Segfault in nxagent and screen flickering when maximizing x2go session window

[HolySephi]

Server O/S: Ubuntu 14.04

x2goserver version: 4.1.0.0-01315ubuntu14.04.1
nxagent version: 3.5.99.0-0~git20160625.1249+t

Client O/S: Windows 10
X2Goclient Version: 4.0.5.1

maybe related to #162

Steps to reproduce:

• Connect to the server as a normal window (800x600)
• Maximize the x2goclient window of the session

I now get a very flickering screen because the resolution of the maximized window gets set multiple times per second:

...
Info: Screen [0] resized to geometry [1920x1027] fullscreen [0].
Info: Screen [0] resized to geometry [1920x1027] fullscreen [0].
Info: Screen [0] resized to geometry [1920x1027] fullscreen [0].
Info: Screen [0] resized to geometry [1920x1027] fullscreen [0].
Info: Screen [0] resized to geometry [1920x1027] fullscreen [0].
Info: Screen [0] resized to geometry [1920x1027] fullscreen [0].
Info: Screen [0] resized to geometry [1920x1027] fullscreen [0].
...

After an undefined amount of time the process segfaults:

x2goagent[733]: segfault at 8 ip 000000000042a263 sp 00007fff95bcec60 error 4 in nxagent[400000+4f0000]

[uli42]

Is this new? Does it also happen with last week's version before the Event patches?

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An: "ArcticaProject/nx-libs" nx-libs@noreply.github.com
Betreff: [ArcticaProject/nx-libs] Segfault in nxagent and screen flickeringwhen maximizing x2go session window (#161)

Server O/S: Ubuntu 14.04
x2goserver version: 4.1.0.0-01315ubuntu14.04.1
nxagent version: 3.5.99.0-0~git20160625.1249+t
Client O/S: Windows 10
X2Goclient Version: 4.0.5.1
Steps to reproduce:
Connect to the server as a normal window (800x600)
Maximize the x2goclient window of the session
I now get a very flickering screen because the resolution of the maximized window gets set multiple times per second:
...
Info: Screen [0] resized to geometry [1920x1027] fullscreen [0].
Info: Screen [0] resized to geometry [1920x1027] fullscreen [0].
Info: Screen [0] resized to geometry [1920x1027] fullscreen [0].
Info: Screen [0] resized to geometry [1920x1027] fullscreen [0].
Info: Screen [0] resized to geometry [1920x1027] fullscreen [0].
Info: Screen [0] resized to geometry [1920x1027] fullscreen [0].
Info: Screen [0] resized to geometry [1920x1027] fullscreen [0].
...
After an undefined amount of time the process segfaults:
x2goagent[733]: segfault at 8 ip 000000000042a263 sp 00007fff95bcec60 error 4 in nxagent[400000+4f0000]
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[HolySephi]

Unfortunately i don't know - i ran into this while debugging #162 but as this segfaults in another location i created a seperate bug and #162 might not be new - i might remember some reports from my first tests with 3.6.0 (3.5.99) when i ran into the segfault from #118 but did not dug any deeper into this issue. We might have multiple things in resolution changing/setting that run into segfaults and not only on session-resume as fixed in #118

[uli42]

Hmm does it also happen with -rrxinerama?

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Von: "Florian Wicke" notifications@github.com
Gesendet: ‎27.‎06.‎2016 14:50
An: "ArcticaProject/nx-libs" nx-libs@noreply.github.com
Cc: "Ulrich Sibiller" uli42@gmx.de; "Comment" comment@noreply.github.com
Betreff: Re: [ArcticaProject/nx-libs] Segfault in nxagent and screenflickering when maximizing x2go session window (#161)

Unfortunately i don't know - i ran into this while debugging #162 but as this segfaults in another location i created a seperate bug and #162 might not be new - i might remember some reports from my first tests with 3.6.0 (3.5.99) when i ran into the segfault from #118 but did not dug any deeper into this issue. We might have multiple things in resolution changing/setting that run into segfaults and not only on session-resume as fixed in #118
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[HolySephi]

Using "-rrxinerama" as X2GO_NXAGENT_DEFAULT_OPTIONS xinerama is no longer working as expected. The "flickering" of setting the resolution a few times per second on maximizing is still present and the segfault is still occuring but i'm unable to trigger the segfault in libX11 from #162

Sorry, #162 is still happening even with -rrxinerama

[uli42]

So just to get this straight:

• it happens with the current source from today
• it has not been seen before
• it is unsure if it happens since my events fix
• there are no SIGHUPs involved

Is that correct?

Do you have coredumps you can examine?

[HolySephi]

• this is happening with the current nightly packages from the ubuntu repo
  http://packages.arctica-project.org/ubuntu-nightly
• this and libX11 segfault when resizing x2go session window #162 do not occur on 3.5.0
• It could have occured before our fix for nxagent segfaults on session resume #118 but i did not test against this until now
• there are no SIGHUPs involved - just screen resizing and sometimes even right after starting the session (might be where the screen size gets set) - the new screen size gets set before the segfault (the taskbar and desktop background image fit the new screen size) correctly
• bonus round: this also happens with -rrxinerama as x2goagent parameter

Unfortunately i'm not familiar with creating core dumps from aldready running processes. Since this segfault does not appear if i start nxagent manually i'm unable to use the method i used in #118 to debug the process.

[uli42]

I tried to setup an LXDE session using the nightly arctica build on Ubuntu 14.04. It crashed after some seconds with a coredump. Here's the backtrace:

Core was generated by `/usr/lib/nx/../x2go/bin/x2goagent +extension XFIXES +xinerama -nolisten tcp -no'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007fa54f9a8dbb in _XSend () from /usr/lib/x86_64-linux-gnu/libX11.so.6
(gdb) bt
#0  0x00007fa54f9a8dbb in _XSend () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#1  0x00007fa54f9a9265 in _XFlush () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#2  0x00007fa54f9abc75 in _XGetRequest () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#3  0x00007fa550cb0041 in XRenderComposite () from /usr/lib/x86_64-linux-gnu/libXrender.so.1
#4  0x00000000004b392e in ?? ()
#5  0x0000000000437312 in ?? ()
#6  0x0000000000432c59 in ?? ()
#7  0x00000000004314d2 in ?? ()
#8  0x000000000040ea5b in ?? ()
#9  0x00007fa54fec7ec5 in __libc_start_main (main=0x40e680, argc=16, argv=0x7ffd57655e98, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, 
    stack_end=0x7ffd57655e88) at libc-start.c:287
#10 0x000000000040ef38 in ?? ()

I am wondering about the output. Why is it using _XSend from libX11 instead of libNX_X11? @sunweaver: can you please check the build?

[uli42]

I can get the crash by running x2goagent -ac :55 and then DISPLAY=:55 startlxde. Resizing the window immediately produces this segfault:

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff5177dbb in _XSend () from /usr/lib/x86_64-linux-gnu/libX11.so.6
(gdb) bt
#0  0x00007ffff5177dbb in _XSend () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#1  0x00007ffff5178265 in _XFlush () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#2  0x00007ffff517ac75 in _XGetRequest ()
   from /usr/lib/x86_64-linux-gnu/libX11.so.6
#3  0x00007ffff6480d8d in XRenderCompositeText8 ()
   from /usr/lib/x86_64-linux-gnu/libXrender.so.1
#4  0x00000000004b3fb0 in ?? ()
#5  0x0000000000436fbb in ?? ()
#6  0x0000000000432c59 in ?? ()
#7  0x00000000004314d2 in ?? ()
#8  0x000000000040ea5b in ?? ()
#9  0x00007ffff5696ec5 in __libc_start_main (main=0x40e680, argc=3, 
    argv=0x7fffffffdfa8, init=<optimized out>, fini=<optimized out>, 
    rtld_fini=<optimized out>, stack_end=0x7fffffffdf98) at libc-start.c:287
#10 0x000000000040ef38 in ?? ()

When there's no LXDE running resizing works fine without crash (tested empty x2goagent and xterm with and without fvwm running). It works when I add -norender

[uli42]

A self compiled nxagent reveals some more info:

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff5169dbb in _XSend () from /usr/lib/x86_64-linux-gnu/libX11.so.6
(gdb) bt
#0  0x00007ffff5169dbb in _XSend () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#1  0x00007ffff516a265 in _XFlush () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#2  0x00007ffff516cc75 in _XGetRequest () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#3  0x00007ffff6472d8d in XRenderCompositeText8 () from /usr/lib/x86_64-linux-gnu/libXrender.so.1
#4  0x00000000004b7250 in nxagentGlyphs (op=<optimized out>, pSrc=pSrc@entry=0xd50bd0, pDst=0xd87a30, maskFormat=<optimized out>, 
    xSrc=<optimized out>, ySrc=<optimized out>, nlists=nlists@entry=1, elts=0xd86ef0, sizeID=1, glyphsBase=glyphsBase@entry=0x7fffffffcf40)
    at Render.c:1516
#5  0x0000000000436ebb in ProcRenderCompositeGlyphs (client=<optimized out>) at NXrender.c:1787
#6  0x00000000004318d9 in ProcRenderDispatch (client=<optimized out>) at NXrender.c:2522
#7  0x0000000000430a82 in Dispatch () at NXdispatch.c:749
#8  0x000000000040ea5b in main (argc=4, argv=0x7fffffffdd68, envp=<optimized out>) at main.c:437

So I suppose there something wrong with xrender

[sunweaver]

11:55 < sunweaver> Sephi: about #161 and #162...
11:57 < sunweaver> do you have anything in /usr/lib/nx/X11/Xinerama on the server?
11:57 < sunweaver> and... is $LD_LIBRARY_PATH set to that path in your X2Go sessions?
11:57 < sunweaver> (the LD_LIBRARY_PATH is probably set, but the dir should not exist).
11:58 < sunweaver> it is old school stuff from nx-libs 3.5.x

[sunweaver]

@HolySephi: Can you please provide output of

ldd /usr/lib/nx/bin/nxagent

? Thanks.

[HolySephi]

root@LTS-SRV ~ # ldd /usr/lib/nx/bin/nxagent
linux-vdso.so.1 => (0x00007ffe55de1000)
libNX_Xext.so.6 => /usr/lib/x86_64-linux-gnu/libNX_Xext.so.6 (0x00007fcb56265000)
libNX_X11.so.6 => /usr/lib/x86_64-linux-gnu/libNX_X11.so.6 (0x00007fcb55f46000)
libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007fcb55c3f000)
libXpm.so.4 => /usr/lib/x86_64-linux-gnu/libXpm.so.4 (0x00007fcb55a2d000)
libxml2.so.2 => /usr/lib/x86_64-linux-gnu/libxml2.so.2 (0x00007fcb556c6000)
libpixman-1.so.0 => /usr/lib/x86_64-linux-gnu/libpixman-1.so.0 (0x00007fcb5541d000)
libXcomp.so.3 => /usr/lib/x86_64-linux-gnu/libXcomp.so.3 (0x00007fcb5513b000)
libXcompext.so.3 => /usr/lib/x86_64-linux-gnu/libXcompext.so.3 (0x00007fcb54f29000)
libXcompshad.so.3 => /usr/lib/x86_64-linux-gnu/libXcompshad.so.3 (0x00007fcb54d1d000)
libXrender.so.1 => /usr/lib/x86_64-linux-gnu/libXrender.so.1 (0x00007fcb54b13000)
libXfixes.so.3 => /usr/lib/x86_64-linux-gnu/libXfixes.so.3 (0x00007fcb5490d000)
libXfont.so.1 => /usr/lib/x86_64-linux-gnu/libXfont.so.1 (0x00007fcb546db000)
libXcomposite.so.1 => /usr/lib/x86_64-linux-gnu/libXcomposite.so.1 (0x00007fcb544d8000)
libXinerama.so.1 => /usr/lib/x86_64-linux-gnu/libXinerama.so.1 (0x00007fcb542d5000)
libXdmcp.so.6 => /usr/lib/x86_64-linux-gnu/libXdmcp.so.6 (0x00007fcb540ce000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fcb53d09000)
libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007fcb53b05000)
libX11.so.6 => /usr/lib/x86_64-linux-gnu/libX11.so.6 (0x00007fcb537cf000)
libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007fcb535b6000)
liblzma.so.5 => /lib/x86_64-linux-gnu/liblzma.so.5 (0x00007fcb53394000)
/lib64/ld-linux-x86-64.so.2 (0x0000558f1ffb5000)
libpng12.so.0 => /lib/x86_64-linux-gnu/libpng12.so.0 (0x00007fcb5316d000)
libjpeg.so.8 => /usr/lib/x86_64-linux-gnu/libjpeg.so.8 (0x00007fcb52f18000)
libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007fcb52c14000)
libXtst.so.6 => /usr/lib/x86_64-linux-gnu/libXtst.so.6 (0x00007fcb52a0d000)
libXrandr.so.2 => /usr/lib/x86_64-linux-gnu/libXrandr.so.2 (0x00007fcb52803000)
libXdamage.so.1 => /usr/lib/x86_64-linux-gnu/libXdamage.so.1 (0x00007fcb52600000)
libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007fcb523e9000)
libfreetype.so.6 => /usr/lib/x86_64-linux-gnu/libfreetype.so.6 (0x00007fcb52146000)
libbz2.so.1.0 => /lib/x86_64-linux-gnu/libbz2.so.1.0 (0x00007fcb51f36000)
libfontenc.so.1 => /usr/lib/x86_64-linux-gnu/libfontenc.so.1 (0x00007fcb51d2d000)
libXext.so.6 => /usr/lib/x86_64-linux-gnu/libXext.so.6 (0x00007fcb51b1b000)
libxcb.so.1 => /usr/lib/x86_64-linux-gnu/libxcb.so.1 (0x00007fcb518fb000)
libXau.so.6 => /usr/lib/x86_64-linux-gnu/libXau.so.6 (0x00007fcb516f7000)

removing the old Xinerama folder does not change the segfaulting behaviour.

[HolySephi]

LD_LIBRARY_PATH is directing to:

/usr/lib/nx/X11/Xinerama:/usr/lib/nx/X11

X11 is empty because i deleted Xinerama as mentioned before.

[HolySephi]

Adding "-norender" to X2GO_NXAGENT_DEFAULT_OPTIONS does not change anything regarding the segfaults or the "screen flickering" when maximizing the window.