linux-kernel - Re: [PATCH 1/2] ALSA: firewire-tascam: Fix infinite loop in snd_tscm_stream_get

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Date:   Mon, 15 May 2017 23:07:28 +0900
From:   Takashi Sakamoto <o-takashi@...amocchi.jp>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Clemens Ladisch <clemens@...isch.de>,
        Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 1/2] ALSA: firewire-tascam: Fix infinite loop in
 snd_tscm_stream_get_rate()

Hi,

On May 15 2017 17:19, Geert Uytterhoeven wrote:
> Obviously the intention was to put a limit on the maximum number of
> operations.  However, for this to work, the check should be
> "&& trials++ < 5", not "|| trials++ < 5".
>
> Fixes: 35efa5c489de63a9 ("ALSA: firewire-tascam: add streaming functionality")
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> ---
> Compile-tested only.
>
> Triggered by a false-positive warning from gcc-4.1.2:
>
>     warning: ‘err’ may be used uninitialized in this function
> ---
>  sound/firewire/tascam/tascam-stream.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/sound/firewire/tascam/tascam-stream.c b/sound/firewire/tascam/tascam-stream.c
> index f1657a4e0621ef49..e433b92ac6904db5 100644
> --- a/sound/firewire/tascam/tascam-stream.c
> +++ b/sound/firewire/tascam/tascam-stream.c
> @@ -84,7 +84,7 @@ int snd_tscm_stream_get_rate(struct snd_tscm *tscm, unsigned int *rate)
>  	unsigned int trials = 0;
>  	int err;
>
> -	while (data == 0x0 || trials++ < 5) {
> +	while (data == 0x0 && trials++ < 5) {
>  		err = get_clock(tscm, &data);
>  		if (err < 0)
>  			return err;

Yep. It looks a bug.

...However, removal of the bug causes issue that the driver fails to 
start a pair of capture/playback PCM substream when application requests 
them mostly the same time, like jackd process.

I think I did apply the bug as a makeshift workaround, then forgot 
itself when developing the driver... I'd like to have a bit time for 
further investigation, then post my fix in this development period.

Please let me keep this patch pending.


Thanks

Takashi Sakamoto