Re: [PATCH] sound/arm: Bad NULL test

[Takashi Iwai <tiwai@suse.de>]

At Mon, 1 Sep 2008 15:23:25 +0200 (CEST),
Julia Lawall wrote:
> 
> On Mon, 1 Sep 2008, Takashi Iwai wrote:
> 
> > 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@diku.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@diku.dk>
> > > > > Signed-off-by:  Julia Lawall <julia@diku.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.
> 
> OK, this seems like a reasonable compromise.  The function aaci_init_card 
> is indeed only used in one place, and -ENOMEM is the only possible error 
> value.  So perhaps it is just as easy to create that where it is called 
> rather than in aaci_init_card itself.

OK, now I applied it to sound git tree.

Thanks!

Takashi


> 
> julia
> 
> > 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;
> >  	}
> >  
> > 
>