// N.B. Only one GC can be running at a time, so this is naturally
	// serialized by the caller.
	trace.seqGC++
}

// STWStart traces a STWBegin event.
func (tl traceLocker) STWStart(reason stwReason) {
	// Although the current P may be in _Pgcstop here, we model the P as running during the STW. This deviates from the

	//
	// N.B. This will also emit a status event for this goroutine.
	tl := traceAcquire()
	tl.Gomaxprocs(gomaxprocs)  // Get this as early in the trace as possible. See comment in traceAdvance.
	tl.STWStart(stwStartTrace) // We didn't trace this above, so trace it now.

	// Record the fact that a GC is active, if applicable.
	if gcphase == _GCmark || gcphase == _GCmarktermination {
		tl.GCActive()
	}

// Returns the STW context. When starting the world, this context must be
// passed to startTheWorldWithSema.
func stopTheWorldWithSema(reason stwReason) worldStop {
	trace := traceAcquire()
	if trace.ok() {
		trace.STWStart(reason)
		traceRelease(trace)
	}
	gp := getg()

	// If we hold a lock, then we won't be able to stop another M
	// that is blocked trying to acquire the lock.
	if gp.m.locks > 0 {