linux-kernel - Re: [PATCH v2] usb: gadget: ffs: Fix sparse error

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Date:	Wed, 24 Dec 2014 03:08:29 -0800
From:	Joe Perches <joe@...ches.com>
To:	Rohith Seelaboyina <rseelaboyina@...dia.com>
Cc:	balbi@...com, gregkh@...uxfoundation.org, mina86@...a86.com,
	r.baldyga@...sung.com, andrzej.p@...sung.com,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] usb: gadget: ffs: Fix sparse error

On Wed, 2014-12-24 at 14:48 +0530, Rohith Seelaboyina wrote:
> Dynamic memory allocation through kcalloc is more safer
> than declaring variable array size, Fix this error by
> using kcalloc for memory allocation, Check if memory
> allocation is successful and return -ENOMEM on failure.
> 
> Signed-off-by: Rohith Seelaboyina <rseelaboyina@...dia.com>
> ---
> Changes in v2:
>    - Use kcalloc to allocate memory instead of using
>      kmalloc and memset.

style trivia:

> diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
[]
> @@ -397,10 +397,13 @@ static ssize_t __ffs_ep0_read_events(struct ffs_data *ffs, char __user *buf,
>  	 * We are holding ffs->ev.waitq.lock and ffs->mutex and we need
>  	 * to release them.
>  	 */
> -	struct usb_functionfs_event events[n];
>  	unsigned i = 0;
> +	int ret;
> +	struct usb_functionfs_event *events = kcalloc(n,
> +			sizeof(struct usb_functionfs_event), GFP_KERNEL);
>  
> -	memset(events, 0, sizeof events);
> +	if (unlikely(!events))
> +		return -ENOMEM;

unlikely is not commonly used here.

I might be better to separate the declaration and the alloc
{
	[...]
	struct usb_functionfs_event *events;

	events = kcalloc(n, sizeof(*events), GFP_KERNEL);
	if (!events)
		return -ENOMEM;


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