*
* "No callbacks": Nothing to do, no callbacks on this CPU.
* "In holdoff": Nothing to do, holding off after unsuccessful attempt.
- * "Dyntick with callbacks": Callbacks remain, but RCU doesn't need CPU.
* "Begin holdoff": Attempt failed, don't retry until next jiffy.
* "More callbacks": Still more callbacks, try again to clear them out.
* "Callbacks drained": All callbacks processed, off to dyntick idle!