEVATOR_BACK_MERGE);
 296                 return true;
 297         case ELEVATOR_FRONT_MERGE:
 298                 if (!blk_mq_sched_allow_merge(q, rq, bio))
 299                         return false;
 300                 if (!bio_attempt_front_merge(rq, bio, nr_segs))
 301                         return false;
 302                 *merged_request = attempt_front_merge(q, rq);
 303                 if (!*merged_request)
 304                         elv_merged_request(q, rq, ELEVATOR_FRONT_MERGE);
 305                 return true;
 306         case ELEVATOR_DISCARD_MERGE:
 307                 return bio_attempt_discard_merge(q, rq, bio);
 308         default:
 309                 return false;
 310         }
 311 }
 312 EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);
 313
 314 /*
 315  * Iterate list of requests and see if we can merge this bio with any
 316  * of them.
 317  */
 318 bool blk_mq_bio_list_merge(struct request_queue *q, struct list_head *list,
 319                            struct bio *bio, unsigned int nr_segs)
 320 {
 321         struct request *rq;
 322         int checked = 8;
 323
 324         list_for_each_entry_reverse(rq, list, queuelist) {
 325                 bool merged = false;
 326
 327                 if (!checked--)
 328                         break;
 329
 330                 if (!blk_rq_merge_ok(rq, bio))
 331                         continue;
 332
 333                 switch (blk_try_merge(rq, bio)) {
 334                 case ELEVATOR_BACK_MERGE:
 335                         if (blk_mq_sched_allow_merge(q, rq, bio))
 336                                 merged = bio_attempt_back_merge(rq, bio,
 337                                                 nr_segs);
 338                         break;
 339                 case ELEVATOR_FRONT_MERGE:
 340                         if (blk_mq_sched_allow_merge(q, rq, bio))
 341                                 merged = bio_attempt_front_merge(rq, bio,
 342                                                 nr_segs);
 343                         break;
 344                 case ELEVATOR_DISCARD_MERGE:
 345                         merged = bio_attempt_discard_merge(q, rq, bio);
 346                         break;
 347                 default:
 348                         continue;
 349                 }
 350
 351                 return merged;
 352         }
 353
 354         return false;
 355 }
 356 EXPORT_SYMBOL_GPL(blk_mq_bio_list_merge);
 357
 358 /*
 359  * Reverse check our software queue for entries that we could potentially
 360  * merge with. Currently includes a hand-wavy stop count of 8, to not spend
 361  * too much time checking for merges.
 362  */
 363 static bool blk_mq_attempt_merge(struct request_queue *q,
 364                                  struct blk_mq_hw_ctx *hctx,
 365                                  struct blk_mq_ctx *ctx, struct bio *bio,
 366                                  unsigned int nr_segs)
 367 {
 368         enum hctx_type type = hctx->type;
 369
 370         lockdep_assert_held(&ctx->lock);
 371
 372         if (blk_mq_bio_list_merge(q, &ctx->rq_lists[type], bio, nr_segs)) {
 373                 ctx->rq_merged++;
 374                 return true;
 375         }
 376
 377         return false;
 378 }
 379
 380 bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio,
 381                 unsigned int nr_segs)
 382 {
 383         struct elevator_queue *e = q->elevator;
 384         struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
 385         struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, bio->bi_opf, ctx);
 386         bool ret = false;
 387         enum hctx_type type;
 388
 389         if (e && e->type->ops.bio_merge)
 390                 return e->type->ops.bio_merge(hctx, bio, nr_segs);
 391
 392         type = hctx->type;
 393         if ((hctx->flags & BLK_MQ_F_SHOULD_MERGE) &&
 394                         !list_empty_careful(&ctx->rq_lists[type])) {
 395                 /* default per sw-queue merge */
 396                 spin_lock(&ctx->lock);
 397                 ret = blk_mq_attempt_merge(q, hctx, ctx, bio, nr_segs);
 398                 spin_unlock(&ctx->lock);
 399         }
 400
 401         return ret;
 402 }
 403
 404 bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq)
 405 {
 406         return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq);
 407 }
 408 EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);
 409
 410 void blk_mq_sched_request_inserted(struct request *rq)
 411 {
 412         trace_block_rq_insert(rq->q, rq);
 413 }
 414 EXPORT_SYMBOL_GPL(blk_mq_sched_request_inserted);
 415
 416 static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
 417                                        bool has_sched,
 418                                        struct request *rq)
 419 {
 420         /*
 421          * dispatch flush and passthrough rq directly
 422          *
 423          * passthrough request has to be added to hctx->dispatch directly.
 424          * For some reason, device may be in one situation which can't
 425          * handle FS request, so STS_RESOURCE is always returned and the
 426          * FS request will be added to hctx->dispatch. However passthrough
 427          * request may be required at that time for fixing the problem. If
 428          * passthrough request is added to scheduler queue, there isn't any
 429          * chance to dispatch it given we prioritize requests in hctx->dispatch.
 430          */
 431         if ((rq->rq_flags & RQF_FLUSH_SEQ) || blk_rq_is_passthrough(rq))
 432                 return true;
 433
 434         if (has_sched)
 435                 rq->rq_flags |= RQF_SORTED;
 436
 437         return false;
 438 }
 439
 440 void blk_mq_sched_insert_request(struct request *rq, bool at_head,
 441                                  bool run_queue, bool async)
 442 {
 443         struct request_queue *q = rq->q;
 444         struct elevator_queue *e = q->elevator;
 445         struct blk_mq_ctx *ctx = rq->mq_ctx;
 446         struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
 447
 448         /* flush rq in flush machinery need to be dispatched directly */
 449         if (!(rq->rq_flags & RQF_FLUSH_SEQ) && op_is_flush(rq->cmd_flags)) {
 450                 blk_insert_flush(rq);
 451                 goto run;
 452         }
 453
 454         WARN_ON(e && (rq->tag != -1));
 455
 456         if (blk_mq_sched_bypass_insert(hctx, !!e, rq)) {
 457                 /*
 458                  * Firstly normal IO request is inserted to scheduler queue or
 459                  * sw queue, meantime we add flush request to dispatch queue(
 460                  * hctx->dispatch) directly and there is at most one in-flight
 461                  * flush request for each hw queue, so it doesn't matter to add
 462                  * flush request to tail or front of the dispatch queue.
 463                  *
 464                  * Secondly in case of NCQ, flush request belongs to non-NCQ
 465                  * command, and queueing it will fail when there is any
 466                  * in-flight normal IO request(NCQ command). When adding flush
 467                  * rq to the front of hctx->dispatch, it is easier to introduce
 468                  * extra time to flush rq's latency because of S_SCHED_RESTART
 469                  * compared with adding to the tail of dispatch queue, then
 470                  * chance of flush merge is increased, and less flush requests
 471                  * will be issued to controller. It is observed that ~10% time
 472                  * is saved in blktests block/004 on disk attached to AHCI/NCQ
 473                  * drive when adding flush rq to the front of hctx->dispatch.
 474                  *
 475                  * Simply queue flush rq to the front of hctx->dispatch so that
 476                  * intensive flush workloads can benefit in case of NCQ HW.
 477                  */
 478                 at_head = (rq->rq_flags & RQF_FLUSH_SEQ) ? true : at_head;
 479                 blk_mq_request_bypass_insert(rq, at_head, false);
 480                 goto run;
 481         }
 482
 483         if (e && e->type->ops.insert_requests) {
 484                 LIST_HEAD(list);
 485
 486                 list_add(&rq->queuelist, &list);
 487                 e->type->ops.insert_requests(hctx, &list, at_head);
 488         } else {
 489                 spin_lock(&ctx->lock);
 490                 __blk_mq_insert_request(hctx, rq, at_head);
 491                 spin_unlock(&ctx->lock);
 492         }
 493
 494 run:
 495         if (run_queue)
 496                 blk_mq_run_hw_queue(hctx, async);
 497 }
 498
 499 void blk_mq_sched_insert_requests(struct blk_mq_hw_ctx *hctx,
 500                                   struct blk_mq_ctx *ctx,
 501                                   struct list_head *list, bool run_queue_async)
 502 {
 503         struct elevator_queue *e;
 504         struct request_queue *q = hctx->queue;
 505
 506         /*
 507          * blk_mq_sched_insert_requests() is called from flush plug
 508          * context only, and hold one usage counter to prevent queue
 509          * from being released.
 510          */
 511         percpu_ref_get(&q->q_usage_counter);
 512
 513         e = hctx->queue->elevator;
 514         if (e && e->type->ops.insert_requests)
 515                 e->type->ops.insert_requests(hctx, list, false);
 516         else {
 517                 /*
 518                  * try to issue requests directly if the hw queue isn't
 519                  * busy in case of 'none' scheduler, and this way may save
 520                  * us one extra enqueue & dequeue to sw queue.
 521                  */
 522                 if (!hctx->dispatch_busy && !e && !run_queue_async) {
 523                         blk_mq_try_issue_list_directly(hctx, list);
 524                         if (list_empty(list))
 525                                 goto out;
 526                 }
 527                 blk_mq_insert_requests(hctx, ctx, list);
 528         }
 529
 530         blk_mq_run_hw_queue(hctx, run_queue_async);
 531  out:
 532         percpu_ref_put(&q->q_usage_counter);
 533 }
 534
 535 static void blk_mq_sched_free_tags(struct blk_mq_tag_set *set,
 536                                    struct blk_mq_hw_ctx *hctx,
 537                                    unsigned int hctx_idx)
 538 {
 539         if (hctx->sched_tags) {
 540                 blk_mq_free_rqs(set, hctx->sched_tags, hctx_idx);
 541                 blk_mq_free_rq_map(hctx->sched_tags);
 542                 hctx->sched_tags = NULL;
 543         }
 544 }
 545
 546 static int blk_mq_sched_alloc_tags(struct request_queue *q,
 547                                    struct blk_mq_hw_ctx *hctx,
 548                                    unsigned int hctx_idx)
 549 {
 550         struct blk_mq_tag_set *set = q->tag_set;
 551         int ret;
 552
 553         hctx->sched_tags = blk_mq_alloc_rq_map(set, hctx_idx, q->nr_requests,
 554                                                set->reserved_tags);
 555         if (!hctx->sched_tags)
 556                 return -ENOMEM;
 557
 558         ret = blk_mq_alloc_rqs(set, hctx->sched_tags, hctx_idx, q->nr_requests);
 559         if (ret)
 560                 blk_mq_sched_free_tags(set, hctx, hctx_idx);
 561
 562         return ret;
 563 }
 564
 565 /* called in queue's release handler, tagset has gone away */
 566 static void blk_mq_sched_tags_teardown(struct request_queue *q)
 567 {
 568         struct blk_mq_hw_ctx *hctx;
 569         int i;
 570
 571         queue_for_each_hw_ctx(q, hctx, i) {
 572                 if (hctx->sched_tags) {
 573                         blk_mq_free_rq_map(hctx->sched_tags);
 574                         hctx->sched_tags = NULL;
 575                 }
 576         }
 577 }
 578
 579 int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
 580 {
 581         struct blk_mq_hw_ctx *hctx;
 582         struct elevator_queue *eq;
 583         unsigned int i;
 584         int ret;
 585
 586         if (!e) {
 587                 q->elevator = NULL;
 588                 q->nr_requests = q->tag_set->queue_depth;
 589                 return 0;
 590         }
 591
 592         /*
 593          * Default to double of smaller one between hw queue_depth and 128,
 594          * since we don't split into sync/async like the old code did.
 595          * Additionally, this is a per-hw queue depth.
 596          */
 597         q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth,
 598                                    BLKDEV_MAX_RQ);
 599
 600         queue_for_each_hw_ctx(q, hctx, i) {
 601                 ret = blk_mq_sched_alloc_tags(q, hctx, i);
 602                 if (ret)
 603                         goto err;
 604         }
 605
 606         ret = e->ops.init_sched(q, e);
 607         if (ret)
 608                 goto err;
 609
 610         blk_mq_debugfs_register_sched(q);
 611
 612         queue_for_each_hw_ctx(q, hctx, i) {
 613                 if (e->ops.init_hctx) {
 614                         ret = e->ops.init_hctx(hctx, i);
 615                         if (ret) {
 616                                 eq = q->elevator;
 617                                 blk_mq_sched_free_requests(q);
 618                                 blk_mq_exit_sched(q, eq);
 619                                 kobject_put(&eq->kobj);
 620                                 return ret;
 621                         }
 622                 }
 623                 blk_mq_debugfs_register_sched_hctx(q, hctx);
 624         }
 625
 626         return 0;
 627
 628 err:
 629         blk_mq_sched_free_requests(q);
 630         blk_mq_sched_tags_teardown(q);
 631         q->elevator = NULL;
 632         return ret;
 633 }
 634
 635 /*
 636  * called in either blk_queue_cleanup or elevator_switch, tagset
 637  * is required for freeing requests
 638  */
 639 void blk_mq_sched_free_requests(struct request_queue *q)
 640 {
 641         struct blk_mq_hw_ctx *hctx;
 642         int i;
 643
 644         queue_for_each_hw_ctx(q, hctx, i) {
 645                 if (hctx->sched_tags)
 646                         blk_mq_free_rqs(q->tag_set, hctx->sched_tags, i);
 647         }
 648 }
 649
 650 void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
 651 {
 652         struct blk_mq_hw_ctx *hctx;
 653         unsigned int i;
 654
 655         queue_for_each_hw_ctx(q, hctx, i) {
 656                 blk_mq_debugfs_unregister_sched_hctx(hctx);
 657                 if (e->type->ops.exit_hctx && hctx->sched_data) {
 658                         e->type->ops.exit_hctx(hctx, i);
 659                         hctx->sched_data = NULL;
 660                 }
 661         }
 662         blk_mq_debugfs_unregister_sched(q);
 663         if (e->type->ops.exit_sched)
 664                 e->type->ops.exit_sched(e);
 665         blk_mq_sched_tags_teardown(q);
 666         q->elevator = NULL;
 667 }