bug#47244: 28.0.50; SIGSEGV in long-runnning Emacs

[Eli Zaretskii]

> From: Michael Welsh Duggan <mwd@cert.org>
> Cc: Michael Welsh Duggan <mwd@md5i.com>,
>         "schwab@linux-m68k.org"
>  <schwab@linux-m68k.org>,
>         "47244@debbugs.gnu.org" <47244@debbugs.gnu.org>
> Date: Thu, 08 Apr 2021 13:11:34 -0400
> 
> I hit the breakpoint in quit.  It looks like Fnconc uses FOR_EACH_TAIL,
> which uses FOR_EACH_TAIL_INTENAL, which calls maybe_quit.  The question
> in my mind now is whether block/unblock_input belongs in window_list or
> in Fnconc.

IMO, the right solution is not block_input but unwind_protect.