rcu: Add sysrq rcu_node-dump capability
Life is hard if RCU manages to get stuck without triggering RCU CPU
stall warnings or triggering the rcu_check_gp_start_stall() checks
for failing to start a grace period. This commit therefore adds a
boot-time-selectable sysrq key (commandeering "y") that allows manually
dumping Tree RCU state. The new rcutree.sysrq_rcu kernel boot parameter
must be set for this sysrq to be available.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 2381506..9ceb93f 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -62,6 +62,7 @@
#include <linux/suspend.h>
#include <linux/ftrace.h>
#include <linux/tick.h>
+#include <linux/sysrq.h>
#include "tree.h"
#include "rcu.h"
@@ -115,6 +116,9 @@ int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
/* panic() on RCU Stall sysctl. */
int sysctl_panic_on_rcu_stall __read_mostly;
+/* Commandeer a sysrq key to dump RCU's tree. */
+static bool sysrq_rcu;
+module_param(sysrq_rcu, bool, 0444);
/*
* The rcu_scheduler_active variable is initialized to the value
@@ -577,6 +581,27 @@ void show_rcu_gp_kthreads(void)
}
EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);
+/* Dump grace-period-request information due to commandeered sysrq. */
+static void sysrq_show_rcu(int key)
+{
+ show_rcu_gp_kthreads();
+}
+
+static struct sysrq_key_op sysrq_rcudump_op = {
+ .handler = sysrq_show_rcu,
+ .help_msg = "show-rcu(y)",
+ .action_msg = "Show RCU tree",
+ .enable_mask = SYSRQ_ENABLE_DUMP,
+};
+
+static int __init rcu_sysrq_init(void)
+{
+ if (sysrq_rcu)
+ return register_sysrq_key('y', &sysrq_rcudump_op);
+ return 0;
+}
+early_initcall(rcu_sysrq_init);
+
/*
* Send along grace-period-related data for rcutorture diagnostics.
*/