perf trace: Fix race in signal handling

Since a lot of stuff happens before the SIGINT signal handler is registered
(scanning /proc/*, etc.), on bigger systems, such as Cavium Sabre CN99xx,
it may happen that first interrupt signal is lost and perf isn't correctly
terminated.

The reproduction code might look like the following:

    perf trace -a &
    PERF_PID=$!
    sleep 4
    kill -INT $PERF_PID

The issue has been found on a CN99xx machine with RHEL-8 and the patch fixes
it by registering the signal handlers earlier in the init stage.
Suggested-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Michael Petlan <mpetlan@redhat.com>
Tested-by: Michael Petlan <mpetlan@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/lkml/YEJnaMzH2ctp3PPx@kernel.org/Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-trace.c

@@ -3964,9 +3964,6 @@ static int trace__run(struct trace *trace, int argc, const char **argv)
 
 	evlist__config(evlist, &trace->opts, &callchain_param);
 
-	signal(SIGCHLD, sig_handler);
-	signal(SIGINT, sig_handler);
-
 	if (forks) {
 		err = evlist__prepare_workload(evlist, &trace->opts.target, argv, false, NULL);
 		if (err < 0) {
@@ -4827,6 +4824,8 @@ int cmd_trace(int argc, const char **argv)
 
 	signal(SIGSEGV, sighandler_dump_stack);
 	signal(SIGFPE, sighandler_dump_stack);
+	signal(SIGCHLD, sig_handler);
+	signal(SIGINT, sig_handler);
 
 	trace.evlist = evlist__new();
 	trace.sctbl = syscalltbl__new();