// In STW mode, disable scheduling of user Gs. This may also
	// disable scheduling of this goroutine, so it may block as
	// soon as we start the world again.
	if mode != gcBackgroundMode {
		schedEnableUser(false)
	}

	// Enter concurrent mark phase and enable
	// write barriers.
	//
	// Because the world is stopped, all Ps will
	// observe that write barriers are enabled by

	// Global runnable queue.
	runq     gQueue
	runqsize int32

	// disable controls selective disabling of the scheduler.
	//
	// Use schedEnableUser to control this.
	//
	// disable is protected by sched.lock.
	disable struct {
		// user disables scheduling of user goroutines.
		user     bool
		runnable gQueue // pending runnable Gs

			print("nil")
		}
		print("\n")
	})
	unlock(&sched.lock)
}

// schedEnableUser enables or disables the scheduling of user
// goroutines.
//
// This does not stop already running user goroutines, so the caller
// should first stop the world when disabling user goroutines.
func schedEnableUser(enable bool) {
	lock(&sched.lock)
	if sched.disable.user == !enable {
		unlock(&sched.lock)