tracing: Switch trace_stat.c code over to use guard()

There are a couple functions in trace_stat.c that have "goto out" or
equivalent on error in order to release locks that were taken. This can be
error prone or just simply make the code more complex.

Switch every location that ends with unlocking a mutex on error over to
using the guard(mutex)() infrastructure to let the compiler worry about
releasing locks. This makes the code easier to read and understand.

Cc: Masami Hiramatsu <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Steven Rostedt (Google) <[email protected]>

Author: rostedt

kernel/trace/trace_stat.c

@@ -128,19 +128,19 @@ static int stat_seq_init(struct stat_session *session)
 	int ret = 0;
 	int i;
 
-	mutex_lock(&session->stat_mutex);
+	guard(mutex)(&session->stat_mutex);
 	__reset_stat_session(session);
 
 	if (!ts->stat_cmp)
 		ts->stat_cmp = dummy_cmp;
 
 	stat = ts->stat_start(ts);
 	if (!stat)
-		goto exit;
+		return 0;
 
 	ret = insert_stat(root, stat, ts->stat_cmp);
 	if (ret)
-		goto exit;
+		return ret;
 
 	/*
 	 * Iterate over the tracer stat entries and store them in an rbtree.
@@ -157,13 +157,10 @@ static int stat_seq_init(struct stat_session *session)
 			goto exit_free_rbtree;
 	}
 
-exit:
-	mutex_unlock(&session->stat_mutex);
 	return ret;
 
 exit_free_rbtree:
 	__reset_stat_session(session);
-	mutex_unlock(&session->stat_mutex);
 	return ret;
 }
 
@@ -308,26 +305,26 @@ static int init_stat_file(struct stat_session *session)
 int register_stat_tracer(struct tracer_stat *trace)
 {
 	struct stat_session *session, *node;
-	int ret = -EINVAL;
+	int ret;
 
 	if (!trace)
 		return -EINVAL;
 
 	if (!trace->stat_start || !trace->stat_next || !trace->stat_show)
 		return -EINVAL;
 
+	guard(mutex)(&all_stat_sessions_mutex);
+
 	/* Already registered? */
-	mutex_lock(&all_stat_sessions_mutex);
 	list_for_each_entry(node, &all_stat_sessions, session_list) {
 		if (node->ts == trace)
-			goto out;
+			return -EINVAL;
 	}
 
-	ret = -ENOMEM;
 	/* Init the session */
 	session = kzalloc(sizeof(*session), GFP_KERNEL);
 	if (!session)
-		goto out;
+		return -ENOMEM;
 
 	session->ts = trace;
 	INIT_LIST_HEAD(&session->session_list);
@@ -336,16 +333,13 @@ int register_stat_tracer(struct tracer_stat *trace)
 	ret = init_stat_file(session);
 	if (ret) {
 		destroy_session(session);
-		goto out;
+		return ret;
 	}
 
-	ret = 0;
 	/* Register */
 	list_add_tail(&session->session_list, &all_stat_sessions);
- out:
-	mutex_unlock(&all_stat_sessions_mutex);
 
-	return ret;
+	return 0;
 }
 
 void unregister_stat_tracer(struct tracer_stat *trace)