linux-kernel - [PATCH workqueue/for-3.18-fixes 1/2] workqueue: invert the order between pool->lock and wq_mayday

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Message-ID: <20141204151104.GD15219@htj.dyndns.org>
Date:	Thu, 4 Dec 2014 10:11:04 -0500
From:	Tejun Heo <tj@...nel.org>
To:	NeilBrown <neilb@...e.de>
Cc:	Jan Kara <jack@...e.cz>, Lai Jiangshan <laijs@...fujitsu.com>,
	Dongsu Park <dongsu.park@...fitbricks.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH workqueue/for-3.18-fixes 1/2] workqueue: invert the order
 between pool->lock and wq_mayday_lock

Currently, pool->lock nests inside pool->lock.  There's no inherent
reason for this order.  The only place where the two locks are held
together is pool_mayday_timeout() and it just got decided that way.

This nesting order turns out to complicate things with the planned
rescuer_thread() update.  Let's invert them.  This doesn't cause any
behavior differences.

Signed-off-by: Tejun Heo <tj@...nel.org>
Cc: NeilBrown <neilb@...e.de>
Cc: Dongsu Park <dongsu.park@...fitbricks.com>
Cc: Lai Jiangshan <laijs@...fujitsu.com>
---
 kernel/workqueue.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1804,8 +1804,8 @@ static void pool_mayday_timeout(unsigned
 	struct worker_pool *pool = (void *)__pool;
 	struct work_struct *work;
 
-	spin_lock_irq(&wq_mayday_lock);		/* for wq->maydays */
-	spin_lock(&pool->lock);
+	spin_lock_irq(&pool->lock);
+	spin_lock(&wq_mayday_lock);		/* for wq->maydays */
 
 	if (need_to_create_worker(pool)) {
 		/*
@@ -1818,8 +1818,8 @@ static void pool_mayday_timeout(unsigned
 			send_mayday(work);
 	}
 
-	spin_unlock(&pool->lock);
-	spin_unlock_irq(&wq_mayday_lock);
+	spin_unlock(&wq_mayday_lock);
+	spin_unlock_irq(&pool->lock);
 
 	mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INTERVAL);
 }
--
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