Re: [PATCH] selftests/ftrace: Fix reading enabled_functions in add_remove_fprobe_module test

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Wed, 8 Jul 2026 15:32:39 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> From: Steven Rostedt <rostedt@goodmis.org>
> 
> The add_remove_fprobe_module test checks the number of functions added to
> the enabled_functions file to make sure that the functions added or
> removed is as expected. The issue is that it expects this file to be empty
> on start up.
> 
> Now that systemd uses BPF that attaches to functions via ftrace, this file
> is not empty in several systems:
> 
>  # cat /sys/kernel/tracing/enabled_functions
>  bpf_lsm_file_open (1) R   D   M 	tramp: ftrace_regs_caller+0x0/0x61 (call_direct_funcs+0x0/0x50)
> 	direct(jmp)-->bpf_trampoline_6442529439+0x0/0xe9
> 
> Change the test to read the number of lines in enabled_functions at the
> start of the test and subtract that from the value of the count for the
> checks within the test.

Oops, good catch! I need to make a test environment which uses
systemd...

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Thanks,

> 
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> ---
>  .../dynevent/add_remove_fprobe_module.tc      | 27 ++++++++++++-------
>  1 file changed, 18 insertions(+), 9 deletions(-)
> 
> diff --git a/tools/testing/selftests/ftrace/test.d/dynevent/add_remove_fprobe_module.tc b/tools/testing/selftests/ftrace/test.d/dynevent/add_remove_fprobe_module.tc
> index 2915206777b6..89660a9adf44 100644
> --- a/tools/testing/selftests/ftrace/test.d/dynevent/add_remove_fprobe_module.tc
> +++ b/tools/testing/selftests/ftrace/test.d/dynevent/add_remove_fprobe_module.tc
> @@ -16,23 +16,32 @@ echo > dynamic_events
>  FUNC1='foo_bar*'
>  FUNC2='vfs_read'
>  
> +:;: "Save enabled functions count" ;:
> +ecount=`cat enabled_functions | wc -l`
> +
> +count_enabled_functions() {
> +    count=`cat enabled_functions | wc -l`
> +    count=$(($count-$ecount))
> +    echo $count
> +}
> +
>  :;: "Add an event on the test module" ;:
>  echo "f:test1 $FUNC1" >> dynamic_events
>  echo 1 > events/fprobes/test1/enable
>  
>  :;: "Ensure it is enabled" ;:
> -funcs=`cat enabled_functions | wc -l`
> +funcs=`count_enabled_functions`
>  test $funcs -ne 0
>  
>  :;: "Check the enabled_functions is cleared on unloading" ;:
>  rmmod trace-events-sample
> -funcs=`cat enabled_functions | wc -l`
> +funcs=`count_enabled_functions`
>  test $funcs -eq 0
>  
>  :;: "Check it is kept clean" ;:
>  modprobe trace-events-sample
>  echo 1 > events/fprobes/test1/enable || echo "OK"
> -funcs=`cat enabled_functions | wc -l`
> +funcs=`count_enabled_functions`
>  test $funcs -eq 0
>  
>  :;: "Add another event not on the test module" ;:
> @@ -40,19 +49,19 @@ echo "f:test2 $FUNC2" >> dynamic_events
>  echo 1 > events/fprobes/test2/enable
>  
>  :;: "Ensure it is enabled" ;:
> -ofuncs=`cat enabled_functions | wc -l`
> +ofuncs=`count_enabled_functions`
>  test $ofuncs -ne 0
>  
>  :;: "Disable and remove the first event"
>  echo 0 > events/fprobes/test1/enable
>  echo "-:fprobes/test1" >> dynamic_events
> -funcs=`cat enabled_functions | wc -l`
> +funcs=`count_enabled_functions`
>  test $ofuncs -eq $funcs
>  
>  :;: "Disable and remove other events" ;:
>  echo 0 > events/fprobes/enable
>  echo > dynamic_events
> -funcs=`cat enabled_functions | wc -l`
> +funcs=`count_enabled_functions`
>  test $funcs -eq 0
>  
>  rmmod trace-events-sample
> @@ -63,12 +72,12 @@ echo "f:test1 $FUNC1" >> dynamic_events
>  echo 1 > events/fprobes/test1/enable
>  echo "f:test2 $FUNC2" >> dynamic_events
>  echo 1 > events/fprobes/test2/enable
> -ofuncs=`cat enabled_functions | wc -l`
> +ofuncs=`count_enabled_functions`
>  test $ofuncs -ne 0
>  
>  :;: "Unload module (ftrace entry should be removed)" ;:
>  rmmod trace-events-sample
> -funcs=`cat enabled_functions | wc -l`
> +funcs=`count_enabled_functions`
>  test $funcs -ne 0
>  test $ofuncs -ne $funcs
>  
> @@ -77,7 +86,7 @@ echo 0 > events/fprobes/test2/enable
>  echo "-:fprobes/test2" >> dynamic_events
>  
>  :;: "Ensure ftrace is disabled." ;:
> -funcs=`cat enabled_functions | wc -l`
> +funcs=`count_enabled_functions`
>  test $funcs -eq 0
>  
>  echo 0 > events/fprobes/enable
> -- 
> 2.53.0
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>