Re: [RFC PATCH bpf-next v3 2/2] selftests/livepatch: update test-ftrace.sh for deprecated ftrace_enabled

On Thu, Aug 6, 2026 at 5:18 PM Song Liu <[email protected]> wrote:
>
> On Thu, Aug 6, 2026 at 8:30 AM Andrey Grodzovsky
> <[email protected]> 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: Joe Lawrence <[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!0iHqKyQrLfspbt4sQvekjrQjWLuiSTtsCXR9obFozOCSUhPg1KCQGTvfgZ9oTwgBkdB3nKZA1RCYtwwYj2qtEXgW$   | 14 ++++++
> >  .../selftests/livepatch/https://urldefense.com/v3/__http://test-ftrace.sh__;!!BmdzS3_lV9HdKG8!0iHqKyQrLfspbt4sQvekjrQjWLuiSTtsCXR9obFozOCSUhPg1KCQGTvfgZ9oTwgBkdB3nKZA1RCYtwwYj6oTNhr1$         | 45 ++++++++++++-------
> >  2 files changed, 42 insertions(+), 17 deletions(-)
> >
> > diff --git a/tools/testing/selftests/livepatch/https://urldefense.com/v3/__http://functions.sh__;!!BmdzS3_lV9HdKG8!0iHqKyQrLfspbt4sQvekjrQjWLuiSTtsCXR9obFozOCSUhPg1KCQGTvfgZ9oTwgBkdB3nKZA1RCYtwwYj2qtEXgW$  b/tools/testing/selftests/livepatch/https://urldefense.com/v3/__http://functions.sh__;!!BmdzS3_lV9HdKG8!0iHqKyQrLfspbt4sQvekjrQjWLuiSTtsCXR9obFozOCSUhPg1KCQGTvfgZ9oTwgBkdB3nKZA1RCYtwwYj2qtEXgW$
> > index 30dc677b2f45..a65b7b1ac8ad 100644
> > --- a/tools/testing/selftests/livepatch/https://urldefense.com/v3/__http://functions.sh__;!!BmdzS3_lV9HdKG8!0iHqKyQrLfspbt4sQvekjrQjWLuiSTtsCXR9obFozOCSUhPg1KCQGTvfgZ9oTwgBkdB3nKZA1RCYtwwYj2qtEXgW$
> > +++ b/tools/testing/selftests/livepatch/https://urldefense.com/v3/__http://functions.sh__;!!BmdzS3_lV9HdKG8!0iHqKyQrLfspbt4sQvekjrQjWLuiSTtsCXR9obFozOCSUhPg1KCQGTvfgZ9oTwgBkdB3nKZA1RCYtwwYj2qtEXgW$
> > @@ -126,6 +126,20 @@ function set_ftrace_enabled() {
> >         echo "livepatch: kernel.ftrace_enabled = $result" > /dev/kmsg
> >  }
> >
> > +# ftrace_disable_supported() - probe whether kernel.ftrace_enabled=0
> > +#      can still disable ftrace on this kernel. Newer kernels deprecate
> > +#      the knob and always refuse the write with -EOPNOTSUPP.
> > +function ftrace_disable_supported() {
> > +       local orig result
> > +
> > +       orig=$(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" ]]
> > +}
>
> Since the selftests are shipped with the kernel code, I think
> we don't need to handle backward compatibility here. Instead,
> we can just assume disabling ftrace is no longer supported.
>
> Thanks,
> Song

I tend to agree but I think here[1] Steve and Miroslav asked for
backward compatability. V1 was actually the way you prefer.

Andrey

[1] - https://lore.kernel.org/bpf/[email protected]/
>
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