From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 03/10] xen/blkfront: reorg info->io_lock
 after using blk-mq API
Date: Wed, 18 Feb 2015 09:05:52 -0800
Message-ID: <20150218170552.GC17813__7532.76086547903$1424279256$gmane$org@infradead.org>
References: <1423988345-4005-1-git-send-email-bob.liu@oracle.com>
	<1423988345-4005-4-git-send-email-bob.liu@oracle.com>
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To: Bob Liu <bob.liu@oracle.com>
Cc: hch@infradead.org, felipe.franciosi@citrix.com, linux-kernel@vger.kernel.org, xen-devel@lists.xen.org, axboe@fb.com, david.vrabel@citrix.com, avanzini.arianna@gmail.com, roger.pau@citrix.com
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On Sun, Feb 15, 2015 at 04:18:58PM +0800, Bob Liu wrote:
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 3589436..5a90a51 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -614,25 +614,28 @@ static int blk_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
>  	blk_mq_start_request(qd->rq);
>  	spin_lock_irq(&info->io_lock);
>  	if (RING_FULL(&info->ring)) {
> +		spin_unlock_irq(&info->io_lock);
>  		blk_mq_stop_hw_queue(hctx);
>  		ret = BLK_MQ_RQ_QUEUE_BUSY;
>  		goto out;
>  	}
>  
>  	if (blkif_request_flush_invalid(qd->rq, info)) {
> +		spin_unlock_irq(&info->io_lock);
>  		ret = BLK_MQ_RQ_QUEUE_ERROR;
>  		goto out;
>  	}
>  
>  	if (blkif_queue_request(qd->rq)) {
> +		spin_unlock_irq(&info->io_lock);
>  		blk_mq_stop_hw_queue(hctx);
>  		ret = BLK_MQ_RQ_QUEUE_BUSY;
>  		goto out;
>  	}
>  
>  	flush_requests(info);
> -out:
>  	spin_unlock_irq(&info->io_lock);
> +out:
>  	return ret;
>  }

I'd rather write the function something like:

 	spin_lock_irq(&info->io_lock);
 	if (RING_FULL(&info->ring))
		goto out_busy;
 	if (blkif_request_flush_invalid(qd->rq, info))
		goto out_error;
  
	if (blkif_queue_request(qd->rq))
		goto out_busy;

  	flush_requests(info);
  	spin_unlock_irq(&info->io_lock);
  	return BLK_MQ_RQ_QUEUE_OK;
out_error:
	spin_unlock_irq(&info->io_lock);
	return BLK_MQ_RQ_QUEUE_ERROR;
out_busy:
	spin_unlock_irq(&info->io_lock);
	blk_mq_stop_hw_queue(hctx);
	return BLK_MQ_RQ_QUEUE_BUSY;
}

Also this really should be merged into the first patch.