Launching any electron app crashes Xorg in ?? from ProcVidModeGetModeLine

[Kyle Fazzari]

If I dare to launch any electron-based app (chrome, spotify, atom, vscode, etc.) there's roughly an 80% chance that it kills X (bringing me back to the login screen). This doesn't _always_ happen. Note that I have a 4k laptop, with a 4k external screen. Things seem to have a better chance of succeeding if I disconnect the external display before launching the electron app. Once it launches successfully things seem to be stable, even after re-connecting the external display.

I SSHd into this machine from another, and connected to X from gdb, then opened vscode to cause the crash. Here is the backtrace I got from that session (this is easy to reproduce, happy to provide any requested info):

root@Pandora:~# gdb /usr/bin/Xorg $(pidof Xorg)
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"/usr/bin/Xorg": not in executable format: File format not recognized
Attaching to process 2325
[New LWP 2480]
[New LWP 2481]
[New LWP 2482]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
0x00007f3302ea95d3 in select () at ../sysdeps/unix/syscall-template.S:84
84 ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) cont
Continuing.

Thread 1 "Xorg" received signal SIGSEGV, Segmentation fault.
0x000055f7cbb6f650 in ?? ()
(gdb) bt f
#0 0x000055f7cbb6f650 in ?? ()
No symbol table info available.
#1 0x000055f7ca8ec6dc in ProcVidModeGetModeLine (client=0x55f7cc218ee0) at ../../Xext/vidmode.c:255
        stuff = <optimized out>
        rep = {type = 1 '\001', pad1 = 0 '\000', sequenceNumber = 254, length = 5, dotclock = 0, hdisplay = 0, hsyncstart = 0, hsyncend = 0,
          htotal = 0, hskew = 0, vdisplay = 0, vsyncstart = 0, vsyncend = 0, vtotal = 0, pad2 = 0, flags = 0, reserved1 = 0, reserved2 = 0,
          reserved3 = 0, privsize = 0}
        pScreen = <optimized out>
        mode = 0x7ffd64d56e20
        dotClock = 32765
#2 0x000055f7ca77ad9f in Dispatch () at ../../dix/dispatch.c:430
        clientReady = 0x55f7cbf9c780
        result = <optimized out>
        client = 0x55f7cc218ee0
        nready = 0
        icheck = 0x55f7cab7b130 <checkForInput>
        start_tick = 12090
#3 0x000055f7ca77ee13 in dix_main (argc=11, argv=0x7ffd64d57018, envp=<optimized out>) at ../../dix/main.c:300
        i = <optimized out>
        alwaysCheckForInput = {0, 1}
#4 0x00007f3302dcc830 in __libc_start_main (main=0x55f7ca769030 <main>, argc=11, argv=0x7ffd64d57018, init=<optimized out>,
    fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7ffd64d57008) at ../csu/libc-start.c:291
        result = <optimized out>
        unwind_buf = {cancel_jmp_buf = {{jmp_buf = {0, -792397858051174054, 94522742050880, 140726295162896, 0, 0, -6839407696988057254,
                -6878888903866822310}, mask_was_saved = 0}}, priv = {pad = {0x0, 0x0, 0xb, 0x55f7ca769030 <main>}, data = {prev = 0x0,
              cleanup = 0x0, canceltype = 11}}}
        not_first_call = <optimized out>
#5 0x000055f7ca769069 in _start ()
No symbol table info available.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: xorg 1:7.7+13ubuntu3
ProcVersionSignature: Ubuntu 4.4.0-116.140-generic 4.4.98
Uname: Linux 4.4.0-116-generic x86_64
NonfreeKernelModules: wl
.tmp.unity_support_test.0:

ApportVersion: 2.20.1-0ubuntu2.15
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CompositorRunning: compiz
CompositorUnredirectDriverBlacklist: '(nouveau|Intel).*Mesa 8.0'
CompositorUnredirectFSW: true
CurrentDesktop: Unity
Date: Fri Mar 9 12:09:59 2018
DistUpgraded: Fresh install
DistroCodename: xenial
DistroVariant: ubuntu
EcryptfsInUse: Yes
ExtraDebuggingInterest: Yes
GraphicsCard:
 Intel Corporation 4th Gen Core Processor Integrated Graphics Controller [8086:0416] (rev 06) (prog-if 00 [VGA controller])
   Subsystem: Dell 4th Gen Core Processor Integrated Graphics Controller [1028:060d]
InstallationDate: Installed on 2016-08-01 (585 days ago)
InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
MachineType: Dell Inc. Dell Precision M3800
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.4.0-116-generic root=UUID=53750055-6616-428b-88f9-c6c555f8c31d ro quiet splash vt.handoff=7
SourcePackage: xorg
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 01/08/2015
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A09
dmi.board.name: Dell Precision M3800
dmi.board.vendor: Dell Inc.
dmi.board.version: A09
dmi.chassis.type: 8
dmi.chassis.vendor: Dell Inc.
dmi.chassis.version: Not Specified
dmi.modalias: dmi:bvnDellInc.:bvrA09:bd01/08/2015:svnDellInc.:pnDellPrecisionM3800:pvrA09:rvnDellInc.:rnDellPrecisionM3800:rvrA09:cvnDellInc.:ct8:cvrNotSpecified:
dmi.product.name: Dell Precision M3800
dmi.product.version: A09
dmi.sys.vendor: Dell Inc.
version.compiz: compiz 1:0.9.12.3+16.04.20180221-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.83-1~16.04.1
version.libgl1-mesa-dri: libgl1-mesa-dri 17.2.8-0ubuntu0~16.04.1
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 17.2.8-0ubuntu0~16.04.1
version.xserver-xorg-core: xserver-xorg-core 2:1.18.4-0ubuntu0.7
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.10.1-1ubuntu2
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:7.7.0-1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20160325-1ubuntu1.2
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.12-1build2
xserver.bootTime: Fri Mar 9 11:49:23 2018
xserver.configfile: default
xserver.errors: open /dev/dri/card0: No such file or directory
xserver.logfile: /var/log/Xorg.0.log
xserver.outputs:
 product id 5169
 vendor SHP
xserver.version: 2:1.18.4-0ubuntu0.7