linux-kernel - [PATCH 2/4] workqueue: Change the comments of the synchronization about the idle

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Date:   Thu, 23 Dec 2021 20:31:38 +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 2/4] workqueue: Change the comments of the synchronization about the idle_list

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

The access to idle_list in wq_worker_sleeping() is changed to be
protected by pool->lock, so the comments above idle_list can be changed
to "L:" which is the meaning of "access with pool->lock held".

And the outdated comments in wq_worker_sleeping() is removed since
the function is not called with rq lock held any more, idle_list is
dereferenced with pool lock now.

Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 kernel/workqueue.c | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 29b070106f34..b3207722671c 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -162,7 +162,7 @@ struct worker_pool {
 	int			nr_workers;	/* L: total number of workers */
 	int			nr_idle;	/* L: currently idle workers */
 
-	struct list_head	idle_list;	/* X: list of idle workers */
+	struct list_head	idle_list;	/* L: list of idle workers */
 	struct timer_list	idle_timer;	/* L: worker idle timeout */
 	struct timer_list	mayday_timer;	/* L: SOS timer for workers */
 
@@ -826,7 +826,7 @@ static bool too_many_workers(struct worker_pool *pool)
  * Wake up functions.
  */
 
-/* Return the first idle worker.  Safe with preemption disabled */
+/* Return the first idle worker.  Called with pool->lock held. */
 static struct worker *first_idle_worker(struct worker_pool *pool)
 {
 	if (unlikely(list_empty(&pool->idle_list)))
@@ -917,13 +917,6 @@ void wq_worker_sleeping(struct task_struct *task)
 		return;
 	}
 
-	/*
-	 * 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
-	 * manipulating idle_list, so dereferencing idle_list without pool
-	 * lock is safe.
-	 */
 	if (atomic_dec_and_test(&pool->nr_running) &&
 	    !list_empty(&pool->worklist)) {
 		next = first_idle_worker(pool);
-- 
2.19.1.6.gb485710b