3 files changed, 125 insertions, 4 deletions

diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 8db0cdc7f450..d49046c79c59 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -152,6 +152,25 @@ struct rcu_node {
         wait_queue_head_t boost_wq;
                                 /* Wait queue on which to park the boost */
                                 /*  kthread. */
+        unsigned long n_tasks_boosted;
+                                /* Total number of tasks boosted. */
+        unsigned long n_exp_boosts;
+                                /* Number of tasks boosted for expedited GP. */
+        unsigned long n_normal_boosts;
+                                /* Number of tasks boosted for normal GP. */
+        unsigned long n_balk_blkd_tasks;
+                                /* Refused to boost: no blocked tasks. */
+        unsigned long n_balk_exp_gp_tasks;
+                                /* Refused to boost: nothing blocking GP. */
+        unsigned long n_balk_boost_tasks;
+                                /* Refused to boost: already boosting. */
+        unsigned long n_balk_notblocked;
+                                /* Refused to boost: RCU RS CS still running. */
+        unsigned long n_balk_notyet;
+                                /* Refused to boost: not yet time. */
+        unsigned long n_balk_nos;
+                                /* Refused to boost: not sure why, though. */
+                                /*  This can happen due to race conditions. */
 #endif /* #ifdef CONFIG_RCU_BOOST */
         struct task_struct *node_kthread_task;
                                 /* kthread that takes care of this rcu_node */
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 4e486255df63..07d346445d12 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1073,6 +1073,33 @@ static void __init __rcu_init_preempt(void)
 
 #include "rtmutex_common.h"
 
+#ifdef CONFIG_RCU_TRACE
+
+static void rcu_initiate_boost_trace(struct rcu_node *rnp)
+{
+        if (list_empty(&rnp->blkd_tasks))
+                rnp->n_balk_blkd_tasks++;
+        else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
+                rnp->n_balk_exp_gp_tasks++;
+        else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
+                rnp->n_balk_boost_tasks++;
+        else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
+                rnp->n_balk_notblocked++;
+        else if (rnp->gp_tasks != NULL &&
+                 ULONG_CMP_GE(jiffies, rnp->boost_time))
+                rnp->n_balk_notyet++;
+        else
+                rnp->n_balk_nos++;
+}
+
+#else /* #ifdef CONFIG_RCU_TRACE */
+
+static void rcu_initiate_boost_trace(struct rcu_node *rnp)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_TRACE */
+
 /*
  * Carry out RCU priority boosting on the task indicated by ->exp_tasks
  * or ->boost_tasks, advancing the pointer to the next task in the
@@ -1108,10 +1135,14 @@ static int rcu_boost(struct rcu_node *rnp)
          * expedited grace period must boost all blocked tasks, including
          * those blocking the pre-existing normal grace period.
          */
-        if (rnp->exp_tasks != NULL)
+        if (rnp->exp_tasks != NULL) {
                 tb = rnp->exp_tasks;
-        else
+                rnp->n_exp_boosts++;
+        } else {
                 tb = rnp->boost_tasks;
+                rnp->n_normal_boosts++;
+        }
+        rnp->n_tasks_boosted++;
 
         /*
          * We boost task t by manufacturing an rt_mutex that appears to
@@ -1197,8 +1228,10 @@ static void rcu_initiate_boost(struct rcu_node *rnp)
 {
         struct task_struct *t;
 
-        if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL)
+        if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
+                rnp->n_balk_exp_gp_tasks++;
                 return;
+        }
         if (rnp->exp_tasks != NULL ||
             (rnp->gp_tasks != NULL &&
              rnp->boost_tasks == NULL &&
@@ -1209,7 +1242,8 @@ static void rcu_initiate_boost(struct rcu_node *rnp)
                 t = rnp->boost_kthread_task;
                 if (t != NULL)
                         wake_up_process(t);
-        }
+        } else
+                rcu_initiate_boost_trace(rnp);
 }
 
 /*
diff --git a/kernel/rcutree_trace.c b/kernel/rcutree_trace.c
index 1cedf94e2c4f..ead5736f99b5 100644
--- a/kernel/rcutree_trace.c
+++ b/kernel/rcutree_trace.c
@@ -157,6 +157,71 @@ static const struct file_operations rcudata_csv_fops = {
         .release = single_release,
 };
 
+#ifdef CONFIG_RCU_BOOST
+
+static void print_one_rcu_node_boost(struct seq_file *m, struct rcu_node *rnp)
+{
+        seq_printf(m,  "%d:%d tasks=%c%c%c%c ntb=%lu neb=%lu nnb=%lu "
+                   "j=%04x bt=%04x\n",
+                   rnp->grplo, rnp->grphi,
+                   "T."[list_empty(&rnp->blkd_tasks)],
+                   "N."[!rnp->gp_tasks],
+                   "E."[!rnp->exp_tasks],
+                   "B."[!rnp->boost_tasks],
+                   rnp->n_tasks_boosted, rnp->n_exp_boosts,
+                   rnp->n_normal_boosts,
+                   (int)(jiffies & 0xffff),
+                   (int)(rnp->boost_time & 0xffff));
+        seq_printf(m, "%s: nt=%lu egt=%lu bt=%lu nb=%lu ny=%lu nos=%lu\n",
+                   "     balk",
+                   rnp->n_balk_blkd_tasks,
+                   rnp->n_balk_exp_gp_tasks,
+                   rnp->n_balk_boost_tasks,
+                   rnp->n_balk_notblocked,
+                   rnp->n_balk_notyet,
+                   rnp->n_balk_nos);
+}
+
+static int show_rcu_node_boost(struct seq_file *m, void *unused)
+{
+        struct rcu_node *rnp;
+
+        rcu_for_each_leaf_node(&rcu_preempt_state, rnp)
+                print_one_rcu_node_boost(m, rnp);
+        return 0;
+}
+
+static int rcu_node_boost_open(struct inode *inode, struct file *file)
+{
+        return single_open(file, show_rcu_node_boost, NULL);
+}
+
+static const struct file_operations rcu_node_boost_fops = {
+        .owner = THIS_MODULE,
+        .open = rcu_node_boost_open,
+        .read = seq_read,
+        .llseek = seq_lseek,
+        .release = single_release,
+};
+
+/*
+ * Create the rcuboost debugfs entry.  Standard error return.
+ */
+static int rcu_boost_trace_create_file(struct dentry *rcudir)
+{
+        return !debugfs_create_file("rcuboost", 0444, rcudir, NULL,
+                                    &rcu_node_boost_fops);
+}
+
+#else /* #ifdef CONFIG_RCU_BOOST */
+
+static int rcu_boost_trace_create_file(struct dentry *rcudir)
+{
+        return 0;  /* There cannot be an error if we didn't create it! */
+}
+
+#endif /* #else #ifdef CONFIG_RCU_BOOST */
+
 static void print_one_rcu_state(struct seq_file *m, struct rcu_state *rsp)
 {
         unsigned long gpnum;
@@ -315,6 +380,9 @@ static int __init rcutree_trace_init(void)
         if (!retval)
                 goto free_out;
 
+        if (rcu_boost_trace_create_file(rcudir))
+                goto free_out;
+