bug#28862: Emacs 25.3.1 segmentation fault on killing *Colors* buffer

[martin rudalics <rudalics@gmx.at>]

 > Have you (or anyone else) been able to reproduce the issue? If not, I can
 > start looking at other potential factors on my system.

I was not able to reproduce it.  But I do not understand some parts of
your scenario:

 > 1) Run `emacs -Q` in a terminal with an X server running, spawning the X
 > frontend for emacs

Is 1) strictly necessary?

 > 2) Paste the above code into the *scratch* buffer and evaluate it (with
 > `M-x eval-buffer`).
 >
 > 3) Spawn a new frame (with `C-x 5 2`)
 >
 > 4) Enter the customization menus (with `M-x customize`)
 >
 > 5) Navigate to any face in the UI, for example `Emacs -> Faces -> Basic
 > Faces -> Cursor face`
 >
 > 6) Expand the options for the face of interest and click on `Choose` for a
 > color. The colors buffer should appear in a new window, splitting the frame
 > in half.
 >
 > 7) Close the window containing the *Customize Group: ...*, such that the
 > only buffer visible in the frame is the *Colors* buffer (I do this by
 > right-clicking the modeline)

Can't you instead of 4)-7) simply run ‘list-colors-display’?

 > 8) Close the frame via the window manager (`X` button, or some hotkey to
 > close the X window).

Does C-x 5 0 not exhibit the bug?

In any case please use GDB to step through delete_frame.  If it survives
‘delete-frame-functions’ it should be easy to see where it crashes.

martin