Need help understanding X server freeze

[jeetu.golani at gmail.com]

Hi everyone,

First, I am a big fan of the remote display capabilities of X, thank
you very much to all who have worked on this project over the years.

Also, I am not sure if this is an Xorg issue per se or a bug in my own
code, however am at wits end and am hoping someone can point me in the
right direction.

For my open source project - eBrainPool (ebrain.in) - I have been
working on a tunnel plugin working over the Retroshare network that
will allow SSH X forwarded sessions.

The tunnel works for the most part of it, though I am seeing the
following behaviour that I have not yet been able to debug :

- The test configurations for the below tests have two machines.

Machine 1: Debian Unstable with X server 1.18.4 and OpenSSH 7.3 (also
tried with OpenSSH 6.9). This machine is an i7 with Intel accelerated
graphics and uses the intel Xorg driver.

Machine 2: Debian Testing with X server 1.16.x and OpenSSH 6.7. This
machine is a Core2Duo with  Radeon graphics and the radeon Xorg
driver.

Both machines use Gnome3.

- Simple X clients such as xclock, etc run without any hitches through
the tunnel over the Internet via Retroshare. More complex X clients
such as gnome-calculator,gedit,etc work for a short while before
causing a freeze of the entire X server. I have to kill SSH by going
into a tty before I can resume using my Gnome session. Once the SSH
session is killed, the session resumes normally and I don't need to
log back in.

- If I use SSH X forwarding between my two machines over LAN and
without my tunnel, then everything works without a hitch.

- If the X server is within a Virtualbox guest running either Debian
Stable, Unstable or Ubuntu 14.04 then all works fine through my
tunnel. I can forward applications to this X server through my tunnel
and use them without any hitch.

- If I start Xephyr on either machine and use ssh to forward to this
display, then even through my tunnel, all works well. No X freezes -
neither of the primary Xorg server nor of Xephyr.

- I tried using the Vesa xorg driver instead of the Intel driver on
Machine 1, just to see if that had any change in behaviour (even
though I see this same behaviour with the radeon driver). No joy. When
using the tunnel, the X server still hangs up.

Again, I am not sure if this is an issue with Xorg, SSH, Retroshare or
most likely my own tunnel code, however since it all works within
Virtualbox and Xephyr but not otherwise I am at wits end as to where
to look.

I realize the above information is sketchy however I feel to debug
this any further I require guidance from someone with more intimate
knowledge of X than myself. Am hoping someone will be able to see
something here that I am missing, or point me out as to how I can
gather more information that would help debug this.

Thank you so much for your time, I truly appreciate any help.

Regards,
Jeetu