Merge pull request containers#12538 from giuseppe/fix-12535

utils: reintroduce moveToCgroup

utils/utils_supported.go

@@ -44,6 +44,15 @@ func RunUnderSystemdScope(pid int, slice string, unitName string) error {
 	ch := make(chan string)
 	_, err = conn.StartTransientUnit(unitName, "replace", properties, ch)
 	if err != nil {
+		// On errors check if the cgroup already exists, if it does move the process there
+		if props, err := conn.GetUnitTypeProperties(unitName, "Scope"); err == nil {
+			if cgroup, ok := props["ControlGroup"].(string); ok && cgroup != "" {
+				if err := moveUnderCgroup(cgroup, "", []uint32{uint32(pid)}); err == nil {
+					return nil
+				}
+				// On errors return the original error message we got from StartTransientUnit.
+			}
+		}
 		return err
 	}