blk-mq.c

				break;
			depth++;
		}

		list_cut_before(&rq_list, &list, pos);
		trace_block_unplug(head_rq->q, depth, !from_schedule);
		blk_mq_sched_insert_requests(this_hctx, this_ctx, &rq_list,
						from_schedule);
	} while(!list_empty(&list));
}

static void blk_mq_bio_to_request(struct request *rq, struct bio *bio,
		unsigned int nr_segs)
{
	int err;

	if (bio->bi_opf & REQ_RAHEAD)
		rq->cmd_flags |= REQ_FAILFAST_MASK;

	rq->__sector = bio->bi_iter.bi_sector;
	rq->write_hint = bio->bi_write_hint;
	blk_rq_bio_prep(rq, bio, nr_segs);

	/* This can't fail, since GFP_NOIO includes __GFP_DIRECT_RECLAIM. */
	err = blk_crypto_rq_bio_prep(rq, bio, GFP_NOIO);
	WARN_ON_ONCE(err);

	blk_account_io_start(rq);
}

static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
					    struct request *rq,
					    blk_qc_t *cookie, bool last)
{
	struct request_queue *q = rq->q;
	struct blk_mq_queue_data bd = {
		.rq = rq,
		.last = last,
	};
	blk_qc_t new_cookie;
	blk_status_t ret;

	new_cookie = request_to_qc_t(hctx, rq);

	/*
	 * 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);
		*cookie = new_cookie;
		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);
		*cookie = BLK_QC_T_NONE;
		break;
	}

	return ret;
}

static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
						struct request *rq,
						blk_qc_t *cookie,
						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 (q->elevator && !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, cookie, 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.
 * @cookie: Request queue cookie.
 *
 * 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_qc_t *cookie)
{
	blk_status_t ret;
	int srcu_idx;

	might_sleep_if(hctx->flags & BLK_MQ_F_BLOCKING);

	hctx_lock(hctx, &srcu_idx);

	ret = __blk_mq_try_issue_directly(hctx, rq, cookie, 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);

	hctx_unlock(hctx, srcu_idx);
}

blk_status_t blk_mq_request_issue_directly(struct request *rq, bool last)
{
	blk_status_t ret;
	int srcu_idx;
	blk_qc_t unused_cookie;
	struct blk_mq_hw_ctx *hctx = rq->mq_hctx;

	hctx_lock(hctx, &srcu_idx);
	ret = __blk_mq_try_issue_directly(hctx, rq, &unused_cookie, true, last);
	hctx_unlock(hctx, srcu_idx);

	return ret;
}

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) {
			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);
			errors++;
		} 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 void blk_add_rq_to_plug(struct blk_plug *plug, struct request *rq)
{
	list_add_tail(&rq->queuelist, &plug->mq_list);
	plug->rq_count++;
	if (!plug->multiple_queues && !list_is_singular(&plug->mq_list)) {
		struct request *tmp;

		tmp = list_first_entry(&plug->mq_list, struct request,
						queuelist);
		if (tmp->q != rq->q)
			plug->multiple_queues = true;
	}
}

/*
 * 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;
}

/**
 * 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.
 *
 * Returns: Request queue cookie.
 */
blk_qc_t blk_mq_submit_bio(struct bio *bio)
{
	struct request_queue *q = bio->bi_bdev->bd_disk->queue;
	const int is_sync = op_is_sync(bio->bi_opf);
	const int is_flush_fua = op_is_flush(bio->bi_opf);
	struct request *rq;
	struct blk_plug *plug;
	struct request *same_queue_rq = NULL;
	unsigned int nr_segs;
	blk_qc_t cookie;
	blk_status_t ret;
	bool hipri;

	blk_queue_bounce(q, &bio);
	__blk_queue_split(&bio, &nr_segs);

	if (!bio_integrity_prep(bio))
		goto queue_exit;

	if (!is_flush_fua && !blk_queue_nomerges(q) &&
	    blk_attempt_plug_merge(q, bio, nr_segs, &same_queue_rq))
		goto queue_exit;

	if (blk_mq_sched_bio_merge(q, bio, nr_segs))
		goto queue_exit;

	rq_qos_throttle(q, bio);

	hipri = bio->bi_opf & REQ_HIPRI;

	plug = blk_mq_plug(q, bio);
	if (plug && plug->cached_rq) {
		rq = plug->cached_rq;
		plug->cached_rq = rq->rq_next;
		INIT_LIST_HEAD(&rq->queuelist);
	} else {
		struct blk_mq_alloc_data data = {
			.q		= q,
			.nr_tags	= 1,
			.cmd_flags	= bio->bi_opf,
		};

		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 (unlikely(!rq)) {
			rq_qos_cleanup(q, bio);
			if (bio->bi_opf & REQ_NOWAIT)
				bio_wouldblock_error(bio);
			goto queue_exit;
		}
	}

	trace_block_getrq(bio);

	rq_qos_track(q, rq, bio);

	cookie = request_to_qc_t(rq->mq_hctx, rq);

	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 BLK_QC_T_NONE;
	}

	if (unlikely(is_flush_fua)) {
		struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
		/* Bypass scheduler for flush requests */
		blk_insert_flush(rq);
		blk_mq_run_hw_queue(hctx, true);
	} else if (plug && (q->nr_hw_queues == 1 ||
		   blk_mq_is_shared_tags(rq->mq_hctx->flags) ||
		   q->mq_ops->commit_rqs || !blk_queue_nonrot(q))) {
		/*
		 * Use plugging if we have a ->commit_rqs() hook as well, as
		 * we know the driver uses bd->last in a smart fashion.
		 *
		 * Use normal plugging if this disk is slow HDD, as sequential
		 * IO may benefit a lot from plug merging.
		 */
		unsigned int request_count = plug->rq_count;
		struct request *last = NULL;

		if (!request_count)
			trace_block_plug(q);
		else
			last = list_entry_rq(plug->mq_list.prev);

		if (request_count >= blk_plug_max_rq_count(plug) || (last &&
		    blk_rq_bytes(last) >= BLK_PLUG_FLUSH_SIZE)) {
			blk_flush_plug_list(plug, false);
			trace_block_plug(q);
		}

		blk_add_rq_to_plug(plug, rq);
	} else if (q->elevator) {
		/* Insert the request at the IO scheduler queue */
		blk_mq_sched_insert_request(rq, false, true, true);
	} else if (plug && !blk_queue_nomerges(q)) {
		/*
		 * We do limited plugging. If the bio can be merged, do that.
		 * Otherwise the existing request in the plug list will be
		 * issued. So the plug list will have one request at most
		 * The plug list might get flushed before this. If that happens,
		 * the plug list is empty, and same_queue_rq is invalid.
		 */
		if (list_empty(&plug->mq_list))
			same_queue_rq = NULL;
		if (same_queue_rq) {
			list_del_init(&same_queue_rq->queuelist);
			plug->rq_count--;
		}
		blk_add_rq_to_plug(plug, rq);
		trace_block_plug(q);

		if (same_queue_rq) {
			trace_block_unplug(q, 1, true);
			blk_mq_try_issue_directly(same_queue_rq->mq_hctx,
						  same_queue_rq, &cookie);
		}
	} else if ((q->nr_hw_queues > 1 && is_sync) ||
		   !rq->mq_hctx->dispatch_busy) {
		/*
		 * There is no scheduler and we can try to send directly
		 * to the hardware.
		 */
		blk_mq_try_issue_directly(rq->mq_hctx, rq, &cookie);
	} else {
		/* Default case. */
		blk_mq_sched_insert_request(rq, false, true, true);
	}

	if (!hipri)
		return BLK_QC_T_NONE;
	return cookie;
queue_exit:
	blk_queue_exit(q);
	return BLK_QC_T_NONE;
}

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(refcount_read(&rq->ref) != 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 (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 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)
{
	struct blk_mq_tags *tags;
	int node;

	node = blk_mq_hw_queue_to_node(&set->map[HCTX_TYPE_DEFAULT], hctx_idx);
	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;
	size_t rq_size, left;
	int node;

	node = blk_mq_hw_queue_to_node(&set->map[HCTX_TYPE_DEFAULT], hctx_idx);
	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, bool reserved)
{
	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_next_and(-1, 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(refcount_read(&flush_rq->ref) != 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);

	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);

	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 int i;

	queue_for_each_hw_ctx(q, hctx, i) {
		if (i == nr_queue)
			break;
		blk_mq_debugfs_unregister_hctx(hctx);
		blk_mq_exit_hctx(q, set, hctx, i);
	}
}

static int blk_mq_hw_ctx_size(struct blk_mq_tag_set *tag_set)
{
	int hw_ctx_size = sizeof(struct blk_mq_hw_ctx);

	BUILD_BUG_ON(ALIGN(offsetof(struct blk_mq_hw_ctx, srcu),
			   __alignof__(struct blk_mq_hw_ctx)) !=
		     sizeof(struct blk_mq_hw_ctx));

	if (tag_set->flags & BLK_MQ_F_BLOCKING)
		hw_ctx_size += sizeof(struct srcu_struct);

	return hw_ctx_size;
}

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;
	return 0;

 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(blk_mq_hw_ctx_size(set), 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;

	if (hctx->flags & BLK_MQ_F_BLOCKING)
		init_srcu_struct(hctx->srcu);
	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 i, j, hctx_idx;
	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) {