linux-kernel - [PATCH 1/5] block/blk-rq-qos: add a new helper rq_qos_add

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Message-Id: <20251116024134.115685-2-yukuai@fnnas.com>
Date: Sun, 16 Nov 2025 10:41:30 +0800
From: "Yu Kuai" <yukuai@...as.com>
To: <axboe@...nel.dk>, <linux-block@...r.kernel.org>, 
	<linux-kernel@...r.kernel.org>, <tj@...nel.org>, <nilay@...ux.ibm.com>, 
	<ming.lei@...hat.com>
Cc: <yukuai@...as.com>
Subject: [PATCH 1/5] block/blk-rq-qos: add a new helper rq_qos_add_freezed()

queue should not be freezed under rq_qos_mutex, see example index
commit 9730763f4756 ("block: correct locking order for protecting blk-wbt
parameters"), which means current implementation of rq_qos_add() is
problematic. Add a new helper and prepare to fix this problem in
following patches.

Signed-off-by: Yu Kuai <yukuai@...as.com>
---
 block/blk-rq-qos.c | 27 +++++++++++++++++++++++++++
 block/blk-rq-qos.h |  2 ++
 2 files changed, 29 insertions(+)

diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c
index 654478dfbc20..353397d7e126 100644
--- a/block/blk-rq-qos.c
+++ b/block/blk-rq-qos.c
@@ -322,6 +322,33 @@ void rq_qos_exit(struct request_queue *q)
 	mutex_unlock(&q->rq_qos_mutex);
 }
 
+int rq_qos_add_freezed(struct rq_qos *rqos, struct gendisk *disk,
+		       enum rq_qos_id id, const struct rq_qos_ops *ops)
+{
+	struct request_queue *q = disk->queue;
+
+	WARN_ON_ONCE(q->mq_freeze_depth == 0);
+	lockdep_assert_held(&q->rq_qos_mutex);
+
+	if (rq_qos_id(q, id))
+		return -EBUSY;
+
+	rqos->disk = disk;
+	rqos->id = id;
+	rqos->ops = ops;
+	rqos->next = q->rq_qos;
+	q->rq_qos = rqos;
+	blk_queue_flag_set(QUEUE_FLAG_QOS_ENABLED, q);
+
+	if (rqos->ops->debugfs_attrs) {
+		mutex_lock(&q->debugfs_mutex);
+		blk_mq_debugfs_register_rqos(rqos);
+		mutex_unlock(&q->debugfs_mutex);
+	}
+
+	return 0;
+}
+
 int rq_qos_add(struct rq_qos *rqos, struct gendisk *disk, enum rq_qos_id id,
 		const struct rq_qos_ops *ops)
 {
diff --git a/block/blk-rq-qos.h b/block/blk-rq-qos.h
index b538f2c0febc..4a7fec01600b 100644
--- a/block/blk-rq-qos.h
+++ b/block/blk-rq-qos.h
@@ -87,6 +87,8 @@ static inline void rq_wait_init(struct rq_wait *rq_wait)
 
 int rq_qos_add(struct rq_qos *rqos, struct gendisk *disk, enum rq_qos_id id,
 		const struct rq_qos_ops *ops);
+int rq_qos_add_freezed(struct rq_qos *rqos, struct gendisk *disk,
+		       enum rq_qos_id id, const struct rq_qos_ops *ops);
 void rq_qos_del(struct rq_qos *rqos);
 
 typedef bool (acquire_inflight_cb_t)(struct rq_wait *rqw, void *private_data);
-- 
2.51.0