bug#52446: 28.0.90; Infinite loop in add_row_entry

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

>> Resent-From: Po Lu <luangruo@yahoo.com>
>> Original-Sender: "Debbugs-submit" <debbugs-submit-bounces@debbugs.gnu.org>
>> Resent-CC: bug-gnu-emacs@gnu.org
>> Resent-Sender: help-debbugs@gnu.org
>> Date: Sun, 12 Dec 2021 13:15:29 +0800
>> From:  Po Lu via "Bug reports for GNU Emacs,
>>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
>> 
>> Emacs froze while I was scrolling through a large image with `C-n'.  The
>> source of the freeze was an infinite loop in this part of
>> `add_row_entry':
>> 
>>     while (entry && !row_equal_p (entry->row, row, 1))
>> --->  entry = entry->next;
>> 
>> The problem seems to be that `entry' points to the same address as
>> `entry->next'.

> Are you sure?  This more-or-less "can't happen".  How did you see that
> this was the problem?

I did `p entry' and `p entry->next' in gdb.  Both pointed to the same
address.