rcu: Record ->gp_state for both phases of grace-period initialization

Grace-period initialization first processes any recent CPU-hotplug
operations, and then initializes state for the new grace period.  These
two phases of initialization are currently not distinguished in debug
prints, but the distinction is valuable in a number of debug situations.
This commit therefore introduces two new values for ->gp_state,
RCU_GP_ONOFF and RCU_GP_INIT, in order to make this distinction.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/tree.c

@@ -1891,6 +1891,7 @@ static bool rcu_gp_init(struct rcu_state *rsp)
 	 * for subsequent online CPUs, and that quiescent-state forcing
 	 * will handle subsequent offline CPUs.
 	 */
+	rsp->gp_state = RCU_GP_ONOFF;
 	rcu_for_each_leaf_node(rsp, rnp) {
 		spin_lock(&rsp->ofl_lock);
 		raw_spin_lock_irq_rcu_node(rnp);
@@ -1950,6 +1951,7 @@ static bool rcu_gp_init(struct rcu_state *rsp)
 	 * The grace period cannot complete until the initialization
 	 * process finishes, because this kthread handles both.
 	 */
+	rsp->gp_state = RCU_GP_INIT;
 	rcu_for_each_node_breadth_first(rsp, rnp) {
 		rcu_gp_slow(rsp, gp_init_delay);
 		raw_spin_lock_irqsave_rcu_node(rnp, flags);

kernel/rcu/tree.h

@@ -380,16 +380,20 @@ struct rcu_state {
 #define RCU_GP_IDLE	 0	/* Initial state and no GP in progress. */
 #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_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. */
+#define RCU_GP_ONOFF     3	/* Grace-period initialization hotplug. */
+#define RCU_GP_INIT      4	/* Grace-period initialization. */
+#define RCU_GP_WAIT_FQS  5	/* Wait for force-quiescent-state time. */
+#define RCU_GP_DOING_FQS 6	/* Wait done for force-quiescent-state time. */
+#define RCU_GP_CLEANUP   7	/* Grace-period cleanup started. */
+#define RCU_GP_CLEANED   8	/* Grace-period cleanup complete. */
 
 #ifndef RCU_TREE_NONCORE
 static const char * const gp_state_names[] = {
 	"RCU_GP_IDLE",
 	"RCU_GP_WAIT_GPS",
 	"RCU_GP_DONE_GPS",
+	"RCU_GP_ONOFF",
+	"RCU_GP_INIT",
 	"RCU_GP_WAIT_FQS",
 	"RCU_GP_DOING_FQS",
 	"RCU_GP_CLEANUP",