fallthrough

		case _Grunnable, _Gsyscall, _Gwaiting:
			// Claim goroutine by setting scan bit.
			// This may race with execution or readying of gp.
			// The scan bit keeps it from transition state.
			if !castogscanstatus(gp, s, s|_Gscan) {
				break
			}

			// Clear the preemption request. It's safe to
			// reset the stack guard because we hold the
			// _Gscan bit and thus own the stack.
			gp.preemptStop = false

			if r {
				acquireLockRankAndM(lockRankGscan)
			}
			return r

		}
	}
	print("runtime: castogscanstatus oldval=", hex(oldval), " newval=", hex(newval), "\n")
	throw("castogscanstatus")
	panic("not reached")
}

// casgstatusAlwaysTrack is a debug flag that causes casgstatus to always track
// various latencies on every transition instead of sampling them.
var casgstatusAlwaysTrack = false