linux-kernel - [PATCH] block: remove redundant explicit memory barrier from rq

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Message-Id: <20241021085251.73353-1-songmuchun@bytedance.com>
Date: Mon, 21 Oct 2024 16:52:51 +0800
From: Muchun Song <songmuchun@...edance.com>
To: axboe@...nel.dk
Cc: josef@...icpanda.com,
	oleg@...hat.com,
	linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	muchun.song@...ux.dev,
	Muchun Song <songmuchun@...edance.com>
Subject: [PATCH] block: remove redundant explicit memory barrier from rq_qos waiter and waker

The memory barriers in list_del_init_careful() and list_empty_careful()
in pairs already handle the proper ordering between data.got_token
and data.wq.entry. So remove the redundant explicit barriers. And also
change a "break" statement to "return" to avoid redundant calling of
finish_wait().

Signed-off-by: Muchun Song <songmuchun@...edance.com>
---
 block/blk-rq-qos.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c
index dc510f493ba57..9b0aa7dd6779f 100644
--- a/block/blk-rq-qos.c
+++ b/block/blk-rq-qos.c
@@ -218,7 +218,6 @@ static int rq_qos_wake_function(struct wait_queue_entry *curr,
 		return -1;
 
 	data->got_token = true;
-	smp_wmb();
 	wake_up_process(data->task);
 	list_del_init_careful(&curr->entry);
 	return 1;
@@ -274,10 +273,9 @@ void rq_qos_wait(struct rq_wait *rqw, void *private_data,
 			 * which means we now have two. Put our local token
 			 * and wake anyone else potentially waiting for one.
 			 */
-			smp_rmb();
 			if (data.got_token)
 				cleanup_cb(rqw, private_data);
-			break;
+			return;
 		}
 		io_schedule();
 		has_sleeper = true;
-- 
2.20.1