perf tests: Add test for trace output loss

Add a test that checks that trace output is not lost to races. This is
accomplished by tracing the exit_group syscall of "true" multiple times and
checking for correct output.

Signed-off-by: Benjamin Peterson <benjamin@engflow.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: Howard Chu <howardchu95@gmail.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20241107232128.108981-3-benjamin@engflow.com
[ Addressed two ShellCheck warnings ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/shell/trace_exit_race.sh

@@ -0,0 +1,31 @@
+#!/bin/sh
+# perf trace exit race
+# SPDX-License-Identifier: GPL-2.0
+
+# Check that the last events of a perf trace'd subprocess are not
+# lost. Specifically, trace the exiting syscall of "true" 10 times and ensure
+# the output contains 10 correct lines.
+
+# shellcheck source=lib/probe.sh
+. "$(dirname $0)"/lib/probe.sh
+
+skip_if_no_perf_trace || exit 2
+
+trace_shutdown_race() {
+	for _ in $(seq 10); do
+		perf trace -e syscalls:sys_enter_exit_group true 2>>$file
+	done
+	[ "$(grep -c -E ' +[0-9]+\.[0-9]+ +true/[0-9]+ syscalls:sys_enter_exit_group\(\)$' $file)" = "10" ]
+}
+
+
+file=$(mktemp /tmp/temporary_file.XXXXX)
+
+# Do not use whatever ~/.perfconfig file, it may change the output
+# via trace.{show_timestamp,show_prefix,etc}
+export PERF_CONFIG=/dev/null
+
+trace_shutdown_race
+err=$?
+rm -f ${file}
+exit $err