linux-kernel - Re: [PATCH 9/10] drivers/mmc: Move a dereference below a NULL test

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Date:	Mon, 20 Jul 2009 11:01:28 +0300
From:	Adrian Hunter <adrian.hunter@...ia.com>
To:	Julia Lawall <julia@...u.dk>
CC:	"Lavinen Jarkko (Nokia-D/Helsinki)" <jarkko.lavinen@...ia.com>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>
Subject: Re: [PATCH 9/10] drivers/mmc: Move a dereference below a NULL test

Julia Lawall wrote:
> From: Julia Lawall <julia@...u.dk>
> 
> If the NULL test is necessary, then the dereference should be moved below
> the NULL test.
> 
> The semantic patch that makes this change is as follows:
> (http://www.emn.fr/x-info/coccinelle/)
> 
> // <smpl>
> @@
> type T;
> expression E,E1;
> identifier i,fld;
> statement S;
> @@
> 
> - T i = E->fld;
> + T i;
>   ... when != E=E1
>       when != i
>   BUG_ON (E == NULL||
> -     i
> +     E->fld
>        == NULL || ...);
> + i = E->fld;
> // </smpl>
> 
> Signed-off-by: Julia Lawall <julia@...u.dk>
> 
> ---
>  drivers/mmc/host/omap.c             |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mmc/host/omap.c b/drivers/mmc/host/omap.c
> index e7a331d..89281ab 100644
> --- a/drivers/mmc/host/omap.c
> +++ b/drivers/mmc/host/omap.c
> @@ -255,11 +255,12 @@ static void mmc_omap_slot_release_work(struct work_struct *work)
>  
>  static void mmc_omap_release_slot(struct mmc_omap_slot *slot, int clk_enabled)
>  {
> -	struct mmc_omap_host *host = slot->host;
> +	struct mmc_omap_host *host;
>  	unsigned long flags;
>  	int i;
>  
> -	BUG_ON(slot == NULL || host->mmc == NULL);
> +	BUG_ON(slot == NULL || slot->host->mmc == NULL);
> +	host = slot->host;
>  
>  	if (clk_enabled)
>  		/* Keeps clock running for at least 8 cycles on valid freq */
> --

If slot is NULL it will oops anyway, so the following is better IMHO:
 
static void mmc_omap_release_slot(struct mmc_omap_slot *slot, int clk_enabled)
{
	struct mmc_omap_host *host = slot->host;
	unsigned long flags;
	int i;

> -	BUG_ON(slot == NULL || host->mmc == NULL);
> +	BUG_ON(host->mmc == NULL);

	if (clk_enabled)
		/* Keeps clock running for at least 8 cycles on valid freq */
--
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