This is a note to let you know that I've just added the patch titled
trace/trace_event_perf: remove duplicate samples on the first tracepoint event
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
trace-trace_event_perf-remove-duplicate-samples-on-t.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit e5cfc4af95550e65753e227b406ab0a5b930fcc0
Author: Levi Yun <yeoreum.yun@xxxxxxx>
Date: Fri Sep 13 03:13:47 2024 +0100
trace/trace_event_perf: remove duplicate samples on the first tracepoint event
[ Upstream commit afe5960dc208fe069ddaaeb0994d857b24ac19d1 ]
When a tracepoint event is created with attr.freq = 1,
'hwc->period_left' is not initialized correctly. As a result,
in the perf_swevent_overflow() function, when the first time the event occurs,
it calculates the event overflow and the perf_swevent_set_period() returns 3,
this leads to the event are recorded for three duplicate times.
Step to reproduce:
1. Enable the tracepoint event & starting tracing
$ echo 1 > /sys/kernel/tracing/events/module/module_free
$ echo 1 > /sys/kernel/tracing/tracing_on
2. Record with perf
$ perf record -a --strict-freq -F 1 -e "module:module_free"
3. Trigger module_free event.
$ modprobe -i sunrpc
$ modprobe -r sunrpc
Result:
- Trace pipe result:
$ cat trace_pipe
modprobe-174509 [003] ..... 6504.868896: module_free: sunrpc
- perf sample:
modprobe 174509 [003] 6504.868980: module:module_free: sunrpc
modprobe 174509 [003] 6504.868980: module:module_free: sunrpc
modprobe 174509 [003] 6504.868980: module:module_free: sunrpc
By setting period_left via perf_swevent_set_period() as other sw_event did,
This problem could be solved.
After patch:
- Trace pipe result:
$ cat trace_pipe
modprobe 1153096 [068] 613468.867774: module:module_free: xfs
- perf sample
modprobe 1153096 [068] 613468.867794: module:module_free: xfs
Link: https://lore.kernel.org/20240913021347.595330-1-yeoreum.yun@xxxxxxx
Fixes: bd2b5b12849a ("perf_counter: More aggressive frequency adjustment")
Signed-off-by: Levi Yun <yeoreum.yun@xxxxxxx>
Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index 5e68447588b7c..22cce5dc0e287 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -349,10 +349,16 @@ void perf_uprobe_destroy(struct perf_event *p_event)
int perf_trace_add(struct perf_event *p_event, int flags)
{
struct trace_event_call *tp_event = p_event->tp_event;
+ struct hw_perf_event *hwc = &p_event->hw;
if (!(flags & PERF_EF_START))
p_event->hw.state = PERF_HES_STOPPED;
+ if (is_sampling_event(p_event)) {
+ hwc->last_period = hwc->sample_period;
+ perf_swevent_set_period(p_event);
+ }
+
/*
* If TRACE_REG_PERF_ADD returns false; no custom action was performed
* and we need to take the default action of enqueueing our event on
