bug#43177: Bug: Emacs 27.1 hangs forever in `FcCharSetSubtractCount' from '/usr/lib/libfontconfig.so.1'

[Pip Cet]

On Thu, Sep 3, 2020 at 7:33 AM Robert Pluim <rpluim@gmail.com> wrote:
>
> >>>>> On Thu, 3 Sep 2020 09:18:53 +0200, Alexander Shukaev 
> >>>>> <emacs@Alexander.Shukaev.name> said:
>
>     Alexander> Hi,
>     Alexander> With latest Emacs, I have a sporadic hang issue when either 
> opening a
>     Alexander> file or scrolling a buffer.  The best part is that it's 
> impossible to
>     Alexander> get break back to evaluation loop of Emacs even with 'USR2'
>     Alexander> signal. That is when 'USR2' is sent, it does show "Entering
>     Alexander> debugger...", though it remains frozen afterwards.  Resending 
> 'USR2'
>     Alexander> leads to the same outcome.  One thing is for certain, every 
> time
>     Alexander> 'USR2' is sent into such a hang, the stack traceback leads to
>     Alexander> `FcCharSetSubtractCount' from '/usr/lib/libfontconfig.so.1':
>
> If you've still got this in gdb, can you go to frame #6 and do
>
> pp entity
>
> (this is assuming you've sourced the .gdbinit in src/)
>
> That will tell us which font weʼre trying to open. Perhaps itʼs a bad
> font or fontconfig configuration.

Is this bug #40733, maybe?

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=40733