[Spice-devel] [PATCH v7 06/14] usbredir: Spawn a different thread for device redirection flow

[Jonathon Jongsma]

So, after adding the g_task_return_boolean back to _open_device_async_cb(), I
noticed that since g_task_return_error() can potentially complete the task
immediately (rather than in an idle handler done previously), we may be
executing the GAsyncReadyCallback while the channel is locked. Currently, I
don't think this causes any problems, but if the callback did anything that
required locking the channel's mutex, that could result in a deadlock. So here's
an additional proposed patch to unlock before completing the task. If this
change is ACKed, I'd probably squash it into this patch.

------------
diff --git a/src/channel-usbredir.c b/src/channel-usbredir.c
index cd2ff4f..aa8e943 100644
--- a/src/channel-usbredir.c
+++ b/src/channel-usbredir.c
@@ -367,17 +367,19 @@ _open_device_async_cb(GTask *task,
 
     spice_usbredir_channel_lock(channel);
 
-    if (!spice_usbredir_channel_open_device(channel, &err)) {
+    spice_usbredir_channel_open_device(channel, &err);
+    libusb_unref_device(priv->device);
+    priv->device = NULL;
+    g_boxed_free(spice_usb_device_get_type(), priv->spice_device);
+    priv->spice_device = NULL;
+
+    spice_usbredir_channel_unlock(channel);
+
+    if (err) {
         g_task_return_error(task, err);
-        libusb_unref_device(priv->device);
-        priv->device = NULL;
-        g_boxed_free(spice_usb_device_get_type(), priv->spice_device);
-        priv->spice_device = NULL;
     } else {
         g_task_return_boolean(task, TRUE);
     }
-
-    spice_usbredir_channel_unlock(channel);
 }
 #endif
 


On Wed, 2016-03-16 at 10:16 -0500, Jonathon Jongsma wrote:
> On Wed, 2016-03-16 at 11:27 +0100, Christophe Fergeau wrote:
> > Hey,
> > 
> > On Tue, Mar 15, 2016 at 02:31:03PM -0500, Jonathon Jongsma wrote:
> > > +#ifndef USE_POLKIT
> > > +static void
> > > +_open_device_async_cb(GTask *task,
> > > +                      gpointer object,
> > > +                      gpointer task_data,
> > > +                      GCancellable *cancellable)
> > > +{
> > > +    GError *err = NULL;
> > > +    SpiceUsbredirChannel *channel = SPICE_USBREDIR_CHANNEL(object);
> > > +    SpiceUsbredirChannelPrivate *priv = channel->priv;
> > > +
> > > +    spice_usbredir_channel_lock(channel);
> > > +
> > > +    if (!spice_usbredir_channel_open_device(channel, &err)) {
> > > +        g_task_return_error(task, err);
> > > +        libusb_unref_device(priv->device);
> > > +        priv->device = NULL;
> > > +        g_boxed_free(spice_usb_device_get_type(), priv->spice_device);
> > > +        priv->spice_device = NULL;
> > > +    }
> > > +
> > > +    spice_usbredir_channel_unlock(channel);
> > > +}
> > > +#endif
> > > +
> > >  G_GNUC_INTERNAL
> > >  void spice_usbredir_channel_connect_device_async(
> > >                                            SpiceUsbredirChannel *channel,
> > > @@ -331,9 +356,6 @@ void spice_usbredir_channel_connect_device_async(
> > >  {
> > >      SpiceUsbredirChannelPrivate *priv = channel->priv;
> > >      GTask *task;
> > > -#ifndef USE_POLKIT
> > > -    GError *err = NULL;
> > > -#endif
> > >  
> > >      g_return_if_fail(SPICE_IS_USBREDIR_CHANNEL(channel));
> > >      g_return_if_fail(device != NULL);
> > > @@ -376,15 +398,7 @@ void spice_usbredir_channel_connect_device_async(
> > >                                          channel);
> > >      return;
> > >  #else
> > > -    if (!spice_usbredir_channel_open_device(channel, &err)) {
> > > -        g_task_return_error(task, err);
> > > -        libusb_unref_device(priv->device);
> > > -        priv->device = NULL;
> > > -        g_boxed_free(spice_usb_device_get_type(), priv->spice_device);
> > > -        priv->spice_device = NULL;
> > > -    } else {
> > > -        g_task_return_boolean(task, TRUE);
> > 
> > Only looked at the diff, not at the full code, but this
> > g_task_return_boolean(task, TRUE); is gone from the threaded version, is
> > this intentional?
> > 
> 
> Good catch. That was unintentional.
> 
> 
> > Christophe
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