syscall: data race in LazyDLL/LazyProc

[dvyukov]

Revision 14791. Experimental windows race detector says:

WARNING: DATA RACE
Read by goroutine 3:
  syscall.(*LazyProc).Addr()
      src/pkg/syscall/dll_windows.go:252 +0x6e
  syscall.CloseHandle()
      src/pkg/syscall/zsyscall_windows_amd64.go:302 +0x5b
  os.(*file).close()
      src/pkg/os/file_windows.go:147 +0x230
  os.(*File).Close()
      src/pkg/os/file_windows.go:136 +0x46
  debug/pe.Open()
      src/pkg/debug/pe/file.go:104 +0xe0
  debug/pe.TestOpenFailure()
      src/pkg/debug/pe/file_test.go:123 +0x4e
  testing.tRunner()
      src/pkg/testing/testing.go:301 +0x92

Previous write by goroutine 4:
  syscall.(*DLL).FindProc()
      src/pkg/syscall/dll_windows.go:85 +0x35a
  syscall.(*LazyProc).Find()
      src/pkg/syscall/dll_windows.go:230 +0x158
  syscall.(*LazyProc).mustFind()
      src/pkg/syscall/dll_windows.go:242 +0x35
  syscall.(*LazyProc).Addr()
      src/pkg/syscall/dll_windows.go:251 +0x35
  syscall.CloseHandle()
      src/pkg/syscall/zsyscall_windows_amd64.go:302 +0x5b
  os.(*file).close()
      src/pkg/os/file_windows.go:147 +0x230
  runfinq()
      src/pkg/runtime/mgc0.c:1170 +0x13d

Goroutine 3 (running) created at:
  testing.RunTests()
      src/pkg/testing/testing.go:377 +0xafb
  testing.Main()
      src/pkg/testing/testing.go:313 +0xd0
  main.main()
      _testmain.go:45 +0xdd
  runtime.main()
      src/pkg/runtime/proc.c:248 +0x94

Goroutine 4 (running) created at:
  runtime.gc()
      src/pkg/runtime/mgc0.c:961 +0x0
  os.OpenFile()
      src/pkg/os/file_windows.go:118 +0x1b7
  os.Open()
      src/pkg/os/file.go:230 +0x65
  debug/pe.Open()
      src/pkg/debug/pe/file.go:98 +0x3f
  debug/pe.TestOpenFailure()
      src/pkg/debug/pe/file_test.go:123 +0x4e

[dvyukov]

Comment 1:

Both LazyDLL and LazyProc contain unsafe double-checked locking.
I have a fix which uses atomics:
https://golang.org/cl/6817086/diff/2001/src/pkg/syscall/dll_windows.go
It's ugly. I can't figure out how to use sync.Once efficiently here. There is no
"constructor" for LazyProc, so I can't even put additional func into it...

[dvyukov]

Comment 2:

This issue was closed by revision 9b4aaa4.

Status changed to Fixed.