linux-kernel - Re: [PATCH 2/2] mfd: ab8500-core: Return zero in get_register

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Date:   Thu, 25 Oct 2018 09:25:08 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Mattias Wallin <mattias.wallin@...ricsson.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 2/2] mfd: ab8500-core: Return zero in
 get_register_interruptible()

On Thu, 18 Oct 2018, Dan Carpenter wrote:

> I just noticed this in review.  The get_register_interruptible() should
> return zero on success but it instead returns the value that it read.
> 
> I looked at all the places that called this directly and they check for
> negatives and treat greater than or equal to zero as success.  This
> function is also called as the ->get_register() function pointer.  Some
> of the callers of that treat all non-zero returns as errors, so it's
> possible that this bug causes some problems in real life.
> 
> I could not find any callers that rely on the current behavior, and this
> makes the function align with the get_register_interruptible() in
> ab3100-core.c.
> 
> Fixes: 47c1697508f2 ("mfd: Align ab8500 with the abx500 interface")
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> ---
>  drivers/mfd/ab8500-core.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/mfd/ab8500-core.c b/drivers/mfd/ab8500-core.c
> index 30d09d177171..66458a329127 100644
> --- a/drivers/mfd/ab8500-core.c
> +++ b/drivers/mfd/ab8500-core.c
> @@ -252,16 +252,18 @@ static int get_register_interruptible(struct ab8500 *ab8500, u8 bank,
>  	mutex_lock(&ab8500->lock);
>  
>  	ret = ab8500->read(ab8500, addr);
> -	if (ret < 0)
> +	if (ret < 0) {
>  		dev_err(ab8500->dev, "failed to read reg %#x: %d\n",
>  			addr, ret);
> -	else
> -		*value = ret;
> +		return ret;

Looks like you just broke the AB8500.

What is it you're trying to achieve here?  Apart from attempting to
return with the mutex still held, what semantics have you changed?

> +	}
> +
> +	*value = ret;
>  
>  	mutex_unlock(&ab8500->lock);
>  	dev_vdbg(ab8500->dev, "rd: addr %#x => data %#x\n", addr, ret);
>  
> -	return ret;
> +	return 0;
>  }
>  
>  static int ab8500_get_register(struct device *dev, u8 bank,

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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