linux-kernel - [PATCH 07/10] blk-mq-sched: add new parameter nr_requests in blk_mq_alloc_sched

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Message-Id: <20250815080216.410665-8-yukuai1@huaweicloud.com>
Date: Fri, 15 Aug 2025 16:02:13 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: axboe@...nel.dk,
	hare@...e.de,
	nilay@...ux.ibm.com,
	ming.lei@...hat.com
Cc: linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	yukuai3@...wei.com,
	yukuai1@...weicloud.com,
	yi.zhang@...wei.com,
	yangerkun@...wei.com,
	johnny.chenyi@...wei.com
Subject: [PATCH 07/10] blk-mq-sched: add new parameter nr_requests in blk_mq_alloc_sched_tags()

From: Yu Kuai <yukuai3@...wei.com>

This helper only support to allocate the default number of requests,
add a new parameter to support specific number of requests.

Prepare to fix tags double free problem if nr_requests is grown by
queue sysfs attribute nr_requests.

Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 block/blk-mq-sched.c | 14 +++++---------
 block/blk-mq-sched.h |  2 +-
 block/blk-mq.h       | 11 +++++++++++
 block/elevator.c     |  3 ++-
 4 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index bf7dd97422ec..f3a918e36589 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -454,7 +454,7 @@ void blk_mq_free_sched_tags_batch(struct xarray *et_table,
 }
 
 struct elevator_tags *blk_mq_alloc_sched_tags(struct blk_mq_tag_set *set,
-		unsigned int nr_hw_queues)
+		unsigned int nr_hw_queues, unsigned int nr_requests)
 {
 	unsigned int nr_tags;
 	int i;
@@ -470,13 +470,8 @@ struct elevator_tags *blk_mq_alloc_sched_tags(struct blk_mq_tag_set *set,
 			nr_tags * sizeof(struct blk_mq_tags *), gfp);
 	if (!et)
 		return NULL;
-	/*
-	 * 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.
-	 */
-	et->nr_requests = 2 * min_t(unsigned int, set->queue_depth,
-			BLKDEV_DEFAULT_RQ);
+
+	et->nr_requests = nr_requests;
 	et->nr_hw_queues = nr_hw_queues;
 
 	if (blk_mq_is_shared_tags(set->flags)) {
@@ -521,7 +516,8 @@ int blk_mq_alloc_sched_tags_batch(struct xarray *et_table,
 		 * concurrently.
 		 */
 		if (q->elevator) {
-			et = blk_mq_alloc_sched_tags(set, nr_hw_queues);
+			et = blk_mq_alloc_sched_tags(set, nr_hw_queues,
+					blk_mq_default_nr_requests(set));
 			if (!et)
 				goto out_unwind;
 			if (xa_insert(et_table, q->id, et, gfp))
diff --git a/block/blk-mq-sched.h b/block/blk-mq-sched.h
index fe83187f41db..8e21a6b1415d 100644
--- a/block/blk-mq-sched.h
+++ b/block/blk-mq-sched.h
@@ -24,7 +24,7 @@ void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e);
 void blk_mq_sched_free_rqs(struct request_queue *q);
 
 struct elevator_tags *blk_mq_alloc_sched_tags(struct blk_mq_tag_set *set,
-		unsigned int nr_hw_queues);
+		unsigned int nr_hw_queues, unsigned int nr_requests);
 int blk_mq_alloc_sched_tags_batch(struct xarray *et_table,
 		struct blk_mq_tag_set *set, unsigned int nr_hw_queues);
 void blk_mq_free_sched_tags(struct elevator_tags *et,
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 2b3ade60c90b..731f4578d9a8 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -109,6 +109,17 @@ static inline struct blk_mq_hw_ctx *blk_mq_map_queue(blk_opf_t opf,
 	return ctx->hctxs[blk_mq_get_hctx_type(opf)];
 }
 
+/*
+ * 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.
+ */
+static inline unsigned int blk_mq_default_nr_requests(
+		struct blk_mq_tag_set *set)
+{
+	return 2 * min_t(unsigned int, set->queue_depth, BLKDEV_DEFAULT_RQ);
+}
+
 /*
  * sysfs helpers
  */
diff --git a/block/elevator.c b/block/elevator.c
index fe96c6f4753c..e2ebfbf107b3 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -669,7 +669,8 @@ static int elevator_change(struct request_queue *q, struct elv_change_ctx *ctx)
 	lockdep_assert_held(&set->update_nr_hwq_lock);
 
 	if (strncmp(ctx->name, "none", 4)) {
-		ctx->et = blk_mq_alloc_sched_tags(set, set->nr_hw_queues);
+		ctx->et = blk_mq_alloc_sched_tags(set, set->nr_hw_queues,
+				blk_mq_default_nr_requests(set));
 		if (!ctx->et)
 			return -ENOMEM;
 	}
-- 
2.39.2