rcu: Enable diagnostic dump of rcu_node combining tree

The purpose of this commit is to make it easier to verify that RCU's
combining tree is set up correctly, which is useful to have when making
changes in how that tree is initialized.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>
[ paulmck: Fold fix found by Fengguang's 0-day test robot. ]

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index f5582dcdf80d56c25816ec133280965b47ba7525..a1cb88d9864e42ace694c70549df35b6ee4ff5db 100644 (file)
--- 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 b49c474e1fffa1cc0b08a815147b2fa6f1f2c8f7..1bc14c670641498b91a7419f81ea4c96f4d9e919 100644 (file)
--- 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);