Traced event can trigger 'snapshot' operation(i.e. calls snapshot_trigger()
or snapshot_count_trigger()) when register_snapshot_trigger() has completed
registration but doesn't allocate buffer for 'snapshot' event trigger. In
the rare case, 'snapshot' operation always detects the lack of allocated
buffer so make register_snapshot_trigger() allocate buffer first.
trigger-snapshot.tc in kselftest reproduces the issue on slow vm:
-----------------------------------------------------------
cat trace
...
ftracetest-3028 [002] .... 236.784290: sched_process_fork: comm=ftracetest pid=3028 child_comm=ftracetest child_pid=3036
<...>-2875 [003] .... 240.460335: tracing_snapshot_instance_cond: *** SNAPSHOT NOT ALLOCATED ***
<...>-2875 [003] .... 240.460338: tracing_snapshot_instance_cond: *** stopping trace here! ***
-----------------------------------------------------------
Signed-off-by: Xiao Yang <yangx.jy@xxxxxxxxxxxxxx>
---
kernel/trace/trace_events_trigger.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)
diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index dd34a1b46a86..3a74736da363 100644
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c
@@ -1088,14 +1088,10 @@ register_snapshot_trigger(char *glob, struct event_trigger_ops *ops,
struct event_trigger_data *data,
struct trace_event_file *file)
{
- int ret = register_trigger(glob, ops, data, file);
-
- if (ret > 0 && tracing_alloc_snapshot_instance(file->tr) != 0) {
- unregister_trigger(glob, ops, data, file);
- ret = 0;
- }
+ if (tracing_alloc_snapshot_instance(file->tr) != 0)
+ return 0;
- return ret;
+ return register_trigger(glob, ops, data, file);
}
static int
--
2.25.1
