Re: [RFC PATCH bpf-next v2 2/2] selftests/livepatch: update test-ftrace.sh for deprecated ftrace_enabled

Thank you Joe and Steven for your comments; I sent V3.

Andrey

On Fri, Jul 31, 2026 at 8:31 PM Joe Lawrence [off-list ref] wrote:

On Fri, Jul 31, 2026 at 01:53:58PM -0400, Andrey Grodzovsky wrote:

quoted

kernel.ftrace_enabled=0 is now refused on kernels that deprecate the
knob, so the old disable/reload flow no longer applies there. Probe
for this with ftrace_disable_supported() and keep the full original
scenario (disable, fail to load a livepatch, re-enable, load, confirm
disable is refused while loaded) on kernels where it still works;
otherwise just confirm the write is refused.

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Suggested-by: Miroslav Benes <mbenes@suse.cz>
Assisted-by: Claude:claude-sonnet-5
Signed-off-by: Andrey Grodzovsky <redacted>
---
 .../testing/selftests/livepatch/https://urldefense.com/v3/__http://functions.sh__;!!BmdzS3_lV9HdKG8!zXXcFqHACaJ7PyoFMFh-_8DFTwWSotPltPcR5ezYC87VaVkoNZcqFkVTtLbYUQp4DKEh9Z-0WLN8c5sMeyug2BCCuslAibAtHJo$   | 13 ++++++
 .../selftests/livepatch/https://urldefense.com/v3/__http://test-ftrace.sh__;!!BmdzS3_lV9HdKG8!zXXcFqHACaJ7PyoFMFh-_8DFTwWSotPltPcR5ezYC87VaVkoNZcqFkVTtLbYUQp4DKEh9Z-0WLN8c5sMeyug2BCCuslAJf9tNxM$         | 45 ++++++++++++-------
 2 files changed, 41 insertions(+), 17 deletions(-)

diff --git a/tools/testing/selftests/livepatch/https://urldefense.com/v3/__http://functions.sh__;!!BmdzS3_lV9HdKG8!zXXcFqHACaJ7PyoFMFh-_8DFTwWSotPltPcR5ezYC87VaVkoNZcqFkVTtLbYUQp4DKEh9Z-0WLN8c5sMeyug2BCCuslAibAtHJo$  b/tools/testing/selftests/livepatch/https://urldefense.com/v3/__http://functions.sh__;!!BmdzS3_lV9HdKG8!zXXcFqHACaJ7PyoFMFh-_8DFTwWSotPltPcR5ezYC87VaVkoNZcqFkVTtLbYUQp4DKEh9Z-0WLN8c5sMeyug2BCCuslAibAtHJo$
index 30dc677b2f45..7fa4bda70221 100644
--- a/tools/testing/selftests/livepatch/https://urldefense.com/v3/__http://functions.sh__;!!BmdzS3_lV9HdKG8!zXXcFqHACaJ7PyoFMFh-_8DFTwWSotPltPcR5ezYC87VaVkoNZcqFkVTtLbYUQp4DKEh9Z-0WLN8c5sMeyug2BCCuslAibAtHJo$
+++ b/tools/testing/selftests/livepatch/https://urldefense.com/v3/__http://functions.sh__;!!BmdzS3_lV9HdKG8!zXXcFqHACaJ7PyoFMFh-_8DFTwWSotPltPcR5ezYC87VaVkoNZcqFkVTtLbYUQp4DKEh9Z-0WLN8c5sMeyug2BCCuslAibAtHJo$

@@ -126,6 +126,19 @@ function set_ftrace_enabled() {
      echo "livepatch: kernel.ftrace_enabled = $result" > /dev/kmsg
 }

+# ftrace_disable_supported() - probe whether kernel.ftrace_enabled=0
+#    can still disable ftrace on this kernel. Newer kernels deprecate
+#    the knob and always refuse the write with -EOPNOTSUPP.
+function ftrace_disable_supported() {
+     local result
+
+     sysctl -q kernel.ftrace_enabled=0 &> /dev/null
+     result=$(sysctl --values kernel.ftrace_enabled)
+     sysctl -q kernel.ftrace_enabled=1 &> /dev/null
+
+     [[ "$result" == "0" ]]
+}

Small nit: AFAICT, it doesn't really affect the test pattern, but it
would be a bit cleaner if this function restored the original value
instead of always turning it on, like (untested):

        orig=$(sysctl --values kernel.ftrace_enabled)
        sysctl -q kernel.ftrace_enabled=0 &> /dev/null
        result=$(sysctl --values kernel.ftrace_enabled)
        sysctl -q "kernel.ftrace_enabled=$orig" &> /dev/null

        [[ "$result" == "0" ]]

--
Joe