[PATCH v2] selftests/ftrace: Add test to exercize function tracer across cpu hotplug

[Naveen N Rao <naveen@kernel.org>]

Add a test to exercize cpu hotplug with the function tracer active to
ensure that sensitive functions in idle path are excluded from being
traced. This helps catch issues such as the one fixed by commit
4b3338aaa74d ("powerpc/ftrace: Fix stack teardown in ftrace_no_trace").

Signed-off-by: Naveen N Rao <naveen@kernel.org>
---
v2: Add a check for next available online cpu, as suggested by Masami.

 .../ftrace/test.d/ftrace/func_hotplug.tc      | 42 +++++++++++++++++++
 1 file changed, 42 insertions(+)
 create mode 100644 tools/testing/selftests/ftrace/test.d/ftrace/func_hotplug.tc

diff --git a/tools/testing/selftests/ftrace/test.d/ftrace/func_hotplug.tc b/tools/testing/selftests/ftrace/test.d/ftrace/func_hotplug.tc
new file mode 100644
index 000000000000..ccfbfde3d942
--- /dev/null
+++ b/tools/testing/selftests/ftrace/test.d/ftrace/func_hotplug.tc
@@ -0,0 +1,42 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+# description: ftrace - function trace across cpu hotplug
+# requires: function:tracer
+
+if ! which nproc ; then
+  nproc() {
+    ls -d /sys/devices/system/cpu/cpu[0-9]* | wc -l
+  }
+fi
+
+NP=`nproc`
+
+if [ $NP -eq 1 ] ;then
+  echo "We cannot test cpu hotplug in UP environment"
+  exit_unresolved
+fi
+
+# Find online cpu
+for i in /sys/devices/system/cpu/cpu[1-9]*; do
+	if [ -f $i/online ] && [ "$(cat $i/online)" = "1" ]; then
+		cpu=$i
+		break
+	fi
+done
+
+if [ -z "$cpu" ]; then
+	echo "We cannot test cpu hotplug with a single cpu online"
+	exit_unresolved
+fi
+
+echo 0 > tracing_on
+echo > trace
+
+: "Set $(basename $cpu) offline/online with function tracer enabled"
+echo function > current_tracer
+echo 1 > tracing_on
+(echo 0 > $cpu/online)
+(echo "forked"; sleep 1)
+(echo 1 > $cpu/online)
+echo 0 > tracing_on
+echo nop > current_tracer

base-commit: b85ea95d086471afb4ad062012a4d73cd328fa86
-- 
2.43.0