linux-kernel - [PATCH 1/3] blk-ioc: add a new helper ioc_lookup_icq

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Message-Id: <20250725070547.3953398-2-yukuai1@huaweicloud.com>
Date: Fri, 25 Jul 2025 15:05:45 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: jack@...e.cz,
	dlemoal@...nel.org,
	axboe@...nel.dk
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 1/3] blk-ioc: add a new helper ioc_lookup_icq_rcu()

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

ioc_lookup_icq() is used by bfq to lookup bfqq from IO path, the helper
have to be protected by queue_lock, which is too heavy. Hence add a new
helper that is lookless, this is safe because both request_queue and ioc
can be pinged by IO that is still issuing.

Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 block/blk-ioc.c | 34 ++++++++++++++++++++++++++++++++++
 block/blk.h     |  1 +
 2 files changed, 35 insertions(+)

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index ce82770c72ab..4945b48dfdb6 100644
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -343,6 +343,40 @@ struct io_cq *ioc_lookup_icq(struct request_queue *q)
 }
 EXPORT_SYMBOL(ioc_lookup_icq);
 
+/**
+ * ioc_lookup_icq_rcu - lookup io_cq from ioc in io path
+ * @q: the associated request_queue
+ *
+ * Look up io_cq associated with @ioc - @q pair from @ioc. Must be called from
+ * io issue path, either return NULL if current issue io to @q for the first
+ * time, or return a valid icq.
+ */
+struct io_cq *ioc_lookup_icq_rcu(struct request_queue *q)
+{
+	struct io_context *ioc = current->io_context;
+	struct io_cq *icq;
+
+	WARN_ON_ONCE(percpu_ref_is_zero(&q->q_usage_counter));
+
+	if (!ioc)
+		return NULL;
+
+	icq = rcu_dereference(ioc->icq_hint);
+	if (icq && icq->q == q)
+		return icq;
+
+	icq = radix_tree_lookup(&ioc->icq_tree, q->id);
+	if (!icq)
+		return NULL;
+
+	if (WARN_ON_ONCE(icq->q != q))
+		return NULL;
+
+	rcu_assign_pointer(ioc->icq_hint, icq);
+	return icq;
+}
+EXPORT_SYMBOL(ioc_lookup_icq_rcu);
+
 /**
  * ioc_create_icq - create and link io_cq
  * @q: request_queue of interest
diff --git a/block/blk.h b/block/blk.h
index 468aa83c5a22..ef31b3ec1c69 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -461,6 +461,7 @@ static inline void req_set_nomerge(struct request_queue *q, struct request *req)
  */
 struct io_cq *ioc_find_get_icq(struct request_queue *q);
 struct io_cq *ioc_lookup_icq(struct request_queue *q);
+struct io_cq *ioc_lookup_icq_rcu(struct request_queue *q);
 #ifdef CONFIG_BLK_ICQ
 void ioc_clear_queue(struct request_queue *q);
 #else
-- 
2.39.2