bug#21745: 25.0.50; emacs infloops after call to vc-annotate

[Ken Brown]

This bug does not occur in 'emacs -Q' or even 'emacs -q'.  But it does 
occur if I start emacs with no .emacs, no .emacs.d, and no default.el. 
To reproduce:

emacs
C-x d ~/src/emacs/master  [This is my clone of the emacs repo.]
v   [To view .dir-locals.el.]
C-x v g

At this point the cursor is in the annotate buffer (but not blinking), 
and emacs starts using a lot of CPU and is unresponsive.  I assume it is 
inflooping.  If I send the emacs process a SIGUSR2, it is responsive 
again.  At this point I can do 'C-x v g' again with no problem.

A bisection shows that the problem started with the following commit:

commit 1431f667504b610471257802aa2f2f4f0d8443de
Author: Eli Zaretskii <eliz@gnu.org>
Date:   Sat Oct 17 15:10:58 2015 +0300

    Avoid crashes when redisplayng a window changes faces or fonts

    * src/xdisp.c (redisplay_internal): If redisplaying the selected
    window or one of the frames turns on the frame's 'redisplay' flag,
    redisplay again.  (Bug#21428)

    * src/frame.c (x_set_font): Set the frame's 'fonts_changed' flag.

In GNU Emacs 25.0.50.48 (x86_64-unknown-cygwin, GTK+ Version 3.14.13)
 of 2015-10-23
Repository revision: 8408f4e38cb4108f8dde971bbc5d5220c66e0f67
Windowing system distributor 'The Cygwin/X Project', version 11.0.11702000
Configured using:
 'configure 'CFLAGS=-g3 -O0''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND DBUS GCONF GSETTINGS NOTIFY
ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
GTK3 X11

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Fundamental

Minor modes in effect:
  diff-auto-refine-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
View mode: type C-h for help, h for commands, q to quit.
Annotating...
Redisplaying annotation...done (Spanned from 2494.8 to 188.8 days old)
Annotating... done
Error during redisplay: (#[128 "\300\301\"\210\300\302\"\207" [apply 
redisplay--pre-redisplay-functions ignore nil] 4 nil nil] nil) signaled 
(quit)
Entering debugger...
Back to top level
Annotating...
Redisplaying annotation...done (Spanned from 2494.8 to 188.8 days old)
Annotating... done

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util
help-fns mail-prsvr mail-utils debug help-mode vc-annotate vc
cl-loaddefs pcase cl-lib vc-dispatcher vc-git diff-mode easy-mmode view
dired finder-inf gap-mode-autoloads info muse-autoloads package easymenu
epg-config time-date mule-util tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel x-win term/common-win x-dnd
tool-bar dnd fontset image regexp-opt fringe tabulated-list newcomment
elisp-mode lisp-mode prog-mode register page menu-bar rfn-eshadow timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
frame cl-generic cham georgian utf-8-lang misc-lang vietnamese tibetan
thai tai-viet lao korean japanese eucjp-ms cp51932 hebrew greek romanian
slovak czech european ethiopic indian cyrillic chinese charscript
case-table epa-hook jka-cmpr-hook help simple abbrev minibuffer
cl-preloaded nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote dbusbind gfilenotify
dynamic-setting system-font-setting font-render-setting move-toolbar gtk
x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 99019 6493)
 (symbols 48 20907 0)
 (miscs 40 124 134)
 (strings 32 19298 4944)
 (string-bytes 1 553817)
 (vectors 16 13331)
 (vector-slots 8 443259 6719)
 (floats 8 187 260)
 (intervals 56 461 21)
 (buffers 976 17))