bug#13611: SEGV during SMOB GC

[Mike Gran]

>>  Is that expected that GC is sometimes called from a 

>>  thread where scm_i_current_thread is null and sometimes
>>  called from a thread where scm_i_current_thread is
>>  not null?
> 
> Can you check whether your GC was built with --enable-parallel-mark?
> 
> I’m confident that the SMOB mark procedure is never called with null
> scm_i_current_thread with 7.2 compiled with the default options (the
> GnuTLS bindings rely on this, and I had not seen any such report until
> someone tried with GC 7.3pre, which uses the parallel marker by
> default.)

It looks like fedora gc rpms do use --enable-parallel-mark
for x86 architectures.

You can see that here:
  http://pkgs.fedoraproject.org/cgit/gc.git/tree/gc.spec?h=f17

But it looks like it has been that way for a long time.
Since 2005 at least.

-Mike