Re: [alsa-devel] [PATCH v2] soundwire: stream: fix bad unlock balance

From: Pierre-Louis Bossart
Date: Thu Jun 06 2019 - 10:32:32 EST

On 6/6/19 6:22 AM, Srinivas Kandagatla wrote:
multi bank switching code takes lock on condition but releases without
any check resulting in below warning.
This patch fixes this.

Question to make sure we are talking about the same thing: multi-link bank switching is a capability beyond the scope of the SoundWire spec which requires hardware support to synchronize links and as Sanyog hinted at in a previous email follow a different flow for bank switches.

You would not use the multi-link mode if you have different links that can operate independently and have no synchronization requirement. You would conversely use the multi-link mode if you have two devices on the same type on different links and want audio to be rendered at the same time.

Can you clarify if indeed you were using the full-blown multi-link mode with hardware synchronization or a regular single-link operation? I am not asking for details of your test hardware, just trying to reconstruct the program flow leading to this problem.

It could also be that your commit message was meant to say:
"the msg lock is taken for multi-link cases only but released unconditionally, leading to an unlock balance warning for single-link usages"?


WARNING: bad unlock balance detected!
5.1.0-16506-gc1c383a6f0a2-dirty #1523 Tainted: G W
aplay/2954 is trying to release lock (&bus->msg_lock) at:
but there are no more locks to release!

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
drivers/soundwire/stream.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/soundwire/stream.c b/drivers/soundwire/stream.c
index ce9cb7fa4724..73c52cd4fec8 100644
--- a/drivers/soundwire/stream.c
+++ b/drivers/soundwire/stream.c
@@ -814,7 +814,8 @@ static int do_bank_switch(struct sdw_stream_runtime *stream)
goto error;
- mutex_unlock(&bus->msg_lock);
+ if (bus->multi_link)
+ mutex_unlock(&bus->msg_lock);
return ret;