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

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Message-ID: <548113DC.9040409@cn.fujitsu.com>
Date:	Fri, 5 Dec 2014 10:09:32 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	Tejun Heo <tj@...nel.org>
CC:	NeilBrown <neilb@...e.de>, Jan Kara <jack@...e.cz>,
	Dongsu Park <dongsu.park@...fitbricks.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH workqueue/for-3.18-fixes 1/2] workqueue: invert the order
 between pool->lock and wq_mayday_lock

On 12/04/2014 11:11 PM, Tejun Heo wrote:
> 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>

Reviewed-by: 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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