bug#42220: 27.0.91; Infinte loop in display_count_lines

[Eli Zaretskii]

> From: Óscar Fuentes <ofv@wanadoo.es>
> Date: Mon, 06 Jul 2020 00:25:19 +0200
> 
> 
> When the third-party mini-modeline [1] is active, certain quick and
> repeated sequence of inputs produce a hang as described here [2].
> 
> Attaching gdb to Emacs and stepping through the code it is clear that
> there is an infinite loop:
> 
> 26649         while (start_byte < limit_byte)
> (gdb) p start_byte
> $32 = 557362
> (gdb) p limit_byte
> $33 = 703917
> (gdb) n
> 26651             ceiling =  BUFFER_CEILING_OF (start_byte);
> (gdb) 
> 26652             ceiling = min (limit_byte - 1, ceiling);
> (gdb) p ceiling
> $34 = 557361
> (gdb) n
> 26653             ceiling_addr = BYTE_POS_ADDR (ceiling) + 1;
> (gdb) p ceiling
> $35 = 557361

Thanks, I think I fixed this now on the emacs-27 branch.