bug#28176: 26.0.50; Emacs hangs on entering a specific article in gnus

[Eli Zaretskii]

> From: Sam Steingold <sds@gnu.org>
> Cc: 28176@debbugs.gnu.org
> Date: Mon, 21 Aug 2017 14:46:30 -0400
> 
> > Can you show a backtrace when it hangs like that?
> 
> Alas, no: I cannot break out of the hang.

You could start Emacs under a debugger to begin with, and when Emacs
hangs, type "kill -USR1".

> Emacs hangs with a yellow triangle in the middle of the frame
> (indicating ding) but C-g and C-] do not interrupt.
> CPU usage is at 90%.

This most probably means Emacs is signaling an error in redisplay
code, which causes an infinite loop of signaling an error, then
redisplaying, then signaling an error again, and so on and so forth.
Still, a C-level backtrace might show which Lisp code runs and what C
call chain is involved.  So it's useful information, if you can
provide it.