internal/poll: be explicit when using runtime netpoller

internal/poll package assumes that only net sockets use runtime
netpoller on windows. We get memory corruption if other file
handles are passed into runtime poller. Make FD.Init receive
and use useNetpoller argument, so FD.Init caller is explicit
about using runtime netpoller.

Fixes #21172

Change-Id: I60e2bfedf9dda9b341eb7a3e5221035db29f5739
Reviewed-on: https://go-review.googlesource.com/65810Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/internal/poll/fd_unix.go

@@ -42,6 +42,7 @@ type FD struct {
 // This can be called multiple times on a single FD.
 // The net argument is a network name from the net package (e.g., "tcp"),
 // or "file".
+// Set pollable to true if fd should be managed by runtime netpoll.
 func (fd *FD) Init(net string, pollable bool) error {
 	// We don't actually care about the various network types.
 	if net == "file" {

src/internal/poll/fd_windows.go

@@ -302,7 +302,8 @@ var logInitFD func(net string, fd *FD, err error)
 // This can be called multiple times on a single FD.
 // The net argument is a network name from the net package (e.g., "tcp"),
 // or "file" or "console" or "dir".
-func (fd *FD) Init(net string) (string, error) {
+// Set pollable to true if fd should be managed by runtime netpoll.
+func (fd *FD) Init(net string, pollable bool) (string, error) {
 	if initErr != nil {
 		return "", initErr
 	}
@@ -323,7 +324,7 @@ func (fd *FD) Init(net string) (string, error) {
 	}
 
 	var err error
-	if !fd.isFile && !fd.isConsole && !fd.isDir {
+	if pollable {
 		// Only call init for a network socket.
 		// This means that we don't add files to the runtime poller.
 		// Adding files to the runtime poller can confuse matters

src/net/fd_windows.go

@@ -52,7 +52,7 @@ func newFD(sysfd syscall.Handle, family, sotype int, net string) (*netFD, error)
 }
 
 func (fd *netFD) init() error {
-	errcall, err := fd.pfd.Init(fd.net)
+	errcall, err := fd.pfd.Init(fd.net, true)
 	if errcall != "" {
 		err = wrapSyscallError(errcall, err)
 	}

src/os/file_windows.go

@@ -54,7 +54,7 @@ func newFile(h syscall.Handle, name string, kind string) *File {
 
 	// Ignore initialization errors.
 	// Assume any problems will show up in later I/O.
-	f.pfd.Init(kind)
+	f.pfd.Init(kind, false)
 
 	return f
 }