linux-kernel - Re: [PATCH 1/2] scsi: core: cleanup scsi_dev_queue

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Date:   Fri, 22 Sep 2023 05:50:01 -0700
From:   Damien Le Moal <dlemoal@...nel.org>
To:     Wenchao Hao <haowenchao2@...wei.com>,
        "James E . J . Bottomley" <jejb@...ux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        open-iscsi@...glegroups.com, linux-scsi@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, louhongxiang@...wei.com
Subject: Re: [PATCH 1/2] scsi: core: cleanup scsi_dev_queue_ready()

On 2023/09/22 2:38, Wenchao Hao wrote:
> This is just a cleanup for scsi_dev_queue_ready() to avoid
> redundant goto and if statement, it did not change the origin
> logic.
> 
> Signed-off-by: Wenchao Hao <haowenchao2@...wei.com>
> ---
>  drivers/scsi/scsi_lib.c | 35 ++++++++++++++++++-----------------
>  1 file changed, 18 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index ca5eb058d5c7..f3e388127dbd 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1254,28 +1254,29 @@ static inline int scsi_dev_queue_ready(struct request_queue *q,
>  	int token;
>  
>  	token = sbitmap_get(&sdev->budget_map);
> -	if (atomic_read(&sdev->device_blocked)) {
> -		if (token < 0)
> -			goto out;
> +	if (token < 0)
> +		return -1;

This is changing how this function works...

>  
> -		if (scsi_device_busy(sdev) > 1)
> -			goto out_dec;
> +	/*
> +	 * device_blocked is not set at mostly time, so check it first
> +	 * and return token when it is not set.
> +	 */
> +	if (!atomic_read(&sdev->device_blocked))
> +		return token;

...because you reversed the tests order.

>  
> -		/*
> -		 * unblock after device_blocked iterates to zero
> -		 */
> -		if (atomic_dec_return(&sdev->device_blocked) > 0)
> -			goto out_dec;
> -		SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
> -				   "unblocking device at zero depth\n"));
> +	/*
> +	 * unblock after device_blocked iterates to zero
> +	 */
> +	if (scsi_device_busy(sdev) > 1 ||
> +	    atomic_dec_return(&sdev->device_blocked) > 0) {

And here too, you are changing how the function works. The atomic_dec may not be
done if the first condition is true.

> +		sbitmap_put(&sdev->budget_map, token);
> +		return -1;
>  	}
>  
> +	SCSI_LOG_MLQUEUE(3, sdev_printk(KERN_INFO, sdev,
> +			 "unblocking device at zero depth\n"));
> +
>  	return token;
> -out_dec:
> -	if (token >= 0)
> -		sbitmap_put(&sdev->budget_map, token);
> -out:
> -	return -1;
>  }
>  
>  /*

-- 
Damien Le Moal
Western Digital Research