bug#22739: 25.0.50; Hangs on revertig buffer

[Eli Zaretskii <eliz@gnu.org>]

> From: Óscar Fuentes <ofv@wanadoo.es>
> Date: Fri, 19 Feb 2016 04:33:03 +0100
> 
> While executing revert-buffer on a file, Emacs hanged using 100% CPU.
> I've executed this operation thousands of times on this file on the past
> without problem. The file contains pure ASCII text.
> 
> I was unable to reproduce the bug on a fresh session.
> 
> Full backtrace attached.

It sounds like Emacs was inflooping somewhere.  When there's a
suspicion that Emacs infloops, the single most important information
is where it loops.  The file etc/DEBUG describes a technique to find
that out (search for "If the symptom of the bug is that Emacs fails to
respond").  So next time this happens, please use that technique and
post the findings.

Just looking at the backtrace, it's hard to say anything intelligent,
as backtraces taken from a looping program tend to be random.  The
below is a feeble attempt to do something with the backtrace
information.

What is in the buffer that visits this file between positions 282624
and 330908?  Are there any display strings or overlays in that range,
or some other properties that affect the display (like invisible
text), and if so, can you describe them?

Thanks.