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 spare buffer for 'snapshot' event trigger.
'snapshot' operation always detects the lack of allocated buffer in the rare
case so make register_snapshot_trigger() allocate spare 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 | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index dd34a1b46a86..00e54cdcef3e 100644
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c
@@ -1088,9 +1088,13 @@ 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);
+ int alloc_ret, ret;
- if (ret > 0 && tracing_alloc_snapshot_instance(file->tr) != 0) {
+ alloc_ret = tracing_alloc_snapshot_instance(file->tr);
+
+ ret = register_trigger(glob, ops, data, file);
+
+ if (ret > 0 && alloc_ret != 0) {
unregister_trigger(glob, ops, data, file);
ret = 0;
}
--
2.25.1
