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 16:22:50 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Takashi Sakamoto <o-takashi@...amocchi.jp>
Cc:     Clemens Ladisch <clemens@...isch.de>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        ALSA Development Mailing List <alsa-devel@...a-project.org>,
        "linux-kernel@...r.kernel.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 Sakamoto-san,

On Mon, May 15, 2017 at 4:07 PM, Takashi Sakamoto
<o-takashi@...amocchi.jp> wrote:
> 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.

Probably you need a small delay in the loop?
Why else do you #include <linux/delay.h>? ;-)

> Please let me keep this patch pending.

OK.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds