[PATCH v3 03/16] tracing/filters: Fix false success return in process_system_preds()

[Masami Hiramatsu (Google)]

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

In process_system_preds(), "fail" is 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.

Move "fail = false;" into the else branch of the error check so that
"fail" is only cleared when at least one event filter succeeds. Because
file->filter is still replaced even when process_preds() fails, check
!list_empty(&filter_list->list) on the fail and fail_mem paths so any
replaced old filters are freed after an RCU grace period via
delay_free_filter().

Fixes: 80765597bc58 ("tracing: Rewrite filter logic to be simpler and faster")
Cc: sta...@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhira...@kernel.org>
---
 kernel/trace/trace_events_filter.c |   15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/trace_events_filter.c 
b/kernel/trace/trace_events_filter.c
index f7c067a58ba4..617bc3c0bb0c 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -2354,8 +2354,10 @@ 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);
+                       fail = false;
+               }
 
 
                filter_item = kzalloc_obj(*filter_item);
@@ -2370,8 +2372,6 @@ 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)
@@ -2386,14 +2386,17 @@ static int process_system_preds(struct 
trace_subsystem_dir *dir,
        return 0;
  fail:
        /* No call succeeded */
-       free_filter_list(filter_list);
+       if (!list_empty(&filter_list->list))
+               delay_free_filter(filter_list);
+       else
+               free_filter_list(filter_list);
        parse_error(pe, FILT_ERR_BAD_SUBSYS_FILTER, 0);
        return -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);