On Fri, Jul 31, 2026 at 01:53:58PM -0400, Andrey Grodzovsky wrote:
> 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 <[email protected]>
> Suggested-by: Miroslav Benes <[email protected]>
> Assisted-by: Claude:claude-sonnet-5
> Signed-off-by: Andrey Grodzovsky <[email protected]>
> ---
> .../testing/selftests/livepatch/functions.sh | 13 ++++++
> .../selftests/livepatch/test-ftrace.sh | 45 ++++++++++++-------
> 2 files changed, 41 insertions(+), 17 deletions(-)
>
> diff --git a/tools/testing/selftests/livepatch/functions.sh
> b/tools/testing/selftests/livepatch/functions.sh
> index 30dc677b2f45..7fa4bda70221 100644
> --- a/tools/testing/selftests/livepatch/functions.sh
> +++ b/tools/testing/selftests/livepatch/functions.sh
> @@ -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
