tracing: Restore system filter behavior

Though not all events have field 'prev_pid', it was allowed to do this:

  # echo 'prev_pid == 100' > events/sched/filter

but commit 75b8e98263fdb0bfbdeba60d4db463259f1fe8a2 (tracing/filter: Swap
entire filter of events) broke it without any reason.

Link: http://lkml.kernel.org/r/4EAF46CF.8040408@cn.fujitsu.com

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index d6e7926dcd26..95dc31efd6dd 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1649,7 +1649,9 @@ static int replace_system_preds(struct event_subsystem *system,
                  */
                 err = replace_preds(call, NULL, ps, filter_string, true);
                 if (err)
-                        goto fail;
+                        call->flags |= TRACE_EVENT_FL_NO_SET_FILTER;
+                else
+                        call->flags &= ~TRACE_EVENT_FL_NO_SET_FILTER;
         }
 
         list_for_each_entry(call, &ftrace_events, list) {
@@ -1658,6 +1660,9 @@ static int replace_system_preds(struct event_subsystem *system,
                 if (strcmp(call->class->system, system->name) != 0)
                         continue;
 
+                if (call->flags & TRACE_EVENT_FL_NO_SET_FILTER)
+                        continue;
+
                 filter_item = kzalloc(sizeof(*filter_item), GFP_KERNEL);
                 if (!filter_item)
                         goto fail_mem;