runtime: exclude extra M's from debug.SetMaxThreads
The purpose of the debug.SetMaxThreads limit is to avoid accidental fork
bomb from something like millions of goroutines blocking on system
calls, causing the runtime to create millions of threads.
By definition we don't create threads created in C, so this isn't a
problem for those threads, and we can exclude them from the limit. If C
wants to create tens of thousands of threads, who are we to say no?
Fixes #60004.
Change-Id: I62b875890718b406abca42a9a4078391e25aa21b
Reviewed-on: https://go-review.googlesource.com/c/go/+/492743
Auto-Submit: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>