//    created in allocm will eventually reach OS thread clone later in
	//    newm.
	// 3. We take allocmLock for write here to prevent allocation of new Ms
	//    while this function runs. Per (1), this prevents clone of OS
	//    threads that are not yet in allm.
	allocmLock.lock()

	// Disable preemption, preventing us from changing Ms, as we handle
	// this M specially.
	//