From: "Steven Rostedt (Red Hat)" <[email protected]> Because tracepoint callbacks are done with preemption enabled, the trace events are always called with preempt disable due to the rcu_read_lock_sched_notrace() in __DO_TRACE(). This causes the preempt count shown in the recorded trace event to be inaccurate. It is always one more that what the preempt_count was when the tracepoint was called.
If CONFIG_PREEMPT is enabled, subtract 1 from the preempt_count before recording it in the trace buffer. Link: http://lkml.kernel.org/r/[email protected] Reported-by: Sebastian Andrzej Siewior <[email protected]> Signed-off-by: Steven Rostedt <[email protected]> --- kernel/trace/trace_events.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index fd449eb138cf..03c0a48c3ac4 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -261,6 +261,14 @@ void *trace_event_buffer_reserve(struct trace_event_buffer *fbuffer, local_save_flags(fbuffer->flags); fbuffer->pc = preempt_count(); + /* + * If CONFIG_PREEMPT is enabled, then the tracepoint itself disables + * preemption (adding one to the preempt_count). Since we are + * interested in the preempt_count at the time the tracepoint was + * hit, we need to subtract one to offset the increment. + */ + if (IS_ENABLED(CONFIG_PREEMPT)) + fbuffer->pc--; fbuffer->trace_file = trace_file; fbuffer->event = -- 2.8.1
