Revert "cgroups: only return path when subsystem really mounted"

This reverts commit 606d906.

cgroups/fs/apply_raw.go

@@ -235,12 +235,6 @@ func (raw *data) parent(subsystem string) (string, error) {
 }
 
 func (raw *data) path(subsystem string) (string, error) {
-	_, err := cgroups.FindCgroupMountpoint(subsystem)
-	// If we didn't mount the subsystem, there is no point we make the path.
-	if err != nil {
-		return "", err
-	}
-
 	// If the cgroup name/path is absolute do not look relative to the cgroup of the init process.
 	if filepath.IsAbs(raw.cgroup) {
 		return filepath.Join(raw.root, subsystem, raw.cgroup), nil

cgroups/fs/blkio.go

@@ -17,12 +17,8 @@ type BlkioGroup struct {
 
 func (s *BlkioGroup) Apply(d *data) error {
 	dir, err := d.join("blkio")
-	if err != nil {
-		if cgroups.IsNotFound(err) {
-			return nil
-		} else {
-			return err
-		}
+	if err != nil && !cgroups.IsNotFound(err) {
+		return err
 	}
 
 	if err := s.Set(dir, d.c); err != nil {

cgroups/fs/cpu.go

@@ -18,11 +18,7 @@ func (s *CpuGroup) Apply(d *data) error {
 	// on a container basis
 	dir, err := d.join("cpu")
 	if err != nil {
-		if cgroups.IsNotFound(err) {
-			return nil
-		} else {
-			return err
-		}
+		return err
 	}
 
 	if err := s.Set(dir, d.c); err != nil {

cgroups/fs/devices.go

@@ -11,11 +11,7 @@ type DevicesGroup struct {
 func (s *DevicesGroup) Apply(d *data) error {
 	dir, err := d.join("devices")
 	if err != nil {
-		if cgroups.IsNotFound(err) {
-			return nil
-		} else {
-			return err
-		}
+		return err
 	}
 
 	if err := s.Set(dir, d.c); err != nil {

cgroups/fs/freezer.go

@@ -13,12 +13,8 @@ type FreezerGroup struct {
 
 func (s *FreezerGroup) Apply(d *data) error {
 	dir, err := d.join("freezer")
-	if err != nil {
-		if cgroups.IsNotFound(err) {
-			return nil
-		} else {
-			return err
-		}
+	if err != nil && !cgroups.IsNotFound(err) {
+		return err
 	}
 
 	if err := s.Set(dir, d.c); err != nil {

cgroups/fs/memory.go

@@ -16,12 +16,9 @@ type MemoryGroup struct {
 
 func (s *MemoryGroup) Apply(d *data) error {
 	dir, err := d.join("memory")
-	if err != nil {
-		if cgroups.IsNotFound(err) {
-			return nil
-		} else {
-			return err
-		}
+	// only return an error for memory if it was specified
+	if err != nil && (d.c.Memory != 0 || d.c.MemoryReservation != 0 || d.c.MemorySwap != 0) {
+		return err
 	}
 	defer func() {
 		if err != nil {