[PATCH] tracing: Drop the synthetic event ref when clearing hist triggers

[David Carlier <devnexen@gmail.com>]

clear_event_triggers() frees a hist trigger on a synthetic event without
dropping the se->ref taken by event_hist_trigger_parse(). Removing an
instance with such a trigger leaves the synthetic event busy forever.

Fixes: 4b147936fa50 ("tracing: Add support for 'synthetic' events")
Cc: stable@vger.kernel.org
Signed-off-by: David Carlier <devnexen@gmail.com>
---
Applies on trace/for-next, depends on 3403d9bb27eb ("tracing/histograms: Verify event_call identity when updating synth_event refcount").
 kernel/trace/trace.h                |  2 ++
 kernel/trace/trace_events_hist.c    | 20 +++++++++++++-------
 kernel/trace/trace_events_trigger.c |  2 ++
 3 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 0f0786700f99..e108f95fd609 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1915,9 +1915,11 @@ extern const struct file_operations event_inject_fops;
 #ifdef CONFIG_HIST_TRIGGERS
 extern int register_trigger_hist_cmd(void);
 extern int register_trigger_hist_enable_disable_cmds(void);
+extern void hist_put_synth_event(struct trace_event_file *file);
 #else
 static inline int register_trigger_hist_cmd(void) { return 0; }
 static inline int register_trigger_hist_enable_disable_cmds(void) { return 0; }
+static inline void hist_put_synth_event(struct trace_event_file *file) { }
 #endif
 
 extern int register_trigger_cmds(void);
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index f39fa8942673..9419edfd1b67 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -6756,6 +6756,17 @@ static bool hist_trigger_check_refs(struct event_trigger_data *data,
 	return false;
 }
 
+void hist_put_synth_event(struct trace_event_file *file)
+{
+	struct synth_event *se;
+
+	lockdep_assert_held(&event_mutex);
+
+	se = find_synth_event_call(file->event_call);
+	if (se)
+		se->ref--;
+}
+
 static void hist_unregister_trigger(char *glob,
 				    struct event_trigger_data *data,
 				    struct trace_event_file *file)
@@ -6811,7 +6822,6 @@ static void hist_unreg_all(struct trace_event_file *file)
 {
 	struct event_trigger_data *test, *n;
 	struct hist_trigger_data *hist_data;
-	struct synth_event *se;
 
 	lockdep_assert_held(&event_mutex);
 
@@ -6824,9 +6834,7 @@ static void hist_unreg_all(struct trace_event_file *file)
 			list_del_rcu(&test->list);
 			trace_event_trigger_enable_disable(file, 0);
 
-			se = find_synth_event_call(file->event_call);
-			if (se)
-				se->ref--;
+			hist_put_synth_event(file);
 
 			update_cond_flag(file);
 			if (hist_data->enable_timestamps)
@@ -6941,9 +6949,7 @@ static int event_hist_trigger_parse(struct event_command *cmd_ops,
 		}
 
 		event_trigger_unregister(cmd_ops, file, glob+1, trigger_data);
-		se = find_synth_event_call(file->event_call);
-		if (se)
-			se->ref--;
+		hist_put_synth_event(file);
 		ret = 0;
 		goto out_free;
 	}
diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index 4d2fde996c0f..a2487ad7fef8 100644
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c
@@ -643,6 +643,8 @@ clear_event_triggers(struct trace_array *tr)
 		list_for_each_entry_safe(data, n, &file->triggers, list) {
 			trace_event_trigger_enable_disable(file, 0);
 			list_del_rcu(&data->list);
+			if (data->cmd_ops->trigger_type == ETT_EVENT_HIST)
+				hist_put_synth_event(file);
 			if (data->cmd_ops->free)
 				data->cmd_ops->free(data);
 		}
-- 
2.55.0