kubelet/kuberuntime: use sync.OnceValue

This was added to Go 1.21, and makes the code simpler.

(Best reviewed ignoring changes in amount of whitespace).

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

pkg/kubelet/kuberuntime/kuberuntime_container_linux.go

@@ -338,17 +338,11 @@ var isCgroup2UnifiedMode = func() bool {
 	return libcontainercgroups.IsCgroup2UnifiedMode()
 }
 
-var (
-	swapControllerAvailability     bool
-	swapControllerAvailabilityOnce sync.Once
-)
-
 // Note: this function variable is being added here so it would be possible to mock
 // the swap controller availability for unit tests by assigning a new function to it. Without it,
 // the swap controller availability would solely depend on the environment running the test.
-var swapControllerAvailable = func() bool {
+var swapControllerAvailable = sync.OnceValue(func() bool {
 	// See https://github.com/containerd/containerd/pull/7838/
-	swapControllerAvailabilityOnce.Do(func() {
 	const warn = "Failed to detect the availability of the swap controller, assuming not available"
 	p := "/sys/fs/cgroup/memory/memory.memsw.limit_in_bytes"
 	if isCgroup2UnifiedMode() {
@@ -356,7 +350,7 @@ var swapControllerAvailable = func() bool {
 		cm, err := libcontainercgroups.ParseCgroupFile("/proc/self/cgroup")
 		if err != nil {
 			klog.V(5).ErrorS(fmt.Errorf("failed to parse /proc/self/cgroup: %w", err), warn)
-				return
+			return false
 		}
 		// Fr cgroup v2 unified hierarchy, there are no per-controller
 		// cgroup paths, so the cm map returned by ParseCgroupFile above
@@ -368,12 +362,11 @@ var swapControllerAvailable = func() bool {
 		if !errors.Is(err, os.ErrNotExist) {
 			klog.V(5).ErrorS(err, warn)
 		}
-			return
+		return false
 	}
-		swapControllerAvailability = true
-	})
-	return swapControllerAvailability
-}
+
+	return true
+})
 
 type swapConfigurationHelper struct {
 	machineInfo cadvisorv1.MachineInfo