cgroups/fs2: make removeCgroupPath faster

libcontainer/cgroups/fs2/fs2.go

@@ -11,6 +11,7 @@ import (
 	"github.com/opencontainers/runc/libcontainer/cgroups"
 	"github.com/opencontainers/runc/libcontainer/configs"
 	"github.com/pkg/errors"
+	"golang.org/x/sys/unix"
 )
 
 type manager struct {
@@ -156,9 +157,22 @@ func (m *manager) Freeze(state configs.FreezerState) error {
 	return nil
 }
 
+func rmdir(path string) error {
+	err := unix.Rmdir(path)
+	if err == nil || err == unix.ENOENT {
+		return nil
+	}
+	return &os.PathError{Op: "rmdir", Path: path, Err: err}
+}
+
 // removeCgroupPath aims to remove cgroup path recursively
 // Because there may be subcgroups in it.
 func removeCgroupPath(path string) error {
+	// try the fast path first
+	if err := rmdir(path); err == nil {
+		return nil
+	}
+
 	infos, err := ioutil.ReadDir(path)
 	if err != nil {
 		if os.IsNotExist(err) {
@@ -175,10 +189,7 @@ func removeCgroupPath(path string) error {
 		}
 	}
 	if err == nil {
-		err = os.Remove(path)
-		if os.IsNotExist(err) {
-			err = nil
-		}
+		err = rmdir(path)
 	}
 	return err
 }

tests/integration/delete.bats

@@ -71,32 +71,29 @@ function teardown() {
 
   # create a sub process
   __runc exec -d test_busybox sleep 1d
-  [ "$status" -eq 0 ]
 
   # find the pid of sleep
   pid=$(__runc exec test_busybox ps -a | grep 1d | awk '{print $1}')
   [[ ${pid} =~ [0-9]+ ]]
 
   # create subcgroups
   cat <<EOF > nest.sh
+  set -e -u -x
   cd /sys/fs/cgroup
-  for f in \$(cat cgroup.controllers); do echo +\$f > cgroup.subtree_control; done
+  echo +pids > cgroup.subtree_control
   mkdir foo
   cd foo
   echo threaded > cgroup.type
   echo ${pid} > cgroup.threads
   cat cgroup.threads
 EOF
   cat nest.sh | runc exec test_busybox sh
-  [[ ${output} =~ [0-9]+ ]]
+  [ "$status" -eq 0 ]
+  [[ "$output" =~ [0-9]+ ]]
 
   # check create subcgroups success
   [ -d $CGROUP_PATH/foo ]
 
-  # check cgroup.threads' value
-  runc exec test_busybox cat /sys/fs/cgroup/foo/cgroup.threads
-  [[ ${output} =~ [0-9]+ ]]
-
   # force delete test_busybox
   runc delete --force test_busybox