[PATCH 4.19 07/18] tracing: Remove unneeded synth_event_mutex

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Masami Hiramatsu <mhiramat@kernel.org>

commit 0e2b81f7b52a1c1a8c46986f9ca01eb7b3c421f8 upstream.

Rmove unneeded synth_event_mutex. This mutex protects the reference
count in synth_event, however, those operational points are already
protected by event_mutex.

1. In __create_synth_event() and create_or_delete_synth_event(),
 those synth_event_mutex clearly obtained right after event_mutex.

2. event_hist_trigger_func() is trigger_hist_cmd.func() which is
 called by trigger_process_regex(), which is a part of
 event_trigger_regex_write() and this function takes event_mutex.

3. hist_unreg_all() is trigger_hist_cmd.unreg_all() which is called
 by event_trigger_regex_open() and it takes event_mutex.

4. onmatch_destroy() and onmatch_create() have long call tree,
 but both are finally invoked from event_trigger_regex_write()
 and event_trace_del_tracer(), former takes event_mutex, and latter
 ensures called under event_mutex locked.

Finally, I ensured there is no resource conflict. For safety,
I added lockdep_assert_held(&event_mutex) for each function.

Link: http://lkml.kernel.org/r/154140864134.17322.4796059721306031894.stgit@devbox

Reviewed-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Tested-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: George Guo <guodongtai@kylinos.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/trace/trace_events_hist.c |   30 +++++++-----------------------
 1 file changed, 7 insertions(+), 23 deletions(-)

--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -443,8 +443,6 @@ static bool have_hist_err(void)
 	return false;
 }
 
-static DEFINE_MUTEX(synth_event_mutex);
-
 struct synth_trace_event {
 	struct trace_entry	ent;
 	u64			fields[];
@@ -1097,7 +1095,6 @@ static int __create_synth_event(int argc
 		return -EINVAL;
 
 	mutex_lock(&event_mutex);
-	mutex_lock(&synth_event_mutex);
 
 	event = find_synth_event(name);
 	if (event) {
@@ -1139,7 +1136,6 @@ static int __create_synth_event(int argc
 	else
 		free_synth_event(event);
  out:
-	mutex_unlock(&synth_event_mutex);
 	mutex_unlock(&event_mutex);
 
 	return ret;
@@ -1159,7 +1155,6 @@ static int create_or_delete_synth_event(
 	/* trace_run_command() ensures argc != 0 */
 	if (name[0] == '!') {
 		mutex_lock(&event_mutex);
-		mutex_lock(&synth_event_mutex);
 		event = find_synth_event(name + 1);
 		if (event) {
 			if (event->ref)
@@ -1173,7 +1168,6 @@ static int create_or_delete_synth_event(
 			}
 		} else
 			ret = -ENOENT;
-		mutex_unlock(&synth_event_mutex);
 		mutex_unlock(&event_mutex);
 		return ret;
 	}
@@ -3660,7 +3654,7 @@ static void onmatch_destroy(struct actio
 {
 	unsigned int i;
 
-	mutex_lock(&synth_event_mutex);
+	lockdep_assert_held(&event_mutex);
 
 	kfree(data->onmatch.match_event);
 	kfree(data->onmatch.match_event_system);
@@ -3673,8 +3667,6 @@ static void onmatch_destroy(struct actio
 		data->onmatch.synth_event->ref--;
 
 	kfree(data);
-
-	mutex_unlock(&synth_event_mutex);
 }
 
 static void destroy_field_var(struct field_var *field_var)
@@ -3810,15 +3802,14 @@ static int onmatch_create(struct hist_tr
 	struct synth_event *event;
 	int ret = 0;
 
-	mutex_lock(&synth_event_mutex);
+	lockdep_assert_held(&event_mutex);
+
 	event = find_synth_event(data->onmatch.synth_event_name);
 	if (!event) {
 		hist_err("onmatch: Couldn't find synthetic event: ", data->onmatch.synth_event_name);
-		mutex_unlock(&synth_event_mutex);
 		return -EINVAL;
 	}
 	event->ref++;
-	mutex_unlock(&synth_event_mutex);
 
 	var_ref_idx = hist_data->n_var_refs;
 
@@ -3892,9 +3883,7 @@ static int onmatch_create(struct hist_tr
  out:
 	return ret;
  err:
-	mutex_lock(&synth_event_mutex);
 	event->ref--;
-	mutex_unlock(&synth_event_mutex);
 
 	goto out;
 }
@@ -5611,6 +5600,8 @@ static void hist_unreg_all(struct trace_
 	struct synth_event *se;
 	const char *se_name;
 
+	lockdep_assert_held(&event_mutex);
+
 	if (hist_file_check_refs(file))
 		return;
 
@@ -5620,12 +5611,10 @@ static void hist_unreg_all(struct trace_
 			list_del_rcu(&test->list);
 			trace_event_trigger_enable_disable(file, 0);
 
-			mutex_lock(&synth_event_mutex);
 			se_name = trace_event_name(file->event_call);
 			se = find_synth_event(se_name);
 			if (se)
 				se->ref--;
-			mutex_unlock(&synth_event_mutex);
 
 			update_cond_flag(file);
 			if (hist_data->enable_timestamps)
@@ -5651,6 +5640,8 @@ static int event_hist_trigger_func(struc
 	char *trigger, *p;
 	int ret = 0;
 
+	lockdep_assert_held(&event_mutex);
+
 	if (glob && strlen(glob)) {
 		last_cmd_set(param);
 		hist_err_clear();
@@ -5741,14 +5732,10 @@ static int event_hist_trigger_func(struc
 		}
 
 		cmd_ops->unreg(glob+1, trigger_ops, trigger_data, file);
-
-		mutex_lock(&synth_event_mutex);
 		se_name = trace_event_name(file->event_call);
 		se = find_synth_event(se_name);
 		if (se)
 			se->ref--;
-		mutex_unlock(&synth_event_mutex);
-
 		ret = 0;
 		goto out_free;
 	}
@@ -5787,13 +5774,10 @@ enable:
 	if (ret)
 		goto out_unreg;
 
-	mutex_lock(&synth_event_mutex);
 	se_name = trace_event_name(file->event_call);
 	se = find_synth_event(se_name);
 	if (se)
 		se->ref++;
-	mutex_unlock(&synth_event_mutex);
-
 	/* Just return zero, not the number of registered triggers */
 	ret = 0;
  out: