rcu: Convert rcu_check_gp_kthread_starvation() to GP sequence number

This commit switches rcu_check_gp_kthread_starvation() from printing
->gpnum and ->completed to printing ->gp_seq upon detecting a starving
RCU grace-period kthread during an RCU CPU stall warning.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/tree.c

@@ -1276,9 +1276,9 @@ static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
 	j = jiffies;
 	gpa = READ_ONCE(rsp->gp_activity);
 	if (j - gpa > 2 * HZ) {
-		pr_err("%s kthread starved for %ld jiffies! g%lu c%lu f%#x %s(%d) ->state=%#lx ->cpu=%d\n",
+		pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n",
 		       rsp->name, j - gpa,
-		       rsp->gpnum, rsp->completed,
+		       (long)rcu_seq_current(&rsp->gp_seq),
 		       rsp->gp_flags,
 		       gp_state_getname(rsp->gp_state), rsp->gp_state,
 		       rsp->gp_kthread ? rsp->gp_kthread->state : ~0,