[PATCH 2/2] perf tests: add test for trace output loss

[Benjamin Peterson <benjamin@engflow.com>]

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.

Conveniently, this test also serves as a regression test for 5fb8e56542a3 ("perf
trace: avoid garbage when not printing a trace event's arguments") because
exit_group triggers the previously buggy printing behavior.

Signed-off-by: Benjamin Peterson <benjamin@engflow.com>
---
 tools/perf/tests/shell/trace_exit_race.sh | 31 +++++++++++++++++++++++
 1 file changed, 31 insertions(+)
 create mode 100755 tools/perf/tests/shell/trace_exit_race.sh

diff --git a/tools/perf/tests/shell/trace_exit_race.sh b/tools/perf/tests/shell/trace_exit_race.sh
new file mode 100755
index 000000000000..8b70324bc5b4
--- /dev/null
+++ b/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" 100 times and ensure
+# the output contains 100 correct lines.
+
+# shellcheck source=lib/probe.sh
+. "$(dirname $0)"/lib/probe.sh
+
+skip_if_no_perf_trace || exit 2
+
+trace_shutdown_race() {
+	for i in $(seq 100); do
+		perf trace -e syscalls:sys_enter_exit_group true 2>>$file
+	done
+	[ $(grep -c -E " +[0-9]+\.[0-9]+ +true/[0-9]+ syscalls:sys_enter_exit_group\(\)$" $file) = "100" ]
+}
+
+
+file=$(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
-- 
2.39.5