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

[Srinivas Kandagatla]

On 23/05/2019 10:20, Sanyog Kale wrote:
> On Thu, May 23, 2019 at 09:43:14AM +0100, Srinivas Kandagatla wrote:
> > 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.
> > > >
> > > > ?? =====================================
> > > > ?? 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:
> > > > ?? do_bank_switch+0x21c/0x480
> > > > ?? 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 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)
> > > > ?????????????????????????? goto error;
> > > > ?????????????????? }
> > > > -?????????????? mutex_unlock(&bus->msg_lock);
> > > > +?????????????? if (mutex_is_locked(&bus->msg_lock))
> > > > +?????????????????????? 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?
>
> In case of multi link we use sdw_transfer_defer instead of sdw_transfer
> where lock is not acquired, hence lock is acquired in do_bank_switch for
> multi link. we should add same check of multi link to release lock in
> do_bank_switch.

probably we should just add the lock around the sdw_transfer_defer call 
in sdw_bank_switch()?
This should cleanup the code a bit too.

something like:

------------------------------------>cut<-----------------------------
diff --git a/drivers/soundwire/stream.c b/drivers/soundwire/stream.c
index d01060dbee96..f455af5b8151 100644
--- a/drivers/soundwire/stream.c
+++ b/drivers/soundwire/stream.c
@@ -676,10 +676,13 @@ static int sdw_bank_switch(struct sdw_bus *bus, 
int m_rt_count)
         */
        multi_link = bus->multi_link && (m_rt_count > 1);

-       if (multi_link)
+       if (multi_link) {
+               mutex_lock(&bus->msg_lock);
                ret = sdw_transfer_defer(bus, wr_msg, &bus->defer_msg);
-       else
+               mutex_unlock(&bus->msg_lock);
+       } else {
                ret = sdw_transfer(bus, wr_msg);
+       }

        if (ret < 0) {
                dev_err(bus->dev, "Slave frame_ctrl reg write failed\n");
@@ -742,25 +745,19 @@ static int do_bank_switch(struct 
sdw_stream_runtime *stream)
        struct sdw_master_runtime *m_rt = NULL;
        const struct sdw_master_ops *ops;
        struct sdw_bus *bus = NULL;
-       bool multi_link = false;
        int ret = 0;

        list_for_each_entry(m_rt, &stream->master_list, stream_node) {
                bus = m_rt->bus;
                ops = bus->ops;

-               if (bus->multi_link) {
-                       multi_link = true;
-                       mutex_lock(&bus->msg_lock);
-               }
-
                /* Pre-bank switch */
                if (ops->pre_bank_switch) {
                        ret = ops->pre_bank_switch(bus);
                        if (ret < 0) {
                                dev_err(bus->dev,
                                        "Pre bank switch op failed: 
%d\n", ret);
-                               goto msg_unlock;
+                               return ret;
                        }
                }

@@ -814,7 +811,6 @@ static int do_bank_switch(struct sdw_stream_runtime 
*stream)
                        goto error;
                }

-               mutex_unlock(&bus->msg_lock);
        }

        return ret;
@@ -827,16 +823,6 @@ static int do_bank_switch(struct sdw_stream_runtime 
*stream)
                kfree(bus->defer_msg.msg);
        }

-msg_unlock:
-
-       if (multi_link) {
-               list_for_each_entry(m_rt, &stream->master_list, 
stream_node) {
-                       bus = m_rt->bus;
-                       if (mutex_is_locked(&bus->msg_lock))
-                               mutex_unlock(&bus->msg_lock);
-               }
-       }
-
        return ret;
 }

------------------------------------>cut<-----------------------------
> > --srini
> >
> > > > ?????????? }
> > > > ?????????? return ret;