cmd/go/internal/test: data race in (*runCache).builderRunTest

[bcmills]

from https://storage.googleapis.com/go-build-log/740b8807/windows-amd64-race_04d83703.log (CL 224038):

        ==================
        WARNING: DATA RACE
        Read at 0x00c000224be0 by goroutine 72:
          os/exec.dedupEnvCase()
              C:/workdir/go/src/os/exec/exec.go:750 +0x161
          os/exec.dedupEnv()
              C:/workdir/go/src/os/exec/exec.go:742 +0x83e
          os/exec.(*Cmd).Start()
              C:/workdir/go/src/os/exec/exec.go:425 +0x84e
          cmd/go/internal/test.(*runCache).builderRunTest()
              C:/workdir/go/src/cmd/go/internal/test/test.go:1184 +0xbaa
          cmd/go/internal/test.(*runCache).builderRunTest-fm()
              C:/workdir/go/src/cmd/go/internal/test/test.go:1067 +0x5c
          cmd/go/internal/work.(*Builder).Do.func2()
              C:/workdir/go/src/cmd/go/internal/work/exec.go:118 +0x5c4
          cmd/go/internal/work.(*Builder).Do.func3()
              C:/workdir/go/src/cmd/go/internal/work/exec.go:178 +0xb1
        
        Previous write at 0x00c000224be0 by goroutine 65:
          cmd/go/internal/base.EnvForDir()
              C:/workdir/go/src/cmd/go/internal/base/env.go:14 +0x8ee
          cmd/go/internal/test.(*runCache).builderRunTest()
              C:/workdir/go/src/cmd/go/internal/test/test.go:1160 +0x7ed
          cmd/go/internal/test.(*runCache).builderRunTest-fm()
              C:/workdir/go/src/cmd/go/internal/test/test.go:1067 +0x5c
          cmd/go/internal/work.(*Builder).Do.func2()
              C:/workdir/go/src/cmd/go/internal/work/exec.go:118 +0x5c4
          cmd/go/internal/work.(*Builder).Do.func3()
              C:/workdir/go/src/cmd/go/internal/work/exec.go:178 +0xb1
        
        Goroutine 72 (running) created at:
          cmd/go/internal/work.(*Builder).Do()
              C:/workdir/go/src/cmd/go/internal/work/exec.go:165 +0x637
          cmd/go/internal/test.runTest()
              C:/workdir/go/src/cmd/go/internal/test/test.go:785 +0x15ed
          main.main()
              C:/workdir/go/src/cmd/go/main.go:189 +0x9c6
        
        Goroutine 65 (running) created at:
          cmd/go/internal/work.(*Builder).Do()
              C:/workdir/go/src/cmd/go/internal/work/exec.go:165 +0x637
          cmd/go/internal/test.runTest()
              C:/workdir/go/src/cmd/go/internal/test/test.go:785 +0x15ed
          main.main()
              C:/workdir/go/src/cmd/go/main.go:189 +0x9c6
        ==================

This race had been masked by missing cmd/go test coverage on the -race builders (#37940).

[bcmills]

@gopherbot, please backport to Go 1.13 and 1.14. This is a data race in cmd/go, and data races can lead to arbitrary memory corruption.

[gopherbot]

Backport issue(s) opened: #38082 (for 1.13), #38083 (for 1.14).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://golang.org/wiki/MinorReleases.

[gopherbot]

Change https://golang.org/cl/225577 mentions this issue: cmd/go: do not append to the global cfg.OrigEnv slice

[gopherbot]

Change https://golang.org/cl/225578 mentions this issue: cmd/go/internal/base: rename EnvForDir to AppendPWD

[gopherbot]

Change https://golang.org/cl/225659 mentions this issue: [release-branch.go1.14] cmd/go: do not append to the global cfg.OrigEnv slice