// already be in _Gwaiting if this is a mark
			// worker or we're in mark termination.
			userG := getg().m.curg
			selfScan := gp == userG && readgstatus(userG) == _Grunning
			if selfScan {
				casGToWaitingForGC(userG, _Grunning, waitReasonGarbageCollectionScan)
			}

			// TODO: suspendG blocks (and spins) until gp
			// stops, which may take a while for
			// running goroutines. Consider doing this in

	mp.preemptoff = "gcing"
	mp.traceback = 2
	curgp := mp.curg
	// N.B. The execution tracer is not aware of this status
	// transition and handles it specially based on the
	// wait reason.
	casGToWaitingForGC(curgp, _Grunning, waitReasonGarbageCollection)

	// Run gc on the g0 stack. We do this so that the g stack
	// we're currently running on will no longer change. Cuts

		ug := untracedG{gp: gp, mid: -1}
		systemstack(func() {
			me := getg().m.curg
			// We don't have to handle this G status transition because we
			// already eliminated ourselves from consideration above.
			casGToWaitingForGC(me, _Grunning, waitReasonTraceGoroutineStatus)
			// We need to suspend and take ownership of the G to safely read its
			// goid. Note that we can't actually emit the event at this point

	casgstatus(gp, old, _Gwaiting)
}

// casGToWaitingForGC transitions gp from old to _Gwaiting, and sets the wait reason.
// The wait reason must be a valid isWaitingForGC wait reason.
//
// Use this over casgstatus when possible to ensure that a waitreason is set.
func casGToWaitingForGC(gp *g, old uint32, reason waitReason) {
	if !reason.isWaitingForGC() {
		throw("casGToWaitingForGC with non-isWaitingForGC wait reason")
	}