From 59d80fd8351b7b9a5dc7bbfa8bc4ca19f6ff3dad Mon Sep 17 00:00:00 2001
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date: Fri, 28 Apr 2017 10:20:28 -0700
Subject: [PATCH] rcu: Print out rcupdate.c non-default boot-time settings

This commit adds a rcupdate_announce_bootup_oddness() function to
print out non-default values of significant kernel boot parameter
settings to aid in debugging.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 include/linux/rcupdate.h |  1 +
 kernel/rcu/tree_plugin.h |  1 +
 kernel/rcu/update.c      | 42 +++++++++++++++++++++++++++++++++++++++-
 3 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index e1e5d002fdb9..393e461d3ea8 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -76,6 +76,7 @@ bool rcu_gp_is_normal(void);     /* Internal RCU use. */
 bool rcu_gp_is_expedited(void);  /* Internal RCU use. */
 void rcu_expedite_gp(void);
 void rcu_unexpedite_gp(void);
+void rcupdate_announce_bootup_oddness(void);
 #endif /* #else #ifdef CONFIG_TINY_RCU */
 
 enum rcutorture_type {
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 3b432fa4c45b..eb5ebdce25ff 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -92,6 +92,7 @@ static void __init rcu_bootup_announce_oddness(void)
 		pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
 	if (IS_ENABLED(CONFIG_RCU_BOOST))
 		pr_info("\tRCU kthread priority: %d.\n", kthread_prio);
+	rcupdate_announce_bootup_oddness();
 }
 
 #ifdef CONFIG_PREEMPT_RCU
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 273e869ca21d..82a5aa10dbc5 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -560,7 +560,8 @@ static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock);
 DEFINE_SRCU(tasks_rcu_exit_srcu);
 
 /* Control stall timeouts.  Disable with <= 0, otherwise jiffies till stall. */
-static int rcu_task_stall_timeout __read_mostly = HZ * 60 * 10;
+#define RCU_TASK_STALL_TIMEOUT (HZ * 60 * 10)
+static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT;
 module_param(rcu_task_stall_timeout, int, 0644);
 
 static void rcu_spawn_tasks_kthread(void);
@@ -851,6 +852,23 @@ static void rcu_spawn_tasks_kthread(void)
 
 #endif /* #ifdef CONFIG_TASKS_RCU */
 
+#ifndef CONFIG_TINY_RCU
+
+/*
+ * Print any non-default Tasks RCU settings.
+ */
+static void __init rcu_tasks_bootup_oddness(void)
+{
+#ifdef CONFIG_TASKS_RCU
+	if (rcu_task_stall_timeout != RCU_TASK_STALL_TIMEOUT)
+		pr_info("\tTasks-RCU CPU stall warnings timeout set to %d (rcu_task_stall_timeout).\n", rcu_task_stall_timeout);
+	else
+		pr_info("\tTasks RCU enabled.\n");
+#endif /* #ifdef CONFIG_TASKS_RCU */
+}
+
+#endif /* #ifndef CONFIG_TINY_RCU */
+
 #ifdef CONFIG_PROVE_RCU
 
 /*
@@ -935,3 +953,25 @@ late_initcall(rcu_verify_early_boot_tests);
 #else
 void rcu_early_boot_tests(void) {}
 #endif /* CONFIG_PROVE_RCU */
+
+#ifndef CONFIG_TINY_RCU
+
+/*
+ * Print any significant non-default boot-time settings.
+ */
+void __init rcupdate_announce_bootup_oddness(void)
+{
+	if (rcu_normal)
+		pr_info("\tNo expedited grace period (rcu_normal).\n");
+	else if (rcu_normal_after_boot)
+		pr_info("\tNo expedited grace period (rcu_normal_after_boot).\n");
+	else if (rcu_expedited)
+		pr_info("\tAll grace periods are expedited (rcu_expedited).\n");
+	if (rcu_cpu_stall_suppress)
+		pr_info("\tRCU CPU stall warnings suppressed (rcu_cpu_stall_suppress).\n");
+	if (rcu_cpu_stall_timeout != CONFIG_RCU_CPU_STALL_TIMEOUT)
+		pr_info("\tRCU CPU stall warnings timeout set to %d (rcu_cpu_stall_timeout).\n", rcu_cpu_stall_timeout);
+	rcu_tasks_bootup_oddness();
+}
+
+#endif /* #ifndef CONFIG_TINY_RCU */