Clean up runtime.SetFinalizer uses (#61008)

lib/client/reexec/reexec.go

@@ -99,6 +99,9 @@ func RunForkAuthenticate(ctx context.Context, params ForkAuthenticateParams) err
 		disownR.Close()
 	}()
 
+	// disownW and killR are going to stay alive until the defer or until the
+	// close after a successful start, so we can pass them to
+	// configureReexecForOS here
 	signalFd, killFd := configureReexecForOS(cmd, disownW, killR)
 	cmd.Args = append(cmd.Args, params.GetArgs(signalFd, killFd)...)
 	cmd.Args[0] = os.Args[0]

lib/client/reexec/reexec_darwin.go

@@ -33,7 +33,8 @@ func getExecutable() (string, error) {
 }
 
 // configureReexecForOS configures the command with files to inherit and
-// os-specific tweaks.
+// os-specific tweaks. The signaling files should be kept alive until the
+// command is started, then the caller should close them.
 func configureReexecForOS(cmd *exec.Cmd, signal, kill *os.File) (signalFd, killFd uint64) {
 	cmd.SysProcAttr = &syscall.SysProcAttr{
 		Setsid: true,

lib/client/reexec/reexec_linux.go

@@ -30,7 +30,8 @@ func getExecutable() (string, error) {
 }
 
 // configureReexecForOS configures the command with files to inherit and
-// os-specific tweaks.
+// os-specific tweaks. The signaling files should be kept alive until the
+// command is started, then the caller should close them.
 func configureReexecForOS(cmd *exec.Cmd, signal, kill *os.File) (signalFd, killFd uint64) {
 	cmd.SysProcAttr = &syscall.SysProcAttr{
 		Setsid: true,

lib/client/reexec/reexec_windows.go

@@ -21,7 +21,6 @@ package reexec
 import (
 	"os"
 	"os/exec"
-	"runtime"
 	"syscall"
 
 	"github.com/gravitational/trace"
@@ -34,10 +33,9 @@ func getExecutable() (string, error) {
 }
 
 // configureReexecForOS configures the command with files to inherit and
-// os-specific tweaks.
+// os-specific tweaks. The signaling files should be kept alive until the
+// command is started, then the caller should close them.
 func configureReexecForOS(cmd *exec.Cmd, signal, kill *os.File) (signalFd, killFd uint64) {
-	// Prevent handle from being closed when signal is garbage collected.
-	runtime.SetFinalizer(signal, nil)
 	cmd.SysProcAttr = &syscall.SysProcAttr{
 		AdditionalInheritedHandles: []syscall.Handle{
 			syscall.Handle(signal.Fd()),

lib/utils/fanoutbuffer/buffer.go

@@ -396,6 +396,10 @@ func (c *Cursor[T]) closeLocked() {
 	if c.closed {
 		return
 	}
+	// reset the finalizer that was set in (*Buffer).NewCursor, if it's still
+	// set - i.e. if this call is not the result of finalizeCursor but it's an
+	// explicit Close
+	runtime.SetFinalizer(c, nil)
 
 	c.closed = true
 

lib/utils/log/writer_finalizer.go

@@ -34,7 +34,7 @@ func NewWriterFinalizer[T io.WriteCloser](writer T) *WriterFinalizer[T] {
 	wr := &WriterFinalizer[T]{
 		writer: writer,
 	}
-	runtime.SetFinalizer(wr, (*WriterFinalizer[T]).Close)
+	runtime.AddCleanup(wr, func(writer T) { _ = writer.Close() }, writer)
 	return wr
 }