[alsa-devel] [PATCH 1/2] ALSA: firewire-tascam: Fix infinite loop in snd_tscm_stream_get_rate()
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@linux-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;
If a loop is intended to be executed at least once, it is better to use "do { ... } while (...)" instead of "while (...) { ... }". The former is easier to understand for the casual reviewer, and doesn't require preinitializing the canary variable.
Signed-off-by: Geert Uytterhoeven geert@linux-m68k.org --- Compile-tested only. --- sound/firewire/tascam/tascam-stream.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/sound/firewire/tascam/tascam-stream.c b/sound/firewire/tascam/tascam-stream.c index e433b92ac6904db5..4ea6845aae87fdef 100644 --- a/sound/firewire/tascam/tascam-stream.c +++ b/sound/firewire/tascam/tascam-stream.c @@ -80,17 +80,17 @@ static int set_clock(struct snd_tscm *tscm, unsigned int rate,
int snd_tscm_stream_get_rate(struct snd_tscm *tscm, unsigned int *rate) { - u32 data = 0x0; unsigned int trials = 0; + u32 data; int err;
- while (data == 0x0 && trials++ < 5) { + do { err = get_clock(tscm, &data); if (err < 0) return err;
data = (data & 0xff000000) >> 24; - } + } while (data == 0x0 && ++trials < 5);
/* Check base rate. */ if ((data & 0x0f) == 0x01)
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@linux-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
Hi Sakamoto-san,
On Mon, May 15, 2017 at 4:07 PM, Takashi Sakamoto o-takashi@sakamocchi.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@linux-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@linux-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
On May 15 2017 23:22, Geert Uytterhoeven wrote:
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>? ;-)
I know PDI1394L40 (link layer) has quirks inconvenient to us. Furthermore, the behaviour of on-board FPGAs with unique firmwares are in black boxes to me.
I prefer deliberate approach for this kind of work, reverse engineering.
Regards
Takashi Sakamoto
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Geert Uytterhoeven -
Takashi Sakamoto