os: data race on os.Process.done

[dvyukov]

When running
$ go test -race -run=none -bench=.* -benchtime=.5 math/big
ThreadSanitizer says:

WARNING: DATA RACE
Write by goroutine 27:
  os.(*Process).wait()
      src/pkg/os/exec_unix.go:27 +0x3a6
  os.(*Process).Wait()
      src/pkg/os/doc.go:43 +0x29
  os/exec.(*Cmd).Wait()
      src/pkg/os/exec/exec.go:302 +0x220
  main.func·022()
      src/cmd/go/test.go:628 +0x3b

Previous read by goroutine 7:
  os.(*Process).signal()
      src/pkg/os/exec_unix.go:38 +0x3a
  os.(*Process).Signal()
      src/pkg/os/doc.go:48 +0x40
  os.(*Process).kill()
      src/pkg/os/exec_posix.go:53 +0x57
  os.(*Process).Kill()
      src/pkg/os/doc.go:36 +0x29
  main.(*builder).runTest()
      src/cmd/go/test.go:634 +0x172d
  main.func·004()
      src/cmd/go/build.go:567 +0x4bb
  main.func·005()
      src/cmd/go/build.go:616 +0x118

Goroutine 27 (running) created at:
  main.(*builder).runTest()
      src/cmd/go/test.go:629 +0xd6a
  main.func·004()
      src/cmd/go/build.go:567 +0x4bb
  main.func·005()
      src/cmd/go/build.go:616 +0x118

Goroutine 7 (running) created at:
  main.(*builder).do()
      src/cmd/go/build.go:618 +0x691
  main.runTest()
      src/cmd/go/test.go:368 +0x26df
  main.main()
      src/cmd/go/main.go:141 +0x6da
  runtime.main()
      src/pkg/runtime/proc.c:247 +0x91

[davecheney]

Comment 1:

http://golang.org/cl/6462081 is a possible fix which uses channels. pkg/os
already imports sync/atomic so an atomic bool solution is an alternative.

[dvyukov]

Comment 2:

I think an atomic variable is a more appropriate solution here. An atomic
flag is what the code inherently needs, trying to mimic it with chan, close
and select looks a bit awkward to me. Note that the race will be there in
any case (Kill may kill another process), we are just trying to make it
MM-conformant.

[davecheney]

Comment 3:

Thanks for the feedback, I've updated http://golang.org/cl/6462081 to use
sync/atomic.

[robpike]

Comment 4:

Labels changed: added priority-soon, removed priority-triage.

Status changed to Accepted.

[davecheney]

Comment 5:

6462081 looks good. I will submit once the builders are looking happier.

Owner changed to @davecheney.

Status changed to Started.

[davecheney]

Comment 6:

This issue was closed by revision 122a558.

Status changed to Fixed.