linux-kernel - Re: [PATCH 2/2] staging: emxx

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Date:	Sat, 4 Apr 2015 18:59:58 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Julia Lawall <Julia.Lawall@...6.fr>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	devel@...verdev.osuosl.org, kernel-janitors@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] staging: emxx_udc: test returned value

This is a clever Coccinelle check.  :)

On Sat, Apr 04, 2015 at 04:59:30PM +0200, Julia Lawall wrote:
> Put NULL test on the result of the previous call instead on one of its
> arguments.  A simplified version of the semantic match that finds this
> problem is as follows (http://coccinelle.lip6.fr/):
> 
> // <smpl>
> r@
> expression *e1;
> expression *e2;
> identifier f;
> statement S1,S2;
> @@
> 
> e1 = f(...,e2,...);
> (
> if (e1 == NULL || ...) S1 else S2
> |
> *if (e2 == NULL || ...) S1 else S2
> )
> // </smpl>
> 
> Signed-off-by: Julia Lawall <Julia.Lawall@...6.fr>
> 
> ---
>  drivers/staging/emxx_udc/emxx_udc.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/emxx_udc/emxx_udc.c b/drivers/staging/emxx_udc/emxx_udc.c
> index fbf82bc..7de1e9e 100644
> --- a/drivers/staging/emxx_udc/emxx_udc.c
> +++ b/drivers/staging/emxx_udc/emxx_udc.c
> @@ -2998,7 +2998,7 @@ static void  nbu2ss_ep_fifo_flush(struct usb_ep *_ep)
>  	}
>  
>  	ep = container_of(_ep, struct nbu2ss_ep, ep);
> -	if (!_ep) {
> +	if (!ep) {
>  		pr_err("udc: %s, bad ep\n", __func__);
>  		return;

The better thing to do here is to remove the condition.  container_of()
takes an pointer and subtracts an offset so testing the return value
is normally meaningless.

Sometimes (and in this case) the offset is zero.  In that situation it
might make sense to check the return value but it's an ugly thing to
do because if we re-order the nbu2ss_ep struct layout so "ep" isn't the
first member then it breaks.

In this case we already verified that "_ep" is non-NULL so the check
isn't needed.

regards,
dan carpenter


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