skip setup signal notifier for detached container

For detached container, we don't need to setup signal notifier, because
there is no customer to consume the signals in `forward()`.

Signed-off-by: lifubang <lifubang@acmcoder.com>

Author: lifubang

signals.go

@@ -5,7 +5,6 @@ import (
 	"os/signal"
 
 	"github.com/opencontainers/runc/libcontainer"
-	"github.com/opencontainers/runc/libcontainer/system"
 	"github.com/opencontainers/runc/libcontainer/utils"
 
 	"github.com/sirupsen/logrus"
@@ -16,13 +15,7 @@ const signalBufferSize = 2048
 
 // newSignalHandler returns a signal handler for processing SIGCHLD and SIGWINCH signals
 // while still forwarding all other signals to the process.
-func newSignalHandler(enableSubreaper bool) chan *signalHandler {
-	if enableSubreaper {
-		// set us as the subreaper before registering the signal handler for the container
-		if err := system.SetSubreaper(1); err != nil {
-			logrus.Warn(err)
-		}
-	}
+func newSignalHandler() chan *signalHandler {
 	handler := make(chan *signalHandler)
 	// signal.Notify is actually quite expensive, as it has to configure the
 	// signal mask and add signal handlers for all signals (all ~65 of them).
@@ -54,13 +47,9 @@ type signalHandler struct {
 
 // forward handles the main signal event loop forwarding, resizing, or reaping depending
 // on the signal received.
-func (h *signalHandler) forward(process *libcontainer.Process, tty *tty, detach bool) (int, error) {
+func (h *signalHandler) forward(process *libcontainer.Process, tty *tty) (int, error) {
 	// make sure we know the pid of our main process so that we can return
 	// after it dies.
-	if detach {
-		return 0, nil
-	}
-
 	pid1, err := process.Pid()
 	if err != nil {
 		return -1, err

utils_linux.go

@@ -18,6 +18,7 @@ import (
 	"github.com/opencontainers/runc/libcontainer"
 	"github.com/opencontainers/runc/libcontainer/configs"
 	"github.com/opencontainers/runc/libcontainer/specconv"
+	"github.com/opencontainers/runc/libcontainer/system"
 	"github.com/opencontainers/runc/libcontainer/system/kernelversion"
 	"github.com/opencontainers/runc/libcontainer/utils"
 )
@@ -217,7 +218,10 @@ type runner struct {
 }
 
 func (r *runner) run(config *specs.Process) (int, error) {
-	var err error
+	var (
+		err       error
+		handlerCh chan *signalHandler
+	)
 	defer func() {
 		if err != nil {
 			r.destroy()
@@ -252,7 +256,15 @@ func (r *runner) run(config *specs.Process) (int, error) {
 	// Setting up IO is a two stage process. We need to modify process to deal
 	// with detaching containers, and then we get a tty after the container has
 	// started.
-	handlerCh := newSignalHandler(r.enableSubreaper)
+	if r.enableSubreaper {
+		// set us as the subreaper before registering the signal handler for the container
+		if err := system.SetSubreaper(1); err != nil {
+			logrus.Warn(err)
+		}
+	}
+	if !detach {
+		handlerCh = newSignalHandler()
+	}
 	tty, err := setupIO(process, r.container, config.Terminal, detach, r.consoleSocket)
 	if err != nil {
 		return -1, err
@@ -297,14 +309,15 @@ func (r *runner) run(config *specs.Process) (int, error) {
 			return -1, err
 		}
 	}
+	if detach {
+		return 0, nil
+	}
+	// For non-detached container, we should forward signals to the container.
 	handler := <-handlerCh
-	status, err := handler.forward(process, tty, detach)
+	status, err := handler.forward(process, tty)
 	if err != nil {
 		r.terminate(process)
 	}
-	if detach {
-		return 0, nil
-	}
 	if err == nil {
 		r.destroy()
 	}