runtime: make NumGoroutine and Stack agree not to include system goroutines

[Repeat of CL 18343 with build fixes.]

Before, NumGoroutine counted system goroutines and Stack (usually) didn't show them,
which was inconsistent and confusing.

To resolve which way they should be consistent, it seems like

	package main
	import "runtime"
	func main() { println(runtime.NumGoroutine()) }

should print 1 regardless of internal runtime details. Make it so.

Fixes #11706.

Change-Id: If26749fec06aa0ff84311f7941b88d140552e81d
Reviewed-on: https://go-review.googlesource.com/18432
Reviewed-by: Austin Clements <austin@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>

misc/cgo/test/issue7978.go

@@ -110,13 +110,13 @@ func test7978(t *testing.T) {
 	go issue7978go()
 	// test in c code, before callback
 	issue7978wait(0, 1)
-	issue7978check(t, "runtime.cgocall(", "", 1)
+	issue7978check(t, "_Cfunc_issue7978c(", "", 1)
 	// test in go code, during callback
 	issue7978wait(2, 3)
 	issue7978check(t, "test.issue7978cb(", "test.issue7978go", 3)
 	// test in c code, after callback
 	issue7978wait(4, 5)
-	issue7978check(t, "runtime.cgocall(", "runtime.cgocallback", 1)
+	issue7978check(t, "_Cfunc_issue7978c(", "_cgoexpwrap", 1)
 	// test in go code, after return from cgo
 	issue7978wait(6, 7)
 	issue7978check(t, "test.issue7978go(", "", 3)

src/runtime/mprof.go

@@ -576,12 +576,17 @@ func Stack(buf []byte, all bool) int {
 		pc := getcallerpc(unsafe.Pointer(&buf))
 		systemstack(func() {
 			g0 := getg()
+			// Force traceback=1 to override GOTRACEBACK setting,
+			// so that Stack's results are consistent.
+			// GOTRACEBACK is only about crash dumps.
+			g0.m.traceback = 1
 			g0.writebuf = buf[0:0:len(buf)]
 			goroutineheader(gp)
 			traceback(pc, sp, 0, gp)
 			if all {
 				tracebackothers(gp)
 			}
+			g0.m.traceback = 0
 			n = len(g0.writebuf)
 			g0.writebuf = nil
 		})

src/runtime/proc.go

@@ -2167,6 +2167,9 @@ func goexit0(gp *g) {
 	_g_ := getg()
 
 	casgstatus(gp, _Grunning, _Gdead)
+	if isSystemGoroutine(gp) {
+		atomic.Xadd(&sched.ngsys, -1)
+	}
 	gp.m = nil
 	gp.lockedm = nil
 	_g_.m.lockedg = nil
@@ -2698,6 +2701,9 @@ func newproc1(fn *funcval, argp *uint8, narg int32, nret int32, callerpc uintptr
 	gostartcallfn(&newg.sched, fn)
 	newg.gopc = callerpc
 	newg.startpc = fn.fn
+	if isSystemGoroutine(newg) {
+		atomic.Xadd(&sched.ngsys, +1)
+	}
 	casgstatus(newg, _Gdead, _Grunnable)
 
 	if _p_.goidcache == _p_.goidcacheend {
@@ -2890,7 +2896,7 @@ func badunlockosthread() {
 }
 
 func gcount() int32 {
-	n := int32(allglen) - sched.ngfree
+	n := int32(allglen) - sched.ngfree - int32(atomic.Load(&sched.ngsys))
 	for i := 0; ; i++ {
 		_p_ := allp[i]
 		if _p_ == nil {

src/runtime/proc_test.go

@@ -9,6 +9,7 @@ import (
 	"net"
 	"runtime"
 	"runtime/debug"
+	"strings"
 	"sync"
 	"sync/atomic"
 	"syscall"
@@ -336,6 +337,23 @@ func TestGCFairness(t *testing.T) {
 	}
 }
 
+func TestNumGoroutine(t *testing.T) {
+	output := runTestProg(t, "testprog", "NumGoroutine")
+	want := "1\n"
+	if output != want {
+		t.Fatalf("want %q, got %q", want, output)
+	}
+
+	buf := make([]byte, 1<<20)
+	buf = buf[:runtime.Stack(buf, true)]
+
+	n := runtime.NumGoroutine()
+
+	if nstk := strings.Count(string(buf), "goroutine "); n != nstk {
+		t.Fatalf("NumGoroutine=%d, but found %d goroutines in stack dump", n, nstk)
+	}
+}
+
 func TestPingPongHog(t *testing.T) {
 	if testing.Short() {
 		t.Skip("skipping in -short mode")

src/runtime/runtime2.go

@@ -408,9 +408,11 @@ const (
 )
 
 type schedt struct {
-	lock mutex
+	// accessed atomically. keep at top to ensure alignment on 32-bit systems.
+	goidgen  uint64
+	lastpoll uint64
 
-	goidgen uint64
+	lock mutex
 
 	midle        muintptr // idle m's waiting for work
 	nmidle       int32    // number of idle m's waiting for work
@@ -418,6 +420,8 @@ type schedt struct {
 	mcount       int32    // number of m's that have been created
 	maxmcount    int32    // maximum number of m's allowed (or die)
 
+	ngsys uint32 // number of system goroutines; updated atomically
+
 	pidle      puintptr // idle p's
 	npidle     uint32
 	nmspinning uint32 // See "Worker thread parking/unparking" comment in proc.go.
@@ -445,7 +449,6 @@ type schedt struct {
 	stopnote   note
 	sysmonwait uint32
 	sysmonnote note
-	lastpoll   uint64
 
 	// safepointFn should be called on each P at the next GC
 	// safepoint if p.runSafePointFn is set.

src/runtime/testdata/testprog/misc.go

@@ -0,0 +1,15 @@
+// Copyright 2016 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import "runtime"
+
+func init() {
+	register("NumGoroutine", NumGoroutine)
+}
+
+func NumGoroutine() {
+	println(runtime.NumGoroutine())
+}