[ltt-dev] [UST commit] TRACEPOINT_EVENT: standardize locking wrt tracepoints and markers

[Mathieu Desnoyers]

commit c72922954e8622cea2d1b8338bb286c15c0b1104
Author: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
Date:   Fri May 20 13:22:08 2011 -0400

    TRACEPOINT_EVENT: standardize locking wrt tracepoints and markers
    
    Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>

diff --git a/include/ust/tracepoint-internal.h b/include/ust/tracepoint-internal.h
index 6b159b4..83ea68d 100644
--- a/include/ust/tracepoint-internal.h
+++ b/include/ust/tracepoint-internal.h
@@ -62,9 +62,6 @@ static inline void tracepoint_synchronize_unregister(void)
 	synchronize_rcu();
 }
 
-extern void lock_trace_events(void);
-extern void unlock_trace_events(void);
-
 struct trace_event_iter {
 	struct trace_event_lib *lib;
 	struct trace_event * const *trace_event;
@@ -72,12 +69,9 @@ struct trace_event_iter {
 
 extern void trace_event_iter_start(struct trace_event_iter *iter);
 extern void trace_event_iter_next(struct trace_event_iter *iter);
+extern void trace_event_iter_stop(struct trace_event_iter *iter);
 extern void trace_event_iter_reset(struct trace_event_iter *iter);
 
-extern int trace_event_get_iter_range(struct trace_event * const **trace_event,
-				      struct trace_event * const *begin,
-				      struct trace_event * const *end);
-
 extern void trace_event_update_process(void);
 extern int is_trace_event_enabled(const char *channel, const char *name);
 
diff --git a/libust/trace_event.c b/libust/trace_event.c
index 6b30b68..854a767 100644
--- a/libust/trace_event.c
+++ b/libust/trace_event.c
@@ -29,20 +29,33 @@
 
 /* libraries that contain trace_events (struct trace_event_lib) */
 static CDS_LIST_HEAD(libs);
-
+/*
+ * Nested mutex is not required here, but provide the same guaranteed
+ * for start/stop iteration vs nested ops as markers and tracepoints.
+ */
+static __thread int nested_mutex;
 static DEFINE_MUTEX(trace_events_mutex);
 
+static
+int trace_event_get_iter_range(struct trace_event * const **trace_event,
+	struct trace_event * const *begin,
+	struct trace_event * const *end);
+
+static
 void lock_trace_events(void)
 {
-	pthread_mutex_lock(&trace_events_mutex);
+	if (!(nested_mutex++))
+		pthread_mutex_lock(&trace_events_mutex);
 }
 
+static
 void unlock_trace_events(void)
 {
-	pthread_mutex_unlock(&trace_events_mutex);
+	if (!(--nested_mutex))
+		pthread_mutex_unlock(&trace_events_mutex);
 }
 
-
+static
 int lib_get_iter_trace_events(struct trace_event_iter *iter)
 {
 	struct trace_event_lib *iter_lib;
@@ -72,7 +85,9 @@ int lib_get_iter_trace_events(struct trace_event_iter *iter)
  *
  * Returns whether a next trace_event has been found (1) or not (0).
  * Will return the first trace_event in the range if the input trace_event is NULL.
+ * Called with trace event mutex held.
  */
+static
 int trace_event_get_iter_range(struct trace_event * const **trace_event,
 	struct trace_event * const *begin,
 	struct trace_event * const *end)
@@ -100,9 +115,13 @@ static void trace_event_get_iter(struct trace_event_iter *iter)
 
 void trace_event_iter_start(struct trace_event_iter *iter)
 {
+	lock_trace_events();
 	trace_event_get_iter(iter);
 }
 
+/*
+ * Called with trace event mutex held.
+ */
 void trace_event_iter_next(struct trace_event_iter *iter)
 {
 	iter->trace_event++;
@@ -114,6 +133,11 @@ void trace_event_iter_next(struct trace_event_iter *iter)
 	trace_event_get_iter(iter);
 }
 
+void trace_event_iter_stop(struct trace_event_iter *iter)
+{
+	unlock_trace_events();
+}
+
 void trace_event_iter_reset(struct trace_event_iter *iter)
 {
 	iter->lib = NULL;
@@ -130,8 +154,7 @@ int trace_event_register_lib(struct trace_event * const *trace_events_start,
 	pl->trace_events_start = trace_events_start;
 	pl->trace_events_count = trace_events_count;
 
-	/* FIXME: maybe protect this with its own mutex? */
-	pthread_mutex_lock(&trace_events_mutex);
+	lock_trace_events();
 	/*
 	 * We sort the libs by struct lib pointer address.
 	 */
@@ -146,7 +169,7 @@ int trace_event_register_lib(struct trace_event * const *trace_events_start,
 	/* We should be added at the head of the list */
 	cds_list_add(&pl->list, &libs);
 lib_added:
-	pthread_mutex_unlock(&trace_events_mutex);
+	unlock_trace_events();
 
 	/* trace_events_count - 1: skip dummy */
 	DBG("just registered a trace_events section from %p and having %d trace_events (minus dummy trace_event)", trace_events_start, trace_events_count);
@@ -158,8 +181,7 @@ int trace_event_unregister_lib(struct trace_event * const *trace_events_start)
 {
 	struct trace_event_lib *lib;
 
-	pthread_mutex_lock(&trace_events_mutex);
-
+	unlock_trace_events();
 	cds_list_for_each_entry(lib, &libs, list) {
 		if(lib->trace_events_start == trace_events_start) {
 			struct trace_event_lib *lib2free = lib;
@@ -168,8 +190,7 @@ int trace_event_unregister_lib(struct trace_event * const *trace_events_start)
 			break;
 		}
 	}
-
-	pthread_mutex_unlock(&trace_events_mutex);
+	unlock_trace_events();
 
 	return 0;
 }
diff --git a/libust/tracectl.c b/libust/tracectl.c
index ef7184f..771e4e1 100644
--- a/libust/tracectl.c
+++ b/libust/tracectl.c
@@ -126,7 +126,6 @@ static void print_trace_events(FILE *fp)
 {
 	struct trace_event_iter iter;
 
-	lock_trace_events();
 	trace_event_iter_reset(&iter);
 	trace_event_iter_start(&iter);
 
@@ -134,7 +133,7 @@ static void print_trace_events(FILE *fp)
 		fprintf(fp, "trace_event: %s\n", (*iter.trace_event)->name);
 		trace_event_iter_next(&iter);
 	}
-	unlock_trace_events();
+	trace_event_iter_stop(&iter);
 }
 
 static int connect_ustconsumer(void)

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com