Mark CGroups as off when missing essential controllers (#19176)

.changelog/19176.txt

@@ -0,0 +1,3 @@
+```release-note:improvement
+cgroupslib: Consider CGroups OFF when essential controllers are missing
+```

client/lib/cgroupslib/mount.go

@@ -9,6 +9,7 @@ import (
 	"bufio"
 	"io"
 	"os"
+	"path/filepath"
 	"strings"
 
 	"github.com/hashicorp/go-set/v2"
@@ -27,7 +28,25 @@ func detect() Mode {
 		_ = f.Close()
 	}()
 
-	return scan(f)
+	mode := scan(f)
+	if mode == CG2 && !functionalCgroups2() {
+		return OFF
+	}
+	return mode
+}
+
+func functionalCgroups2() bool {
+	const controllersFile = "cgroup.controllers"
+	requiredCgroup2Controllers := []string{"cpuset", "cpu", "io", "memory", "pids"}
+
+	controllersRootPath := filepath.Join(root, controllersFile)
+	content, err := os.ReadFile(controllersRootPath)
+	if err != nil {
+		return false
+	}
+
+	rootSubtreeControllers := set.From[string](strings.Fields(string(content)))
+	return rootSubtreeControllers.ContainsSlice(requiredCgroup2Controllers)
 }
 
 func scan(in io.Reader) Mode {