bug#17986: 24.3.92; Evaluating (setq default-directory nil) freezes Emacs

[Eli Zaretskii <eliz@gnu.org>]

> From: Stephen Berman <stephen.berman@gmx.net>
> Date: Thu, 10 Jul 2014 14:27:30 +0200
> 
> 0. Start Emacs with -Q or -Q -D
> 1. Type (setq default-directory nil) in *scratch* and evaluate it.
> => Emacs freezes uninterruptibly and uses up to 90% CPU; I have to kill
> it from outside.

Should be fixed in revision 117376 on the emacs-24 branch.

> This happens in both emacs-24 and the trunk.  The C backtrace seems to
> differ depending on how quickly I type `z' in gdb and whether I start
> Emacs with -Q or with -Q -D.  If no one else can reproduce this, I can
> supply backtraces.  So far, I've gotten as the only Lisp backtrace
> "redisplay_internal (C function)" (twice with emacs-24 from July 7) and
> (after updating to current sources) "command-error-default-function"
> (twice with trunk, once with emacs-24).

When Emacs becomes unresponsive, it is best to attach a debugger to a
running Emacs process, and then use the procedure described in
etc/DEBUG (under "If the symptom of the bug is that Emacs fails to
respond") to find out which function infloops; then include this
information in the bug report.

Thanks.