From mboxrd@z Thu Jan  1 00:00:00 1970
From: Asias He <asias@redhat.com>
Subject: Re: [PATCH V3] block: Mitigate lock unbalance caused by lock switching
Date: Wed, 30 May 2012 14:28:05 +0800
Message-ID: <4FC5BDF5.2040000@redhat.com>
References: <20120528102214.GB15202@dhcp-172-17-108-109.mtv.corp.google.com> <1338255542-22247-1-git-send-email-asias@redhat.com> <4FC4D2F2.2070309@gmail.com>
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Cc: Jens Axboe <axboe@kernel.dk>, Tejun Heo <tj@kernel.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	tim.gardner@canonical.com
To: Tim Gardner <rtg.canonical@gmail.com>
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On 05/29/2012 09:45 PM, Tim Gardner wrote:
> 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);

Well, this saves a if clause but adds an unnecessary assignment if the 
lock is already internal lock.

-- 
Asias