rcu-tasks: Make show_rcu_tasks_generic_gp_kthread() check all CPUs

Currently, the show_rcu_tasks_generic_gp_kthread() function only looks
at CPU 0's callback lists.  Although this is not fatal, it can confuse
debugging efforts in cases where any of the Tasks RCU flavors are in
per-CPU queueing mode.  This commit therefore causes this function to
scan all CPUs' callback queues.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/tasks.h

@@ -582,7 +582,17 @@ static void __init rcu_tasks_bootup_oddness(void)
 /* Dump out rcutorture-relevant state common to all RCU-tasks flavors. */
 static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s)
 {
-	struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, 0); // for_each...
+	int cpu;
+	bool havecbs = false;
+
+	for_each_possible_cpu(cpu) {
+		struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
+
+		if (!data_race(rcu_segcblist_empty(&rtpcp->cblist))) {
+			havecbs = true;
+			break;
+		}
+	}
 	pr_info("%s: %s(%d) since %lu g:%lu i:%lu/%lu %c%c %s\n",
 		rtp->kname,
 		tasks_gp_state_getname(rtp), data_race(rtp->gp_state),
@@ -590,7 +600,7 @@ static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s)
 		data_race(rcu_seq_current(&rtp->tasks_gp_seq)),
 		data_race(rtp->n_ipis_fails), data_race(rtp->n_ipis),
 		".k"[!!data_race(rtp->kthread_ptr)],
-		".C"[!data_race(rcu_segcblist_empty(&rtpcp->cblist))],
+		".C"[havecbs],
 		s);
 }
 #endif // #ifndef CONFIG_TINY_RCU