linux-kernel - Re: [PATCH V3] block: Mitigate lock unbalance caused by lock switching

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Message-ID: <4FC4D2F2.2070309@gmail.com>
Date:	Tue, 29 May 2012 07:45:22 -0600
From:	Tim Gardner <rtg.canonical@...il.com>
To:	Asias He <asias@...hat.com>
CC:	Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	tim.gardner@...onical.com
Subject: Re: [PATCH V3] block: Mitigate lock unbalance caused by lock switching

On 05/28/2012 07:39 PM, Asias He wrote:

<snip>

> @@ -440,6 +435,11 @@ void blk_cleanup_queue(struct request_queue *q)
>  	del_timer_sync(&q->backing_dev_info.laptop_mode_wb_timer);
>  	blk_sync_queue(q);
>  
> +	spin_lock_irq(lock);
> +	if (q->queue_lock != &q->__queue_lock)
> +		q->queue_lock = &q->__queue_lock;
> +	spin_unlock_irq(lock);
> +

Isn't the 'if' clause superfluous ? You could just do the assignment, e.g.,

+	spin_lock_irq(lock);
+	q->queue_lock = &q->__queue_lock;
+	spin_unlock_irq(lock);

rtg
-- 
Tim Gardner tim.gardner@...onical.com
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