2 files changed, 44 insertions, 35 deletions

diff --git a/daemon/daemon_unix.go b/daemon/daemon_unix.go
index 5bb61d5fe1..4a0779b116 100644
--- a/daemon/daemon_unix.go
+++ b/daemon/daemon_unix.go
@@ -1694,51 +1694,32 @@ func setupOOMScoreAdj(score int) error {
 	return err
 }
 
-func (daemon *Daemon) initCgroupsPath(path string) error {
+func (daemon *Daemon) initCPURtController(mnt, path string) error {
 	if path == "/" || path == "." {
 		return nil
 	}
 
-	if daemon.configStore.CPURealtimePeriod == 0 && daemon.configStore.CPURealtimeRuntime == 0 {
-		return nil
-	}
-
-	if cgroups.IsCgroup2UnifiedMode() {
-		return fmt.Errorf("daemon-scoped cpu-rt-period and cpu-rt-runtime are not implemented for cgroup v2")
-	}
-
 	// Recursively create cgroup to ensure that the system and all parent cgroups have values set
 	// for the period and runtime as this limits what the children can be set to.
-	daemon.initCgroupsPath(filepath.Dir(path))
-
-	mnt, root, err := cgroups.FindCgroupMountpointAndRoot("", "cpu")
-	if err != nil {
+	if err := daemon.initCPURtController(mnt, filepath.Dir(path)); err != nil {
 		return err
 	}
-	// When docker is run inside docker, the root is based of the host cgroup.
-	// Should this be handled in runc/libcontainer/cgroups ?
-	if strings.HasPrefix(root, "/docker/") {
-		root = "/"
-	}
 
-	path = filepath.Join(mnt, root, path)
-	sysInfo := daemon.RawSysInfo(true)
-	if err := maybeCreateCPURealTimeFile(sysInfo.CPURealtime, daemon.configStore.CPURealtimePeriod, "cpu.rt_period_us", path); err != nil {
+	path = filepath.Join(mnt, path)
+	if err := os.MkdirAll(path, 0755); err != nil {
 		return err
 	}
-	return maybeCreateCPURealTimeFile(sysInfo.CPURealtime, daemon.configStore.CPURealtimeRuntime, "cpu.rt_runtime_us", path)
+	if err := maybeCreateCPURealTimeFile(daemon.configStore.CPURealtimePeriod, "cpu.rt_period_us", path); err != nil {
+		return err
+	}
+	return maybeCreateCPURealTimeFile(daemon.configStore.CPURealtimeRuntime, "cpu.rt_runtime_us", path)
 }
 
-func maybeCreateCPURealTimeFile(sysinfoPresent bool, configValue int64, file string, path string) error {
-	if sysinfoPresent && configValue != 0 {
-		if err := os.MkdirAll(path, 0755); err != nil {
-			return err
-		}
-		if err := ioutil.WriteFile(filepath.Join(path, file), []byte(strconv.FormatInt(configValue, 10)), 0700); err != nil {
-			return err
-		}
+func maybeCreateCPURealTimeFile(configValue int64, file string, path string) error {
+	if configValue == 0 {
+		return nil
 	}
-	return nil
+	return ioutil.WriteFile(filepath.Join(path, file), []byte(strconv.FormatInt(configValue, 10)), 0700)
 }
 
 func (daemon *Daemon) setupSeccompProfile() error {
diff --git a/daemon/oci_linux.go b/daemon/oci_linux.go
index da1de47470..180cd4e992 100644
--- a/daemon/oci_linux.go
+++ b/daemon/oci_linux.go
@@ -824,15 +824,32 @@ func WithCgroups(daemon *Daemon, c *container.Container) coci.SpecOpts {
 			cgroupsPath = filepath.Join(parent, c.ID)
 		}
 		s.Linux.CgroupsPath = cgroupsPath
+
+		// the rest is only needed for CPU RT controller
+
+		if daemon.configStore.CPURealtimePeriod == 0 && daemon.configStore.CPURealtimeRuntime == 0 {
+			return nil
+		}
+
+		if cgroups.IsCgroup2UnifiedMode() {
+			return errors.New("daemon-scoped cpu-rt-period and cpu-rt-runtime are not implemented for cgroup v2")
+		}
+
+		// FIXME this is very expensive way to check if cpu rt is supported
+		sysInfo := daemon.RawSysInfo(true)
+		if !sysInfo.CPURealtime {
+			return errors.New("daemon-scoped cpu-rt-period and cpu-rt-runtime are not supported by the kernel")
+		}
+
 		p := cgroupsPath
 		if useSystemd {
 			initPath, err := cgroups.GetInitCgroup("cpu")
 			if err != nil {
-				return err
+				return errors.Wrap(err, "unable to init CPU RT controller")
 			}
 			_, err = cgroups.GetOwnCgroup("cpu")
 			if err != nil {
-				return err
+				return errors.Wrap(err, "unable to init CPU RT controller")
 			}
 			p = filepath.Join(initPath, s.Linux.CgroupsPath)
 		}
@@ -843,8 +860,19 @@ func WithCgroups(daemon *Daemon, c *container.Container) coci.SpecOpts {
 			parentPath = filepath.Clean("/" + parentPath)
 		}
 
-		if err := daemon.initCgroupsPath(parentPath); err != nil {
-			return fmt.Errorf("linux init cgroups path: %v", err)
+		mnt, root, err := cgroups.FindCgroupMountpointAndRoot("", "cpu")
+		if err != nil {
+			return errors.Wrap(err, "unable to init CPU RT controller")
+		}
+		// When docker is run inside docker, the root is based of the host cgroup.
+		// Should this be handled in runc/libcontainer/cgroups ?
+		if strings.HasPrefix(root, "/docker/") {
+			root = "/"
+		}
+		mnt = filepath.Join(mnt, root)
+
+		if err := daemon.initCPURtController(mnt, parentPath); err != nil {
+			return errors.Wrap(err, "unable to init CPU RT controller")
 		}
 		return nil
 	}