rcu: Additional information on RCU-tasks stall-warning messages

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

kernel/rcu/update.c

@@ -48,6 +48,7 @@
 #include <linux/delay.h>
 #include <linux/module.h>
 #include <linux/kthread.h>
+#include <linux/tick.h>
 
 #define CREATE_TRACE_POINTS
 
@@ -461,6 +462,8 @@ EXPORT_SYMBOL_GPL(rcu_barrier_tasks);
 static void check_holdout_task(struct task_struct *t,
 			       bool needreport, bool *firstreport)
 {
+	int cpu;
+
 	if (!ACCESS_ONCE(t->rcu_tasks_holdout) ||
 	    t->rcu_tasks_nvcsw != ACCESS_ONCE(t->nvcsw) ||
 	    !ACCESS_ONCE(t->on_rq) ||
@@ -477,6 +480,12 @@ static void check_holdout_task(struct task_struct *t,
 		pr_err("INFO: rcu_tasks detected stalls on tasks:\n");
 		*firstreport = false;
 	}
+	cpu = task_cpu(t);
+	pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n",
+		 t, ".I"[is_idle_task(t)],
+		 "N."[cpu < 0 || !tick_nohz_full_cpu(cpu)],
+		 t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout,
+		 t->rcu_tasks_idle_cpu, cpu);
 	sched_show_task(t);
 }