linux-kernel - Re: [PATCH 2/4] arch/arm/mach-at91/clock.c: Add missing IS

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Date:	Tue, 25 Jan 2011 08:56:20 +1300
From:	Ryan Mallon <ryan@...ewatersys.com>
To:	Julia Lawall <julia@...u.dk>
CC:	Russell King <linux@....linux.org.uk>,
	kernel-janitors@...r.kernel.org,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Andrew Victor <linux@...im.org.za>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] arch/arm/mach-at91/clock.c: Add missing IS_ERR test

On 01/25/2011 08:55 AM, Julia Lawall wrote:
> Function clk_get, defined just below this code, returns ERR_PTR not NULL in
> an error case.
> 
> The semantic match that finds this problem is as follows:
> (http://coccinelle.lip6.fr/)
> 
> // <smpl>
> @r@
> identifier f;
> @@
> f(...) { ... return ERR_PTR(...); }
> 
> @@
> identifier r.f, fld;
> expression x;
> statement S1,S2;
> @@
>  x = f(...)
>  ... when != IS_ERR(x)
> (
>  if (IS_ERR(x) ||...) S1 else S2
> |
> *x->fld
> )
> // </smpl>

I'm always really impressed by this tool :-).

> 
> Signed-off-by: Julia Lawall <julia@...u.dk>
> 
> ---
>  arch/arm/mach-at91/clock.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mach-at91/clock.c b/arch/arm/mach-at91/clock.c
> index 9113da6..c9ee6d0 100644
> --- a/arch/arm/mach-at91/clock.c
> +++ b/arch/arm/mach-at91/clock.c
> @@ -224,7 +224,7 @@ void __init at91_clock_associate(const char *id, struct device *dev, const char
>  {
>  	struct clk *clk = clk_get(NULL, id);
>  
> -	if (!dev || !clk || !IS_ERR(clk_get(dev, func)))
> +	if (!dev || IS_ERR(clk) || !IS_ERR(clk_get(dev, func)))
>  		return;

I think we want:

	if (!dev || !clk || IS_ERR(clk) || !IS_ERR(clk_get(dev, func)))
		return;

Since it is valid to return a NULL clk, and we don't want to try and
dereference it if that is the case.

We could also probably drop the !IS_ERR(clk_get(dev, func)) check, since
as far as I can tell it is just checking to see if the clock is already
associated, but there is no harm in re-assigning the same values, and
the two assignments in at91_clock_associate are going to be much quicker
than the lookup in clk_get.

~Ryan

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