From 288e984e622336bab8bc3dfdf2f190816362d9a1 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Thu, 20 Jun 2013 19:38:06 +0200
Subject: [PATCH] tracing/kprobes: Avoid perf_trace_buf_*() if ->perf_events is
 empty

perf_trace_buf_prepare() + perf_trace_buf_submit() make no sense
if this task/CPU has no active counters. Change kprobe_perf_func()
and kretprobe_perf_func() to check call->perf_events beforehand
and return if this list is empty.

For example, "perf record -e some_probe -p1". Only /sbin/init will
report, all other threads which hit the same probe will do
perf_trace_buf_prepare/perf_trace_buf_submit just to realize that
nobody wants perf_swevent_event().

Link: http://lkml.kernel.org/r/20130620173806.GA13151@redhat.com

Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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