Since the crash is in CVRCompositorSharedTextures::AcquireSync() I should probably say that I am using the patchset at https://github.com/lostgoat/mesa/tree/wip-semaphore-gl-v2 in my mesa.

The crash does not happen always. Opening the SteamVR frame time graph seems to trigger it often.

Backtrace:

Program terminated with signal SIGABRT, Aborted.
#0  0x00007faf057d68a0 in raise () from /usr/lib/libc.so.6
[Current thread is 1 (Thread 0x7faf08af2f80 (LWP 28826))]
(gdb) bt
#0  0x00007faf057d68a0 in raise () from /usr/lib/libc.so.6
#1  0x00007faf057d7f09 in abort () from /usr/lib/libc.so.6
#2  0x000056360f07f95e in handle_crash (sig=11) at platform/x11/crash_handler_x11.cpp:107
#3  <signal handler called>
#4  0x00007faeec4602f2 in CVRCompositorSharedTextures::AcquireSync() () from /home/chris/.local/share/Steam/SteamApps/common/SteamVR/bin/linux64/vrclient.so
#5  0x00007faeec45b26d in CVRCompositorClient::PostPresentHandoff() () from /home/chris/.local/share/Steam/SteamApps/common/SteamVR/bin/linux64/vrclient.so
#6  0x00007faeec45bcd4 in CVRCompositorClient::WaitGetPoses(vr::TrackedDevicePose_t*, unsigned int, vr::TrackedDevicePose_t*, unsigned int) ()
   from /home/chris/.local/share/Steam/SteamApps/common/SteamVR/bin/linux64/vrclient.so
#7  0x00007faeece80ae3 in godot_arvr_process (p_data=0x56361410e730) at src/ARVRInterface.cpp:297
#8  0x000056360f103c6e in ARVRInterfaceGDNative::process (this=0x563613de7680) at modules/gdnative/arvr/arvr_interface_gdnative.cpp:211
#9  0x00005636108c9365 in VisualServerViewport::draw_viewports (this=0x5636139a72b0) at servers/visual/visual_server_viewport.cpp:243
[#10](/issue/ValveSoftware/SteamVR-for-Linux/10) 0x000056361075b363 in VisualServerRaster::draw (this=0x56361392cb20) at servers/visual/visual_server_raster.cpp:103
[#11](/issue/ValveSoftware/SteamVR-for-Linux/11) 0x0000563610794af9 in VisualServerWrapMT::draw (this=0x563613a7afb0) at servers/visual/visual_server_wrap_mt.cpp:100
[#12](/issue/ValveSoftware/SteamVR-for-Linux/12) 0x000056360f0adafc in Main::iteration () at main/main.cpp:1732
[#13](/issue/ValveSoftware/SteamVR-for-Linux/13) 0x000056360f0886bb in OS_X11::run (this=0x7ffc76d15410) at platform/x11/os_x11.cpp:2126
[#14](/issue/ValveSoftware/SteamVR-for-Linux/14) 0x000056360f07e16f in main (argc=9, argv=0x7ffc76d158d8) at platform/x11/godot_x11.cpp:54

building it is basically

git clone https://github.com/godotengine/godot.git && cd godot && scons platform=x11 -j12
git clone https://github.com/BastiaanOlij/godot_openvr/ && cd godot_openvr && GODOT_HEADERS=/wherever/godot/modules/gdnative/include OPENVR_PATH=/wherever/openvr scons platform=linux

then start godot/bin/godot.x11.tools.64 and import the demo project from the godot_openvr directory and it'll just work (if you have libopenvr_api.so in LD_LIBRARY_PATH probably)