The gc.collecting field doesn't necessarily imply that all threads are paused:

• gc.collecting is set before the stop-the-world pause
• The GC resumes threads while calling finalizers

You could check tstate->interp->stoptheworld.world_stopped and maybe also that tstate matches stoptheworld.requester. (The faulting thread may not be attached to the interpreter when it crashes.)

I'm not fully convinced that this is worth the extra complexity or the extra chance of crashing during the faulthandler:

• Most crashes probably won't occur during a stop-the-world pause and for those that do, the stack traces of other threads are even less likely to be relevant (because they're paused).
• Even during a stop-the-world pause, looping over the linked list of thread states is not safe without a HEAD_LOCK(), which you can't do during a signal handler.

Yeah, I was on the fence about it too. I threw it in there because it seemed simple enough at first, but I think it's better to remove it too.