linux-kernel - Re: [PATCH] staging: gpib: Remove a dead condition in if statement

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Message-ID: <59521671-db23-42ba-8db3-ed48cef53c05@linuxfoundation.org>
Date: Tue, 15 Oct 2024 16:47:42 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: "Everest K.C." <everestkc@...restkc.com.np>, dpenkler@...il.com,
 gregkh@...uxfoundation.org
Cc: linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
 Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] staging: gpib: Remove a dead condition in if statement

On 10/15/24 14:06, Everest K.C. wrote:
> The variable `residue` is an unsigned int, also the function
> `fluke_get_dma_residue` returns an unsigned int. The value of
> an unsigned int can only be 0 at minimum.
> The less-than-zero comparision can never be true.
> Fix it by removing the dead condition in the if statement.
> 
> This issue was reported by Coverity Scan.
> Report:
> CID 1600782: (#1 of 1): Macro compares unsigned to 0 (NO_EFFECT)
> unsigned_compare: This less-than-zero comparison of an unsigned value
> is never true. residue < 0U.
> 
> Fixes: 55936779f496 ("staging: gpib: Add Fluke cda based cards GPIB driver")
> Signed-off-by: Everest K.C. <everestkc@...restkc.com.np>
> ---
>   drivers/staging/gpib/eastwood/fluke_gpib.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/gpib/eastwood/fluke_gpib.c b/drivers/staging/gpib/eastwood/fluke_gpib.c
> index f9f149db222d..51b4f9891a34 100644
> --- a/drivers/staging/gpib/eastwood/fluke_gpib.c
> +++ b/drivers/staging/gpib/eastwood/fluke_gpib.c
> @@ -644,7 +644,7 @@ static int fluke_dma_read(gpib_board_t *board, uint8_t *buffer,
>   	 */
>   	usleep_range(10, 15);
>   	residue = fluke_get_dma_residue(e_priv->dma_channel, dma_cookie);
> -	if (WARN_ON_ONCE(residue > length || residue < 0))
> +	if (WARN_ON_ONCE(residue > length))

Are you sure this is the right fix? length is size_t
fluke_get_dma_residue() returns unsigned int - yes
the coverity report is correct, but should fluke_get_dma_residue()
return size_t?

>   		return -EFAULT;
>   	*bytes_read += length - residue;

bytes_read is also size_t

>   	dmaengine_terminate_all(e_priv->dma_channel);

The patch should indicate it is against next. [PATCH next].

thanks,
-- Shuah