Regression - gdb hang when 'thread apply all bt full' is used

I've reported a bug[1] regarding the issue I am seeing but briefly the
problem is that gdb is hanging (using 100% CPU and not returning
anything) when retracing core dumps from vim on Ubuntu 16.10 and the
command 'thread apply all bt full' is issued.

The most recent version of gdb which I've recreated the problem with is:

GNU gdb (Ubuntu 7.12.50.20170314-0ubuntu1) 7.12.50.20170314-git

I believe this is a regression because this problem did not manifest
with gdb version 7.9, and first started happening with gdb version 7.10.

Full details can be found in the bug report and I'm happy to help dig
into this further.

[1] https://sourceware.org/bugzilla/show_bug.cgi?id=21324

Thanks!
--
Brian Murray