Fix error on doulbe Kill calls

This returns a typed error for calls to Kill when the process has
already finished.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

linux/shim/exec.go

@@ -167,7 +167,10 @@ func (e *execProcess) Resize(ws console.WinSize) error {
 }
 
 func (e *execProcess) Signal(sig int) error {
-	return unix.Kill(e.pid, syscall.Signal(sig))
+	if err := unix.Kill(e.pid, syscall.Signal(sig)); err != nil {
+		return checkKillError(err)
+	}
+	return nil
 }
 
 func (e *execProcess) Stdin() io.Closer {

linux/shim/init.go

@@ -20,6 +20,7 @@ import (
 	shimapi "github.com/containerd/containerd/api/services/shim/v1"
 	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/mount"
+	"github.com/containerd/containerd/plugin"
 	"github.com/containerd/fifo"
 	runc "github.com/containerd/go-runc"
 	"github.com/pkg/errors"
@@ -234,7 +235,7 @@ func (p *initProcess) Kill(context context.Context, signal uint32, all bool) err
 	err := p.runc.Kill(context, p.id, int(signal), &runc.KillOpts{
 		All: all,
 	})
-	return p.runcError(err, "runc kill failed")
+	return checkKillError(err)
 }
 
 func (p *initProcess) killAll(context context.Context) error {
@@ -245,7 +246,7 @@ func (p *initProcess) killAll(context context.Context) error {
 }
 
 func (p *initProcess) Signal(sig int) error {
-	return unix.Kill(p.pid, syscall.Signal(sig))
+	return checkKillError(unix.Kill(p.pid, syscall.Signal(sig)))
 }
 
 func (p *initProcess) Stdin() io.Closer {
@@ -352,3 +353,13 @@ func copyFile(to, from string) error {
 	_, err = io.Copy(tt, ff)
 	return err
 }
+
+func checkKillError(err error) error {
+	if err == nil {
+		return nil
+	}
+	if strings.Contains(err.Error(), "os: process already finished") || err == unix.ESRCH {
+		return plugin.ErrProcessExited
+	}
+	return err
+}

linux/shim/service.go

@@ -274,12 +274,16 @@ func (s *Service) Kill(ctx context.Context, r *shimapi.KillRequest) (*google_pro
 		}
 		return empty, nil
 	}
-
+	if int(r.Pid) == s.initProcess.pid {
+		if err := s.initProcess.Kill(ctx, r.Signal, r.All); err != nil {
+			return nil, err
+		}
+		return empty, nil
+	}
 	pids, err := s.getContainerPids(ctx, s.initProcess.id)
 	if err != nil {
 		return nil, err
 	}
-
 	valid := false
 	for _, p := range pids {
 		if r.Pid == p {
@@ -287,15 +291,12 @@ func (s *Service) Kill(ctx context.Context, r *shimapi.KillRequest) (*google_pro
 			break
 		}
 	}
-
 	if !valid {
 		return nil, errors.Errorf("process %d does not exist in container", r.Pid)
 	}
-
 	if err := unix.Kill(int(r.Pid), syscall.Signal(r.Signal)); err != nil {
-		return nil, err
+		return nil, checkKillError(err)
 	}
-
 	return empty, nil
 }