[PATCH v4 2/4] rcu: Add a trace event for synchronize_rcu_normal()

["Uladzislau Rezki (Sony)" <urezki@gmail.com>]

Add an rcu_sr_normal() trace event. It takes three arguments
first one is the name of RCU flavour, second one is a user id
which triggeres synchronize_rcu_normal() and last one is an
event.

There are two traces in the synchronize_rcu_normal(). On entry,
when a new request is registered and on exit point when request
is completed.

Please note, CONFIG_RCU_TRACE=y is required to activate traces.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
 include/trace/events/rcu.h | 27 +++++++++++++++++++++++++++
 kernel/rcu/tree.c          |  7 ++++++-
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 2ef9c719772a..31b3e0d3e65f 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -707,6 +707,33 @@ TRACE_EVENT_RCU(rcu_invoke_kfree_bulk_callback,
 		__entry->rcuname, __entry->p, __entry->nr_records)
 );
 
+/*
+ * Tracepoint for a normal synchronize_rcu() states. The first argument
+ * is the RCU flavor, the second argument is a pointer to rcu_head the
+ * last one is an event.
+ */
+TRACE_EVENT_RCU(rcu_sr_normal,
+
+	TP_PROTO(const char *rcuname, struct rcu_head *rhp, const char *srevent),
+
+	TP_ARGS(rcuname, rhp, srevent),
+
+	TP_STRUCT__entry(
+		__field(const char *, rcuname)
+		__field(void *, rhp)
+		__field(const char *, srevent)
+	),
+
+	TP_fast_assign(
+		__entry->rcuname = rcuname;
+		__entry->rhp = rhp;
+		__entry->srevent = srevent;
+	),
+
+	TP_printk("%s rhp=0x%p event=%s",
+		__entry->rcuname, __entry->rhp, __entry->srevent)
+);
+
 /*
  * Tracepoint for exiting rcu_do_batch after RCU callbacks have been
  * invoked.  The first argument is the name of the RCU flavor,
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index b756c40e4960..7d2ed89efcb3 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3672,9 +3672,11 @@ static void synchronize_rcu_normal(void)
 {
 	struct rcu_synchronize rs;
 
+	trace_rcu_sr_normal(rcu_state.name, &rs.head, TPS("request"));
+
 	if (!READ_ONCE(rcu_normal_wake_from_gp)) {
 		wait_rcu_gp(call_rcu_hurry);
-		return;
+		goto trace_complete_out;
 	}
 
 	init_rcu_head_on_stack(&rs.head);
@@ -3695,6 +3697,9 @@ static void synchronize_rcu_normal(void)
 	/* Now we can wait. */
 	wait_for_completion(&rs.completion);
 	destroy_rcu_head_on_stack(&rs.head);
+
+trace_complete_out:
+	trace_rcu_sr_normal(rcu_state.name, &rs.head, TPS("complete"));
 }
 
 /**
-- 
2.39.2