CPU hogging by dysfunctional bash or zsh when started via mintty Cygwin terminal link

[Jan-Marek Glogowski <glogow@fbihome.de>]

Hi *,

I've already been on IRC (jmux) and had a longer debug session, trying
various stuff suggested by MetaNova. This is a Cygwin64 install.

Quoting from IRC: "After a longer time (probably months), I tried to
open a cygwin terminal, which now fails. It results in an empty window
with a blinking cursor and a bash process with 100% CPU load. The box is
a Windows 10 VM and also runs an cygwin openssh server, which I normally
use for development. SSH still works fine. I also installed gdb and
tried to attach to the CPU hogging bash, but I never see a gdb prompt
just some gdb startup output."

The condensed version, of what I already did and didn't change the result:

* updated cygwin install
* gdb -p <bash hog pid> -> hangs
  - killing bash will "start" gdb with the message, that the process
already exited
* starting zsh via the mintty link results in zsh hogging the CPU.
* cygwin.bat works; same for starting bash.exe from cmd
* reinstall mintty incl. "rebase-trigger fullrebase" didn't help
* strace mintty from a cygwin.bat shell results in a SIGSEGV
  - log currently at http://paste.debian.net/1130528/
  - expires: 2020-02-17 01:57:45
* gdb mintty results in ~ the same result, then gdb -p
  - it creates some threads, a bash hog window is created with all the
other "helpers" and gdb returns with "[Inferior 1 (<pid I guess)>)
exited with normally]" to the gdb prompt
  - quitting gdb and returning to the bash prompt won't happen, until I
kill the bash window, so basically the same, then doing "gdb -p"

This all looks like a mintty problem.

What else can I do to debug / fix this problem?

Regards,

Jan-Marek

P.S. Windows installed some updates today, but since I don't know when I
opened a terminal the last time, I can't tell if that is related.

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