[Spice-devel] help debugging: Assertion `!xcb_xlib_threads_sequence_lost' failed.

[Frediano Ziglio]

> 
> On Thu, Jan 23, 2020 at 11:54:50AM -0500, Cole Robinson wrote:
> > Hi all,
> > 
> > For the past year+ we have had a steady trickle of virt-manager X11
> > threading crashes. This is the f31 bug I've duped all the other ones
> > too, but there were a handful that were auto closed by Fedora
> > end-of-life bug cleanup:
> > https://bugzilla.redhat.com/show_bug.cgi?id=1756065
> > 
> > The message that goes along with this is:
> > 
> > [xcb] Unknown sequence number while processing queue
> > [xcb] Most likely this is a multi-threaded client and XInitThreads has
> > not been called
> > [xcb] Aborting, sorry about that.
> > remote-viewer: xcb_io.c:263: poll_for_event: Assertion
> > `!xcb_xlib_threads_sequence_lost' failed.
> > Aborted (core dumped)
> > 
> > That may not apply to all the poll_for_error() bugs but it's most of the
> > ones I have dug into.
> > 
> > I figured there was some threading issue in virt-manager and I was
> > mostly ignoring the bugs until I found time to try and diagnose. I'm not
> > really finding anything in virt-manager though, and some similar issues
> > make me think maybe this is spice-gtk or something lower.
> > 
> > This user can reproduce the same error with remote-viewer + spice + X11
> > ssh forwarding: https://bugzilla.redhat.com/show_bug.cgi?id=1758384
> > 
> > This user can reproduce the virt-manager crash multiple times a day, and
> > it's always when interacting with a spice-gtk console:
> > https://bugzilla.redhat.com/show_bug.cgi?id=1792576
> > 
> > Anyone have any ideas how to debug this further? What spice-gtk
> > debugging info would be helpful?
> 
> FWIW if you're trying to reproduce this yourself, the key factor here
> is that they are using X11, not Wayland. Given that Fedora defaults
> to Wayland this likely explains why only certain people are seeing
> it.
> 
> The error message strongly suggests that there are multiple threads
> making X11 calls at the same time. This in turn means multiple threads
> are making GTK calls at the same time, and this is expressly forbidden
> by GTK - GTK APIs are only permitted to be invoked from the main thread
> which runs the event loop.
> 
> It does look like a probable spice issue given the common crash in
> remote-viewer, as aside from GTK itself and GTK-VNC, that's the only
> UI library both apps use.
> 
> Regards,
> Daniel

Hi,
  found the root cause, a bug in libX11, see updates to
https://bugzilla.redhat.com/show_bug.cgi?id=1758384.
As it's not specifically related to virt-manager/virt-viewer which
Product/Component should the bug moved to?

Regards,
  Frediano