Re: [PATCH] soundwire: stream: fix bad unlock balance

[Srinivas Kandagatla]

On 22/05/2019 17:41, Pierre-Louis Bossart wrote:
> On 5/22/19 11:25 AM, Srinivas Kandagatla wrote:
> > This patch fixes below warning due to unlocking without locking.
> >
> > Â =====================================
> > Â WARNING: bad unlock balance detected!
> > Â 5.1.0-16506-gc1c383a6f0a2-dirty #1523 Tainted: GÂÂÂÂÂÂÂ W
> > Â -------------------------------------
> > Â aplay/2954 is trying to release lock (&bus->msg_lock) at:
> > Â do_bank_switch+0x21c/0x480
> > Â but there are no more locks to release!
> >
> > Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
> > ---
> > Â drivers/soundwire/stream.c | 3 ++-
> > Â 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/soundwire/stream.c b/drivers/soundwire/stream.c
> > index 544925ff0b40..d16268f30e4f 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)
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂ goto error;
> > ÂÂÂÂÂÂÂÂÂ }
> > -ÂÂÂÂÂÂÂ mutex_unlock(&bus->msg_lock);
> > +ÂÂÂÂÂÂÂ if (mutex_is_locked(&bus->msg_lock))
> > +ÂÂÂÂÂÂÂÂÂÂÂ utex_unlock(&bus->msg_lock);
>
> Does this even compile? should be mutex_unlock, no?
>
> We also may want to identify the issue in more details without pushing 
> it under the rug. The locking mechanism is far from simple and it's 
> likely there are a number of problems with it.
msg_lock is taken conditionally during multi link bank switch cases, 
however the unlock is done unconditionally leading to this warning.

Having a closer look show that there could be a dead lock in this path 
while executing sdw_transfer(). And infact there is no need to take 
msg_lock in  multi link switch cases as sdw_transfer should take care of 
this.

Vinod/Sanyog any reason why msg_lock is really required in this path?

--srini

> > ÂÂÂÂÂ }
> > ÂÂÂÂÂ return ret;