> suspending threads in your own process is kind of necessary for e.g. many GC algorithms
I think this is typically done by having the compiler/runtime insert safepoints, which cooperatively yield at specified points to allow the GC to run without mutator threads being active. Done correctly, this shouldn't be subject to the problem the original post highlighted, because it doesn't rely on the OS's ability to suspend threads when they aren't expecting it.
This is a good approach but can be tricky. E.g. what if your thread spends a lot of time in a tight loop, e.g. doing a big inlined matmul kernel? Since you never hit a function call you don't get safepoints that way -- you can add them to the back-edge of every loop, but that can be a bit unappetizing from a performance perspective.
If you don’t create any GC-able objects in the loop, why would you need to call the GC? And if you are, that should involve a function call.
And if you do need to call the GC, you could manually insert function calls every x loop iterations.