Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version go1.8.3 windows/amd64

What operating system and processor architecture are you using (go env)?

set GOARCH=amd64
set GOBIN=
set GOEXE=.exe
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOOS=windows
set GOPATH=C:\Users\ifilippo\go
set GORACE=
set GOROOT=C:\Users\ifilippo\Desktop\go
set GOTOOLDIR=C:\Users\ifilippo\Desktop\go\pkg\tool\windows_amd64
set GCCGO=gccgo
set CC=gcc
set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0
set CXX=g++
set CGO_ENABLED=1
set PKG_CONFIG=pkg-config
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2

What did you do?

I compile the following reproducer, which contains LockOSThread calls for two goroutines.

package main
import (
"runtime"
"os"
"runtime/trace"
"time"
)
func main() {
f, err := os.Create("trace.out")
if err != nil {
panic(err)
}
defer f.Close()
err = trace.Start(f)
if err != nil {
panic(err)
}
defer trace.Stop()
go func() {
runtime.LockOSThread()
heavyFunc1()
}()
go func() {
runtime.LockOSThread()
heavyFunc2()
}()
time.Sleep(1 * time.Second)
}
func heavyFunc1() {
for {
for i := 0; i < 10000; i++ {}
runtime.Gosched()
}
}
func heavyFunc2() {
for {
for i := 0; i < 10000; i++ {}
runtime.Gosched()
}
}

What did you expect to see?

After using "go tool trace trace.out" I expect to see that each proc is used by only one of two goroutines

What did you see instead?

I see that both goroutines use both Procs without any locking goroutine to proc.

Is it my misunderstanding of LockOSThread documentation or go tool trace documentation? Or is it a bug?