util: vircgroupv2: enable CPU controller only if it's available

It might happen that we are not able to enable CPU controller so we
can enable it for thread sub-cgroups only if it's available in parent
cgroup.
Signed-off-by: NPavel Hrdina <phrdina@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/util/vircgroupv2.c

@@ -404,7 +404,8 @@ virCgroupV2MakeGroup(virCgroupPtr parent ATTRIBUTE_UNUSED,
                 return -1;
             }
 
-            if (virCgroupV2EnableController(parent,
+            if (virCgroupV2HasController(parent, VIR_CGROUP_CONTROLLER_CPU) &&
+                virCgroupV2EnableController(parent,
                                             VIR_CGROUP_CONTROLLER_CPU) < 0) {
                 return -1;
             }