rcu: Rename RCU_GP_DONE_FQS to RCU_GP_DOING_FQS

The grace-period kthread sleeps waiting to do a force-quiescent-state
scan, and when awakened sets rsp->gp_state to RCU_GP_DONE_FQS.
However, this is confusing because the kthread has not done the
force-quiescent-state, but is instead just starting to do it.  This commit
therefore renames RCU_GP_DONE_FQS to RCU_GP_DOING_FQS in order to make
things a bit easier on reviewers.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/tree.c

@@ -2088,7 +2088,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
 			rsp->gp_state = RCU_GP_WAIT_FQS;
 			ret = wait_event_interruptible_timeout(rsp->gp_wq,
 					rcu_gp_fqs_check_wake(rsp, &gf), j);
-			rsp->gp_state = RCU_GP_DONE_FQS;
+			rsp->gp_state = RCU_GP_DOING_FQS;
 			/* Locking provides needed memory barriers. */
 			/* If grace period done, leave loop. */
 			if (!READ_ONCE(rnp->qsmask) &&

kernel/rcu/tree.h

@@ -535,7 +535,7 @@ struct rcu_state {
 #define RCU_GP_WAIT_GPS  1	/* Wait for grace-period start. */
 #define RCU_GP_DONE_GPS  2	/* Wait done for grace-period start. */
 #define RCU_GP_WAIT_FQS  3	/* Wait for force-quiescent-state time. */
-#define RCU_GP_DONE_FQS  4	/* Wait done for force-quiescent-state time. */
+#define RCU_GP_DOING_FQS 4	/* Wait done for force-quiescent-state time. */
 #define RCU_GP_CLEANUP   5	/* Grace-period cleanup started. */
 #define RCU_GP_CLEANED   6	/* Grace-period cleanup complete. */