2 files changed, 32 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index f5582dcdf80d..a1cb88d9864e 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2992,6 +2992,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         Set maximum number of finished RCU callbacks to
                         process in one batch.
 
+        rcutree.dump_tree=      [KNL]
+                        Dump the structure of the rcu_node combining tree
+                        out at early boot.  This is used for diagnostic
+                        purposes, to verify correct tree setup.
+
         rcutree.gp_cleanup_delay=       [KNL]
                         Set the number of jiffies to delay each step of
                         RCU grace-period cleanup.  This only has effect
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index b49c474e1fff..1bc14c670641 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -113,6 +113,9 @@ RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh);
 static struct rcu_state *rcu_state_p;
 LIST_HEAD(rcu_struct_flavors);
 
+/* Dump rcu_node combining tree at boot to verify correct setup. */
+static bool dump_tree;
+module_param(dump_tree, bool, 0444);
 /* Control rcu_node-tree auto-balancing at boot time. */
 static bool rcu_fanout_exact;
 module_param(rcu_fanout_exact, bool, 0444);
@@ -4144,6 +4147,28 @@ static void __init rcu_init_geometry(void)
         rcu_num_nodes -= n;
 }
 
+/*
+ * Dump out the structure of the rcu_node combining tree associated
+ * with the rcu_state structure referenced by rsp.
+ */
+static void __init rcu_dump_rcu_node_tree(struct rcu_state *rsp)
+{
+        int level = 0;
+        struct rcu_node *rnp;
+
+        pr_info("rcu_node tree layout dump\n");
+        pr_info(" ");
+        rcu_for_each_node_breadth_first(rsp, rnp) {
+                if (rnp->level != level) {
+                        pr_cont("\n");
+                        pr_info(" ");
+                        level = rnp->level;
+                }
+                pr_cont("%d:%d ^%d  ", rnp->grplo, rnp->grphi, rnp->grpnum);
+        }
+        pr_cont("\n");
+}
+
 void __init rcu_init(void)
 {
         int cpu;
@@ -4154,6 +4179,8 @@ void __init rcu_init(void)
         rcu_init_geometry();
         rcu_init_one(&rcu_bh_state, &rcu_bh_data);
         rcu_init_one(&rcu_sched_state, &rcu_sched_data);
+        if (dump_tree)
+                rcu_dump_rcu_node_tree(&rcu_sched_state);
         __rcu_init_preempt();
         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);