linux-kernel - [PATCH] blk-cgroup: Remove unnecessary rcu_read

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Date:   Tue, 17 May 2022 01:39:30 +0800
From:   bh1scw@...il.com
To:     tj@...nel.org, axboe@...nel.dk
Cc:     cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, songmuchun@...edance.com,
        Fanjun Kong <bh1scw@...il.com>
Subject: [PATCH] blk-cgroup: Remove unnecessary rcu_read_lock/unlock()

From: Fanjun Kong <bh1scw@...il.com>

spin_lock_irq/spin_unlock_irq contains preempt_disable/enable().
Which can serve as RCU read-side critical region, so remove
rcu_read_lock/unlock().

Signed-off-by: Fanjun Kong <bh1scw@...il.com>
---
 block/blk-cgroup.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index a91f8ae18b49..7bdc16a36560 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1283,14 +1283,13 @@ int blkcg_init_queue(struct request_queue *q)
 	preloaded = !radix_tree_preload(GFP_KERNEL);
 
 	/* Make sure the root blkg exists. */
-	rcu_read_lock();
+	/* spin_lock_irq can serve as RCU read-side critical section. */
 	spin_lock_irq(&q->queue_lock);
 	blkg = blkg_create(&blkcg_root, q, new_blkg);
 	if (IS_ERR(blkg))
 		goto err_unlock;
 	q->root_blkg = blkg;
 	spin_unlock_irq(&q->queue_lock);
-	rcu_read_unlock();
 
 	if (preloaded)
 		radix_tree_preload_end();
@@ -1316,7 +1315,6 @@ int blkcg_init_queue(struct request_queue *q)
 	return ret;
 err_unlock:
 	spin_unlock_irq(&q->queue_lock);
-	rcu_read_unlock();
 	if (preloaded)
 		radix_tree_preload_end();
 	return PTR_ERR(blkg);
-- 
2.36.0