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

[Steven Rostedt <rostedt@goodmis.org>]

On Thu, 30 Jul 2026 12:35:44 -0400
Andrey Grodzovsky <andrey.grodzovsky@crowdstrike.com> wrote:

> kernel.ftrace_enabled=0 is now always refused, so the old scenario
> (disable, fail to load a livepatch, re-enable, load) no longer applies.
> Replace it with a single check that the write is refused with the new
> error, and drop the now-stale disable/reload flow.
> 
> Assisted-by: Claude:claude-sonnet-5
> Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@crowdstrike.com>
> ---
>  .../selftests/livepatch/test-ftrace.sh        | 49 ++-----------------
>  1 file changed, 3 insertions(+), 46 deletions(-)
> 
> diff --git a/tools/testing/selftests/livepatch/test-ftrace.sh b/tools/testing/selftests/livepatch/test-ftrace.sh
> index d2c3dea63104..c88f4d13a134 100755
> --- a/tools/testing/selftests/livepatch/test-ftrace.sh
> +++ b/tools/testing/selftests/livepatch/test-ftrace.sh
> @@ -9,56 +9,13 @@ MOD_LIVEPATCH=test_klp_livepatch
>  setup_config
>  
>  
> -# - turn ftrace_enabled OFF and verify livepatches can't load
> -# - turn ftrace_enabled ON and verify livepatch can load
> -# - verify that ftrace_enabled can't be turned OFF while a livepatch is loaded
> +# - verify that kernel.ftrace_enabled=0 is refused (deprecated knob)
>  
> -start_test "livepatch interaction with ftrace_enabled sysctl"
> +start_test "ftrace_enabled sysctl write is refused (deprecated)"
>  
> -set_ftrace_enabled 0
> -load_failing_mod $MOD_LIVEPATCH
> -
> -set_ftrace_enabled 1
> -load_lp $MOD_LIVEPATCH
> -if [[ "$(cat /proc/cmdline)" != "$MOD_LIVEPATCH: this has been live patched" ]] ; then
> -	echo -e "FAIL\n\n"
> -	die "livepatch kselftest(s) failed"
> -fi
> -

This test should work for both old and new kernels. I would have it still
do everything here but if setting ftrace_enabled returns -EOPNOTSUPP then
do the simple path.

-- Steve


> -# Check that ftrace could not get disabled when a livepatch is enabled
>  set_ftrace_enabled --fail 0
> -if [[ "$(cat /proc/cmdline)" != "$MOD_LIVEPATCH: this has been live patched" ]] ; then
> -	echo -e "FAIL\n\n"
> -	die "livepatch kselftest(s) failed"
> -fi
> -disable_lp $MOD_LIVEPATCH
> -unload_lp $MOD_LIVEPATCH
>  
> -check_result "livepatch: kernel.ftrace_enabled = 0
> -% insmod test_modules/$MOD_LIVEPATCH.ko
> -livepatch: enabling patch '$MOD_LIVEPATCH'
> -livepatch: '$MOD_LIVEPATCH': initializing patching transition
> -livepatch: failed to register ftrace handler for function 'cmdline_proc_show' (-16)
> -livepatch: failed to patch object 'vmlinux'
> -livepatch: failed to enable patch '$MOD_LIVEPATCH'
> -livepatch: '$MOD_LIVEPATCH': canceling patching transition, going to unpatch
> -livepatch: '$MOD_LIVEPATCH': completing unpatching transition
> -livepatch: '$MOD_LIVEPATCH': unpatching complete
> -insmod: ERROR: could not insert module test_modules/$MOD_LIVEPATCH.ko: Device or resource busy
> -livepatch: kernel.ftrace_enabled = 1
> -% insmod test_modules/$MOD_LIVEPATCH.ko
> -livepatch: enabling patch '$MOD_LIVEPATCH'
> -livepatch: '$MOD_LIVEPATCH': initializing patching transition
> -livepatch: '$MOD_LIVEPATCH': starting patching transition
> -livepatch: '$MOD_LIVEPATCH': completing patching transition
> -livepatch: '$MOD_LIVEPATCH': patching complete
> -livepatch: sysctl: setting key \"kernel.ftrace_enabled\": Device or resource busy
> -% echo 0 > $SYSFS_KLP_DIR/$MOD_LIVEPATCH/enabled
> -livepatch: '$MOD_LIVEPATCH': initializing unpatching transition
> -livepatch: '$MOD_LIVEPATCH': starting unpatching transition
> -livepatch: '$MOD_LIVEPATCH': completing unpatching transition
> -livepatch: '$MOD_LIVEPATCH': unpatching complete
> -% rmmod $MOD_LIVEPATCH"
> +check_result "livepatch: sysctl: setting key \"kernel.ftrace_enabled\": Operation not supported"
>  
>  
>  # - verify livepatch can load