i3lock screen locker crashing compton --experimental-backends commit 76e574d

[Ropid]

When "i3lock" is locking the screen, compton crashes when using --experimental-backends. I can reproduce this here reliably by manually starting i3lock like this:

i3lock

or like this:

i3lock --nofork --color=000000 --pointer=default

The crash happens with both:

compton --experimental-backends --backend glx

and also:

compton --experimental-backends --backend xrender

Compton doesn't crash when using the normal backends, for example the following work fine:

compton --backend glx
compton --backend xrender

Platform

ArchLinux

GPU, drivers, and screen setup

• RX 480
• single monitor
• Mesa 19.1.0-rc5
• xf86-video-amdgpu 19.0.1
• Xorg 1.20.5

Environment

XFCE, xfwm4 v4.12.5

Compton version

$ compton --diagnostics
**Version:** v6-rc1-166-g76e574d

### Extensions:

* Shape: Yes
* XRandR: Yes
* Present: Present

### Misc:

* Use Overlay: Yes
* Config file used: /home/deep/.config/compton.conf

### Drivers (inaccurate):

AMDGPU, Radeon  

Compton configuration:

backend = "glx";
# backend = "xrender";
vsync = true;

use-damage = true;

# glx-no-stencil = true;
# glx-no-rebind-pixmap = true;
# glx-swap-method = -1;

shadow = true;

shadow-radius = 16;
shadow-offset-x = -16;
shadow-offset-y = -12;
shadow-opacity = 0.35;

detect-rounded-corners = true;

shadow-exclude = [
    "class_g = 'Xfwm4'",
    "(class_g = 'Firefox' || class_g = 'Nightly') && window_type = 'utility'",
    "_GTK_FRAME_EXTENTS@:c",
    "name = 'XOSD'",
    # "bounding_shaped && !rounded_corners",
    # "window_type = 'normal' && !I3_FLOATING_WINDOW@:c",
];

inactive-opacity = 1;
active-opacity = 1;
frame-opacity = 1;
inactive-opacity-override = false;

blur-background = false;
# blur-background-frame = true;
# blur-background-fixed = true;
# blur-kern = "7x7box";
# blur-background-exclude = [
#     "window_type = 'dock'",
#     "window_type = 'desktop'",
#     "_GTK_FRAME_EXTENTS@:c"
# ];

fading = false;
# fade-delta = 4;
fade-in-step = 0.2;
fade-out-step = 0.2;
# no-fading-openclose = true;

fade-exclude = [ ];

mark-wmwin-focused = true;
mark-ovredir-focused = true;
use-ewmh-active-win = true;

detect-client-opacity = true;

unredir-if-possible = true;

unredir-if-possible-exclude = [
    "_NET_WM_BYPASS_COMPOSITOR@:c = 2",
    "class_g = 'MComix'",
    "class_g = 'vlc'",
    # "class_g = 'Firefox'",
    # "class_g = 'Nightly'",
];

focus-exclude = [ ];

detect-transient = true;
detect-client-leader = true;

wintypes:
{
    tooltip = { full-shadow = true; fade = true; shadow = false; opacity = 0.8; focus = true; };
    dock    = { shadow = false; };
    dnd     = { shadow = false; };
};

Stack trace

Core was generated by `build/src/compton --experimental-backends'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x000055c6dc8a70b8 in gl_destroy_blur_context (base=0x55c6dd216880, ctx=0x0)
    at ../src/backend/gl/gl_common.c:703
703		for (int i = 0; i < bctx->npasses; ++i) {
[Current thread is 1 (Thread 0x7f15c57cc940 (LWP 9674))]
(gdb) bt
#0  0x000055c6dc8a70b8 in gl_destroy_blur_context (base=0x55c6dd216880, ctx=0x0)
    at ../src/backend/gl/gl_common.c:703
#1  0x000055c6dc871fa8 in destroy_backend (ps=0x55c6dd1e68b0) at ../src/compton.c:669
#2  0x000055c6dc8737ac in redir_stop (ps=0x55c6dd1e68b0) at ../src/compton.c:1149
#3  0x000055c6dc871c38 in paint_preprocess (ps=0x55c6dd1e68b0, fade_running=0x7ffecfc9d696)
    at ../src/compton.c:604
#4  0x000055c6dc874014 in _draw_callback (loop=0x7f15c6cfc720, ps=0x55c6dd1e68b0, revents=8192)
    at ../src/compton.c:1306
#5  0x000055c6dc874249 in draw_callback (loop=0x7f15c6cfc720, w=0x55c6dd1e6970, revents=8192)
    at ../src/compton.c:1352
#6  0x00007f15c6cf0993 in ev_invoke_pending () from /usr/lib/libev.so.4
#7  0x00007f15c6cf42dd in ev_run () from /usr/lib/libev.so.4
#8  0x000055c6dc876f88 in session_run (ps=0x55c6dd1e68b0) at ../src/compton.c:2134
#9  0x000055c6dc877237 in main (argc=2, argv=0x7ffecfc9d8f8) at ../src/compton.c:2216
(gdb) 

Here is a second stack trace produced with the experimental xrender backend instead of the glx one:

Core was generated by `build/src/compton --experimental-backends --backend xrender'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x000055974d7c68ff in destroy_blur_context (base=0x55974f4a88e0, ctx_=0x0)
    at ../src/backend/xrender/xrender.c:512
512		for (int i = 0; i < ctx->x_blur_kernel_count; i++) {
(gdb) bt
#0  0x000055974d7c68ff in destroy_blur_context (base=0x55974f4a88e0, ctx_=0x0)
    at ../src/backend/xrender/xrender.c:512
#1  0x000055974d795fa8 in destroy_backend (ps=0x55974f4818b0) at ../src/compton.c:669
#2  0x000055974d7977ac in redir_stop (ps=0x55974f4818b0) at ../src/compton.c:1149
#3  0x000055974d795c38 in paint_preprocess (ps=0x55974f4818b0, fade_running=0x7ffc354296e6)
    at ../src/compton.c:604
#4  0x000055974d798014 in _draw_callback (loop=0x7efe0259d720, ps=0x55974f4818b0, revents=8192)
    at ../src/compton.c:1306
#5  0x000055974d798249 in draw_callback (loop=0x7efe0259d720, w=0x55974f481970, revents=8192)
    at ../src/compton.c:1352
#6  0x00007efe02591993 in ev_invoke_pending () from /usr/lib/libev.so.4
#7  0x00007efe025952dd in ev_run () from /usr/lib/libev.so.4
#8  0x000055974d79af88 in session_run (ps=0x55974f4818b0) at ../src/compton.c:2134
#9  0x000055974d79b237 in main (argc=4, argv=0x7ffc35429948) at ../src/compton.c:2216
(gdb) 

[Ropid]

I got the idea to test --blur-background when I saw this line of code here printed by gdb:

for (int i = 0; i < ctx->x_blur_kernel_count; i++) {

When I set blur-background = true in my config, then compton --experimental-backends does not crash anymore. The crash only happens when I use blur-background = false in my config.

[yshui]

Fixed in next. Can you confirm?

[Ropid]

Yes, it's fixed and working fine now. Thank you.