linux-kernel - Re: [PATCH] drivers: usbtouchscreen: use kzalloc

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Date:   Sat, 12 Mar 2022 19:14:37 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Michael Estner <michaelestner@....de>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        kernel-janitor-commits@...r.kernel.org,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers: usbtouchscreen: use kzalloc

On Sat, Mar 12, 2022 at 06:22:30PM +0100, Michael Estner wrote:
> Use kzalloc instead of kmalloc + memset.
> 
> The semantic patch that makes this change is:
> (https://coccinelle.gitlabpages.inria.fr/website/)
> 
> Signed-off-by: Michael Estner <michaelestner@....de>
> ---
>  drivers/input/touchscreen/usbtouchscreen.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/input/touchscreen/usbtouchscreen.c b/drivers/input/touchscreen/usbtouchscreen.c
> index 43c521f50c85..159e1ac6198a 100644
> --- a/drivers/input/touchscreen/usbtouchscreen.c
> +++ b/drivers/input/touchscreen/usbtouchscreen.c
> @@ -975,7 +975,7 @@ static int nexio_init(struct usbtouch_usb *usbtouch)
>  	if (!input_ep || !output_ep)
>  		return -ENXIO;
> 
> -	buf = kmalloc(NEXIO_BUFSIZE, GFP_NOIO);
> +	buf = kzalloc(NEXIO_BUFSIZE, GFP_NOIO);
>  	if (!buf)
>  		goto out_buf;
> 
> @@ -998,7 +998,6 @@ static int nexio_init(struct usbtouch_usb *usbtouch)
> 
>  	/* read replies */
>  	for (i = 0; i < 3; i++) {
> -		memset(buf, 0, NEXIO_BUFSIZE);
>  		ret = usb_bulk_msg(dev, usb_rcvbulkpipe(dev, input_ep),
>  				   buf, NEXIO_BUFSIZE, &actual_len,
>  				   NEXIO_TIMEOUT);

NAK

The new code is not equivalent to the old so that semantic patch must be
broken.

The current code is clearing the buffer before each read, after this
patch it would only be cleared once.

Johan