linux-kernel - Re: [PATCH] sound/arm: Bad NULL test

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Date:	Mon, 01 Sep 2008 14:43:12 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Julia Lawall <julia@...u.dk>
Cc:	Julien Brunel <brunel@...u.dk>, perex@...ex.cz,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] sound/arm: Bad NULL test

At Mon, 1 Sep 2008 14:30:29 +0200 (CEST),
Julia Lawall wrote:
> 
> On Mon, 1 Sep 2008, Takashi Iwai wrote:
> 
> > At Mon, 1 Sep 2008 10:59:54 +0200,
> > Julien Brunel wrote:
> > > 
> > > From: Julien Brunel <brunel@...u.dk>
> > > 
> > > In case of error, the function aaci_init_card returns an ERR pointer,
> > > but never returns a NULL pointer. We have noticed a bad NULL test,
> > > which comes after a call to this function. Rather than doing an IS_ERR
> > > test, we suggest to duplicate the label out: one label for the case where
> > > aaci_init_card returns a valid pointer, and another for the case where
> > > aaci_init_card returns an ERR pointer.
> > > 
> > > The semantic match that finds this problem is as follows:
> > > (http://www.emn.fr/x-info/coccinelle/)
> > > 
> > > // <smpl>
> > > @match_bad_null_test@
> > > expression x, E;
> > > statement S1,S2;
> > > @@
> > > x =  aaci_init_card(...)
> > > ... when != x = E
> > > *  if (x != NULL) 
> > > S1 else S2
> > > // </smpl>
> > > 
> > > Signed-off-by:  Julien Brunel <brunel@...u.dk>
> > > Signed-off-by:  Julia Lawall <julia@...u.dk>
> > 
> > The fix below is simpler.  Could you check whether it's OK?
> 
> It is indeed simpler, and looks correct, but it seems a little odd to take 
> a value that can never be NULL and set it to NULL just to avoid changing a 
> test.  Another alternative would be to leave the value as it is, and put 
> an IS_ERR test at the out label.  But the value of the test is statically 
> determined by the goto that reaches it, so the original patch proposes 
> just getting rid of the test completely.

OTOH, double labels are pretty ugly and hard to follow.
Maybe the patch like below is a bit cleaner.


Takashi

diff --git a/sound/arm/aaci.c b/sound/arm/aaci.c
index b0a4744..89096e8 100644
--- a/sound/arm/aaci.c
+++ b/sound/arm/aaci.c
@@ -999,7 +999,7 @@ static struct aaci * __devinit aaci_init_card(struct amba_device *dev)
 	card = snd_card_new(SNDRV_DEFAULT_IDX1, SNDRV_DEFAULT_STR1,
 			    THIS_MODULE, sizeof(struct aaci));
 	if (card == NULL)
-		return ERR_PTR(-ENOMEM);
+		return NULL;
 
 	card->private_free = aaci_free_card;
 
@@ -1083,8 +1083,8 @@ static int __devinit aaci_probe(struct amba_device *dev, void *id)
 		return ret;
 
 	aaci = aaci_init_card(dev);
-	if (IS_ERR(aaci)) {
-		ret = PTR_ERR(aaci);
+	if (!aaci) {
+		ret = -ENOMEM;
 		goto out;
 	}
 
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