[PATCH 1/2] tracing: Add check for NULL event field when creating hist field

[Tom Zanussi]

Smatch flagged create_hist_field() as possibly being able to
dereference a NULL pointer, although the current code exits in all
cases where the event field could be NULL, so it's not actually a
problem.

Still, to prevent future changes to the code from overlooking new
cases, make the NULL pointer check explicit and warn once in that
case.

Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
---
 kernel/trace/trace_events_hist.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index f98b6b3..0c05b8a 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -371,6 +371,9 @@ static struct hist_field *create_hist_field(struct ftrace_event_field *field,
 		goto out;
 	}
 
+	if (WARN_ON_ONCE(!field))
+		goto out;
+
 	if (is_string_field(field)) {
 		flags |= HIST_FIELD_FL_STRING;
 
-- 
1.9.3