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From:   Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Date:   Mon, 26 Oct 2020 13:38:51 -0700
Message-ID: <CABBYNZJ3=e5kFxn-o0_L8j5aKpLDk88CGx=gcKP0eaPjQchO=g@mail.gmail.com>
Subject: Re: [PATCH BlueZ] audio/a2dp: a2dp_channel should have a refcount on
 avdtp session
To:     Marijn Suijten <marijns95@gmail.com>
Cc:     "linux-bluetooth@vger.kernel.org" <linux-bluetooth@vger.kernel.org>,
        =?UTF-8?Q?Pali_Roh=C3=A1r?= <pali@kernel.org>
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Hi Marijn,

On Mon, Oct 26, 2020 at 1:22 PM Marijn Suijten <marijns95@gmail.com> wrote:
>
> Hi Luiz,
>
> On Mon, 26 Oct 2020 at 21:15, Luiz Augusto von Dentz
> <luiz.dentz@gmail.com> wrote:
> >
> > Hi Marijn,
> >
> > On Sun, Oct 25, 2020 at 9:27 AM Marijn Suijten <marijns95@gmail.com> wrote:
> > >
> > > a2dp_channel keeps a reference to an avdtp session without incrementing
> > > its refcount.  Not only does this appear wrong, it causes unexpected
> > > disconnections when the remote SEP responds with rejections.
> > >
> > > During testing with an audio application disconnections are observed
> > > when a codec config change through MediaEndpoint1.SetConfiguration
> > > fails.  As soon as BlueZ receives this failure from the peer the
> > > corresponding a2dp_setup object is cleaned up which holds the last
> > > refcount to an avdtp session, in turn starting the disconnect process.
> > > An eventual open sink/source and transport have already closed by that
> > > time and released their refcounts.
> > >
> > > Adding refcounting semantics around a2dp_channel resolves the
> > > disconnections and allows future calls on MediaEndpoint1 to safely
> > > access the sesion stored within this channel.
> > > ---
> > >  profiles/audio/a2dp.c | 7 ++++++-
> > >  1 file changed, 6 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/profiles/audio/a2dp.c b/profiles/audio/a2dp.c
> > > index cc4866b5b..0eac0135f 100644
> > > --- a/profiles/audio/a2dp.c
> > > +++ b/profiles/audio/a2dp.c
> > > @@ -1507,6 +1507,9 @@ static void channel_free(void *data)
> > >
> > >         avdtp_remove_state_cb(chan->state_id);
> > >
> > > +       if (chan->session)
> > > +               avdtp_unref(chan->session);
> > > +
> > >         queue_destroy(chan->seps, remove_remote_sep);
> > >         free(chan->last_used);
> > >         g_free(chan);
> > > @@ -2065,7 +2068,7 @@ static void avdtp_state_cb(struct btd_device *dev, struct avdtp *session,
> > >                 break;
> > >         case AVDTP_SESSION_STATE_CONNECTED:
> > >                 if (!chan->session)
> > > -                       chan->session = session;
> > > +                       chan->session = avdtp_ref(session);
> >
> > Afaik this was done on purpose since we only need a weak reference as
> > taking a reference would prevent the session to be disconnected when
> > there is no setup in place, so I pretty sure this will cause
> > regressions, instead we should probably add a reference when
> > reconfiguring is in place and have a grace period for switching to
> > another codec.
>
> Allright, so it's either an in-progress setup or ongoing transport
> keeping the session alive, nothing else?  I guess this is as simple as
> setting a higher dc_timeout when calling set_disconnect_timer in
> avdtp_unref?

Yep, actually now that you mentioned the dc_timeout that should have
prevented us to disconnect immediately when reconfiguring as we should
have been in AVDTP_SESSION_STATE_CONNECTED state but I think the
problem is that we use avdtp_close to reconfigure which does set the
dc_timeout to 0 since that is normally used for cleaning up the
session, so I think we may need to restore the dc_timeout to
DISCONNECT_TIMEOUT if we attempt to set a configuration:

diff --git a/profiles/audio/avdtp.c b/profiles/audio/avdtp.c
index ae93fb26f..97b4d1b44 100644
--- a/profiles/audio/avdtp.c
+++ b/profiles/audio/avdtp.c
@@ -3498,6 +3498,7 @@ int avdtp_set_configuration(struct avdtp *session,
                session->streams = g_slist_append(session->streams, new_stream);
                if (stream)
                        *stream = new_stream;
+               session->dc_timeout = DISCONNECT_TIMEOUT;
        }

        g_free(req);


> >
> > >                 load_remote_seps(chan);
> > >                 break;
> > >         }
> > > @@ -2145,6 +2148,7 @@ found:
> > >                 channel_remove(chan);
> > >                 return NULL;
> > >         }
> > > +       avdtp_ref(chan->session);
> > >
> > >         return avdtp_ref(chan->session);
> > >  }
> > > @@ -2165,6 +2169,7 @@ static void connect_cb(GIOChannel *io, GError *err, gpointer user_data)
> > >                         error("Unable to create AVDTP session");
> > >                         goto fail;
> > >                 }
> > > +               avdtp_ref(chan->session);
> > >         }
> > >
> > >         g_io_channel_unref(chan->io);
> > > --
> > > 2.29.1
> > >
> > > Marijn Suijten
> >
> >
> >
> > --
> > Luiz Augusto von Dentz
>
> Marijn Suijten


-- 
Luiz Augusto von Dentz