Do not wait for container on stop if the process doesn't exist.

This fixes an issue that caused the client to hang forever if the
process died before the code arrived to exit the `Kill` function.

Signed-off-by: David Calavera <david.calavera@gmail.com>

daemon/container_operations_unix.go

@@ -1099,7 +1099,9 @@ func killProcessDirectly(container *container.Container) error {
 				if err != syscall.ESRCH {
 					return err
 				}
-				logrus.Debugf("Cannot kill process (pid=%d) with signal 9: no such process.", pid)
+				e := errNoSuchProcess{pid, 9}
+				logrus.Debug(e)
+				return e
 			}
 		}
 	}

daemon/kill.go

@@ -11,6 +11,22 @@ import (
 	"github.com/docker/docker/pkg/signal"
 )
 
+type errNoSuchProcess struct {
+	pid    int
+	signal int
+}
+
+func (e errNoSuchProcess) Error() string {
+	return fmt.Sprintf("Cannot kill process (pid=%d) with signal %d: no such process.", e.pid, e.signal)
+}
+
+// isErrNoSuchProcess returns true if the error
+// is an instance of errNoSuchProcess.
+func isErrNoSuchProcess(err error) bool {
+	_, ok := err.(errNoSuchProcess)
+	return ok
+}
+
 // ContainerKill send signal to the container
 // If no signal is given (sig 0), then Kill with SIGKILL and wait
 // for the container to exit.
@@ -89,6 +105,9 @@ func (daemon *Daemon) Kill(container *container.Container) error {
 		// So, instead we'll give it up to 2 more seconds to complete and if
 		// by that time the container is still running, then the error
 		// we got is probably valid and so we return it to the caller.
+		if isErrNoSuchProcess(err) {
+			return nil
+		}
 
 		if container.IsRunning() {
 			container.WaitStop(2 * time.Second)
@@ -100,6 +119,9 @@ func (daemon *Daemon) Kill(container *container.Container) error {
 
 	// 2. Wait for the process to die, in last resort, try to kill the process directly
 	if err := killProcessDirectly(container); err != nil {
+		if isErrNoSuchProcess(err) {
+			return nil
+		}
 		return err
 	}
 
@@ -111,8 +133,9 @@ func (daemon *Daemon) Kill(container *container.Container) error {
 func (daemon *Daemon) killPossiblyDeadProcess(container *container.Container, sig int) error {
 	err := daemon.killWithSignal(container, sig)
 	if err == syscall.ESRCH {
-		logrus.Debugf("Cannot kill process (pid=%d) with signal %d: no such process.", container.GetPID(), sig)
-		return nil
+		e := errNoSuchProcess{container.GetPID(), sig}
+		logrus.Debug(e)
+		return e
 	}
 	return err
 }