[PATCH v5 3/4] rcu: Add a trace event for synchronize_rcu_normal()

[Uladzislau Rezki (Sony)]

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) <ure...@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 1328da63c3cd..3bf6b3c5ef05 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3863,9 +3863,11 @@ 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);
@@ -3886,6 +3888,9 @@ 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