[PATCH tip/core/rcu 2/2] rcu: Add a trace event for kfree_rcu() use of kfree_bulk()

[paulmck]

From: "Uladzislau Rezki (Sony)" <urezki@xxxxxxxxx>

The event is given three parameters, first one is the name
of RCU flavour, second one is the number of elements in array
for free and last one is an address of the array holding
pointers to be freed by the kfree_bulk() function.

To enable the trace event your kernel has to be build with
CONFIG_RCU_TRACE=y, after that it is possible to track the
events using ftrace subsystem.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 include/trace/events/rcu.h | 28 ++++++++++++++++++++++++++++
 kernel/rcu/tree.c          |  3 +++
 2 files changed, 31 insertions(+)

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 5e49b06..49a49e6 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -624,6 +624,34 @@ TRACE_EVENT_RCU(rcu_invoke_kfree_callback,
 );
 
 /*
+ * Tracepoint for the invocation of a single RCU callback of the special
+ * kfree_bulk() form. The first argument is the RCU flavor, the second
+ * argument is a number of elements in array to free, the third is an
+ * address of the array holding nr_records entries.
+ */
+TRACE_EVENT_RCU(rcu_invoke_kfree_bulk_callback,
+
+	TP_PROTO(const char *rcuname, unsigned long nr_records, void **p),
+
+	TP_ARGS(rcuname, nr_records, p),
+
+	TP_STRUCT__entry(
+		__field(const char *, rcuname)
+		__field(unsigned long, nr_records)
+		__field(void **, p)
+	),
+
+	TP_fast_assign(
+		__entry->rcuname = rcuname;
+		__entry->nr_records = nr_records;
+		__entry->p = p;
+	),
+
+	TP_printk("%s bulk=0x%p nr_records=%lu",
+		__entry->rcuname, __entry->p, __entry->nr_records)
+);
+
+/*
  * Tracepoint for exiting rcu_do_batch after RCU callbacks have been
  * invoked.  The first argument is the name of the RCU flavor,
  * the second argument is number of callbacks actually invoked,
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 51a3aa8..909f97e 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2792,6 +2792,9 @@ static void kfree_rcu_work(struct work_struct *work)
 		debug_rcu_head_unqueue_bulk(bhead->head_free_debug);
 
 		rcu_lock_acquire(&rcu_callback_map);
+		trace_rcu_invoke_kfree_bulk_callback(rcu_state.name,
+			bhead->nr_records, bhead->records);
+
 		kfree_bulk(bhead->nr_records, bhead->records);
 		rcu_lock_release(&rcu_callback_map);
 
-- 
2.9.5