[Spice-devel] [PATCH spice-gtk 2/2] channel: Abort migration in delayed unref

[Pavel Grunt]

Hi,

On Tue, 2016-04-26 at 12:05 +0200, Victor Toso wrote:
> Hi,
> 
> On Fri, Apr 22, 2016 at 04:47:48PM +0200, Pavel Grunt wrote:
> > When channel is unref'ed during migration migrate_channel_event_cb
> > is called causing a crash by coroutine yielding to nonexistent channel.
> > 
> > As comment in spice_channel_coroutine says:
> >   Co-routine exits now - the SpiceChannel object may no longer exist,
> >   so don't do anything else now unless you like SEGVs
> > 
> > Related: rhbz#1318574
> > ---
> >  src/spice-channel.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/src/spice-channel.c b/src/spice-channel.c
> > index 19237b3..7b0a3dc 100644
> > --- a/src/spice-channel.c
> > +++ b/src/spice-channel.c
> > @@ -2296,6 +2296,7 @@ static gboolean spice_channel_delayed_unref(gpointer
> > data)
> >      SpiceChannel *channel = SPICE_CHANNEL(data);
> >      SpiceChannelPrivate *c = channel->priv;
> >      gboolean was_ready = c->state == SPICE_CHANNEL_STATE_READY;
> > +    SpiceSession *session;
> >  
> >      CHANNEL_DEBUG(channel, "Delayed unref channel %p", channel);
> >  
> > @@ -2303,6 +2304,13 @@ static gboolean spice_channel_delayed_unref(gpointer
> > data)
> >  
> >      c->state = SPICE_CHANNEL_STATE_UNCONNECTED;
> >  
> > +    session = spice_channel_get_session(channel);
> > +    if (spice_session_is_for_migration(session)) {
> > +        /* error during migration - abort migration */
> > +        spice_session_abort_migration(session);
> > +        return FALSE;
> > +    }
> > +
> 
> Just to be sure if I got it right. The migration fails for some reason which
> triggers and error in the migration process for spice-gtk. That will make the
> channel for the target host to be delayed_unref.
> 
> If we don't spice_session_abort_migration() now, migrate_channel_event_cb()
> will
> be called for the channel for the former host which will try to yield to a
> coroutine and cause the crash.
yes
> 
> Does this only happen under failure in the migration like [0] or it could
> happen
> if we do cancel the migration in the right moment?

if migration is canceled by the SPICE_MSG_MAIN_MIGRATE_CANCEL
message, spice_session_abort_migration() is called.

Looking at the backtrace of [0] the patch addresses the same issue.

Pavel

> 
> [0] https://bugs.freedesktop.org/show_bug.cgi?id=92019
> 
> Cheers,
>   toso
> 
> >      if (c->event != SPICE_CHANNEL_NONE) {
> >          g_coroutine_signal_emit(channel, signals[SPICE_CHANNEL_EVENT], 0,
> > c->event);
> >          c->event = SPICE_CHANNEL_NONE;