rcu: Rename ->onofflock to ->orphan_lock

The ->onofflock field in the rcu_state structure at one time synchronized
CPU-hotplug operations for RCU.  However, its scope has decreased over time
so that it now only protects the lists of orphaned RCU callbacks.  This
commit therefore renames it to ->orphan_lock to reflect its current use.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index a240f03..a7c945d 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -383,9 +383,8 @@
 
 	/* End of fields guarded by root rcu_node's lock. */
 
-	raw_spinlock_t onofflock ____cacheline_internodealigned_in_smp;
-						/* exclude on/offline and */
-						/*  starting new GP. */
+	raw_spinlock_t orphan_lock ____cacheline_internodealigned_in_smp;
+						/* Protect following fields. */
 	struct rcu_head *orphan_nxtlist;	/* Orphaned callbacks that */
 						/*  need a grace period. */
 	struct rcu_head **orphan_nxttail;	/* Tail of above. */
@@ -394,7 +393,7 @@
 	struct rcu_head **orphan_donetail;	/* Tail of above. */
 	long qlen_lazy;				/* Number of lazy callbacks. */
 	long qlen;				/* Total number of callbacks. */
-	/* End of fields guarded by onofflock. */
+	/* End of fields guarded by orphan_lock. */
 
 	struct mutex onoff_mutex;		/* Coordinate hotplug & GPs. */