linux-kernel - [PATCH 1/4] workqueue: Remove the mb() pair between wq_worker_sleeping() and insert

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Date:   Thu, 23 Dec 2021 20:31:37 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: [PATCH 1/4] workqueue: Remove the mb() pair between wq_worker_sleeping() and insert_work()

From: Lai Jiangshan <laijs@...ux.alibaba.com>

In wq_worker_sleeping(), the access to worklist is protected by the
pool->lock, so the memory barrier is unneeded.

Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 kernel/workqueue.c | 11 -----------
 1 file changed, 11 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 33f1106b4f99..29b070106f34 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -918,10 +918,6 @@ void wq_worker_sleeping(struct task_struct *task)
 	}
 
 	/*
-	 * The counterpart of the following dec_and_test, implied mb,
-	 * worklist not empty test sequence is in insert_work().
-	 * Please read comment there.
-	 *
 	 * NOT_RUNNING is clear.  This means that we're bound to and
 	 * running on the local cpu w/ rq lock held and preemption
 	 * disabled, which in turn means that none else could be
@@ -1372,13 +1368,6 @@ static void insert_work(struct pool_workqueue *pwq, struct work_struct *work,
 	list_add_tail(&work->entry, head);
 	get_pwq(pwq);
 
-	/*
-	 * Ensure either wq_worker_sleeping() sees the above
-	 * list_add_tail() or we see zero nr_running to avoid workers lying
-	 * around lazily while there are works to be processed.
-	 */
-	smp_mb();
-
 	if (__need_more_worker(pool))
 		wake_up_worker(pool);
 }
-- 
2.19.1.6.gb485710b