bug#33014: 26.1.50; 27.0.50; Fatal error after re-evaluating a thread's function

[Eli Zaretskii]

> From: Gemini Lasswell <gazally@runbox.com>
> Cc: 33014@debbugs.gnu.org
> Date: Sat, 13 Oct 2018 10:17:10 -0700
> 
> When eval-region evaluates the defun for erb--benchmark-monitor-func, it
> replaces the symbol's function definition, so it removes that reference
> to the byte-code.  AFAIK the only other reference to the byte-code
> is on the stack of Thread 7, which is running the byte-code.

So you are saying that the call to mark_stack inside mark_one_thread
doesn't do its job well enough?  AFAIU, it's supposed to scan the
stack of each and every thread, and mark Lisp objects referenced from
those stacks.

How do we know there's a reference to that vector on thread 7's stack?
Could it be that there is no reference at all?