Re: [PATCH] samples/ftrace: reject zero ftrace-ops call count

[Steven Rostedt]

On Tue,  9 Jun 2026 00:44:23 +0000
Samuel Moelius <sam.moelius@xxxxxxxxxxxxxxx> wrote:

> The ftrace-ops sample exposes nr_function_calls as a module parameter
> and uses it as the divisor when printing the measured time per call.
> Loading the module with nr_function_calls=0 skips the benchmark loop and
> then divides the elapsed time by zero, crashing the kernel during sample
> module initialization.

This change is rather pointless, but whatever.

> 
> Reject a zero call count before registering any ftrace ops.
> 
> Assisted-by: Codex:gpt-5.5-cyber-preview
> Signed-off-by: Samuel Moelius <sam.moelius@xxxxxxxxxxxxxxx>
> ---
>  samples/ftrace/ftrace-ops.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/samples/ftrace/ftrace-ops.c b/samples/ftrace/ftrace-ops.c
> index 68d6685c80bd..d5adaa61484f 100644
> --- a/samples/ftrace/ftrace-ops.c
> +++ b/samples/ftrace/ftrace-ops.c
> @@ -190,6 +190,11 @@ static int __init ftrace_ops_sample_init(void)
>  		tracer_irrelevant = ops_func_count;
>  	}
>  
> +	if (!nr_function_calls) {
> +		pr_err("nr_function_calls must be non-zero\n");
> +		return -EINVAL;

No need to print that the admin did something stupid.

> +	}
> +
>  	pr_info("registering:\n"
>  		"  relevant ops: %u\n"
>  		"    tracee: %ps\n"

In fact, I would just change the output to be:

        pr_info("Attempted %u calls to %ps in %lluns (%lluns / call)\n",
                nr_function_calls, tracee_relevant,
                period, nr_function_calls ? div_u64(period, nr_function_calls) : -1LL);

and have garbage in, garbage out.

-- Steve