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 #include <linux/list_sort.h>
11 
12 #include <trace/events/block.h>
13 
14 #include "blk.h"
15 #include "blk-mq.h"
16 #include "blk-mq-debugfs.h"
17 #include "blk-mq-sched.h"
18 #include "blk-mq-tag.h"
19 #include "blk-wbt.h"
20 
21 /*
22  * Mark a hardware queue as needing a restart. For shared queues, maintain
23  * a count of how many hardware queues are marked for restart.
24  */
blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx * hctx)25 void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx)
26 {
27 	if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
28 		return;
29 
30 	set_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
31 }
32 EXPORT_SYMBOL_GPL(blk_mq_sched_mark_restart_hctx);
33 
__blk_mq_sched_restart(struct blk_mq_hw_ctx * hctx)34 void __blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
35 {
36 	clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state);
37 
38 	/*
39 	 * Order clearing SCHED_RESTART and list_empty_careful(&hctx->dispatch)
40 	 * in blk_mq_run_hw_queue(). Its pair is the barrier in
41 	 * blk_mq_dispatch_rq_list(). So dispatch code won't see SCHED_RESTART,
42 	 * meantime new request added to hctx->dispatch is missed to check in
43 	 * blk_mq_run_hw_queue().
44 	 */
45 	smp_mb();
46 
47 	blk_mq_run_hw_queue(hctx, true);
48 }
49 
sched_rq_cmp(void * priv,const struct list_head * a,const struct list_head * b)50 static int sched_rq_cmp(void *priv, const struct list_head *a,
51 			const struct list_head *b)
52 {
53 	struct request *rqa = container_of(a, struct request, queuelist);
54 	struct request *rqb = container_of(b, struct request, queuelist);
55 
56 	return rqa->mq_hctx > rqb->mq_hctx;
57 }
58 
blk_mq_dispatch_hctx_list(struct list_head * rq_list)59 static bool blk_mq_dispatch_hctx_list(struct list_head *rq_list)
60 {
61 	struct blk_mq_hw_ctx *hctx =
62 		list_first_entry(rq_list, struct request, queuelist)->mq_hctx;
63 	struct request *rq;
64 	LIST_HEAD(hctx_list);
65 	unsigned int count = 0;
66 
67 	list_for_each_entry(rq, rq_list, queuelist) {
68 		if (rq->mq_hctx != hctx) {
69 			list_cut_before(&hctx_list, rq_list, &rq->queuelist);
70 			goto dispatch;
71 		}
72 		count++;
73 	}
74 	list_splice_tail_init(rq_list, &hctx_list);
75 
76 dispatch:
77 	return blk_mq_dispatch_rq_list(hctx, &hctx_list, count);
78 }
79 
80 #define BLK_MQ_BUDGET_DELAY	3		/* ms units */
81 
82 /*
83  * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
84  * its queue by itself in its completion handler, so we don't need to
85  * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
86  *
87  * Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
88  * be run again.  This is necessary to avoid starving flushes.
89  */
__blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx * hctx)90 static int __blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
91 {
92 	struct request_queue *q = hctx->queue;
93 	struct elevator_queue *e = q->elevator;
94 	bool multi_hctxs = false, run_queue = false;
95 	bool dispatched = false, busy = false;
96 	unsigned int max_dispatch;
97 	LIST_HEAD(rq_list);
98 	int count = 0;
99 
100 	if (hctx->dispatch_busy)
101 		max_dispatch = 1;
102 	else
103 		max_dispatch = hctx->queue->nr_requests;
104 
105 	do {
106 		struct request *rq;
107 		int budget_token;
108 
109 		if (e->type->ops.has_work && !e->type->ops.has_work(hctx))
110 			break;
111 
112 		if (!list_empty_careful(&hctx->dispatch)) {
113 			busy = true;
114 			break;
115 		}
116 
117 		budget_token = blk_mq_get_dispatch_budget(q);
118 		if (budget_token < 0)
119 			break;
120 
121 		rq = e->type->ops.dispatch_request(hctx);
122 		if (!rq) {
123 			blk_mq_put_dispatch_budget(q, budget_token);
124 			/*
125 			 * We're releasing without dispatching. Holding the
126 			 * budget could have blocked any "hctx"s with the
127 			 * same queue and if we didn't dispatch then there's
128 			 * no guarantee anyone will kick the queue.  Kick it
129 			 * ourselves.
130 			 */
131 			run_queue = true;
132 			break;
133 		}
134 
135 		blk_mq_set_rq_budget_token(rq, budget_token);
136 
137 		/*
138 		 * Now this rq owns the budget which has to be released
139 		 * if this rq won't be queued to driver via .queue_rq()
140 		 * in blk_mq_dispatch_rq_list().
141 		 */
142 		list_add_tail(&rq->queuelist, &rq_list);
143 		count++;
144 		if (rq->mq_hctx != hctx)
145 			multi_hctxs = true;
146 
147 		/*
148 		 * If we cannot get tag for the request, stop dequeueing
149 		 * requests from the IO scheduler. We are unlikely to be able
150 		 * to submit them anyway and it creates false impression for
151 		 * scheduling heuristics that the device can take more IO.
152 		 */
153 		if (!blk_mq_get_driver_tag(rq))
154 			break;
155 	} while (count < max_dispatch);
156 
157 	if (!count) {
158 		if (run_queue)
159 			blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
160 	} else if (multi_hctxs) {
161 		/*
162 		 * Requests from different hctx may be dequeued from some
163 		 * schedulers, such as bfq and deadline.
164 		 *
165 		 * Sort the requests in the list according to their hctx,
166 		 * dispatch batching requests from same hctx at a time.
167 		 */
168 		list_sort(NULL, &rq_list, sched_rq_cmp);
169 		do {
170 			dispatched |= blk_mq_dispatch_hctx_list(&rq_list);
171 		} while (!list_empty(&rq_list));
172 	} else {
173 		dispatched = blk_mq_dispatch_rq_list(hctx, &rq_list, count);
174 	}
175 
176 	if (busy)
177 		return -EAGAIN;
178 	return !!dispatched;
179 }
180 
blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx * hctx)181 static int blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
182 {
183 	unsigned long end = jiffies + HZ;
184 	int ret;
185 
186 	do {
187 		ret = __blk_mq_do_dispatch_sched(hctx);
188 		if (ret != 1)
189 			break;
190 		if (need_resched() || time_is_before_jiffies(end)) {
191 			blk_mq_delay_run_hw_queue(hctx, 0);
192 			break;
193 		}
194 	} while (1);
195 
196 	return ret;
197 }
198 
blk_mq_next_ctx(struct blk_mq_hw_ctx * hctx,struct blk_mq_ctx * ctx)199 static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
200 					  struct blk_mq_ctx *ctx)
201 {
202 	unsigned short idx = ctx->index_hw[hctx->type];
203 
204 	if (++idx == hctx->nr_ctx)
205 		idx = 0;
206 
207 	return hctx->ctxs[idx];
208 }
209 
210 /*
211  * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
212  * its queue by itself in its completion handler, so we don't need to
213  * restart queue if .get_budget() returns BLK_STS_NO_RESOURCE.
214  *
215  * Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
216  * be run again.  This is necessary to avoid starving flushes.
217  */
blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx * hctx)218 static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
219 {
220 	struct request_queue *q = hctx->queue;
221 	LIST_HEAD(rq_list);
222 	struct blk_mq_ctx *ctx = READ_ONCE(hctx->dispatch_from);
223 	int ret = 0;
224 	struct request *rq;
225 
226 	do {
227 		int budget_token;
228 
229 		if (!list_empty_careful(&hctx->dispatch)) {
230 			ret = -EAGAIN;
231 			break;
232 		}
233 
234 		if (!sbitmap_any_bit_set(&hctx->ctx_map))
235 			break;
236 
237 		budget_token = blk_mq_get_dispatch_budget(q);
238 		if (budget_token < 0)
239 			break;
240 
241 		rq = blk_mq_dequeue_from_ctx(hctx, ctx);
242 		if (!rq) {
243 			blk_mq_put_dispatch_budget(q, budget_token);
244 			/*
245 			 * We're releasing without dispatching. Holding the
246 			 * budget could have blocked any "hctx"s with the
247 			 * same queue and if we didn't dispatch then there's
248 			 * no guarantee anyone will kick the queue.  Kick it
249 			 * ourselves.
250 			 */
251 			blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
252 			break;
253 		}
254 
255 		blk_mq_set_rq_budget_token(rq, budget_token);
256 
257 		/*
258 		 * Now this rq owns the budget which has to be released
259 		 * if this rq won't be queued to driver via .queue_rq()
260 		 * in blk_mq_dispatch_rq_list().
261 		 */
262 		list_add(&rq->queuelist, &rq_list);
263 
264 		/* round robin for fair dispatch */
265 		ctx = blk_mq_next_ctx(hctx, rq->mq_ctx);
266 
267 	} while (blk_mq_dispatch_rq_list(rq->mq_hctx, &rq_list, 1));
268 
269 	WRITE_ONCE(hctx->dispatch_from, ctx);
270 	return ret;
271 }
272 
__blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx * hctx)273 static int __blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
274 {
275 	struct request_queue *q = hctx->queue;
276 	const bool has_sched = q->elevator;
277 	int ret = 0;
278 	LIST_HEAD(rq_list);
279 
280 	/*
281 	 * If we have previous entries on our dispatch list, grab them first for
282 	 * more fair dispatch.
283 	 */
284 	if (!list_empty_careful(&hctx->dispatch)) {
285 		spin_lock(&hctx->lock);
286 		if (!list_empty(&hctx->dispatch))
287 			list_splice_init(&hctx->dispatch, &rq_list);
288 		spin_unlock(&hctx->lock);
289 	}
290 
291 	/*
292 	 * Only ask the scheduler for requests, if we didn't have residual
293 	 * requests from the dispatch list. This is to avoid the case where
294 	 * we only ever dispatch a fraction of the requests available because
295 	 * of low device queue depth. Once we pull requests out of the IO
296 	 * scheduler, we can no longer merge or sort them. So it's best to
297 	 * leave them there for as long as we can. Mark the hw queue as
298 	 * needing a restart in that case.
299 	 *
300 	 * We want to dispatch from the scheduler if there was nothing
301 	 * on the dispatch list or we were able to dispatch from the
302 	 * dispatch list.
303 	 */
304 	if (!list_empty(&rq_list)) {
305 		blk_mq_sched_mark_restart_hctx(hctx);
306 		if (blk_mq_dispatch_rq_list(hctx, &rq_list, 0)) {
307 			if (has_sched)
308 				ret = blk_mq_do_dispatch_sched(hctx);
309 			else
310 				ret = blk_mq_do_dispatch_ctx(hctx);
311 		}
312 	} else if (has_sched) {
313 		ret = blk_mq_do_dispatch_sched(hctx);
314 	} else if (hctx->dispatch_busy) {
315 		/* dequeue request one by one from sw queue if queue is busy */
316 		ret = blk_mq_do_dispatch_ctx(hctx);
317 	} else {
318 		blk_mq_flush_busy_ctxs(hctx, &rq_list);
319 		blk_mq_dispatch_rq_list(hctx, &rq_list, 0);
320 	}
321 
322 	return ret;
323 }
324 
blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx * hctx)325 void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
326 {
327 	struct request_queue *q = hctx->queue;
328 
329 	/* RCU or SRCU read lock is needed before checking quiesced flag */
330 	if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
331 		return;
332 
333 	hctx->run++;
334 
335 	/*
336 	 * A return of -EAGAIN is an indication that hctx->dispatch is not
337 	 * empty and we must run again in order to avoid starving flushes.
338 	 */
339 	if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN) {
340 		if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN)
341 			blk_mq_run_hw_queue(hctx, true);
342 	}
343 }
344 
blk_mq_sched_bio_merge(struct request_queue * q,struct bio * bio,unsigned int nr_segs)345 bool blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio,
346 		unsigned int nr_segs)
347 {
348 	struct elevator_queue *e = q->elevator;
349 	struct blk_mq_ctx *ctx;
350 	struct blk_mq_hw_ctx *hctx;
351 	bool ret = false;
352 	enum hctx_type type;
353 
354 	if (e && e->type->ops.bio_merge) {
355 		ret = e->type->ops.bio_merge(q, bio, nr_segs);
356 		goto out_put;
357 	}
358 
359 	ctx = blk_mq_get_ctx(q);
360 	hctx = blk_mq_map_queue(q, bio->bi_opf, ctx);
361 	type = hctx->type;
362 	if (!(hctx->flags & BLK_MQ_F_SHOULD_MERGE) ||
363 	    list_empty_careful(&ctx->rq_lists[type]))
364 		goto out_put;
365 
366 	/* default per sw-queue merge */
367 	spin_lock(&ctx->lock);
368 	/*
369 	 * Reverse check our software queue for entries that we could
370 	 * potentially merge with. Currently includes a hand-wavy stop
371 	 * count of 8, to not spend too much time checking for merges.
372 	 */
373 	if (blk_bio_list_merge(q, &ctx->rq_lists[type], bio, nr_segs))
374 		ret = true;
375 
376 	spin_unlock(&ctx->lock);
377 out_put:
378 	return ret;
379 }
380 
blk_mq_sched_try_insert_merge(struct request_queue * q,struct request * rq,struct list_head * free)381 bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq,
382 				   struct list_head *free)
383 {
384 	return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq, free);
385 }
386 EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);
387 
blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx * hctx,struct request * rq)388 static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
389 				       struct request *rq)
390 {
391 	/*
392 	 * dispatch flush and passthrough rq directly
393 	 *
394 	 * passthrough request has to be added to hctx->dispatch directly.
395 	 * For some reason, device may be in one situation which can't
396 	 * handle FS request, so STS_RESOURCE is always returned and the
397 	 * FS request will be added to hctx->dispatch. However passthrough
398 	 * request may be required at that time for fixing the problem. If
399 	 * passthrough request is added to scheduler queue, there isn't any
400 	 * chance to dispatch it given we prioritize requests in hctx->dispatch.
401 	 */
402 	if ((rq->rq_flags & RQF_FLUSH_SEQ) || blk_rq_is_passthrough(rq))
403 		return true;
404 
405 	return false;
406 }
407 
blk_mq_sched_insert_request(struct request * rq,bool at_head,bool run_queue,bool async)408 void blk_mq_sched_insert_request(struct request *rq, bool at_head,
409 				 bool run_queue, bool async)
410 {
411 	struct request_queue *q = rq->q;
412 	struct elevator_queue *e = q->elevator;
413 	struct blk_mq_ctx *ctx = rq->mq_ctx;
414 	struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
415 
416 	WARN_ON(e && (rq->tag != BLK_MQ_NO_TAG));
417 
418 	if (blk_mq_sched_bypass_insert(hctx, rq)) {
419 		/*
420 		 * Firstly normal IO request is inserted to scheduler queue or
421 		 * sw queue, meantime we add flush request to dispatch queue(
422 		 * hctx->dispatch) directly and there is at most one in-flight
423 		 * flush request for each hw queue, so it doesn't matter to add
424 		 * flush request to tail or front of the dispatch queue.
425 		 *
426 		 * Secondly in case of NCQ, flush request belongs to non-NCQ
427 		 * command, and queueing it will fail when there is any
428 		 * in-flight normal IO request(NCQ command). When adding flush
429 		 * rq to the front of hctx->dispatch, it is easier to introduce
430 		 * extra time to flush rq's latency because of S_SCHED_RESTART
431 		 * compared with adding to the tail of dispatch queue, then
432 		 * chance of flush merge is increased, and less flush requests
433 		 * will be issued to controller. It is observed that ~10% time
434 		 * is saved in blktests block/004 on disk attached to AHCI/NCQ
435 		 * drive when adding flush rq to the front of hctx->dispatch.
436 		 *
437 		 * Simply queue flush rq to the front of hctx->dispatch so that
438 		 * intensive flush workloads can benefit in case of NCQ HW.
439 		 */
440 		at_head = (rq->rq_flags & RQF_FLUSH_SEQ) ? true : at_head;
441 		blk_mq_request_bypass_insert(rq, at_head, false);
442 		goto run;
443 	}
444 
445 	if (e) {
446 		LIST_HEAD(list);
447 
448 		list_add(&rq->queuelist, &list);
449 		e->type->ops.insert_requests(hctx, &list, at_head);
450 	} else {
451 		spin_lock(&ctx->lock);
452 		__blk_mq_insert_request(hctx, rq, at_head);
453 		spin_unlock(&ctx->lock);
454 	}
455 
456 run:
457 	if (run_queue)
458 		blk_mq_run_hw_queue(hctx, async);
459 }
460 
blk_mq_sched_insert_requests(struct blk_mq_hw_ctx * hctx,struct blk_mq_ctx * ctx,struct list_head * list,bool run_queue_async)461 void blk_mq_sched_insert_requests(struct blk_mq_hw_ctx *hctx,
462 				  struct blk_mq_ctx *ctx,
463 				  struct list_head *list, bool run_queue_async)
464 {
465 	struct elevator_queue *e;
466 	struct request_queue *q = hctx->queue;
467 
468 	/*
469 	 * blk_mq_sched_insert_requests() is called from flush plug
470 	 * context only, and hold one usage counter to prevent queue
471 	 * from being released.
472 	 */
473 	percpu_ref_get(&q->q_usage_counter);
474 
475 	e = hctx->queue->elevator;
476 	if (e) {
477 		e->type->ops.insert_requests(hctx, list, false);
478 	} else {
479 		/*
480 		 * try to issue requests directly if the hw queue isn't
481 		 * busy in case of 'none' scheduler, and this way may save
482 		 * us one extra enqueue & dequeue to sw queue.
483 		 */
484 		if (!hctx->dispatch_busy && !run_queue_async) {
485 			blk_mq_run_dispatch_ops(hctx->queue,
486 				blk_mq_try_issue_list_directly(hctx, list));
487 			if (list_empty(list))
488 				goto out;
489 		}
490 		blk_mq_insert_requests(hctx, ctx, list);
491 	}
492 
493 	blk_mq_run_hw_queue(hctx, run_queue_async);
494  out:
495 	percpu_ref_put(&q->q_usage_counter);
496 }
497 
blk_mq_sched_alloc_map_and_rqs(struct request_queue * q,struct blk_mq_hw_ctx * hctx,unsigned int hctx_idx)498 static int blk_mq_sched_alloc_map_and_rqs(struct request_queue *q,
499 					  struct blk_mq_hw_ctx *hctx,
500 					  unsigned int hctx_idx)
501 {
502 	if (blk_mq_is_shared_tags(q->tag_set->flags)) {
503 		hctx->sched_tags = q->sched_shared_tags;
504 		return 0;
505 	}
506 
507 	hctx->sched_tags = blk_mq_alloc_map_and_rqs(q->tag_set, hctx_idx,
508 						    q->nr_requests);
509 
510 	if (!hctx->sched_tags)
511 		return -ENOMEM;
512 	return 0;
513 }
514 
blk_mq_exit_sched_shared_tags(struct request_queue * queue)515 static void blk_mq_exit_sched_shared_tags(struct request_queue *queue)
516 {
517 	blk_mq_free_rq_map(queue->sched_shared_tags);
518 	queue->sched_shared_tags = NULL;
519 }
520 
521 /* called in queue's release handler, tagset has gone away */
blk_mq_sched_tags_teardown(struct request_queue * q,unsigned int flags)522 static void blk_mq_sched_tags_teardown(struct request_queue *q, unsigned int flags)
523 {
524 	struct blk_mq_hw_ctx *hctx;
525 	unsigned long i;
526 
527 	queue_for_each_hw_ctx(q, hctx, i) {
528 		if (hctx->sched_tags) {
529 			if (!blk_mq_is_shared_tags(flags))
530 				blk_mq_free_rq_map(hctx->sched_tags);
531 			hctx->sched_tags = NULL;
532 		}
533 	}
534 
535 	if (blk_mq_is_shared_tags(flags))
536 		blk_mq_exit_sched_shared_tags(q);
537 }
538 
blk_mq_init_sched_shared_tags(struct request_queue * queue)539 static int blk_mq_init_sched_shared_tags(struct request_queue *queue)
540 {
541 	struct blk_mq_tag_set *set = queue->tag_set;
542 
543 	/*
544 	 * Set initial depth at max so that we don't need to reallocate for
545 	 * updating nr_requests.
546 	 */
547 	queue->sched_shared_tags = blk_mq_alloc_map_and_rqs(set,
548 						BLK_MQ_NO_HCTX_IDX,
549 						MAX_SCHED_RQ);
550 	if (!queue->sched_shared_tags)
551 		return -ENOMEM;
552 
553 	blk_mq_tag_update_sched_shared_tags(queue);
554 
555 	return 0;
556 }
557 
blk_mq_init_sched(struct request_queue * q,struct elevator_type * e)558 int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
559 {
560 	unsigned int flags = q->tag_set->flags;
561 	struct blk_mq_hw_ctx *hctx;
562 	struct elevator_queue *eq;
563 	unsigned long i;
564 	int ret;
565 
566 	if (!e) {
567 		blk_queue_flag_clear(QUEUE_FLAG_SQ_SCHED, q);
568 		q->elevator = NULL;
569 		q->nr_requests = q->tag_set->queue_depth;
570 		return 0;
571 	}
572 
573 	/*
574 	 * Default to double of smaller one between hw queue_depth and 128,
575 	 * since we don't split into sync/async like the old code did.
576 	 * Additionally, this is a per-hw queue depth.
577 	 */
578 	q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth,
579 				   BLKDEV_DEFAULT_RQ);
580 
581 	if (blk_mq_is_shared_tags(flags)) {
582 		ret = blk_mq_init_sched_shared_tags(q);
583 		if (ret)
584 			return ret;
585 	}
586 
587 	queue_for_each_hw_ctx(q, hctx, i) {
588 		ret = blk_mq_sched_alloc_map_and_rqs(q, hctx, i);
589 		if (ret)
590 			goto err_free_map_and_rqs;
591 	}
592 
593 	ret = e->ops.init_sched(q, e);
594 	if (ret)
595 		goto err_free_map_and_rqs;
596 
597 	mutex_lock(&q->debugfs_mutex);
598 	blk_mq_debugfs_register_sched(q);
599 	mutex_unlock(&q->debugfs_mutex);
600 
601 	queue_for_each_hw_ctx(q, hctx, i) {
602 		if (e->ops.init_hctx) {
603 			ret = e->ops.init_hctx(hctx, i);
604 			if (ret) {
605 				eq = q->elevator;
606 				blk_mq_sched_free_rqs(q);
607 				blk_mq_exit_sched(q, eq);
608 				kobject_put(&eq->kobj);
609 				return ret;
610 			}
611 		}
612 		mutex_lock(&q->debugfs_mutex);
613 		blk_mq_debugfs_register_sched_hctx(q, hctx);
614 		mutex_unlock(&q->debugfs_mutex);
615 	}
616 
617 	return 0;
618 
619 err_free_map_and_rqs:
620 	blk_mq_sched_free_rqs(q);
621 	blk_mq_sched_tags_teardown(q, flags);
622 
623 	q->elevator = NULL;
624 	return ret;
625 }
626 
627 /*
628  * called in either blk_queue_cleanup or elevator_switch, tagset
629  * is required for freeing requests
630  */
blk_mq_sched_free_rqs(struct request_queue * q)631 void blk_mq_sched_free_rqs(struct request_queue *q)
632 {
633 	struct blk_mq_hw_ctx *hctx;
634 	unsigned long i;
635 
636 	if (blk_mq_is_shared_tags(q->tag_set->flags)) {
637 		blk_mq_free_rqs(q->tag_set, q->sched_shared_tags,
638 				BLK_MQ_NO_HCTX_IDX);
639 	} else {
640 		queue_for_each_hw_ctx(q, hctx, i) {
641 			if (hctx->sched_tags)
642 				blk_mq_free_rqs(q->tag_set,
643 						hctx->sched_tags, i);
644 		}
645 	}
646 }
647 
blk_mq_exit_sched(struct request_queue * q,struct elevator_queue * e)648 void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
649 {
650 	struct blk_mq_hw_ctx *hctx;
651 	unsigned long i;
652 	unsigned int flags = 0;
653 
654 	queue_for_each_hw_ctx(q, hctx, i) {
655 		mutex_lock(&q->debugfs_mutex);
656 		blk_mq_debugfs_unregister_sched_hctx(hctx);
657 		mutex_unlock(&q->debugfs_mutex);
658 
659 		if (e->type->ops.exit_hctx && hctx->sched_data) {
660 			e->type->ops.exit_hctx(hctx, i);
661 			hctx->sched_data = NULL;
662 		}
663 		flags = hctx->flags;
664 	}
665 
666 	mutex_lock(&q->debugfs_mutex);
667 	blk_mq_debugfs_unregister_sched(q);
668 	mutex_unlock(&q->debugfs_mutex);
669 
670 	if (e->type->ops.exit_sched)
671 		e->type->ops.exit_sched(e);
672 	blk_mq_sched_tags_teardown(q, flags);
673 	q->elevator = NULL;
674 }
675