[PATCH] tracing: Increase stack skip on event trigger

[Namhyung Kim]

When 'stacktrace' trigger is used for event tracing, it should skip 4
functions instead of 3.  Otherwise it'll contain ftrace_raw_event_XXX
like below:

  # echo stacktrace > events/sched/sched_switch/trigger
  # tail trace
   => rcu_gp_kthread
   => kthread
   => ret_from_fork
       ksoftirqd/0-3     [000] d..3    53.343993: <stack trace>
   => ftrace_raw_event_sched_switch
   => __schedule
   => schedule
   => smpboot_thread_fn
   => kthread
   => ret_from_fork

Reported-by: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
---
 kernel/trace/trace_events_trigger.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index 8712df9decb4..c58fbdd3053e 100644
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c
@@ -965,12 +965,13 @@ static __init int register_trigger_snapshot_cmd(void) { return 0; }
 
 #ifdef CONFIG_STACKTRACE
 /*
- * Skip 3:
+ * Skip 4:
  *   stacktrace_trigger()
  *   event_triggers_post_call()
+ *   ftrace_event_buffer_commit()
  *   ftrace_raw_event_xxx()
  */
-#define STACK_SKIP 3
+#define STACK_SKIP 4
 
 static void
 stacktrace_trigger(struct event_trigger_data *data)
-- 
2.3.3

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