Linux: Segfault when reloading configuration after opening second Ghostty window

[slovdahl]

1. Start Ghostty
2. Close the Ghostty window with ctrl-d
3. Due to Process hangs around after closing last window with 'Destroying EGL context' #3495, the process keeps running in the background (despite quit-after-last-window-closed = true)
4. Start Ghostty again (which will just have the existing process spawn a window)
5. Press the "Reload configuration" keybind or select it from the menu

Both release and debug builds built from latest main crash. I started bisecting it because I thought it was a recent regression, but turns out this has been broken at least 3 weeks (randomly picked 2e14017 and it has the same crash). I'm on Ubuntu 24.04.

jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: /home/slovdahl/dev/ghostty/src/apprt/gtk/winproto.zig:118:17: 0x32ddca7 in updateConfigEvent (ghostty)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:         switch (self.*) {
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:                 ^
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: /home/slovdahl/dev/ghostty/src/apprt/gtk/Window.zig:377:52: 0x32ddd66 in updateConfig (ghostty)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:     if (self.winproto) |*v| try v.updateConfigEvent(config);
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:                                                    ^
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: /home/slovdahl/dev/ghostty/src/apprt/gtk/App.zig:920:32: 0x31dbf4f in configChange (ghostty)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:             window.updateConfig(new_config) catch |err| {
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:                                ^
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: /home/slovdahl/dev/ghostty/src/apprt/gtk/App.zig:521:44: 0x31dbde3 in performAction__anon_102849 (ghostty)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:         .config_change => self.configChange(target, value.config),
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:                                            ^
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: /home/slovdahl/dev/ghostty/src/Surface.zig:1203:34: 0x31dc8dd in updateConfig (ghostty)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:     try self.rt_app.performAction(
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:                                  ^
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: /home/slovdahl/dev/ghostty/src/Surface.zig:813:57: 0x31e36f5 in handleMessage (ghostty)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:         .change_config => |config| try self.updateConfig(config),
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:                                                         ^
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: /home/slovdahl/dev/ghostty/src/App.zig:147:47: 0x31e52f0 in updateConfig (ghostty)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:         try surface.core_surface.handleMessage(.{ .change_config = config });
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:                                               ^
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: /home/slovdahl/dev/ghostty/src/apprt/gtk/App.zig:971:47: 0x31e5763 in reloadConfig (ghostty)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:         .app => try self.core_app.updateConfig(self, &config),
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:                                               ^
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: /home/slovdahl/dev/ghostty/src/apprt/gtk/App.zig:1718:22: 0x326b537 in gtkActionReloadConfig (ghostty)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:     self.reloadConfig(.app, .{}) catch |err| {
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:                      ^
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f40fb22f9 in ??? (libgobject-2.0.so.0)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: Unwind information for `libgobject-2.0.so.0:0x7c0f40fb22f9` was not available, trace may be incomplete
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f40fe190b in ??? (libgobject-2.0.so.0)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f40fd2590 in ??? (libgobject-2.0.so.0)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f40fd27c0 in ??? (libgobject-2.0.so.0)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f40fd2882 in ??? (libgobject-2.0.so.0)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f41c40bf4 in ??? (libgio-2.0.so.0)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f41207144 in ??? (libgtk-4.so.1)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f4120bcdb in ??? (libgtk-4.so.1)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f41290422 in ??? (libgtk-4.so.1)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f41290701 in ??? (libgtk-4.so.1)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f411a5ed1 in ??? (libgtk-4.so.1)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f411a6a9e in ??? (libgtk-4.so.1)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f414023bb in ??? (libgtk-4.so.1)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f41495927 in ??? (libgtk-4.so.1)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f40fd26bc in ??? (libgobject-2.0.so.0)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f40fd27c0 in ??? (libgobject-2.0.so.0)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f40fd2882 in ??? (libgobject-2.0.so.0)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f41535826 in ??? (libgtk-4.so.1)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f4141acc5 in ??? (libgtk-4.so.1)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f40eb15b4 in ??? (libglib-2.0.so.0)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f40f10716 in ??? (libglib-2.0.so.0)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x7c0f40eb0a52 in ??? (libglib-2.0.so.0)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: /home/slovdahl/dev/ghostty/src/apprt/gtk/App.zig:1276:39: 0x31e6ea4 in run (ghostty)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:         _ = c.g_main_context_iteration(self.ctx, 1);
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:                                       ^
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: /home/slovdahl/dev/ghostty/src/main_ghostty.zig:112:24: 0x31e8374 in main (ghostty)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:     try app_runtime.run();
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:                        ^
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: /snap/zig/11625/lib/std/start.zig:524:37: 0x31e8e7e in main (ghostty)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:             const result = root.main() catch |err| {
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]:                                     ^
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ../sysdeps/nptl/libc_start_call_main.h:58:16: 0x7c0f4062a1c9 in __libc_start_call_main (../sysdeps/x86/libc-start.c)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ../csu/libc-start.c:360:3: 0x7c0f4062a28a in __libc_start_main_impl (../sysdeps/x86/libc-start.c)
jan 11 22:54:31 laptop com.mitchellh.ghostty.desktop[396394]: ???:?:?: 0x2c986d4 in ??? (???)

[slovdahl]

With gtk-single-instance = false I actually don't seem to get a crash. But I also don't get any "Reloaded configuration" toast, even though the log says the configuration is reloaded.

EDIT: After I e.g. resize the window the toast starts appearing when reloading the config.

[jcollie]

I'm unable to reproduce so far, but there definitely seems to be an environmental issue here. Can you share the results of ghostty +version?

[slovdahl]

$ ghostty +version
Ghostty 1.0.2-main+caddf59d

Version
  - version: 1.0.2-main+caddf59d
  - channel: tip
Build Config
  - Zig version: 0.13.0
  - build mode : builtin.OptimizeMode.ReleaseFast
  - app runtime: apprt.Runtime.gtk
  - font engine: font.main.Backend.fontconfig_freetype
  - renderer   : renderer.OpenGL
  - libxev     : main.Backend.io_uring
  - desktop env: other
  - GTK version:
    build      : 4.14.2
    runtime    : 4.14.2
  - libadwaita : enabled
    build      : 1.5.0
    runtime    : 1.5.0
  - libX11     : enabled
  - libwayland : enabled

[slovdahl]

Does Ghostty somehow still believe the first window is present and tries to do something with it?

[jcollie]

Yes, the crash is very likely a use-after-free bug.

[mitchellh]

This looks related to recent changes, so I'm inclined to believe there is definitely some broken logic here.