[Spice-devel] [PATCH spice-gtk 08/14] usb: remove useless device ref/unref

[Jonathon Jongsma]

----- Original Message -----
> From: "Marc-André Lureau" <marcandre.lureau at gmail.com>
> To: "Jonathon Jongsma" <jjongsma at redhat.com>
> Cc: "Uri Lublin" <uril at redhat.com>, "Marc-André Lureau" <mlureau at redhat.com>, spice-devel at freedesktop.org
> Sent: Monday, April 28, 2014 11:54:03 AM
> Subject: Re: [Spice-devel] [PATCH spice-gtk 08/14] usb: remove useless device ref/unref
> 
> On Mon, Apr 28, 2014 at 6:48 PM, Jonathon Jongsma <jjongsma at redhat.com>wrote:
> 
> > ----- Original Message -----
> > > From: "Marc-André Lureau" <marcandre.lureau at gmail.com>
> > > To: "Uri Lublin" <uril at redhat.com>
> > > Cc: "Marc-André Lureau" <mlureau at redhat.com>,
> > spice-devel at freedesktop.org
> > > Sent: Monday, April 28, 2014 9:49:59 AM
> > > Subject: Re: [Spice-devel] [PATCH spice-gtk 08/14] usb: remove useless
> >      device ref/unref
> > >
> > >
> > > On Mon, Apr 28, 2014 at 4:42 PM, Uri Lublin < uril at redhat.com > wrote:
> > >
> > >
> > >
> > > On 04/28/2014 03:49 PM, Marc-André Lureau wrote:
> > >
> > >
> > >
> > > ----- Original Message -----
> > >
> > >
> > > On 04/23/2014 09:09 PM, Marc-André Lureau wrote:
> > >
> > >
> > > A code doing an unref() on an object just before manipulating it looks
> > > horribly suspicious...
> > > Suspicious indeed.
> > >
> > > But probably it's better to move the unref below instead of removing the
> > > ref/unref (see below).
> > >
> > > A device is ref'ed when install/uninstall starts and is unref'ed when
> > > install/uninstall finishes.
> > >
> > > Possibly during install the ref is not needed (as there is another ref
> > > for the redir operation),
> > > but I think it is needed during uninstall.
> > >
> > > It wasn't needed until now (or we would have had crashes before), why
> > would
> > > it be now?
> > >
> > > Generally, no crashes does not mean ref/unref are not needed.
> > >
> > >
> > > When I read this code:
> > >
> > > @@ -1122,7 +1120,6 @@ static void spice_usb_device_manager_drv_
> > > uninstall_cb(GObject *gobject,
> > > g_clear_error(&err);
> > > }
> > >
> > > - spice_usb_device_unref(cbinfo->device);
> > > spice_usb_device_set_state(cbinfo->device, SPICE_USB_DEVICE_STATE_NONE);
> > >
> > > It seems pretty clear that this cbinfo ref wasn't involved to keep the
> > device
> > > alive (same fo the install case).
> >
> >
> > Well, it could simply mean that there is a race and the async operation
> > usually completes before it is freed? Or maybe it means there's a leak
> > somewhere else and we never
> 
> 
> that potential race would still exists, with or without the extra ref. Here
> the extra ref is useless, since the object was already unref before it was
> manipulated.


Not if you move the unref after the line where you manipulate it... I agree with you that the *current* code is pointless.  But if you move the unref to the very end of the function, the ref ceases to be pointless.  right? 


> 
> actually free these SpiceUsbDeviceInfo structs.  And if we fix that leak,
> > we'll then start crashing here.  I don't see any downside to holding the
> > ref, even if doesn't seem necessary at the moment.
> >
> >
> >
> > >
> > > --
> > > Marc-André Lureau
> > >
> > > _______________________________________________
> > > Spice-devel mailing list
> > > Spice-devel at lists.freedesktop.org
> > > http://lists.freedesktop.org/mailman/listinfo/spice-devel
> > >
> >
> 
> 
> 
> --
> Marc-André Lureau
>