Re: perf regression: failed to stat syscalls events

From: Peter Zijlstra
Date: Thu Jun 24 2010 - 01:58:58 EST

On Thu, 2010-06-24 at 09:44 +0800, Wu Fengguang wrote:
> On Thu, Jun 24, 2010 at 09:39:15AM +0800, Wu Fengguang wrote:
> > Greetings,
> >
> > I noticed that
> >
> > # perf stat -e syscalls:sys_enter_mmap true
> >
> > refuse to work on 2.6.35-rc1. The last working kernel is 2.6.34.
> Other events like lock:* or block:* or whatever continue to work.
> So this is a problem specific to syscalls:*.

Does your tree contain:

commit a8fb2608053547bc3152ea61a5ec7cdfce5d942c
Author: Steven Rostedt <srostedt@xxxxxxxxxx>
Date: Thu Jun 10 14:53:16 2010 -0400

perf/tracing: Fix regression of perf losing kprobe events

With the addition of the code to shrink the kernel tracepoint
infrastructure, we lost kprobes being traced by perf. The reason
is that I tested if the "tp_event->class->perf_probe" existed before
enabling it. This prevents "ftrace only" events (like the function
trace events) from being enabled by perf.

Unfortunately, kprobe events do not use perf_probe. This causes
kprobes to be missed by perf. To fix this, we add the test to
see if "tp_event->class->reg" exists as well as perf_probe.

Normal trace events have only "perf_probe" but no "reg" function,
and kprobes and syscalls have the "reg" but no "perf_probe".
The ftrace unique events do not have either, so this is a valid
test. If a kprobe or syscall is not to be probed by perf, the
"reg" function is called anyway, and will return a failure and
prevent perf from probing it.

Reported-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
Tested-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
Acked-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>

diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index e6f6588..8a2b73f 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -96,7 +96,9 @@ int perf_trace_init(struct perf_event *p_event)
list_for_each_entry(tp_event, &ftrace_events, list) {
if (tp_event->event.type == event_id &&
- tp_event->class && tp_event->class->perf_probe &&
+ tp_event->class &&
+ (tp_event->class->perf_probe ||
+ tp_event->class->reg) &&
try_module_get(tp_event->mod)) {
ret = perf_trace_event_init(tp_event, p_event);

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