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 <[email protected]> wrote:
>
> 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/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
>