node->parent == NULL when moving to screen with no application windows.

[jrwrigh]

Crashes when changing from an empty screen (no windows) to a screen with windows. Results in the following error message:

picom: ../src/wm/tree.c:228: wm_tree_find_toplevel_for: Assertion `!__bug_on_tmp && "Original expr: " "(node->parent) == NULL"' failed.

Platform

Manjaro Linux, Kernel 6.6.60
Window Manager: qtile

GPU, drivers, and screen setup

• GPU: Intel i5-1135G7 (Intel® Iris® Xe Graphics) (Intel Corporation TigerLake-LP GT2 [Iris Xe Graphics])
• Drivers: lscpi reports Kernel driver in use: i915
• Configuration: 2 monitors, side-by-side with xrandr.

❯ xrandr
Screen 0: minimum 320 x 200, current 3840 x 1280, maximum 16384 x 16384
eDP-1 connected 1920x1280+1920+0 (normal left inverted right x axis y axis) 285mm x 190mm
...  
DP-4-1 connected primary 1920x1080+0+100 (normal left inverted right x axis y axis) 521mm x 293mm

• glxinfo -B

❯ glxinfo -B
name of display: :0
display: :0  screen: 0
direct rendering: Yes
Extended renderer info (GLX_MESA_query_renderer):
    Vendor: Intel (0x8086)
    Device: Mesa Intel(R) Xe Graphics (TGL GT2) (0x9a49)
    Version: 24.2.6
    Accelerated: yes
    Video memory: 15941MB
    Unified memory: yes
    Preferred profile: core (0x1)
    Max core profile version: 4.6
    Max compat profile version: 4.6
    Max GLES1 profile version: 1.1
    Max GLES[23] profile version: 3.2
OpenGL vendor string: Intel
OpenGL renderer string: Mesa Intel(R) Xe Graphics (TGL GT2)
OpenGL core profile version string: 4.6 (Core Profile) Mesa 24.2.6-arch1.1
OpenGL core profile shading language version string: 4.60
OpenGL core profile context flags: (none)
OpenGL core profile profile mask: core profile

OpenGL version string: 4.6 (Compatibility Profile) Mesa 24.2.6-arch1.1
OpenGL shading language version string: 4.60
OpenGL context flags: (none)
OpenGL profile mask: compatibility profile

OpenGL ES profile version string: OpenGL ES 3.2 Mesa 24.2.6-arch1.1
OpenGL ES profile shading language version string: OpenGL ES GLSL ES 3.20

Environment

qtile window manager

picom version

v12 (git@github.com:yshui/picom.git revision 4529db7)

Diagnostics

### Extensions:

* Shape: Yes
* RandR: Yes
* Present: Present

### Misc:

* Use Overlay: No

* Config file specified: None
* Config file used: /home/jrwrigh/.config/picom.conf

### Drivers (inaccurate):

modesetting
[ 11/09/2024 09:48:45.114 egl_init WARN ] The egl backend is still experimental, use with care.

### Backend: egl

* Driver vendors:
 * EGL: Mesa Project
 * EGL driver: iris
 * GL: Intel
* GL renderer: Mesa Intel(R) Xe Graphics (TGL GT2)

### Backend: glx

* Driver vendors:
 * GLX: Mesa Project and SGI
 * GL: Intel
* GL renderer: Mesa Intel(R) Xe Graphics (TGL GT2)
* Accelerated: 1

Configuration:

I see that my configuration has a few deprecated options. I'll leave them for now, but let me know if I should fix them for this debugging.

Configuration file

shadow = false;
shadow-radius = 5;
shadow-opacity = .5
shadow-offset-x = -5;
shadow-offset-y = -5;
shadow-ignore-shaped = false;
shadow-exclude = [
    "! name~=''",
    "name = 'Notification'",
    "name = 'Plank'",
    "name = 'Docky'",
    "name = 'Kupfer'",
    "name = 'xfce4-notifyd'",
    "name = 'cpt_frame_window'",
    "name *= 'VLC'",
    "name *= 'compton'",
    "name *= 'picom'",
    "name *= 'Chromium'",
    "name *= 'Chrome'",
    "name *= 'Firefox'",
    "class_g = 'Conky'",
    "class_g = 'Zoom'",
    "class_g = 'Kupfer'",
    "class_g = 'Synapse'",
    "class_g ?= 'Notify-osd'",
    "class_g ?= 'Cairo-dock'",
    "class_g ?= 'Xfce4-notifyd'",
    "class_g ?= 'Xfce4-power-manager'",
    "_GTK_FRAME_EXTENTS@:c"
];
fading = false
fade-in-step = 0.03;
fade-out-step = 0.03;
inactive-opacity = 0.8;
frame-opacity = 1.0;
inactive-opacity-override = false;
focus-exclude = [ "class_g = 'Cairo-clock'" ];
opacity-rule = [
  # "0:_NET_WM_STATE@:32a *= '_NET_WM_STATE_HIDDEN'",
  "99:_NET_WM_STATE@[0]:32a = '_NET_WM_STATE_FULLSCREEN'", # don't use opacity for full screen apps
  "99:_NET_WM_STATE@[1]:32a = '_NET_WM_STATE_FULLSCREEN'",
  "99:_NET_WM_STATE@[2]:32a = '_NET_WM_STATE_FULLSCREEN'",
  "99:_NET_WM_STATE@[3]:32a = '_NET_WM_STATE_FULLSCREEN'",
  "99:_NET_WM_STATE@[4]:32a = '_NET_WM_STATE_FULLSCREEN'",
];
blur-kern = "3x3box";
blur-background-exclude = [
  "window_type = 'dock'",
  "window_type = 'desktop'",
  "_GTK_FRAME_EXTENTS@:c"
];
backend = "glx";
vsync = true
mark-wmwin-focused = true;
mark-ovredir-focused = false;
detect-rounded-corners = false;
detect-client-opacity = false;
refresh-rate = 0
use-ewmh-active-win = true
unredir-if-possible = true
detect-transient = true
detect-client-leader = false
glx-no-stencil = true
use-damage = true
log-level = "warn";
wintypes:
{
  tooltip = { fade = true; shadow = true; opacity = 0.75; focus = true; full-shadow = false; };
  dock = { shadow = false; }
  dnd = { shadow = false; }
  popup_menu = { opacity = 1.0; }
  dropdown_menu = { opacity = 1.0; }
};

Steps of reproduction

1. Have one monitor empty and the other have something
2. Switch to the other monitor (using qtile's next_screen() function and a custom function that moves the cursor to the new monitor)

Expected behavior

Picom to not crash

Current Behavior

picom crashes

Stack trace

(gdb) bt
#0  0x00007f4ae42e73f4 in ?? () from /usr/lib/libc.so.6
#1  0x00007f4ae428e120 in raise () from /usr/lib/libc.so.6
#2  0x00007f4ae42754c3 in abort () from /usr/lib/libc.so.6
#3  0x00007f4ae42753df in ?? () from /usr/lib/libc.so.6
#4  0x00007f4ae4286177 in __assert_fail () from /usr/lib/libc.so.6
#5  0x000055f9440a91f8 in wm_tree_find_toplevel_for (tree=0x55f95f1ec7a8, node=0x55f95f1ec880) at ../src/wm/tree.c:228
#6  0x000055f9440a592b in wm_find_by_client (wm=0x55f95f1ec7a0, client=1282) at ../src/wm/wm.c:193
#7  0x000055f94406043f in update_ewmh_active_win (req_base=0x55f95f2d51d0, reply_or_error=0x55f95f1f4ef0)
    at ../src/event.c:231
#8  0x000055f944079ad3 in x_complete_async_requests (c=0x55f95f1e8740, e=0x55f95f3f67f0) at ../src/x.c:1024
#9  0x000055f944079b61 in x_feed_event (c=0x55f95f1e8740, e=0x55f95f3f67f0) at ../src/x.c:1032
#10 0x000055f944079e0d in x_poll_for_event (c=0x55f95f1e8740, queued=false) at ../src/x.c:1088
#11 0x000055f94406f0ae in x_event_callback (loop=0x7f4ae48f3060, w=0x55f95f1e8600, revents=1) at ../src/picom.c:1800
#12 0x00007f4ae48e813b in ev_invoke_pending () from /usr/lib/libev.so.4
#13 0x00007f4ae48ebd22 in ev_run () from /usr/lib/libev.so.4
#14 0x000055f944073963 in session_run (ps=0x55f95f1e8600) at ../src/picom.c:2589
#15 0x000055f944073ce2 in main (argc=1, argv=0x7fff6a9a7008) at ../src/picom.c:2704

Log file with --log-level trace: picom_log_file_debug.log

Other details

It's kinda hard to see in the video, but notice that when the cursor appears in the middle of the right monitor, picom crashes.

[yshui]

oooo, qtile sets _NET_ACTIVE_WINDOW to root. i kinda feel that's not allowed by EWMH, but OTOH EWMH is pretty vague on this.

it's not too difficult to add a check.

[jrwrigh]

Thanks for the quick fix! Happy that it wasn't too hard to diagnose and resolve. I'll try it out in a bit to verify on my side.

[jrwrigh]

Confirmed that the fix works on my side. Thanks again!