linux-kernel - Re: [PATCH] staging: comedi: usbduxsigma: Improve unlocking of a mutex in three functions

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Date:   Fri, 3 Nov 2017 14:10:46 +0000
From:   Ian Abbott <abbotti@....co.uk>
To:     SF Markus Elfring <elfring@...rs.sourceforge.net>,
        devel@...verdev.osuosl.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        H Hartley Sweeten <hsweeten@...ionengravers.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] staging: comedi: usbduxsigma: Improve unlocking of a
 mutex in three functions

On 02/11/17 20:23, SF Markus Elfring wrote:
> From: Markus Elfring <elfring@...rs.sourceforge.net>
> Date: Thu, 2 Nov 2017 21:16:50 +0100
> 
> * Add a jump target so that a call of the function "mutex_unlock" is stored
>    only twice in these function implementations.
> 
> * Replace seven calls by goto statements.
> 
> This issue was detected by using the Coccinelle software.
> 
> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> ---
>   drivers/staging/comedi/drivers/usbduxsigma.c | 48 +++++++++++++++-------------
>   1 file changed, 26 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/staging/comedi/drivers/usbduxsigma.c b/drivers/staging/comedi/drivers/usbduxsigma.c
> index 456e9f13becb..7e8284ed265a 100644
> --- a/drivers/staging/comedi/drivers/usbduxsigma.c
> +++ b/drivers/staging/comedi/drivers/usbduxsigma.c
> @@ -672,10 +672,8 @@ static int usbduxsigma_ai_cmd(struct comedi_device *dev,
>   	devpriv->dux_commands[8] = sysred;
>   
>   	ret = usbbuxsigma_send_cmd(dev, USBBUXSIGMA_AD_CMD);
> -	if (ret < 0) {
> -		mutex_unlock(&devpriv->mut);
> -		return ret;
> -	}
> +	if (ret < 0)
> +		goto unlock;
>   
>   	devpriv->ai_counter = devpriv->ai_timer;
>   
> @@ -686,8 +684,7 @@ static int usbduxsigma_ai_cmd(struct comedi_device *dev,
>   					      devpriv->n_ai_urbs, 1);
>   		if (ret < 0) {
>   			devpriv->ai_cmd_running = 0;
> -			mutex_unlock(&devpriv->mut);
> -			return ret;
> +			goto unlock;
>   		}
>   		s->async->inttrig = NULL;
>   	} else {	/* TRIG_INT */
> @@ -697,6 +694,10 @@ static int usbduxsigma_ai_cmd(struct comedi_device *dev,
>   	mutex_unlock(&devpriv->mut);
>   
>   	return 0;

You could also remove that call by replacing the above three lines with:

	ret = 0;

and falling through to the 'unlock:' label.  (Actually, you don't even 
need the above line, as ret should already be 0 at this point, but I 
think it is easier to understand the code if ret is set to 0 explicitly.)

> +
> +unlock:
> +	mutex_unlock(&devpriv->mut);
> +	return ret;
>   }
>   
>   static int usbduxsigma_ai_insn_read(struct comedi_device *dev,
> @@ -714,8 +715,8 @@ static int usbduxsigma_ai_insn_read(struct comedi_device *dev,
>   
>   	mutex_lock(&devpriv->mut);
>   	if (devpriv->ai_cmd_running) {
> -		mutex_unlock(&devpriv->mut);
> -		return -EBUSY;
> +		ret = -EBUSY;
> +		goto unlock;
>   	}
>   
>   	create_adc_command(chan, &muxsg0, &muxsg1);
> @@ -730,19 +731,15 @@ static int usbduxsigma_ai_insn_read(struct comedi_device *dev,
>   
>   	/* adc commands */
>   	ret = usbbuxsigma_send_cmd(dev, USBDUXSIGMA_SINGLE_AD_CMD);
> -	if (ret < 0) {
> -		mutex_unlock(&devpriv->mut);
> -		return ret;
> -	}
> +	if (ret < 0)
> +		goto unlock;
>   
>   	for (i = 0; i < insn->n; i++) {
>   		u32 val;
>   
>   		ret = usbduxsigma_receive_cmd(dev, USBDUXSIGMA_SINGLE_AD_CMD);
> -		if (ret < 0) {
> -			mutex_unlock(&devpriv->mut);
> -			return ret;
> -		}
> +		if (ret < 0)
> +			goto unlock;
>   
>   		/* 32 bits big endian from the A/D converter */
>   		val = be32_to_cpu(get_unaligned((__be32
> @@ -753,6 +750,10 @@ static int usbduxsigma_ai_insn_read(struct comedi_device *dev,
>   	mutex_unlock(&devpriv->mut);
>   
>   	return insn->n;

Similarly, you could replace the above three lines with:

	ret = insn->n;

and fall through to the label.

> +
> +unlock:
> +	mutex_unlock(&devpriv->mut);
> +	return ret;
>   }
>   
>   static int usbduxsigma_ao_insn_read(struct comedi_device *dev,
> @@ -782,8 +783,8 @@ static int usbduxsigma_ao_insn_write(struct comedi_device *dev,
>   
>   	mutex_lock(&devpriv->mut);
>   	if (devpriv->ao_cmd_running) {
> -		mutex_unlock(&devpriv->mut);
> -		return -EBUSY;
> +		ret = -EBUSY;
> +		goto unlock;
>   	}
>   
>   	for (i = 0; i < insn->n; i++) {
> @@ -791,15 +792,18 @@ static int usbduxsigma_ao_insn_write(struct comedi_device *dev,
>   		devpriv->dux_commands[2] = data[i];	/* value */
>   		devpriv->dux_commands[3] = chan;	/* channel number */
>   		ret = usbbuxsigma_send_cmd(dev, USBDUXSIGMA_DA_CMD);
> -		if (ret < 0) {
> -			mutex_unlock(&devpriv->mut);
> -			return ret;
> -		}
> +		if (ret < 0)
> +			goto unlock;
> +
>   		s->readback[chan] = data[i];
>   	}
>   	mutex_unlock(&devpriv->mut);
>   
>   	return insn->n;

Ditto.

> +
> +unlock:
> +	mutex_unlock(&devpriv->mut);
> +	return ret;
>   }
>   
>   static int usbduxsigma_ao_inttrig(struct comedi_device *dev,
> 


-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@....co.uk> )=-
-=(                          Web: http://www.mev.co.uk/  )=-