perf trace: Filter out the trace pid when no threads are specified

To avoid tracing the tracer.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-shmwd1khzpaobr3i0j1ygapg@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-trace.c

@@ -2151,6 +2151,15 @@ static int trace__run(struct trace *trace, int argc, const char **argv)
 	if (err < 0)
 		goto out_error_open;
 
+	/*
+	 * Better not use !target__has_task() here because we need to cover the
+	 * case where no threads were specified in the command line, but a
+	 * workload was, and in that case we will fill in the thread_map when
+	 * we fork the workload in perf_evlist__prepare_workload.
+	 */
+	if (evlist->threads->map[0] == -1)
+		perf_evlist__set_filter_pid(evlist, getpid());
+
 	err = perf_evlist__mmap(evlist, trace->opts.mmap_pages, false);
 	if (err < 0)
 		goto out_error_mmap;