runtime/race: TestRaceChanCloseSend failed once

[rsc]

Seen during an unrelated trybot run on linux-amd64-race builder.
https://storage.googleapis.com/go-build-log/51c1aa35/linux-amd64-race_e41788ba.log

/cc @dvyukov

    === RUN   TestRaceChanCloseSend
    ==================
    WARNING: DATA RACE
    Read by goroutine 60:
      runtime.chansend()
          /tmp/workdir/go/src/runtime/chan.go:115 +0x0
      command-line-arguments_test.TestRaceChanCloseSend()
          /tmp/workdir/go/src/runtime/race/testdata/chan_test.go:577 +0xbe
      testing.tRunner()
          /tmp/workdir/go/src/testing/testing.go:473 +0xdc

    Previous write by goroutine 59:
      runtime.closechan()
          /tmp/workdir/go/src/runtime/chan.go:292 +0x0
      command-line-arguments_test.TestRaceChanCloseSend.func1()
          /tmp/workdir/go/src/runtime/race/testdata/chan_test.go:574 +0x2e

    Goroutine 60 (running) created at:
      testing.RunTests()
          /tmp/workdir/go/src/testing/testing.go:582 +0xae2
      testing.(*M).Run()
          /tmp/workdir/go/src/testing/testing.go:515 +0x11d
      main.main()
          command-line-arguments/_test/_testmain.go:736 +0x210

    Goroutine 59 (running) created at:
      command-line-arguments_test.TestRaceChanCloseSend()
          /tmp/workdir/go/src/runtime/race/testdata/chan_test.go:576 +0x91
      testing.tRunner()
          /tmp/workdir/go/src/testing/testing.go:473 +0xdc
    ==================
    --- FAIL: TestRaceChanCloseSend (0.00s)

[mikioh]

On freebsd-amd64-race builder: http://build.golang.org/log/70e1fc51b96bbac00e875f6c8ca3305dc1c39c12

[gopherbot]

CL https://golang.org/cl/18968 mentions this issue.

[rsc]

Reopening because that CL can only explain false negatives. This is a false positive.

[dvyukov]

This test sends on a closed chan. The intention is that only the race is reported but no panic happens, but in this case it actually paniced. It is a legit outcome. Again due to unexpected scheduling order.