os/exec: TestStdinCloseRace flake on freebsd-amd64

[mvdan]

freebsd-amd64-110 at bf7bd9f767bba4647b1c67b8bcb1e163351adb84

[...]

##### Testing race detector
ok  	runtime/race	10.602s
ok  	flag	1.102s
ok  	os	1.035s
ok  	os/exec	3.167s
PASS
scatter = 0x5f1110
hello from C
sqrt is: 0
ok  	_/tmp/workdir/go/misc/cgo/test	5.195s
ok  	flag	1.017s
==================
WARNING: DATA RACE
Write at 0x00c4200844c0 by goroutine 11:
  internal/poll.(*FD).destroy()
      /tmp/workdir/go/src/internal/poll/fd_unix.go:63 +0xa4
  internal/poll.(*FD).decref()
      /tmp/workdir/go/src/internal/poll/fd_mutex.go:211 +0x55
  internal/poll.(*FD).Close()
      /tmp/workdir/go/src/internal/poll/fd_unix.go:81 +0xf5
  os.(*file).close()
      /tmp/workdir/go/src/os/file_unix.go:201 +0x45
  os.(*File).Close()
      /tmp/workdir/go/src/os/file_unix.go:193 +0x52
  os/exec.(*closeOnce).close()
      /tmp/workdir/go/src/os/exec/exec.go:547 +0x4d
  os/exec.(*closeOnce).(os/exec.close)-fm()
      /tmp/workdir/go/src/os/exec/exec.go:542 +0x41
  sync.(*Once).Do()
      /tmp/workdir/go/src/sync/once.go:44 +0xe1
  os/exec.(*closeOnce).Close()
      /tmp/workdir/go/src/os/exec/exec.go:542 +0x81
  os/exec.(*Cmd).closeDescriptors()
      /tmp/workdir/go/src/os/exec/exec.go:273 +0x5c
  os/exec.(*Cmd).Wait()
      /tmp/workdir/go/src/os/exec/exec.go:459 +0x295
  os/exec_test.TestStdinCloseRace()
      /tmp/workdir/go/src/os/exec/exec_test.go:285 +0x264
  testing.tRunner()
      /tmp/workdir/go/src/testing/testing.go:748 +0x169

Previous read at 0x00c4200844c0 by goroutine 13:
  os.epipecheck()
      /tmp/workdir/go/src/os/file_unix.go:133 +0xa8
  os.(*File).Write()
      /tmp/workdir/go/src/os/file.go:148 +0xf2
  os.(*File).WriteString()
      /tmp/workdir/go/src/os/file.go:204 +0x7b
  os/exec.(*closeOnce).WriteString()
      <autogenerated>:1 +0x6e
  io.WriteString()
      /tmp/workdir/go/src/io/io.go:291 +0x83
  strings.(*Reader).WriteTo()
      /tmp/workdir/go/src/strings/reader.go:133 +0x144
  io.copyBuffer()
      /tmp/workdir/go/src/io/io.go:431 +0x3bd
  io.Copy()
      /tmp/workdir/go/src/io/io.go:411 +0x74
  os/exec_test.TestStdinCloseRace.func2()
      /tmp/workdir/go/src/os/exec/exec_test.go:280 +0xf5

Goroutine 11 (running) created at:
  testing.(*T).Run()
      /tmp/workdir/go/src/testing/testing.go:791 +0x535
  testing.runTests.func1()
      /tmp/workdir/go/src/testing/testing.go:1015 +0xa4
  testing.tRunner()
      /tmp/workdir/go/src/testing/testing.go:748 +0x169
  testing.runTests()
      /tmp/workdir/go/src/testing/testing.go:1013 +0x4bf
  testing.(*M).Run()
      /tmp/workdir/go/src/testing/testing.go:933 +0x270
  main.main()
      os/exec/_test/_testmain.go:98 +0x228

Goroutine 13 (running) created at:
  os/exec_test.TestStdinCloseRace()
      /tmp/workdir/go/src/os/exec/exec_test.go:274 +0x256
  testing.tRunner()
      /tmp/workdir/go/src/testing/testing.go:748 +0x169
==================
--- FAIL: TestStdinCloseRace (0.00s)
	testing.go:701: race detected during execution of test
FAIL
FAIL	os/exec	2.070s

/cc @ianlancetaylor since this smells a lot like the recent 8cb2952

[kardianos]

Another instance of this failure:
https://storage.googleapis.com/go-build-log/d37ac330/freebsd-amd64-110_2591781a.log

[gopherbot]

Change https://golang.org/cl/65750 mentions this issue: os: don't refer directly to Sysfd in epipecheck