[PATCH v4 02/15] tracing/filters: Fix false success return in process_system_preds()

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

In process_system_preds(), "fail" was initialized to true to indicate
whether any event in the subsystem successfully applied the filter.
However, "fail = false;" was placed at the end of the event loop outside
the error check, unconditionally clearing "fail" on every iteration even
when process_preds() returned an error.

As a result, if every event in the subsystem fails to match the filter
(e.g., an invalid field), process_system_preds() returns 0 (success)
instead of -EINVAL. Consequently, create_system_filter() considers the
operation successful and silently resets the subsystem filter display to
the default global filter message instead of reporting the parse error.

Replace "fail" with "ret", clearing it to 0 only when at least one event
filter succeeds. If "ret" is still non-zero after the loop, jump to
"fail" to report FILT_ERR_BAD_SUBSYS_FILTER and fall through to
"fail_mem". In "fail_mem", free any replaced filters via
delay_free_filter() if !list_empty(&filter_list->list), or via
free_filter_list() otherwise, consolidating the cleanup paths.

Fixes: 80765597bc58 ("tracing: Rewrite filter logic to be simpler and faster")
Cc: stable@vger.kernel.org
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
Changes in v4:
 - Clean up process_system_preds() by replacing the 'fail' boolean with
   'ret' and consolidating the cleanup logic between fail and fail_mem,
   as suggested by Steven Rostedt.
---
 kernel/trace/trace_events_filter.c |   19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 28977d10e60b..b35ecb01697b 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -2337,7 +2337,7 @@ static int process_system_preds(struct trace_subsystem_dir *dir,
 	struct filter_list *filter_item;
 	struct event_filter *filter = NULL;
 	struct filter_head *filter_list;
-	bool fail = true;
+	int ret = -ENOMEM;
 	int err;
 
 	filter_list = kmalloc_obj(*filter_list);
@@ -2364,8 +2364,10 @@ static int process_system_preds(struct trace_subsystem_dir *dir,
 			filter_disable(file);
 			parse_error(pe, FILT_ERR_BAD_SUBSYS_FILTER, 0);
 			append_filter_err(tr, pe, filter);
-		} else
+		} else {
 			event_set_filtered_flag(file);
+			ret = 0;
+		}
 
 
 		filter_item = kzalloc_obj(*filter_item);
@@ -2380,11 +2382,9 @@ static int process_system_preds(struct trace_subsystem_dir *dir,
 		filter_item->filter = event_filter(file);
 		event_set_filter(file, filter);
 		filter = NULL;
-
-		fail = false;
 	}
 
-	if (fail)
+	if (ret)
 		goto fail;
 
 	/*
@@ -2396,19 +2396,18 @@ static int process_system_preds(struct trace_subsystem_dir *dir,
 	return 0;
  fail:
 	/* No call succeeded */
-	free_filter_list(filter_list);
 	parse_error(pe, FILT_ERR_BAD_SUBSYS_FILTER, 0);
-	return -EINVAL;
+	ret = -EINVAL;
  fail_mem:
 	__free_filter(filter);
 
-	/* If any call succeeded, we still need to sync */
-	if (!fail)
+	/* If any filter was replaced, we still need to sync */
+	if (!list_empty(&filter_list->list))
 		delay_free_filter(filter_list);
 	else
 		free_filter_list(filter_list);
 
-	return -ENOMEM;
+	return ret;
 }
 
 static int create_filter_start(char *filter_string, bool set_str,