linux-kernel - Re: [PATCH 2/14] sound: Move dereference after NULL test and drop unnecessary NULL tests

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Date:	Fri, 30 Oct 2009 12:02:05 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Julia Lawall <julia@...u.dk>
Cc:	Jaroslav Kysela <perex@...ex.cz>, alsa-devel@...a-project.org,
	linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 2/14] sound: Move dereference after NULL test and drop unnecessary NULL tests

At Sat, 17 Oct 2009 08:33:22 +0200 (CEST),
Julia Lawall wrote:
> 
> From: Julia Lawall <julia@...u.dk>
> 
> In pcm.c, if the NULL test on pcm is needed, then the dereference should be
> after the NULL test.
> 
> In dummy.c and ali5451.c, the context of the calls to
> snd_card_dummy_new_mixer and snd_ali_free_voice show that dummy and pvoice,
> respectively cannot be NULL.
> 
> A simplified version of the semantic match that detects this problem is as
> follows (http://coccinelle.lip6.fr/):
> 
> // <smpl>
> @match exists@
> expression x, E;
> identifier fld;
> @@
> 
> * x->fld
>   ... when != \(x = E\|&x\)
> * x == NULL
> // </smpl>
> 
> Signed-off-by: Julia Lawall <julia@...u.dk>

Thanks, applied now.


Takashi

> 
> ---
>  sound/core/pcm.c            |    5 +++--
>  sound/drivers/dummy.c       |    2 --
>  sound/pci/ali5451/ali5451.c |    2 +-
> 
> diff --git a/sound/core/pcm.c b/sound/core/pcm.c
> index 0c14401..c69c60b 100644
> --- a/sound/core/pcm.c
> +++ b/sound/core/pcm.c
> @@ -953,11 +953,12 @@ static int snd_pcm_dev_register(struct snd_device *device)
>  	struct snd_pcm_substream *substream;
>  	struct snd_pcm_notify *notify;
>  	char str[16];
> -	struct snd_pcm *pcm = device->device_data;
> +	struct snd_pcm *pcm;
>  	struct device *dev;
>  
> -	if (snd_BUG_ON(!pcm || !device))
> +	if (snd_BUG_ON(!device || !device->device_data))
>  		return -ENXIO;
> +	pcm = device->device_data;
>  	mutex_lock(&register_mutex);
>  	err = snd_pcm_add(pcm);
>  	if (err) {
> diff --git a/sound/drivers/dummy.c b/sound/drivers/dummy.c
> index 6ba066c..146ef00 100644
> --- a/sound/drivers/dummy.c
> +++ b/sound/drivers/dummy.c
> @@ -808,8 +808,6 @@ static int __devinit snd_card_dummy_new_mixer(struct snd_dummy *dummy)
>  	unsigned int idx;
>  	int err;
>  
> -	if (snd_BUG_ON(!dummy))
> -		return -EINVAL;
>  	spin_lock_init(&dummy->mixer_lock);
>  	strcpy(card->mixername, "Dummy Mixer");
>  
> diff --git a/sound/pci/ali5451/ali5451.c b/sound/pci/ali5451/ali5451.c
> index b458d20..aaf4da6 100644
> --- a/sound/pci/ali5451/ali5451.c
> +++ b/sound/pci/ali5451/ali5451.c
> @@ -973,7 +973,7 @@ static void snd_ali_free_voice(struct snd_ali * codec,
>  	void *private_data;
>  
>  	snd_ali_printk("free_voice: channel=%d\n",pvoice->number);
> -	if (pvoice == NULL || !pvoice->use)
> +	if (!pvoice->use)
>  		return;
>  	snd_ali_clear_voices(codec, pvoice->number, pvoice->number);
>  	spin_lock_irq(&codec->voice_alloc);
> 
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