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/[email protected]

Acked-by: Masami Hiramatsu <[email protected]>
Signed-off-by: Oleg Nesterov <[email protected]>
Signed-off-by: Steven Rostedt <[email protected]>

0 files changed, 0 insertions, 0 deletions